POPULAR HAND BOOK FOR CEMENT AND CONCRETE USERS A COMPREHENSIVE AND POPULAR TREATISE ON THE PRINCIPLES INVOLVED AND METHODS EMPLOYED IN THE DESIGN AND CONSTRUCTION OF MODERN CONCRETE WORK. A Standard Reference Book Covering the Uses of Plain and Reinforced Concrete. Everything of Value to tbe Concrete User is Given, Including Kinds of Cement Employed in Construction, Concrete Architecture, Inspection and Testing, Waterproofing, Coloring and Painting, Rules, Tables, Working and Cost Data. By MYRON H. LEWIS, C.E. Author of "Examinations for Civil Engineers," " Waterproofing of Concrete," Etc., Etc., and ALBERT H. CHANDLER, C.E. Author of " Materials Employed in Construction," Etc. FULLY NEW YORK THE NORMAN W. HENLEY PUBLISHING COMPANY 132 NASSAU STREET 1911 v> v Copyrighted, 1911, by The Norman W. Henley Publishing Co. PREFACE ALTHOUGH the literature of cement and concrete has expanded enormously during the past few years, it is, nevertheless, the con- viction of the Publishers that there is still a place for a semi-popular book of this general type. Many of the technical works are either high in price or contain a great deal of theory, or devote so many pages to academic discussions of points, not yet settled by current practice, as to be imperfectly adapted to the wants of the non- technical reader. On the other hand, with few exceptions, the popular books on the subject contain no systematic treatment of the subject of design, and fail to give any conception of the costs of different types of construction. To compile material, all of which shall possess some definite value; to explain the principles of design and methods of construc- tion in concise and, so far as possible, non-technical language; to describe the variation of costs for different kinds of concrete work; to give the reader a handbook that will prove interesting as well as useful; to bring home the great economic and artistic qualities of concrete as a building material; and finally to help in producing a better, higher grade of concrete work: these are the criteria which have helped to shape the character of this book, criteria difficult to satisfy and impossible of complete attainment. Just how far these purposes have been carried out can only be left to the judg- ment of the readers to decide. In the preparation of the text, many sources of information have been consulted, including the standard text books on the subject, the published transactions of the American Society of Civil En- gineers, the American Society for Testing Material, and the National Association of Cement Users; also recent files of the Engineering News, Engineering Record, Engineering-Contracting, Cement Era, and other periodical literature. Particular acknowledgment is also due to the publications of the Atlas Portland Cement Co., [iii] 268763 Preface for many suggestions, tables, and other valuable data. The bulle- tins of the Universal, American, Vulcanite, and Edison Cement Companies have also been freely drawn upon. In the preparation of the manuscript many suggestions were also received from individual sources, and particular acknowledg- ment is due to the following engineers, for valuable contributions and advice: Mr. Reginald Van Deerlin, C.E., Chief Engineer Hennebique Construction Co.; Mr. James G. Ray, C.E., Consulting Reinforced Concrete Engineer; Messrs. Edmund P. Murray, C.E.; S. B. Balland, C.E.; and L. B. Manheimer. The authors would also be glad to receive and to acknowledge, in future editions, further suggestions, criticisms, cost data, or examples of recent practice from any of their readers. They especially solicit cost data in connection with all kinds of concrete work, and will acknowledge and publish same in future editions of this book. MYRON H. LEWIS, February, 1911. ALBERT H. CHANDLER. [iv] CONTENTS CHAPTER I INTRODUCTORY PAGE The Renaissance of Concrete. The Concrete Age. Concrete Architecture. Concrete Literature. The Future of Concrete, . . ... . 1-4 CHAPTER II KINDS OF CEMENT AND HOW THEY ARE MADE Common Lime. Lime Mortar. Hydraulic Lime. Puzzuolana. Hydraulic Cements. Theory of Setting. How Natural Cement is Made. How Portland Cement is Made. White Portland Cement. Slag Cements. Plaster Cements. Choice of Cements. How Portland Cement Comes 5-17 CHAPTER III PROPERTIES, TESTING, AND REQUIREMENTS OF HYDRAULIC CEMENTS Description of Tests. How the Tests Are Made. Standard Requirements for Natural and Portland Cements, . . -. ' . . . . 18-25 CHAPTER IV CONCRETE AND ITS PROPERTIES What Concrete Is. Kinds of Concrete. Function and Effect of the Cement. Aggregates, Water, Chemicals, Weather Conditions, Gases, Sewage, etc. Laws of Strength and Permeability, 2 6~35 CHAPTER V SAND, BROKEN STONE, AND GRAVEL FOR CONCRETE Selection of Sand. Tests for Sand. Washing Sand. Mixture of Bank Sand and Gravel. Broken Stone. Gravel, 36-41 CHAPTER VI HOW TO PROPORTION THE MATERIALS Nature of the Problem. Voids in Concrete. Methods of Proportioning. Tables for Proportioning, 42-46 [v] Contents CHAPTER VII HOW TO MIX AND PLACE CONCRETE PAGE Methods of Mixing. How to Mix by Hand. Materials Required for Two- Bag Batch. Mixing by Machine. Placing the Concrete. Protection of Concrete After Placing. -Placing Concrete Under Water, . . 47-63 CHAPTER VIII FORMS FOR CONCRETE CONSTRUCTION Kinds of Forms. Pressure of Concrete on Forms. Dressing and Lubrica- tion of Forms. Design of Forms. Removing Forms. Cost of Forms 64-77 CHAPTER IX THE ARCHITECTURAL AND ARTISTIC POSSIBILITIES OF CONCRETE A New Style of Architecture, 78-81 CHAPTER X CONCRETE RESIDENCES The Use of Concrete for Residences. Best Method of Obtaining Architec- tural Effects. Stucco and Reinforced Concrete for Residences. The Edison Poured Concrete House. Cost of Different Types of Resi- dences Compared, . . . . . . . . . 82-89 CHAPTER XI MORTARS, PLASTERS, AND STUCCOS, AND HOW TO USE THEM The Art of Stuccoing. Lime Mortars and Plasters. Interior Plasters and Plastering. Gypsum Plasters. Portland Cement Plasters or Stucco. Exterior Lathing and Plastering. Application of Stucco to Stone. Stucco on Brick. Stucco on Concrete. Quantities of Materials for Stucco, 90 105 CHAPTER XII THE ARTISTIC TREATMENT OF CONCRETE SURFACES Imperfections in Concrete Surfaces. Methods of Finishing Surfaces. Spad- ing. Stucco. Mortar Facing. Grouting. Scrubbing and Washing. Etching. Tooling. Selected Aggregates. Tinting and Coloring. Panelling. Mosaics, Carving, etc., Prevention of Cracking and Crazing 106-117 CHAPTER XIII CONCRETE BUILDING BLOCKS - Advantages and Disadvantages of Concrete Blocks. Materials for Concrete Blocks. Types of Blocks. Block Machines. Making the Blocks. Coloring the Blocks. Waterproofing the Blocks. Building Details. Cost of Blocks. Objections to Concrete Blocks and Remedies for Same. Table of Concrete Block Data. Concrete Tiles, etc. Specifications for Concrete Blocks, . . . * . 118-138 [vi] Contents CHAPTER XIV THE MAKING OF ORNAMENTAL CONCRETE PAGE Methods Employed. Modelling. Moulding. Wooden, Metal, Plaster, Glue, and Sand Moulds, . . . . . . . 139-149 CHAPTER XV CONCRETE PIPES, FENCE POSTS, ETC. Advantages of Concrete Pipes. Moulds, Machines, and Manufacture of Re- inforced Concrete Pipes. Concrete Tile, Data, and Costs. Advan- tages of Concrete Fence Posts. Moulds, Machines, and Manufacture. Reinforcement for Fence Posts. Fastening Fence to Posts. Quantity of Materials for Fence Posts, . 150-164 CHAPTER XVI ESSENTIAL FEATURES AND ADVANTAGES OF REINFORCED CONCRETE Essential Features. Materials Employed, ....... 165-168 CHAPTER XVII HOW TO DESIGN REINFORCED CONCRETE BEAMS, SLABS, AND COLUMNS Nature of the Problem. Kinds of Stresses. Rules for Designing Beams. Rules for Designing Slabs. Tables for Designing. Solution of Ex- amples. Summary of Procedure in Design. Design of Reinforced Concrete Columns. Examples and Solution, ..... 169-193 CHAPTER XVIII EXPLANATION OF THE THEORY OF THE DESIGN OF REINFORCED CONCRETE BEAMS AND SLABS Explanation of the Theory of the Design of Reinforced Concrete Beams and Slabs, and General Specifications for Reinforced Concrete. The Mechanics of the Beam. Stresses and Moments. Derivation of For- mulas,. . . --_ . . . . . . . . . 194-212 CHAPTER XIX SYSTEMS OF REINFORCEMENT EMPLOYED Systems of Reinforcement Employed. Different Forms of Rods and Bars. Special Fabrics and Types of Reinforcement, 213-222 CHAPTER XX REINFORCED CONCRETE IN FACTORY AND GENERAL BUILDING CONSTRUCTION Advantages of Reinforced Concrete in Building Construction. Practical Details of Construction. Slabs, Columns, Floors, Loads, Walls. Roofs. Attaching Machinery, 223-232 [vii] Contents CHAPTER XXI CONCRETE IN FOUNDATION WORK PAGE Importance of Foundations. Loads on Foundations. Methods of Securing Good Foundations. Essential Requirements in Construction. Con- crete in Foundations. Reinforced Concrete Piles. Caissons. Cribs 233-244 CHAPTER XXII CONCRETE RETAINING WALLS, ABUTMENTS, AND BULKHEADS Design of Walls in General. Methods of Failure. Kinds of Retaining Walls. Design of Gravity Walls. Reinforced Concrete Walls. Details of Construction. Foundations. Abutments. Bulkheads. Appearance of Walls. Tables for Design of Walls, .... 245-260 CHAPTER XXIII CONCRETE ARCHES AND ARCHED BRIDGES Definitions. Parts of an Arch. Methods of Failure. Design of an Arch. Abutments and Piers. Reinforced -Concrete Arches. Arch Bridges. Arch Centres. Concreting the Arch, ....... 261-272 CHAPTER XXIV CONCRETE BEAM AND GIRDER BRIDGES Advantages of Concrete Bridges. Kinds of Girder Bridges. Reinforced Concrete. Trusses. Viaducts. Concrete Floors. Abutments. Cen- tring. Depositing Concrete. Surface Finish, . . . . . 273-280 CHAPTER XXV CONCRETE IN SEWERAGE AND DRAINAGE WORKS Advantages of Concrete for Sewers. Forms of Sewers. Combined and Separate Systems. Dimensions of Sewers. Construction of Sewers and Conduits. Quantity of Flow. Culverts and Drains. Types of Culverts. Imperviousness of Sewers and Conduits. Tables of Dimen- sions for Culverts, ,.-.., 281-293 CHAPTER XXVI CONCRETE TANKS, DAMS, AND RESERVOIRS Uses of Concrete Tanks. How to Build Tanks. Reinforcement for Tanks. Concrete Dams. Small Reinforced Concrete Dams. Concrete Reservoirs, 294-304 CHAPTER XXVII CONCRETE SIDEWALKS, CURBS, AND PAVEMENTS Advantages of Concrete Sidewalks. Materials, Equipment, and Forms. Construction of the Sidewalk. Coloring and Protection. Tables of Dimensions and Materials Required. Concrete Curbs and Gutters. Concrete Roads and Pavements. Table of Offsets for Crowning Roads 305-316 [ viii ] Contents CHAPTER XXVIII CONCRETE IN RAILROAD CONSTRUCTION PAGE Foundations and Retaining Walls. Bridges and Trestles. Train Sheds and Platforms. Signal Towers. Power Houses. Shops and Warehouses. Coal and Sand Pockets. Ash Plants. Round Houses. Turntables, Pits, Tank Supports, and Bumping Posts. Concrete Ties and Road- bed. Posts and Fences. Telegraph Poles. Tunnels. Docks. Reser- voirs. Elevators, . . . . . . ... . . . 317-331. CHAPTER XXIX THE UTILITY OF CONCRETE ON THE FARM Advantages of Concrete for the Farmer. Concrete Types Found on the Farm. Posts. Troughs. Tanks. Farm Drainage. Cisterns. Cess Pools. Stalls. Silos. Miscellaneous. Useful Hints for the Farmer 332-343 CHAPTER XXX THE WATERPROOFING OF CONCRETE STRUCTURES The Necessity for Waterproofing. Modern Methods of Waterproofing. General Conditions of the Work. Principles to be Followed. The Membrane Method in Detail. The Integral Method in Detail. Water- proofing by Means of Surface Coatings. Tabular Outline of Modern Waterproofing Processes, . . . 344~374 CHAPTER XXXI GROUT, OR "LIQUID CONCRETE" AND ITS USES Preparing and Mixing Grout. Mixing Machines. Various Uses of Grout 375-385 CHAPTER XXXII INSPECTION OF CONCRETE WORK A SUMMARY OF ESSENTIAL RULES AND PRINCIPLES OF CONSTRUCTION, FOR SECURING GOOD CONCRETE WORK The Work of the Inspector. Inspection of the Cement, Sand, and Aggre-' gates. Proportioning and Mixing. Inspection of Forms, Reinforce- ment and Placing Concrete. Rules for Removing Forms. Rules for Surface Finish. Rules for Blocks, Piles, and Castings, .... 386-399 CHAPTER XXXIII COST OF CONCRETE WORK General Cost of Main Classes of Work. Elements of Cost. Cost of Mate- rials. Cost of Mixing. Cost of Placing. General Expenses. Sum- mary of Costs. Cost of Mortar. Actual Examples of Cost. Building Blocks. Paving. Removing Efflorescence. Stucco. Forms. Cost of Buildings in Terms of Cubical Contents. Cost of Residences. Cost of Sewers. Concrete Pipes. Bridge Piers and Bridges. Piles. Trestles, Sidewalks, Curbs, and Gutters. Fence Posts. Poles. Roofs. Tunnel Lining. Waterproofing. Cost of Concrete Dams, .... 400-421 [ix] SECTION I PRELIMINAKY INFORMATION FOR THE CEMENT AND CONCEETE USEK CHAPTER I INTRODUCTORY The Renaissance of Concrete. The Concrete Age. Concrete Architecture. Con- crete Literature. The Future of Concrete. The Renaissance of Concrete. The history of concrete is a history of an ancient and highly developed art, long lost and for- gotten during the dark centuries of the middle ages, and having a new awakening and renaissance nearly two thousand years later. Some of the costly and magnificent structures of concrete built by the Romans during the period of their supremacy still remain as time-defying evidence of their great skill as constructors, and as monuments to the utilitarian character of their art. As a seed planted in an arid soil springs to life at the first visiting of rain, so has concrete been born anew in the twentieth century when the state of industrial and constructive art became favorable to its develop- ment ; and with such new life, it has reached a much higher state of development, and attained a wider application and a more per- manent place in our civilization than was ever dreamed of by our Roman predecessors. How broadly concrete has entered into our modern lives has been well put by Kerwin in an address before the National Associa- tion of Cement Users in the following words: The Concrete Age. "Our ancestors progressed from the Stone Age to the Iron Age; we seem to be passing from the Steel Age to the Cement Stone or Concrete Age. We tread on concrete walks, travel in concrete subways, over concrete bridges, live and work in Handbook For Cement and Concrete Users concrete buildings, store our grain in concrete elevators, draw our water from concrete reservoirs and cisterns, sanitate our cities with concrete sewers, and are finally buried in concrete cases deposited in concrete tombs, and our numerous virtues are inscribed on concrete monuments." It is certainly well that this development has come at a time when our rapidly disappearing forests have given serious alarm as to our future supply of timber, and what a boon the concrete in- dustry will be to humanity and civilization throughout the world, cannot be appreciated so well to-day as it will years hence when the supply of timber has fallen far below the normal requirements. Mr. Andrew Carnegie is probably best known as a philanthropist interested in education and free libraries, but it should not be for- gotten that he is also probably the greatest living authority on questions relating to the production of steel, and that any statement made by him relating to the position of steel should carry great weight. At the recent conference of governors and scientists at the White House, Washington, which was held under the chairmanship of ex- President Roosevelt, there was a discussion on the conservation of the natural resources of the United States, in the course of which Mr. Carnegie, speaking of iron, said : "The next great use of iron is in construction, especially of buildings and bridges. Fortunately the use of concrete, simple and reinforced, is already reducing the consumption of structural steel. The materials for cement and concrete abound in every part of the country; and while the arts of making and using them are still in their infancy, the products promise to become superior to steel and stone in strength, durability and convenience, and economy and use." For a great steelmaker to announce his conviction that concrete promises to become superior to steel and stone in strength, dur- ability, convenience, and economy, is indeed a matter that should claim the attention of our economists. The period of the most rapid development of the concrete in- dustry was inaugurated when the value of the combination of steel and concrete was recognized. This combination, fortunate as Carnegie says, opened up a field of unlimited usefulness and gave Introductory to our civilization a new material, possessing nearly all the virtues of the materials hitherto employed in construction and few of their defects, and so superior in strength, heat-resisting, and other qualities as to make its universal adoption a matter of certainty. Concrete Architecture. It was at first these utilitarian qualities that were recognized and made use of by engineers, but another great step forward was taken when the artistic and aesthetic possi- bilities of concrete were recognized by architects and builders. The recognition thus accorded has given the latter what it had sought almost in vain for centuries a new style of architecture; a style entirely free from the hereditary tendencies of the ancient and mediaeval styles, and which could be rendered possible only by the introduction of a new material, possessing properties entirely distinct from those whose possibilities had been studied and studied for ages. The essential features of the new style, which will be distinctive of the early years of the present century, are pointed out under the section on Concrete Architecture. Concrete Literature. Another potent influence in the modern development of concrete work is the broad-mindedness and liber- ality of the manufacturers of cement and cement products, in bring- ing home to the public the many marked advantages and possible uses of cement and concrete. Foremost in this class are the many publications of the Atlas Portland Cement Co., the excellence of which, from a typographical, authoritative, and readable standpoint, cannot be overestimated, and in the preparation of this volume the Authors have availed themselves of the Company's kindness in permitting them to extract a number of excellent tables and illustra- tions from their various publications. The excellent series of bulletins issued by the American Associa- tion of Portland Cement Manufacturers are another source by means of which a wide dissemination of knowledge of the possi- bilities of cement has been effected, and from which the Authors have drawn some valuable material. A great deal has been contributed to the industry by the numer- ous organizations formed for the promotion of knowledge on cement and concrete work. The cement shows held in various parts of the country during the past few years have also given an acceleration to the development of the industry. The proceedings of the [3] Handbook for Cement and Concrete Users National Association of Cement Users at their Conventions during these shows have been brimful of new ideas and their annual bulletins have preserved the best of these for future reading and study. The Authors have also used these books in drawing material for this volume. The cement and concrete press of the country have done a great work in spreading widely the gospel of concrete, defending it against attacks by its older but worried competitors and keeping the building public informed of the latest developments in this rapidly growing field. The Future of Concrete. Many other influences have con- tributed to the growth of the concrete industry and these are dis- cussed in the appropriate sections of the book. No doubt the future will witness many new contributing causes, and there is every reason for believing that the future holds out the most brilliant prospect for this apparently homely but invaluable building material. We can prophesy that future ages will be grateful to the present one for the renaissance of concrete, for with it, as time goes on, will come more beauty in our structures, more healthful conditions of life resulting from the sanitary nature of the material, more buildings of historic fame, and temples far more creditable to our architecture; for when the present monumental structures of timber, steel, and iron shall have succumbed to the corroding hand of time, our concrete structures, built of more enduring stuff, will still live and endure to tell the story of the rebirth of concrete in the twentieth century. Ul CHAPTER II .KINDS OF CEMENT AND HOW THEY ARE MADE Common Lime. Lime Mortar. Hydraulic^Lime. Puzzuolana. Hydraulic Cements. Theory of Setting. How Natural Cement is Made. How Portland Cement is Made. White Portland Cement. Slag Cements. Plaster Cements. Choice of Cements. How Portland Cement Comes. LIMES and cements which are used to unite brick, stone, and concrete are nearly all derived from the roasting of pure and impure limestones and can be grouped into three classes. 1. Common, fat, or quick lime, which hardens in air. 2. Hydraulic lime, which hardens in air when slaked, and sets on the addition of water, either when exposed to the air or sub- merged. 3. Hydraulic cement, which, when water is added, sets either in air or under water and acquires great strength. Common Lime. Common lime is a combination of calcium and oxygen, and is obtained by driving off carbon dioxide gas from limestone. When it contains not more than about 12 per cent of impurities, it has the property of absorbing water with great avidity. The process of absorption of water is accompanied by a great rise of temperature, by the evolution of hot and slightly caustic vapors, and finally by the reduction of the lime to a powder. The powder thus formed is called slaked lime, and the operation of adding water to quicklime is thus known as slaking. Good lime comes in hard lumps, and contains but little dust. When slaked, its bulk increases from 2^ to 3^ times its original volume, while the amount of water which it will absorb is nearly 1/4 of its weight. When just enough water is added to lime to cause it to slake, it forms a powder; when more water is added it forms a paste. Lime mortar is made by mixing the paste of slaked lime with sand, and is extensively used in the building trades. The ordinary method of slaking lime consists in first placing the lumps in a layer, 6 or 8 inches deep, in either a water-tight [5] Handbook for Cement and Concrete Users or a basin formed in the sand, and then pouring upon the lumps a quantity of water equal to 2 % to 3 times the volume of the lime. In slaking lime, it is important "that enough water be added, but not too much. If too much is added, the slaked lime is reduced to a semi-fluid condition. If not enough, the addition of water during the slaking chills the lime and renders it granular and lumpy. Covering the bed of lime with a tarpaulin or with a layer of sand retains the heat and accelerates the slaking. All the lime necessary for any required quantity of mortar should be slaked at least one day before it is incorporated with the sand. Lime Mortar. The paste of slaked lime is mixed with from 2j to 3 volumes of sand to form mortar. Sand is used to reduce the cost, and to prevent the mortar from cracking. It also causes the lime paste to spread out in thin films around each grain and thus enables it to harden. Too much sand should not, however, be used, as it tends to make the mortar porous. The hardening of lime mortar is a double process and consists of : 1. The formation of crystals, as the lime gradually dries out. 2. The slow formation of carbonate of lime or limestone through the absorption of carbonic acid from the air. Lime mortar acquires strength only by the absorption of carbonic acid. This is a slow process, and does not take place unless there is a free circulation of air to carry the carbonic acid to the mortar. Hence in a thick wall, lime mortar will harden only after the lapse of years or perhaps never. Lime mortar can neither harden nor acquire strength when used under water or in soil that is constantly wet, because slaked lime cannot crystallize until it dries out, and it cannot absorb carbonic acid when submerged. Lime mortar is also weak, because the absorption of carbonic acid is a very slow process, especially in the interior of the mass. The surface hardens, but the interior remains soft. The carbonic acid penetrates about i/io of an inch into the joint the first year, forming a skin or film which opposes its further absorption, except at a decreasing ratio. So slow is its penetration after the surface film has formed, that the Scotch have a proverb, " When a hundred years are past and gane, then gude mortar turns into stane." Hydraulic Lime. Hydraulic lime is obtained by roasting a [6] Kinds of Cement and How They are Made limestone which contains from 15 to 25 per cent of silica and alumina. In hydraulic limes, there are two principal constituents: i. Free slaked lime; 2. Lime chemically combined with silica and alumina. When a limestone containing silica and alumina is roasted, the two latter elements combine with a portion of the lime, forming silicates and aluminates of lime. The rest remains as free lime in an uncombined state. When treated witri water the free lime is slaked. The action is, however, retarded by the silicates and aluminates, and is much less energetic than that of fat lime. When mixed with water to form a paste, hydraulic lime can be used in the same way as common lime. When so treated the free slaked lime in its composition dries, hardens, and slowly absorbs carbonic acid on exposure to the air. The free lime also causes it to crack when used without sand, but the swelling and cracking are much less pronounced than in the case of fat limes. When used in water or in damp places, the actions of common and hydraulic limes differ greatly from each other. While common lime remains soft, hydraulic lime sets with more or less rapidity. Its property of setting is due to the crystallization of the combined lime, the free lime being inert if not actually washed away by the action of the water. The crystallization of the combined lime and consequent hardening of the mortar is identical with the re- actions which take place in hydraulic cement. Hydraulic lime is, however, much inferior to cement in respect to reliability and strength, and is in consequence but little used in the United States. Hydraulic lime is commonly slaked at the manufactory and shipped in the form of powder. It may be kept without injury in this form if covered and protected from the air. Puzzuolana. The term "Puzzuolana" is commonly applied to a class of materials which, when made into a mortar with either fat or feebly hydraulic lime, impart to the lime the property of setting on the addition of water. This set will take place both when sub- merged and when left exposed to the air. Puzzuolana is a material of volcanic action, which derives its name from Pozzuoli, a city of Italy near the foot of Mount Vesuvius, . [7] Handbook for Cement and Concrete Users where its properties were first discovered. It was extensively used by the Romans in their hydraulic constructions, being pulverized and mixed with slaked lime and a small amount of sand for the formation of hydraulic mortar. HYDRAULIC CEMENTS Hydraulic cements, which are ,the kinds used in concrete con- struction, may be classified according to the method of manu- facture, under three general headings: 1. Portland cements. 2. Natural cements. 3. Puzzolan or slag cements. The term Portland cement is commonly used to designate hydraulic cement formed by burning a mixture of limestone and clay in proper proportions to the point where they begin to fuse or melt. The materials then combine chemically and form a hard clinker, which when ground to a powder acquires the property of setting under water. The term Natural cement is commonly employed to designate a large number of widely varying products formed by burning natural rock without pulverization or the admixture of other ma- terials. When thus roasted a clinker is formed, which when ground to a powder acquires the property of setting under water. The materials used for this purpose are limestones which contain silica, alumina, and iron oxide in quantities greater than would be needed for Portland cement. There are many brands of natural cement. Perhaps the most familiar are Rosendale, Utica, Akron, and Roman cements. Puzzolan or Slag Cements are formed by the admixture of slaked lime with ground blast-furnace slag. The slag has ap- proximately the composition of a hydraulic cement, but lacks a proper proportion of lime to give it the property of setting under water. These cements are sometimes called puzzolana cements, on account of their resemblance to the Puzzolana of Italy. The Setting of Cement. When cement powder is mixed with water to a plastic condition, a chemical action takes place which causes the materials to solidify or set. [81 Kinds of Cement and How They are Made The setting of cement, according to the general theory, is prob- ably due to the action of water in releasing the lime from its chemical union with alumina. This free lime, the moment that it is liberated, is in solution in the water, but owing to the rapidity with which it is liberated the water soon becomes supersaturated with hydrated lime, and the latter crystallizes out in a network of crystals which binds the particles of undecomposed cement together. This action causes the first hardening, or initial set, as it is called. After the initial set has taken place, cements slowly increase in strength. The final hardening is due to the slower liberation of lime from its union with silica. This lime also crystallizes out and the network .of crystals so formed also serves as a binder to hold the particles together. Hydraulic cements increase in strength with time, the increase extending over months or even years. This increase is due to the slow setting of the coarser particles. The whole subject of cement setting is, however, yet in a con- troversial stage. Dr. Michaeles, one of the world's leading cement experts, does not accept the crystallization theory, but advocates what is termed the colloidal theory or the formation of mineral glue in the process of hardening. While to many the theory of setting appears to have only a passing value, the question is really of great importance to the cement manufacturer, as the process, if the colloidal theory were true, could be much simplified and the cost of manufacture largely reduced. HOW CEMENTS ARE MADE The difference between Portland, Natural, and Slag cements is best illustrated by comparing their methods of manufacture as de- scribed in Table I. Manufacture of Natural Cement. Natural cement is produced by the burning at low heat and subsequent pulverization of natural limestone, no preliminary mixing or grinding being required. This natural limestone is composed of an argillaceous carbonate of lime containing varying amounts of silica, alumina, and iron oxide. In the process, the carbon dioxide of the lime stone is almost entirely driven off and the silica, alumina, and iron oxide Handbook for Cement and Concrete Users unite with the lime to form various compounds. When this burned mass is finely ground to a powder and mixed with water it hardens or sets, either in air or under water. TABLE I. OUTLINE OF PROCESS OF MANUFACTURE OF HYDRAULIC CEMENTS Portland Cement. Natural Cement. Slag Cement. i. Grinding of raw ma- terials. 2. Proportioning and mix- ing. 3. Burning. 4. Grinding of the clinker. i. Burning of the natural rock without pulveriza- tion. 2. Grinding of the clinker. i. Cooling of hot blast-fur- nace slag by sudden immersion. 2. Grinding. 3. Mixing with slaked lime. Quarrying and Crushing. Since the rock in its native state contains the proper proportion of the ingredients for natural cement, it is only necessary to break up the quarried rock into convenient sizes and load it into the kiln. In order to insure uniformity of product, it is common practice to mix rock from various layers in the quarry, so that the deficiency of any element in the rock from any particular stratum may be corrected by a corresponding excess in another stratum. The rock is broken up in ordinary rock crushers and conveyed either by belting or tramway to the loading platform at the top of the kiln. Burning and Grinding. The kiln used in the manufacture of natural cement is usually of the vertical continuous mixed-feed type and is built of masonry or iron lined with fire brick. The crushed rock and the fuel, which may be either anthracite or bitu- minous coal of good quality, are spread in the kiln in alternate layers and the mass is burned at an average temperature of about 1,600 F., depending upon the character of the rock. After removal from the kiln the mass is sorted, all underburnt and overburnt clinker being rejected. The material thus rejected usually represents about one-fourth of the total. The calcined rock is then crushed in a pot crusher or other rotary type, and screened. The finer materials are removed to the bins, while the coarse particles go through a further process of grinding. The product then passes to mixers, by means of which a uniformly fine product is assured. [10] Kinds of Cement and How They are Made From the storage bins the material is passed through chutes, and then to the bags or barrels in which it is packed for final shipment. Manufacture of Portland Cement. Portland Cement is pro- duced by burning to incipient fusion, a mixture of finely ground argillaceous and calcareous material, and the subsequent pulveriza- tion of the clinker thus obtained. It will be seen, therefore, that Portland cement differs from natural cement not only in the char- acter of the raw material employed, but also in the quantity of heat required in its manufacture. The Raw Materials. The materials should contain approxi- mately the following quantities of the essential ingredients: Silica, 21-24 P er cent; alumina, 6-8 per cent; lime, 60-65 P er cent ; with small amounts of iron oxide, magnesia, -sulphuric and carbonic acids, and water. These materials may be either limestone and clay, marl and clay, chalk and clay, or cement rock and lime- stone, the last named being the most commonly used. Processes. The method of mixing of the raw materials in preparation for their calcining has given rise to two processes, known as the wet process and dry process respectively. The first is best for soft or wet material such as marl and clay, or chalk and clay. The combined mass is mixed in a vat or wash mill with a large excess of water. The lumps are broken up with agitators and the particles are so finely divided as to be held in suspension by the water. The stuff is then drawn off into a settling basin and the resultant slurry moulded into bricks which are dried and finally calcined in stationary kilns. Owing to the introduction of rotary kilns, the above method has been, to a great extent, super- seded by a semi-wet process which is substantially as follows: The Semi-wet Process. The marl or chalk is passed through a disintegrator and run into storage basins, while the clay is dried and pulverized and mixed with the proper proportion of marl in pans, enough water being added to give the mass a thick, creamy consistency. The wet mixture is then ground either in a pug mill or edge runner and run into slurry tanks, where it is constantly stirred by means of pedals or compressed air. The wet slurry is then pumped directly into rotary kilns and burned at a high tem- perature. Handbook for Cement and Concrete Users The rotary kiln consists of a brick-lined steel cylinder varying from 50 to 200 ft. in length and from 5 to 12 ft. in diameter. By means of appropriate machinery it is slowly rotated at an average speed of one revolution a minute. The cylinder is usually slightly inclined to the horizontal so as to facilitate the movement of the material to the point of discharge. The raw material is introduced at the upper end, and in passing through, it is calcined to all clinker, leaving the kiln at the lower end as hard, glassy lumps ranging from sand to pieces one inch in diameter. The fuel used is generally finely pulverized coal, which is blown in at the lower end, forming a sheet of flame extending through the cylinder. When properly burned, the clinker should appear in the form of an irregular ball of greenish-black color, with faint metallic lustre, and contain but few large pieces. This clinker, red hot when it emerges from the rotary, drops into a conveyor which passes under water jets, cooling the clinker. When thoroughly cool, the clinker passes to the crusher and is then ready for grinding. The material undergoes a preliminary grinding which reduces it to a fineness such that it will pass through a No. 20 or 30 sieve. This is usually done by the ball-mill. A second grinding renders the material fine enough for 90 per cent to pass through a No. 100 sieve, this finer grinding being accomplished by either a tube-mill, Griffin mill, or Lehigh Fuller mill. The powder is then conveyed to a stock-house and seasoned for a time, and finally passes into the discharging bins whence it is weighed out into bags or barrels as required for shipment. The Dry Process. In the dry process, the material is conveyed from the quarry to the mill and is crushed to pieces varying from dust to two inches in diameter. It is then placed into storage bins and the proper proportions decided upon by chemical analysis of samples taken from various portions. An extremely accurate mixture is obtained by using an automatic weighing machine of the tandem type. The mixture is conveyed to a dryer which usually consists of a rotary cylinder worked on the same principle as the rotary kiln, heat being supplied by a small furnace. The tempera- ture is sufficiently high to cause all moisture to be driven off. The material is then ground to a fineness which will permit it to pass through a screen having 20 or 30 meshes to the linear inch; then is [12] Kinds of Cement and How They are Made passed on to the fine grinder where it is still further reduced until from 80-90 per cent will pass a screen of 100 meshes to the linear inch. From the grinding, machines, the finely powdered material is conveyed to bins from which it is automatically fed into the rotary kiln for calcining; the roasting to a high temperature and the subsequent grinding of the clinker thus formed being the same as in the semi-wet process already described. White Portland Cements. Within recent years Portland cements of pure white color have come into the market. Such cements cost about four times as much as ordinary Portland, owing to the ex- pense of manufacture. They are, however, so well adapted to the attainment of architectual and artistic effects as to have come into extensive use for the following purposes: 1. Building ornamentation. For exteriors, steps, railings, columns, doorways, windows, casings, cornices, and panels. 2. Stucco. 3. Concrete building blocks. 4. Interior Decoration. Staircases, wainscoting, panels, reliefs, floors. 5. Statuary. An improved substitute for plaster in reproducing statuary figures and groups for galleries of casts, or exterior and interior decoration. 6. Cemetery Work. For monuments, vaults, columns, urns, etc. 7. Parks and Grounds. For fountains, seats, railings, walks, bridges, etc. 8. Tile, Mosaic, etc. In the production of white or delicate tints and as a cement in place of Keene's cement. 9. Colored Concrete. Permits the use of bright or delicate colors. 10. Painting iron work or concrete. 11. Stainless mortar. For laying up Bedford limestone, sand- stone, or marble. 12. Setting and pointing between blocks or slabs of white marble, limestone, or brick. White cement is mixed with white sand, crushed white quartz, ground marble (not dust), or ground white limestone to produce white concrete or white artificial stone. For the development of this material, credit is due to the Sandusky Portland Cement Co., Handbook for Cement and Concrete Users and to the Vulcanite Cement Co., who are the pioneers in its production. Slag or Puzzuolan Cement is produced by the mixture of granulated blast-furnace slag and slaked lime, and the reduction of the mass to a fine powder. Slag of proper composition, as it comes from the blast furnace, is sprayed with a stream of cold water under pressure; the water granulates the slag and also combines with the elements contained therein, causing evolution of sulphuretted hydrogen and the forma- tion of lime. The slag is dried and then ground, first in a Griffin mill and then in a tube-mill. The lime is burned from very fine limestone, slaked, screened, and dried, and is then incorporated with the slag. The resulting material is fine enough to permit 95 per cent passing through a No. 200 sieve. Caustic soda is added during the slaking of the lime in order to produce a quick-setting cement. Plaster Cements. The activity of the cements previously discussed is presumably due to the formation of crystals containing lime and water. There is another class of cements, the activity of which is due to the crystallization of lime, water, and sulphur when chemically combined. This substance is called calcium sulphate or gypsum. When heated and reduced to powder, it is known as plaster, plaster of Paris, and white cement. Plaster is used for interior walls, ceilings, and decorations; also for reproducing works of marble, pottery, and bronze. Plaster is either quick or slow setting. The former, when mixed with its own weight of water, sets in five minutes, while the latter, under similar conditions, takes fifteen minutes. Plaster heated to redness and mixed in the ordinary manner, will no longer set ; but if, instead of applying a large quantity of water, the smallest possible portion is used, it will set in ten to twelve hours, and become extremely hard. The compressive strength of plaster is about 120 Ibs. per sq. in. Plaster adheres to itself better than to stone or brick. The adhesion to iron is from 24 to 37 Ibs. per sq. in. The quality of plaster may be tested by simply squeezing it with the hand. If it coheres slightly, and keeps in position after the hand has been gently opened, it is good; but if it immediately falls to pieces, it has been injured by damp. [M] Kinds of Cement and How They are Made Plaster forms the basis of many white cements, which are usually laid in two coats; the first of cement and sand is about 1/2 to 3/4 in. thick. The second coat is thinner and is composed of neat cement without the admixture of sand. Portland cement with a large proportion of sand, as much as 90 per cent being used, is useful for interior work. It may be used as a backing for a thin floating of the white cements. White Port- land cements are also used as a final coat where great durability and strength are required. Among the best known gypsum cements are Parian Cement, Keene's Cement, Martin's Cement, and Adamant. These all have plaster of Paris for their base, and are eminently suited to interior work. They can all be brought to a good surface, and can be painted. Parian Cement is hard and quick-setting and well adapted to withstand rough usage. Keene's Cement is harder than the other kinds made from plaster of Paris, and is much used for pilasters, columns, etc. At the present time Portland cement almost exclusively is used for exterior plastering and stucco work. Choice of Cements. The selection of the proper grade of cement to be used in any given structure is, to a great extent, de- pendent upon the character of the work. That cement should be selected which will give the best and most permanent results con- sistent with the limits of cost of the work in question. A few general rules may be formulated for guidance in making a selection. Portland Cement should be used in mortar and concrete for structures subjected to severe or frequently recurring stresses; for all work laid under water or which will come into contact with water immediately after placing; for masonry exposed to the action of the elements. The White Portland is eminently fitted for high- class ornamental work as already stated. Natural Cement may be used in concrete for dry unexposed foundations with moderate compression; for backing or filling in massive concrete or stone masonry; for sewer foundations and for sub-pavements of streets. It is also adapted for use in mortar, for ordinary brick work, and for ordinary stone masonry where the chief hsl Handbook for Cement and Concrete Users requisite is weight or mass. It should never be used in work under water, in marine construction, in columns, beams, floors, or other members subjected to severe or suddenly applied stresses. Puzzolan or Slag Cement is limited to use in sea water, and generally to structures constantly exposed to moisture, as foundations of buildings, sewers and drains, and in the interior of heavy masonry or concrete. It is unfit for use when subjected to mechanical wear, abrasion, or blows, and should never be used where it may be ex- posed to the action of dry air for long periods. Under such con- ditions it will turn white and disintegrate, owing to the oxidation of its sulphides at the surface. Hydraulic Lime is extensively employed on the Continent, especially in France, in the form of Beton-Coignet (a mixture of hydraulic lime with sand and cement). Common Lime mortar is usually limited to brick work and to chimney construction in frame houses. Lime and Cement Mortar is suitable for ordinary brickwork, for light rubble foundations, and for building walls. Portland cement, owing to its greatly superior strength and reliability, is rapidly displacing all other kinds of cement, and it will continue to do so even more rapidly as its cost is lowered. In the following chapters, Portland cement is always referred to unless another is specifically mentioned. How Portland Cement Comes. Portland cement comes in paper bags, cloth sacks, or wooden barrels. The best way to handle it for the average user is in cloth sacks. The manufacturers charge more for this kind of a package, but allow a rebate for the return of the empty bags. The bags must be kept dry and untorn, and shipped back by freight, in exact accord with the requirements of the cement company. Paper bags tear too easily and cause a big percentage of loss, especially on small jobs where any carrying has to be done. Barrels are too bulky to handle easily and are too large a unit for measuring. The weight of the shipping units of cement varies slightly, but in general a paper or cloth bag contains 95 Ibs. of cement, and four such bags make a barrel of 380 Ibs. How to Keep Portland Cement. Cement must be stored in a dry place. It absorbs moisture from the atmosphere with great readiness, and soon becomes lumpy, or even a solid mass, when [16] Kinds of Cement and How They are Made kept in a damp place. Such cement is useless and must be thrown away. Lumpy cement should not be broken up and used again, even if this can be readily done, as it has lost by far the greater part of its adhesive value. In storing cement, throw wooden blocks on the floor, place boards over them, and pile the cement on the boards, covering the pile with canvas or pieces of roofing paper. CHAPTER III PROPERTIES, TESTING, AND REQUIREMENTS OF HYDRAULIC CEMENTS Description of Tests. How the Tests are Made. Standard Requirements for Natural and Portland Cements. Properties of Hydraulic Cements. The properties of a cement which are usually examined to determine its constructive value, are : first, color; second, weight; third, activity; fourth, soundness; fifth, fineness; and sixth, strength. Color indicates the thoroughness of burning and the presence of impurities. With Portland cement, gray or greenish-gray is an indication of good quality. A yellowish shade indicates under- burned material; bluish-gray an excess of lime; and brown, an ex'cess of clay. For decorative purposes, white Portland cements, having all of the properties of gray, are also employed. In these the color does not indicate any inferiority in strength or setting power. Natural cements are generally brown, in light or darker shades. A light color generally indicates an inferior underburned rock. For any particular cement the weight varies with the degree of heat in burning, the degree of fineness in grinding, and the density of packing. Other things being the same, the harder-burned varieties are the heavier. The finer a cement is ground, the more bulky it becomes, and consequently the less it weighs. Hence light weight may be caused either by laudable fine grinding or by objec- tionable under-burning. A barrel of Portland cement, containing 3.8 cu. ft., should weigh about 380 pounds net; natural cements weigh from 250 to 300 pounds net per barrel. The activity of a cement is determined by its rate of setting. For most purposes, where immediate setting is not required to prevent disturbance of the mortar before hardening, the moderately Testing and Requirements of Hydraulic Cements FIG. i. Showing Normal Ce- ment Pat in Good Condition. (After W. Purves Taylor.) slow-setting cements are found most convenient, as they need not be handled so quickly and may be mixed in somewhat larger quanti- ties. Soundness is the most important quality of a cement, as it means the power of the cement to resist the disintegrating influences of the atmosphere or water in which it may be placed. Soundness refers to the property of not expanding, contracting, or cracking during the time of setting. These effects may be due to free lime, free magnesia, or to unknown causes. The question of fineness is wholly a matter of economy. Cement, until ground, is a mass of partially vitrified clinker, which is not affected by water, and which has no setting power. It is only after it is ground that the addition of water induces crystallization. The coarse parts of the cement may be considered as practically inert material which sets only after the lapse of months or years if at all. It is the impalpable powder whicH gives the cement its value, and if this be omitted, the cement is worthless. It is possible to reduce a cement to an impalpable powder. Fine grinding is, however, expensive. The proper degree of fineness is reached when it becomes cheaper to use more cement in proportion to the aggre- gate, than to pay the extra cost of additional grinding. The strength of cement is usually determined by submitting a specimen of known cross-section to a tensile strain. The reason for adopt- ing tensile tests is that comparatively light strains produce rupture. This will be referred to later. FIG. 2. Pat Showing Shrinkage Cracks Due to Overwet Mixture or Too Rapid Drying. Handbook for Cement and Concrete Users HOW CEMENT IS TESTED Having outlined the nature and properties of hydraulic cements, we now propose to take up the methods that may be employed by the cement user to determine whether the material he purchases is up to the standard and fit for use. The testing of cement for use on extensive work has become an art in itself and only men experienced in the work can obtain results that are uniform and reliable. It is therefore not intended to go into details of apparatus and methods employed by the skilled FlG. 3. Pats Showing Cracks Due to Incipient Disintegration and which Warrant Rejection. tester which are of little use to the practical cement user, but an idea of what is done is of general interest. Physical Tests for Cement. On all large works, an inspector is kept at the mills to watch the process of manufacture, and special laboratories are provided for making both chemical and physical examinations. As already stated, the physical examination is employed to determine whether the cement possesses the necessary requirements to make it fit for use. Thus a good cement: First. Should be sufficiently well ground. This is referred to as a test for fineness and is made by passing the cement through sieves of varying meshes. In a good Portland 98 per cent should pass through a No. 100 sieve, having 10,000 holes to the square inch. The finer the cement is ground the greater will be its hydrau- licity, and the greater the proportions of sand that can be used with it. [20] Testing and Requirements of Hydraulic Cements Second. Setting. Cement which sets much too rapidly or does not set rapidly enough may not be fit for use. This may be due to the presence of too much gypsum or the cement may not be suffi- ciently hydraulic. Furthermore, a quick-setting cement may be desired for certain work and slow-setting for other. To determine the setting properties it is customary to prepare pats about 3 inches in diameter and 1/2 inch thick in the middle and with thin edges on glass plates, and allow them to set. When the pat just resists the pressure of a needle -^ inch in diameter weighted with 1/4 pound it is said to have had its initial set. This is usually within 1/2 FIG. 4. Pats Showing Cracks of Complete Disintegration which Begin by the Radial Cracks Shown in Fig. 3. hour to i hour and the process of manufacture may be regulated to obtain the required time of initial set for the work in hand. Cement for use under water or in freezing weather should be quick-setting. When cement has once received its initial set after being mixed for use, it should not be remixed with water or retempered for use, as the setting properties and strength have been greatly disturbed, although when hardened cement is reground it still possesses con- siderable setting power. The final set of cement occurs when it can just resist the pressure of a needle 1/24 inch in diameter weighted with i pound. The time of final setting varies from 3 or 4 to 10 hours; the quick-setting cements are usually stronger at first, but the slower-setting cements acquire greater strength than the others in course of time. An excellent method of testing for setting is to prepare a ball of [21] Handbook for Cement and Concrete Users cement and allow it to set protected from sun and wind. At the end of 20 minutes it should be soft and pliable, damp and not warm on exterior surface. At 10 hours it should be dry, firm, and hard enough to resist pressure of thumb nail. If it hardens or heats in less than 20 minutes the cement should be rejected, as it will set before the concrete is put into place. A cement which will not set in 10 hours will cause difficulty in placing the concrete and a satis- factory cement should set within these limits. The heating referred to is due to free lime and, if in excess, the cement should not be used. Storage will convert the free lime into a hydrated condition in time, and it can then possibly be used. Both the pat and ball tests are also serviceable in determining the presence of free lime. This free lime causes heating when mixed with water and also expands in volume, causing cracking of the pat or ball. When used in the work, over-limed cement may cause disintegration. The presence of free lime can better be determined by subjecting the pat or ball to a hot steam bath for an hour or two, after which it should still remain sound and free from cracks. The presence of lime may also be determined by treating the cement with muriatic acid 3 parts, water i part, cement 1/3 part. A good cement will effervesce about two seconds. If it effervesces continually it con- tains too much limestone or natural cement and should not be used. Cement in the laboratory is also subjected to what is known as the " Specific Gravity" test made by special apparatus and not available to the cement user on the work. The usual specific gravity of a good Portland is about 3.2. A much greater value shows everburning and a lower quantity indicates underburning or adulteration. The test most frequently quoted is that for tensile strength which, like the previous one, cannot usually be made by the cement user, as time and apparatus are required, while uniform and reliable results depend upon the skill and experience of the tester. The tests are made by moulding briquettes into shape like a figure 8 having a cross-section in the centre of exactly i square inch. These briquettes are allowed to set either i, 7, or 28 days and sometimes for even longer periods running into many years. They are then broken in testing machines. The briquettes are made both of pure Testing and Requirements of Hydraulic Cements cement and of cement mortar mixed with varying proportions of sand. These tests are of value because long years of experience have fixed certain values which a good cement should obtain and although pure cement is little used in practice, a standard is thus fixed which serves as a basis of comparison for different cements. Tests are also made on large works by moulding beams, slabs, blocks, and columns of various mixtures of concrete, which are later subjected to special machines, and broken by bending, shear- ing, or compression, and the actual strength determined. It is proper to say here that to the credit of American cement manufacturers, the consumer need have but little fear of the quality of the cement he uses. The great bulk of cement of any of the standard brands will pass the ordinary requirements. Moreover the cement work in most structures is never subjected to anything like the stresses that the strength tests show it is able to withstand. It is only in work where very high unit stresses are employed, such as in reinforced concrete structures that the actual strength of the material is really -approached. It is due largely to the uniformly good quality of cement turned out that the greatest confidence has been established in the mind of the consumer as to its use without testing, and it is due largely to such confidence that the cement industry owes its rapid growth, for without it the present phenomenal expansion would have been impossible. The ordinary cement user should be particularly careful about two things in a newly received shipment of cement. In times of great building activity when the cement mills are run up to fall capacity, there is danger of having the cement too fresh, and in such cases he should order it a month or so ahead of time so as to improve it by storage as already referred to. The second thing is to see that the cement has not been injured in transit or storage, for if dampness has reached the cement it will be lumpy and partially set and its usefulness be largely destroyed. REQUIREMENTS FOR CEMENTS The following are the requirements for natural and Portland cement prepared by the National Association of Cement Users, after an exhaustive study of the subject. Handbook for Cement and Concrete Users STANDARD REQUIREMENTS FOR NATURAL CEMENT Definition. This term shall be applied -to the finely pulverized product resulting from the calcination of an argillaceous limestone at a temperature only sufficient to drive off the carbonic acid gas. Fineness. It shall leave by weight a residue of not more than 10 per cent on the No. 100, and 30 per cent on the No. 200 sieve. Time of Setting. It shall not develop initial set in less than ten minutes, and shall not hard set in less than thirty minutes, or in more than three hours. Tensile Strength. The minimum requirements for tensile strength for briquettes one inch square in cross-section shall be within the following limits, and shall show no retrogression in strength within the periods specified: NEAT CEMENT. Age. Strength, Lbs. 24 hours in moist air 50-100 7 days (i day in moist air, 6 days in water) 100-200 28 days (i day in moist air, 27 days in water) 200-300 ONE PART CEMENT, THREE PARTS STANDARD SAND. 7 days (i day in moist air, 6 days in water) 25- 75 28 days (i day in moist air, 27 days in water) 75-150 Constancy of Volume. Pats of neat cement about three inches in diameter, one-half inch thick at centre, tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. (a) A pat is then kept in air at normal temperature. (b) Another is kept in water maintained as near 70 F. as practicable. These pats are observed at intervals for at least 28 days, and, to satisfactorily pass the tests, should remain firm and hard and show no signs of distortion, checking, cracking, or disintegrating. STANDARD REQUIREMENTS FOR PORTLAND CEMENT Definition. This term is applied to the finely pulverized product resulting from the calcination to incipient fusion of an [24] Testing and Requirements of Hydraulic Cements intimate mixture of properly proportioned argillaceous and calcare- ous materials, and to which no addition greater than 3 per cent has been made subsequent to calcination. Specific Gravity. The specific gravity of the cement ignited at a low red heat shall not be less than 3.10; and the cement shall not show a loss on ignition of more than 4 per cent. Fineness. It shall leave by weight a residue of not more than 8 per cent on the No. 100, and not more than 25 per cent on the No. 200 sieve. Time of Setting. It shall not develop initial set in less than thirty minutes; and must develop hard set in not less than one hour, nor more than ten hours. Tensile Strength. The minimum requirements for tensile strength for briquettes one inch square in section shall be within the following limits, and shall show no retrogression in strength within the periods specified: NEAT CEMENT. Age. Strength, Lbs. 24 hours in moist air 150-200 7 days (i day in moist air, 6 days in water) 450-550 28 days (i day in moist air, 27 days in water) 550-650 ONE PART CEMENT, THREE PARTS SAND. 7 days (i day in moist air, 6 days in water) 150-200 28 days (i day in moist air, 27 days in water) 200-300 Constancy of Volume. Pats of neat cement about three inches in diameter, one-half inch thick at the centre, and tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. (a) A pat is then kept in air at normal temperature and observed at intervals for at least 28 days. (b) Another is kept in water maintained as near 70 F. as practicable and observed at intervals of at least 28 days. (c) A third pat is exposed in any convenient way in an atmos- phere of steam, above boiling water, in a loosely closed vessel, for five hours. These pats, to satisfactorily pass the requirements, shall remain firm and hard and show no sign of checking, crack- ing, and disintegrating. CHAPTER IV CONCRETE AND ITS PROPERTIES What Concrete Is. Kinds of Concrete. Function and Effect of the Cement, Aggregates, Water, Chemicals, Weather Conditions, Gases, Sewage, etc. Laws of Strength and Permeability. CONCRETE is an artificial rock, made by uniting sand, broken stone, gravel, etc., by means of lime or cement. Its principal ingredients are as follows: 1. The matrix or mortar; consisting of cement and sand mixed with water. 2. The coarse aggregate; broken stone, gravel, etc. Concrete made with good Portland cement, in proper propor- tions, becomes so hard and strong that when pieces are broken, the line of fracture will often be found to pass through the particles of stone, showing that the adhesion of the cement to the stone is greater than the strength of the stone itself. Kinds of Concrete. While concrete is generally composed of cement, sand, and broken stone or gravel, the following special combinations are also used : 1. Rubble concrete, also called Cyclopean masonry. 2. Cinder concrete. 3. Asphalt concrete. 4. Reinforced concrete. In constructing massive walls and dams, a reduction in cost may often be obtained by introducing large stones into the concrete. Concrete of this character is called Rubble Concrete or Cyclopean Masonry. The percentage of rubble stones employed varies from a few per cent to over half the volume. The saving effected comes partly from the reduction in the cement required per cubic yard of concrete and partly from the saving in crushing. Cinder concrete is used where great strength is not required. Its most valuable properties are its light weight and the resistance which it offers to heat. It is therefore used for fireproofing and light floor construction. [26] Concrete and Its Properties Cinder concrete is weak and porous. It is not adapted to reinforced work because it is so porous that it does not protect the steel from corrosion. When used, great care must be taken in the mixing and proportioning of the ingredients. A rich mixture of cement should always be required. Asphalt or tar concrete, in which broken stone or cinders are mixed with asphaltum or tar instead of cement paste, is used for CEMENT SAND STONE CONCRETE FIG. 5. Relative Proportions of Ingredients for a 1:2:4 Concrete Mixture. Note that the volume of Concrete is but slightly larger than the volume of Stone, the Cement and Sand filling the voids. waterproofing and for lining reservoirs and constructing mill floors. Such mixtures differ in degree only from the asphaltic cements that are employed for street pavings. Their most valuable proper- ties are, imperviousness to water and elasticity. Reinforced concrete, in which concrete is combined with steel or iron to develop the elastic properties of the latter and at the same time utilizing the great compressive resistance of the former. This is fully discussed in Chapter XVI and those following. FUNCTION AND EFFECT OF VARIOUS AGENCIES ON CONCRETE WORK In considering the properties of concrete and how it is af- fected by various agencies, it is well to keep clearly in mind what concrete actually is and what its constituent parts actually are. The sand and gravel is natural rock disintegrated by natural forces. The broken stone is natural rock disintegrated by artificial forces. The water is just ordinary H 2 O which is clean and free from acids or alkalis. The cement has already been described. An ideal concrete is a mixture with a minimum percentage of voids. This result is obtained by grading the aggregate and Handbook for Cement and Concrete Users mixing in such proportions that the voids in the coarsest aggregate are filled by a finer aggregate, the voids in which are, in turn, filled by a still finer aggregate, the cement itself being so finely ground that its granules will completely coat those of the finest aggregate. When this condition obtains, the set will produce a mass of ever- lasting stone. Many experiments have been made to show the effect on the strength of concrete of the admixture of various materials such as loam, clay, lime, plaster, peat, puzzolan, cement, salt, sawdust, soda, sugar, alcohol, glycerine, and tallow. While some valuable practical use is made of such admixtures, the results are largely of theoretical interest. Cement is the vital element of concrete. Upon its quality the strength and durability of the concrete largely depends. It binds the particles of aggregate together, helps to fill the voids, gives density, and according to its strength or weakness, imparts like qualities to the concrete. Influence of the Aggregates. Crushed quartz, crushed brick, crushed terra cotta, crusher dust and sand have all been used as the finer aggregate in concrete, the use of sand being most prevalent. While the properties and selection of sand are fully discussed in the next chapter we may state here that sand should be coarse rather than fine, and of graded rather than of uniform size in order that a dense concrete shall result. It is customary to specify that sand shall be free from clay or loam. In a rich mortar, the surplus cement furnishes enough fine material for the density required. The addition of clay tends to increase the density and the strength, particularly in lean mixtures. Five per cent may be allowed. A similar effect is produced by the addition of a small quantity; of hydrated lime or waterproofing compound to cement mortar, the density and water-tightness being increased. For the coarse aggregate a variety of materials are in common use. Crushed stone, such as trap rock, granite, limestone, conglom- erate, sandstone, and slate, also gravel and cinders, give satisfac- tion. Trap and granite give a hard wearing surface to the concrete, and are useful as aggregates in all classes of concrete work. Gravel and conglomerate are almost equally valuable. These are fully discussed in Chapter V. [28] Concrete and Its Properties Function and Influence of the Water. The function of water in mixing concrete is to develop the chemical activity of the cement. The proportion of water used has an important bearing on the results attained. Both the time of setting and the strength are affected. A very fine cement will require a larger proportion of water than a coarser cement, in order to give the same degree of consistency. Too little water will produce a weak mortar, as part of the cement will be unaffected. Too much water will cause a slight decomposition of the cement, some of which will pass off in solution, and thus weaken the mortar. The phenomenon of "Laitance" is the result of an excess of water. This is particularly noticeable when concrete is deposited under water, a white scum appearing at the surface. "The effect of different proportions of water upon the ultimate strength depends chiefly upon the density of the resulting mortar; the consistency which produces with a given weight of the same materials, the smallest volume, after setting, of Portland cement paste or mortar, gives the highest strength. Dry-mixed mortars usually test higher than wet after short periods, as they set and harden more rapidly, but more uniform results -in practice can be attained with plastic mixtures." Experiment has shown that coarse, medium, and fine sand require respectively 3 per cent, 9 per cent, and 23 per cent by weight of water. "In many classes of structures where there is an excess of strength, cheapness in placing, the appearance of the surface, or the proper inbedding of reinforcing metal may be of primary importance. In such cases the quantity of water must be suited to the attendant conditions." Dry concrete may be employed in dry locations for mass founda- tions, which must withstand severe compression strain within one month after placing, provided it is carefully spread in layers not over 6 inches thick and thoroughly rammed. Medium wet concrete is adapted for ordinary mass concrete, such as foundations, heavy walls, large arches, piers, and abutments. Very wet concrete is suitable for rubble concrete and for rein- - forced concrete, such as thin walls, columns, floors, conduits, and tanks. Grout or liquid concrete is discussed in Chapter XXXI. Effect of Coloring Matter. Various coloring matters, such as Handbook for Cement and Concrete Users carbon black, iron oxide, ochre, ultramarine, marble dust, and white sand are used in concrete for aesthetic effects. As a rule, the color is not permanent. The effect of these ingredients upon the strength of the concrete varies with the material used. They may be mixed dry with the cement and then submitted to the usual tests. If of mineral origin, their addition in small quantities will not affect the concrete. They rather increase its density. If of vegetable origin, they are apt to impair the strength. In general, it is safe to specify that coloring matter shall be made from metallic oxides free from sulphur. Five per cent of materials of a mineral character may be allowed. Effect of Oils. Mineral oil when mixed with concrete forms an emulsion with the alkali and water, resulting in a less brittle mortar and one much more free from expansion and contraction cracks. The oil also has the effect of delaying the initial and final set somewhat and of decreasing the strength to a small extent. The use of animal or vegetable oils is not recommended, because the result is the formation of acids, which are apt to cause disinte- gration of the concrete. Oil emulsions have formed the basis of many waterproofing compounds and when mineral oils are used they add to the density and quality of the work. Fire-resisting Properties. Concrete possesses great fire-resisting properties. In a severe fire when subjected to a heat as great as 2,000 F., concrete is injured to a depth of perhaps one inch, its body being unaffected. Two inches of good concrete is ample protection against fire for I-beams or steel rod reinforcements. " When brick and terra-cotta are heated, no chemical action occurs, but when concrete is heated up to 1,000 F., its surface becomes decomposed, dehydration occurs, and water is driven off. This process takes a relatively great amount of heat. It would take about as much heat to drive the water out of this outer quarter inch of the concrete partition, as it would to raise that quarter inch to 1,000 F. Now a second action begins. After dehydration, the concrete is much improved as a non-conductor, and yet through this layer of non-conducting material must pass all the heat to dehydrate and raise the temperature of the layers below, a process which cannot proceed with great speed." Effect of Weather Conditions. Heat hastens and cold retards [30] Concrete and Its Properties the set of cement. Therefore, a quick-setting cement should be employed in winter and a slow-setting cement in summer. The sun's heat will cause too rapid evaporation which must be guarded against as it weakens the concrete. Severe cold or frost rarely causes greater damage than surface disintegration. The setting process discontinues at freezing, but starts again when the temperature rises above the freezing-point. This does not injure the concrete, but merely prolongs the attain- ment of its ultimate strength. Alternate freezing and thawing, however, absolutely ruin concrete. Salt water, up to a lo-per-cent solution for concrete, delays the set, but does not weaken the concrete. If a stronger solution is used the salt is apt to work to the surface and cause unsightly stains. Effect of Sea Water. Sea water is objectionable for gauging mortars and concrete not because of its salt, but because the mag- nesium sulphate in water reacts chemically with the lime in the cement, forming various compounds and resulting in the gradual rotting of the cement and the eventual failure of the concrete. A dense concrete protected from the action of the sea water until the cement has thoroughly set is in little danger of injury. Some concrete masonry has remained intact for a very long time in sea water; on the other hand, structures subject to similar conditions have been ruined in a few years. Experience has shown that the cement for use in marine construction should be as low as possible in aluminum and lime. Puzzolan material is a valuable addition to the cement, as it unites with the lime to form insoluble compounds upon which the sulphuric acid of the sea water finds difficulty in making an impression. As little gypsum as possible should be added for regulating the time of setting. Sand containing a large proportion of fine grains is unsuitable altogether, as the per cent of voids is dangerously large. The concrete should be pro- portioned to secure as great a density and impermeability as possible, thereby excluding chemical action from the interior of the mass. Effect of Gases, Acids, Sewage, etc. Gases have little or no effect upon the durability of" the concrete, unless the peculiar character of the aggregate happens to have a chemical affinity for the par- ticular gas to which it is subjected. Certain surface effects have been noted in concrete arches and tunnel linings, which have been Handbook for Cement and Concrete Users exposed to the hot gases from passing locomotives, but in no case has the integrity of the concrete mass been threatened. The great objection to gases is the resulting disfigurement of the surface. Strong acids will affect a concrete surface, but with a silicious or igneous aggregate, the effect will be a slight surface etching. Marked disintegration has been noted in concrete exposed to certain kinds of sewage. The conditions favoring disintegration are altern- ate immersion of the concrete surface in the sewage and exposure to the air. Sewage contains large amounts of sulphuretted hydrogen in solution. When the level of the liquid falls, it leaves the concrete wet with this solution, which may cause oxidation and disintegration. Alternate rise and fall of the liquid level erodes the decomposed cement and exposes new concrete to the attack of the acid. The effect being cumulative, the integrity of the concrete mass is eventu- ally threatened. These effects will not be found unless the sewage in question is of a highly corrosive character, and where there is no free air supply to induce rapid oxidation. Here, as in previous cases, disintegration will not occur in a dense and waterproof concrete, only slight surface injury being possible. (See Chapter XXX.) The following comments on this subject appeared in Engineer- ing Contracting of June 15, 1910: " Failures recorded chiefly in Montana and Colorado demon- strate with certainty that concrete can be completely disintegrated by alkali water and that no brand of cement is less susceptible to damage than others. They also show conclusively two other facts: (i) That porosity of the concrete increases the chances of disinte- gration and, (2) that porous brick and porous stone suffer equally. "The alkali solution must penetrate the concrete if it is to be dangerous. It is known, however, as certainly as may be, that the condition of porosity is essential to the disintegrating action of alkali whether the material be concrete or brick or stone. The obvious preventative is, then, to provide against the penetration of the con- crete by the destructive salt -laden water, and this brings us around to the undetermined problem of making an impermeable concrete. "There are cases where an acid water or an acid sewage has destroyed a cement structure by contact, and also cases- where such a contact in no way injured the structure, but where serious injury [32] Concrete and Its Properties has been caused by gases above the waters after escaping from them; so that, in one case the cement has deteriorated only below the water surface, and in the other it has deteriorated only above it. "The preventative, as in the former case, if practicable, is to ex- clude the objectionable element, or to give the cement a protective coating or lining. "The effects of the gases produce an entirely different condition. The most serious of these is that of the sulphuretted hydrogen which may be converted into sulphuric acid in the sewer above the water. This acid transformed the carbonate of lime in the cement joints into sulphate of lime, a soft, friable gypsum, which gradually caused the complete destruction of the binding quality of the mortar. "In this case, no doubt, a good forced ventilation might have prevented the formation of sulphuric acid, or the sewer might have been given a vitrified lining, or it may be possible to apply a coating which will protect sewers from this sort of destruction. "Structures have been protected against injury from sulphuric acid and other organic acids in peat or similar soils by a complete covering of three layers of asphalt paper. "The foregoing data seem to indicate the following inferences: " i. When the immediate agent of destruction is carried by water, disintegration will be found below the permanent water surface. If such water is flowing inside of a structure, as in a sewer (acid or alkali factory waste), the disintegration will be inside and as far as the water penetrates the material. If the water is ground-water in alkali soil, swamp, or peat, the disintegration will be on the outside and chiefly between high and low ground-water levels, and may penetrate porous material toward the inside of the structure. " 2. When, on the other hand, the agent of destruction is caused by gases (generally sulphuretted hydrogen), arising from waters, whether on the outside or the inside of a structure, the disintegration will take place above the permanent water surface." Strength of Concrete. The strength of concrete as has already been stated, depends upon the mixture employed, character of mixing, care in placing and protecting the work, and upon the age of the concrete. The strength of plain concrete is principally in resisting com- pression or crushing forces, and in this direction it can withstand * [33] Handbook for Cement and Concrete Users very heavy loads, 500 Ibs. per square inch being an average safe working value, which is used in computations for various purposes. While it possesses a good deal of resistance to tensile stresses, it is not economical to employ concrete when such stresses are to be taken care of. As will be seen later, steel performs this duty admirably and in the combination of the two, an excellent new material results, possessing the combined virtues of both. The loads which can safely be placed on concrete structures of various kinds are discussed in the respective chapters of the book. In 1904 and 1905 the Aqueduct Commissioners of New York had an elaborate series of tests made on the strength of concrete, and the following laws were deduced relative to strength and per- meability of concrete. \ 1. The largest size storjj? makes the strongest concrete under both compression and transverse loading, i.e., an aggregate whose maximum size stone is 2 1/4 in. diameter gives stronger concrete than an aggregate with i in. maximum size, and the i-in. stone gives a stronger concrete than a i/2-in. stone. 2. The largest stone makes the densest concrete. Concrete made with stone having a maximum diameter of 2 1/4 in. is notice- ably denser than that with i -in. stone, and this is denser than that with i/2-in. stone. 3. Round material like gravel gives under similar conditions a denser concrete than broken stone. 4. Sand produces a denser concrete than screenings when used with the same proportions of stone and cement. 5. Cement, sand, and gravel concrete is stronger than concrete of cement, screenings, and broken stone, probably because of this greater density. Concrete of cement, sand, and broken stone, how- ever, is found to be stronger than concrete of cement, sand, and gravel, although the latter mix is denser, thus indicating a stronger adhesion of cement to broken stone than to gravel. 6. In ordinary proportioning with two given kinds of aggregates and a given percentage of cement, the densest and strongest mixture is attained when the volume of the mixture of sand, cement, and water is so small as to just fill the voids in the stone. In other words, in practical construction use as small a proportion of sand .134] Concrete and Its Properties and as large a proportion of stone as is possible without producing visible voids in the concrete. 7. Permeability or rate of flow through concrete is less as the per cent of cement is increased, and in very much larger inverse ratio. 8. Rate of flow is less as the maximum size of the stone is greater. Concrete with maximum size stone of 2 1/4 in. diameter is in general less permeable than one with i-in. diameter maximum stone, and this is less permeable than one with i/2-in. stone. 9. Concrete of cement, sand, and gravel is less permeable that is, the rate of flow is less than concrete of cement, screenings, and broken stone. 10. Concrete of mixed broken stone and sand is more permeable than concrete of gravel and sand, and less permeable than concrete of broken stone and screenings, which indicates that for water- tightness less cement is required with rounded sand and gravel than with broken stone and screenings. 11. The rate of flow decreases materially with age. 12. Rate of flow increases nearly uniformly with the increase in pressure. 13. Rate of flow increases as thickness of concrete decreases, but in a much larger inverse ratio. [35] CHAPTER V SAND, BROKEN STONE, AND GRAVEL FOR CONCRETE Selection of Sand. Tests for Sand. Washing Sand. Mixture of Bank Sand and Gravel. Broken Stone. Gravel. THE importance of selecting good aggregates for concrete is second only in importance to the selection of cement, forming as it does by far the greater part of the structure. The gradation in size, proportioning, etc., of these materials, which is treated later, have, as has been seen, an important bearing upon the density and economy of the work and all reasonable means should be taken to secure as good material as is available. Selection of Sand. The value of sand for concrete depends largely on its coarseness, graduation in size of the grains, and clean- liness. Fine sand contains more voids, more surfaces to coat, and requires more cement and water than coarse sand. The sharpness of the grains of sand has little to do with its value. It has commonly been supposed that sand should be sharp. This, however, is one of the theories which have been exploded. In fact, there are many arguments in favor of coarse, round-grain sand. Compactness is what is desired, giving density to the mortar; round grains compact more readily than sharp grains, and the cement will cling to the surface of round grains as well as sharp grains, the character of the surface being identical. Sharp sand is only of value as indicating a silicious sand. Good sand cannot be easily denned, or an inflexible specification written, as sands of various properties may make equally good concrete. All things being equal, a coarse sand containing a large percentage of coarse particles is far superior to a fine sand in which few coarse particles are present. The best sand is that which, when mixed with cement and water in the required proportions by weight, produces the least volume of mortar. Economy can be practised in the matter of the selection of sand. It will nearly always pay the concrete con- 136] Sand, Broken Stone, and Gravel for Concrete structor to haul sand even from a considerable distance, paying a higher price, provided he cannot get a sand in the immediate locality of the work, which sand is so graduated in size of grains as to give the greatest density. Sand containing vegetable matter is of doubtful quality, as a small quantity may sometimes prevent hardening. The kind of impurity is really of more importance than the quantity. How to Test for a Clean Sand.* Two rough tests are as follows: (a) Pick up a double handful of moist sand from the bank; open the hands, holding them with the thumbs up; rub the sand lightly between the hands, keeping them about 1/2 inch apart, allowing the sand to slip quickly between them. Repeat this operation five or six times, then rub the hands lightly together so as to remove the fine grains of sand which adhere to them, and examine to see whether or not a thin film of sticky matter adheres to the fingers; if so, do not use the sand, for it contains loam. A further test is to scrape some of this matter from the fingers on the end of a penknife and take a little of it between the teeth. If it does not feel gritty or sharp it indicates vegetable loam, which is bad. Do not use this sand, or if no other can be obtained test it further to make sure that there is not sufficient loam present to prevent the cement from getting thoroughly hard. The sand for the test given above must be moist, just as it comes from the bank. When dry the dirt will not stick to the fingers, hence this test cannot be used. Some idea can be obtained, however, by the appearance of the sand, even if it is dry. If it looks "dead," an appearance which is caused by the particles of dirt sticking in little lumps to the grains of sand, sometimes also making the grains of sand stick together in little bunches when picked up, it is almost a sure sign of vegetable matter, and the sand should not be used. Fine roots in a sand will also indicate the presence of vegetable matter. (b) Make up two 6-inch cubes of concrete, using the same cement and the same sand and gravel or stone as will be used in the structure to be built, and mixing them in the same proportion * From " Concrete Construction about the Home and on the Farm," published by The Atlas Portland Cement Co. [37] Handbook for Cement and Concrete Users and of the same consistency. Keep one block in the air out of doors for 7 days and the other in a fairly warm room. The specimen in the warm room should set so that on the follow- ing day it will bear the pressure of the thumb without indentation, and it should also begin to whiten out at this early period. The specimen out of doors should be hard enough to remove from the moulds in 24 hours in ordinary mild weather, or 48 hours in cold, damp weather. At the end of a week, test both blocks by hitting them with a hammer. If the hammer does not dent them under F/ne Trough to run off " dirty wafer Trough /o 6e //nect wjfh Sarrecf/ja/zer FIG. 6. Washing Trough for Sand and Gravel. light blows, such as would be used for driving tacks, and the blocks sound hard and are not broken under medium blows, the sand, as a general rule, can be used. How to Wash Sand. Sand cannot be washed simply by wetting the pile of sand with a hose, for this only washes or transfers the dirt to a lower part of the pile. Sand, provided it is not too fine, can be satisfactorily washed, however, by making a washing trough. For sands a screen with 30 meshes to the linear inch is necessary to prevent the good particles from passing through it. This must be supported by cleats placed quite near together, or it will break through. The sand is shoveled on to the upper end of the trough by one man, while another one can wash it with a hose. The flow of water will wash the sand down the incline, and as the sand and water pass over the screen the dirty water will drain off through the screen, leaving the clean sand for use. By this arrangement the [38] Sand, Broken Stone, and Gravel for Concrete dirt which is washed out cannot in any way get mixed with the clean sand. Natural Mixtures of Bank Sand and Gravel. Very often the sand and gravel found in a bank are used by inexperienced people, just as it is found without regard to the proportions of the two materials. This may be all right in some cases, but generally there is too much sand for the gravel or stone, so that the resulting con- crete is not nearly as strong as it would be if the proportions between the sand and gravel were right. It is better then to screen the sand from the gravel through a i/ 4-inch sieve, and then mix the materials in the right proportions, using generally about half as much sand as stone. By so doing a leaner mix can be used than where the sand and gravel are taken from the bank direct. The cost of the cement saved will more than pay for the extra labor required to screen the material. For example: Using even a very good gravel bank, a mixture one part cement to four parts natural gravel must be employed instead of one part cement to two parts sand to four parts of screened gravel. So much more cement is thus required with the natural gravel that a saving of one bag of cement in every seven is made by screening and remixing in the right proportion. Crusher Screenings. Screenings from broken stone make an excellent fine aggregate, which can be substituted for sand unless the stone is very soft, shelly, or contains a large percentage of mica. Broken Stone for Concrete.* The purpose for which the concrete is intended must always influence the selection of the stone. For a very strong concrete, a hard stone without any surface scale is necessary; a rich mortar will not entirely counterbalance a deficiency in the strength of the stone. For a medium strong concrete the hardest stone need not be insisted upon, but rather one to which the mortar will best adhere, such as some of the limestones. For fireproof construction some of the limestones and rocks containing feldspar should be avoided; good boiler furnace cinders have proved best for fire-resisting concrete. For all classes of concrete, stone breaking in cubical form is far better than one breaking in flat layers such as shale or slate, it * Condensed from paper on "Concrete Aggregates," by Albert Moyer. [39] Handbook for Cement and Concrete Users being almost impossible to ram or tamp such stone into as dense and compact a mass as that breaking in cubical fracture. The size of the stone aggregates depends on the purpose for which the concrete is to be used. For large masses of concrete, 2-1/2 -inch stone is usually considered the maximum size, but for 12-inch walls and the usual class of concrete construction, 3/4 inch will be found sufficiently large. Quarry tailings, etc., in crushed stone, are not a detriment, as is commonly supposed, but in fact a decided advantage, for the reason that the voids are thus reduced, giving greater density and consequently greater strength. Material which is foreign to the stone, such as vegetable mould, scale, or loam, which cling to the surface will reduce the strength of the concrete. Numerous tests conducted during the last several years by competent engineers have shown that clay in small pro- portions, not over 15 per cent, when well mixed in the mortar, does not reduce the strength of the concrete; in fact, tests have shown that the strength has been increased. This applies particularly to the leaner mixtures. If carefully mixed, therefore, the clay will not cling to the stone, but will become part of the mortar, and in testing for proportions of stone, sand, and cement, the amount of clay present should be figured as part of the mortar and not as part of the stone. Gravel for Concrete. Gravel is often superior to broken stone, being usually found graded from coarse to fine; the roundness of the pebbles lends aid to compactness. It is not likely to bridge and leave holes in the concrete. The percentage of voids is usually less than in broken stone; the quartz pebbles are harder, stronger, and less liable to fracture. Sandstone pebbles are not considered as good as the better grades of crushed stone. The usual argument against gravel is that the mortar is not supposed to adhere as well to the surface as to that of freshly broken stone. This is one of the theories which is practically due to the appearance of the surface to the eye or touch; the adhesion of mortar to limestone of a smooth surface, may be far greater than to sand stone or rougher materials. If roughness was the only requirement for adhesion it would seem impossible to cement together two pieces of glass. From the standpoint of durability, gravel must be superior to Sand, Broken Stone, and Gravel for Concrete stone for the reason that, by the laws of the survival of the fittest* and by process of elimination, nature has supplied us with the most durable. Short-time tests for compression strength usually show broken stone concrete to be superior, but long-time tests of from six months to a year show gravel concrete on an average to be equal if not stronger. In construction work where tensile or other stresses are to be cared for, as may occur in reinforced concrete, crushed gravel should be used. The cement will adhere more readily to crushed than to the rounded, polished surface of the gravel. CHAPTER VI HOW TO PROPORTION THE MATERIALS Nature of the Problem. Voids in Concrete. Methods of Proportioning. Tables for Proportioning. Nature of the Problem. A great deal of study has been given to the question of proportioning the materials of concrete, and most of the study has been directed to one end; viz., to find a mixture that will give the maximum density and strength with a minimum amount of cement. The difficulties in arriving at any definite rules for obtaining this result arise from the great variation in the various elements affecting the work, no two materials being exactly alike, and rules deduced from one set of experiments being of very doubtful value when applied to other conditions. Although a good deal of care in proportioning is warranted, to obtain the best mix with any given material, too great refinement is unnecessary and the theoretical methods which have been gone into with such great detail in many of the books on concrete work have more of an aca- demic interest than a practical value. The principal thing to bear in mind in order to obtain the densest possible mixture is to eliminate the voids in the concrete mass, and to do this, it is desirable that the sand and gravel be well graded from coarse to fine and enough cement be used to obtain a rich mixture. Plenty of water, to obtain a wet mix, should be employed, as water will drive out the air entrained between the particles of the aggregates. The density, strength, and watertightness of concrete will be increased in accordance with the richness, variation in size of aggregate, and with the plasticity of the mixture. Mix rich and mix wet to obtain the best work. The question of proportioning is, of course, also dependent upon the use to which the concrete is to be put and in many locations density and strength may not be the prime requisites, and then a very small percentage of cement will suffice to obtain a hardened mass; as low as 5 per cent has given a strong concrete, [42] How to Proportion the Materials Voids in Concrete. American engineers proportion concrete mixtures by measure, thus a 1:2:4 concrete is composed of i volume of cement, 2 volumes of sand, and 4 volumes of broken stone. Both the sand and the coarse aggregates employed for concrete contain voids or empty spaces between their particles. In a perfect mixture the cement would fill the voids in the sand and coat each grain, while the sand with its coating of cement would fill the voids in the aggregate and also cover each stone with a film of mortar. In practice, it is impossible to fill all of the voids in concrete. In the first place, the cement and sand cannot be perfectly dis- tributed, and in the second place, the water used in the mixing causes the sand to swell, thus increasing the voids about 10 per cent. This swelling is due to a film of water between the grains, and this film cannot be entirely displaced by the cement. When the water evaporates after a wall of concrete has set, voids always remain throughout the mass, and some shrinkage of the mass occurs. A rich mixture is obtained when the cement is somewhat in excess of the quantity that would, theoretically, be sufficient to fill the voids in the sand. Sand and gravel contain from 30 to 50 per cent of voids, while the voids in broken stone range from 40 to 50 per cent. The proportion of voids may be approximately determined in either sand or broken stone in the following way : Wet the loose aggregate thoroughly; fill a vessel of known capacity with the material, and then pour in all the water the vessel will contain. Measure the volume of water required and divide this by the volume of the vessel. The quotient represents the proportion of voids. Method of Proportioning. The ordinary mixture for watertight concrete is about i : 2\ : 4% which requires 1.32 barrel of cement per cu. yd. of concrete. The most scientific method for proportion- ing the ingredients is that known as the Mechanical Analysis. In this method the available materials, including the' cement, are separated into various sizes by means of a series of sieves. Curves are then plotted on cross-section paper which indicate the per- centages of the whole mass that pass the several sieves. From a study of these curves, the proportions of the different ingredients [43] Handbook for Cement and Concrete Users are determined. This method is, however, not available in the usual course of concrete work. In hand-mixing, cement is generally measured by specifying the number of bags to a batch. Machine mixers frequently have automatic measuring devices. When removed from the bag or barrel, cement occupies about 15 per cent more space than when in the original package; or a i : 2 : 4 mixture measured by counting the number of bags will be 1 5 per cent richer than a 1:2:4 mixture, which is proportioned by measuring the cement loose. Hence in determining the proportions, the methods of measuring the cement should be considered and specifications should clearly provide how this shall be done. Volume of Barrel of Cement. The difference between the volume of a barrel of cement when measured packed and loose, and variations in size and weight have been subjects of extended controversy and often bitterness between engineer and contractor, and has resulted in much friction and litigation. The tendency now is to fix an arbitrary but average value for the volume of the cement barrel as a standard, and have this used as a basis on all concrete work. The value of 4 cu. ft. to the barrel is preferred, the actual volume being about 3.75 cu. ft. packed and 4.2 cu. ft. loose. The fixing of such a standard of value is highly de- sirable, and would be of great benefit to engineers and contractors alike. Proportions by Formula. A number of formulas have been introduced for proportioning the sand, cement and stone and it is worth the cement user's while to take note particularly of the one here given, as it is exceedingly simple and may save much trouble in proportioning. While proportioning by formula is not employed as frequently as proportioning by rule of thumb, the method has been employed to work out some excellent tables for proportioning concrete and these tables are extremely useful in estimating the amount of cement required on any particular job as well as for other construction purpose. The simplest formula for this purpose is: 27 s ~ng 21 g [44] How to Proportion the Materials B = number of barrels of cement per cu. yd. of concrete. n = number of cubic feet in barrel of cement as specified. g = number of parts of gravel to i part cement as specified. C = number of cubic feet of sand per cu. yd. of concrete, s = number of parts of sand to i part of cement as specified. This formula assumes that the voids in the gravel are filled by the sand and the voids in the sand are filled by the mortar, and therefore the results are approximate. Thus for a i : 2 : 4 concrete, when i bbl. cement is specified as 4 cubic feet, B = 27 4X4 1.7 bbls. cement. C = 27XY~ = = I 3-5 cubic feet sand. 2 The following table was computed by Gillette's formula, giving the quantities of cement, sand, aggregate, and water required to produce one cubic yard of wet concrete : TABLE II. INGREDIENTS IN ONE CUBIC YARD OF CONCRETE. Voids in Sand, 40 per cent. Voids in Stone, 45 per cent. Proportions by Volume. 1:2:4 1:2^:4$ 1:2:5 1:2*15 ^3:5 i:3:6 Per Cent of Voids in Concrete. . . . 10% 8% 12% 12% 12% 14% Bbls. Cement: Measured Packed per cu. yd. of Concrete, i bbl . = 7 8 cu ft I 4.6 I 32 i .2tr I 2O I .I^ i .00 Cu. yds. Sand per cu. yd. Concrete .41 .46 35 .42 48 .42 Cu. yds. Stone per cu. yd Concrete. .82 .83 .88 .84 .80 .84 Approximate per cent of water for wet mixtures IT.% 12*% 17% 12*% 12% 12% In Table II, the approximate amount of water required for a wet mixture is expressed as a percentage of the combined weight of sand and cement. These percentages are, however, only approximate. More water is required in dry than in moist atmo- spheres, and more in summer than in winter. A wetter mixture is also required when the material cannot be tamped. While a dry mixture is theoretically the stronger when carefully deposited and [45] Handbook for Cement and Concrete Users well tamped, yet a wet mixture is more frequently employed be- cause stronger under working conditions. Wet mixtures flow readily into the corners and angles of the forms and between and around the reinforcing bars, with only a small amount of puddling and slicing. TABLE III. MATERIALS FOR ONE CUBIC YARD COMPACT PLASTIC MORTAR BASED ON BARREL OF 3.8 CUBIC FEET. From " Concrete Plain and Reinforced," by Taylor & Thompson. RELATIVE PROPORTIONS BY PARTS. RELATIVE PROPORTIONS BY VOLUME. Packed Cement Barrels. Loose Sand Cubic Yard. Cement. Sand. Cement Barrel. Sand Cubic Feet. 8.31 i 1.9 6-73 0.47 I 3-8 5.01 0.71 J i 5-7 4.00 0.84 2 7-6 3-32 o-93 2 I 9-5 2.84 i .00 3 i 11.4 2.48 1.05 3* I J 3-3 2 .20 i. 08 4 i 15 .2 .98 i .11 4l 17.1 .80 1.14 5 19 .0 65 1.16 5l 20 .9 52 1.18 6 22.8 .41 1.19 6| 24.7 32 I. 21 7 26.6 23 I .21 7i 28-5 .16 I .22 8 30-4 .10 1.24 [46] CHAPTER VII HOW TO MIX AND PLACE CONCRETE Methods of Mixing. How to Mix by Hand. Materials Required for Two-Bag Batch. Mixing by Machine. Placing the Concrete. Protection of Concrete After Placing. Placing Concrete Under Water. THE proper mixing and placing of concrete is fully as important as is the proportioning of its ingredients. Two general methods are in use : (i) Hand mixing; (2) Machine mixing. MIXING CONCRETE BY HAND The making and placing of concrete by hand is divided into the following operations : 1. Loading into barrows, buckets, carts, or cars, which are used to transport the cement, sand, and stone to the mixing board. 2. Transporting and dumping the materials. 3. Mixing the materials by turning with shovels and hoes. 4. Loading the concrete by shovels into barrows, buckets, carts, or cars. 5. Transporting the concrete to piace. 6. Dumping, spreading, and ramming. Hand mixing is used for small batches. The stone and sand are measured in bottomless boxes and the cement by counting the number of bags to a batch, each bag representing a quarter of a barrel. As hand mixing is so largely employed throughout the country on the smaller jobs, the following detailed description is given, and if carefully followed, any intelligent person should be able to secure a satisfactory mix. In this description * we have taken as a basis a " Two-bag Batch" of i : 2 : 4 concrete. The amount of material re- quired is given in the Tables IV and V. * This description is adapted from Bulletin No. 20, published by American Associa- tion of Portland Cement Manufacturers. [47] Handbook for Cement and Concrete Users Concrete Board. A concrete board for two men should be 9 feet x 10 feet. Make it out of i-inch boards, 10 feet long, surfaced on one side, using five 2 inch x 4 inch x 9 foot cleats to hold them together. If i inch x 6 inch tongue-and-groove roofers can be obtained, they will do very nicely if fairly free from knots. The object of the surfaced board is to make the shovelling easy. The boards are so laid as to enable the shovelling to be done with, and not against, the cracks between the boards. The boards must be drawn up close in nailing so that no cement grout will run through while mixing. Knot-holes may be closed by nailing a strip across them on the under side of the board. It is a good precaution against losing cement grout to nail a 2 inch x 2 inch or 2 inch x 4 inch piece around the outer edge of the board. Often 2-inch planks are used in making concrete boards, but these are unnecessarily heavy and very cumbersome to move. Placing the Concrete Board. The concrete board is a manu- facturing plant, and the advantages of its location should be care- fully considered. Generally it is best placed as close as possible to the forms in which the concrete is to be deposited, but " local conditions" must govern this point. Pick a place giving plenty of room, near the storage piles of sand and stone (or pebbles). Block up your concrete board level, so that the cement grout will not run off on one side, and so that the board will not sag in the middle under the weight of the concrete. Runs. Do not use any old boards that are handy for the wheelbarrow runs. Make a good run, smooth, and at least 20 inches wide if much above the ground. .It is surprising how this one feature will lighten and quicken the work. Tools and Plant. List of tools and plant to be used in mixing, giving sizes, quantities, etc. Concrete Board for 2-Bag Batch, 9' x 10' in size. 9 pcs. f" X 12" X IO'Q", surfaced one side and two edges. (Any width of plank may be used; 12" is specified only for convenience.) 5 pcs. 2" X 4" X 9'o" rough. 2 pcs. 2" X 2" X IO'Q" rough. 2 pcs. 2" X 2" X 9'o" rough. [48] How to Mix and Place Concrete Concrete Board for 4-Bag Batch, 12' x 10' in size. 12 pcs. f" X 12" X ro'o", surfaced one side and edges. (Any width of plank may be used; 12" is specified only for convenience.) 5 pcs. 2" X 4" X 1 2V rough. 2 pcs. 2" X 2" X 10 V rough. 2 pcs. 2" X 2" X i2'o" rough. . 2", 2 1/2", or 3" plank 10" or 12" wide. Measuring Boxes for Sand and Stone or Gravel. For 2-Bag Batch 1:2:4 Mixture : 4 pcs. i" X n$ X 2'o" rough. 2 pcs. i" X n$" X 4'o" rough. 2 pcs. i* X n$" X 6V rough. NOTE. The 2 pcs. 4V long and the 2 pcs. 6V long have an extra foot in length at each end to be made into a handle. For 2-Bag Batch 1:3:6 Mixture: 2 pcs. i" X n$" X 2V 2 pcs. i" X n$" X 3V 2 pcs. i" X 1 4" X s'o" 2 pcs. i" X n$" X 6V NOTE. The 2 pcs. 5V long and the 2 pcs. 6V' long have an extra foot in length at each end to be made into a handle. For 4-Bag Batch: Double cubic contents of boxes and order lumber accordingly. Shovels. No. 3 square point. Wheelbarrows. At least two necessary for quick work; sheet- iron body preferred. Rake. Water-barrel. Water-buckets. 2-gallon size. Tamper. 4" x 4" x 2'6", with handles nailed to it. Garden spade or "spading" tool, as shown in Fig. 13. Sand Screen. Made by nailing a piece of 1/4" mesh wire screen 2 1/2' x 5' in size to a frame made of 2" x 4". Mixing. With the mixing board placed and the "runs" made, the concrete plant is ready. First load your sand in wheelbarrows from the sand pile, wheel on to the "Board," and fill the sand-measuring box, which is placed 4 [49] Handbook for Cement and Concrete Users about two feet from one of the lo-foot sides of the board. When the sand box is filled, lift it off and spread the sand over the board in a layer 3 inches or 4 inches thick. Take the two bags of cement and place the contents as evenly as possible over the sand. With two men start mixing the sand and cement, each man turning over the half on his side. Starting at his feet and shovelling away from him, each man takes a full shovel-load, turning the shovel over. In turning the shovel, do not simply dump the sand and cement but shake the materials off the end and sides of the shovel, so that the sand and cement are mixed as they fall. This is a great assistance in mixing FIG. 7. Homemade Tools for the Concrete Worker. these materials. In this way the material is shovelled from one side of the board to the other. After the last turning, spread the sand and cement out carefully, place the gravel or stone measuring box beside it and fill from the gravel pile. Lift off the box and shovel the gravel on top of the sand and cement, spreading it as evenly as possible. With some experience equally good results can be obtained by placing the gravel measuring box on top of the carefully levelled sand and cement mixture, and filling it, thus placing the gravel on top without an extra shovelling. Add about three-fourths the required amount of water, using a bucket and dashing the water over the gravel on top of the pile as evenly as possible. Be careful not to let too much water get near the edges of the pile, as it will run off, taking some [50] How to Mix and Place Concrete cement with it. This caution, however, does not apply to a properly constructed mixing board, as the cement and water cannot get away. Starting the same as with the sand and cement, turn the materials over in much the same way, except that, instead of shaking the materials off the end of the shovel, the whole shovel load is dumped and dragged back toward the mixer with the square point of the shovel. This mixes the gravel with the sand and cement, the wet gravel picking up the sand and cement as it rolls over when dragged back by the shovel. Add water to the dry spots as the mixing goes on until all the re- quired water has been used. Turn the mass back again, as was done with the sand and cement. With experienced laborers, the concrete would be well mixed after three such turnings ; but if it shows streaky or dry spots, it must be turned again. After the final turning, shovel into a compact pile. The con- crete is now ready for placing. Mixing Natural Mixture of Bank Sand and Gravel. Spread out the mixture of sand and gravel as much as the board will readily permit, add enough water to wet the gravel and sand thoroughly, spread the cement evenly in a thin layer over the sand and gravel, and turn over, as described previously, at least three times, adding the rest of the water nec- essary to get the required consistency while the materials are being turned. It requires some experience to work up a natural mix- ture of bank sand and gravel, and if at all doubtful about the concrete made from it, first screen the sand from the gravel and then mix in the regular way. Number of Men. For the above operation only two men are required, although more can be used to advantage. If three men are available, let two of them mix as described above and the third man supply the water, help mix the concrete by raking over the dry or unmixed spots as the two mixers turn the concrete, help load the wheelbarrows with sand and stone or gravel, etc. [SO FIG. 8. Homemade Con- crete Tamper. Handbook for Cement and Concrete Users If four men are available, it is best to increase the size of the batch mixed to a four-bag batch, doubling the quantities of all materials used. The cement board should also be increased to 10 feet x 12 feet, as shown under " Tools." In this case the mixing is in the middle of the board, each pair of men mixing exactly as if for a two-bag batch, except that the concrete is shovelled into one big mass each time it is turned back on to the centre of the board. When more than four men are available, the rest may place the concrete, make new runs, load wheelbarrows, etc., taking the con- crete away from the board as fast as it is mixed. In this case another small concrete board should be placed next to the big " board," so that in the last turning the batch can be shovelled over on to the small board for placing, making room on the big board to mix the next batch. The small platform need be only just big enough to hold the pile of mixed concrete. TABLE IV. SHOWING THE QUANTITIES OF MATERIALS AND THE RESULTING AMOUNT OF CONCRETE FOR TWO-BAG BATCH. PROPOR- TIONS BY TWO-BAG BATCH. PARTS. KIND OP CONCRETE MIXTURE. 13 > Materials. Size of Measuring Boxes. Inside Measurements. ss . pi O O m o *i TJ 1 -5J .ss^ 0> V > (_, fli ^5 I 1 a 3 CO 1 c g 1 1 l| r^ Bags. Cu. Ft. Cu. Ft. Cu. Ft. Gallons. 1:2:4 Concrete i 2 4 2 3i 7^ 8^ 2' X 2' 2' X4' 10 XnJ* xny 1:3:6 Concrete i 3 6 2 5f ni 12 2' X 3 ' 3'X4' '31 MIXING CONCRETE BY MACHINE Machine mixers are more efficient and economical than hand labor and are used exclusively on all large jobs. In machine mixing, the making and placing of concrete is divided into the following operations: [52] How to Mix and Place Concrete 1. Transportation of the raw materials to the stock piles or bins. 2. Transportation from the stock piles or bins to the mixer. 3. Proportioning, mixing, and discharge of the batch into buckets, cars, or other vehicles. 4. Transportation from the mixer to the work. 5. Dumping, spreading, and ramming. TABLE V. SHOWING THE QUANTITIES OF MATERIALS AND THE RESULTING AMOUNT or CONCRETE FOR TWO-BAG BATCH USING NATURAL MIXTURE OF BANK SAND AND GRAVEL. KIND OF CONCRETE MIXTURE. PROPOR- TION BY PARTS. TWO-BAG BATCH FOR NATURAL MIXTURE OF BANK SAND AND GRAVEL. Cement. 11 _x fe Materials. o c . Size of Measur- ing Boxes. 10 Cement. Natural Mix- ture of Sand and Gravel. Mixture of Sand and Gravel. 1:2:4 Concrete I i 4 6 Bags. 2 2 Cu. Ft. Cu. Ft. 12 2' X4' X ni" 3' X4' X iij" 1:3:6 Concrete.. The plant required depends upon the size of the job. Boats, cars, cableways, conveyors, derricks, hoists, and other appliances are frequently employed for transportation purposes. Types of Mixing Machines. The following types of mixers are in general use : a. Tilting mixtures. b. Non-tilting mixtures. i. Batch mixers ( a. Hand proportioning of ingredients. 2. Continuous mixers. 4 . ,. ( 0. Machine proportioning of ingredients. 3. Gravity mixers. . . . a. Trough form with deflectors. 6. Hopper form. i. In the batch mixers, a charge of cement, sand, aggregate, and water is put into the machine, which mixes and discharges the batch before taking in another charge. In tilting machines the concrete is discharged by raising one end of the drum and causing the mixture to flow out by gravity. [53] Handbook for Cement and Concrete Users In non-tilting mixers, steel deflectors are provided in the drums, which plough through and pick up the batch as the drum revolves. To discharge the batch, a chute is provided. When this chute is tilted so that one end projects into the mixer, the material picked up by the deflectors drops back on to the chute and runs out. The special features of the batch mixer are as follows. 1. It is suitable for either a constant delivery of large quantities of concrete, or for small quantities at irregular intervals. It is, therefore, the only type fit for light work such as reinforced concrete. 2. The exact proportions specified for the concrete can be assured with the greatest accuracy. 3. The engineer can at any time check the proportions being used. FIG. 9. Concrete Mixer with Automatic Measuring Devices. (English Type.) 4. The amount of water can be measured exactly. 5. The amount of mixing given to the concrete is under the control of the engineer, and by specifying a definite number of revolutions of the drum, or a definite time, a perfect mixing can be assured. 6. A preliminary dry mixing can be given, if desired, by the machine. . 7. The different materials may be fed to the mixing apparatus separately. There is therefore no necessity for hand mixing before 54] How to Mix and Place Concrete 2. Continuous mixers are those in which the cement, sand, and stone are fed to the charging hopper in a continuous stream, while the mixed concrete is discharged in another continuous stream. In one form of continuous mixer the cement, sand, and stone properly proportioned are shovelled directly into the mixing drum. In the other form, these materials are dumped into separate charg- ing hoppers and are automatically fed into the mixing drum in any relative proportions desired, the proportioning being accom- plished by the machine. Special features of the continuous mixer. 1. It is of use chiefly where large quantities of concrete have to be delivered without intermission, as in the construction of sea and dock walls, foundations, etc. It is not suitable where only small quantities of concrete are required at irregular intervals, as in the case of block-making or reinforced concrete-work. 2. No method of continuous measuring is capable of the same accuracy, for all the materials concerned, as is measuring in boxes or skips. 3. It is impossible for the engineer to exercise the necessary supervision over the proportions of the ingredients used. 4. The amount of water in the concrete will depend somewhat on the rate of running of the machine, and cannot be accurately measured. 5. The amount of mixing given to the concrete is not under the control of the engineer, but is fixed chiefly by the makers of the machine. 6. The materials cannot be satisfactorily mixed together dry by the mixer before being wetted, although the attempt to do this has been made by delivering the water at some distance from the feed opening. 7. All the materials must be fed into the mixer simultaneously, since there is a continuous movement from end to end, and if fed separately they would travel separately along the machine. This means that a preliminary dry mixing by hand is necessary before feeding into the machine. 3. Gravity mixers are constructed in two general forms. The first form is a trough whose bottom and sides are provided with pegs or other deflectors which give the material a zig-zag motion as it [55] Handbook for Cement and Concrete Users flows along. The second form consists of a series of hoppers, set one above the other, so that the batch is spilled from one into the next and is thus mixed. With a good mixer the output depends upon the methods of FIG. 10. Trump Automatic Measuring Arrangement. conveying the materials. On a well organized job, a batch mixer will average about 300 batches in ten hours. On large jobs with labor at $2.00 per day, the labor cost of putting concrete in place is about 50 cents per cu. yd. When mixed by machine and deposited by hand, this cost will run from 75 cents to 90 cents per cu. yd. Precautions in Mixing. In mixing concrete by machinery the important points to be observed are: i. That the specified proportions of the ingredients are fed into the mixer at all times. [56] How to Mix and Place Concrete 4 2. That the quantity of water is uniform and of proper amount to produce the desired consistency. 3. That the ingredients are thoroughly incorporated before leaving the mixer. /?0/>/>er \ L^ FIG. ii. Typical Arrangement of Concrete Mixing Plant. (Atlas Portland Cement Co.) 4. That the entire contents of the mixer are taken out at each emptying. 5. When the mixer is stopped it should be flushed with water and no concrete partially set or otherwise should be permitted to remain in it. is?] Handbook for Cement and Concrete Users 6. The mixer should be located as near the work as possible. 7. The concrete should have a low fall when leaving the mixer, not giving the ingredients an opportunity to separate. 8. If transported the concrete must be carried in water-tight cars or barrows. 9. As soon as placed the concrete should be well compacted, all corners being thoroughly filled. 10. The forms must be firm, unyielding, have the closest possible joints and smoothed on the inside. 1 1. A richer concrete should be deposited near all exposed surfaces. 12. The work should be supervised by a competent inspector. PLACING THE CONCRETE How Placed.* After the concrete is properly mixed it should be placed at once. Concrete may be handled and placed in any way, best suited to the nature of the work, provided the materials do not separate in placing. Hand- mixed concrete may be properly placed by shovel- ling off the concrete board directly into the work, by shovelling into wheelbarrows, wheeling to place and dumping, by shovelling down an inclined chute, or by shovelling into buckets and hoisting into place. Concrete should be deposited in layers about 6 inched thick unless otherwise specified. Consistency. There are three kinds of mix- tures used in general concrete work as follows : i. Very Wet Mixture. Con- crete wet enough to be mushy and run off a shovel when handling. Used for rein- forced work, thin walls, or other thin sections, etc. ; no ramming necessary. 2. Medium Mixture. Concrete just wet enough to make it * See foot note page 47. [58] FIG. 12. Gravity Mixer for Lining Tunnel. How to Mix and Place Concrete jelly-like. Used for some reinforced work, also foundations, floors, etc. Ramming with tamper or treading with feet necessary to remove air-bubbles and fill voids. In concrete of a medium con- sistency, a man would sink ankle-deep if he were to step onto the top of the pile. 3. Dry Mixture. Concrete like damp earth: used for founda- tions, etc., where it is important to have the concrete set up as quickly as possible. This must be spread out in a 4-inch to 6-inch I FIG. 13. Spading Fine Material Adjacent to Form. layer in placing and thoroughly tamped until the water comes to the surface. Spading. Concrete of any of the three degrees of consistency mentioned above should be carefully "spaded" next to the form where the finished concrete will be exposed to view. "Spading" consists of running a spade or flattened shovel down against the face of the form and working up and down. This action causes the stone or gravel to be pushed back slightly from the form, and allows the cement grout to flow against the face of the form and fill any voids [59] Handbook for Cement and Concrete Users that might be there, thus making the face of the work present an even, homogeneous appearance. Where the narrowness of the concrete section, such as in a 6-inch silo wall, prevents the use of a spade, a i-inch-by-4-inch board, sharpened to chisel edge on the end, will do as well. Only sharpen on one side and place the flat side against the form as shown in illustration. In the case of a dry mixture, "spading" must be done with greatest care by experienced hands to get uniform results, but with a medium or wet mixture it is very easy to obtain first-class work; indeed, with a wet mixture ^Support for \BeH-Co rse fvrrr* 1 i \ i \ 1 r\ 1 A 1 *\ 1 ^ V ^ FIG. 14. Enclosing Building with Canvas Curtains to Protect the Concrete. spading is required only as an added precaution against the poss- ibility of voids in the face of the work, and is really necessary in few cases. Cleaning the Concrete Board. When the day's work is done, carefully clean all the tools, especially the concrete board. Remove with a shovel all the loose cement, sand, and stone. Then scrub the board with a broom and water. If this is not done, small particles of stone are glued to the board by the cement, and render shovelling the next day most difficult. Protection of Concrete after Placing. Green concrete should not be exposed to the sun until after it has been allowed to set for How to Mix and Place Concrete five or six days. Each day during that period the concrete should be wet down by sprinkling water on it, both in the morning and afternoon. This is done so that the concrete on the outside will not dry out much faster than the concrete in the centre of the mass, and should be carried out carefully, especially during the hot summer months. Old canvas, sheeting, burlap, etc., placed so as to hang an inch or so away from the face of the concrete will do very well as a protection. Wet this as well as the concrete. Often the concrete forms can be left in place a week or ten days; this protects FIG. 15. Method of Depositing Concrete by Chutes. the concrete during the setting-up period and the above precautions are then unnecessary. Placing Concrete in Freezing Weather. When concrete is to be placed in freezing weather, one or more of the following methods should be employed to protect it from injury: 1. Lowering the freezing-point of the mixing- water. 2. Heating the sand, stone, and mixing- water. 3. Covering and housing the work. Common salt is most frequently employed for the purpose of lowering the point at which the water will freeze. The rule is to add salt in the proportion of i per cent of the weight of the water for each degree F., below 32. In no case, however, is it good practice to add more than 10 per cent of salt. Sand and stones are heated either in portable heaters or in bins. [61] Handbook for Cement and Concrete Users When bins are employed, steam pipes are used to thaw out the materials. Methods of covering concrete to protect it from light frosts include the use of sacking, shavings, straw, and manure. In cold climates, frame buildings that completely house in the construction are frequently erected. Such buildings are heated and the tem- perature kept well above the freezing-point. Placing Concrete Under Water. Mixed concrete if emptied loose and allowed to sink through water is destroyed; the cement paste is washed away and the sand and stone settle on to the bottom more or less segregated and practically without cementing value. To overcome these difficulties, the follow- ing methods are employed for depositing con- crete under water: i. Depositing in j a. Bottom dumping. closed buckets ( b. Revolving buckets. --X 2. Depositing in ( a. Bottom dumping bags. bags ( Z>. Bags to be left in the work. 3. Depositing through a tremie. 4. Grouting submerged stone. Buckets for depositing concrete under water are provided with covers, so that the water cannot flow in and wash out the cement as the material is being lowered. Bottom dump- ing buckets also possess an unlocking device to open the bottom doors and allow the concrete to pass out. Revolving buckets are turned upside down before emptying. Two methods of depositing concrete in bags are available to the engineer. In the first method a bag of heavy tight-woven material is filled with concrete and emptied at the bot- ;-;*:; *.-;*.>-.*. torn, the bag serving like the buckets as a ' ^Concrete f&SS&S-fSK? r means of conveyance. FIG. 1 6. Tremie In the second method bags of paper or Tube for Depositing . . . , ,_, Concrete underwater! loose-woven gunny-sack are employed. The [62] How to Mix and Place Concrete bags are filled with concrete and are left in the work, the idea being that the paper will soften or the cement ooze out through the openings in the cloth sufficiently to bond the separate bagfuls into a solid mass. A tremie consists of a tube of wood or sheet metal, which reaches from above the surface to the bottom of the water. It is operated by filling the tube with concrete and keeping it full by successive additions, while allowing the concrete to flow out gradually at the bottom by slightly raising the tube to provide the necessary opening. Masses of gravel, broken or rubble stone deposited under water may be cemented into what is virtually a solid concrete by charging the interstices with grout forced through pipes from the surface. The grout employed is a i : i mixture of Portland cement and sand, with sufficient water to form a thick paste. This is readily forced through 2 in. pipes into depths of 50 ft. and over. In heavy subaqueous operations concrete is also placed by constructing a coffer dam around the site, pumping out the water, and working in the dry or by placing large specially prepared blocks by means of derricks, the setting being done by divers. A new method has recently come into use for building subaqueous concrete walls, by means of pontoons constructed on shore, floated into place and sunk by means of ballast. [63] CHAPTER VIII FORMS FOR CONCRETE CONSTRUCTION Kinds of Forms. Pressure of Concrete on Forms. Dressing and Lubrication of Forms. Design of Forms. Removing Forms. Cost of Forms. THE design and construction of forms are among the most difficult of the problems imposed upon the worker in concrete. Forms should be stiff, strong, and economical in labor and materials. They should be built with a view to economy in taking down rather than to cheapness in erecting or in first cost. Roughly built forms which cannot be removed without being ripped to pieces are always expensive. Kinds of Forms. The principal kinds of forms in general use are as follows: 1. Simple braced forms. 2. Wired and bolted forms for walls. 3. Forms made of studding and matched boards. 4. Panel forms. 5. Column forms and braces. 6. Forms for beams and slabs. 7. Arch centres. 8. Special, collapsible facing forms and templets. Forms are most commonly constructed of wood, which must be planed and oiled to present a smooth surface, since the concrete takes the impress of any irregularity that presents itself. Stiff, close-grained woods are the best, such as white pine, yellow pine, spruce, Oregon pine, or redwood. Hemlock should not be employed, as it is rough, splintery, and weak. Oak is hard to nail, expensive and imprints grain marks on the concrete even when the form is well oiled. Forms should be constructed in such a way as to avoid the use of nails whenever possible. Braces are seldom less than i in. thick and it takes hard driving to get spikes through them. When- [64] Forms for Concrete Construction ever possible, blocks or wedges held in place by thin nails, should be substituted for the large spikes so often employed. Lagging and panel strips are made of i 1/4 to 2 inch stuff, short struts and braces of 2 x 4 inch timber, while long struts range from 4 x 4 to 8 x 8 inch sectional area. Simple braced forms are used for foundations, retaining walls, and ordinary construction. They consist of from i to i 1/2 inch boards, which are supported by 2 x 4 inch studs, set about 2 feet apart. The studs are also braced with 2x4 inch diagonals. The diagonal braces are held in position by posts driven into the ground. FIG. 17. Simple Forms for Cellar Walls. This type is faulty in that the braces are nailed to the sides. "As a rule it is best to drive a line of posts and to lay against them a heavy timber or thick plank. This provides a stiff support against which braces may be placed at any point when needed. At any sign of giving way in the forms, intermediate braces may be quickly introduced without the delay consequent upon driving new posts." "Bracing is not good practice for the holding of wall forms in place." Failures of such forms are frequently caused by the giving way of the posts due to the yielding of earth. Earth is a poor material to depend upon for holding forms rigid, and bracing is only excusable when the form can be secured from but one side and that usually the outside. In all narrow forms, the studding on opposite sides should be tied together by bolts or wires. 5 [65] Handbook for Cement and Concrete Users In all braced forms, the posts against which the ends of the diagonals rest should be driven deep. "They should also be driven as nearly vertical as possible. The usual way is to drive them on a slant," but experience has shown that vertical posts are the stiff er, especially when the ground is poor. "The top soil is seldom able to carry much of a load," hence the brace should be driven deep in order that it may obtain sufficient anchorage. Wired and Bolted Forms. Forms, when used on both sides of a narrow wall, should be tied together by wires or bolts. The wire FIG. 1 8. Showing Method of Wiring Forms. is preferably passed twice through the forms, the ends twisted together and any surplus cut off with nippers, while the wire is tightened by twisting, the two strands together inside of the forms, a stick being employed for the purpose. Before it is drawn up, a wooden spacer of length equal to the required width of the wall is placed beside the wire, where it is left until the concrete reaches that height, after which it is removed. Wired forms are much more secure than those which are merely braced. They possess, however, the following objectionable features : [66] Forms for Concrete Construction 1. The ends of the wires are exposed when the forms have been removed. 2. The wooden spacers are sometimes left in the concrete. 3. The wire gives a little, as the concrete is tamped, causing the form to bulge. There is no practicable way of taking up this give. To overcome these objections bolts are frequently employed instead of twisted wire. Wooden spacers can be removed as soon FIG. 19. The Dietrich Plank Holders. as the bolts are tightened, while the give can be taken up by tightening the nuts on the bolts. Such bolts are withdrawn after the forms have been removed and the holds are filled with cement paste mixed with some waterproofing compound. This method is, however, objectionable where an impervious seal is required, as the oil placed on the bolts to permit of their removal prevents a watertight bond between the post and the body of the wall. To avoid this difficulty a number of arrangements are in use whereby two short bolts are connected to wire loops in the body of the wall. The wire loops remain in the wall, so that the main portion is solid and impervious, while the shallow holes, left on each side when the bolts are withdrawn, are filled with cement paste to preserve its sightliness. Mr. Ernest McCullough uses a device consisting of two thumb-nuts connected by wire loops into which the threaded ends of the bolts are placed. They are then screwed up until the head of the bolt bears against the face of the form, which is protected by a washer. See Fig. 18. Handbook for Cement and Concrete Users Forms Made of Studding and Matched Boards. Two designs are in use: i. Where the boards are nailed to the inside of the studding and the form erected as a unit. FlG. 20. Forms for Reinforced Concrete Retaining Wall. FIG. 21. The Farrel Plank Holder. 2. Where the studding is erected and braced, and the boards set one at a time without nailing. This design is much more con- venient for pouring, as the concrete is only the width of a board below the top of the form, which is built up as the work proceeds. [68] Forms for Concrete Construction Good inspection, however, is required to insure proper construction and bracing where form work and placing of concrete are going on simultaneously. Panel Forms are an amplification of the " board-by-board " method, several boards being fastened together and erected as a unit, or united by nails and braces into box-like forms. The follow- ing types are in general use : a. The Ransome panel consists of a number of boards, which are fastened together by cleats on the back and held in position by slotted frames or studs. The studs are set opposite each other and are bolted through at top and bottom. Spacers are also set in position to keep the frames the proper distance apart. As soon as the panel has been filled with concrete, "the lower bolt is withdrawn, FIG. 22. Panel Method of Framing for Wall Construction. and the slotted frames raised to a height as great as may be obtained when the upper bolt reaches the bottom of the slot. The lower bolt is then passed through the upper part of the slot with a new spacer to preserve the interval, and work is recommenced." b. Framed panels consist of i-inch boards braced with 2x4 inch wales and uprights, the panels being about 12 feet long by 4 feet in height. For any wall at least two lines of panels are em- ployed, and for high walls, three sets should be available to avoid delays to the work. The panels are braced by bolts and spacers. Bolts are placed at the top of the forms, and are provided with large washers which also bear against the bottom of the superimposed forms and hold them in position when placed. Column Forms. For columns it is customary to provide a vertical trough and to brace the forms by horizontal frames made of [69] Handbook for Cement and Concrete Users 2x4 inch stuff. These frames are of several types of which the following are in common use : a. Timber frames which consist of four strips, one on each side of the column. These are held together by means of lugs and hardwood wedges. b. Bolted frames which consist of two strips on opposite sides of the column form. These are tied together by bolts. The strips FIG. 23. Movable Wall Forms. exert pressure on opposite sides of the form, while the other two sides are secured by hardwood wedges between the bolts and the form. These are placed as close as possible to the ends of the bolts. c. Clamped frames, in which metal clamps are used to hold the form together, as the Hennebique Column Form Clamp. In some cases the sides of the form are made up of narrow strips. This is to facilitate the reduction in size of the columns from floor to floor. In warm weather there is no need of having more column forms than one complete set for one story. Each of the narrow strips represents the reduction in diameter of the column from one story to the next. In removing forms the column moulds are taken down first. It is therefore necessary to so design the details about the Forms for Concrete Construction tops of the forms as to permit of their removal without in any way disturbing the beam and girder moulds. Beam and Slab Forms. Beam forms are horizontal troughs made of i or i 1/4 inch lumber. The bottom piece rests on two 2x4 inch stringers which in turn are supported by 4 x 4 inch caps resting on posts. The side pieces are braced with 2x4 inch horizontal strips at top and bottom, and by vertical and inclined FIG. 24. Column Form and Method of Bracing. webbing of the same size. For shallow beams, a lighter construc- tion can be employed. When the floor slabs and their supporting girders are built monolithic, a 2 x 4 inch strip is nailed along the outside of the beam forms to carry the flooring for the slabs. Cross bracing is also wedged between ihe girder forms in order to stiffen the con- struction and to assist in carrying the loads to the parts under the girders which support the entire load. The middle of the floor slab form is further supported by a 2 x 4 inch piece resting on the cross bracing. In removing beam and girder forms, the posts should be taken from only one girder at a time, and as soon as the form for this has been removed, the posts should be immediately replaced Handbook for Cement and Concrete Users and wedged up. By this procedure, danger of failure of concrete through poor workmanship is much diminished, as a defective member is supported by the members on either side of it until the defect can be remedied. "An essential thing about arch centres is that they must be perfectly rigid so that the arch will not be stressed in the slightest Sicr/at TMMOV&I Guwtna FlG. 25. Typical Forms for Reinforced Concrete Factory Floors. degree before the concrete attains a perfect set, and yet they must be so placed that their removal will be accomplished without injuring the surface of the concrete and without straining the arch. All centres must be dropped away from the arch readily. Salvage of material is an important item, but as a rule the salvage is higher with arch centres than with forms for buildings. Much of the [72] Forms for Concrete Construction material consists of posts and sway braces, and these require but little cutting." Special Forms. Pressed steel forms are used to a limited extent in concrete column, girder, and slab construction and their use is likely to increase in the near future on account of the rapid rise in the price of lumber. The chief difficulties in the use of such forms are their liability to leakage, tendency to rust and possible injury by dents in removing. Centering. Collapsible centres which consist of a steel or timber shell supported by interior bracing and so constructed that the shell can be readily removed and placed in a new position are extensively used for pipes and conduits. Several forms are built, of which the following are examples : Half round steel centres on circular conduits. Full round steel centres for monolithic construction. Box centres for concrete culvert construction. Shaft lining and tunnel centering. Centres for cut and cover conduit construction. A facing form is a steel plate which is placed on edge at the proper distance back from the lagging and the space between filled with facing mortar. The form is finally lifted up and the backing and facing thoroughly bonded by tamping them .together. It is used when a mortar finish is required, of greater thickness than can be obtained by spading the coarser aggregate back from the surface of the forms. Pressure of Concrete on Forms. The forms for concrete must be strong enough to withstand the pressure of the "soupy " mass, and girder forms must be stiff enough so that their deflection as the weight increases will not cause partial rupture of the concrete or sagging of the beam. Experiments have shown that forms designed on the assump- tion that the pressure produced by wet concrete is equivalent to that of a fluid weighing 80 pounds per cubic foot are reasonably safe. "In ordinary walls where the concrete is placed in layers, compu- tation is not usually necessary, since general experience has shown that maximum spacing for i-inch boards is 2 feet, for 1-1/2 inch plank is 4 feet, and for 2 -inch plank is 5 feet. Studding generally varies from 2x4 inches to 4 x 6 inches, according to the character [73] Handbook for Cement and Concrete Users of the work and the distance between the horizontal braces or walling." Dressing and Lubrication of Forms. Dressed lumber should be employed for all exposed surfaces in order to give a smooth finish. Dressed timber also permits tighter joint construction, and facilitates the removal and cleaning of the forms. All forms for concrete require a coating of some lubricant to prevent the concrete from adhering to the wood with which it comes TABLE VI. SHOWING THE PRESSURE ON FORMS PRODUCED BY CONCRETE AT VARIOUS DEPTHS. Depth in Feet. i 2 4 6 8 12 16 20 24 Pressure on Vertical strip, i foot wide in pounds . . 40 160 640 I4.4O 2t;6o ^760 10240 16000 23040 Pressure on i square foot in pounds 80 1 60 32O A8O 640 060 1280 1600 IO2O in contact. Crude oil is generally employed for the purpose, but any grease that will spread evenly and fill the pores of the wood will answer equally well. The use of lubricants reduces the cost of removing the forms and also gives a smoother finish to the concrete. Forms should not be removed until the concrete has attained sufficient strength to carry the load. Wet concrete sets more slowly than dry mixtures, and concrete is slower setting in cold weather than it is when the weather is warm. For walls, the forms should be left up from i to 5 days; for slabs, from 6 days to 2 weeks; for beams and girders, from 2 to 4 weeks; and for large-sized arches, from i to 3 months. Design of Forms. The following formula is employed in designing forms and is recommended by Sanford E. Thompson: Assume 1. Weight of concrete, including reinforcement, 154 Ibs. per cu. ft. 2. Live load 75 Ibs. per sq. ft. upon slab; 50 Ibs. per sq. ft. in figuring beam and girder forms; and struts. 3. For allowable compression in struts use 600 to 1,200 Ibs. per [74] Forms for Concrete Construction sq. in., varying with the ratio of the size of the strut to its length. If timber beams are calculated for strength, use 750 Ibs. per sq. in., extreme transverse fibre stress. 4. Compute plank joists and timber beams by the following formula, allowing a maximum deflection of 1/8 inch: 384 El and (x) in which d = Greatest deflection in inches. W = Total load on plank or joist in pounds. I = Distance between supports in inches. E = Modulus of elasticity of lumber used. / = Moment of inertia of cross-section of plank or joist. b = Breadth of lumber. h = Depth of lumber. For spruce lumber and other woods commonly used in form construction, E may be assumed as 1,300,000 pounds per square inch. Formula (i) may be solved for /, from which the size of joist required may be readily estimated from formula (2). Time to Move Forms after Placing.* The proper time for removing forms depends upon the character of the construction. The following rules are applicable to ordinary practice: Walls in mass work: one to three days, or until the concrete will bear pressure of the thumb without indentation. Thin walls: in summer, two days; in cold weather, five days. Slabs up to 6 feet span: in summer, six days; in cold weather, two weeks. Beams and girders and long span slabs: in summer, ten days or two weeks; in cold weather, three weeks to one month. If shores are left without disturbing them, the time of removal of the sheeting in summer may be reduced to one week. * By Sanford E. Thomson. [75] Handbook for Cement and Concrete Users Column forms: in summer, two days; in cold weather, four days, provided girders are shored to prevent appreciable weight reaching columns. Conduits: two or three days, provided there is not a heavy fill upon them. Arches: of small size, one week; for large arches with heavy dead load, one month. All of these times are, of course, simply approximate, the exact time varying with the temperature and moisture of the air, and the character of the construction. Even in summer during a damp, cloudy period, wall forms sometimes cannot be removed inside of five days with other members in proportion. Occasionally, too, batches of concrete will set abnormally slow either because of slow- setting cement or impurities in the sand, and the foreman and inspector must watch very carefully to see that the forms are not removed too soon. Trial with a pick may assist in reaching a decision. Beams and arches of long spans must be supported for a longer time than short spans because the dead load is proportionately large, and therefore the compression in the concrete is large even before the live load comes upon it. Cost of Forms. The cost of form work per cubic yard of con- crete depends largely on the thickness of the walls. With very thin walls the cost for forms is comparatively high, and for such work a method of estimating which is based on the surface area should be employed. There are three methods of estimating the cost of form work: 1. In cents per cubic yard of concrete. 2. In cents per square foot of surface area of concrete. 3. In dollars per 1,000 ft. B. M. of lumber used. The cost of form work is made up. of the cost of the lumber and the labor of framing, erection, and removal of the forms. Lumber costs from $20 to $30 per 1,000 ft. B. M., and if used three times, the cost of the lumber will range from 2 to 3 cents per square foot of surface area of concrete. Ordinary forms for walls and mass work can be erected and Forms for Concrete Construction taken down for $10 per M. For beams and arches the labor cost is much higher. Such work cannot be even approximately estimated from any rule of thumb, but must be carefully computed from the detailed plans of the structure; taking account of the size of the job, the special difficulties to be overcome, and the prevailing cost of common and skilled labor in the locality. [77] SECTION II CONCRETE ARCHITECTURE CHAPTER IX THE ARCHITECTURAL AND ARTISTIC POSSIBILITIES OF CONCRETE A New Style of Architecture. For a century or more architects have been vainly trying to create a new style of architecture; back and forth they have vacillated, but never forward. They have tried every possible combination of the ancient masterpieces but without results; and it seems that again, as in the fable of old, the hidden treasure was not in foreign lands but right at our own door, beneath our very feet. It is a recognized principle of architecture that the material of which a structure or monument is made is (after the idea or need that called it into existence) the main factor in determining the form, color, and structure of the monument. This being true, it is likely that a material, having so many char- acteristics that no other material has, is certain to introduce many new features into a structure and finally create a new style of architecture; and this is especially probable because designs hitherto attainable in other material only at great expense, can be obtained so cheaply in concrete. It is so easy to obtain very high ornamentation in concrete that it is necessary for the artist to exercise self denial in refraining from unmeaning display for the sake of show. The popular notion that architecture is the heaping of pretty things onto a structure to hide its construction is wrong. True art is always the result of a clear and forceful expression of the idea and use of the structure. Ex- pression in art must be obtained by making some parts plainer than others, thus bringing out the richness or elegance of the main idea. Make your structure look like what it is, concrete; solid, strong, substantial, beautiful. The ornamentation chosen taste- [78] Architectural Possibilities of Concrete fully to accord with the idea expressed and with the natural sur- roundings, construct with a feeling of modesty, dignity, simplicity, and repose, and you will have a design alive with purpose that will live through the ages. Mr. R. VanDeerlin, Chief Engineer, Hennebique Construction Company, says: "Concrete, with the aid of steel, is adaptable to almost every kind of structure, not only economically but architecturally. Un- fortunately it has been handicapped by the attempt to force it to imitate other materials. This probably results from its plasticity and reluctance to depart from well recognized methods of architect- ural design. Being generally composed of stone for an aggregate, it somewhat naturally suggests that the same line of design would be appropriate for concrete as has become the recognized standard for stone. Such, however, is not the case, as there is a material difference in the general appearance. After the temptation to imitate is overcome the plasticity of concrete makes it not only an excellent building material but also an architectural one as well. "The most striking examples of architectural beauty are noted for their simplicity and freedom from confusing details and effects that distract the attention from the ,keynote of the design. Previous to this century, the limitations of building operations have made it necessary to have the size of the units of construction small in order ' to keep the cost within bounds. This gave definite construction joints which were accentuated and developed along certain lines to create certain impressions. Now that concrete is available, it is no longer necessary to have these lines or joints and they can be eliminated entirely or used only where they are really an architectural benefit. Simplicity in concrete design is to be desired also from an economical standpoint, because one of the most expensive items in concrete construction is the form work. The cost can be trebled easily if the forms are complicated. " The future of concrete treated architecturally lies in a development on surfaces and not lines. Who, for instance, would prefer a concrete bridge, built to represent one of cut stone to one where the con- crete is honestly shown on pleasing surfaces, free from the lines which are supposed to represent the joints of the stones, and only showing the lines which are there for purely architectural reasons. [79] Handbook for Cement and Concrete Users If it were possible to economically eliminate the joint lines from the stone bridge, it is very probable that no one would ever have at- tempted to use similar artificial lines for effect. Compare a con- crete tower treated as a monolith with one built to imitate stone. The plain surface is far more pleasing than the other. Compare also the many pleasing concrete-surfaced houses with those con- structed with the rough concrete blocks. " When the problem of arranging the structural parts of a building is considered, there is no material that so readily lends itself to the FIG. 26. Section of Reinforced Concrete Cathedral at Poti, Russia. Showing Architectural Possibilities on Important Edifices. (Hennebique.) required adjustment as reinforced concrete, both economically and effectively. If a perfectly flat ceiling is desired, the structural floor can be designed in the mushroom system or constructed with terra- cotta and concrete. The slight additional expense of these two methods over an ordinary slab-and-beam construction is less than the cost of an expanded metal lath and plaster ceiling, as plaster can be very easily applied directly to the surface of either. If the rooms are small the doubly armed panel allows them to be freed from projecting beams as the beams can be placed over the par- Architectural Possibilities of Concrete titions. This system is also adaptable to large rooms, where paneled ceilings are desired." Concrete block architecture and handsome stucco effects, both of which are treated in succeeding chapters, have come into extensive use, the former now emerging from a period of doubt and suspicion following the influx into the market of poorly made material, a question which will be discussed later on. The preparation and artistic treatment of concrete surfaces have done a great deal in developing the architectural possibilities of concrete, and much credit is due to the pioneers in bringing out the many beautiful surface finishes. It is only necessary to go to sections like Long Beach on the Long Island southern coast and see the varied styles of beautiful concrete residences, to realize that a new architecture has been born, which, owing to its economy and fireproofness, as well as beauty, will supplant the classics of bygone days. 81] CHAPTER X CONCRETE RESIDENCES The Use of Concrete for Residences. Best Method of Obtaining Architectural Effects. Stucco and Reinforced Concrete for Residences. The Edison Poured Concrete House: Cost of Different Types of Residences Compared. As stated in the previous chapter, the architectural treatment of concrete, until recent years, was limited to an attempted imitation of stone masonry, which tended to cheapen its appearance and to destroy its character. As an imitation of stone, concrete is not an artistic success. There is a sameness to its appearance, an air of sombreness, an absence of light and color that destroys its architec- tural value. Within the present century the secret of the artistic use of con- crete has been revealed, and with this discovery has come such recognition by architects and owners alike, that concrete has already taken its place within the front ranks of building materials, and its growing use is indicative of a future whose possibilities and benefits to humanity are transcendent. The secret of the successful use of concrete for architectural purposes consists in such treatment of its surface as will serve to bring out its true character and to reveal its hidden beauties. These methods are in part described in the chapter on " Artistic Treatment of Concrete Surfaces," and consist in the use of carefully chosen aggregates; tooled, scrubbed, etched, or pebble-finished surfaces, stuccos of varied tints and textures; the artistic use of half -timber framing, of columns, cornices, pediments and balusters to lend variety; and an attractive shingled or tiled roof to form an effective covering. Concrete is now employed in the construction of all classes of residences, such as bungalows, costing from $500 to $1,000; cot- tages, from $1,500 to $2,500; moderate priced houses from $3,000 to $5,000; and palaces in which the cost of construction requires five, six, or even seven figures for its expression. [82] Concrete Residences Kinds of Concrete Residences. In these different classes of residences, Portland cement mortar and concrete are used in one or more of the following forms: 1. Hollow concrete blocks. 2. Monolithic concrete. 3. Stucco. Concrete Block Residences. Hollow concrete blocks have outnumbered all other forms in which concrete is employed in residential construction, owing to their cheapness and ease of construction. Their description and manufacture will be found in Chapter XIII. Early manufacturers of concrete blocks were unfortunate in try ing to mould the surfaces in imitation of quarry-faced stone, and the effect of their efforts was to produce a structure without beauty or variety. "A rock-faced stone is the result of an actual treatment of the stone with tools, and no two rock-faced stones are alike. There is variety to the surface." But with concrete blocks the variety is lacking. " Even when several rock-faced moulds are used and the blocks are made of different patterns, it generally happens that several having exactly the same face from the same mould come together, and that is exceedingly noticeable." Surface Finishes for Block Residences. The best architectural effects in concrete block residences are produced with the following surfaces : 1. Perfectly plain surfaces. 2. Roughened, or pebble-finished surfaces. 3. Surfaces produced by casting in sand moulds. 4. Surfaces of pure white color or delicately tinted. Some of the finest, as well as the least expensive residences are now constructed of plain blocks, the facades being relieved by columns and cornices in moulded concrete, the roofs covered with ornamental tiles of red or other warm tones, and the piazzas having concrete rails and balusters of appropriate design. Roughened surfaces are produced by scrubbing, etching with acid, and treating with wire brushes, the object being to destroy the film of surface cement and to expose the aggregate. By the use of granite chips, colored gravel, crushed marble, or coarse white sand, various effects are obtained, and the architect who possesses [83] Handbook for Cement and Concrete Users originality and a knowledge of the possibilities of his material, can produce striking and artistic effects at a very moderate cost. These will be treated further in Chapter XII. Casting in sand moulds is generally confined to mouldings, balus- ters, columns, and other ornamental' features. " Sand moulding gives, perhaps, the handsomest ornament of any kind of moulding process, the surface texture and detail of the block being especially fine." (Gillette.) Surface tints are best produced by the use of colored gravels. Pure white surfaces are obtained by using facing mortars composed of white limestone or crushed white marble and white Portland cement. Such mortars can also be tinted with delicate colors by the use of appropriate pigments. Monolithic Residences. Houses having solid walls of monolithic concrete are best treated by making the surfaces of the walls un- broken without attempting to imitate masonry or joints in stones. The following methods of surface treatment, which are more fully explained in Chapter XII, are well adapted to such construc- tion: 1. Spading the concrete so as to cause the grout to flush to the surface of the forms. This prevents the exposure of the aggregate and any defects can be remedied by trowelling and grouting after the forms have been removed. 2. Roughening the surface by scrubbing, etching with acid, tooling with bushhammers or pneumatic hammers, etc. 3. Use of colored aggregate or of granite chips, white quartz pebbles, or other special materials which are exposed by scrubbing or tooling. 4. Surfacing with mortar or stucco. 5. Tinting. Stucco Residences. Any mortar employed as an exterior sur- facing for walls is called stucco. Cement stucco is extensively used both for renovating old buildings and improving their appearance and in new construction. The methods of application are fully described in the succeeding chapter. The classes of residences in which a stucco finish is of advan- tage are as follows : [84] Concrete Residences 1. Old houses composed of wood, stone, brick, concrete, or other materials in which the surface is worn or decayed. 2. New houses composed of wood, stone, brick, concrete, or other materials, in which the surface is left rough or unfinished. 3. Houses having hollow walls of expanded metal, terra cotta or concrete tile, or other fabric, and covered inside and out with mortar or stucco. Portland cement stucco is easily applied to any material such as wood, brick, stone, etc., by covering the surface with a metal fabric over furrowing strips to serve as an anchorage for the mortar. Wooden lathing can also be employed for this purpose, and in the case of frame houses spaces can be left between the boards to serve as a key. Stucco is composed of: (a) cement and sand; (b) white Port- land cement and either white sand, crushed white quartz, ground marble, or ground white limestone; (c) cement and granite chips; (d) cement and colored gravel; (e) cement and pebbles, etc. White stucco is also readily tinted with delicate colors by the admixture of colored pigments. Concrete for residences, whether in the form of hollow blocks, or monolithic walls, requires waterproofing. Basement walls should be surrounded by a bituminous shield, or a waterproofing compound should be mixed with the cement employed in the blocks or walls since it is desirable to render the entire exterior surface as impervious to moisture as possible. In old leaky buildings, a coat of damp-resisting paint on the exterior surface will be effective. Reinforced Concrete, which is extensively employed in factory construction, is coming into use for dwellings in order to permit of lighter walls and partitions. The reinforcement is chiefly in the form of expanded metal or other fabric which is nailed to the studding on both sides, thus forming a support for the plastering. In pretentious houses, rods are also employed to distribute the loads over foundation areas and to prevent temperature cracks. Concrete beams are employed only to a limited extent in residences, as the interior joists are almost invariably of wood, as are also the floors, purlins, rafters, and roof trusses. While this is the present practice, it is, however, no criterion of the state of the art a few [85] Handbook for Cement and Concrete Users years hence, when it is probable that the "all-concrete" house will have ceased to be a novelty. Special Architectural Features. At present concrete is used to a limited extent for roofing purposes in the form of slabs and tiles, although red terra cotta tiles and wooden shingles are chiefly employed for. pitched roofs and tin plates or gravel for flat roofs. Concrete houses, especially those of a suburban character, are frequently built with a prominent roof of steep pitch, large piazzas, bay-windows and the English half-timbered construction above the lower stories. This consists of wooden strips around the windows forming the trim and radiating from the upper windows to the roof. These strips are also used as mouldings and serve to bring out the lines of the gables, adding much to the appearance of the dwelling. Other decorative features of concrete houses are the columns, rails, and balusters of the piazzas which may be of wood or concrete, preferably the latter; the free use of dormer windows in the roof, chimneys of concrete blocks or of monolithic construction in har- mony with the general design, horizontal mouldings between the stones, prominent lintels, and massive cornices. The use of concrete in interiors is at present confined chiefly to stairs, panels, fireplaces, and bath rooms. Stairs are reinforced with bars and surfaced with a white mortar or are tinted to harm- onize with the woodwork of the halls; fireplaces are built of concrete bricks moulded and tinted to any desired shade; while concrete slabs and tiling or mosaic laid in white Portland cement mortar is used for mosaic floors, wainscoating, bath-rooms, and fireplaces, taking the place of Keene's cement which it excels in strength and dur- ability. Edison Cast Concrete House. Thomas A. Edison, the electrical wizard, has experimented for several years in developing a sub- stantial and cheap house of cement, and has published the following particulars of his work : "I believe a cement house can be built by machinery in lots of 100 or more at one location for a price which will be so low that it can be purchased or rented by families whose total income is not more than $550 per annum. My experiments have proven that it is possible to cast a house complete in six hours by pouring [86] Concrete Residences a very wet mixture of gravel, sand, and cement into iron moulds having the form of a house, and after the removal of the forms or moulds, leave standing a complete house with a fine surface, plain or ornamental, all in one solid piece, including the cellar, partitions, floors, roof, stairs, mantels, veranda in fact everything except the windows and doors, which are of wood and the only parts of the house that are combustible. "The house is to be heated by boiler and radiators in the usual manner, the plumbing to be open and jointed by electric welding. "The experimental house has the partitions arranged to give, besides the cellar, two rooms on first story (one to be used as a living room and the other for a kitchen); the second story to have two rooms and bath; the roof story to have two rooms. When large numbers of houses are made, the partitions can be changed to make more rooms. Once the house is cast, however, no changes can ever be made nothing but dynamite could be used to remove a partition without great expense. "With a few simple additions to the iron forms, a great many variations in the type of the houses can be made. For instance, by adding or subtracting iron sections, the house can be made smaller and cheaper. By adding sections, the number of stories can be increased, or it can be widened or lengthened. By a few additional forms, the whole appearance of the veranda can be changed. A contracting company having the smallest unit possible to permit of cheap and rapid production, must have six sets of moulds with the other necessary machinery. From these iron sections almost any variation in the size, appearance, and orna- mentation of the row of houses can be made. The concrete could be tinted with any kind of color, but the general type would be the same. The units might be divided and thereby three complete moulds for one type of house and three sets for an entirely different type, would be secured. "This scheme of constructing houses cheaply and in quantities does not permit of the building of one house at a time, for the reason that the moulds are heavy. The machinery necessary to handle the materials as well as for the erection of the iron moulds, is large and expensive, [87] Handbook for Cement and Concrete Users "The hardening of the cement requires four days. While one house was hardening the men would either have to remain idle or be laid off during this period, and this would not be practicable; whereas, if the full unit of a minimum of six sets of moulds, and machinery was in operation, the thirty-seven men necessary could be employed continuously erecting, pouring, and removing forms from one lot to another, at a minimum of expense. "Houses of this type, I believe, can be built for $1,200 each, in any community where material excavated from the cellar is sand and gravel, so it can be used. If the sand and gravel must be obtained elsewhere, the cost will be much more. A change in the forms can be made so that a house can be built that will look just as well, but smaller, at a less cost. On the other hand, by addition to the forms, houses costing $2,000 or $3,000 or more can be built. "To give a rough idea of the cost, I estimate that six sets of iron forms for the house I am to build will cost about $25,000 per house a total cost of $150,000. The cranes, traction steam shovel, conveying and hoisting machinery, I estimate, will cost $25,000 additional, making a total investment of $175,000. With this machinery twelve (12) houses per month can be made every month in the year, with the aid of one foreman, one engineer, and thirty- five (35) laborers. This gives one hundred and forty-four (144) houses per year for the unit. If I can prove this, then the labor cost per house will not exceed $150 each. "If we allow 6 per cent interest and 4 per cent for breakage on the cost of the forms, and 6 per cent interest with 15 per cent depreciation on machinery, the yearly expense will be about $20,000. Dividing this into the 144 houses built in the year, gives approxi- mately $140 per house, for cost of moulds and machinery. 220 barrels of cement will be mixed with the sand and gravel excavated from the cellar, and will provide sufficient material to build the house. Allowing $1.40 per barrel for cement, adds a further sum of $310. The reinforcing steel rods cost $125; and the heating system and bath $150. These items total $875. This leaves a margin between that sum and $1,200 of $325 to provide for doors, windows, etc., painting, and the correction of any possible defects. "If the houses are smaller and 225 can be built in the year for the same investment and labor, it will, from the above data, be [881 Concrete Residences easy to approximate the cost per house; the same is true with larger size houses. "These houses will be waterproof and dampproof. The roofs, after the forms are removed, are painted with a paint made of cement tinted with red oxide of iron, which hardens and never deteriorates. Cement can be tinted to any color and any shade of that color, and the inside or outside can be painted, and is per- manent. The cost of the paint for the whole house, inside and out, including roof, will be very small. " Should the experiment succeed, I will, without cost, furnish all plans, give full license to reputable building corporations without cost, as I am not making these experiments for money. "I think the age of concrete has started and I believe I can prove that the most beautiful houses that our architects can conceive can be cast in one operation in iron forms at a cost, which by com- parison with present methods, will be surprising. Then even the poorest man among us will be enabled to own a home of his own a home that will last for centuries with no cost for insurance or repairs, and be as exchangeable for other property as a United States Bond." The following table, compiled by the National Fireproofing Co., gives a good idea of the comparative cost of various classes of residences. COMPARATIVE COST OF VARIOUS TYPES OF RESIDENCES. (A $10,000 frame residence is taken as a unit.) Frame construction, all wood $10,000 Brick outside walls, wooden interior 11,000 Stucco or expanded metal, wooden interior 10,250 Hollow terra cotta blocks, stuccoed, wooden interior 10,500 Hollow terra cotta blocks, stuccoed, fireproof throughout, except roof. 12,000 Hollow terra cotta blacks faced with brick, fireproof floors. . . . 14,000 Brick walls, fireproof floors i5>ooo Houses can be built with terra cotta blocks for walls and floors with wooden roofs at a cost of twenty-two cents per cubic foot; if built with wooden floors and roof, at eighteen cents per cubic foot. [89] CHAPTER XI MORTARS, PLASTERS, AND STUCCOS, AND HOW TO USE THEM The Art of Stuccoing. Lime Mortars and Plasters. Interior Plasters and Plastering. Gypsum Plasters. Portland Cement Plasters or Stucco. Exterior Lathing and Plastering. Application of Stucco to Stone. Stucco on Brick. Stucco on Concrete. Quantities of Materials for Stucco. THE art of using mortars is as old as civilization; the pyramids of Egypt contain plaster work executed at least four thousand years ago; very early in Greek architecture a true lime stucco of thin white composition was employed as a ground on which to paint their decorative ornament; the Romans were familiar not only with lime and plaster, but with hydraulic cement as well. There is every reason to believe that originally these stuccoes were intended to cover up and protect inferior building stone and sunburned straw brick. The archaeology of stucco would tend to show that from an artistic standpoint this method of decoration was a development of the wattled buildings, which were plastered with clay and different muds hardened by being baked in the heat of the sun. Therefore, in this instance, the use of clay plaster over wattled houses was to protect an inferior building material. At the present time, mortars and plasters are among the most familiar materials employed by the builder. These consist of three general classes, which, however, grade into each other when mixed in different proportions : 1. Lime plasters. 2. Gypsum plasters. 3. Portland cement plasters or stucco. Lime is used for interior plastering where the walls are to be papered; gypsum or plaster of Paris, where a white or hard surface is desired; and Portland cement mortar for exteriors where strength and durability are required. Lime Mortars and Plasters. As already explained in Chapter II, lime is produced by heating a pure or nearly pure limestone in a Mortars, Plasters, and Stuccos kiln to such a temperature as will drive off the carbonic acid gas and leave calcium oxide or " quick lime." When water is added to quick lime it changes from a lumpy condition to a soft, im- palpable powder known as "slaked lime." When more water is added, the slaked lime becomes a paste, and this paste is mixed with sand to form a mortar. Mortar for plaster work is usually composed of slaked lime, mixed with sand and hair. The sand should be hard, sharp, gritty, and free from all organic matter. Pit sand is generally sharp and angular and is preferable to river and sea sands, which are more rounded and are apt to contain saline particles that may cause efflorescence. Hair is used as a binding medium to increase the cohesion and tenacity. Good hair should be long, strong, and free from grease or other impurities. Ox hair is generally used, although sometimes adulterated with the short hair of horses. Substitutes for hair include manila fibre and sawdust. Interior Plastering. Lime mortar, when used as a plaster for walls and ceilings, is placed preferably in three coats on wooden or metal laths. On brick or tile walls, and in residence construction two coats are often considered sufficient, and for rough plastering, one coat. Three-coat work makes a straight, smooth, strong, and sanitary surface for walls and ceilings when properly executed. The processes employed for the different coats are as follows: 1. Scratch coat. 2. Brown coat. 3. Finish. First or Scratch Coat. The first or scratch coat should be from 3/8 to 5/8 of an inch thick, composed of i part of lime paste to 2 of sand, and i bushel of hair to 2 of lime. The plaster should be stiff enough to cling and hold up when laid, yet sufficiently soft and plastic to go through the interstices between the laths, leaving a trowelful partly overlapping the previous one, the one binding the other. Scratching consists in scoring the surface of the first coat to obtain a key for the following one. It is done with a wooden or iron scratch, which may have from one to five points. The first coat should be allowed to stand for an hour or two so as to allow Handbook for Cement and Concrete Users the stuff to become firm, after which the surface is cross-scratched diagonally, the scores being about 11/4 inch centre to centre. Scratching with a single point is more easily controlled and less likely to make the scores too deep than is the case where a four- or five-pointed scratch is used. It requires, however, considerably more time for the operation. Scratching with the point of a trowel should not be permitted. The use of a trowel as a scratch is detrimental to the strength of the mortar, as its sharp edge cuts the hair. It also leaves a smooth and narrow key, which presents no means of attachment for the second coat. When the first coat is applied to brick, stone, or concrete walls, the superfluous mortar in the joints should be raked out and the walls roughened to form a bond; the walls should also be well swept and thoroughly wetted to prevent the absorption of water from the mortar. Second or Brown Coat. The brown coat should be from 3/8 to 5/8 of an inch thick and should contain i part of lime to 3 of sand and i bushel of hair to five of lime. Before the second coat is applied, the scratch coat should be well swept to clean off any dust that may have accumulated and a damp brush passed lightly over the surface to prevent the absorption of moisture from the second layer. The object of the second or brown coat is to form a straight surface for the finishing coat. The process consists of the following operations : a. Plumbing and levelling "screeds" to act as bearings for the floating rule and running mould. b. Filling in the spaces between the screeds. c. Scouring. d. Keying the surface for the finishing coat. Screeds are" the guides on the margins of walls and ceilings between which the plastering is placed. They consist of narrow strips of plaster, which are leveled in the case of a ceiling, or tested by plumb line in the case of a wall. Large surfaces on walls or ceilings should be divided into bays by narrow screeds placed from 6 to 9 feet apart. This affords more freedom and regularity for filling in and ruling off the bays. Filling in consists of laying the intervening spaces between the screeds with mortar, and then ruling the surface straight and flush [92] Mortars, Plasters, and Stuccos with the screeds by means of a floating rule. In this operation, two men are required for each bay. These work the rule up and down with a cutting motion, keeping it in a slightly angular posi- tion, so that any surplus stuff will not fall on the man below. A rule should not be worked on either of its face edges, as by so doing it becomes round and uneven. The filling in and ruling' off is con- tinued until all the walls are completed. Scouring. This consists in consolidating the surface by sprink- ling it with water and rubbing it vigorously with a hand float. The work should be done as soon as the surface is firm and before it becomes dry. The operation is of great importance, as it tends to prevent cracks in its own body and in the subsequent or finishing coat. The float is applied with a rapid circular motion, using a little fine mortar to fill up any small holes or inequalities that may have been left after the floating rule. The floating should be scoured twice, or for best work three times. The final scouring should be continued until there is little or no moisture left on the surface. From three to five hours should be allowed to elapse between the first and second scouring; and at least twelve hours between the second and last. Keying. This consists in roughening the surface by means of a wire brush or a hand float with the point of a nail projecting about 1/8 inch beyond its sole. A tool, called a " devil" is also employed for this purpose, and consists of a small float with four nail points projecting from the sole. Third or Finishing Coat. The application of the final coat consists of three operations, as follows: a. Laying. b. Scouring. c. Trowelling. The material employed for the final coat is" called setting-stuff and consists of lime putty and washed, fine, sharp sand, in the proportions of 3 parts of sand to i of putty. Lime putty may be kept for an indefinite time without injury if protected from the atmosphere, but when exposed an inert crust is formed by the action of the carbonic acid gas which it absorbs from the air. The setting stuff is laid in two coats, the second following im- mediately upon the first. The laying is best done with a skimming [93] Handbook for Cement and Concrete Users float, which leaves the face of the first coat rougher to receive the second than if done by a laying trowel. The second coat should also be laid with a skimming float, which leaves a more open grain for the purpose of scouring. Scouring the Finishing Coat. This consists of sprinkling with water and rubbing vigorously to consolidate, harden, and render the surface of a uniform texture and evenness. The work should be well and thoroughly scoured, twice with water and an ordinary hand float and finally with a cross-grained float, which, having sharp square edges, cuts off all inequalities and leaves the setting with a uniform and even surface. The scouring is continued until a dense, even and close-grained surface is obtained for the trowelling. Trowelling. This is the final operation and follows immediately after the scouring. The plasterer sprinkles . water on the surface and works the trowel in long and vigorous strokes, first downwards and upwards, and then crossways or diagonally. Water is applied with a brush, and the operation is repeated, using the water more sparingly, and finishing or trowelling off with an up-and-down motion which should leave the surface free from "fat" or " gleet." The finishing coat should average 1/8 of an inch in thickness, and should not be less than 1/6 nor more than 3/16 of an inch. If too thick, it is liable to crack and flake; and if too thin, to peel. Where extra strength is desired, the first coat of the setting should contain a little white hair, which does not show through the last coat. Colored Finish. A beautiful color and brilliant finish for walls may be obtained by mixing an equal quantity of sifted marble dust with setting stuff and using this as a final coat. Ordinary finish is greatly improved by substituting a part of marble, alabaster, or gypsum dust, equal in bulk to half the sand generally used. The marble dust should be as coarse as the sand. Brick dust is also used for coloring, while ground glass, when added, produces a sparkling surface. Any of the pigments employed in coloring stucco can also be used for tinting the finishing coat. Gypsum Plasters Gypsum is a sulphate of lime, and when heated so as to drive off the water of crystallization, and ground to a powder, it acquires the property of hardening on the application of water, with which it combines in the proportion of about 4 parts of gypsum to i of water by weight. When prepared for the use of [94] Mortars, Plasters, and Stuccos the plasterer, gypsum is commonly called plaster or plaster of Paris. The finest gypsum is called alabaster, which is soft, pure in color and fragile, and is used for making statuary, vases, and ornaments. Gypsum plasters produce a hard, white surface of fine texture and are used for all plastered walls and ceilings unless intended to be covered by paper. They are extensively employed in the follow- ing classes of construction : 1. For walls and ceilings, applied in two or three coats. 2. Applied as a finishing coat over Portland cement mortar. 3. Applied as a finishing coat over lime mortar. 4. As a cement for ceramic tiles, mosaics, etc. Gypsum plasters are also of the following types : a. Plaster or plaster of Paris. b. Ready-mixed plasters. c. Keene's, Parian, Martin's and other white cements. Plaster of Paris is prepared by calcining or heating gypsum, thus driving off some of the water which it contains. When plaster is again mixed with water, they re-combine to make gypsum and the minute crystals of this substance in forming, interlace and cause the plaster to set. Ready-mixed plasters, containing plaster of Paris, mixed with the proper proportions of sand for scratch, brown, or finishing coats, are put up by manufacturers in various parts of the United States. Among the advantages which are said to accrue from their use may be mentioned: uniformity in strength and quality, extra hardness and toughness, freedom from pitting and saving in time. The white gypsum cements, such as Keene's, Parian, and Martin's, are employed for their hardness and strength. The operation of plastering with gypsum cements and plasters is essentially similar to that which has been described for lime. From two to three coats are employed, and these are floated, scoured, scratched, and trowelled, as in the case of lime mortar. Greater care, however, is required as the plaster is generally either exposed or kalsomined and a perfect surface appearance without seams, cracks, or flaws is essential. In using Parian or other white cement on lath-work, exceptional care must be observed that all the lath nails be galvanized or painted over, or covered with shellac to prevent rust. For first-coating and [95] Handbook for Cement and Concrete Users floating ceilings with this material, the proportions for best work are i part of cement to 2 of sharp sand, adding about the same quantity of hair as for lime plaster. For the sake of economy or for the purpose of excluding damp- ness, walls are generally floated with Portland cement mortar in the proportion of i part of cement to 3 of sand, and finished with neat Parian or other white cement. Portland cement is much cheaper than Parian, but produces an efflorescence on the finished surface, which is inimical to successful painting if attempted before the material has had time to dry out. Gypsum cements, on the other hand, cannot resist the effects of moisture. It is, therefore, imperative that damp walls should be floated with Portland cement, where a white cement finish is desired. Plaster of Paris is used as a finishing coat over lime mortar to improve the appearance of the surface, and is also mixed with the lime putty for the same purpose. When a harder finish is desired, Keene's cement is employed. Keene's cement is employed as a binder for ceramic tiles and mosaics, although for exterior work, white Portland cement is now used, on account of its superiority when exposed to the weather. By the use of white cements a great saving in time can be effected, as work can be begun and finished in one operation without waiting for the different coats to dry, as in ordinary lime plastering. For sanitary purposes they are unequalled. This, combined with their chemical properties, which enables them to be painted, papered, or kalsomined as soon as finished, renders them the most valuable of all plastering materials for interior work. They are free-working, sanitary, durable, and practically fireproof, and when properly manipulated can be worked to a porcelain-like surface. PORTLAND CEMENT PLASTERS OR STUCCO Portland cement mortar is now employed for external plastering or stucco work on account of its durability and resistance to moist- ure. It is also used as a scratch coat for interior walls and ceilings where Parian or Keene's cement is used as a finishing coat; while white Portland cement is used as a final coat for both interiors and exteriors. [96] Mortars, Plasters, and Stuccos Stucco is a composite coat, about i 1/2 inches thick, placed on the outside of a building in one, two, or three coats. Stucco may be applied to wood, stone, brick, tile or concrete, either by roughen- ing the surface or by means of wood or metal lath, supported on furring strips. Stucco may be composed of: a. Portland cement and sand. b. Portland cement, sand, and pebbles. c. Portland cement and sand mixed with about 1/6 of its volume of lime paste. Moyer also recommends the addition of 15 per cent of mineral oil to the wet mortar, after the latter has been thoroughly mixed. i 9 or> cnf re ^-Obeofbioq /*i~a - ~K m b e r re L n 4-c d r rPJcisfcr- 3 orvcenfrr- FIG. 27. Application of Stucco to Frame Building. Lime mortar is employed, chiefly, when the stucco is applied to stone, the object being to prevent hair cracks, retard the rate of setting and render the mortar easier to work. Application of Stucco to Laths. Lime mortar and gypsum plasters for interior plastering and fresco work are generally applied to wooden laths nailed j;o the studding. The laths are separated about 3/8 of an inch apart, so that the mortar will be forced into the interstices and serve as a key. The best laths are of split pine. Oak laths formerly used are very liable to warp. Sawn laths are cheaper than riven but are weaker because of cross-graining. The defects that are to be avoided in laths are sap, knots, crookedness, and undue smoothness. i [97] Handbook for Cement and Concrete Users For exterior work and for hollow-walled interiors, metal laths are employed. These consist of woven wire, expanded metal, rib- lath, and other forms of steel fabric, and may be obtained either painted or galvanized. Specifications for Lath. Metal lath is generally specified by gauge and it is always designated by gauge in catalogues. All purchasers of lath should specify the gauge and weight. The weight per square yard of the lath in different gauges is given in the table below. TABLE VII. SIZES OF METAL LATHS. Size of Sheet r 8 X 96 Inches. Weight per Bundle. Yards per Bundle. Sheets per Bundle. Weight per Yard. Yards in 100 Pounds. No. 27 Gauge. 27^ Ibs. 12 9 2j Ibs. 43 No. 26 " 3 " 12 9 ** " 40 No. 25 " 35 12 9 2.9 . 34l No. 24 " 40^ " 12 9 3-4 " 29 TABLE VIII. QUANTITIES FOR 100 SQUARE YARDS OF LATH. Lineal Feet POUNDS I REQUIRED. Width of Furring. Material. per Lb. 12 In. Ctrs. 1 6 In. Ctrs. ^ inch Flat wire. 20 50 77 Band iron. 20 40 ?4 3 67 IO 90 67 Rib-lath is made by the Trussed Concrete Steel Co., Detroit, Mich., and consists of a series of parallel ribs which are deeply corrugated or beaded. In application these ribs act as small steel beams spanning between the studs and giving the lath extraordinary stiffness and rigidity. Owing to this stiffness the studs may be placed a much greater distance apart than with the ordinary forms of lath, thus saving in the cost of studding and the labor of in- stallation. Rib-lath is so expanded as to provide a perfect clinch or key for the plaster. The key thoroughly anchors the plaster to the lath, allowing only a minimum amount of plaster to flow through. [98] Mortars, Plasters, and Stuccos By the use of rib studs and lath, hollow partitions may be built of ample strength and rigidity. Hollow exterior walls supported on metal lath also furnish a practicable and damp-resisting structure, when the construction is properly safeguarded. A stucco finish possesses many advantages over the ordinary wood exterior it presents a handsome appearance, it does not require painting, and it is exceedingly durable. Either metal lath or wood lath can be used, but the metal is preferable. The wood lath, if used, should be wet enough to prevent absorption of moisture from the plaster, but not wet enough to cause it to swell, because it will shrink again upon drying, and cause the plaster to crack. Green wood lath is better than dry. The use of wooden lath should be restricted to small and unim- portant work. In the case of small buildings, or such as may need patching, it offers a cheap method of obtaining a pleasing exterior, but is very apt to prove a failure. The reason is as follows: If the lath is too dry when the stucco is applied, it will absorb moisture from the plaster to the degree that the cement will not set properly and in time the stucco will fall off. On the other hand, wood made too wet will contract when it becomes dry and the same disastrous results are apt to follow. For the reasons given above it is best to employ a metal lath where the importance of j the undertaking will warrant the slight additional expense imposed by its use. Practical Considerations. The following principles and rules should be taken into consideration when specifying the use of metal lath for plastering or stucco. Painting adds but little weight to the lath. Galvanizing adds from 0.75 Ib. to 0.9 Ib. per square yard accord- ing to the gauge of the lath. Beware of lath cut from sheets galvanized before cutting and expanding, for only two sides of the four in each strand have any galvanizing on them, and these are badly cracked and scaled during the process of expanding. Be sure to specify the gauge of the metal from which the lath is cut, and in addition thereto the weight per square yard, and if coated or galvanized add the weight of the protection. Fasten the sheets horizontally, i.e., the long way of the mesh [991 Handbook for Cement and Concrete Users being horizontal, so that the length of the sheets is across the stud- ding instead of being placed vertically. The dip of the strand should be inward and downward, away from the workmen, so that a perfect key can be formed. Grounds should allow 3/8 inch over face of lath. Edges of sheets should lap about the width of one mesh and no more, simply to make the lath stiff, and the meshes should nest. When using metal studding, the lath will be fastened in the manner provided, which differs with the studs made by different makers. When the lath is placed on wooden studding, it is advisable to use crimped metal furring to provide a key between the lath and the studding, to maintain a uniform thickness of plaster, and also to prevent the line of studding from showing through the plaster, owing to the difference in the moisture in the plaster against the studding and that between adjacent studs. For walls place studs 12 to 16 inches on centres. Twelve inches is best for ceiling beams, channels, or T's. Staples should be about 5 inches apart and of sufficient length to go through lath and astride of furring strip into the wood at least one inch. When fastened to metal channels or T's, galvanized wire is used. When plastering on walls of brick, concrete, etc., metal furring should always be used. In building a cement stucco-finished house the usual construction is completed as far as the exterior sheathing. Precaution must be taken to make the framework as stiff as possible. Often all the exterior sheathing is placed diagonally so that no swaying will occur to crack the plaster, although metal lath reinforces the cement work considerably and prevents to a great extent any surface cracking. SPECIFICATIONS FOR EXTERIOR LATHING AND PLASTERING (American Association of Portland Cement Manufacturers) " Lathing. Cover all exterior walls, etc., shown for plaster with an approved galvanized woven wire lath secured to 5/8-inch by i -inch furring strips, set 9 inches apart, with i-inch galvanized [100] Mortars, Plasters, and Stuccos staples every 5 inches. All lath must run at right angles to furring, and all joints are to be made where they will be covered with half timber, and joints are to be broken every course. " Plaster. All walls, etc., shown on elevation for plaster to be three-coat work on wire lath as follows: The first coat is to be composed of 2 parts rich lime-mortar and i part Portland cement, with a large proportion of long cow-hair. The lime-mortar is to be mixed four days before using, and the cement is not to be added until the mortar is ready to be used, and is to be mixed in small quantities as the work progresses. The face of the first coat must be well scratched to make a key for the second coat, and shall be thoroughly dry and surface cracks appear before the second coat is applied. The second coat will be the same composition as the first, except that the cow-hair is omitted. The scratch coat will be dampened before the second coat is applied. The third coat will be the same as the second, except that a coarse sand will be used and the third coat will be floated up to a rough finish. All sand used in the exterior work is to be approved by the architect. The contractor will be careful to bring his plaster work up perfectly flush with nailing grounds furnished and set by carpenter. No exterior plaster will be attempted until the building is under roof and all interior partitions are studded up and braced." Application of Stucco to Stone. When stucco is applied without the aid of fabrics, special care must be taken to obtain a sufficient bond. When applied to stone, the surface must be thoroughly cleaned of all loose mortar and disintegrated stone, and before the plaster is applied the surface must be thoroughly wet. The amount of wetting necessary depends upon the character of the stone of which the house is built. If it be a soft, porous stone, a great deal of water must be applied, if it be a hard, compact stone, not so much. In every case the old surface must be sufficiently saturated so that no water will be absorbed from the plaster This is an important point, and one which is often overlooked, and many failures can be traced to the fact that the surface was not thoroughly saturated with water. There are several methods of wetting the exterior to be plastered. A large brush can be used, and in a manner similar to that employed in whitewashing a wall. In this way the whole surface can be wet, [101] Handbook for Cement and Concrete Users or the water can be applied with a hose. When a hose is used, the best way is to spray the water. This can be easily accomplished by compressing the end of the hose. Care must be taken to apply the plaster at once, and before the wall has had an opportunity to dry. If the plaster is applied to a dry, porous surface, the latter will take up so much water that the cement in the plaster will not set. This causes the plaster to dry out, crack, and fall off, and is usually FIG. 28. Stucco on Hollow Concrete Tile Walls. the cause of most of the unsatisfactory results in the use of cement plaster. Application of Stucco to Brick. The treatment of a brick surface is very similar to that of a stone exterior. The porous nature of the brick, however, necessitates the utmost care in wetting before the first coat is applied, or the results will not be satisfactory. If the brick wall has been painted and this paint is scaling off, as it so often does, it should be thoroughly scraped and cleaned, and all loose mortar removed. If possible, the old mortar should be picked out 1/2 to 3/4 of an inch from the face of the brick-work, and when the first coat is applied it is forced into these crevices and forms an excellent bond. The comparatively smooth surface of the brick [102] Mortars, Plasters, and Stuccos wall will require less material for the first coat than a rough surface of stone. The first coat over the brick-work must be scratched thoroughly and allowed to set until it is strong enough to support the second coat. The second coat is then applied in the same way as has been described. The original smooth surface of the brick wall lends itself very readily to a smooth plaster finish. This is obtained by using a Light Furring letat Lath ar\d Plaster < Concrete! Piaster' Rods Stucco FIG. 29. Hollow Concrete Tile and Stucco Wall and Floor Construction. finish coat containing rather fine sand and placed with a steel trowel. When it is desired to obtain an Old English style of ex- terior, the smooth finish coat is necessary. Very artistic and de- sirable results have been secured by thus renovating brick exteriors. Stucco on Hollow Tile. Walls of hollow tile form an ideal framework for stucco houses, on account of their strength, in- destructibility by fire and insulation against heat and cold. When properly surfaced, such blocks also furnish an excellent bond to the stucco, so that plastering can be applied directly to the tile without furring or lathing. This bond is obtained by indenting or scoring the surface of the tiles by a series of corrugations, by leaving the surfaces rough, and by the use of dovetailed grooves to receive cement, plaster, and stucco. The tile should in all cases Handbook for Cement and Concrete Users be well wetted before applying the mortar, and if the weather is hot, it will be necessary to spray the finished wall twice a day for a period of three or four days after the completion of the work. Application of Stucco to Concrete. The treatment of a concrete surface that needs to be plastered depends upon whether the wall is new or old. The best results are obtained by placing the plaster immediately after the forms have been removed and while the concrete is still green. In this case very little or no preparation of the concrete is necessary to receive the plaster, which is applied FIG. 30. Artistic Garage. Stucco on Pipe Frame. before the wall has dried out. A single coat is usually all that is required, and the finish desired may be secured in the same manner as with the final coat over a stone or brick exterior. If the concrete wall is old, much care must be taken in preparing it for the plaster. The excess of cement likely to have flushed to the surface must be removed and the surface thoroughly cleaned and well wet before applying the plaster, or it will crack and fall off. By the use of facing forms, new. wall's may be constructed in which the plaster finish and concrete wall are carried up simultaneously, resulting in a perfect bond between the two. [ 104] Mortars, Plasters, and Stuccos Renovating Frame Buildings. Old frame buildings can be readily renovated by the use of cement stucco. The exterior is covered with lath furred out as already described and either two or three coats are applied. In such a case it is necessary to bring out the door and window trim unless the plaster is to finish flush with the old trim, or if it is desired to keep the old frames and have them project, it will be necessary to remove the old siding and staple the furring directly to the old studding. Frequently the trim is removed and the lath brought around the casing, thus getting a recessed window with no wood showing. Quantities of Materials for Stucco. The quantities of cement and sand required for stucco work vary with the thickness of the coat and the proportions of the ingredients. The following table shows the covering power of a barrel of cement when made into mortar for thicknesses varying from 1/2 to i inch, and for proportions varying from i : i to i : 3 mixtures of cement and sand. TABLE IX. AREA COVERED BY MORTAR. Produced from One Barrel of Portland Cement Mortar (3.8 cu. ft. Cement Paste). No Lime. Composition of Mortar. Thickness of Coat. Square Feet of Area Covered. i Cement, i Sand. . . J i inch 3 " 6? oo I i Cement, 2 Sand < i inch f " 134 104 i Cement, 3 Sand. . . . . ^ 1 (C i inch 1 " 208 140 187 i 280 105 CHAPTER XII THE ARTISTIC TREATMENT OF CONCRETE SURFACES Imperfections in Concrete Surfaces. Methods of Finishing Surfaces. Spading. Stucco. Mortar Facing. Grouting. Scrubbing and Washing. Etching. Tooling. Selected Aggregates. Tinting and Coloring. Panelling, Mosaics, Carving, etc. Prevention of Cracking and Crazing. CONCRETE is a plastic material which can be moulded and mod- elled at will, and as such the temptation is strong to cast it into forms strongly suggestive of some other material. " Beauty, however, in structural design is worthy the name only when, like beauty in Nature, it has character. It must not be a servile copy of the style peculiar to some other material, but in fact must express its own individuality without dissimulation." * Imperfections in Concrete Surfaces. Good design requires that the surface must be finished so as to produce a pleasing effect. In many concrete structures the surface is irregular, uneven in texture, and stained or discolored or of lifeless hue. Imperfections in the surface of concrete are due to -one or more of the following causes : 1. Imperfectly made forms. 2. Carelessly mixed or placed concrete. 3. Use of forms with dirt or cement adhering to the boards. 4. Efflorescence and discoloration of the surface. 5. Shrinkage cracks, and crazing of surface. In well mixed and placed concrete, the film of cement paste which flushes to the surface will take the impress of every flaw in the surface of the forms. It will even show the grain marks in well- dressed lumber. Joint marks may be eliminated wholly or in part by pointing the joints with clay or mortar or by pasting strips of paper or cloth over them. Grain marks and surface imperfections can be reduced by oiling the lumber so as to fill the pores or by first oiling and then filling the coat of oil with fine sand blown against the boards. * A. O. Elzner on " The Artistic Treatment of Concrete." [106] Artistic Treatment of Concrete Surfaces Imperfectly mixed and placed concrete gives irregularly colored, pitted, and honeycombed surfaces with here a patch of smooth mortar and there a patch of exposed stone. Careful mixing and placing will avoid this defect. Spading forks should be used to ull the coarse stones back and cause the mortar to flush to the surface. Surface coatings can also be used to cover up any defects. Efflorescence is the term applied to the whitish or yellowish accumulations which often appear on concrete surfaces. Efflores- cence is due to certain salts leaching out of the concrete and accumulating into .thin layers after the water has evaporated. It is most troublesome at horizontal joints where new work is placed on concrete that has already set. Scrubbing the top surface with wire brushes and flushing it with a hose before the new work is started is the best preventative. Where the efflorescence extends over the surface of the wall, it may (i) be covered up by the use of cement coatings or water- proofing compounds, (2) or removed by scraping and chipping or (3) washed away with acids. Muriatic acid is generally used for this purpose. It is diluted with 4 or 5 times its bulk of water and applied with scrubbing brushes. Water should also be played with a hose on the concrete while being cleaned to prevent penetration of the acid. The cost of scrubbing with acid is from 30 cents to 50 cents per square yard. The question of efflorescence is further discussed in Chapter XXX. METHODS OF FINISHING SURFACES The usual methods of finishing concrete surfaces are as follows: 1. Spading and trowelling the surface. 2. Facing with stucco. 3. Facing with mortar. 4. Grouting. 5. Scrubbing and washing. 6. Etching with acid. 7. Tooling the surface with bush-hammers or other tools. 8. Surfacing with gravel or pebbles. 9. Tinting the surface. 10. Panelling, mosaics, carving, etc. Handbook for Cement and Concrete Users Spading and Trowelling. With wet concrete and ordinarily good form construction a reasonably good surface appearance may be obtained by pushing a spade down between the lagging and the fresh concrete and pulling back the stones, so that the grout can flush to the surface. Trowelling should be done while the concrete is still green. In this condition the edges of copings, etc., can be rounded by edging tools such as are used for finishing cement sidewalks. Facing with Stucco. When properly applied, stucco finishes are most pleasing and artistic, especially for residences. By the use of white Portland cement, white sand or crushed marble, a most beautiful effect can be produced. Cream-colored or other delicate tints can also be obtained by mixing pigments with the cement or by the use of colored sand and gravel. The most successful stucco finishes are as follows : a. Smooth float. b. Rough cast. c. Slap-dash finish. d. Pebble-dash finish. A smooth float finish on a building is always pleasing, especially when white or delicately tinted materials are used. Such finishes are ordinarily produced with a wooden float. Floats should be made of hard, close-grained timber such as beech or birch, and should be drawn straight along the wall, without twisting or turning. Smoother finishes can be obtained by the use of steel trowels or with wooden floats covered with felt. Trowelling brings the neat cement to the surface while the float tends to bring out the grains of sand. In Germany by the use of felt-covered floats beautiful effects have been obtained, and this method is used to some extent in the United States, although the tendency in this country is in the direction of rougher finishes. A rough cast surface is one of the most pleasing finishes and is especially appropriate for residences, rustic bridges, and suburban villas. A rough cast surface can best be put on with a broom dipped into a solution of mortar, half and half, or two of sand to one of cement, and applied by stepping back a distance of two or three feet from the wall and striking the broom with the hand in such a way as to drive the mortar against the wall, on which it collects like [108] Artistic Treatment of Concrete Surfaces raindrops. The cement crystallizes and adheres firmly to the wall. By the use of white mortar, a sparkling, glistening effect is obtained. The slap-dash finish is pleasing on account of the variety and the light-and-shade effects which are obtained. It is especially adapted to foundation courses and to suburban houses. It is applied by stepping back a distance of two or three feet from the wall and throwing the mortar against the surface with a trowel. For its successful applications, the workman must possess considerable skill and the scratch-coat to which it is attached should not have attained too great a set to prevent bond. The pebble-dash finish is well adapted to foundation courses, rustic bridges, etc. It is obtained by embedding round half-inch pebbles in the finishing coat. Excellent effects are obtained with white quartz pebbles, and warm effects with colored stones or gravel. The pebbles should be of uniform size and tossed into the cement mortar so as to be half exposed. Stucco finishes may by proper bonding be applied to any surface, whether of wood, stone, or concrete. They are also well adapted to the renovation of old buildings, as well as to the embellishment of new structures. Unless, however, the stucco is keyed to the underlying material by means of metal laths or fabrics, such finishes when applied to concrete are lacking in adhesive properties and one of the following methods which are especially adapted to concrete, should preferably be employed. Facing with Mortar. A facing mortar of cement and sand is used in thicknesses of from i to 2 inches when a surface finish of fine texture or of some special color or composition is desired. When this is used the mortar facing and the concrete backing should be constructed simultaneously in order to obtain a perfect bond. This is usually accomplished by the use of facing forms, which are placed temporarily the proper distance back of the lagging; after which the facing mortar is tamped into the narrow space between the two forms, the body of the wall is poured, the facing form raised, and both backing and facing thoroughly bonded by tamping them together. Grout finishes serve only to fill the small pits and pores in the surface coating. Cavities or joint lines must first be removed by [109] Handbook for Cement and Concrete Users plastering or rubbing. The grout is then applied with a brush, and should have the consistency of whitewash. A i : 2 mixture of cement and sand is often used. Where a dark finish is desired, a grout is made by mixing neat cement and lampblack in equal parts. Scrubbing and Washing. The use of granite chips, colored stones, white pebbles, and other special aggregates, affords a success- ful finish for concrete structures. This consists in removing the forms while the concrete is still green, and then scrubbing the surface with wire brushes and water until the film of cement has been removed, and the clean sand and stone exposed. Warm tones can be secured by the use of crushed brick or red gravel ; a dark colored stone with light sand gives a color much resembling granite; fine gravel or coarse sand gives a texture like sandstone. There is no artistic reason for allowing only the bonding material to be displayed to the eye. On very large jobs the surface can be cleaned off by means of a sand blast, and on smaller jobs the surface may be cleaned exposing each grain of sand by means of muriatic acid in dilute solution, i part commercial muriatic acid, to 4 to 5 parts clear water. Where white aggregates are used the surface may be cleaned off with a solution of sulphuric acid, i part acid, 4 to 5 parts clear water. The sulphuric acid leaves a white deposit and therefore should not be used excepting where the aggregates are white. Another method is to scrub the surface while yet green, say within 24 hours, with a house scrubbing brush and clear water. This is more difficult than the others for the reason that if the stucco is allowed to remain too long before scrubbing, it will be too hard to remove the coat of neat cement from the outside of each particle of sand or other aggregates; and if scrubbed when it is too soft, the surface may be damaged and difficult to repair. If the character of the available aggregates will not present a pleasing surface when exposed, the following surface treatment may be used as recommended by Moyer. While the last coat is still thoroughly damp, apply a Portland cement paint composed of i part Portland cement, 12 per cent of the volume of the cement of well hydrated lime in pulverized form, r part of the volume of the cement of fine white sand. Mix with water to the consistency of cream or the ordinary cold water paint. [no] Artistic Treatment of Concrete Surfaces Stir constantly and apply by using a whisk broom, throwing this paint on with some force. Keep this finish surface damp for at least six days or longer if economy will permit. Do not allow it to dry out in any one place during the week. If necessary protect by hanging tarpaulins and using a fine spray of water playing on several times during the day by means of a hose. This will give a pleasing light gray color of excellent texture. In the construction of monolithic concrete masonry for bridges for the city of Philadelphia, it is the practice to use a fine concrete or granolithic face composed of i cement; 2 bank sand, and 3 crushed and cleaned black slaty shale,. of the size commonly used for roofing, say one-fourth to three-eighths inch. The mixture is placed against the face forms and the body concrete is poured behind and both removed together immediately. In general the washing is done on the day following that on which the concrete was deposited, and an ordinary house scrubbing brush with a free flow of water is used. When the surface is too hard for the scrubbing brush, a wire brush is first employed, then a small block of wood or a brickbat with water and sand in order to cut the film. If the surface has hardened so as to require the grinding action of the sand and block, the aggregate will not be brought into very decided relief and the face will therefore be comparatively smooth. In cold weather when crystallization proceeds slowly the forms may require to remain two days before the washing can be done with safety, and in very cold weather they have been left a whole week, and the scrub- bing was successful. In general, however, the aggregate is best brought out by scrubbing as soon after the concrete has been placed as possible. Etching with Acid. Etching with acid is a further development of the scrubbing process, and is also employed for the purpose ol removing the outer skin of cement and exposing the aggregate. It consists in first washing the surface with dilute muriatic acid, and then with an alkaline solution to remove all free acid; and finally with clean water in sufficient volume to cleanse and flush the surface thoroughly. The operation is simple and always effective. It can be done at any time after the forms have been removed, im- mediately or within a month or more. It requires no skilled labor [in] Handbook for Cement and Concrete Users only judgment as to how far the acid or etching process should be carried. It has been applied with equal success to trowelled sur- faces, like pavements, to moulded forms, such as steps, balusters, coping, flower vases, etc., and to concrete placed in forms in the usual way. It, of course, means that in the concrete facing only such material shall be used as will not be affected by acid, such as sand or crushed granite. Limestone cannot be used, as it is disintegrated by the acid. The treated surface can be made of any desired color by selection of colored aggregates or by the addition of mineral pigments. The colors obtained by the selection of colored stone are perhaps the most agreeable and are doubtless the more durable. Tooling. Concrete surfaces may be bush-hammered or other- wise tool-finished like natural stone. To secure good results, however, the concrete should be at least 30 days old before it is worked. The cost runs from 3 to 12 cents per square foot, accord- ing to the character of the work. Tooling is also done with an axe, pick, chisel, or pneumatic hammer. The tool should be light, and the blows only heavy enough to " scalp" the work, heavy tools and blows being liable to "stun" the concrete, particularly at or near the edges. This scalping partially exposes the material of the aggregate, but does not clean it. The complete exposure and cleansing will come with time and exposure to the weather if the work be outdoors; or the action of the elements can be anticipated by washing the tooled surface with a half-and-half dilution of muriatic acid, which of course must be thoroughly rinsed off. Another method of tooling consists in removing the skin with a coarse-grained emery or carborundum wheel. The skin is cut about as quickly as the block can well be passed over the wheel. This method is well adapted to the surfacing of moulded blocks, slabs, and artificial stone. Selected Aggregates. An effective variation of the ordinary stone concrete surface is secured by using an aggregate of rounded pebbles of nearly uniform size, and by scrubbing or etching to remove the cement enough to leave the pebbles about half exposed to view. This gives a finish similar to that obtained in pebble-dash stucco work and is very pleasing, especially for rustic bridges and cottages. [112] Artistic Treatment of Concrete Surfaces The scrubbing is best done when the concrete is 24 hours old, at which time the outer skin is readily removed. Where the forms are required to remain in position for a longer period, as in the case of arch or girder forms, the acid treatment is required. Tinting and Coloring. The use of colored or tinted surfaces includes : a. Pure white or cream-colored tints. b. Colors produced by the use of pigments. c. Colors obtained from the use of colored aggregates. d. Colors produced by painting the surface. White surfaces are readily obtained by the use of white Portland cement, mixed with either white sand, crushed white quartz, ground marble, or ground white limestone. White surfaces when scrubbed or acid-etched present a pure sparkling appearance of rare beauty when touched by sunlight, and are used extensively by architects for suburban residences. The use of white cements and aggregates also permits the use of delicate tints, which are obtained either by the use of pigments or colored aggregates. Pigments which are unaffected by the action of lime or cement are now obtainable for the purpose of tinting concrete, facing mortar and stucco. Blue, red, green, and yellow pigments cost from 8 to 30 cents per pound, and by proper mixture the intermediate shades may be obtained. The quantity of pigment required is from 2 to 3 per cent of the mixture by weight in order to produce a well colored mortar. The following table (Table X) is recom- mended in the bulletins of the American Association of Portland Cement Manufacturers. In painting concrete surfaces, the material employed should either be neutral, free from saponifying oil, or the surface to be painted should be previously neutralized with dilute sulphuric acid in order to convert the free lime into gypsum. If such precau- tion be neglected, the oil and free lime will react chemically and form soap which will destroy the paint. Coloring by the use of Selected Aggregates. Many engineers and architects prefer to color their concrete by the use of colored sand and gravels in the" mortar which are exposed by scrubbing and etching. While this treatment is more expensive than the use of colored facing mortars, the colors are more permanent, and the acid 8 [113] Handbook for Cement and Concrete Users etched surface exhibits more life and variety. Excellent effects are produced by mixing the cement with screenings produced by crushing a natural stone of the desired color. Panelling. In the construction of buildings, a simple and dignified variation in the surface treatment is obtained by the use of panels or freehand modelling. "In the case of panels it is best TABLE X. MATERIALS USED IN COLORING MORTARS.* Pounds of Color to 100 Pounds of Cement. Pounds Color to Barrels of Cement. Color. Mineral. I 2 3 Gray Germantown Lamp Black 1-4 1-2 2 Black Manganese Dioxide. 12 48 Black Excelsior Carbon Black 2 Blue Ultramarine tr s to 6 2O Green Ultramarine Green 6 6 24 Red Iron Oxide 6 6 to 10 24 Bright Red Pompeian or English Red 6 6 24 Sandstone Red-Purple Oxide of Iron 6 24 Violet Violet Oxide of Iron 6 24 Brown Roasted Iron Oxide or Brown Ochre 6 6 24 Yellow or Buff. Yellow Ochre 6 6 to 10 24 and simplest to adopt sunken work, as this can readily be produced by merely planting a board or block of desired shape against the inside face of form work which leaves its impress upon being re- moved from the concrete. Or else a reverse mould made of some artistic bit of carving for a panel or over a door or window, or a frieze, etc., may be nailed against the forms, and the resulting impress will be thoroughly effective, although a much higher artistic value would be due such work if it were modelled by hand directly in the cement mortar as it is applied and before it has had a chance to harden. "This sort of work is being done extensively and successfully in Germany, where the modern style 'of 'Nouyeau Art' presents abundant opportunities for endless designs. It is already finding * Differences are due to different authorities quoted. Artistic Treatment of Concrete Surfaces much favor in our own country, and ought to reach a high degree of development." Ornamenting Surfaces with Mosaics, Carving, etc. Mosaics, similar to those made with colored glass and lead outlines, can be made with burned clays and cement outlines. Patterns from one foot to twenty feet in diameter have been made, simply by burning slabs of clay in many colors, either glazed or unglazed, and cutting the slabs into such shapes as to show the outline of an artistic design. These parts are assembled in a bed of cement, a bead being left between the pieces of clay similar to the lead bead of glass windows. This bead shows the outline of the design, its width being propor- tional to the size of the figure. As it becomes increasingly wide, the figure becomes more and more conventional. These cement outlines can be colored black or red, but as a rule the best results are obtained with the natural dead gray, as it harmonizes with all the colors of the clay. These decorative inlays or mosaics are very beautiful over mantels and fireplaces as an inside decoration, and are also used to break up wall surfaces in exterior work. Many other substances besides clay have been used in this way, such as tiles, papier mache, etc., with more or less success. Another method sometimes used to ornament the surface of mouldings, cornices, etc., while concrete is green, is to press blocks of wood, cut to desired shapes, such as the classical "leaf and dart," " beads and reels," or any simple figure, into the green concrete, thus leaving a shallow imprint in the surface. These imprints can be spread at appropriate intervals along a frieze or moulding, and produce very beautiful appearances. Templets moulded in clay or cut out of sheet iron can be used in place of the carved wood, if desired. Concrete surfaces can also be economically decorated by carving before the concrete has set. As soon as the concrete is sufficiently hard to resist the imprint of the thumb nail, the forms are removed, and the design is carved out with sharp steel tools of proper shape very much as wood is carved. In this way, scrolls and floral designs can be accomplished with less skill and very much less time than in cut-stone work. Prevention of Cracking and Crazing of Surfaces. The following ["5] Handbook for Cement and Concrete Users is quoted from Mr. Albert Meyer's article on this subject, to which he has given a great deal of study : "It has been known for some time that a very wet mixture of concrete is more apt to craze and show these undesirable hair cracks than a medium dry mixture of concrete. "Neat cement, or the richer mortars, are found to be much more liable to hair cracks and crazing than mortars containing a larger proportion of sand or finely crushed stone. This is particularly true in the manufacture of cement stone by the use of sand moulds in which the mixture is poured very wet. It has also been noted that, when the stone is properly seasoned by keeping the surface covered with a thick layer of very wet sand, or when the stone is immersed entirely and for some time in water, the trouble has been overcome almost entirely. "In the past this trouble has been partially overcome by brush- ing off the surface of the concrete or cement stone with a stiff steel brush; or by scrubbing the surface with a cement brick and wet sand or carborundum stone, thus partially removing what might be termed a neat cement face. It has been found, however, that this does not entirely overcome the trouble, the remedy proving but temporary, the cracks appearing several months afterward. The brushing or scrubbing is merely an assistance; the real remedy lies in keeping the surface thoroughly and continuously wet as long as possible. "It is desirable to have the surface of the concrete or cement stone as near the same texture as the body of the concrete. The exterior should then be kept wet by the application of wet sand, clean sawdust, hay, etc., sprinkled from time to time with water or hanging wet cloths over the perpendicular surfaces, keeping the exterior wet and the cloths wet by sprinkling, or by any other method which will accomplish this result and supply similar or same con- ditions as when hardened under water. By so doing not only is crazing avoided, but a stronger, tougher, and harder concrete is obtained. It is reasonable to conclude that if so treated the surface will slightly expand, but not to a greater extent than the body of the concrete which is already wet. "Hair cracks may be avoided by the addition of mineral oil to the wet mixed concrete. Artistic Treatment of Concrete Surfaces "Mineral oils added to wet mixed concrete and the concrete immediately remixed has the effect of emulsifying the oils. The proportion of oil used should be 10 to 15 per cent of oil to the weight of the cement. Oil weighs from 7 1/2 to 8 pounds per gallon. "This oil-mixed concrete, when hard, appears to be non-evap- orative, indicating that the emulsifying oils held all the excess water in the mortar or concrete, keeping the cement particles moist until the water had been taken up in crystallization and ultimate strength reached. Thus similar conditions are supplied as apply to concrete set under water." In this chapter the readier methods that can be employed in producing artistic effects have been considered. "This humble material, so replete with possibilities, but as yet so little understood, is manifestly destined to take an important place in the construction of our buildings and must therefore strongly influence their design." Our leading architects are beginning to find in concrete a new and useful friend, and with its help will evolve a new architecture that will be full of life and character, strength and dignity and all else that goes to make up a living style." * " The Artistic Treatment of Concrete," by A. O. Elzner, in Proceedings of the National Association of Cement Users, 1907. SECTION III THE MAKING OF CONCRETE PRODUCTS IN THE SHOP CHAPTER XIII CONCRETE BUILDING BLOCKS Advantages and Disadvantages of Concrete Blocks. Materials for Concrete Blocks. Types of Blocks. Block Machines. Making the Blocks. Coloring the Blocks. Waterproofing the Blocks. Building Details. Cost of Blocks. Objections to Concrete Blocks and Remedies for Same. Table of Concrete Block Data. Concrete Tiles, etc. Specifications for Concrete Blocks. THE concrete products manufacturing industry has had a very phenomenal growth, and in fact, the growth has been too rapid for the good of the business, as it has caused a large volume of poor products to be placed upon the market and the disrepute into which much of the industry had fallen on account of this, has not yet been fully removed; the tendency now, however, is toward better products and with renewed confidence due to wider experience and the law of the survival of the fittest, we expect to see an accelerated increase in all lines of manufactured concrete. The use of concrete blocks as a substitute for wood, brick, and stone has become very extensive. Concrete blocks, when properly made and used, form an excellent material for building construction. They commend themselves for their cheapness when compared with brick and stone, and their greater durability when compared with wood; they also possess the advantage over the latter of being fireproof. When concrete was first applied to building construction, it was used to build monolithic walls. The idea of making a wall hollow for the sake of economy, or for prevention of moisture or frost working through the wall was a later development. At the present time practically the whole concrete-block industry aims to [118] Concrete Building Blocks produce a wall made of hollow blocks, with continuous air chambers, or of blocks which, though not themselves hollow, can be laid so as to produce a hollow wall. Advantages of Concrete Blocks. Briefly enumerated, the following advantages are claimed for concrete blocks: 1. A properly constructed concrete-block wall is as strong or stronger than a brick wall of equal thickness. 2. The hollow form results in a saving of materials over brick walls, amounting to from 20 to 50 per cent. 3. It costs less to build a concrete-block wall than one of brick. This is due to the much larger dimensions of the concrete block. 4. The hollow chambers in the concrete walls tend to prevent moisture from penetrating to the interior face of the wall; lathing can often, therefore, be dispensed with, and the plastering done directly on the wall, particularly when the blocks or the wall has received a waterproofing treatment. 5. The hollow chambers form an air cushion that prevents sudden changes of temperature, and tends to keep the building cool in summer and easily heated in winter. 6. The fireproofing qualities of concrete blocks are superior or at least equal to those of brick. 7. Pipes and wires can be run through the hollows of the blocks, resulting in a saving of space and labor and avoiding ugly appear- ances. 8. Concrete blocks can be manufactured near the building site. This will save breakage, also part of the cost of transportation as compared with brick, as cement in bags requires less handling than brick. Materials for Concrete Building Blocks. Building blocks are made of cement, sand, and water mixed in proper proportions, in which case they are properly called " mortar" blocks; or, the above materials can be combined with either broken stone, gravel, or cinders, in which cases a concrete block is produced. Sand and gravel will usually be found the cheapest and most available materials to employ. Since the space for concrete in the mould is very small, the block- builder is limited to the use of gravel and stone not exceeding 1/2 to 3/4 inch in size, A I : 5 mixture containing such gravel or screen- Handbook for Cement and Concrete Users ings will produce a block as strong and as durable as a i : 3 mixture with sand only. Cement. Only Portland cement should be used in the manu- facture of concrete blocks, as, owing to its present cheapness, nothing is gained by using substitutes. Natural and slag cements are sometimes used for blocks that are supposed to remain constantly wet, but such blocks rapidly deteriorate when dry. No cement is as fully reliable as Portland cement, and only the latter should be considered for concrete blocks. Broken Stone. This should be small enough to pass through a i -inch mesh screen. If there is much dust present it must be removed by means of a small mesh screen. Another way is to wash out the dust. A barrel having a wire-sieve bottom is filled with the broken stone, and water is run through the stone; the water, as it runs out, will carry with it all the dust. Gravel. If gravel is used it should be screened through a i-inch screen. If it contains much clay or earth, they must be removed in the manner described for broken stone. The strength of the concrete will not be impaired if the quantity of clay and earth present does not exceed 3 per cent. Cinders. Cinders are sometimes used for concrete blocks with fair results. Such blocks are inferior in strength to those made with broken stone and gravel because the cinders are very porous and are easily crushed. For these reasons they should be used only where great strength is not required; for instance, in interior walls carrying light loads. Lime is sometimes mixed with cement mortar to improve its qualities. The dry-slaked or hydrated lime is the most convenient form to use, and it is mixed in the proportion of one-quarter to one- half of the cement employed. As lime is about as expensive as Portland cement there is no saving in its use. It will, however, cause the blocks to set more rapidly, will make them lighter in color, and the concrete will be denser and will resist better the penetration of moisture. In i : 4 and i : 5 sand mixtures at least one-third of the cement can be replaced with lime without appreciable loss of strength. Proportion of Water. The quality of concrete blocks will. depend greatly upon the amount of water used. A dry mixture is necessary [120 1 Concrete Building Blocks if the block is to be removed from the mould as soon as made. Too much water will cause the block to sag out of shape, should the plates be removed before the concrete has set. Processes of Manufacture. There are two ways of making concrete blocks, depending upon the amount of water used in the mixing. These are called the "dry" and the "wet" processes. In the dry process just enough water is added to give the concrete the consistency of damp earth. When such concrete is tamped into a block machine, the mould can be removed immediately after, and the process continued. In the wet process sufficient water is used to render the concrete mass semi-fluid. When poured into the moulds, the concrete must, of necessity, remain there until hardened. The "wet" process produces a superior block both in point of strength and waterproofing qualities, but the "dry" process is by far the most extensively used. Blocks made of too dry concrete will be weak and will crumble no matter what process of curing they are later subjected to. It is possible, however, to obtain a mixture with enough water to give the required density and hardening qualities, and still be able to remove the block at once from the mould. It is impossible to give a fixed percentage of the amount of water required as this varies with the character of the materials, the moisture in the atmosphere, and other causes. Generally speaking, about 8 or 9 per cent of the weight of the dry mixture will be found satisfactory. Types of Concrete Blocks. Concrete blocks may be classed under two headings : 1. One-piece blocks in which a single block provided with one or more hollow cores makes the whole thickness of the wall. 2. Two-piece blocks in which the face and back of the wall are made up of different pieces, so lapping over each other as to give a bond and hold the wall together. These blocks are made in various shapes and sizes, the standard size having the following dimensions: Length 32 inches, height 9 inches, and thickness 8, 10, and 12 inches. Blocks are also made with lengths of 24, 16, and 8 inches. Because of the excessive weight of the 32-inch block, [121] Handbook for Cement and Concrete Users the 24-inch size is rapidly gaining in favor among architects and builders. The simplest block made has one hollow core and a wall erected with such blocks will have a series of vertical air spaces running through the entire height of the wall. The block which is by far the most extensively manufactured block on the market, is reinforced with a single transverse web, thus giving two hollow cores. It is favored not so much because of its good qualities as the cheapness of manufacture. This block is superior to the single-core block in point of strength. It has, how- FIG. 31. Concrete Block Having Multiple Air Space. ever, its disadvantages. The transverse webs present so many additional paths for moisture to penetrate from the outer wall to the inner. The tamping of concrete around two cores is more difficult than around one, and a block of smaller density and uni- formity is produced. Also, a block with two cores is more liable to injury in the process of removing the cores than a block with one core. The penetration of moisture is the chief defect of concrete blocks, and to reduce this to a minimum various forms have been evolved. Chief among these are blocks with staggered air spaces and the two- piece block. [ 122! Concrete Building Blocks In the staggered air space block, known as the Miracle block, the web and air spaces are so arranged that no web extends directly from the outer to the inner wall. The air spaces register exactly so as to create two series of continuous, perpendicular air chambers throughout, all solid sections being backed by air spaces. This practically assures a block that is frost and moisture proof. The Blakeslee block is another type of block having a width equal to the whole thickness of the wall in which there is no direct connection between the exterior and interior walls. Unlike the Miracle block, however, the continuous air chambers are horizontal. FIG. 32. Self Lining and Interlocking Concrete Block. In the blocks of the American Hydraulic Stone Company, each block has one long and two short arms which break joint with the corresponding arms of the adjacent courses. This system possesses many advantages over other systems since it permits a continuity of both horizontal and vertical air spaces; it produces, in effect, two walls, thus securing thorough insulation and making a concrete wall construction which is impenetrable by moisture. Two-piece blocks are made having the two faces tied together with galvanized wire during the process of manufacture, making one whole block to handle in the field. [ml Handbook for Cement and Concrete Users Concrete Block Machines. There is a great variety of concrete block machines on the market, and these may be roughly divided into four classes: 1. Machine in which the face plate is vertical. 2. Machine in which the face plate is horizontal. 3. Machine for pouring blocks from wet concrete. 4. Machine for making blocks of the two-piece system. Machines of the first class have removable hinged sides, and upright interior cores. There is a great variety of labor-saving FIG. 33. Hollow Wall of Two-piece Block. devices to be found in the different machines, but the principle of manufacturing the blocks is essentially the same in all. The blocks are made by tamping under the "dry" process and immediately removed on iron pallets. In some machines the labor needed to move the blocks is saved by turning the mould over and releasing the block on wood, or by making the block on a wooden board and lifting the mould bodily away from the green block. Several types of machines have contrivances for mechanically raising and lowering the cores, while in others the cores remain stationary, and the bottom and sides are adjustable. There is some disadvantage in using vertical-face machines when it is desired to make a block with facing of richer concrete than is used in the body of the block. Such a facing is often desired to secure greater impermeability and better appearance. It is [124] Concrete Building Blocks necessary then to provide a vertical parting plate, and great care must be exercised to secure an intimate bond between the two mixtures; otherwise, the facing may fall off in rough hand- ling or with the freezing of moisture which may settle between the two mixtures. In the second class of machines the face plate forms the bottom of the mould. The facing mixture is first deposited and tamped, after which the cores slide in laterally, and the filling and tamping continued ; the mould with the block is then tipped to bring the face plate to a vertical position and the block removed. The third class of machines for making blocks from very wet concrete consists of a large number of separable moulds made from sheet metal, and provided with interior cores. The wet concrete is poured into the moulds and allowed to harden there for 24 hours. The principal contentions of the manufacturers of these moulds are that the blocks possess excellent hardening and waterproofing qualities; that they are actual stone, and are cheaply made. Machines of the fourth class differ radically from all other types. This is due to the fact that the shape of the "two-piece" blocks made on these machines, permits the use of mechanical and hydraulic press- ure. The machines are, therefore, of heavy and complicated con- struction, and capable of large output. The mixture is shovelled into the mould, pressed almost instantaneously, and forthwith released. Where it is desired to have a facing differing in color and texture from the body of the block, about three-quar- ters of an inch of the coarse concrete is first raked out before it is pressed, the facing is applied to this loose mass, and all pressed at one time. This insures a firm bond between the face and body of the block, and as the pressure is applied directly to the face of the block, a beautiful face of great hardness and density is produced. Making the Block. Dry Process. The concrete should be placed in the mould in layers about 3 inches thick; tamping should begin immediately upon the placing of the first shovelful, and should be continued until the mould is full. The material should be tamped with a tamper having a small face, and short, quick, sharp blows should be struck. Handbook for Cement and Concrete Users To insure a block of the same consistency throughout, the tamping must be very thorough and should be continued until water appears at the top. This will insure a minimum of air spaces and voids. Wet Process. When placing the material in the mould, the entire mould is filled with one pouring. Of late, the tamping of concrete by means of mechanical or pneumatic pressure has come into extensive use. Moulding concrete by pressure is not successful unless the pressure is applied to the face of a comparatively thin layer. If compression of thick layers is attempted, the materials arch and are not compacted at any considerable depth from the surface. Moulding blocks by pressure is therefore practical only in the two-piece system, in which the load is applied to the surface of pieces having no great thickness. Facing. It is customary now to use for the facing of a block a richer mixture than is employed for the body of the block. The following are the advantages of facing: 1. Saving in Cost. The facing being not more than 1/2 inch thick, there is a considerable saving by employing a coarser material for the body of the block. 2. A dense and impervious facing is secured by using a richer mixture and selected aggregates. 3. A pleasing appearance is given to the block. This may be attained by introducing a coloring mixture; since there is some danger of the color fading, colored sand and stone may be used. It is of the utmost importance that the facing and the rest of the block be thoroughly bonded together, otherwise there is danger of a cleavage plane being formed. The manner in which this may be accomplished is explained under the heading "Making the Block." Concrete blocks being moulded from a plastic material, their faces are capable of endless variations. The faces most commonly used are the smooth face, panelled, corrugated, and rock faces, also special ornamental designs. In choosing a facing it should be borne in mind that a concrete block possesses ornamental and artistic properties of its own, and a far more pleasing appearance can be obtained by bringing these out than by imitating other kinds of stone. [126] Concrete Building Blocks Curing. The curing of concrete blocks is a very important consideration. A block badly cured may lose all the good qualities imparted to it by careful manufacture. All blocks made by the medium wet or medium dry process, should be made under cover, and should remain on the pallet at least 24 hours. They should be kept under cover for at least ten days, protected from the dry currents of air. Under no circum- stances should blocks be made under the direct rays of the sun, nor should blocks be exposed either to sunshine or dry winds while curing. The blocks should be gently sprinkled as soon as possible after making; that is, just as soon as the cement has set sufficiently so that it will not wash. Plenty of water is absolutely necessary. The process of harden- ing in the concrete goes on for a great many days, and crystallization, upon which depends the strength of concrete, cannot go on without the presence of a sufficient amount of water. As soon as a block begins to turn white, it is a sure indication that water is lacking. Care should be taken to so pile the blocks that they will receive water on all sides. A block should never be allowed to dry out on the sides before the centre is thoroughly cured. Blocks should be kept wet from ten days to two weeks, and should never be removed for the purpose of using in a building until they are from thirty to sixty days old. It is well to remember that the longer a block is cured, the harder and better it will become. Coloring. In using coloring matter with concrete, the color should always be mixed with the cement dry, before any sand or water is added. The mixing should be thorough, so that the mixture is uniform in color. After this mixing, the combination is treated in the same way as clear cement. Pure white is impossible where great strength and durability are required, unless white Portland cement is employed. The following formula will make a white .block which is stronger than some sandstones. One part pulverized lime, or hydrated lime, two parts white Portland cement, two parts pulverized marble, two parts fine washed silica sand, two parts coarse silica sand. Blue-gray. A blue-gray color is often obtained without coloring matter at all, by using a blue Portland cement. Light-colored [127] Handbook for Cement and Concrete Users Portland cement may be blended to its proper color by the addition of seven pounds of Ultramarine blue to every barrel of cement. Gray. Add two pounds of Germantown lamp black to every barrel of cement used, when sand is of light color. Dark sand will require less. Lampblack is a protector against the elements, but reduces the strength of the product; not enough, however, to be detrimental in ordinary dwelling-house construction. Blue. Add from ten to fifteen pounds of Ultramarine blue to every barrel of cement. Use dark-colored cement. Black. From forty to fifty pounds of Peroxide of Manganese to each barrel of cement. Red. Twenty-five pounds of Oxide of Iron to a barrel of cement. Bright Red. The above amount of English Red to each barrel of cement. Lake Superior Red Sandstone. Twenty pounds Violet Oxide of Iron to a barrel of cement. Less with light sand. Indiana Bedford. Ochres, which are detrimental to the stone by reducing its strength, must be used for making buff stone. Twelve to fifteen pounds of Yellow Ochre to every barrel of cement will produce an excellent buff stone. Waterproofing Concrete Blocks. The waterproofing of concrete has been treated at length in another chapter; it is well, however, at this point, to enumerate and describe the various methods in so far as they are applicable for securing impermeability of concrete building blocks. Concrete blocks, as ordinarily made, are exceedingly porous and readily absorb water; this is especially true of blocks made by the "dry" process. This tendency to absorb water gives ground to one of the chief objections to concrete blocks. Concrete blocks, however, are no more water-absorbing than ordinary bricks and it is well known that brick walls must be furred and lathed to avoid dampness; but concrete block walls can and should be sufficiently waterproof so that plastering can be done directly on the wall. The different methods available for securing impermeability in concrete blocks are as follows: Concrete Building Blocks 1. Use of properly graded materials. 2. Use of rich mixtures. 3. Use of a facing. 4. Use of an impervious partition. 5. Use of waterproofing compounds. 6. Applications to surface after erecting. All the above methods except the use of an impervious partition have been dwelt upon elsewhere in this book. Suffice it to say here that the use of a waterproofing compound will be found to be an effective and economical method, provided the compound is judi- ciously selected and the work done conscientiously. The following explains the method of waterproofing by securing an impervious partition. In face-down machines, it is a simple matter, after the face is tamped and cores pushed into place, to throw into each spacing a small amount of rich and rather wet mortar, spread this evenly, and then tamp the ordinary mixture until the mould is filled. A dense layer across each of the cross-walls is thus obtained, which effectually prevents moisture from passing beyond it. Recently a method was patented for accomplishing the same results with vertical-face machines. Tapered wooden blocks are inserted in the middle of the cross-walls. After tamping, the blocks are with- drawn, and the spaces filled with rich mortar. Building Construction Details. It is usual to employ the follow- ing thicknesses of walls in concrete block construction: For one-story buildings 8 in. walls For two-story buildings 10 in. walls For three-story buildings 10 and 12 in. walls For four-story buildings 10, 12, and 15 in. walls the thickness, of course, varying from the foundation upward. The mortar for laying concrete blocks should be composed of i part of Portland cement to 3 parts of sharp sand. It is well to add a little hydrated lime to the mortar when mixing. This will prevent it from becoming brittle. The blocks should be wet when set in the wall, otherwise they will absorb moisture from the mortar, making it very weak. Point- ing should be done the same way as in laying brick. Joists can be fastened by cutting into the blocks. It is far preferable, however, to use hangers for this purpose; these not 9 I I2 9] Handbook for Cement and Concrete Users only facilitate construction, but possess the additional merit of distributing the load on the joists over a greater section of the wall. Several special devices are employed to enable one to lay metal plugs in the joists; another way is to cast a wooden plug in the concrete when moulding the block. Cost of Concrete Blocks. The success of the hollow concrete block industry depends to a great extent on cheapness of product, since it is necessary, in order to build up a large business, to compete in price with common brick and rubble stone. At equal cost, well-made blocks are certain to be preferred, owing to their super- iority in strength, convenience, accurate dimensions, and appearance. For the outside walls of handsome buildings, blocks come into competition with pressed brick and dressed stone, which are, of course, far more costly. Concrete blocks can be sold and laid up at a good profit at 25 cents per cubic foot of wall. Common red brick costs generally about 12 dollars per thousand, laid. At 24 to the cubic foot, a thousand brick are equal to 41.7 cu. ft. of wall; or, at $12, 2QC. per cu. ft. Brick walls with pressed brick facing cost from 4oc. to 5oc. per cubic foot, and dressed stone from $1.00 to $1.50 per foot. The factory cost of concrete blocks varies according to the cost of materials. Let us assume cement to be $1.50 per barrel of 380 Ibs., and sand and gravel 25c. per ton. With a i to 4 mixture, i barrel cement will make 1,900 Ibs. of solid concrete, or at 130 Ibs. per cu. ft., 14.6 cubic feet. The cost of materials will then be Cement, 380 Ibs $i . 50 Sand and gravel, 1,5 20 Ibs o. 19 Total $i . 69 or n.5c. per cu. ft. solid concrete. Now, blocks 9 inches high and 32 inches long make 2 square feet of face of wall, each. Blocks of this height and length, 8 inches thick, make 11-3 cubic feet of wall; and blocks 12 inches thick make 2 cubic feet of wall. From these figures we may calculate the cost of materials for these blocks, with cores or openings equal to 1/3 or 1/2 the total volume, as follows: Concrete Building Blocks Per cu. ft. of block, 1-3 opening 7.7 cts. Per cu. ft. of block, 1-2 opening 5.8 " Block 8 X 9 X 32 inches, 1-3 opening 10.3 " Block 8X9X32 inches, 1-2 opening 7.7 " Block 12 X 9 X 32 inches, 1-3 opening 15.4 " Block 12 X 9 X 32 inches, 1-2 opening n.6 " If one-third of the cement is replaced by hydrated lime the quality of the blocks will be improved, and the cost of material reduced about 10 per cent. The cost of labor required in manufacturing, handling, and delivering blocks will vary with the locality and the size and equip- ment of factory. With hand-mixing, 3 men at average of $1.75 each will easily make 75 8-inch or 50 1 2-inch blocks, with 1-3 openings, per day. The labor cost for these sizes of blocks will therefore be 7c. and 10 i/2C. respectively. At a factory equipped with power concrete mixer and cars for transporting blocks, in which a number of machines are kept busy, the labor cost will be considerably less. An extensive industry located in a large city is, however, subject to many expenses which are avoided in a small country plant, such as high wages, management, office rent, adver- tising, etc., so that the total cost of production is likely to be about the same in both cases. A fair estimate of total factory cost is as follows : Material. Labor. Total. 8 X 32 inch, J space 10 .3 7 17.3 cts. 8X32 inch, \ " 7.7 6 13.7 " 12 X 32 inch, \ " 15 .4 10.5 25.9 " 12 X 32 inch, \ " ii .6 9 20.6 " With fair allowance for outside expenses and profit, 8-inch blocks may be sold at 3oc. and 1 2-inch at 4oc. each. For laying i2-inch blocks in the wall, contractors generally figure about ice. each. Adding 5c. for teaming, the blocks will cost 55c. each, erected, or 27 i/2c. per cubic foot of wall. This is less than the cost of common brick, and the above figures show that this price could be shaded somewhat, if necessary, to meet competition. Objections to Concrete Blocks and Remedies for Same. In spite of the admirable qualities of concrete blocks as a building material, their use has not been so extensive as their merits would seem to warrant. There is still considerable opposition from architects and builders to the use of blocks. This is not due to Handbook for Cement and Concrete Users prejudice against the new material concrete, but rather to the manner in which this material is used. In the past few years, a great many inexperienced men have ventured into the business of block manufacture, allured by the glowing prospects of profit held out by an army of block-machine agents. As a result, everywhere are seen glaring examples of concrete-block buildings that fall far short of the standard of excellence that is claimed can be attained. The following have been the main objections to the use of con-, crete blocks : Imitation of natural stone. Poor workmanship. Fixed dimensions. Similarity of blocks. Too great weight. Unpleasing appearance. Anything that savors of imitation, that pretends to be what it is not, will be shunned by right-minded architects and builders. The common rock-faced block is an imitation of the cheapest form of quarry stone, and a poor imitation at that. But why imitate granite or anything else? Why not bring out in the concrete the beauty that is peculiarly its own? A very prominent architect recently said in a conversation: "These block makers come in here and say, 'Why don't you use blocks? I can make a block that ten feet away you can't tell from red sandstone or marble or what not.' No, I don't wish a concrete block that I can't tell from sandstone. I wish a concrete block that won't 'flower.' When I wish sandstone, I can get sandstone." The rebuke is just; the concrete block maker must confine his energies to making concrete blocks and not to imitating sandstone. Poor workmanship can be eliminated with proper inspection. Blocks made from too dry mixtures will always be weak and will crumble, and can easily be detected, no matter how much they were cured. Good concrete produces a hard and dense block and emits a musical tone when struck with a hammer. Contractors and masons often object to the size of the block. A 12 x 32 inch block weighs 180 Ibs., and to hoist a number of these and properly handle them is quite a task. For this reason the use of 32-inch blocks is decreasing, except for large buildings and Concrete Building Blocks foundations; and the 24-inch block now meets with most favor. Such a block, having a width of 12 inches and a height of 9 inches, weighs only 97 Ibs., and if properly made, possesses sufficient strength and durability to meet all requirements. Concrete Tiles and Other Products. There are now being manufactured on a large scale, concrete wall tiles, shingles, and FIG. 34. Standard Shapes of Concrete Tile. other accessories for building construction. While the machinery employed varies with the different processes employed by different makers, the general principles as to mixing, curing, etc., are essen- tially the same as in ordinary block-making. HOW TO FIGURE THE COST OF BLOCKS (SEE TABLE XI) One barrel contains 3! cubic feet. One cubic yard contains 7^ barrels. One yard of sand and 3! bbls. of cement equals 2 to i mixture. One yard of sand and gravel and i^ bbls. of cement equals 5 to i mixture. In making blocks we recommend a mixture for the facing of one part cement, 2 parts coarse sharp clean sand, and the body of the block, i part cement, 2 parts sand, and three parts gravel or broken stone. The gravel or broken stone to range in size from to f " in diameter. For manufacturing 100 blocks 8 x 8 x 16 inches there is needed 2.24 barrels of cement, 0.68 cubic yards of sand, and 1.06 cubic yards of gravel or broken stone which, at the following estimated cost of materials, will amount to: EXAMPLE 2.24 barrels of best Portland cement at $2.00 per bbl. . . . 0.68 cubic yards of sand at $1.00 cu. yd i. 06 cubic yards of gravel or broken stone at $1.50 cu. yd. Cost for labor for 100 blocks Incidentals for safe margin per 100 blocks Total cost for 100 blocks 8 x 8 x 16" $4-48 .68 -5 $9.00 The above are approximate and conservative prices for materials and labor. These may vary, however, to a less or higher degree governed by locality. The cost of concrete blocks in any locality will be found to be much less than that of common brick and they are also a better and more lasting material. [133] Handbook for Cement and Concrete Users TABLE XI. CONCRETE BLOCK DATA.* Giving size and weight of blocks, the number one barrel of cement will make, the number to one cubic yard of material and the number per square of one hundred superficial feet. 5^5 g 1 & 5 3 SOLID BLOCKS. HOLLOW BLOCKS. No. per Square of 100 Square Feet. Weight of Block. Pounds. No. per Bbl. of Cement at i to 5. No. per Cubic Yard. Weight of Block. Pounds. No. per Bbl. of Cement at i to 5. No. per Cubic Yard. 8 X 8 X 16 73 34 48 5 49 71 IT2 8 X 10 X 16 92 2 7 38 67 37 53 112 8 X 12 X 16 109 22 32 80 3i 44 112 4 X 8 X 16 35 68 99 24 100 144 224 4 X 10 X 16 44 54 79 3 2 76 109 2J4 4 X 12 X 16 53 44 66 39 63 9 1 224 8 X 4 X 16 37 68 95 112 8 X 8 X 24 112 22 3i 77 3 2 45 75 8 X 10 X 24 140 18 2 5 9 2 2 5 38 75 8 X 12 X 24 1 66 15 21 112 21 3 1 75 4 X 8 X 24 54 46 65 37 66 94 15 4 X 10 X 24 67 36 5 2 46 52 76 i$ 4 X 12 X 24 79 3 44 55 44 63 150 8 X 4 X 24 55 44 63 75 EXPLANATION. To find the number of blocks for a building, get the surface feet of the building by multiplying the length around the building by the height of the wall. Add to this the surface of gables, then deduct the surface feet of all the openings, thus giving the actual surface to cover. Rule. Multiply the number of squares to cover by the number in the last column, for the size block you are to use, which will give the number of blocks for any building. * Published by the Ideal Concrete Machinery Company. [134] Concrete Building Blocks STANDARD SPECIFICATIONS FOR CONCRETE BLOCKS RULES AND REGULATIONS FOR BLOCKMAKERS, AS REVISED, CORRECTED, AND ADOPTED BY THE NATIONAL ASSOCIATION OF CEMENT USERS AT THEIR CONVENTION, 1908. Concrete hollow blocks made in accordance with the following specifications, and meeting the requirements thereof, may be used in building construction, subject to the usual form of approval required of other materials of construction by the Bureau of Building Inspection: 1. Cement. The cement used in making sand blocks shall be Portland cement, capable of passing the requirements as set forth in the "Standard Specifications for Cement," by the American Society for Testing Materials. 2. Sand. The sand used shall be suitable silicious material, passing the one -fourth- inch mesh sieve, clean, gritting, and free from impurities. 3. Stone or Coarse Aggregate. This material shall be clean broken stone, free from dust, or clean screened gravel passing the three-quarter (f) inch, and refused by the one-quarter (^) inch, mesh sieve. 4. Unit of Measurement. The barrel of Portland cement shall weigh 380 pounds net, either in barrels or sub-divisions thereof, made up of cloth or paper bags, and a cubic foot of cement shall be called not to exceed 100 pounds or the equivalent of 3.8 cubic feet per barrel. Cement shall be gauged or measured either in the original package as received from the manufacturer, or may be weighed and so proportioned; but under no circumstances shall it be measured loose in bulk. 5. Proportions. For exposed exterior or bearing walls: (a) Concrete hollow blocks, machine-made, using semi-wet concrete or mortar, shall contain one (i) part cement, not to exceed three (3) parts sand, and not to exceed four (4) parts stone, of the character and size before stipulated. When the stone shall be omitted, the proportions of sand shall not be increased, unless it can be demonstrated that the percentage of voids and tests of absorption and strength, allow in each case of greater proportions, with equally good results, (b) When said blocks are made of slush concrete, in individual moulds, and allowed to harden undisturbed in same before removal, the proportions may be one (i) part cement to not exceed three (3) parts sand and five (5) parts stone, but in this case also, if the stone be omitted, the proportions of sand shall not be increased. 6. Mixing. Thorough and vigorous mixing is of the utmost importance. (a) Hand Mixing. The cement and sand in correct proportions shall be first perfectly mixed dry, the water shall then be added carefully and slowly in proper pro- portions, and thoroughly worked into and throughout the resultant mortar; the moist- ened gravel or broken stone shall then be added, either by spreading same uniformly over the mortar, or spreading the mortar uniformly over the stones, and then the whole mass shall be vigorously mixed together until the coarse aggregate is thoroughly incorporated with and distributed throughout the mortar. (b) Mechanical Mixing. Preference shall be given to mechanical mixers of suitable design and adapted to the particular work required of them; the sand and cement, or sand and cement and moistened stone shall, however, be first thoroughly mixed before the addition of water, and then continued until the water is uniformly dis- tributed or incorporated with the mortar or concrete (such as will quake or flow). This procedure may be varied with the consent of the Bureau of Building Inspection, archi- tect, or engineer in charge. 7. Moulding. Due care shall be used to secure density and uniformity in the blocks by tamping or other suitable means of compression. Tamped blocks shall not Handbook for Gement and Concrete Users be finished by simply striking off with a straight edge, but, after striking off, the top sur- faces shall be trowelled or otherwise finished to secure density and a sharp and true arris. 8. Curing. Every precaution shall be taken to prevent the drying out of the blocks during their initial set and first hardening. A sufficiency of water shall first be used in the mixing to perfect the crystallization of the cement, and, after moulding, the block shall be carefully protected from wind currents, sunlight, dry heat, or freezing, for at least five (5) days, during which time additional moisture shall be supplied by approved methods, and occasionally thereafter until ready for use. 9. Ageing. Concrete hollow blocks in which the ratio of cement to sand be one-third () (one part cement to three parts sand), shall not be used in the con- struction of any building in the (City) of , (Town) of , until they have attained the age of not less than three (3) weeks. Concrete hollow blocks in which the ratio of cement to sand be one-half (2) (one part cement to two parts sand), may be used in construction at the age of two (2) weeks, with the special consent of the Bureau of Building Inspection, and the architect or engineer in charge. Special blocks of rich composition, required for closures, may be used at the age of seven (7) days with the special consent of same authorities. The time herein named is conditional, however, upon maintaining proper con- ditions of exposure during the curing period. 10. Marking. All concrete blocks shall be marked for purposes of identification, showing name of manufacturer or brand, date (day, month, and year) made, and composition or proportions used; as, for example, 1:3:5, meaning one cement, three sand, and five stone. n. Thickness of Watts. The thickness of bearing walls for any building where concrete hollow blocks are used, may be ten (10) per cent less than is required by law for brick walls. For curtain walls, or partition walls, the requirements shall be the same as in the use of hollow tile, terra-cotta, or plaster blocks. 12. Party Watts. Hollow concrete blocks shall not be permitted in the construction of party walls, except when filled solid. 13. Walls, Laying Of. Where the face only is of hollow concrete block, and the backing is of brick, the facing of hollow block must be strongly bonded to the brick either with headers projecting four (4) inches into the brickwork, every fourth course being a heading course, or with approved ties; no brick backing to be less than eight (8) inches. Where the walls are made entirely of concrete blocks, but where said blocks have not the same width as the wall, every fifth course shall extend through the wall, forming a secure bond, when not otherwise sufficiently bonded. All walls, where blocks are used, shall be laid up with Portland cement mortar. 14. Girders or 'Joists. Wherever girders or joists rest upon walls so that there is a concentrated load on the block of over two (2) tons, the block supporting the girder or joists must be made solid for at least eight (8) inches from the inside face. Where such concentrated load shall exceed five (5) tons, the blocks for at least three courses below, and for a distance extending at least eighteen (18) inches, each side of said girder shall be made solid for at least eight (8) inches from the inside surface. Wherever walls are decreased in thickness, the top course of the thicker wall shall afford a full solid bearing for the webs or walls of the course of blocks above. 15. Limit of Loading. No wall, nor any part thereof, composed of concrete hollow blocks, shall be loaded to an excess of eight (8) tons per superficial foot of the area of such blocks, including the weight of the wall, and no blocks shall be used in bearing Concrete Building Blocks walls that have an average crushing at less than 1,000 pounds per sq. in. of area, at the age of twenty-eight (28) days; no deduction to be made in figuring the area for the hollow spaces. 1 6. Sills and Lintels. Concrete sills and lintels shall be reinforced by iron or steel rods in a manner satisfactory to the Bureau of Building Inspection, and the architect or engineer in charge, and any lintels spanning over four feet six inches shall rest on block solid for at least eight inches from the face next the opening and for at least three courses below the bottom of the lintel. 17. Hollow Space. The hollow space in building blocks, used in bearing walls, shall not exceed the percentage given in the following table for different height walls, and in no case shall the walls or webs of the block be less in thickness than one-fourth their height. The figures given in the table represent the percentage of such hollow space for different height walls. TABLE XII. HOLLOW SPACES IN BLOCKS. Stories. ist. 2nd. 3rd. 4 th. sth. 6th. i and 2 33 33 3 and 4 2 5 33 33 33 5 and 6 20 2 5 25 33 33 33 1 8. Application for Use. Before any such material be used in buildings, an applica- tion for its use and for a test of the same must be filed with the Bureau of Building Inspection. In the absence of such a bureau the application shall be filed with the chief of any department having such matters in charge. A description of the material and a brief outline of its manufacture and proportions used must be embodied in the application. The name of the firm or corporation, and the responsible officers thereof, shall also be given, and changes in same thereafter promptly reported. 19. Preliminary Test. No hollow concrete blocks shall be used in the construction of any building unless the maker of said blocks has submitted his product to the full tests required herein, and placed on file with the Bureau of Building Inspection, or other duly authorized official, a certificate from a reliable testing laboratory, showing that representative samples have been tested and successfully passed all requirements thereof, and giving in detail the results of the tests made. No concrete blocks shall be used in the construction of any building until they have been inspected and approved, or, if required, until representative samples be tested and found satisfactory. The results of all tests made, whether satisfactory or not, shall be placed on file in the Bureau of Building Inspection. These records shall be open to inspection upon application, but need not necessarily be published. 20. Additional Tests. The manufacturer and user of such hollow concrete blocks, or either of them, shall, at any and all times, have made such tests of the cement used in making such blocks, or such further tests of the completed blocks, or of each of these, at their own expense, and under the supervision of the Bureau of Building In- spection, as the chief of said bureau shall require. In case the result of tests made under this condition should show that the standard of these regulations is not maintained, the certificate of approval issued to the manu- facturer of said blocks will at once be suspended or revoked. [137] Handbook for Cement and Concrete Users 21. Certificate of Approval. Following the application called for in clause No. 18, and upon the satisfactory conclusion of the tests called for, a certificate of approval shall be issued to the maker of the blocks by the Bureau of Building Inspection. This certificate of approval will not remain in force for more than four months, unless there be filed with the Bureau of Building Inspection, at least once every four months fol- lowing, a certificate from some reliable physical testing laboratory showing that the average of at least three (3) specimens tested for transverse strength, comply with the requirements herein set forth. The said samples to be selected by a building in- spector, or by the laboratory, from blocks actually going into constructing work. 22. Test Requirements. Concrete hollow blocks must be subjected to the following tests: Transverse, compression, and absorption, and may be subjected to the freezing and fire tests, but the expense of conducting the freezing and fire tests will not be im- posed upon the manufacturer of said blocks. The test samples must represent the ordinary commercial product, of the regular size and shape used in construction. The samples may be tested as soon as desired by the applicant, but in no case later than sixty days after manufacture. Transverse Test. The modulus of rupture for concrete blocks at 28 days must average one hundred and fifty, and must not fall below one hundred in any case. Compression Test. The ultimate compressive strength at 28 days must average one thousand (1,000) pounds per square inch, and must not fall below seven hundred in any case. Absorption Test. The percentage of absorption (being the weight of water ab- sorbed, divided by the weight of the dry sample) must not average higher than 15 per cent, and must not exceed 22 per cent in any case. 23. Condemned Block. Any and all blocks, samples of which on being tested under the direction of the Bureau of Building Inspection, fail to stand at twenty-eight (28) days the tests required by this regulation, shall be marked condemned by the manu- facturer or user and shall be destroyed. 24. Cement Brick. Cement brick may be used as a substitute for clay brick. They shall be made of one part cement to not exceeding four parts clean sharp sand, or one part cement to not exceeding three parts clean sharp sand and three parts broken stone or gravel passing the one-half inch and refused by the one-quarter inch mesh sieve. In all other respects cement brick must conform to the requirements of the foregoing specifications. CHAPTER XIV THE MAKING OF ORNAMENTAL CONCRETE Methods Employed. Modelling. Moulding. Wooden, Metal, Plaster, Glue, and Sand Moulds. ORNAMENTAL concrete, as has already been referred to in the section on Concrete Architecture (under which this chapter might also have been included), is now playing a large part, and is des- tined to play a still greater part in enhancing the elegance and beauty of our modern homes, gardens, and landscapes. The development of the various methods of manufacture has given us the possibility of the highest, as well as the most enduring, architectural effects, and most of these are within the financial reach of the most modest home. Simple pottery, garden furniture, and other handsome decorative work can be made at home by the exercise of care, patience, and some study and the possible enhance- ment of any home in appearance by their use cannot be over- estimated. The principal methods of making these products are given in the following pages. All the precautions to be observed in ordinary concrete work are especially important in ornamental work. The sand must be clean and free from loam, or the ornament will have a dirty color, and if any color work is to be attempted either with pigments or colored stones, cleanliness of sand is absolutely necessary. Sound- ness of cement is important because sharp edges will crumble if the cement is not sound. The aggregate, too, must be selected to produce the desired effect. Ordinary concrete is dull and monoto- nous, and this must be remedied in ornamental work by using selected aggregate, either marble dust and small marble chips to produce a white effect, or selected red, brown, or blue stones for color effects. The color and sparkle of the stones must be brought out by surface treatment as explained in Chapter XII. Methods of Manufacture. The methods of making concrete ornaments and producing ornamental effects in concrete can be [i39] Handbook for Cement and Concrete Users divided into two general classes: first, modelling, which includes all concrete work built without moulds, usually onto wire mesh founda- tions and modelled into shape by hand or by scraping with templets of wood or metal; and second, moulding which includes all concrete work made in forms. Modelling. The cheapest and quickest way to make simple designs where only one or two of a kind are planned is that of modelling. It is surprising how great a variety of forms can be FIG. 35. Wire -mesh Frames for Modelling Concrete Pottery. CIRCULAR WOOD FORM, __^M COVfRCO WIRE FRAM6 FIG. 36. How Rough-Coated Jar is Attached to Circular Wood Form. obtained by a little ingenuity. The fundamental principle in every , case, no matter how simple or complicated, is to make a skeleton of wire mesh, or some rough material, or build up the body solid, approximately the form of the finished product, and lay onto this rough body the concrete to the proper lines. Then finish with a templet by revolving the concreted form about its centre, the templet being held still. We will describe a simple case from which the reader will be able to see the method and easily make more com- plicated designs. [140] The Making of Ornamental Concrete To make a cylindrical vase by modelling, procure sufficient wire mesh, and with a compass or piece of string and chalk, describe a circle on the mesh about the size of the base of the vase to be made. With a pair of wire-cutters, cut the mesh at each point on the circle. Now cut a rectangular piece an inch and a half longer than the circumference of the circle just made, and an inch broader than the height of the vase. Roll this piece on a table or board into a cylinder the size of the vase; the extra inch and one-half will overlap. This is to hold the cylinder fast. Lay this on the table and place the bottom on top of it, and bend the wires of the sides around the bottom. This makes a firm and tight cage on which to build your ornament. Now mix up sufficient concrete for the scratch coat and with a small trowel or knife force this into the mesh, leaving the outside rough as possible so as to form a bond with the finishing coat. Cut an inch board into a circle a little larger than the frame, equal to the outside diameter of the ornament and in the centre of the board drive a nail ; place the unfinished piece on this board with the projecting nail in its centre so that when the piece is revolved about this nail, every point of the frame will be an equal distance from the circumference of the board. Now make a scraping tool by attaching two pieces of inch wood together to form right angles and bevel the edge of one to form a cutting edge. Next mix your finishing coat and apply as before with a small trowel when the concrete is built out to the circular base. Take your scraping tool and hold it on a table or board so that the cutting edge is vertical and rests tight against the wooden base. Revolve the base board and concreted frame together; the tool will scrape off the projections. Fill in all holes with more concrete and continue revolving until the cutting edge touches at every point and there are no projections. Next level off the top to the right height by similar method, having the tool fixed at proper height and revolving your piece until a smooth surface is procured. The inside is built out to the desired thickness and finished by scraping and filling until its surface is parallel to the outside surface. This can best be done by using three pieces of wood formed into a U, the distance between the two vertical legs being the thickness of the piece and their lengths equal to the height of the piece. The inside should not be started until after the outer coat has set for about [141] Handbook for Cement and Concrete Users 6 to 12 hours; it will then be sufficiently hard so that the tool will not injure its surface. The inside bottom is finished by hold- ing a board about as wide as the inside diameter and revolving the ornament as before. A small amount of goats' hair added to the concrete makes it hold together and the concrete should not be mixed very wet. No matter how complicated the form is, the method is essentially the same, a cutting edge being used to form a guide, usually of wood, on which the ornament rests and is centered. If the ornament is square or oblong, the cutting edge is moved along each side of the piece of wood until all are formed. If the form has a spherical surface, a templet of a circular shape must be cut to scrape to the right lines. This method of scraping is often used to form solid mould- ings, copings, etc., the ornament being built in place by moulds and the top built up and scraped to the desired lines by temp- lets formed of sheet iron backed with lumber. The templet is moved along the top edge of the form. The ornaments made in this way can be further decorated by one or other of the ways to be described later. Moulding. The method of making concrete ornaments most generally in use and the one most economical and satisfactory where any number of a similar form are to be made, is that of moulding. There are many different methods of moulding, and each is especially adapted to special classes of work. The simplest, perhaps, is the wooden mould, where the object to be formed is composed of straight lines such as square or oblong boxes decorated with diamonds or some such simple impression, or ornamental concrete lattice work for porches, fences, etc. When the forms become more complicated, standard plaster, sand, or glue moulds must be employed. Standard moulds are best wherever ornaments are to be made on a commercial scale large enough to warrant their first cost, and when they can be procured of proper size and form for the purpose. As ornamental concrete work is in its infancy, the variety of standard forms on the market at present is not very large, and it is much better to make a form for yourself than to accept one that does not fill your requirements. With present progress, there is no doubt that in a very short time there will be such a variety of forms that The Making of Ornamental Concrete it will be absurdly extravagant to make one for yourself, unless your need is unique. Wooden Moulds. In making ornaments with wooden forms or moulds, all that is necessary is to build an outside mould of such form that its inside corresponds to the outside of desired orna- ment; if your ornament is to be hollow or have an open bowl, make a core or inside mould, the outside of the core corresponding to the inside of the ornament. The core must be in so many parts that it can be removed without injuring the ornament after it is hard. The outside mould is placed on a board or working table bottom down. All surfaces that are to come into contact with the concrete are shellacked and oiled well. A layer of concrete is then poured into the mould, as thick as the bottom of the ornament; the core having been shellacked and oiled is then set in place on this bed of concrete. The remaining concrete is poured around the core and well tamped and the top is carefully smoothed off. After this has set about 24 hours the core and outside mould are removed and the surface of the ornament is treated in one of the many ways sug- gested. It" is then laid aside to cure. It should be wetted once or twice a day for a week or two to prevent crumbling. In making wooden moulds, the core must be made collapsible so as to be easily removed, and as few nails as possible must be used to avoid unnecessary hammering. Rounded or bevelled edges can be obtained in wooden forms by using picture moulding and tri- angular strips, blocks of wood, diamond shape, square or round can be tacked in the form, and thus produce corresponding indentations in the concrete. These indentations can be filled with colored cement, clay or tiles, producing very interesting effects. Tiles can be placed in the forms held by light strings in proper positions and the concrete carefully tamped around them. After the concrete has set, the string is cut, and the form is removed, thus leaving the tile in the finished ornament. Metal Moulds. Forms made of galvanized sheet iron stamped and bent to the desired lines have been used with some success as moulds for concrete work. They can usually be made by any cornice mason and with the bending machines used in cornice work. For large designs the sheet iron must be braced with wood to prevent bending. Handbook for Cement and Concrete Users FlG. 37. Moulds for Orna- mented Column. Plaster Moulds. In making concrete mould work with any but wooden forms, the first thing is to obtain a model. These models may be made of wood for simple designs or modelled in clay, or plaster of Paris for more complicated designs. Metal or China ornaments, vases, and jardinieres can also be reproduced. Take a simple case of making a concrete box. First, construct a box of wood of the required size, make the inside of the box taper slightly so that the material is thicker at the bottom than at the top; this will allow the model to be slipped out from the mould when the same is hard. Now lay your wooden box upon a working board, shellac and oil all sur- faces, and mix up enough plaster of Paris to make a layer about one-half inch thick around the sides of the box. By means of thumb tacks or small tacks attach a strip of paper at each of two opposite edges of the box. This paper is to separate the mould and make two halves of it. Now apply the plaster to the model, making a wall about one-half inch thick. When this is hard, remove same from the box and proceed to make the core or inside portion of mould. First shellac and oil well the inside of the box, then mix up sufficient plaster of Paris and fill the box with same. Level off the top and allow to harden about 15 minutes, then hold the box upside down over the working board and tap gently. Owing to the taper of the box, the plaster will slip out easily. This core should be smoothed off and corners rounded if desired. All that is necessary now is to shellac and oil the parts of the mould which come in contact with the concrete as well as the working board on which they rest; properly centre the core and outside walls on the board, the two parts of the outside mould being held together by a string tied around them. As they are on the board now, the bottom of the box is up, so that the core must be placed with its largest side down. The outsides will project up above the core an amount equal to the thickness of the bottom. Now mix up your concrete and pour same into the annular layer between the core and [ J 44] The Making of Ornamental Concrete the outer mould and over the core to the top of the mould. Carefully tamp your concrete down into he mould, preventing air holes, etc. When mould is full, scrape off the top with a straight edge and allow to stand until concrete has set. This takes about 8 hours. At the end of this time, the mould can be removed as follows: Gently tap the working board on its edges and it will fall free from the mould, then place the mould and model together on some BOI FIG. 38. Plaster Moulds for Concrete Baluster. Sketch showing progressive steps in moulding same. blocks of wood a few inches high on the board, supported so that the concrete ornament and the outside mould rest on the blocks and the inside core is free. Gently tap the mould until the core drops out. The outside form is next removed by similar tapping, the string that binds the two parts being severed. To make more complicated designs in plaster moulds, all that is 10 Handbook for Cement and Concrete Users necessary is to procure a model, and cover same with plaster, making it in so many parts as to avoid all reentrant angles, undercuts, or overhanging corners. If a core is used, it can be cut up into small wedges so as to be easily removed. Plaster of Paris can be cut with a fine saw very nicely if kept wet. Handles or ears to vases can be moulded separately and fitted to holes prepared in the vase and cemented in place. Glue Moulds. For designs in concrete which have considerable undercut, glue moulds have been used almost exclusively in the past, because they are flexible and can be strained so as to allow the finished product to be removed. A glue mould can be reused about six times and the glue can then be boiled down and used again for other moulds, but they are not quite so good as plaster moulds, which will last indefinitely if handled carefully. Sand moulds are displacing to some extent, the use of glue moulds, because of certain advantages, of which more will be said later. In concrete work formed from glue moulds, as with all other mould work, a model of the piece to be formed must first be ob- tained or made. The model is laid on the table or working board and a pencil line is drawn around it on the board, so as to mark its position. This enables the workman to put the model back again in the precise position after it has been moved. The model is next covered with a damp newspaper, the paper being pressed into all the corners and angles of the model. A layer of damp clay about 3/4 of an inch thick is then laid over the model following its contours roughly. Next, a plaster case is moulded over the clay, filling this case about 3/4 inch thick, and is made flat on its outside so as to be able to rest on this side when in use. The outside of the case is marked on the board in the same way as the model was. When the plaster case is sufficiently hard, it is removed and the clay and paper taken from the model which is now shellacked, oiled, and re- placed, in its original position, by means of the line on the board. The plaster case has two holes bored into it, one about 3/4 inch in diameter to permit the glue to flow through it; the other, a small hole, to allow the air to pass out as the glue is poured in, is bored in the highest point in the case, thus serving to tell when the space [146] The Making of Ornamental Concrete between the model and case is full, by the glue coming out of it. The plaster case is next put into the position indicated by the line on the board, and fastened in this position by straps passing over it. The glue should be of a good quality of white glue; it is heated in a double boiler until it is thin enough to pour. The space be- tween the plaster case and the model is filled with the glue by slowly pouring it into the hole provided until it runs out of the air vent. It is then allowed to stand about 12 hours to congeal. The plaster case is removed, and the glue mould is taken from the model by springing its ends and sides slightly so as to allow the undercuts to slip out without injuring the model or the mould. The mould is kept in the plaster case so as to preserve its shape. Before using the glue mould, its surface must be treated so as to make it waterproof; this is accomplished by washing it with a saturated solution of alum. Two or three coats are necessary, and each coat must be dry before the next is applied. In lieu of the foregoing, the surface can be varnished and oiled. Sand Moulds. Sand moulds are probably the cheapest moulds in which concrete can be cast, and at the same time they offer some advantages over all other methods of moulding. In a sand mould, it is of no account how great the undercut or how small the orifice through which the core has to be removed, for the sand after it has dried out can be crumpled into little grains and poured out of an orifice or scraped out of an undercut with great ease and without possibly injuring the ornament. The process of making artificial stone by casting in moistened sand is described by W. P. Butler, the inventor, as follows: "Opening Casting. The first step in the process is to make a wooden pattern of the stone to be made. This pattern or model is made of the exact size of the stone desired, and it may be made in one or in several pieces. The size and style of the block usually determine the method to use in the casting of it. "The most common method of casting is that of casting on the floor, or 'open-casting,' as it is commonly called. Nearly all large stones as well as small ones are cast in this way. The pattern is embedded solidly upon the compound (which for brevity we will call the sand), which is then packed solidly around it and built up until it is fully embedded in the same manner that a pattern is set Handbook for Cement and Concrete Users in the sand in a foundry. To remove the pattern from the sand it should be lightly tapped, so as to loosen it without noticeably en- larging the mould, from which it should then be withdrawn with the greatest care so as not to break down the edges. "If, on examination, the surfaces of the mould are not perfectly smooth, or if any edge is broken down, or if any detail is imperfect or damaged, it may be 'touched up' or repaired with the moulder's tools which it is necessary to have. " One perfect mould having been made, as many others as are desired can be made in like manner from the same pattern. A competent moulder can make from five to fifty moulds in a day, according to the difficulty or size of each. If the pattern has no projecting parts which would prevent its being withdrawn from the sand, it may best be made in one piece, but if there are projecting details or undercuts on the pattern, then it must be made in two or more pieces so as to make it possible to withdraw it from the sand without breaking down the mould This necessitates not only good workmanship on the part of the pattern-maker, but a thorough knowledge on his part of the necessities of the moulding process. "The removal from the sand of a pattern of two or more pieces is done in the same manner as though there was but one piece, but it requires more time and care. "Compartment Casting. If the block to be cast is for a cornice, belt-course, water-table, or any similar purpose where there is an ornamental or moulded face, with the other sides plain, a better and more rapid method of casting is to fasten two planks on edge, and parallel with each other, with partitions, fashioned between the planks at proper distances, forming a series of compartments in each of which is to be cast a stone. The length of the pattern or distance between the planks is made to equal the length of the block. "The pattern in this case need be only the face of the block which is adjusted within the compartment at such a distance from the partition back of it as to give the proper width to the block. Then in the space in front of the pattern, solidly tamp the sand. " Next loosen the pattern and draw it away from the sand, which retains the design of the face. This process is repeated in the The Making of Ornamental Concrete several compartments, and the moulds are then filled. By this method a minimum of time is required and blocks are formed much more rapidly than when moulded in a bed of material on the floor. "Casting in Open-end Flasks. This method will prove to be the best in many cases, especially where it is desired to pack the moulding compound vertically on the face of the pattern. In this process a box or collapsible 'flask' is open at the top and bottom. Within the flask and at the proper distance from the bottom is fastened the pattern or face-plate. "Over and upon the top of the pattern tamp the sand and then fasten over this the cover to hold the sand in position while the flask is being turned over. Next loosen and remove the pattern, leav- ing the mould ready for the cast, wherein the face of the block alone is in the sand. When the cement is hardened the flask is loosened and removed. "Casting in Closed Flask. Many pieces, such as balusters, balls, or similar turned forms, or forms which are symmetrical on all sides, must be cast in closed boxes or flasks. "The pattern of the baluster is, in the case shown, made in two pieces which are embedded in the lower and upper halves of the flask. The patterns are then withdrawn and the two halves of the flask are carefully locked together. The cast is then made by pouring the liquid cement through the opening in the end of the flask. A great variety of the finest ornamental work is cast in this manner. "In all cases the cement and powdered stone, in the proportions of one of cement to three of stone dust, are mixed with water until of the consistency of thick gravy, and then carefully poured into the mould, using a pouring board or pipe to guide the stream and prevent its tearing up the sand. The mass is then allowed to set and harden for about a week before it is removed from the mould. This protection of the cement in the moistened mould prevents the cracking or checking of the surface. When the stone is fully dried out, the surface is brushed off with a wire brush to remove the surplus sand, and, if a tooled appearance is desired, the" surface can be gone over with tools and then the block cannot be distinguished from one carved from the natural stone." 149 CHAPTER XV CONCRETE PIPES, FENCE POSTS, ETC.* Advantages of Concrete Pipes. Moulds, Machines, and Manufacture of Reinforced Concrete Pipes. Concrete Tile, Data, and Costs. Advantages of Concrete Fence Posts. Moulds, Machines, and Manufacture. Reinforcement for Fence Posts. Fastening Fence to Posts. Quantity of Materials for Fence Posts. CONCRETE PIPES* A LARGE amount of concrete pipe is now being manufactured and used in this country. They possess many advantages over and are far superior to any other kind of pipe for many purposes. Advantages of Concrete Pipe. Concrete pipe can be manu- factured practically anywhere. But little equipment is required and this can readily be obtained. Of the material necessary for man- ufacture, the sand and stone can always be found locally. The cement may have to be shipped some distance, but the cement constitutes but a small portion of the bulk. Thus, easily obtained materials, low freight charges, and low cost of equipment all make for a low-priced pipe. It costs less to make concrete pipe than to make clay pipe, and a better, truer, and stronger pipe is the result. Properly made concrete pipe does not, under usual conditions, deteriorate with age, but instead grows stronger. The life of the pipe is therefore indefinite. This can be said of no other form of pipe. If made impervious it is immune from injury by acids, oils, alkali, and other disintegrating influences as explained in a previous chapter. Concrete pipe, if properly made, is perfectly shaped and is true at both ends. This uniformity greatly simplifies the laying of the pipe, as because of it all members will fit together easily and accurately. * The best treatise on cement pipe will be found in "Cement Pipe and Tile," by E. S. Hanson, editor of Cement Era, published by Cement Era Publishing Co., Chicago, 111. Concrete Pipes, Fence Posts, Etc. Enlarged bells are not necessary for the proper jointing of concrete pipes. The pipe therefore may be of uniform diameter throughout, which greatly facilitates bedding and aligning. Concrete pipe is not limited to the circle in shape, but may be varied to suit the conditions. Where the flow is variable the egg shape may be desired, and again where a greater area of bed is necessary a pipe with a flattened invert may be decided upon. Such shaped pipes may be as readily made in concrete as the more generally used circular ones. Concrete pipe maybe made of any strength desired by intro- ducing suitable reinforcement. It may, therefore, be used for pipes under pressure. Manufactured vs. Cast-in-Place Pipe. When compared with a concrete pipe cast in place, the following advantages are claimed for a concrete pipe, made in short lengths in some convenient place, and then laid. The pipe may be readily inspected both during and after manu- facture. Reinforcing metal may be accurately placed and kept in place until the concrete has been poured. The forms may be used over and over again, thereby decreasing the cost of the pipe. Being laid in short lengths, each length may be allowed to settle firmly on its bed before closing the joints. In large pipes the back fill may even be placed before cementing the joints. This minimizes the danger of the pipe straining or cracking due to unequal settlement. Also, under these conditions, when once closed there should be little or no tendency for the joints to reopen. The disadvantage of a pipe laid in short sections is the number of joints. These joints are of necessity the weakest part of the pipe, and are therefore the controlling element. This inherent weakness is overcome to a certain extent by various special methods, as the use of metal ties between sections, or by lapping the reinforcement of one section over that of the next. Moulds, Machines, and Manufacture. Various kinds of moulds and machines for the manufacture of concrete pipe have been de- signed and patented. The simplest of these consists of an iron pallet, an outer hinged Handbook for Cement and Concrete Users shell and an inner collapsible core, both of sheet steel, a cap to fit over the core and a tamper. To these may be added an attachment for forming a bell end on the pipe. The method of using is as follows : The iron pallet is placed on the floor, the core is backed inside and the conical cap is placed over it. The outer shell is then backed in place, and the mould is ready to be filled. Concrete is shovelled in a little at a time and thoroughly tamped. The whole outfit is then removed to the curing shed where the inner core is first collapsed and removed, then the outer shell expanded and removed, leaving the finished pipe standing on the pallet. The "Schenk Siam" tile* machine consists essentially of a pyramidal frame about 8' high, a revolving table for carrying moulds, a revolving shaft carrying the packer head, a loot from which the moulds are filled, and a bucket elevator which delivers .the concrete to the loot. The tile are made in galvanized iron jackets, made in two parts, and provided with hinges and lock. These jackets are set on pallets carried by the revolving table, the table carrying six pallets of any size. These pallets are held by pins in the table, the change from one size to another being made by simply lifting off one set of pallets and dropping another into place. The table is revolved and the jacket placed in a position for making tile by means of a cam at the rear of the machine. There is a ring, or rather a combination ring and a small hopper, which drops down on to the jacket after it is revolved into posi- tion, and holds the jacket solidly in position while the tile is being made. When the jacket is in place, the packer head, which is on a sliding shaft, operated by another cam at the rear of the machine, drops down through the jacket and into and fills the bottom ring; and just at this point, where the packer fills the ring, the concrete is dumped in from the top by means of the elevator. The cup on the elevator holds just enough material to make a tile, different cups being put on for the different sizes. Thus the concrete is dumped down inside of the jacket and around the packer, and the packer * From " Cement Pipe and Tile," by Hanson. Concrete Pipes, Fence Posts, Etc. head revolves up through the concrete and packs, forces, and presses the material between the jacket and the packer. This packer head has concave sides and is graduated out from the size of shaft on which it revolves, to the full size of the inside of the tile at the lower end. Thus, it is in one sense the core, for it forms the inside of the tile, and revolves up out of the jacket through the top ring, and the ring rises with it and releases the jacket, and the tile is made; then the table revolves and another jacket moves into place. As the tile are made they are removed from the machine and taken to the drying shelves where the jackets are taken off. The machine has a square upright plane and the pallets are carried on a sliding rack which holds two pallets, so that as one finished tile is carried away, another jacket slides into place. The power head is made in two parts, the main part attached to the shaft revolving at one speed while the wings attached to the outer shaft revolve at a much higher speed, pressing the concrete outward against the walls of the jacket and trowelling it down smooth. When the carriage is at its highest point the head fills the lower ring, or pallet; then the concrete is dumped in automatically; the head revolves continually and forms the tile. When the carriage is at its lowest point the table shifts automatically and the tile in the jacket is taken to the curing shelves, where the jacket is removed immediately and returned to the machine. The machine is set in motion by a lever which operates a friction clutch. The lever at the left of the machine is used to start the cable. After this is put in motion, the concrete is thrown into the hopper, the buckets taking up a sufficient amount for one tile. This is dumped in just at the time the carriage is at its highest point. The head at once presses the concrete against the jacket and as the carriage is lowered, the tile is formed. The cable then shifts to one side, putting the finished tile in position to be put away and bringing another jacket into position under the tamper. The machine makes tile from 4 to 16 inches in diameter. The Miracle Power Tile Machine consists of a base from which rises a hollow shaft carrying the operating mechanism, and around which shaft revolves the table carrying the moulds. The tile are made by means of a peculiarly shaped revolving packer which operates inside the steel mould or casing. The circular Handbook for Cement and Concrete Users table around the column of this machine is moved vertically by the mechanism and carries the casing with it. When the table or carriage is at its highest point the packer completely fills the ring or pallet upon which the casing rests. At this moment the machine automatically dumps the proper amount of concrete into the casing, which then goes downward with the table and the revolving packer gradually moves up inside the casing, forcing and packing the con- crete against the latter and forming the tile. When the casing reaches the bottom, the packer and casing are free and the table revolves and brings the next casing into position, and the operation is re- peated. In the meantime the tile are carried away in the casing to the curing shelves. The casing is then removed from the tile and returned to the machine to be used over again. The packer head of this machine is made reversible, so that when worn out in one position by the grinding action of the sand, it can be used in another. The manufacturers claim that 6 to 8 horse-power is ample for operating the machine. In the manufacture of concrete pipe, the concrete used is of a sufficient consistency to permit of the immediate removal of the moulds. The mixture is therefore comparatively dry. After the pipe is moulded it is taken to the curing shed where it remains from four to seven days, during which time it is kept con- stantly moist by frequent sprinkling. In some plants steam, under low pressure, is used in the curing shed. This assures an equal distribution of moisture, and under this condition it is impossible for any pipe to dry out. After curing, the pipes are taken to the drying yard. Here they may or may not be sprinkled occasionally, depending upon atmospheric conditions. Pipe is kept in the drying yard until it is about 30 days old, when it is ready for laying. Reinforced Concrete Pipe. Various forms of reinforced concrete pipe have beert used where the strength of the manufactured pipe is insufficient. They are reinforced either by steel rods in flats placed both circumferentially and longitudinally or by wire mesh or expanded metal. Particular attention is now being paid to the joints, the object being to make the joint equally as strong as the rest of the pipe, thus giving a truly monolithic pipe line. Concrete Pipes, Fence Posts, Etc. The Jackson Concrete Pipe is one where particular attention has been given to the method of jointing. This pipe is manufactured in sizes ranging from 24 to 108 inches. The forms for making this pipe are assembled by first setting up the inner wall in rolled sheet sections on the upper and inner flange of the bottom plate or ring. The lateral reinforcement, consisting of steel slabs, is inserted in pockets in this ring. The circumferential reinforcing, consisting usually of one or two cylinders of triangular mesh reinforcement is now placed, after which the outer wall is assembled on the lower or outer flange of the bottom plate. Space clips at the top of the wall hold the reinforcement in position. The mould is then filled and rammed by hand. The longitudinal reinforcement extends beyond the sections and terminates in hooked ends which fit into the rebated space which forms an outside groove, when the two sections are placed together. The sections are then interlocked with a tie band pass- ing completely around the pipe at the groove and through the hooked ends of the longitudinal reinforcing bars. A joint shield is then drawn up snugly around the pipe and the joint first flushed with water and then grouted. In the latest form of this pipe, the pipe is so shaped that the lower half of the groove is on the inside and the upper half is on the outside of the pipe. In this case the lower half of the joint is interlocked and grouted from the inside and the upper half from the outside. This pipe is usually manufactured at the trench. Local labor and material are therefore used and there are little or no freight charges. This method also leaves the pipe open for inspection at all times. Another pipe, where the distinctive feature is the method of jointing, is the Lock Bar Pipe (Meriwether System). This pipe is manufactured in sizes ranging from 24 to 96 inches in diameter and in either three- or four-foot lengths. The standard pipe has a circular section. The reinforcement is placed concentric with the circumference of the pipe and toward the interior of the section. Each section is cast with a bell and a spigot end. The bell, however, does not project beyond the circumference of the pipe, but is flush with it. Handbook for Cement and Concrete Users For unusual conditions, a pipe of special design with a flat base section is made. In pipes of this design, the reinforcement is placed toward the interior of the crown and inverted toward the exterior at the sides. Usually in the expanded metal or American Steel & Wire Co.'s Triangular Mesh, the reinforcing metal extends throughout the length of the section and projects both into the bell end and out of the spigot end for several inches. The spigot is shorter than the bell, so that when two sections of the pipe are placed together the reinforcing metal from one section overlaps the reinforcement of the other section in an internal recess. The recess in this joint is filled with cement mortar, thus locking the section together and sealing the joint at one operation. On all pipe of 36 inches in diameter, or larger, the joints are made from the interior after the back filling has been placed by forcing grout behind a shield* with a grout gun. On sizes less than 36 inches in diameter the joints are made from the outside through openings in the crown portion of the bells before the back filling is placed. By placing the back filling before the joints of the larger pipe are sealed, any settle- ment caused by the fill will occur before the joint is made; thus any strain on the joints that would tend to injure their efficiency is eliminated. TABLE XIII. CONCRETE TILE DATA AND COSTS.* Inside Diameter of Tile in Inches. Thickness of Walls in Inches. No. of Tile from Bag of Cement. Cost per Tile for Cement at $1.50 per Bbl. 2-Foot Lengths. No. of Tile from Yard of Sand. i ^ |i fei - fsi*l F s tP Cost per Length for Labor $2.50 and $1.75. Total Cost per Length. Total Cost per Foot of Cement Tile. Average Selling Price Clay Tile, per Foot. 6 ,1 10 $0.03 60 $0.02 00 $o 06 $0.11 $0.06 $0.15 8 ii 6i .06 45 . 02 07 J 5 .08 . 20 10 if 5 .09 32 .03 7o 08 . 20 . 10 30 I 2 i 3 . 12 25 .04 65 09 25 13 .36 \l i^ 2 i 9/10 .18 . 2 I 19 16 05 .06 57 50 10 ii 33 38 ill 2O 2 rj 24 14 .07 45 12 43 . 22 I .00 24 2 ? I I/IO 34 9 . ii 40 .14 59 30 1 .50 30 2* ^ 45 7 .14 35 .16 75 38 2.00 36 3 .60 6 30 .18 96 .48 2-50 42 -? r -. 75 r 20 1 7 35 i .30 .65 48 4 1 i 15 3i 30 10 65 2. 10 i -05 * Besser Manufacturing Co. Concrete Pipes, Fence Posts, Etc. CONCRETE FENCE POSTS Principal Advantages. Owing to the decreasing supply of available timber, the cost of wooden fence posts is constantly in- creasing. This, together with their short life, makes imperative the adoption of some other form of fence post. The ideal fence post should be cheap, strong, and permanent. FIG. 39. Artistic Corner Fence Post Construction. f These three qualifications are possessed only by reinforced concrete posts. Wood posts, as before stated, are becoming expensive, and owing to their being subject to decay, and damage by fire, their life is at best short. Steel posts have been tried, but are expensive, and unless con- stantly painted will soon deteriorate by rusting. Reinforced concrete posts, however, are cheaply and easily made, may be as strong as desired, and are practically everlasting. Reinforced concrete posts may be made near their final location, of material obtained locally, necessitating very little cartage and the importation of only a comparatively small amount of cement and reinforcing steel. The manufacture of a reinforced concrete fence post is a com- paratively simple operation. A suitable mould is made or procured and the reinforcement placed in it. The mould is then filled with concrete, which is then compacted. If a dry concrete has been used, the moulds may be removed imme- diately; if the concrete was wet, the post should remain in the moulds about 24 hours. After being removed from the moulds [i57] Handbook for Cement and Concrete Users the post should be cured and dried in the same manner as de- scribed for concrete pipes. Moulds, Machines, and Manufacture. Various moulds and ma- chines for the manufacture of concrete fence posts have been made FIG. 40. Concrete Fence Posts and Accessories. and are on the market, all of which appear to be more or less satisfactory. Simple moulds, such as could be made by almost any man, consist of two end pieces having notches which hold in place the longitudinal boards. Cross-pieces or hooks are provided to prevent PLANT FOR 150 POSTS A DAY FIG. 41. Layout of Plant for Making Concrete Fence Posts. the longitudinal pieces from bulging. The mould is placed on a platform, oiled or soaped, after which the post may be made as described above. The "Haas" Post Machine is 8' 8" long, and 28" wide, weighs about 300 Ibs., and is made of 2" high-grade cypress lumber rein- forced with steel trussed bands and bolts. The machine is treated to two coats of oil and white lead. Concrete Pipes, Fence Posts, Etc. The'"D. & A." Post Moulds are made from one piece of sheet steel about 1/16" thick. They are U-shaped in sections with flanges bent at right angles to the body of the moulds to stiffen them. The moulds .are provided with square detachable sheet steel end plates, which fasten to the moulds by means of projections which fit into slots in the flange of the mould and a clasp riveted to the bottom of the moulds at the ends. These end plates serve to hold the moulds upright as well as to hold the sides of the mould together. The post is released by removing the square end pieces. These FIG. 42. A Set of Six Post Machines, Showing Method of Piling One Machine on the Other. Can be run under the Mixer and through the Kilns or direct to curing rails. moulds are usually set up ten at a time on a shaker, and after rilling, the concrete is compacted by agitating the shaker. The "Ohio" Post Machines consist of two strong cast-iron end frames into which are fitted six or twelve moulds of 2O-gauge sheet iron. The ends fit tightly between lugs cast on the frames so that the moulds are sprung slightly to gether in placing, thus when remov- ing the moulds, the sides will spring away from the posts. Two side rails hold the end moulds in position. One side rail is removed when placing or removing the moulds. To compact the concrete the frames are placed on a shaker and agitated. The finished post is T-shaped in cross-section. Handbook for Cement and Concrete Users The "Scott" concrete fence post mould is of galvanized iron, shaped to contain the post face up in its plastic form. The form is placed in a rack which holds four. After placing the reinforce- ment and concrete, and as soon as the concrete has taken its initial set, the face of the post is corrugated by a special tool for same. To remove the posts the racks are set on end with the small end of the post on top. One man then pushes the forms out of the rack while the other takes care of the posts. In the foregoing moulds a wet mixture of concrete is usually used. The post must therefore be left in the moulds for a period of about 24 hours, thereby necessitating a number of moulds. The FlG. 43. Moulds for Fence Posts, all Sides Tapering. manufacturers of these machines claim that this loss in frames is more than offset by the increased strength of the post resulting from the use of the wet mixture. In the following moulds a dry mixture of concrete is used, and the mould removed immediately. In this way, with but one mould, innumerable posts may be made without loss of time. Pallets of some sort are necessary with these machines. The " Bulldog" Cement Post Machine consists of an angle iron frame to which is riveted a corrugated steel apron, thus forming the sides of the moulds and giving the post its characteristic corruga- tions. Hinged end gates are fitted to these sides which when inter- locked, permit the sides to be spread and the post thus released. The " Monarch" Post Machine is made entirely of steel and is composed of a double frame securely braced and bolted together. Concrete Pipes, Fence Posts, Etc. The inside walls are hung on double hinges so that the slightest upward motion of the moulds releases the post. The "Bailey" Post Machine is made of cast metal. The sides taper and are hinged at the top. A hinged bottom plate holds the sides together. To release the post, the hinged bottom plate is removed and the sides spread. The "Scott" Concrete Fence Post Machine is made of steel and makes a post with a U-shaped cross-section. This machine differs from the other in that it must be turned over to release the post. The "Luck" Cement Post Mould is made in two sections of heavy galvanized iron, held together by clamps on the flange. The FIG. 44. The Scott Fence Post Machine. posts are octagonal in shape and are cast in a vertical position, using wet concrete. It is practically the only post mould in which the post is cast in a vertical position. Methods of Reinforcement. Various methods of reinforcing fence posts are in use and recommended by the various manu- facturers. The advantages of some of these systems of reinforce- ment are more fanciful than real, and in some cases the reinforce- ment recommended would materially increase the cost of the post. For ordinary conditions, plain rods, wire, etc., may be used and entirely satisfactory results obtained. Scrap steel may frequently be used to advantage. The matter of reinforcement should depend entirely on what is most easily and economically available. For posts ii [161] Handbook for Cement and Concrete Users where a dry concrete is used, however, some sort of mechanical bond between the reinforcing and the concrete would be advisable. TABLE XIV. QUANTITY OF MATERIAL FOR FENCE POSTS.* All posts are 4 X 5 inches at top; all posts are 5 X 6 inches at bottom. One-half small single load f of sand required per barrel of cement;' one small single load f of screened gravel or stone required per barrel of cement. Propor- tion: i part "Atlas" Portland cement; 2 parts sand; 4 parts gravel or stone. Length of Posts, Feet. No. of Posts per Barrel (4 Bags) of Cement. Weight per Post, Pounds. 5 20 130 6 17 1 60 7 14 1 80 8 12 210 9 II 234 Methods of Fastening Fence to Posts. Various methods of fastening the fence to the post are in use at the pres- ent time, a few of which follow. Removable pins in the moulds form holes through the concrete posts, which holes receive long wire staples which clinch at the back of the post. These staples can be replaced at any time. Another method consists of a tie wire passed around the post and then twisted tightly around the longitudinal fence wire. This method would appear to be particularly satisfactory where the face of the post is corrugated. A variation of the above in which one contin- uous binding wire is used instead of a number of short pieces. The advantage of this and the above method is that the position of the ties does not have to be determined in advance, but may be readily shifted to suit any position of the fence wires. In another method, holes are made in the con- crete into which wires are inserted. These wires FIG. 45. Method of Fas- tening Fence to Post. * From " Concrete Construction Around the Home and on the Farm," published by the Atlas Portland Cement Co. f Small single load =15 cubic feet. [162] Concrete Pipes, Fence Posts, Etc. are then carried to the front of the post and wrapped tightly around the fence wire. In the "Monarch" Fasteners and Spring Steel Staples, the fastener is inserted in the post while same is being manufactured. FIG. 46. Method of Hanging Gate on Fence Post. The staple is inserted in the fastener by means of a pair of pliers made especially for the purpose. The " Taut wire " Fence fastener is moulded into the post when TABLE XV. QUANTITY OF MATERIAL FOR CORNER POSTS.* One-half small single load f of sand required per barrel of cement; one small single load f of screened gravel or stone required per barrel of cement. Proportions: i part "Atlas" Portland cement to 2 parts sand to 4 parts gravel. SIZE OF POSTS. No. of Posts per Barrel (4 Bags) Cement. Weight per Post, Pounds. Length, Feet. Top, Inches. Bottom, Inches. 6 12 12 l 900 7 12 12 2 2 1,050 8 12 12 2 1 I,2OO 9 12 12 2 i,35 9 10 10 3 940 9 6 6 8 337 7 24 24 1 4,200 * From " Concrete Construction Around the Home and on the Farm," published by the Atlas Portland Cement Co. t Small single load =15 cubic feet. Handbook for Cement and Concrete Users same is being manufactured. To hold the fence a common wire staple is driven into +he fastener. In all wire fences considerable tension must be put on the wires if a satisfactory fence is to result. To resist this tension occasional fence posts should be braced, and in no case should this bracing be omitted at the corner posts, and the post in many cases should be made heavier than the posts in the rest of the fence. SECTION IV PRINCIPLE OF DESIGN AND CON STRUCTION IN REINFORCED CONCRETE CHAPTER XVI ESSENTIAL FEATURES AND ADVANTAGES OF REIN- FORCED CONCRETE REINFORCED concrete is the term applied to that combination of concrete and steel wherein each element of the combination lends a helping hand to make up for the deficiency in strength of the other. The proverb that "In Union There is Strength," was never more exemplified than in the combination of two materials, different in so many respects yet acting together as a unit in resisting any in- fluences that tend to disrupt the structure built therefrom. Beginning with the building of flower pots by a French gardener 40 years ago, the business of reinforced concrete had a haphazard growth for over twenty years, owing to unfamiliarity with the nature of the materials, distrust on the part of consumers and antagonism of union labor. Through the establishment of safe, rational, and scientific methods of design, made possible by tests and studies carried on consistently by men like Melan, Hennebique, Ransome, Considere, Hyatt, Thatcher, Thompson, and others, confidence has given place to distrust and what only ten years ago was looked upon with suspicion is now hailed as a blessing. The fire at Balti- more and the earthquake and fire at San Francisco have removed the last lingering doubt, and constructors are now agreed that in point of fireproofness, and the ability to withstand severe shock and strains, reinforced concrete has no equal among structural materials. Handbook for Cement and Concrete Users Concrete itself is very weak in resisting tension, or pulling strains, and possesses but little elasticity, while steel, on the other hand, possesses both these qualities in a high degree. It is thus that the introduction of steel converts a practically inelastic body into one possessing a high degree of elasticity, and thus results in a material having the following inherent qualities: strength, which increases with time, lightness, rapidity of construction, and many other im- portant advantages. So much are the resisting properties increased that reinforced concrete is bound to supplant almost entirely brick and stone masonry in most all of the forms of construction into BEAM 6'S' ':'', $>> /' ; ^f$jjf$fr$, ' '"JQ"*'':^ : . 1 'V.TV&t5?V FIG. 47. Comparative Sizes of Plain and Reinforced Concrete Beam for Same Span and Loading. which the latter so largely enters, particularly in such structures as factories, walls, sewers, aqueducts, bridges, arches, chimneys, dams, tanks, foundations, etc. The economy of reinforced concrete arises also from the fact that unskilled labor may be employed in the work, and owing to its inherent strength a great saving in material and space is made possible over ordinary brick and stone construction. There are also some disadvantages attending its use, such as the necessity for wooden forms and the difficulties which attend their use, but these are more than offset by the accompanying benefits. Ease and rapidity of erection arise from the fact that walls can be quickly moulded and floors and roofs are moulded at the same time as the beams which support them. No dressing or dimension cutting is required and material is readily procured in all localities. The fireproofness of concrete is due to the fact that i* is a very poor heat conductor. It expands and contracts at the same rate as the reinforcing steel and there is no tendency of separation be- [166] Essential Features of Reinforced Concrete tween them. In fact, the bond or adhesion of concrete to steel is very strong and is an important element in the design of reinforced concrete work, as it is due to this very adhesive property that strains coming upon the concrete are partly taken up by the steel, for with- out such adhesion they could not act as a unit. The bond between the concrete and steel is due both to friction, molecular adhesion, and shrinkage of the concrete during the process of setting or hardening which causes it to take a hard, firm grip on the steel. The proportion of the strain taken by the concrete and by the steel is in direct ratio to the relative moduli of elasticity of the two materials, the ratio between them being from 10 to 18; that is, steel is 10 to 18 times as elastic as concrete, or will carry 10 to 1 8 times the load with the same amount of deformation. The whole secret of the successful design of reinforced concrete lies in distributing the steel in such positions and quantities as to relieve the concrete of any pull or tension as well as any excessive shearing or cutting stresses, and leave it to resist the crushing stresses which it is so well able to do. The rigidity of a reinforced concrete structure arises from the fact that each part of the structure is inseparably bound to every other part by a continuous network of beams, rods, and pillars, and the structure is one whole unit and not a collection of parts. The monolithic nature of these structures reduces the vibration caused by machinery and external shocks, and has proved the best type of construction in earthquake countries, and where unequal settle- ment would be dangerous. The durability and permanence of reinforced concrete arises from the very nature of the constituent materials. The concrete becomes stronger as times goes on, and the steel is protected from rusting by its concrete envelope. In fact, so great is this protection that painting of steel work is very objectionable while on the other hand a little initial rust does no harm. Abundant experience proves that' such rust is removed by some little understood chemical process and in good concrete the steel will always remain bright and clean. Special advantages appertaining to individual structures will be discussed in appropriate chapters. Materials for Reinforced Concrete. As reinforced concrete is generally used where strength and stiffness are required, it is essential [167] Handbook for Cement and Concrete Users that a rich mixture of Portland cement be employed and that sand be well graded and clean. In massive work, the coarse aggregate may run as high as 2 1/2 inches in size, as in foundations and large piers. In columns, girders, beams, and slabs, no stone or other aggregate should be used larger than what will pass a one-inch screen. In important beams and columns, especially when the reinforcing bars are closely spaced, the size should be made even smaller. Good trap rock or gravel should preferably be used. The best proportions for the materials which enter into the concrete depend upon the size and character of the construction. With proper limits on the size of the aggregate and with coarse sand containing a percentage of fine grains, a mixture of one part of Portland cement, two parts sand, and four parts of stone or gravel is always reliable. For reinforced concrete work, no mixture should be used that does not develop a strength of at least 2,000 Ibs. per sq. in., in compression at the age of 28 days. It is not the province of this book to go into the higher intricate details of the design of reinforced concrete as the subject is com- plicated at best, and the reader must be referred to the many ex- cellent treatises on design now to be had. It is well to state, how- ever, that the whole subject of design resolves itself into the study of a few elementary types of structure such as the beam or girder, the slab, the column, and the arch and all structures, however com- plicated, are either a modification or a combination of these element- ary types; in fact, the slab is even a modification of the beam, being a beam supported on all sides. The amount of bending or other forces produced by external loading is computed in the same way as in any other structure, the problem in reinforced concrete being to distribute the resultant stresses in such a manner between the concrete and steel as to have the concrete take the compressive stresses and the steel take the tensile stresses, and thus require the least amount of each material. How this is done is explained in the two chapters following. 168] CHAPTER XVII HOW TO DESIGN REINFORCED CONCRETE BEAMS, SLABS, AND COLUMNS * Nature of the Problem. Kinds of Stresses. Rules for Designing Beams. Rules for Designing Slabs. Tables for Designing. Solution of Examples. Summary of Procedure in Design. Design of Reinforced Concrete Columns. Examples and Solution. Nature of the Problem. ^Concrete and reinforced concrete structures when called upon to sustain loads or pressures, are thrown into a state of stress. When the loads are within the safe carrying capacity of the material, this condition of stress is shown by a slight increase or diminution in size. When the loads exceed this limit the material is no longer able to withstand the internal stress and the structure cracks, ruptures, or exhibits other signs of failure. In order to properly design a concrete structure, it is necessary to make an investigation to determine whether or not the material is so disposed as to be able to withstand the effects of the external loads without on the one hand being stressed beyond the point of safety, or on the other hand without waste of material. Such an investigation should comprise the following operations: (1) Determination of the amount and position of the external loads, including the weight of the structure itself. (2) Determination of the kind, amount, and position of the greatest internal stress produced by such loads. (3) Determination of the resisting power of the material to withstand such an internal stress. Kinds of Stress. According to the position of the external loads a body may be called upon to sustain one or more of the following kinds of stress : (i) Tension; (2) Compression; (3) Shear; (4) Bending. [169] Handbook for Cement and Concrete Users A body is subjected to tension or is under a tensile stress when acted upon by forces which tend to tear or pull it apart, as a stretched rope. A body is under compression or undergoes a compressive stress when the external forces tend to crush the material of which it is composed as a bridge abutment or pier. A body is subjected to shear or is under a shearing stress when acted upon by forces which tend to cut or shear it across, as the rivets in a boiler tube, when the overlapping edges of the tube tend to slide apart under the action of the internal pressure. A body is subjected to bending when used as a beam or girder to carry a load over an opening. This action is illustrated in the case of a plank. When a plank is laid flatwise and supported at the ends, a comparatively slight load at the centre will cause it to sag or bend. The effect of this bending is to compress the material in the upper surface of the plank and to stretch the material in the lower surface. Between these surfaces, there is a plane which is neither compressed nor lengthened. Such a plane is called the neutral surface. A plank laid flatwise makes a very weak beam, because of the excessive bending. When set up on edge, a plank is far stiffer and stronger. Nevertheless, such a joist tends to sag at the centre, so that the upper surface is in compression and the lower surface in tension, but the amount of sag or deflection is slight compared with what it would be were the plank turned on its broad side. Both plain and reinforced concrete is used in columns, piers, foundations, walls, etc., where it is subjected to a compressive stress. Reinforced concrete is also employed in beams, slabs, and other structures which are subjected to a bending stress, the steel being so disposed as to take care of the tension in the lower part of the beam or slab. Concrete is never employed in direct tension for carrying a suspended load, as steel is far lighter and more economical for the purpose. Action of Steel and Concrete in Combination. When steel rods are embedded in concrete, the adhesion between the steel and concrete is practically equal to the bond between the ingredients (cement, sand, and stone) of which the mixture is composed. In [170] Horizontal reinforcement only. Method of failure when tested to destruction. , L>ight load. Sudden failure caused by ends of reinforcement slipping and orizontal shear diagonal cracks in concrete. zfitKirasx*'* no diagonal cracks. A-ch action in beam with horizontal reinforcement and stirrups. Note the unbalanced horizontal stress. Stirrups slip along the horizontal reinforcement, which, therefore, cannot be developed. Beam with horizontal reinforcement only. Note arch action. Reinforcement furnishes no abutment for the inclined stresses, and will slip. Truss action in beam reinforced with Kahn Trussed Bars. Note the actio that of a complete Pratt truss No tendency to slip or slide. /A ^ Truss action in beam with horizontal reinforcement and stirrups. Note th unbalanced horizontal component of the inclined stress and the tendency of th Stirrups to slip along the horizontal reinforcement Arch action in beam reinforced with Kahn Trussed Bars. Note the perfect abutment for t:.e inclined stresses., _Perfectljr rigid and no possibility of slipping. Kahn reinforcement. Method of failure when tested to destruction. Max- imum load. Very gradual and ideal tailure. Steel stretching in center. FIG. 48. Sketches Showing Failure of Concrete Beams Reinforced in Different Ways, When Tested to Destruction. (Kahn.) Handbook for Cement and Concrete Users general for ordinary round or square bars, the bond strength may be taken -at from 200 to 300 Ibs. per sq. in. of surface, and for indented bars, having in addition a mechanical bond, at from 300 to 500 Ibs. per sq. in. These are breaking strains, and for the purpose of safe design, the bond strength is considered to be only 50 to 75 pounds per sq. in. of steel surface. ^7 ! f^^ j FIG. 49. Test of Girder under Load with and without Stirrups. (Hennebique.) Steel and concrete also expand at practically the same rate when heated, so that change of temperature does not cause any tendency for the steel to slip or separate from the concrete. Action of Steel and Concrete in Sustaining Stress. When a reinforced concrete member is subjected to stress, as for example, a column or post containing vertical rods, the stress will be divided How to Design Reinforced Concrete between the steel and concrete in direct proportion to the ability of each to carry the load. Steel, as already stated, is said to have a modulus of elasticity from 10 to 18 times as great as that of con- crete, which means that the steel rods in a column will carry from 10 to 1 8 times as much stress per sq. in. of cross-section as the surrounding concrete. The reason of this is that the loads on a column tend to shorten it, and from 10 to 18 times as much weight is required to shorten a steel column by a given amount as is needed to compress a concrete column having the same dimensions by an equal amount. Effect of Spiral Wrappings. Posts are frequently reinforced with spiral bands or hoops as well as with vertical rods. Such wrappings do not support any part of the load directly. Their object is to increase the bearing power of the concrete by preventing lateral expansion or bulging under the action of the compressive forces. Tests published by Considere in 1903 indicate that steel in the form of spiral reinforcements is 2.4 times as efficient as in the form of longitudinal rods, provided the spacing of the wire is not too great (1/4 to i/io of the diameter of the spiral). The chief effect of hooping is to increase the toughness or ductility of the concrete, which is desirable on account of the comparatively brittle nature of the column with longitudinal reinforcement only. In hooped columns only that portion of the concrete which is within the spirals can be regarded as bearing any part of the load. When so regarded, and when the wrapping is circular in form and the reinforcement sufficient to insure a lateral resistance of at least 65 pounds per square inch, the hooping can be considered as in- creasing the bearing capacity of the concrete by 50 per cent. DESIGN OF SIMPLE BEAMS AND SLABS CARRYING ''UNIFORMLY DISTRIBUTED LOADS" . V While the design- of a reinforced concrete structure requires both a working knowledge of the mechanics of materials, and practical experience with the constructor's side of the art, it is nevertheless feasible for anyone with a little practice to compute the dimensions of simple beams and slabs. Simple beams are beams which are supported at each end. Handbook for Cement and Concrete Users Continuous girders have one or more intermediate supports. In simple horizontal beams the steel is placed near the bottom at the centre of the span and part of the bars are bent up near the ends and anchored over the supports by bending. If the beam is con- tinuous the bent rods stop at the top, and in addition a system of horizontal rods is placed in the upper part of the beam and these extend over the supports to the quarter points. Stirrups are also employed in both simple and continuous girders, especially when the loads are heavy in proportion to the span. The proper placing of the steel and its anchorage at the supports are just as important as is the computation of loads and stresses. In this chapter simple practical formulas are given for determining the proper size of simple beams and the amount of steel required for their reinforcement. They can be used for continuous girders, only when proper provision is made for the placing of steel over the supports, at the top of the beams. The percentage of steel required for a reinforced concrete girder is generally a little less than one per cent. Perhaps the most economical percentage is seven-tenths of one per cent. This applies to the main steel bars in the bottom of the beam. The steel employed for stirrups and the horizontal rods at the top of continuous girders are not included in this percentage. The load carried by a reinforced concrete girder is generally considered to be uniformly distributed over its length. This applies to girders which support floor slabs, and to the general run of factory construction. It does not apply to a girder carrying a heavy machine at the centre of the span. Points to be Considered in the Design. The rational design of beams and slabs of reinforced concrete involves the study of the features enumerated below. For complete analysis of all these points reference must be had to special works on Reinforced Con- crete Design. We give below in this chapter the rules and formulas for such design reduced to the simplest forms for practical use, and in the succeeding chapter the origin and explanation of these formulas are discussed for those who wish to study the theory as well as the practical applications of the formulas. The following data * are usually considered in the design : * From " Concrete in Factory Construction," by the Atlas Portland Cement Co. [174] How to Design Reinforced Concrete " (i) The bending moment due to the live and dead loads, this involving the selection of the proper formula for the computation. " (2) Dimensions of beams which will prevent an excessive compression of the concrete in the top, and which will give the depth and width which is otherwise most economical. " (3) Number and size of rods to sustain tension in the bottom of the beam. " (4) Shear or diagonal tension in the concrete. " (5) Value of bent-up rods to resist shear or diagonal tension. "(6) Stirrups to supplement the bent-up rods in assisting to resist the shear or diagonal tension. " (7) Steel over the supports to take the tension due to negative bending moments. " (8) Concrete in compression at the bottom of the beam near the supports due to negative bending moment. " (9) Horizontal shear under flange of slab. " (10) Shear on vertical planes between beams and flanges. "(n) Distance apart of rods to resist splitting. " (12) Length of rods to prevent slipping. " (13) End connections at wall." Rules for Designing Beams. In a horizontal reinforced concrete beam carrying a uniformly distributed load, the proper dimensions may be obtained from the following formula, which is based on the straight -line theory of stress as explained in the next chapter: bd2= ysi(w + w>) 74 and the sectional area of steel required in the lower portion of the beam by the formula : A = .007 b d (2) Where b denotes the breadth of the beam in inches, d denotes the depth in inches from the top or compressive face of the beam to the plane of the steel. / = the length of span in inches. W = the external load on the beam in pounds and includes the weight of the floor slab which is supported by the beam. W = the estimated weight of the beam itself in pounds. A = the sectional area of the steel in square inches. p = the percentage of steel. h75] Handbook for Cement and Concrete Users The above formulas are based on seven-tenths of one per cent of steel being employed for reinforcement in the bottom flange. If other proportions of steel are employed, the same formulas can be used by changing the denominator from 74 to the appropriate value as shown in the following table. This table is based on' a maximum compressive stress in the concrete of 500 pounds per sq. in., a ratio of 12 between the modulus of elasticity of concrete and that of steel, and a tensile stress in the steel ranging from 15,000 to 8,000 Ibs. per sq. in., according as the percentage of steel is low or high. TABLE XVI. DENOMINATORS FOR USE IN FORMULA I. FOR DIFFERENT PERCENTAGES OF STEEL.* Percentage of Steel, p .005 .606 .007 .008 .009 .010 -Oil .012 .013 .014 .015 Denominator for formula (i) . 66 70 74 78 81 84 86 8 9 9 1 93 95 Thus if one per cent of steel is desired, the formulas become : / (W + W) bd 2 = and 84 .010 b d (3) (4) Example. Compute the dimensions of a horizontal reinforced concrete beam, which can be used to support a uniformly distributed load of 15,000 pounds, including the weight of the floor slab, over a span of 14 feet. Solution. An economical value for p is .007; W = 15,000 Ibs. Assume W 5,000 Ibs., I = 14 X 12 = 168 inches. Hence sub- stituting in formula (i) we have: 77 2 _ y% X 1 68 (15000+ 5000) 420000 74 74 Assume any practicable width for b, as b = 13 inches, then, 5676 = 436.6 * The derivation of Table XVI. is given in Chap. XVIII. [176] How to Design Reinforced Concrete and solving for d, which may be facilitated by the use of a table of squares, we have: d = 21 inches A = .007 X 13 X 21 = 1.911 sq. ins. If the 1.911 sq. ins. is divided among 4 rods, the area of each will be 1.911 *- 4 = 0.478 sq. ins. If square rods are employed, the required dimensions will be 4-11/16 inch rods, since 11/16 X 11/16 = 0.478 (nearly) d = 21 inches is the effective depth or depth to the plane of the steel. At least 2 inches of concrete should be placed below the steel for protection and bond. Hence the total depth of .the beam must be 21 +2 =23 inches. If a heavy rock concrete weighing 144 pounds per cu. ft., in- cluding the steel, is employed, the weight of the beam 23 ins. deep, 13 ins. wide, and 14 feet long, will be ^3 x ^xH x !44 x = 4>l86 pounds . 12 12 I I This is 814 pounds less than the assumed weight, and if the dimen- sions are again computed, using the actual weight of 4,186 pounds in place of the assumed weight of 5,000 pounds, it will be found to make a difference of half an inch in the required depth of the beam. An inspection of the above computation for weight reveals a quick method for obtaining the weight of heavy rock concrete; viz., multiply together the total depth in inches by the breadth in inches by the length of the beam in feet. The above method of designing a beam will probably impress the novice as faulty in that too much is assumed in advance. A very little practice will, however, enable him to estimate the probable weight very much more closely than was done in the above example, where the beam was purposely overestimated by 20 per cent in order to show that such an overestimate has very little effect on the design, and even if the first estimate should be extremely wide of the mark, two trials at the most should be all that would be required to determine the proper dimensions. In assuming the percentage of lower flange steel in advance, the designer has two things to consider; first the most economical 12 [177] Handbook for Cement and Concrete Users percentage; and second, whether he wishes to make the com- pression or tension half of his beam the stronger. Probably .007 is the most economical percentage, as less than this amount of steel unduly increases the volume of concrete, while more than .007 affects unfavorably the cost of the steel. Below .01 the steel will probably be weaker than the concrete at a breaking load, while above .01 the steel is likely to prove the stronger. Near this point either the steel or the concrete may be the first to fail if the beam is tested to destruction, depending chiefly on the materials and work- manship employed in mixing and placing the concrete. The designer should be sufficiently familiar with the quality of the work so that he can fix the percentage of steel at such a rate that the steel will begin to stretch before the concrete commences to crumple, thus producing deflection and giving warning in advance, in case the beam should be loaded beyond its capacity. In addition to this percentage, upper flange steel over the supports and stirrups should in general be provided. In assuming the breadth and computing the effective depth, after the design has reached the stage where the product b d 2 = a known number, several trials may be necessary to give the best proportions for the beam. For economy a beam is made as narrow as possible, but there are practical limits to decreasing the breadth which must not be encroached upon. Thus a beam should not be narrower than 1/24 of the span. It must be wide enough to provide at least i 1/2 diameters and prefer- ably 2 between the reinforcing bars and between the bars and sides of the beam. Moreover, the breadth should not be less than half of the depth, excepting for very large beams. Probably the best width is between 1/2 and 3/4 of the effective depth, d. How to Design Reinforced Concrete Slabs. For the purpose of design, a reinforced concrete slab placed as a continuous sheet over several girders and carrying a uniformly distributed load, may be treated as though the slab was divided into nar- row strips, each having a width equal to the spacing of the reinforcing bars, and a length equal to the distance between the supporting girders. The slab can then be designed by the following formulas: How to Design Reinforced Concrete (W + W>) ' 74 A = .007 b d (6) Formulas (5) and (6) are identical in form with those employed for beams, and differ only in the coefficient of /, i/io being used instead of 1/8. The nomenclature is also the same, and if a per- centage of steel different from .007, is desired, the corresponding denominator for formula (5) can be obtained from Table XVI in the same way as for beams. Such a slab requires top reinforcement extending over the girders for at least one-fourth of the span, on both sides of the girder; or if expanded metal or other fabric is employed the fabric must be placed so that in the centre of the span it will sag to near the bottom of the slab, while over the supports it will be near the top. The sectional area of lower flange steel may be obtained from formula (6), when seven-tenths per cent is used, or the coefficient .007 may be varied to suit the requirements. Example. Design a reinforced concrete slab supported by beams spaced 8 feet apart, which may be used to sustain a uniform load of 125 pounds per square foot, exclusive of its own weight. Solution. Assume a steel percentage of .007, a spacing of the reinforcing bars of 6 inches; and the weight of a strip 6 inches wide, and 8 feet long at 240 pounds. By spacing the bars 6 inches apart, the breadth, 6, becomes 6 inches, and the external load, W, at 125 pounds per sq. ft., will be: W = 8 ft. X 6/i2 ft. X 125 Ibs. per sq. ft. = 500 pounds while / = 8 X 12 = 96 inches. Substituting in formula (5) we have : i/ioX 96 (500 + 240) o a = -+r 74 d 2 = 1 6 sq. ins. d = 4 ins. depth to the plane of the steel. If i inch of concrete is placed below the steel, the required thickness of the slab will be 4 + i = 5 inches. [179] Handbook for Cement and Concrete Users From (6) the area of steel will be A = .007 X 4 X 6 = .168 sq. ins. This may be obtained from 1-1/2 inch round rod. When fabric is employed instead of steel rods, a strip i foot wide is taken as the basis of the design, or b = 12 inches, while formula (6) will give the sectional area of fabric required for the i-foot strip, for seven-tenths per cent of steel. In general, a reinforced concrete slab should not be less than 3 inches thick and should have at least 3/4 inch of concrete below the steel. In an oblong slab the steel is placed crosswise from girder to girder. In a square slab supported on four girders, equidistant from each other, the rods are placed both ways. When reinforced in this manner, the same amount of steel is usedas for the oblong slab, but there is a saving in concrete, as the concrete for a square slab need only be designed for half the load. In an oblong slab, a few rods should also be placed longitudinally to prevent temperature cracks and to serve as binders for the main tension bars which run crosswise between the supporting girders. Tables for Use in Designing Beams and Slabs. Such tables may be divided into two classes: (a) those which give the required dimensions without computation, and (b) those which are used to facilitate computation by saving arithmetical labor. Tables XVII, XVIII, and XIX are of the latter and Table XX of the former class. Table XVII is a table of squares for facilitating the computation of beam depths. Table XVIII gives the weight per lineal foot of re- inforced concrete beams at 144 pounds per cubic foot, and is used for estimating the weight of beams. Table XVIII also shows com- parative costs of beams at $10.00 per cu. yd. This is for the purpose of comparing the cost of beams of different proportions of depth to breadth and of different percentages of steel, in order to employ those which are most economical. Table XIX gives the sectional areas of round and square bars, and their weights and cost at the rate of 2 cents per pound. This is also convenient for making a comparison of costs. The costs given in Tables XVIII and XIX do not represent the actual costs, which may be 50 per cent more or less for any given structure. They are relative costs for gauging the [180] How to Design Reinforced Concrete relative economy of different beams having equal strength or capacity. Table XX, which is reproduced with slight modifications, by courtesy of the Atlas Portland Cement Co., from their book on the utilization of "Concrete in Factory Construction/' gives the proper dimensions for beams and slabs that will carry uniformly distributed floor or roof loads of 125, 50, and 30 pounds respectively, per square foot. These beams, if checked over, by the straight line formulas (10) and (u), of Chapter XVIII, will be found to average about seven-tenths per cent of steel, to have a fibre stress in the concrete of about 500 pounds per square inch, and in the steel of between 12,000 and 15,000 pounds per square inch. TABLE XVII. BEAM DEPTHS AND THEIR SQUARES. No. Square. No. Square. No. Square. No. Square. No. Square. No. Square. 2.00 4.00 5.00 25 -00 8.00 64.00 12 .00 144.00 18.00 324.00 24.00 576.00 2.25 5.06 5- 2 5 27.56 8.25 68.06 12 .50 156-25 18.50 342.25 24.50 600.25 2.50 6.25 5-50 30-25 8.50 72.25 13 .OO 169.00 19.00 361 .00 25 .00 625.00 2 -75 7-5 6 5-75 33-0 6 8-75 76.56 I3-50 182 .25! 19.50 380.25 2 5 -5 650.25 3.00 9.00 6.00 36.00 9.00 81.00 14.00 196.00 20.00 400.00 26.00 676.00 3-25 10.56 6.25 39 -.06; 9-25 85-56 14.50 210.25 20.50 420.25 26.50 702.25 3-50 12.25 6.50 42.25 9-50 90.25 15.00 225 .00 21 .OO 441 .00 27 .00 729.00 3-75 14.06 6-75 45-5 6 , 9-75 95.06 I5-50 240.25 21 .50 462.25 27.50 756.25 4.00 16.00 7.00 49-0 10. OO 100.00 16.00 256.00 22 .OO 484.00 28.00 784.00 4-25 18.06 7-25 52-56 10.50 110.25 16.50 272.25 22 .50 506.25 28.50 812.25 4-5 20.25! 7-50 56-25 II .00 121 .OO 17 .00 289 .00 23.00 529.00 29.00 841.00 4-75 22 .56 7-75 60.06 II .50 132-25 I7-50 306-25 23-50 552-25 29.50 870.25 Example, Involving Use of Tables. Compute the cost of beams spaced 8 feet apart, and having a span of 12 feet which will support a 6-inch slab of concrete in addition to a floor load of 140 pounds per square foot. Solution. Surface area, 12 X 8 = 96 sq. ft. Load 96 X 140 = I3,44olbs. Weight of slab 12 X 8 X -- X 144 Ibs. per cu. ft. = 6,912 Ibs. Estimated weight of beam, Table XVIII, 12 x 24 ins. (288 X 12) = 3,456 Ibs. 13,440 + 6,912 + 3,45 6 = 23,808 Ibs. [181] Handbook for Cement and Concrete Users TABLE XVIII. Weight of Heavy Reinforced Concrete Beams in Pounds per Lineal Foot, also Cost of the Concrete in Dollars per Lineal Foot at the Rate of $10. oo per Cubic Yard. BREADTH IN INCHES. 4 5 6 7 8 9 10 12 14 16 "[ ,j 12 15 18 21 24 27 30 36 42 48 54 Weight 3 i .031 039 .046 054 .062 .070 .077 093 .108 .124 139 Cost j 16 20 24 28 32 36 40 48 56 64 72 Weight 4 1 .041 .052 .062 .072 083 093 .103 .124 .144 .165 .185 Cost - j 20 2 5 3 35 40 45 5 60 7 80 90 Weight 5 1 .052 .065 .077 .090 .103 .116 .129 155 .180 .206 .232 Cost 6 24 30 36 42 48 54 60 72 84 96 108 Weight I .062 .077 093 .108 .124 J 39 155 .185 .216 247 .278 Cost 7^ 28 35 42 49 56 63 70 84 98 112 126 Weight M .072 .090 -.108 .126 .144 .162 .180 .216 .252 .288 324 Cost gj 32 40 48 56 64 72 80 9 6 112 128 144 Weight 1 .083 .103 .124 .144 165 185 .206 .247 .288 33 37 1 Cost OJ 36 45 54 63 72 81 90 108 126 144 162 Weight 9 ! 093 .116 *39 .162 -185 .208 .232 .278 3 2 4 37 1 .417 Cost g H - \ 40 5 60 7 80 90 IOO 120 140 1 60 1 80 Weight fe I .103 .129 J 55 .180 .206 .232 257 309 .360 .412 463 Cost fc 12 J 60 72 84 96 1 08 120 144 1 68 192 216 Weight H 1 155 .185 .216 .247 .278 39 371 433 494 556 Cost _. J 84 98 112 126 140 1 68 196 224 252 Weight 5 U 1 .216 .252 .288 324 .360 432 504 .576 .648 Cost j < bi i6J 112 128 144 1 60 192 224 256 288 Weight 1 1 .288 330 37 1 .412 494 576 6 59 .741 Cost **\ 144 162 1 80 216 252 288 324 Weight 1 371 .417 463 .556 .648 .741 834 Cost 20 Weight per lineal foot = 1 80 200 240 280 320 360 Weight 1 H Breadth in inches multi- plied by total depth in inches. 463 198 509 515 220 .566 .617 264 .679 .720 308 793 .823 35 2 .906 .926 39 6 i .019 Cost Weight Cost 4 4 240 288 336 384 43 2 Weight 4 1 ,6J Cost in dollars at $10.00 per cu. yd. = weight per lineal foot .617 741 312 .864 3 6 4 .988 416 i .in 468 Cost Weight ( multiplied by .002572. 803; .936 i .070 i .204 Cost 28 J 336 392 448 504 Weight 1 .865 i .009 I - I 53 1.297 Cost 30 -! 360 420 480 540 Weight I .926 1.081 1-235 1.389 Cost 182 How to Design Reinforced Concrete TABLE XIX. PROPERTIES OF STEEL BARS. ROUND BARS. SQUARE BARS. Diameter in Inches. Sectional Area in Square Inches. Weight per Lineal Foot in Pounds. Cost in Dollars per Lineal Foot at 2 Cents per Pound. Circum- ference in Inches. Sectional Area in Square Inches. Weight per Lineal Foot in Pounds. Cost in Dollars per Lineal Foot at 2 Cents. Peri- meter in Inches. 1/8 . .0123 .042 .001 3927 .0156 053 .001 0.50 3/1 6 .0276 .094 .002 .5890 0352 .120 .002 0-75 i/4 .0491 .167 .003 7854 .0625 .213 .004 I .00 5/i 6 .0767 .261 .005 .9817 0977 332 .007 1-25 3/8 . 1104 376 .008 i . 1781 . 1406 .478 .010 1.50 7/i 6 1503 .511 .010 1-3744 .1914 .651 .013 i./S i/a .1963 .668 013 i.57o8 .2500 .850 .017 2 .00 0/16 .2485 .845 .017 i .7671 .3164 .076 .022 2.25 5/8 .3068 i .043 .021 1-9635 -39o6 .328 .027 2.50 i '/i 6 3712 i . 262 .025 2 . 1598 .4727 .607 .032 2-75 3/4 .4418 i .502 .030 2.3562 5625 913 .038 3 .00 13/16 5185 i .763 035 2.5525 .6602 245 045 3 -25 7/8 6013 2.044 .041 2.7489 .7656 .603 .052 3 -50 15/16 .6903 2-347 047 2.9452 .8789 .989 . 060 3 -75 7854 2 .670 053 3 .1416 . oooo 3 -400 .068 4.00 1 1/16 .8866 3-014 .060 3 -3379 . 1289 3-838 .077 4-25 1/8 .9940 3-379 .068 3-5343 .2656 4.303 .086 4-50 3/1 6 1075 3.766 075 3.7306 .4102 4-795 .096 4-75 i/4 .2272 4-173 .083 3.9270 .5625 5-312 .106 5 -oo 5/i 6 3530 4.600 .092 4-1233 .7227 5.857 .117 5.25 3/8 .4849 5-049 . 101 4.3197 .8906 6.428 .128 5-50 7/1 6 .6230 5.518 . no 4.5160 .0664 7 .026 .141 5-75 1/2 .7671 6.008 . 120 4.7124 .2500 7.650 153 6.00 From formula (i) with steel ratio .007. L j? b d 2 = X 144 in. span X 23808 = 5,791 cu. ins. lib = 12 ins., d 2 = From Table XVII, d = 22 ins. With 2 inches of concrete below the steel, the dimensions will be 12 x 24 ins. From Table XVIII, the concrete will cost, at the rate of $10.00 per cu. yd. .741 X 12 = $8.89 From formula (2) the steel area will be, .22 X 12 X .007 = 1.85 sq. ins. Handbook for Cement and Concrete Users From Table XIX, this is equal to the area of 5-5/8 inch square bars, and from the same table the cost at the rate of 2 cents per pound will be 5 X 12 X .027 = $1.62 add 60 per cent for the cost of upper flange bars, stirrups, bent ends, and fabricating, and the total cost will be -Cost of steel 1.6 X $1.62 = $2.59 Cost of concrete 8 . 89 Total cost $11 .48 The corresponding costs with different steel ratios will be found to be as follows : .0055 lower flange steel dimensions 12 X 25 ins., steel 5-9/16 in. sq. bars, cost $11.37 .007 " " " " 12 X 24 " " 5-5/8 " " " " 11.48 .010 " " 12 X 23 " " 5-3/4 " " " " 12.17 .012 " " " " 12 X 22 " " 5-13/16" " " " 12.47 These are relative costs based on concrete at $10.00 per cu. yd., and steel at 2 cents per pound. With concrete at $15.00 per cu. yd., the beam with .007 steel would be the cheapest in cost. Design of Stirrups. In a beam supporting a uniformly dis- tributed load, stirrups are required when the total load, including the weight of the beam in pounds, divided by the sectional area in square inches, exceeds 60, or when W + W r-^ exceeds 60 (7) u d Thus in the previous example, W + W = 23808, 6 = 12, and d = 22, and since 23808 = 00.2 12 X 22 stirrups should be employed. Stirrups are, however, desirable in all beams, as they add considerably to their strength and ability to withstand shocks. Stirrups may be either vertical or inclined. They are most efficient when inclined at an angle of 45 degrees toward the end of the girder. Ransome's Rule. Mr. E. L. Ransome's rule is to employ four stirrups at each end of the beam, the first at 1/4 of the depth from the end, the second at 1/2 the depth from the first, while the spacing [184] How to Design Reinforced Concrete of the third is 3/4 of the depth and of the fourth, a distance equal to the depth. These stirrups are in general composed of 1/4 to 3/8 inch rods. Stirrups should go through the beam into the floor slab, where they are bent to run parallel with the slab for about six inches. Stirrups should always be fastened to or looped around the bottom rods. In place of stirrups a sheet of expanded metal or other wire fabric may be placed in the web of the beam. An improvement over the use of loose rods and stirrups consists in the unit system of reinforcement, where all of the members are assembled into one frame. These are illustrated in another chapter, and include the Kahn, Cummings, Unit, and Girder frames. Design of Bond. The steel bars may be considered safe against slipping when not called upon to sustain more than 50 pounds bond stress per square inch of surface area. In a beam carrying a symmetrical or uniform load, this con- dition may be expressed by the following formula: 4 (W + W) -j - must not exceed 50 .... (8) where W denotes the load on the beam in pounds. W denotes the weight of the beam itself. n denotes the sum of the perimeters of the steel bars in inches. d denotes the depth to the plane of the steel in inches. In the previous example, W 4- W f = 23,808, d = 22 ins., and since 5 5/8 inch square bars are used, 4 X 5 11 = 5 X ~~8 = I2 ' 5 mches and 4 X 23808 - =49.5 Ibs. per sq. inch, 7 X 12.5 X 22 which is barely within the required limit of 50. With a greater bond stress, the number of bars would need to be increased. Summary of Method of Procedure in Design of Beams and Slabs. The following is a brief summary of the different steps involved in the design of a beam or slab carrying a uniformly dis- tributed load, as previously described in this chapter. [185] Handbook for Cement and Concrete Users (1) Compute the total load, W, on the beam. (2) Estimate the weight, W, of the beam itself. (3) Compute the dimensions of the beam from the formula : . .... . . . (4) Compute the sectional area, A, of the steel from the formula : A == p b d ....... (10) b denotes the breadth of the beam in inches. d denotes the effective depth in inches to the plane of the steel. / denotes the length of the span in inches. p denotes the percentage of lower flange steel. D denotes the denominator of formula (9) and is obtained from Table XVI for the desired value of p; thus for p = .007, D = 74; for p = .008, D = 78, etc. (5) Employ from 7/10 to i per cent of steel in the lower or tension part of the beam. (6) If girders are built in one monolithic length over three or more supports, they are called continuous girders, and should have at least four-tenths per cent of steel in the upper part of the beam, extending to the quarter-points. In continuous slabs the steel should be in the lower part of the slab at the centre and in the upper part at the supports. (7) In large beams, employ from three to four stirrups or pair of stirrups at each end, composed of 1/4 to 3/8 inch rods, and spaced according to Ransome's rule, as described in this chapter. In small beams use steel wire or metal fabric. Anchor all bars as previously explained, and securely wire all loose bars in such a way that they will not be displaced in concreting, and so that the concrete will cover all bars by from i 1/2 to 2 diameters in large beams and by at least 3/4 of an inch in thin slabs. Always employ W + W stirrups when - - exceeds 60. b d (8) Test the bond between the steel and concrete by the formula : 4 (W + W) 7 - must not exceed so. . . . (n) 7 nd , . where n denotes the sum of the perimeters of the steel bars in inches. [186] How to Design Reinforced Concrete Observe the following general rules. (9) The best-shaped beam is one in which the breadth is from one-half to three-fourths of the effective depth. (10) The breadth should not be less than 1/24 of the span, (n) Stirrups must be amply provided especially when the depth is greater than i/io of the span. (12) The breadth must be sufficient for the spacing of the bars. A minimum clear spacing of at least 11/2 diameters should be provided, with an equal distance between the outside rod and the surface of the beam. (13) Sufficient rods should be employed; so that the diameter of each will not exceed i / 200 of the span. (14) The length of rod on each side of the centre of the beam should be at least 80 diameters for plain and 50 diameters for de- formed bars. (15) Compare the computed weight with the estimated weight of the beam, and revise the design if the difference exceeds 10 per cent. How to Design a Reinforced Concrete Column. This consists in determining proper dimensions for the post or column, and the steel required for its reinforcement. The following order of com- putations should be observed. (1) Compute the load, P, to be supported by the column. (2) Estimate the weight, W, of the column itself. (3) Determine the load per sq. in. of sectional area which the concrete can be designed to carry, also the ratio between the moduli of concrete and steel. (4) Choose the percentage of vertical reinforcement. In general this should be between i and 2% per cent. (5) If spiral wrappings are to be used, choose the sectional area, and spacing of the bands. (6) Compute the sectional area required for the column by the following formula, and check its weight. P + W A e = C + pC(r ^ ' * A s = pA e . . . . . "... . . (13) [187] Handbook for Cement and Concrete Users A c = the sectional area of the column. A s = the sectional area of the vertical reinforcement. A e = the effective area of the column. A h = the sectional area of the hooping. P = the load to be supported. W = the estimated weight of the column itself. C = the safe compressive stress for concrete. p = the percentage of vertical steel reinforcement. r = the ratio between the modulus of elasticity of steel and that of concrete in compression. Where bands are used, the section of the column contained within the spirals may be designed to carry 50 per cent more stress than the column without bands, providing: (a) The wrapping is circular in form. (b) A thickness of two inches of concrete is placed outside of the bands, for protection, but not considered as taking any part of the load. (c) The bands are of sufficient size so that their sectional area, A h , divided by the pitch, s, or distance between spirals is not less than the diameter of the spiral, D, divided by 500, or - must not be less than . . . . (14) 5 500 The following practical rules should also be observed: (7) The length of the column must not exceed more than 12 times its least lateral dimension. (8) The vertical steel must be as straight as possible, and rest upon bed plates at the bottom. When the bars are spliced, the bars must not be lapped and wired, but the end of the upper bar must rest on the top of the lower one, and be held in place by sleeves made of pipe. The sleeves should be 24 diameters long and the joints should also be stiffened by a half-inch bar about four times as long as the sleeve, which is set alongside of but not in contact with the reinforcement. (9) In all large columns the steel should be protected by at least two inches of concrete, and in small columns by not less than one inch. (10) The percentage of steel which can carry the entire load when stiffened by the concrete can be found by dividing the load [188] Handbook for Cement and Concrete Users to be supported in pounds by 16,000. In general this will run from 4 to 6 per cent. (n) The load on the column must be symmetrically placed, so that the centre of the load coincides with the centre of the column. If the load bears more on one side of the column than it does on the other, it is called an eccentric load; and it requires a larger column to carry an eccentric than it does to carry a symmetrical load. An eccentrically loaded column cannot be designed by the methods explained in this chapter. Example. Design a square reinforced concrete post, 10 feet long, which will support a load of 20 tons without spiral wrappings. Solution. (i) P = 20 X 2,000 = 40,000 Ibs. (2) Estimate W at 1,500 Ibs. (3) A safe load for concrete in compression is 350 Ibs. per sq. in., and a safe value of the ratio, r, is 12. (4) Employ 1.7 per cent of vertical reinforcement. . N 40,000 + 1500 41500 (5) A= r = tL^__ = I00 sq . ms . 350 + .017 X 350 (12 - i) 4I5-45 or 10 x 10 ins. This column will weigh about 10/12 X 10/12 X 10 X 144 = 1,000 Ibs., which is less than the assumed weight and therefore safe. The area of the steel will be : .017 X 10 X 10 = 1.70 sq. ins. If 4 square bars are used the area of each will be : 1.70 -4- 4 = .43 sq. ins. or 4-11/16 in. square bars are required. (6) The least lateral dimension is 10 inches". 10 inches X 12 = 10 feet. As the length of the post is 10 feet or equal to the above value, the design is permissible. Summarying the results of the design, we have, External load, 20 tons. Weight of column, 1,000 Ibs. Dimensions, 10 ins. x 10 ins. X 10 feet. Vertical reinforcement, 4-11/16 inch square bars. Example 2. Design a circular reinforced concrete column with spiral wrappings 12 feet long which will support a load of 59 tons. How to Design Reinforced Concrete Solution. (i) P = 59 x 2,000 = 118,000 Ibs. (2) Estimate W r at 4,000 Ibs. (3) Take C at 350 and r at 12. (4) Take p at 1.5 per cent. (5) For hooping, use 5/i6-inch round steel or oval bars having the same sectional area of .076 sq. ins. and let the spirals be spaced apart or have a pitch of 2 inches. ,,. 118000 + 4000 122000 1.5 [(35Q or diameter of spirals = A 2O = 16 ins. M 7854 With 2 inches of concrete outside of the hooping, the diameter of the post will be 4 + 16 = 20 inches, and will weigh .7854 X 20/12 X 20/12 X 12 X 144 = 3>77o Ibs., which is less than the estimated weight and is therefore safe. 1.5. per cent of steel is 3 sq. ins., which is equivalent to 6 3/4 inch square rods. From (5) A h = .076 and s = 2 ins., also from (6), D = 16 ins., and since must not be less than , '-* must not be less than s 500 2 16 - ; or since .038 is greater than .032 the hooping is in conformity with the condition. (7) The least lateral dimension is 20 inches. 20 inches X 12 = 20 feet. As this is greater than the length of the post, the design easily satisfies the condition as to the ratio of length to least lateral dimension. Summarizing the results of the design, we have for the circular column External load, 59 tons. Weight of column, 3,770 pounds. Diameter of column, 20 inches. Diameter within hooping, 16 inches. Length of column, 12 feet. Vertical reinforcement, 6-3/4 inch square rods. Hooping, 5/16 inch round or oval bars with spirals spaced 2 inches apart. How to Design Reinforced Concrete 1 REINFORCEMENT OF SLABS N| 'ill - \OOt-* \O\Ot^ \O vO r^- vard, one rod in three, or two rods in four from $ points in beam to top of beam and over supports, shaped with bent ends, s placed at right angles to supporting beams. Cross reinforcement of slightly smaller rods or same rods farther apart labs parallel to beams, ded metal mesh may be substituted for rods in the slabs, provided the area of section of metal is kept the same as the rods, .d not be used for beams. 6. Cinder concrete may be used for roof slabs if thickness is increased one inch. s, test two of the slabs and one beam by loading two panels with sand to depth of: 18 inches deep for heavy floor loading; ght floor loading; 5 inches deep for roof loading, ctory Construction," published by the Atlas Portland Cement Co. * Place first stirrup in every case 6 inches from support. Diameter of Rods Inches \O vO vO vO H |ao Hf M co|oo HM M cdoo Hf c^|oo HIN V) \n \r> \n THICKNESS OF SLABS till QW^c NI HI M e-sH* MN M H* <* M HI nn* H Total Thickness Inches. wl-* nH< Hi wr* r<3 fO u-> ro ro LO ro fO O fO ro u-J REINFORCEMENT OF BEAMS Spacing* of Stirrups VO O vb 000000 00 00 00 000000 Diameter of Stirrup Rods Inches ^-" M |oo i-i M fdoo (oo * n|oo |oo two * 1O IO LO IO 111 JP*1 ^ H MMW Wro CjfO^- NfO^ Diameter of Rods Inches O vO VO \0 M M HNMidW HNMiolao Mii^ooX^ HIM MN \ > ^ > s , ? 111 il ii?j DIMENSIONS OF BEAMS. fiii &m%* Hf* Hn HN HN Hc Hf> HM MMM MMC^ MC^W MCSW vC W Q; O rovot^. ^t~-O vOOW OOrfTf- II ?<= vOt^-00 t>.C\O\ OOw OMCO i. Bend, diagonally up^ 2. Stirrups are made U- 3. Slab reinforcement i is also placed in s 4. Wire fabric or expan 5. Cinder concrete shou 7. After setting 30 day 8 inches deep for li i From " Concrete in Fa S^S ill! %*& Q * n-\ooo rj-vooo ^-^ooo ^tvooo o 8 fill >-3 "o cd o N" 4 * M H M 191] Handbook for Cement and Concrete Users I C/) i pq u & $> Q C/3 w Q tf g w < H 1 o U X X W h-} w < H ^6 is PU bow M CtJ 0) h "o - c ! |l XO^XO to <- .0 *. *$ ,0^-. REINFORCE SLAI Diameter of Rods Inches vO \O O vO H-* ^ e*o H-* ^ ! ^N ^ cc,=o H^ ^ "He IO V> ' O -> 1 ' h 4J g F BEAMS Diameter of Stirrup Rods Inches in beam to nforcement H M Ig^w 1 i : O 1^ s o W s ft e^|ao \ HM |ao M M|QO "-tN >nioo M M icloo \ i 1 ' G bfi P c l 1|1 f^^^ ^^^ ^^^ ^^^ \ 1 ; l^| o 2 ua 5^-8 ^1"' ft^ O)^ _;-* r-M HtN r-'- - 'I - - 1 - : 1 r-'l i-H|M HM .S c c S Cd PQ Q w - b rS o O^ro 0,^0 rot-00 OOvM l|f| aJ 1^2 H^i:, s Q 11 xovO ^ ^.00 t^oo OS ^00 Ipf hi? iiii Isl? "<;^ ^Ilj t 5 "o -g&'S' 3 3 | ^^^, v-r^ ^^-^ nSj' 9 ' ft 1 5 o 00 O > VO IO t~ \O IO !>. \O O t* hree, or two rods in four from i points in beam to top of beam and over supports, nds. angles to supporting beams. Cross reinforcement of slightly smaller rods or same rods farther apart ims. ay be substituted for rods in the slabs, provided the area of section of metal is kept the same as the rods earns. 6. Cinder concrete may be used for roof slabs if thickness is increased one inch, labs and one beam by loading two panels with sand to depth of : 18 inches deep for heavy floor loading; inches deep for roof loading. j|l E o y vo \0 vO MH^icoiao M H-* c-fco M H^I M)UO w H* c*o fO f5 fO CO THICKNESS OF SLABS tiii Qpq^>S HiNiecH" N< ** NI nj* n|* nH* whuwNwN Total Thickness Inches wHiH^t**f4*nHii-Hi**H^ M fj fi W CO r*j N CO fO cjfOco REINFORCEMENT OP BEAMS .! I I s ! CO W Diameter of Stirrup Rods Inches Number of Stirrups at Each End Diameter of Rods Inches vO vO \O NO vO vo IH njocHHN MHNM HfMt MHao\ t^ t^* Q\ Q\ Q\ M 111 5 & Z^& rororo T)fOfO O fO *O fOfO-t>.OO t^-OOO\ I4&* o -3 Tj-000 ^vOOO rl-\OOO rfvOOO i J 9$ 6 Jl 4 M 11 M M M m 9 , 6 - 4i6 = 9,29 Ibs. per sq. in. These are below the limits of 500 for concrete and 16,000 for steel and are, therefore, safe values. Design of a Rectangular Reinforced Concrete Beam. The dimensions of a hor- izontal reinforced concrete beam of rectangular section may be accurately determined by observing the following order of computations: (1) Assume safe values for C, S, and r. Values permitted under the provisions of the New York building-code, are as follows: C = 500, S = 16,000, and r 12. (2) Prepare a table giving values of 5* and the product S p j for different percent- ages of steel, p. Table XVI A of this chapter gives these values for percentages of steel ranging from .005 to .02 of the area of the section, based on C = 500 and r = 12. (3) Determine the amount and position of the loads supported by the beam, in- cluding the estimated weight of the beam itself. (4) Compute the amount and position of the maximum bending moment, M, at any section of the beam, as explained in the earlier part of this chapter. (5) Assume a percentage of steel, p, and note whether the corresponding value of S, in the table, is within the specified limits. The values of p, most commonly used, are from .007 to .012. For example, in Table XVI A for p = .010, the corresponding value of S is 9600, which is well below the limit of 16,000 and therefore a safe unit stress for steel according to the New York building-code. (6) Pick out the corresponding value of the product S p j from the table for use in the formula, b d 2 = . For example, in Table XVI A, for p = .010, S p j 83.7. (7) Assume a value for the breadth of the beam, b, and compute the corresponding value of the effective depth, d, using the formula b d 2 = -^ .. If necessary try several values of b in order to obtain the best proportions of depth to breadth. The best shaped beam is one in which I) lies between 1/2 d and 3/4 d. b should not be less than 1/24 of the span, while d should not exceed 1/8 of the span. [206] Explanation of the Theory (8) Compute the sectional area of the steel from the formula A = p b d. The area A should be distributed over several bars. Thus for p = .0095, the area of steel required in a beam of 12 x 20 ins. is A = .0095 X 12 X 20 = 2.28 sq. ins. area of steel. If 3/4 inch square bars are employed, the area of each bar will be 3/4 X 3/4 = 9/16 sq. ins., and the number of bars required will be 2.28 -f- 9/16 = 4. The breadth of the beam should be sufficient for the spacing of the bars. A mini- mum clear spacing of at least i 1/2 diameters should be provided with an equal distance between the outside rod and the surface of the beam. Sufficient rods should be employed, so that the diameter of each rod will not exceed one two-hundredths of the span. The length of rod on either side of the point of maximum bending moment should be at least eighty diameters for plain and fifty diameters for deformed bars. (9) Check the assumed weight of the beam. EXAMPLE. It is required to find the dimensions and reinforcement required for a reinforced concrete beam, supported at each end, which will carry a uniformly dis- tributed weight of 15,000 pounds over a span of 14 feet, in conformity with the require- ments of the New York building-code. Solution. (i) According to the requirements, C = 500; r= 12; and S 16,000. (2) Table XVI-A of this chapter may be employed in this design. (3) Assume the weight of the beam to be 3,700 pounds; then the total load to be supported will be 15,000 + 3,700 = 18,700 pounds. (4) Since the weight is uniformly distributed, the maximum bending moment will be at the centre of the span, and its value be given by the formula: M = 1/8 / (W+W) or substituting M = 1/8 X 18,700 Ibs. X 1 68 ins., or M = 392,700 inch-pounds. (5) Assume a value of p = .0095 for the percentage of steel. Then from Table XVI A, 5 will be between the values of 10,250 and 9,600 pounds per sq. inch, which is well below the limiting value of 16,000 pounds required for safe design according to the conditions, and is therefore safe. (6) The value of the product .S p j, corresponding to p = .0095, will lie between the values 80.9 and 83.7 in Table XVI A, and for practical purposes can be taken as midway between these values or (7) Assume a breadth, &, as 3/5 of the depth, or b = 3/5 d, and substituting in the formula bd 2 = - :, we have Solving for d, we have d = 20 ins., and since b = 3/5 d, therefore b = 3/5 X 20 or 12 ins. (8) Since p = .0095, A the area of the steel reinforcement will be .0095 b d or A = .0095 X 12 X 20, or A = 2.28 sq. ins. If 3/4 inch square bars are employed, the number of bars required will be 2.28 -f- (3/4 X 3/4) = 4 plus a very small fraction which can be ignored. (9) The beam was assumed to weigh 3,700 pounds, and if the actual design shows it to be materially heavier, a revision must be made. [207] Handbook for Cement and Concrete Users The volume of the beam in cu. ft., as designed, is: ; 12 X 22* 14 X = 25.7 cu. ft. 144 If the concrete is a dense mixture, weighing 144 pounds per cu. ft., its weight will be 144 X 25.7 = 3,700 pounds as assumed. Having checked the weight, the design should now be investigated to determine whether it is in conformity with the following practical considerations. (a) Whether the breadth is between the limits of 1/2 and 3/4 the depth. (b) Whether the breadth is greater than 1/24 of the span. (c) Whether the diameter of the bars is less than 1/200 of the span. (d) Whether the breadth is sufficient to provide at least i 1/2 diameters spacing between the bars, and between the bars and the sides of the beam. Summarizing the results of the design, we have Total depth of beam, 22 ins. Depth to plane of steel, 20 ins. Breadth of beam, 12 ins. Reinforcement 4-3/4 inch medium steel square bars. Design of Web Reinforcement or Stirrups. Stirrups are required when the vertical shear exceeds a safe value for concrete. The vertical shear at any section of a beam is equal to the reaction at a support diminished by the sum of the intervening loads. Thus in the preceding example, each of the end supports carries one-half of the load or 9,350 pounds, and the vertical shear at a support will also have this value. Shearing stresses are not, however, uniformly distributed over the cross-section, and the maximum value is approximately 8/7 of the average value, while the unit stress or stress per sq. inch of cross-section, is found by dividing the maximum value by the area of the section, or v=8/ 7 V/bd (23) in which v is the unit shearing stress and V the total vertical shear produced by the loads at any section of a beam, having a breadth, b, and effective depth, d. Concrete can safely sustain a unit shearing stress, v, of from 30 to 50 pounds per sq. inch, and if this value is exceeded, stirrups must be provided to take care of the excess. In large and important girders stirrups should, however, always be provided even if the shearing stress is low. In the previous example, the maximum shear at either support is 9,350 pounds, and substituting in formula (23), with b = 12, and d = 20 ins., we have 8 Q,^O * v = y x i 2 x' 2 o = 44 * 5 per sq * m> ' which is large enough to necessitate the use of stirrups in a conservative design. Design of Stirrups. Where the unit shearing stress, v, is in excess of a safe value for concrete, say over 30 pounds per sq. in., stirrups should be provided, or the rods 8 V bent up at intervals, beginning at the point where r-j exceeds 30. Let 5 = the horizontal spacing of the stirrups along the beam, and let F' = y V- 3 obd . \ . .... (2 4 ) * 20 ins,, plus 2 ins. below the plane of the steel. Explanation of the Theory Call i)' the average intensity of the shear over the same section, that must be carried by the stirrups, then V and the total tension in the stirrups will be T = v f while the sectional area required for the steel will be V * T = v f b s = -- ........ (26) If the stirrups are inclined instead of vertical, the distance, s, is the perpendicular distance between the inclined members. Where the stirrups are perpendicular to the horizontal members, s, to be effective, should not exceed 1/2 the depth of the beam, and where inclined at an angle of 45 should not exceed 3/4 of the depth. S, the unit stress in the steel, should not exceed 10,000 Ibs. per sq. in. For example, if the vertical shear at the end section of a beam, 24 ins. deep by 14 ins. wide, is 13,125 Ibs., and two square rods are bent up vertically at the centre of the section, the section being 12 inches long, it is required to find the sectional area required for the steel, the unit shearing stresses being taken at 30 and 10,000 Ibs. per sq. in., respectively in the concrete and steel. From (24) V = V - 30 b d or V = y X 13,125 - (30 X 14 X 24) = 4,920 Ibs. , v V S 4,02O X 12 From (27) A = - or A = -22 - = 0.246 sq. ins. Sd 10,000 X 24 If two square rods are employed, the area of each should be 0.123 sq. ins., or the dimen- sions 3/8 X 3/8 ins. In general from three to four pair of stirrups should be used at each end of the beam, according to the span. Bond Strength Between Steel and Concrete.- For the purposes of design this should not exceed 50 pounds per sq. in. of steel area and if this amount be exceeded, the area of the steel must be increased, either by increasing the percentage of steel or the number of bars or both. The bond between steel and concrete may be tested by the approximate formulas *- f -5- ......... c-o and u = .......... (29) in which V = the maximum vertical shear produced by the loading, U the bond stress per unit length of beam, u the bond stress per unit area, say 50 Ibs. per sq. in., and o the sum of the perimeters of the steel sections. In the example worked out on page 207 the reaction at the supports was found to be 9,350 Ibs., which is equal to V, while d=2o ins., and the sum of the perimeters of the steel sections, o, for 4-3/4 inch square bars is 4 x 4 x 3/4= 12 ins. Hence from (28) from (29), u = 534 ~ 12 = 44.5 Ibs. per sq. inch, which is below the limiting value of 50 Ibs. per sq. in. Hence the design is satisfactory as regards bond. 14 [209] Handbook for Cement and Concrete Users Design of Reinforced Concrete Slabs. For the strength of slabs, the same formulas apply as for beams. The slab may be treated as a rectangular beam of unusual width, or it may be considered as a series of beams set one alongside of another, of a width equal to the spacing of the reinforcing bars, using one rod for each beam. In the case of square slabs, the reinforcement should be of equal amount in the two directions. It may be calculated on the assumption that one-half the load is carried by each system of reinforcement. The concrete is proportioned for one system only, or one-half the load, as the stresses due to the two systems are at right angles to each other, and the stresses in one direction do not weaken the concrete with respect to stresses in the other. In the case of oblong slabs, the relative amount of load carried by the longitudinal system is so small that it cannot be considered in the design. While longitudinal reinforcement is of little value in carrying loads, a small amount is nevertheless often desirable in preventing cracks and in binding the entire structure together. For this purpose 1/4 or 3/8 inch rods spaced about two feet apart, are frequently used. Metal fabrics are also commonly employed for reinforcing slabs. The successive steps to be followed in the design of a slab are explained and illustrated in the preceding chapter. T'-beams generally occur in the practice where a slab and its supporting girder are cast at the same time, as in floor construction. The width of slab that may be taken as part of the beam is generally limited to from four to six times the width of the stem, but in any case the width of slab must not be taken as more than the distance between beams. Where the neutral axis is not below the junction of web and flange, T-beams may be designed by the same formulas as are used for simple beams by substituting for the actual T-section the area found by multiplying the breadth of the flange by the effective depth of the beam. Such a beam, however, must be very carefully checked for shear between the flange and web, for bond between the steel and concrete, and for negative bending moments at the supports, which, if present, would produce tension in the slab at the top of the beam and compression in the narrow stem at the bottom of the beam. For a thorough treatment of the design of T-beams, double-reinforced beams, arches, etc., the reader is referred to Turneaure and Maurer's "Principles of Reinforced Concrete Construction," and other standard text-books on the subject. Further practical principles of design in so far as they relate to foundations, retaining walls, piers, and abutments, building construction, etc., will be found in the appropriate chapters of this book. RECOMMENDED PRACTICE FDR DESIGNING REINFORCED CONCRETE STRUCTURES* (i) The materials and workmanship for reinforced concrete should meet the re- quirements of the " Specifications for Plain and Reinforced Concrete " presented in this report of the Committee on Masonry. The concrete recommended for general use is a mixture of one part of cement to six parts of fine and coarse aggregates. A richer mixture will be found advantageous for special conditions. * From the report of the committee on Masonry of the American Railway Engineering and Maintenance of Way Association, presented at their annual convention in Chicago, 1910. [210] Explanation of the Theory (2) The dead load is to include the estimated weight of the structure and all other fixed loads and forces acting upon the structure. (3) The live load is to include all variable and moving loads or forces acting upon the structure in any direction. (4) As the working stresses herein recommended are for static loads, the dynamic effect of moving loads is to be added to the live load stresses. (5) The span length for beams and slabs is to be taken as the distance from centre to centre of the supports, but not to exceed the clear span plus the depth of beam or slab. (6) The internal stresses are to be calculated upon the basis of the following as- sumptions: (a) A plane section before bending remains plane after bending. (&) The distribution of compressive stresses in members subject to bending is rectilinear. (c) The ratio of the moduli of elasticity of steel and concrete is 12.* (d) The tensile stresses in the concrete are neglected in calculating the moment of resistance of beams. (e) The initial stress in the reinforcement due to contraction or expansion in the concrete is neglected. (/) The depth of a beam is the distance from the compressive face to the centroid of the tension reinforcement. (g) The effective depth of a beam at any section is the distance from the centroid of the compressive stresses to the centroid of the tension reinforcement. (ti) The maximum shearing unit stress in beams is the total shear at the section divided by the product of the width of the section and the effective depth at the section considered. This maximum shearing unit stress is to be used in place of the diagonal tension stress in calculations for web stresses. (*) The bond unit stress is equal to the vertical shear divided by the product of the total perimeter of the reinforcement in the tension side of the beam and the effective depth at the section considered. (6) In concrete columns the concrete to a depth of i$ in. is to be considered as a protective covering and is not to be included in the effective section. (7) When the maximum shearing stresses exceed the value allowed for the concrete alone, web reinforcement must be provided to aid in carrying the diagonal tension stresses. This web reinforcement may consist of bent bars, or inclined or vertical members, attached to or looped about the horizontal reinforcement. Where inclined members are used, the connection to the horizontal reinforcement shall be such as to insure against slip. " In the calculation of web reinforcement when the concrete alone is insufficient to take the diagonal tension, the concrete may be counted upon as carrying one-third of the shear. The remainder is to be provided for by means of metal reinforcement consisting of bent bars or stirrups, but preferably both. The requisite amount of such reinforcement may be estimated on the assumption that the entire shear on a section, less the amount assumed to be carried by the concrete, is carried by the reinforcement in a length of beam equal to its depth." (8) The following recommended working stresses, in pounds per square inch of section, are for use in concrete of such quality as to be capable of developing an average * The unit stresses as recommended in the report were higher than these values, which have been reduced in conformity with the fibre stresses employed in other por- tions of the chapter. Handbook for Cement and Concrete Users compress! ve strength of at least 2,000 Ibs. per square inch, when tested in cylinders 8 in. in diameter and 16 in. long, and 28 days old, under laboratory conditions of manu- facture and storage, the mixture being of the same consistency as is used in the field. Structural steel in tension . 14,000 High carbon steel in tension 17,000 t Steel in compression, 12 times the compressive stress in the surrounding con- crete Concrete in bearing where the surface is at least twice the loaded area 700 f Concrete in direct compression, without reinforcement on lengths not ex- ceeding twelve times the least width 350 t Concrete in direct compression with not less than i per cent, nor over 4 per cent longitudinal reinforcement on lengths not exceeding twelve times the least width 350 f Concrete in compression, on extreme fibre in cross bending 500 f Concrete in shear, where the shearing stress is used as the measure of web stress 30 NOTE. The limit of shearing stresses in the concrete, even when thoroughly reinforced for shear and diagonal tension, should not exceed 120 f Bond for plain bars 50 f Bond for drawn wire 30 t Bond for deformed bars, depending upon form 80-1 20 NOTE: Chapters XVII and XVIII differ, in that, the former chapter is applicable only to the column and to the special case of the simple horizontal beam carrying a uniformly distributed load, while, in the latter chapter, the methods are general and applicable to beams loaded in any manner. The methods of design are, however, identical in both chapters, and in order to render each one complete in itself, a certain amount of matter has been repeated. It is thought that the reading of this chapter will be rendered easier by first showing the application of the theory of design to a simple case, as was done in Chapter XVII. f The unit stresses as recommended in the report were in general higher than these values, which have been reduced in conformity with the fibre stresses employed in other portions of the chapter. [212] CHAPTER XIX SYSTEMS OF REINFORCEMENT EMPLOYED Systems of Reinforcement Employed. Different Forms of Rods and Bars. Special Fabrics and Types of Reinforcement. REINFORCEMENT is used in a variety of shapes and combina- tions, nearly all of them patented, and some of them forming the basis for so-called systems. All these systems of reinforcement have been developed princi- pally during the last decade, each one of them having its adherents and all of them giving substantial structures if intelligently em- ployed. The selection of the type for any particular case will depend upon the nature of the structure, the local conditions, the experience of the designer, and often upon the argument of the salesman. The illustrations will serve to bring out the essential features of the different systems. Specifications for Reinforcing Steel. The quality of steel to be used for reinforced concrete work has received a great deal of attention from engineers and steel-makers and the rules given below represent the latest practice in this respect : SPECIFICATIONS FOR STEEL REINFORCEMENT * 1. Steel shall be made by the open-hearth process. Rerolled material will not be accepted. 2. Plates and shapes used for reinforcement shall be of structural steel only. Bars and wire may be of structural steel or high carbon steel. * From the report of the Committee on Masonry at the annual convention of the American Railway Engineering and Maintenance of Way Association, Chicago, March 16, 1910. Handbook for Cement and Concrete Users 3. The chemical and physical properties shall conform to the following limits : Elements Considered. Structural Steel. High Carbon Steel. ( Basic o 04 per cent o 04 per cent Phosphorus, max . . . . i 1 Acid o 06 per cent o 06 per cent Sulphur, maximum 0.05 per cent. 0.05 per cent. Ultimate tensile strength. Pounds per square inch Desired. 60,000 Desired. 88,000 Elong., min per cent in 8" 2( ;% 20% Character of Fracture Silky Silky or finely Cold Bends without Fracture 1 80 flatf granular 1 80 d 4/*t 4. The yield point for bars and wire, as indicated by the drop of the beam, shall be not less than 60 per cent of the ultimate tensile strength. 5. If the ultimate strength varies more than 4,000 Ibs. for structural steel or 6,000 Ibs. for high carbon steel, a retest shall be made on the same gauge, which, to be acceptable, shall be within 5,000 Ibs. for structural steel, or 8,000 Ibs. for high carbon steel, of the desired ultimate. 6. Chemical determinations of the percentages of carbon, phosphorus, sulphur, and manganese shall be made by the manu- facturer from a test ingot taken at the time of the pouring of each melt of steel, and a correct copy of such analysis shall be furnished to the engineer or his inspector. Check analyses shall be made from finished material, if called for by the railroad company, in which case an excess of 25 per cent above the required limits will be allowed. 7. Plates, Shapes, and Bars. Specimens for tensile and bending tests for plates and shapes shall be made by cutting coupons from the finished product, which shall have both faces rolled and both edges milled to the form of a standard test specimen; or with both edges parallel; or they may be turned to a diameter of J inch with enlarged ends. * See paragraphs n and 12. f" d = 4}" signifies "around a pin whose diameter is four times the thickness of the specimen." Systems of Reinforcement Employed 8. Bars shall be tested in their finished form. 9. At least one tensile and one bending test shall be made from each melt of steel as rolled. In case steel differing 3/8 in. and more in thickness is rolled from one melt, a test shall be made from the thickest and thinnest material rolled. 10. For material less than 5/16 in. and more than 3/4 in. in thickness the following modifications will be allowed in the require- ments for elongation : (a) For each 1/16 in. in thickness below 5/16 in., a deduction of 2 1/2 will be allowed from the specified percentage. (b) For each 1/8 in. in thickness above 3/4 in., a deduction of i will be allowed from the specified percentage. 11. Bending tests may be made by pressure or by blows. Shapes and bars less than one inch thick shall bend as called for in para- graph 3. 12. Test specimens one inch thick and over shall bend cold 1 80 around a pin, the diameter of which, for structural steel, is twice the thickness of the specimen, and for high carbon steel is six times the thickness of the specimen, without fracture on the outside of the bend. 13. Finished material shall be free from injurious seams, flaws, cracks, defective edges, or other defects, and have a smooth, uniform, and workmanlike finish. 14. Every finished piece of steel shall have the melt number and the name of the manufacturer stamped or rolled upon it, except that bar steel and other small parts may be bundled with the above marks on an attached metal tag. 15. Material, which, subsequent to the above tests at the mills, and its acceptance there, develops weak spots, brittleness, cracks or other imperfections, or is found to have injurious defects, will be rejected and shall be replaced by the manufacturer at his own cost. 1 6. All reinforcing steel shall be free from excessive rust, loose scale, or other coatings of any character, which would reduce or destroy the bond. Types of Reinforcement. The reinforcement consists of steel in one or more of the following forms : 1. Round or square rods. 2. Twisted or deformed rods, . j [215] Handbook for Cement and Concrete Users 3. Unit systems. 4. Woven wire, expanded metal, welded, or other fabrics. 5. Spiral reinforcement for columns. 6. Various patented systems. The plain bars either depend upon the adhesion of the steel and concrete for the action of the two materials in combination, or the ends of rods are anchored in the concrete for the purpose of developing their full tensile strength. In the deformed bars the adhesion of the concrete to the steel is supplemented by a mechanical bond due to the shape of the bar. The following bars are among the best known of this class : 1. Ransome twisted bars are made of square bars twisted cold. 2. Johnson corrugated bar in which the mechanical bond is effected by a series of corrugations on the sides of a square rod. 3. Diamond bar which is a round bar crossed by diagonals. 4. Cold twisted lug bar, which is a Ransome bar having small projections at intervals. 5. Cup bar in which the mechanical bond is effected by a series of cups. 6. DeMan undulated bar. 7. Universal type corrugated bar. 8. The Kahn and Golding bars which are provided with attached shear members. Unit Systems, Fabrics, and Spiral Reinforcement. In the unit systems, the reinforcement, including the tension rods and stirrups, are so tied and framed together that after being placed in the forms the possibility of shifting their positions with re- spect to the other surfaces of the beam, or to one another, is practically removed. Steel fabrics are largely employed in slab and floor construction, also in conduits, tanks, foundations, etc. Spiral wrappings for columns are employed for the purpose of permitting a higher unit stress to come upon the concrete than could safely be used without such reinforcement. The spirals have the effect of confining the concrete and preventing it from bulging or splitting. Special Systems of Reinforcement. The following are among the so-called special systems of construction; [216] Systems of Reinforcement Employed The Expanded Metal System* Expanded metal is made from mild steel, having an ultimate resistance of 48,000 pounds per square inch and an elongation of 21 per cent in a length of 8 inches. It is manufactured from flat plates of thickness varying from 1/4 to about 1/8 of an inch, and when expanded, the usual meshes are from 6 inches to 3 inches in width. The operation of making it consists in placing the sheets vertically, resting on their edges. They are then slotted and pulled out at one operation. After being slotted, they are drawn out laterally so that the width of the finished sheet is in reality produced from the height of the original plate when placed with its edge downward. The expan- sion effect varies from about 6 to 12 times the original width of the plate. However, no alteration is made in the length, the strands being consequently somewhat stretched. A por- tion is left uncut, thereby forming a strong "selvedge 77 edge. It has been found that the ultimate strength is increased from 48,000 to about 63,000 pounds per square inch through the operation of expanding. Expanded metal is mainly used for slab construction, although in a few instances, it has also been used in the construction of beams. The Clinton System. A reinforcing for concrete construction of all kinds which is being extensively used in this country is the electrically welded fabric manufactured by the Clinton Wire Cloth Company, of Clinton, Mass. The late Frank E. Kidder stated that from a theoretical standpoint at least this fabric would seem to offer the ideal reinforcement for slab construction, as the carrying wires may be varied both in size and spacing to give the necessary area for any given weight and span. The distributing or cross wires may likewise be varied in the same way. The direction of the wires coincides with the line of stress so that there is no tendency to distort the rectangle of the mesh. As this fabric comes in 3oo-foot rolls it can, in a building say, for instance, 200 feet long, be secured at the front or rear and carried through the entire distance without a break. Owing to the con- tinuous bond the reinforcing is equally strong at all points and the reinforcing members are exactly spaced 2, 3, or 4 inches apart as * Description adapted partly from American Cement Company's publication, by Walter Muller. Handbook for Cement and Concrete Users the case may be. This spacing is exact; it is established by ma- chinery and is not subject to the carelessness of employees. The Kahn System. This system, which is being advocated by the Trussed Concrete Steel Co., of Detroit, Mich., embodies the use of what is known as the Kahn trussed steel bar. This bar is rolled of a diamond section with projecting wings on either side. The wings are slotted off along the edge of the diamond for certain distances and are bent up to an angle of about forty-five degrees to form the reinforcements resisting the shearing stresses. They are consequently rigidly connected to the main bottom bars. The three principal advantages claimed for the employment of this form of reinforcement are : 1. The reinforcement in the vertical plane is rigidly attached to the main horizontal member and lies in such a direction as to cross at right angles the lines of rupture. 2. The design of the diagonals economizes in the amount of metal required and enables same to be placed with a maximum amount of speed and economy. 3. Absolute fireproofness of structures is the result because this reinforcement does not depend upon the lower part of the concrete, which is affected by fire. The Hennebique System. This system, which is one of the best known and most extensively used in Europe, was brought out in 1892 by M. Hennebique, who was one of the first to introduce the reinforced concrete beam and is sometimes mistakenly designated as its original inventor. The floors, according to the Hennebique system, are formed in several ways, the most commonly employed being the flat single floor with exposed beams. The floor rods are in two series, one bent up to pass over the support near the upper surface of the slab and the other set straight throughout and embedded near the lower surface. The Hinchman-Renton System. While plain iron rods have never been known to slide or slip in concrete yet on account of the possibility that the sliding resistance along the embedded steel will decrease in time under frequently repeated loads, American en- gineers have deemed it wise to use the reinforcing steel in such shape that sliding in the concrete will be impossible without tearing and crushing. Systems of Reinforcement Employed In seeking for material that would satisfactorily supply the tensile strength required by floor slabs it occurred to Mr. J. B. Hinchman of the Hinchman-Renton Company, Denver, Colorado, that ordinary barbed wire would afford the necessary reinforcement. Roebling System. The Roebling system is employed in connec- tion with a structural steel frame of I-beam or girder construction. For all flat construction of floors, the reinforcing system used consists of flat bars placed upon edge, secured at the ends to the steel beams and bridged with bar separators. The object of the edgewise position of the bars is the increased protection thus secured FIG. 58. The Hennebique System of Reinforced Concrete in Building Construction. to the reinforcing steel. With this type of floor the structural steel frame is generally completely encased with concrete. For light roof construction where the steel work need not be protected, a continuous slab is built over the beams, reinforced with flat steel bars, 3-16 by 11/4 inches, placed edgewise and held in position by spacers. For floor construction the Roebling Company also uses segmental arches of cinder concrete laid upon permanent stiffened wire lath centering, or upon wood centering which is carried on steel tees and supported by the steel I-beams of the floor system, which are gener- ally placed about 7 feet on centres. In this system the material is [219] Handbook for Cement and Concrete Users placed upon the centering without puddling or tamping, in order to obtain a light porous concrete of high fire-resisting quality. The Turner Mushroom System. The promoter of this system, Mr. C. A. P. Tuiner, claims that in warehouse work it is perfectly feasible to put up a building with columns at 1 6-foot centres with a 5111 FIG. sg. The Merrick Floor System. 6/rtfer fleam *<*> Gti/o FIG. 60. The Cummings System. floor of 7 1/2 in. rough slabs, using no ribs at all, and test it with 800 Ib. per sq. ft., without injury to the construction. Furthermore he claims that it can be put up at less cost without the ribs, and will require less metal, as the load will travel more directly to the sup- ports, instead of around a corner, as in the case where beams are [220] Systems of Reinforcement Employed used. The method of construction which he employs is known as the mushroom system. Merrick System. To lighten the weight of the concrete slab, Mr. Ernest Merrick has designed a hollow floor construction, Concrete / '" 2 parts sand T . .:...:: :: :^,::. : ---'^::'i'---:---^.--- ;:'>: *::.:,.:;:. -..v.^--""-'--"-ij t -let illiiii^iiiiH 1 -7 f: iM^MMiiKMM^ \ f 1 part portlMd e Concrete j 2 parts (and (.Hair requirtd FIG. 61. consisting of a series of reinforced concrete beams connected by a concrete plate at the top and a ceiling plate at the bottom. Melan System. In the Melan system of constructing bridges, steel ribs or I-beams of considerable size are employed; the steel carrying the major portion of the stress, while the concrete serves as protective covering. The Columbian System. This is a flat concrete system with TYPICAL DETAILS H r - " L::: a_ FIG. 62. The Gabriel System of Reinforcement. ribbed steel tension members. Rolled joists are used for beams, embedded in concrete, the double cross floor reinforcement being held in place by flat iron inverted stirrups placed over the top flanges of the joists. [221] Handbook for Cement and Concrete Users The Unit System. In the Unit System, which is 'controlled by the Unit Concrete Steel Frame Company of Philadelphia, all of the metallic reinforcement for each beam or girder is made into a single unit and placed as a unit in the form. This is accomplished by having both the straight and camber bars fastened together by stirrups and clamps, so that each tension and shear member is rigidly held in its proper position. This precludes the possibility of one or more members being omitted or incorrectly placed by workmen at the building, and affords opportunity for inspection prior to use. The advantages claimed for this system are absolute accuracy in the placing of the reinforcing material; the ease with which it can be inspected and errors, if any, detected and corrected before con- creting; the impossibility of omitting any tension or shear member; the additional strength secured by binding the slab concrete to the beam concrete by means of lacing of the slab reinforcement through the stirrups. The girder frames may thus be set in advance of the concrete workj and provision made for shafting or other overhead fixtures. [222] CHAPTER XX REINFORCED CONCRETE IN FACTORY AND GENERAL BUILDING CONSTRUCTION Advantages of Reinforced Concrete in Building Construction. Practical Details of Construction. Slabs, Columns, Floors, Loads, Walls. Roofs. Attaching Ma- chinery. IN the factory, where the primal considerations are serviceability, fireproofness, and cost, concrete has found one of its leading appli- cations. When reinforced with steel, a structure is obtained which is lower in first cost than an all-steel building, which can be more quickly erected, and which is freer from vibration and more fire- proof. As compared with what is known as the " slow-burning," or "mill" type of construction, reinforced concrete is more fireproof, durable, and carries a lower rate of insurance as the mill type is a combination of brick, stone, or concrete walls with timber floors and columns. Cost. While all statements as to cost of reinforced concrete buildings may be somewhat unreliable, it is safe to figure that in the simple factory building where elaborate forms are not required and building material prices not excessive, the cost will be about 8 cents per cu. foot. This price will increase with elaboration of surface finish and ornamentation and other unfavorable conditions to 12 cents per cubic foot. The volume includes the building from footing to roof and the price does not include interior work such as lighting or heating plants, machinery, plastering, plumbing, or elevators. Fire resistance is one of the chief inducements that has led to the extensive use of concrete in factories. The materials to be employed are first-class Portland cement, quartz sand, and broken trap rock. Limestone aggregates are more easily injured by ex- treme heat and gravel is more readily dislodged. Cinders make a [223] Handbook for Cement and Concrete Users good aggregate for fire resistance, but the concrete made therefrom is not sufficiently strong for reinforced concrete work excepting for partition walls and short spans. A reinforced concrete factory is necessarily a very stiff structure, every part being inseparably connected with every other part by continuous beams, girders, and slabs. This permits the operation of the heaviest machinery with much less vibration than equivalent steel structures. In taking up the question of a concrete factory, the layout and arrangement of machinery should first be made and the building designed to accommodate the resulting loads. One of the distinct advantages of a concrete factory is the large amount of window space and light thus made available which is due to the inherent strength of concrete and the thin members required to support the windows, etc. In addition to these ad- vantages the floors of concrete may be made absolutely watertight, can readily be flushed with a hose, and are fire- and vermin-proof. Practical Construction Details. The essential principles govern- ing the design of girders, columns, and slabs, have already been given in Chapters XVII and XVIII. The following data is of importance in connection with building and factory construction, and is taken from "Reinforced Concrete in Factory Construction," by Sanford E. Thompson.* Floor Slabs. The thickness and reinforcement of the floor slabs are determined by the distance between the beams, and by the loading which will come upon them. The most usual thicknesses are 31/2 inches to 5 inches, with reinforcement calculated from the bending moment produced by the loads. An economical quantity of steel is apt to be from 0.8 per cent to i per cent of the sectional area of the slab above the steel. A few rods are usually placed at right angles to the main bearing rods of the slab to assist in preventing contraction cracks, and these also add to the strength of the slab. In a factory or warehouse the most economical floor surface is generally a granolithic finish, consisting of a layer of i : 2 mortar about three-quarter inch thick, spread upon the surface of the con- * Published by the Atlas Portland Cement Co. [224] Reinforced Concrete in Building Construction crete slab before it has begun to set, and trowelled to a hard finish just like a concrete sidewalk. Machines are readily bolted to the concrete by drilling small holes in the concrete at the proper points for the standards and grouting the lag screws in place, or else bolting them through the slab. If for any reason a wood floor is required, stringers may. be laid upon the top of the concrete and spaces left between them or filled with cinders or with cinder concrete. Stirrups. Besides the ordinary compression and pull in a beam, there are secondary stresses of shear or diagonal tension, which, if FIG. 63. Ordinary Type of Ribbed Slab. not provided for, will produce diagonal cracks. These will run in a general direction from the bottom of the beam near the supports on an incline toward the top of the beam, and may cause the beam to fail. To prevent this cracking, unless the beam is so wide that the concrete can take the whole of the stress without exceeding 60 pounds per square inch in shear, vertical or inclined steel bars, of sizes accurately computed, must be placed. The bent-up tension rods take care of a part of this shear, or diagonal tension, but if these are not sufficient, stirrups, which are usually made in the form of a U, must be inserted at the proper locations to take the remainder. Handbook for Cement and Concrete Users Columns. The most important of all the members of the building are the columns, for if a column fails, the entire building is liable to go down. If columns, as ordinarily built in building construction, are made of i : 2 : 4 proportions, it is safe in an ordinary building to allow a direct compressive strength of 450 pounds per square inch, pro- vided the columns are at least 12 inches square. A customary manner of designing is to figure the entire compression upon the concrete to the full size of the column, but to place four or possibly six rods of 5/8 inch or 3/4 inch diameter near the corners or sides of FIG. 64. Column Reinforcement. FIG. 65. Reinforced Concrete Column Footing. the column, with i/ 4-inch wire loops around these rods at occasional intervals in the height, say, from 8 to 1 2 inches apart. Vertical steel rods of larger size may be introduced when it is necessary to decrease the size of the columns. These may be com- puted to bear a portion of the compressive load, but they cannot be figured at their full safe value of 16,000 pounds per square inch because they have a different modulus of elasticity and compressive strength from concrete and can only shorten the same amount as the concrete. Under ordinary circumstances, therefore, they cannot be assumed to bear more than the safe compressive stress in the con- crete times the ratio of elasticity of steel to concrete, or about 7,000 pounds per square inch. Because of this small amount of compres- [226] Reinforced Concrete in Building Construction sion which they can bear, it is always cheaper to enlarge the column rather than to insert steel of large diameter to assist in taking the load. Another means of increasing the strength of the column is to use a richer mixture. This is legitimate provided the same mixture is carried up through the floor system at the column so that there will be no weak places. By using proportions i : i : 3, a safe working compression in the concrete of 700 pounds per square inch may be adopted. Hooped columns, that is, columns reinforced with bands placed near together or with spirals, are frequently adopted to reduce the size of the column. It is a serious question in the minds of conservative engineers as to whether it is good practice to assume that a large proportion of the load can be borne by such hoops. Although tests have shown that hooped columns have a high ultimate strength, these same tests prove that the con- crete within the hoops is overstrained before the hoops begin to take any of the tension which must reach them before they can strengthen the columns. Basement Floor. The earth under a basement floor must be well drained. If necessary, drains of tile pipe or of screened gravel or stone may be placed in trenches just below the concrete, or the entire level may be covered with cinders or stone. If the basement is below tide water or ground water level, it is not safe to depend upon the concrete itself being water-tight, and waterproofing should be provided for as described in Chapter XXX. For a basement floor in dry ground a 3-inch or 4-inch thickness of ordinary 1:3:5 concrete, that is, concrete composed of i part Port- land cement to 3 parts -sand to 5 parts broken stone or gravel may be laid and the surface screeded to bring it to the required level. As it sets, this concrete should be trowelled just as the wearing surface of a sidewalk is trowelled, but without the mortar or granolithic finish which is customarily laid upon a walk. If the floor is to have a great deal of wear or trucking, the usual 3/4-inch or i-inch layer of i : 2 mortar may be laid upon the concrete before it has set, forming a part of the total thickness of 4 inches; but usually this is an unwarranted expense in a basement, as the plain concrete will give as good service. [227] Handbook for Cement and Concrete Users It is well in any case to divide the floor into blocks, say, 8 or 10 feet square, so that any shrinkage cracks will come in the joints. This is readily accomplished by laying alternate blocks, and then filling in the intermediate ones the next day. Design of Floor System. Loading. In designing a rein- forced concrete building, the first consideration is the loading which the various floors must sustain; in other words, the strength which each floor must have to support the weights which may come upon it under all conceivable conditions. In a factory or warehouse it is frequently possible to accurately cal- culate the maximum weight which will come upon a given area of floor. For the very heaviest loading the problem is frequently the simplest, since the heavy weights are apt to be due to the storage of merchandise whose weight per cubic foot, and there- fore per square foot of floor, can be readily calculated. Some- times the underside of the floor must support tracks which carry certain definite weights, and the beams or girders must be calculated for these concentrated loads in addition to the uniform loads upon the floor. In computing the strength of the floor system, the weight of the concrete itself must always be allowed for. In very long spans the concrete frequently weighs more than the load which will be placed upon it. In many cases the loading must be assumed without actual computation. A maximum load must frequently be selected to support machinery whose weight is slight but whose vibrations , require a stiff floor system. The various conditions met with in warehouse or factory con- struction may thus necessitate loadings varying from 100 to 500 pounds per square foot of floor area, very wide limits and yet not more than occur in practice. As a guide to the selection of floor loads, the following values are suggested: Office floors 100 pounds per square foot Light -running machinery 150 pounds per square foot Medium heavy machinery 200 pounds per square foot Heavy machinery 250 pounds per square foot Storage of parts or finished products, depending upon actual calculated loads 150 to 500 pounds per square foot Reinforced Concrete in Building Construction When the loads are apt to occur only over a part of the floor, the slabs and beams are calculated for the full load, and when com- puting the girders and columns a slightly smaller load is sometimes used. For example, if the slabs and beams are figured for 200 pounds per square foot of floor area, it might be assumed that the whole of the total area supported by a girder or column would never be loaded at once, and the load per square foot actually reach- TABLE XXI. ALLOWABLE FLOOR LOADS IN ACCORDANCE WITH THE BUILDING LAWS OF VARIOUS CITIES. (From Kahn's Pocketbook.) Live Loads for Floors in Different Classes of Build- ings Exclusive of the Weight of the Materials of Construction. New York 1902. Chicago 1902 Philadelphia 1902. li San Francisco 1906. Pounds per Square Foot. Dwellings, Apartment Houses, Hotels, Tene- ment Houses or Lodging Houses 60 75 75 75 90 120 5 30 ' 300 40 100 100 40* 100 100 25 25 70 100 100 120 120 15 ' 3 3 So 100 100 80 150 250 2 5t 2 5t 15 60 150 75 75 75 125 120 250 5 3 300 Office Buildings, ist Floor Office Buildings Above ist Floor . . Schools or Places of Instruction Stables or Carriage Houses Buildings for Public Assembly Buildings for Ordinary Stores, Light Manufactur- ing and Light Storage . Stores for Heavy Materials, Warehouses, and Factories .. . Roofs Pitch less than 20 degrees . . . Sidewalks Public Buildings Except Schools ing the girder and column at any one time would be therefore not more than 1 50 pounds per square foot of floor area. Layout. The general layout of the beams and girders and columns depends upon the loading, the uses to which the building is to be put, and the ground area. Frequently in a large building, * Stables less than 500 square feet in area. f Stables over 500 square feet in area. J Make proper allowance for wind at 30 Ibs. per square foot horizontal pressure. [2291 Handbook for Cement and Concrete Users it will be worth while to require the engineer to make several com- parative estimates with different spacings of columns and sizes of panels, so as to determine that which is most economical consistent with the floor area required for the machinery. Common spacings of columns in a reinforced concrete building are from 12 feet to 20 feet. Longer spans are not usually so eco-4 nomical, but may frequently be necessary to give the floor space required for machinery or storage. Walls. The walls of reinforced concrete factories are sometimes built up with the columns, but it is generally considered more economical to erect the skeleton structure and fill in the wall panels afterwards. Slots in the columns are made by nailing a strip on the inside of the column forms. In this way the panels are mortised into the columns. Ordinary concrete walls require light reinforcement to prevent shrinkage and give them stiffness while setting. All that is required for, say a 4-inch or 6-inch wall, are i/ 4-inch rods spaced from 12 to 24 inches apart, according to the size and importance of the wall. At window and door openings a larger amount of reinforcement is, of course, necessary, and in these cases the amount of steel must be calculated just as though the lintels were reinforced concrete beams. Roofs. Reinforced concrete roofs are designed like floors. A roof load commonly assumed in temperate climates, to provide for roof covering, snow and wind pressure, is 40 pounds per square foot, in addition to the weight of the concrete itself. It is not safe to assume that the concrete roof of itself will be water-tight unless special provision is made in the construction. Although tanks and walls can readily be made to hold water, a roof is under extraordinarily disadvantageous conditions because of the rays of the sun. Usually, therefore, a tar and gravel or other form of roof covering must be provided. Methods for Attaching Shafting, etc. The attachment of shafting, piping, etc., to the ceilings of reinforced concrete buildings presents no special difficulty, provided adequate provision is made in the design. The following methods are employed : [230] Reinforced Concrete in Building Construction i. Bolts are embedded in the concrete beams with their threaded ends hanging down. After the forms have been removed timbers are bolted to the undersides of the beams and the hangers for the FIG. 66. WoodSMp ffpg/t 'es FIG. 67. toy scnwfr /o 4*f ^fe ? ^;W.^^pl &&'tfmm jy/s/v/v. -*j j fit MHO* \\ fia @ before /"/> fo//eer orn* Washed Cnmt>er Excavated. rm *. ut, FIG. 76. Concrete Pile with Enlarged End Showing Progressive Stages in Driving. perforator against the sides of the hole, thus forming an almost water-tight lining. The hole is thus carried down a suitable depth, concrete is then placed in it, and is rammed with a drop tamper. This results in a pillar of large diameter, in which the concrete is forced into the surrounding soil, thus greatly increasing its bear- ing power. Both perforator and tamper are operated by a pile- driver. When soft material overlies strata of firm material, the com- pressed system is particularly advantageous, as by its means a large pier, resting on the firm soil and extending through the soft strata, results. [242] Concrete in Foundation Work Caissons. Where all other methods of securing a satisfactory foundation fail, caissons, either open or pneumatic, carried down to bed rock or hard pan, are used. An open caisson is a strong, water-tight, bottomless box, usually constructed of steel or timber. It is sunk by excavating the material inside of it, and if necessary by adding additional weight at its top. Open caissons of reinforced concrete have been used in many instances, notably in the Cockle Creek Bridge, New South Wales, and in the Catskill Aqueduct, in New York State. In the Cockle Creek Bridge, two open cylindrical reinforced concrete caissons were driven through a depth of 36 ft. of silt, sand, and gravel to hard clay. When finally seated in this clay, they were filled with concrete and used as piers for the bridge. In the Catskill Aqueduct, three open reinforced-concrete caissons were sunk in constructing the Rondout Siphon. These caissons were sunk to rock, by excavating, under ordinary air pressure, the material within, and allowing the caissons to sink of their own weight. When the aqueduct is completed two of the caissons will serve as part of the permanent lining. Pneumatic Caissons. A pneumatic caisson is a strong, water- tight box, open at the bottom and closed at the top. This forms a working or air chamber. Usually the sides of the caisson are continued above the top, thus forming a second box closed at the bottom but open at the top. This is called the cofferdam. The pier is built within this cofferdam and on top of the caisson as the sinking progresses. The working chamber is supplied with compressed air which serves the double purpose of forcing out all water, and supplying the men with the necessary fresh air. Pneumatic caissons are usually constructed of steel or timber, though a few have been made of reinforced concrete. Reinforced concrete was recently used in the construction of the large tunnel caisson on the Jersey shore connecting the tunnels of the Hudson Co., crossing the Hudson River. Caissons are mostly used in constructing the foundations of bridges and high buildings. When the work is under water or in water-bearing soil, the pneumatic caisson is usually used, al- though at times an open caisson and a bucket dredge are sub- stituted. [ 2 43] Handbook for Cement and Concrete Users Cribs. A crib is usually a timber grillage, which instead of being built in place, is first constructed, then floated to its final resting-place and sunk in a single mass. The superstructure is then built on the crib, either in the open or in a caisson, and the function of this crib is to distribute the load carried by the superstructure over the foundation bed. While cribs are usually constructed of timber there is no reason why reinforced concrete could not be used with economy. [244] CHAPTER XXII CONCRETE RETAINING WALLS, ABUTMENTS, AND BULKHEADS Design of Walls in General. Methods of Failure. Kinds of Retaining Walls. Design of Gravity Walls. Reinforced-Concrete Walls. Details of Construction. Foundations. Abutments. Bulkheads. Appearance of Walls. Tables for De- sign of Walls. UNTIL the advent of concrete, retaining walls for the support of embankments and cuts as well as reservoir walls, bulkheads, etc., were constructed of rubble or ashlar masonry laid with or without mortar as the importance of the problem demanded. Concrete, especially when reinforced, has supplied a material which gives a far greater power of resistance, occupies a minimum of space and may be built at a much lower cost. The design of concrete retaining walls follows the same general methods that are employed for ordinary masonry, the design being based upon the action of the wall when the load caused by earth, water, or other material from behind, comes upon it. Certain conditions of failure deduced from observation, experience, and mathematical reasoning are assumed to be possible and the wall so proportioned that it will be safe against any and all such possible failures. Thus it is- assumed that: Assumptions Made in Design. A wall holding up a bank of earth, or water will be subjected to a pressure: the amount of which will depend upon the depth of the wall below the surface and upon the weight and mobility of the material pressing against it. The question as to how much pressure is produced by banks of earth resting against walls has given rise to much discussion, and even to-day there is no general agreement among engineers as to what this pressure is. The difficulty arises from the fact that earths vary so much, their weight, consistency, and cohesive power are so constantly changing with change of the contained water, that no general pressure rule can be applied. It is thus that most com- [245] Handbook for Cement and Concrete Users putations for earth pressure assume a theoretical condition, that of perfectly dry sand, and yet this condition is but seldom found, but as it gives safe values, its assumption is justified. When a bank of such sand has an unrestricted surface its sides will assume a natural slope of about 11/2 feet horizontal to i foot vertical. This is referred to as the " Angle of Repose," or " Angle of Friction." If a wall is placed at the edge of a bank and the space between the back of the wall and the bank filled in, this earth or "back- ing " will tend to slide along the line of repose, and thus produce a pressure against the wall. The upper half of this prism is con- sidered as producing the maximum pressure effect on the wall and its weight is employed in computing this pressure. Effect of Earth Pressure. Mathematical investigations have determined : I. That the entire effect of this pressure may be considered as concentrated at a point 1/3 the height from the bottom. II. That this pressure will tend to either slide or push the wall bodily out of place, or to rotate it about its toe and overturn, or both. III. That since the wall is rigidly constructed and cannot yield, the effect of the external pressure is to induce strains in the material of the wall. IV. That the material of the wall can resist safely certain specified strains per unit of area of material such as the square inch or square foot, the amount of such safe strains varying with the kind of strain and the material. V. That the foundation material must not be subjected to un- safe strains. From these assumed conditions the dimensions of the wall are fixed so that the strain in the material will never exceed what it can safely stand. It is thus seen that the following methods of failure are possible. Methods of Failure. A retaining wall may fail in one or more of the following ways: i. By revolving about any horizontal line in the face. This is the most frequent mode of failure, and it is due to the overturning moment, due to the earth backing being greater than the righting jnornent of the wall itself. A failure of this type indicates too light Concrete Retaining Walls a wall for the work imposed upon it or too heavy a load on the soil at the base of the wall. A wall which shows signs of failure by this method may be strengthened by buttressing. 2. By Sliding on any Horizontal Plane. This is the least frequent method of failure, and in a monolithic wall free from all horizontal joints as is the case in a wall of concrete, is prac- tically impossible except by the sliding of the entire wall on its foundation bed. This is a rare occurrence, and when it occurs is probably the result of the wall having been founded on an . unstable material, perhaps an inclined bed of moist and uncer- tain soil. When the foundation rests upon piles, a simple expe- dient is to drive piles in front of and against the edge of the foundation. When the foundation rests on rock, the resistance to sliding may be increased by leaving the surface of the bed rough, or in case the rock quarries out with smooth surfaces, the bed of the foundation may be channelled longitudinally, and the channels afterward filled with masonry. In case of the wall resting on earth, increasing the depth of the foundation below the ground level at the face of the wall, thereby increasing the area against which the face of the wall abuts, greatly increases its stability against sliding. 3. By the Bulging of the Body of the Masonry. This form of failure can occur only in walls restrained at both top and bottom, as in cellar walls, some abutments, walls with land ties, etc. A failure of this type indicates too light a design. Some of the causes of failure of retaining walls which cannot readily be taken care of in computation are : settlement of founda- tion, bulging due to poor drainage, formation of ice, etc. These must be looked after in the plans and construction and will be referred to later. Types of Retaining Walls. Concrete retaining walls are con- structed in three general types, depending upon local conditions and often upon the mood of the designer. These are: I. Gravity walls, with or without reinforcement which depend for their stability entirely upon the weight of concrete. II. Reinforced-concrete cantilever walls of uniform thickness and wide reinforced base footing. [247] Handbook for Cement and Concrete Users III. Reinforced-concrete walls having buttresses at regular intervals on the rear face of the walls. Gravity Retaining Walls. The gravity wall is adapted for low banks or fills as in any large work the amount of concrete necessary to give the required weight makes it very costly. In such cases the reinforced-concrete wall is always employed. In the gravity wall the side subjected to pressure is stepped, and the exposed side slopes away from the bank to give increased stability. It is an important principle of mechanics that the resultant of all forces acting on a wall should never pass outside of the middle third of the cross-section, and it is in order to follow this principle that the outside of the wall is stepped or sloped. By following this principle, no tensional or pulling stresses develop in the plain con- crete which, by assumption, it cannot safely carry. This principle holds true in all homogeneous masonry structures. Design of Gravity Walls. The design of the gravity wall is usually a rather simple matter, as it is only necessary to assume a width of base of about .4 of the height. Make it 2 feet or up, wide on the top, according to practical requirements, and then compute its weight .and the pressure due to the earth backing (or water in case of a dam), and compare the effect of this pressure to produce sliding and rotation, with the power of resistance as deduced from the weight. If the .latter is greater, the wall is theoretically safe. The steps followed in the theoretical design of a gravity retaining wall are well outlined in Lewis and Kempners' Manual of Examina- tions, as follows: 1. The height of the wall is determined by local conditions. 2. Assume total thickness of wall. 1/5 the height at top. 2/5 the height at bottom. 3. Plot the wall to scale. 4. Compute the weight of the maximum earth prism. Also compute the thrust of same, which equals' about .64 of this weight. (Earth weighs 100 Ibs. per cu. ft.) 5. Compute weight of wall concrete weighing about 140 Ibs. per cu. ft. Also compute position of centre of gravity. Concrete Retaining Walls 6. Draw to scale, the line of thrust making an angle equal to the angle of friction with the normal to the back of the wall (see Fig. 77), and passing through the centre of pressure, which is i/3 of the height from the bottom. 7. To same scale draw line representing weight of wall through its centre of gravity. 8. Combine these as shown. The resulting pressure line should fall within the middle third of the base to insure absence of tension in the joints. 9. Compute the overturning moment due to thrust. Also compute resisting moment of the wall. The resisting moment should exceed the overturning moment by a safe margin. FIG. 77. Diagram Showing Forces Acting on Gravity Retaining Wall. 10. Compute the horizontal thrust, also frictional resistance to sliding (weight X coefficient friction). The latter should be equal to or exceed 3 times the former. 11. Test security of foundation by computing unit load at the toe (total load per running foot divided by 1/2 width of base). All conditions of stability must be satisfied and all unit loads should be within safe limits; if not, change dimensions and recom- pute. REINFORCED-CONCRETE WALLS Reinforced-concrete walls are designed along different lines. The external loading is the same as in the gravity wall, but the wall itself and the buttresses are considered as cantilever slabs or beams [249] Handbook for Cement and Concrete Users supported at the bottom only, and the stresses figured somewhat in the same way as in the beam or slab computations. The footing is also considered as an inverted cantilever beam or slab with the pressure acting upward against it, tending to rupture it at the junction, and the proportions of steel and concrete must be so arranged as to prevent unsafe strains from being developed. Reinforced-concrete walls do not depend upon the weight of the masonry alone to resist overturning, but utilize also the weight of the earth backing resting on the base of the wall. The economy of a reinforced-concrete retaining wall is due 80 FlG. 78. Reinforced Concrete Retaining Wall. FIG. 79. Reinforced Concrete Retaining Wall with Counterfort. FIG. 80. Reinforced Concrete Retaining Wall with Counterfort and Centre Platform. chiefly to the utilization of the downward pressure of the backing in resisting overturning. In reinforced-concrete retaining walls as in masonry ones, pro- visions must be made against sliding, and the wall must have a suitable foundation. Classes of Reinforced-Concrete Walls. Reinforced-concrete retaining walls may be divided into three classes : i. Walls without counterforts; 2. Walls with counterforts; 3. Walls restrained at top and bottom. Walls without Counterforts. This type is generally economical for walls of low or medium height. More material is used than in Concrete Retaining Walls a wall with counterforts, but the decreased cost of form work and of placing the reinforcing and concrete will, in a wall of average height, more than offset the cost of the extra material. These walls are simple in form, consisting of a thin reinforced vertical wall rigidly attached to a base formed by a reinforced- concrete slab. The vertical wall acts as a cantilever, with its maximum bending moment at the upper face of the base. This also is the point of maximum shear, and the vertical wall should be designed accordingly. As the bending moment and shear de- crease, as the top of the wall is approached, the thickness of the wail and the amount of reinforcing may also be decreased. The base at the heel also acts as a cantilever, and must resist the weight of the earth resting upon it. The moment and shear are maximum at the rear of the vertical wall and the base should be designed accordingly. The toe of the wall also acts as a cantilever resisting the upward thrust of the earth caused by the tendency of the wall to overturn. It takes its maximum moment and shear at the face of the vertical wall. Walls with Counterforts. These walls consist of a broad base, a thin, vertical, curtain wall, and ribs or counterforts spaced 3 to 10 feet on centres, connecting the base with the vertical wall. This type of wall is very economical of material, and this economy increases in proportion to the height. The cost of form work, however, is great, and except in the case of high walls, the wall without counterforts is generally more economical. In this type of wall the bending moment produced by the earth pressure is resisted entirely by the counterforts. The vertical wall acts like a floor slab and transmits the horizontal earth pressure to the counterforts. The base at the back of the wall also acts as a floor slab, carrying the weight of the earth above it, and serving as an anchorage to the counterforts. That portion of the base in front of the vertical wall should be designed as a cantilever, fixed into the wall, and resisting the upward pressure of the earth, caused by the tendency of the wall to overturn. The counterforts should be designed to take care of all stresses due to overturning. Sufficient horizontal and vertical reinforcing rods should be placed in the counterforts to properly tie them to the face wall and base. Handbook for Cement and Concrete Users In the foregoing types of walls the walls should be so proportioned that the maximum pressure at the toe does not exceed the safe bear- ing value of the soil. Walls Restrained at Top and Bottom. Cellar walls and walls with land ties are of this type. They may consist, in a cellar wall, of a slab reinforced vertically to withstand the pressure of the earth backing, and supported by the adjacent floors, or the slab may be reinforced horizontally carrying the load to vertical beams which in turn are supported by the adjacent floors. A wall with land ties is similar with the exception that a horizontal 8 1 82 83 FIGS. 81, 82, 83. Sections of Typical Types of Concrete Foundation Walls. girder extending from tie to tie is necessary to properly deliver the load to the land tie. The resistance to sliding in a wall of this type depends on frictional resistance and the abutting power of the earth in front of the face at its toe. Details of Construction. In the construction of retaining walls, of both plain and reinforced concrete, the same general rules apply as to quality of material, details of form work, placing, and in- spection, as are given for other structures; the difference between the plain and reinforced concrete being that in the former a much larger aggregate can be used both for the purpose of adding weight and saving cement, and it is excellent practice in the construction of large gravity walls, to employ a rubble concrete, or to embed in successive layers of concrete large blocks of stone. Concrete Retaining Walls The special points which must be looked for in the construction of retaining walls of any type are : 1. The preparation of a secure and satisfactory foundation below the frost line (2 to 4 feet, depending upon the climate). 2. The drainage of the foundation and removal of springs, etc., under same. Removal of poor material, stepping of rock surfaces, etc. 3. The construction of a drainage system behind and adjacent to the back of the wall, by means of gravel, channels, or other means and outlets, as weepers or pipes through the wall to carry off the water. 4. The compacting of the material or backing behind the wall (except that immediately adjacent) to reduce the pressure on same as much as possible. 5. The construction of a substantial coping along the top of the wall. 6. Expansion joints should extend through the walls either directly or by means of special connections to prevent temperature cracks. These may be 20 to 30 feet apart in plain concrete walls and 40 to 50 apart in reinforced walls, the reinforcement helping materially to avoid such cracks. Five per cent additional reinforce- ment will usually be sufficient for this purpose. Foundations for Retaining Walls. The management of the foundation of a retaining wall is an important matter, and it is generally admitted that a large majority of the failures of retaining walls are due to defects in the foundations. The nature of the soil should first be determined, and tests made to ascertain its bearing capacity, and the wall then so proportioned that no portion of the soil shall be overloaded. If necessary, the bearing capacity of the soil may be increased by: i. deeper excavation; 2. drainage; 3. consolidating the soil; or, 4. by means of sand piles. If none of the above methods give satisfactory results, piles of either timber or reinforced concrete must be used. If the foundation is on rock it is only necessary to cut away the loose and decayed portion of the rock and to dress it to a plane as nearly perpendicular to the direction of the pressure as possible, any fissures being filled with concrete. Other methods of providing adequate foundations are described in Chapter XXI. [253] Handbook for Cement and Concrete Users Drainage. Next to faulty foundations, water behind the wall is the most frequent source of failure of retaining walls. The water not only adds to the weight of the backing material, but also softens the material and causes it to flow more readily, thus greatly increasing its lateral thrust. To guard against the possibility of the backing becoming saturated with water, holes, called weep holes, are left through the wall. The holes should be spaced generally from i to 3 sq. yds. of face of wall. When the backing is clean sand the weep holes will allow the water to escape; but if the backing is retentive of water, blind drains should be placed in back of the wall and lead the water to the weep holes. Land Ties. Retaining walls may have their stability increased by being anchored to a suitable anchorage embedded in a firm strata of earth a distance behind the wall. The amount of load taken by these rods will depend on their position in the face of the wall. If they are fastened to the wall at the top, they will take one-third of the total earth pressure. If they are fastened in the wall at one-third the height from the top, they will take one-half the total pressure. Relieving Arches. In extreme cases the pressure of the earth may be sustained by relieving arches. These consist of one or more rows of arches having their axes at right angles to the face of the bank of earth. Their front ends may not be closed, which then prevents the appearance of a retaining wall, although the length of the archway is such as to prevent the earth from abutting against the wall. Concrete Abutments. An abutment has two offices to perform: i. to support one end of a bridge; 2. to act as a retaining wall. There are four forms of abutments in more or less general use : 1. A straight abutment a plain wall with or without wings. 2. Wing abutment wing walls make an angle with the face of the abutment (usually about 30 degrees). 3. U-abutment when the ring makes an^ angle of 90 degrees with the face of the abutment. 4. T-abutment when the wings are moved to the centre of the abutment and merged into one stem. The dimensions of an abutment are to be determined as for a retaining wall. These dimensions must be such that the abutment can safely carry the superimposed load. [254] Concrete Retaining Walls The form of abutment adopted in any case will depend on the locality. If the shore is flat, and not liable to be cut away by the current, a straight abutment will be sufficient and most economical. However, this form is seldom used owing to the danger of the water flowing along immediately behind the wall. When there is a contraction of the waterway at the bridge site, a wing abutment may be adopted, since the deflecting wing walls, above and below, slightly in- crease the amount of water that can pass. The use of U- and T-abut- ments seems to be mainly a matter of choice. To equal amounts of masonry wing abut- ments give better protection to the embankment than either U- or T-abutments. The latter are more stable, as the centre of gravity of the masonry is farther back from the line of the face of the abut- ment, about which line the abutment will turn or along which it will crash. Reinforced - Concrete Abut- ments. When reinforced con- crete is used to replace masonry in abutments a considerable reduction in cost will result. The construction usually consists of a rectangular slab for a base, whose width will depend on the load to be distributed. Counter- forts transmit the load from the bridge seat to the base. A face wall heavy enough to resist the earth pressure is firmly anchored to the counterforts. The face wall may continue beyond the bridge seat so as to form wing walls, which in reality are nothing more or less than retaining walls. The bridge seat consists of a heavy reinforced-concrete slab supported by the counterforts. A parapet wall at the back and ends of the bridge seat forms the mud wall. The construction and design of the reinforced-concrete abutments [255] FIG. 84. Forms of Concrete Abutments. Handbook for Cement and Concrete Users closely resemble the construction and design of a reinf orced-concrete retaining wall, with the exception of the bridge seat and supporting counterforts. It is desirable, if possible, to place the main but- tresses directly under the girders or trusses, thereby eliminating bending in the slab forming the bridge seat. Bulkheads. Bulkhead walls are essentially retaining walls having a large portion of their depth under water. This makes the calculation of their dimensions much more complicated than the ordinary wall, and the computations are still further complicated by the varying densities of the materials adjacent to the wall. FIG. 85. Reinforced Concrete Abutment. In Fig. 86 is shown a typical section of a bulkhead wall ex- tensively employed in New York City. The forces acting for stability are : 1. The weight of the submerged portion of the wall. 2. The weight of the exposed portion of the wall. 3. The vertical pressure of the water. The forces acting against stability are: 1. The horizontal pressure of the water. 2. The pressure of the earth filling. 3. The live load on the wall. The amount and position of the resultant pressure of all these op- posing forces must be found in order to properly proportion the wall. The type of bulkhead wall depends upon the character of the foundation. On rock foundations the area is dredged and the rock cleaned and stepped off when too smooth. Concrete is deposited in accord- ance with methods outlined in Chapter VII. Divers then smooth off the surface with mortar to receive the concrete blocks. These blocks weight about 70 tons, being 17X6X12 feet. Upon these heavy foundation blocks, granite with concrete backing is laid, and the riprap deposited as filling. [256] Concrete Retaining Walls The Hennebique Construction Company and several others have patented methods of building bulkhead walls of reinforced concrete by constructing portions on shore, floating them to place and sinking by depositing concrete in prepared chambers. While the method has been employed in Europe, it has as yet been little tried in this country : Appearance of Retaining Walls. While the object of the retain- ing walls mainly is utility, pleasing and aesthetic appearance may FIG. 86. Concrete Blocks in New York City Bulkheads. be obtained at but slight additional cost, and often at no additional cost whatever. The maintenance of a pleasing surface once obtained depends upon the construction and materials in and about the walls. We frequently see long stretches of carefully shaped and built walls disfigured by rust and smoke stains, efflorescence, checks, and cracks, and other disagreeable causes. In most cases these may be avoided by the use of a rough instead of smooth surface finish, and the avoidance of ironwork above the wall, the rust from which, carried down by water, is the cause of the rust stains. Efflorescence may largely be avoided by adding a small i? [ 2 57] Handbook for Cement and Concrete Users percentage of water-repellant compound to the cement in the concrete placed against the exposed surface forms. This will render the surface water-repellant and prevent absorption during rainstorms, which bring out the stain. t The prevention of percolation of water through walls and arches is frequently desirable and is readily effected by enveloping the structure in a 2 or more ply bituminous shield, using the mem- brane method as described in the chapter on waterproofing. With this on the earth side, and the surface, water-repellant, the wall will maintain its fresh appearance if iron work above it is avoided, or proper drainage from same provided, and if a crack- free surface has been obtained. The disfigurement by smoke and locomotive gases can be avoided only in one way: by giving the face of the wall a dark color during construction so that such staining will not be noticeable. Considering the large amount of money spent by the railroads to obtain pleasing effects in concrete work, it seems wrong to construct surfaces which particularly invite such disfigurement from the very start. [258] Concrete Retaining Walls TABLE XXII. EARTH PRESSURES.* Angle of Repose = = 33 Degrees. Depth, in ft. ' Total Inclined Press. Total Hor. Press, per lin. ft. Hor. Press, per Square Foot. Depth, in ft. Total Inclined Press. Total Hor. Press, per lin. ft. Hor. Press, per Square Foot. 5 335 280 112 2 3 7080 5935 5i6 6 480 405 135 24 7710 6460 538 7 655 55 157 25 8365 7 OI 5 56i 8 855 720 1 80 26 945 7585 ' 583 9 1085 910 202 27 9755 8180 606 10 1340 II2O 224 28 10490 8800 628 n 1620 1355 2 4 6 29 11255 9435 650 12 1930 1615 269 3 12040 IOIOO 673 r 3 2260 1895 291 3 1 12860 10780 696 14 2625 22OO 3*4 3 2 13700 11490 718 15 3010 25 2 5 337 33 1457 I222O 741 16 3425 2870 359 34 15455 12960 763 J 7 3865 3 2 45 38i 35 16390 !3745 785 18 4335 3635 404 36 17340 14540 808 *9 4830 4050 426 37 18315 i53 6 o 830 20 5350 449 449 38 19320 16200 853 21 5900 495 471 39 20350 17065 875 22 6475 543 493 40 21410 17950 896 cos eh 2 = . i 33 Seh? for 0=33 Earth Level. Total Inclined Pressure = 2(1 + sin \/2) Total Hor. Pressure = 11.22 h 2 acting at depth = 2/3 h. Note. e = 100 Ibs. per cu. ft.; h = depth in feet. TABLE XXIII. THICKNESSES or WALLS AND QUANTITIES or MATERIALS FOR DIFFERENT HEIGHTS OF BASEMENTS. Proportions: i Part Portland Cement to 2^ Parts of Sand to 5 Parts of Gravel or Stone. Height of Basement. Depth of Foundation Below Ground Level. Thickness of Wall at Bottom. Thickness of Wall at Top. Cement per 10 Feet of Length of Wall. Sand per 10 Feet of Length of Wall. Gravel or Stone per 10 Feet of Length of Wall. Feet. Feet. Inches. Inches. Bags. Cubic Feet. Cubic Feet. 6 4 6 6 6 14 l /a 29 8 6 10 8 12 29 58 10 8 15 10 24 57 114 * Trussed Steel Concrete Co. [259] Handbook for Cement and Concrete Users TABLE XXIV. DIMENSIONS OF GRAVITY RETAINING WALLS AND QUANTITY OF MATERIALS FOR DIFFERENT HEIGHTS OF WALLS.* Proportions: i Part Portland Cement to 2^ Parts Sand to 5 Parts Gravel or Stone. Qi Is *o ^-J | AMOUNT OP MATERIALS PER ONE > j3 ct Oj > r^ FOOT LENGTH OF WALL. -. S 5?=: i a? Mh-5 "rt "GO ^ oj C- M C Tl t/5 -u " Ew ^ rX Q ^c 0) 11 1 g .a s 9 H Cement. Sand. Gravel or Stone. Feet. Feet. Ft. In. Ft. In. Inches. Bags. Cu. Ft. Cu. Ft. 2 6 2 2 i 6 10 if 4K 9 3 7 2 5 i 7K IO 2K 5^ ii 4 8 2 9 i ii 12 3 7 14 5 9 3 2 2 I 12 3K 9 18 6 10 3 6 2 4M 15 4f ii K 23 7 ii 3 1 2 8 18 6 14 28 8 12 4 2 2 10 18 7 16* 33 FIG. 87. Section of Gravity Retaining Wall Note. A large single load of sand or gravel is about 20 cu. ft. A large double load of sand or gravel is about 40 cu. ft. * From " Concrete Construction about the Home and on the Farm," published by the Atlas Portland Cement Co, [260] CHAPTER XXIII CONCRETE ARCHES AND ARCHED BRIDGES Definitions. Parts of an Arch. Methods of Failure. Design of an Arch. Abut- ments and Piers. Reinforced-Concrete Arches. Arch Bridges. Arch Centres. Concreting the Arch. THE value of the arch as a structure of great beauty and economy has been known for many thousands of years, and while many elabo- rate arches have been constructed of the finest stones, it has remained for the present generation to see arches of masonry of such light sections and such beautiful lines as to challenge the admiration of observers. This combination of beauty, lightness, and consequent economy has been rendered possible only by combining in the arch the resisting power of steel in tension and of concrete in compression, as described in this chapter. DEFINITIONS PARTS OF AN ARCH Soffit. The inner or concave surface of the arch. Intrados. The line of intersection between the soffit and a vertical plane normal to the axis of the arch. Extrados. The line of intersection between the outer surface of the arch and a vertical plane normal to the axis of the arch. Crown. The highest point of the arch. Skewback. The inclined surface on which the end of the arck rests. Abutment. A skewback and the masonry which supports it. Springing Line. The inner edge of the skewback. Haunch. That part of the arch between the crown and the skewback. Spandrel. The space between the extrados and the roadway. Spandrel Filling. Material placed on top of arch between spandrel walls. It may be either earth or masonry, or a combina- tion of both, or a system of relieving arches which carry the roadway. Handbook for Cement and Concrete Users Span. The perpendicular distance between springing lines. Rise. The vertical distance between the highest of the intrados and the plane of the springing line. Voussoirs. The wedge-shaped stones of which the arch is composed also called arch stones. Keystone. The centre or highest voussoir or arch stone. Springer. The lowest voussoir or arch stone. Kind of Arches. Circular Arch. One in which the intrados is an arc of a circle. Semi-circular or Full-centred Arch. One whose intrados is a semi-circle. Segmental Arch. One whose intrados is an arc of a circle but less than a semi-circle. Elliptical Arch. One whose intrados is part of an ellipse. Basket Handle Arch. One whose intrados resembles a semi- ellipse, but which is composed of arcs of circles tangent to each other. Pointed Arch. One in which the intrados consists of two arcs of equal circles intersecting over the middle of the span. Catenarian Arch. One whose intrados is a catenary. Right Arch.^Any arch terminated by two planes normal to the axis of the arch. Skew Arch. Any arch terminated by two planes that are not normal to the axis of the arch. Groined and Cloistered Arches. Those formed by the inter- section of two or more arches, each having the same rise, and with axes in the same planes. In concrete, only right arches need be considered, as any skew arch may be regarded as composed of a number of infinitely short right arches. This treatment for masonry skew arches is also quite common in this country, the arch being made of a number of short right arches or ribs, in contact with each other, but with each successive rib off centre slightly from the preceding one. Line of Resistance. At any joint in an arch the forces acting may be replaced by a single force, so situated as to be in every way the equivalent of the distributed forces it replaces. The line con- necting the points of application of these forces is the line of resist- ance of the arch. [262] Concrete Arches and Arched Bridges Methods of Failure. An archway may fail in any of the four following ways: 1. By Crushing. An arch will fail by crushing if the pressure on any part is greater than the crushing strength of the material used. This may be caused by too light an arch being designed or by the line of resistance passing too far from the centre line of the archway. 2. By Sliding of One Voussoir on Another. An arch will fail by this method when the line of resistance makes, with the normal at any joint, an angle greater than the angle of friction for the joint. This type of failure is unlikely in a concrete arch, as, owing to its homogeneous construction, the angle of friction is very large. Tens/on FIG. 88. Failure of Arch by Flattening FIG. 89. Failure of Arch by Flat- of the Crown. tening of the Haunches. 3. By Rotation About the Edge of Some Joint. If the arch were incompressible, failure of this type could occur only when the line of resistance touched the intrados at two points and the extrados at one higher intermediate point, or vice versa. In a compressible arch, and all masonry arches are compressible, failure by crushing would probably occur before the conditions necessary for failure by rotation could be realized. 4. Because of Unsatisfactory Foundations. More arches fail because of unsatisfactory foundations than for any other reason. Failure of this type is due either to unequal settlement, rotation, or sliding of the abutments. Design of an Arch. There are several theories for the design of an arch, each of which is complex and at best only an approxima- tion. In practically all theories the stability of the arch depends on the position of the line of resistance. The position of the line of resistance is influenced greatly by the external forces acting on the [263] Handbook for Cement and Concrete Users arch. These external forces may be divided into three parts: i. The moving or live load; 2. The permanent or dead load, which includes the weight of the spandrel filling and the weight of the arch itself; 3. The pressure or thrust of the spandrel filling. This pressure is more or less indeterminate. In the case of the spandrel filling being earth, it may take any value between the pressure of earth due to its own weight only, and the abutting power of the earth. In the case of the spandrel filling being masonry, the value of the pressure may vary between the limits of zero and the working resistance to compression of either the backing or ring stones. In the design of an arch, it is customary to limit the position of the line of resistance to the middle third of the arch ring, in which case there could be no tension in the ring, and therefore no tendency for the joint to open. It does not follow, however, that the joint will necessarily begin to open if the line of resistance fall outside the middle third of the arch ring, or that the stability of the arch is necessarily endangered. If the greatest intensity of stress does not exceed the ultimate resist- ance to compression of the material, there can be no opening, except that due to the elasticity of the material, which is not considered. Abutments and Piers. As before stated, most arch failures are caused by the failure of the abutment due to unsatisfactory founda- tions. Such failure may occur in either of three ways: i. By overturning of the abutment; 2. By sliding of the abutment; 3. By settling of the abutment. 1. Failure by overturning is usually caused by the pressure at the base of the abutment exceeding the bearing capacity of the soil. A failure of this type cannot occur when the line of resistance falls at the centre of the base, as, in order that rotation shall take place, the pressure on the soil at one side of the abutment must be larger than at the other. 2. Failure by sliding of the abutment is caused by the thrust of the arch being greater than the sum of the friction between the abutment and the soil on which it rests, and the pressure of the earth behind the abutment. In an extreme case where the abut- ment is very high, the pressure of the earth behind the abutment may be greater than the thrust of the arch plus friction at the base [264] Concrete Arches and Arched Bridges of the abutment, in which case the abutment would fail by sliding forward. Hence, for a large arch under a light surcharge, the abutment should be proportioned to resist the thrust of the arch; but for small arches with a heavy surcharge, the abutment should be proportioned as a retaining wall. 3. Failure by settlement of the abutment implies a load on the foundation greater than its bearing capacity. This load on the foundation will be practically uniform as otherwise failure would occur by the overturning of the abutment. As a safeguard against failure in a masonry arch, it is necessary (i) to limit the position of the line of resistance to the middle third of the arch ring, (2) not to permit the unit stress to exceed in inten- sity the safe crushing strength of the material employed; and (3) not to allow the pressure on the soil to exceed its safe bearing value. REINFORCED-CONCRETE ARCHES While concrete is a more economical material for arches than cut stone and is now replacing masonry to a great extent, a still greater economy may be realized by the use of reinforcement. Design. The method of designing an arch of reinforced concrete is practically the same as that employed in the design of a plain structure. The position of the line of resistance need not, however, be so rigidly fixed as in the plain arch ; also the intensity of stress may exceed the crushing strength of the concrete, as by introducing sufficient steel, a resistance to crushing equal to this higher intensity may be easily obtained. In any arch, should the line of resistance fall outside the middle third of the arch ring, tension is developed at one end of the joint and an increased compression at the other end. In a plain concrete arch the tension would tend to open cracks in the arch, as previously described. In a reinforced arch, this tension would be taken by the reinforcement placed there for that purpose, so that the opening of cracks would be impossible. General Types of Reinforced-Concrete Arch Bridges. There are two types of reinforced-concrete arch bridges. The first type, and the one most generally used in this country, consists of an arched slab, the full width of the bridge, extending from abutment [265] Handbook for Cement and Concrete Users to abutment. This arched slab supports the spandrel filling, or the system of relieving arches, which in turn carries the roadway. This type of arch is similar in all respects to the masonry arch, except that owing to the introduction of the steel reinforcement, higher unit stresses may be permitted, thus making a longer span possible. The second type might well be called an arched-rib bridge. This type has been but little used in this country, but has been ex- tensively employed abroad, particularly in France. A bridge -of this type consists of a series of heavily reinforced arched ribs. The ribs support a series of columns, which in turn support the beams and slabs that go to form the roadway. This type of bridge is considerably lighter than the arched-slab type and is therefore more economical of material. The cost of form work, however, is higher. A modification of the arched-slab type of bridge is the Suten Arch. The difference lies in the horizontal thrust being taken up by ties between the abutments, underneath the bed of the stream which are embedded in concrete. The usual heavy abutments, where the foundation is not of rock, are thus dispensed with. This system of tying the abutments may also be used in the arched-rib type of bridge. Arches of the above types may be built either as continuous from abutment to abutment, or as two or three hinged arches. Either style of construction, if properly constructed, will give entire satisfaction. The advantages of a reinforced-concrete arch may be sum- marized as follows: (i) Such a structure is more economical than a masonry arch; (2) the cost of maintenance is less than that required for a steel bridge, and (3) Its life is longer than that of a metal structure. (4) Its light weight sometimes makes it possible to construct a reinforced-concrete arch where a masonry arch would be practically impossible. (5) The materials necessary are always easily obtain- able, and usually in the vicinity of the work. Another advantage of reinforced-concrete arches is their stiffness under shocks, and the small deflection under heavy loads. This has been shown repeatedly in actual practice and in special tests. [266] Concrete Arches and Arched Bridges [267] Handbook for Cement and Concrete Users Perhaps the most thorough tests in this line were those carried on at the bridge at Chatellnault, Vienne, France. This bridge is 443 ft. long and composed of three arches whose spans are 135, 164, and 135 ft., respectively. On the removal of the forms this bridge was subjected to the following test. 1. Each day the spans were loaded, first over their total length, then on each half, then in the middle, with sand at the rate of 165 Ibs. per sq. ft., on the. roadway and 123 Ibs. per sq. ft. on the side- walk. The maximum deflections under these loads were, end spans 1/4 inch or 1/7300 of the span, centre arch 13/32 inch or i / 5000 of the span. 2. One 1 6-ton steam roller, two 1 6-ton two-axled carts, six 8-ton one-axled carts, total weight, including horses, 100 tons, passed at once over the bridge, the sidewalk at the same time carrying a load of 80 Ibs. per sq. ft. 3. 250 soldiers (infantry) crossed the bridge, first in regular marching step, second in double time. The maximum deflection under these tests did not exceed 1/9000 of the span, and all vibration ceased almost immediately on the removal of the load. Arch Centres. A centre is a temporary structure for supporting an arch while in process of construction. It is usually made of a number of circular ribs spaced a few feet apart, and lying in a plane perpendicular to the axis of the arch. These ribs are covered with narrow planks (lagging), running parallel to the axis of the arch, upon which the arch rests while in course of construction. In concrete arches, except in those that are very flat, provision for maintaining the extradosal line of the arch must also be made. All centres should be made as strong and as rigid as possible, as any deformation of the centre due to insufficient strength or improper bracing will cause a corresponding change in the intrados of the arch, and consequently in the line of resistance, and may endanger the whole structure. Arch centring in general may be divided into two classes. ' In the first class the ribs are supported by struts braced together so as to form transverse bents. These bents are spaced at convenient distances along the axis of the arch and braced longitudinally. Where the subsoil is sufficiently firm, the struts may rest on mud [268] Concrete Arches and Arched Bridges sills, but in poorer soil temporary masonry or pile foundations are frequently used. In the second form trusses are employed. These trusses may carry the lagging directly, in which case they must conform to the curve of the intrados of the arch, or they may support short braces which in turn support the ribs. Where trusses are used they should be cambered slightly so that after deflection the arch may be of the desired curvature. The ribs are usually made of planks spiked together so as to break joints, and cut to a curve parallel to the intrados of the arch, but a sufficient distance below it so that the lagging, when applied, FIG. 91. Centre for 50 ft. Arch Span (supported). shall coincide with the intrados of the arch. Sometimes the ribs are steel shapes bent to the desired curvature. In order that the centres may be struck, or lowered, uniformly and without shock, either sand boxes or wedges are used under all of the supports. The wedges usually consist of a pair of folding wedges, preferably of hard wood, having a slight taper. This taper should vary with the- span of the arch, the longer the span the less the taper. To lower the centres equally the wedges should be driven back uni- formly. To facilitate this, compound wedges are sometimes used. By driving the wedge all work resting on the wedge will be lowered uniformly. [269] Handbook for Cement and Concrete Users Sand boxes usually consist of a steel cylinder in which sand is confined. A wooden plunger rests on the sand, and on these wooden plungers is carried the centring of the arch. Near the bottom of the cylinder is a plug which may be withdrawn and replaced at pleasure, by means of which the outflow of the sand is regulated. As the sand is allowed to escape, the centres will lower and the amount of this lowering can be easily controlled by the amount of sand allowed to escape. In using sand boxes particular care should be exercised first to secure a proper sand, and second to exclude all Cn>ss Stringer FIG. 92. End View of Centre for Short Elliptical Arch Spans. foreign material from the boxes, which must also be properly sealed. Where any of these precautions are lacking trouble is likely to be experienced either through the sand flowing prematurely, or its failure to flow at the proper time. The type of centres to be used in any case will depend entirely upon local conditions. Where it is desirable to obstruct the opening as little as possible, the trussed form of centring would probably be best adapted. In other cases where the restriction of the opening is of little or no importance, bents would probably be the most economical and satisfactory. [270] Concrete Arches and Arched Bridges Concreting the Arch. For convenience in concreting, an arch is frequently divided into a number of strips, which are practically arches in themselves. In all cases the concreting should be carried up from the springing line toward the crown, uniformly on each side of the arch. While this concreting is in progress the action of the centres should be carefully observed. Generally as the load on the haunch increases, the crown will tend to rise. If this tendency becomes excessive, it may be overcome by loading the crown with any material that is convenient, or by placing the concrete for that foot Blocks. &&*%/> El-o NEWS. P~~I tlova-ri FIG. 93. Travelling Form for Roof Arch, New York Subway Tunnels. portion of the arch before proceeding further with the haunches. It is well, if this method of placing the concrete is used, to so divide the arch that a complete ring .may be placed without intermis- sion. Another method is to divide the arch in strips extending the full width of the arch. The strips are first placed near the springing line, then, to overcome the tendency of the crown to rise, the strip at the crown is placed and so on until the arch is completed. Backfilling. Backfilling is usually begun after the arch has hardened but before the centres are struck. The reason for this is obvious. If the filling were placed after the removal of the centres, it would be necessary to place the filling uniformly over the [271] Handbook for Cement and Concrete Users arch, as filling a large weight on one side while the other is unloaded might so seriously deform an arch as to endanger its safety. On the other hand, when parapet wall and railing are built before the centres are removed, the settlement of the arch may cause these to crack badly, and while this would in no way endanger the safety of the arch, still it is unsightly and therefore to be avoided. It would therefore appear that in some cases, particularly, where, instead of earth backfill, a system of relieving arches, etc., are used, that when possible the centres should be removed and the arch allowed to settle in place before that portion of the work above the arches is begun. A properly designed and executed concrete or reinforced arch, is economical, permanent, strong, rigid, and last but not least, can easily be made a thing of beauty. Various concrete arch bridges have been built where the effect is as pleasing as the best stone arches, and at a considerable saving in cost. Also the introduction of reinforced, concrete permits of a light, graceful arch being built which is not attainable in stone masonry. [272] CHAPTER XXIV CONCRETE BEAM AND GIRDER BRIDGES Advantages of Concrete Bridges. Kinds of Girder Bridges. Reinforced-Concrete Trusses. Viaducts. Concrete Floors. Abutments. Centring. Depositing Concrete. Surface Finish. Advantages of Concrete in Bridge Work. The use of concrete in bridges was, until quite recently, limited to the arch. This limitation was caused by the low tensile strength of concrete, and where, for any reasons, the arch was considered undesirable, the use of steel or timber became necessary. With the introduction of reinforced concrete, however, the limitation of concrete work ceased to exist, as by the proper placing of steel reinforcement, the concrete could be relieved of all tensile stresses, and at the same time its great compressive strength called into play. We, therefore, at the present time, find not only arches of reinforced concrete, but also various types of flat bridges, and in a few cases even trusses constructed of this reliable material. Bridges, of all engineering structures, are probably the most exposed to the action of external destructive forces, and at the same time receive the severest load treatment. In bridges of steel or wood, constant inspection, painting, and repairing are necessary if the structure is to be kept in anything like first-class condition, and even when these are carried on, almost continually, periodic renewals will be necessary. This causes the cost of maintenance to be very high, and this cost of maintenance is a large and important factor in the final cost of the bridge. With concrete bridges this continual painting and repairing is entirely unnecessary and the cost of maintenance is therefore very small. Also as concrete increases in strength with age, and as it is in no way affected by atmospheric conditions, a well designed and constructed concrete bridge may be said to be everlasting. A 18 [273] Handbook for Cement and Concrete Users concrete bridge, therefore, when once built is built for all time, and periodic renewals are entirely obviated. The initial cost of a concrete bridge is therefore practically its final cost. It would appear, moreover, that even should the first cost of a concrete bridge be considerably higher than the initial cost of a steel or timber structure, that in view of its extremely long life and very low cost of maintenance, a concrete bridge would be the most economical in the end. The initial cost of a concrete bridge, while somewhat greater than that of a timber structure, is frequently lower than the first cost of a steel bridge. In localities where suitable sand, gravel, and broken stone are easily available, necessitating the transportation of only a comparatively small amount of cement, and reinforcing steel, the initial cost of a concrete bridge will be considerably less than that of a steel bridge, and will approach very closely the first cost of a timber structure. Another advantage of concrete bridges is that the major portion of the work can be readily done by local labor, and a great portion of the material can be purchased locally. Thus a large percentage of the money spent in the construction remains in the community, and the community is therefore doubly benefited. Traffic passing over a concrete bridge makes little or no noise. The same amount of traffic passing over a steel or timber bridge would cause a noise that would be heard for a considerable distance. This is particularly true where either steam or electric cars form part of the traffic. This elimination of all noise is particularly desirable in built-up communities, such as cities and large towns. Concrete, before 'it has set, is extremely plastic, and can there- fore be moulded into practically any shape or form desired. Thus in building a bridge of concrete, a very pleasing and artistic design may be executed, at but a small increase of cost, resulting in an efficient and beautiful bridge. With but few exceptions steel bridges are far from being things of beauty, and at their best, can in no way compare with concrete structures. Classes of Concrete Bridges. Concrete bridges may be classified as either arch bridges or flat bridges. Arch bridges of both plain and reinforced concrete have been discussed in the preceding chapter. A flat bridge is one in which the load on the structure acts vertically [274] Concrete Beam and Girder Bridges on the supports. A flat bridge may consist of either a straight flat slab, or of a combination of beams and slabs or of a combination of beams, girders, and slabs. All flat bridges require reinforcement. Flat- Slab Bridges. The simplest form of a reinforced -concrete bridge is the flat slab. This consists of t a sheet of concrete of uniform thickness, supported at each end. It is designed as a slab whose span is the distance between the abutments. The main reinforcement, therefore, extends from abutment to abutment, and may be of any of the numerous forms of reinforcing bars common to reinforced concrete. Structural shapes and even old railroad rails have been used in this capacity, and have given complete satisfaction. A secondary reinforcement perpendicular to the longitudinal bars or shapes should be placed in all bridges of this type. The function of this secondary reinforcement is to aid in the distribution of stresses due to concentration, to take temperature stresses, and to prevent the formation of cracks. Generally no special pro- visions for shear are necessary in flat slabs. It is customary, however, to bend a portion of the main reinforcement up to the top of the slab near the point of support. Should the bridge be continuous over two or more spans, additional reinforcement should be placed at the top of the slab, over the points of support, to take the tensile stresses caused by the negative bending-moment. Bridges of this type will generally be found economical for spans up to 15 feet. For larger spans the thickness of the slab and, hence the dead load, becomes excessive, and some other type of bridge should be used. Beam-and-Slab Bridges. Beam-and-slab bridges consist of two or more reinforced-concrete beams extending from abutments to abutments and supporting a slab on which the roadway is laid. These beams are in the majority of cases entirely below the slab, but in some instances are carried up above the slab to form the side rail. The design of a beam-and-slab bridge is essentially the same as that of a slab and beam in ordinary floor construction. The slab is supported by the beams and carries the superimposed live and dead loads. The beams are supported by the abutments and carry the slab with its attendant live load. The beams must be carefully [275] Handbook for Cement and Concrete Users investigated for shear and where necessary for this purpose additional reinforcement should be introduced. Where the beams are entirely below the slab they may be con- sidered as T-beams and designed as such. In this case the slab and floor beams should be poured at the same time so as to assure a proper bonding of the slab and beam. Bridges of this type, on account of their low cost and light weight, are particularly adapted to light highway bridges, etc., and are economical in general for spans up to 20 feet. Girder Bridges. Girder bridges are usually composed of two or more large reinforced-concrete girders supporting intermediate beams, which in turn carry the slab on which the roadway is laid. In designing a girder bridge, the slabs are designed to carry the superimposed loads to the beams. The beams are designed to V i Fro. 94. Typical Reinforced-Concrete Girder Bridge. carry the loads to the girders, and the girders are designed to carry the loads to the abutments. Both the beams and the girders should be carefully investigated for shear and where necessary reinforcing for this purpose should be introduced. The girder should also be carefully investigated to see that sufficient compressive strength is obtained in their upper portion. Steel for temperature stresses and to prevent cracking should be placed where necessary throughout the structure. Girder bridges have been constructed with spans as great as TOO feet. They are not, however, economical for such long spans and should be used for these only where the restriction of the water- * way or poor foundations make the arch inadvisable. In some girder bridges the girders have been designed as canti- levers at the points of supports, and carrying a simple span at the [276] Concrete Beam and Girder Bridges centre. In such cases the girders are deepest at the abutment, and have somewhat the appearance of an arched rib. The position of the reinforcement is, however, radically different. If some of the very flat arches had been designed thus instead of as arches, the unsightly cracks over the haunches so common to them would probably have been avoided. Reinforced-Concrete Trusses. A true truss of reinforced concrete was constructed by Considere in France. The compression mem- bers were of concrete reinforced by spiral hooping as in a hooped column. The tension members were of steel surrounded by concrete. This bridge was built only as a test of the strength of the hooped member and when finished was loaded until failure took place. It demonstrated, however, that bridges of this type may be built in reinforced concrete. The economy of such a bridge is doubtful, as the cost of form work must have been excessive. Girder bridges are occasionally constructed with open webs. The girder is thus given the appearance of a truss. Beyond the saving of a little weight, this type of bridge has no advantage over a bridge with a solid girder, and as anything approaching an exact determination of the stress acting in the open girder is impossible, they should be avoided. Concrete Floors for Steel Bridges. In long- span highway bridges, when steel trusses, are necessary, the wood planking, which until recently was the standard flooring, is now being largely re- placed by reinforced-concrete slabs, supported on the steel beams. On these slabs the wearing surface of the roadway is placed. A floor of this type is more expensive in- first cost than a plank floor, but it will outlast the bridge itself, while a wood floor requires re- newing in from one to five years. In steel railroad bridges, reinforced-concrete floors are now being extensively used to replace trough and open floors. These reinforced-concrete floors are practically noiseless, and may be ballasted in the same way as the rest of the roadway, thus making a uniform roadbed throughout the line. Reinforced concrete may also be used to strengthen existing steel bridges when same have become insufficient for the present need, or so badly corroded as to be considered dangerous. In the bridge at Perigueux, France, the lattice bars of the main girders [277] Handbook for Cement and Concrete Users and the webs of the cross beams were so badly corroded by the gases from locomotives stopping under them that the safety of the bridge was threatened. The bridge was protected and strengthened by incasing all the old steel members in reinforced concrete, and a new reinforced-concrete floor was then built. This resulted in a new bridge, stronger and stiffer than the old one, that would not be acted upon by the gases from the locomotives. If it had been necessary, the strength of the bridge could have been still further increased by the addition of reinforcing rods parallel to and along- side of the beams and girders. Abutments. The abutments of a concrete bridge may be constructed in either plain or reinforced concrete. They should be designed to resist overturning due to the pressure of the earth backing, and at the same time to so distribute the load on the foundation caused by this pressure, and the load of the bridge, that in no place will the load on the soil exceed its safe bearing value. In some cases the bridge is rigidly attached to the abutments while in others it simply rests in the seat. In the first case all tendency of the bridge to expand or contract, due to temperature stresses, must be resisted by the abutments or internally by the bridge itself. In the second case the bridge slides on its seat as this expansion or shortening takes place. For long bridges the second method is preferable while for short bridges either method will give satisfactory results. Centring. The form work for flat reinforced-concrete bridges is essentially the same as for floor construction. Troughs are formed in the centring to receive the beams and girders when they extend below the slab, and when the girders or beams are above, the slab formwork is built up to receive them. The formwork should be as firm and unyielding as possible, so that there will be no deflection or distortion when the concrete is placed. It should also be sufficiently tight to prevent the cement and water from leaking out, thereby causing a poor porous concrete. Depositing Concrete. In general the concrete should be de- posited as quickly as possible so as to insure a monolithic structure. Beams, girders, and slabs should, if possible, be deposited at the same time, especially where the beams have been designed as T- beams. Where the beams or girders are deep, it is sometimes in- [278] Concrete Beam and Girder Bridges advisable to do this, as the contraction of the beam or girder in setting may cause it to crack away from the slab. In such cases it would be well to concrete the beam or girder first, and the slab after a sufficient interval had elapsed. In this case, however, if T-action is desired, special reinforcement will be necessary to bond the beam and the slab properly together. Finish. In some structures, where appearance is of little im- portance, the concrete can be left just as it comes from the moulds, and if sufficient care has been taken in building the form work and placing the concrete, a very satisfactory finish will result. A better finish may be obtained by placing against the forms a one-inch coat- TABLE XXV. PRINCIPAL DIMENSIONS AND QUANTITIES OF MATERIALS FOR SLAB BRIDGES. (From "Concrete in High way Construction," published by Atlas Portland Cement Co.) i 5 LONGITUDINAL BARS. ABUTMENT WALLS. LENGTH OF SIDE WALLS. FEET. Cu. YDS. OF CONCRETE. POUNDS OF STEEL RODS. l i TO O *jL 8d L * ^tn 01 J 1 " 1 T^ CH _o "" _N "S I s ! 11 'S c 6 Ft.* 8 Ft.* 6 Ft.* 8 Ft.* 6 Ft.* 8 Ft.* (J P s Q "^ P ^fcM 8 9 . 6 8 20 32.0 38.0 43 53 2715 3440 10 ir f 5 1 1 23 34-5 40.5 49 60 3195 3880 12 13 ^ 5 13 27 37-0 43-0 57 69 3420 4100 16 IS 4 5 15 45 41-5 47-5 73 87 4375 5035 ing of cement mortar and then placing the concrete behind it. This mortar may be applied with a trowel or behind a steel plate which separates it from the concrete backing. In the removal of forms this facing may be treated in various ways as described in Chapter XII. If the mortar is not set too hard, it may simply be brushed with a stiff wire brush and water. This will remove the outer film of cement and bring the grains of sand into prominence. If the mortar is set too hard to be acted upon by the wire brush, sand or a cement block may be used and the same effect attained. By a proper selection of the sand, various color effects may be obtained in this way. * Distance in feet from top of footing course to bottom of slab. [279] Handbook for Cement and Concrete Users If a mortar facing is not desired, the concrete itself may be rubbed, sanded, or tooled until the outer film of cement is removed and the aggregate exposed. Where proper thought has been given to the selection of the aggregate, very pleasing effects may be ob- tained in this manner. If further treatment is thought advisable, the surface of the concrete may be washed with a weak solution of acid. After the acid wash it is well to again wash it with an alkaline solution to neutralize any acid that may remain in the concrete. [280] SECTION V THE USES OF CONCRETE FOR SPECIAL PURPOSES CHAPTER XXV CONCRETE IN SEWERAGE AND DRAINAGE WORKS Advantages of Concrete for Sewers. Forms of Sewers. Combined and Separate Systems. Dimensions of Sewers. Construction of Sewers and Conduits. Quan- tity of Flow. Culverts and Drains. Types of Culverts. Imperviousness of Sewers and Conduits. Tables of Dimensions for Culverts. Advantages of Concrete for Sewers. In no situation perhaps are constructive materials subjected to greater destructive forces than in subsurface work, particularly where the ground is charged with corrosive chemical and electrical influences. Under such conditions, many sewers and water-carrying conduits built of iron and steel have been destroyed in the course of comparatively few years. It is therefore with reason that municipal engineers throughout the country rejoice that in concrete, both plain and rein- forced, a material has been found that will not only be cheaper than brick or masonry but more enduring than steel and iron and more susceptible to use under any condition from the largest conduit to the smallest pipe. While in Europe, factory-made cement pipe has been largely used up to 7 feet in diameter, American engineers have found it more economical up to the present time to mould all pipes and sewers exceeding 3 feet in diameter right in place. For pipes smaller than 3 feet, difficulty in securing and using adequate forms have made it advisable to manufacture them in factories specially equipped for turning them out in large quantities and standard sizes. [28l] Handbook for Cement and Concrete Users The economy in the manufacture of the smaller sizes arises from the fact that the specially moulded pipes have very much thinner shells, 6 inches being about the thinnest that can be moulded on the job, while the manufactured pipe runs from 1/2 to 3 1/2 inches thick. There is thus a large saving of material, but this economy disappears when sizes larger than 3 or 4 feet are reached. A well-constructed concrete pipe will give as good results as a vitrified clay pipe and be less costly than the latter. The process of making these pipes has already been described in the chapter on concrete products. Another advantage in the use of concrete for sewer work is the smooth surface obtainable, and smoothness of surface is very de- sirable to reduce the frictional resistance of the flowing sewerage. Systems of Sewerage. Sewers are built in circular, egg-shaped, and other forms, depending upon the relative quantity to be carried during low and high stages of flow, and upon whether the rain or storm water is to be carried in the same system as the sewerage proper. This is a very important question and is usually one of the first things to be decided upon in any extensive sewer project. When the storm water and sewage are carried in the same set of sewers, we have a " combined" system. Separate sewers for the storm water and for the sewage proper is referred to as the ''separ- ate" system. While for a detailed discussion of the merits of each system, the reader must be referred to special works on sewerage, a few remarks on the controlling features may not be out of place. Separate and Combined Systems. The separate system is employed principally when the sewage must receive some purifica- tion treatment before being discharged into streams. In such cases the storm water is excluded to reduce the maintenance charge at the disposal plant. Where the sewage discharges directly into running water without preliminary treatment, the combined system is to be preferred, as the storm water acts as a cleansing agent and but little artificial flushing is required. Forms of Sewers. The circular sewer is built wherever con- ditions permit its use, as with a given external area the circular section requires less material than any other form, and is thus the most economical. Where, however, the amount of sewage fluctu- [282] . .V 1 Concrete in Sewerage and Drainage Works ates largely, the circular section offers greater frictional resistance to flow at low stages and the egg-shaped section is employed. The increased frictional resistance to flow in the circular section arises from the fact that a greater area of surface is covered for the same quantity of flow than in the case of the narrower egg-shaped section. In the latter the dimensions are so fixed that a fairly uniform rate of flow is obtained under all conditions of flow, and, as in the com- bined system the flow is sometimes very large, and sometimes very slight, the egg-shape is very well adapted. Many horseshoe-shaped conduits and sewers have been con- structed, this shape being usually easier to build, particularly when made of brick; but with the introduction of concrete and improve- ment in collapsible forms, the circular section is the predominating type. The horseshoe section is, however, employed in very large conduits for water supply where the flow is fairly uniform and the greater frictional losses and the extra material required, being counterbalanced by the greater ease of construction. Depth of Flow. Sewers and conduits not flowing under pressure reach their maximum capacity when flowing about 0.9 full, the flow being greater at this depth than when the whole section is filled, owing to the increased surface friction at the top and the consequent reduction in velocity. Velocity in Sewers. The velocity in sewers is kept within the limits of 2 1/2 to 10 feet per second and the grades so established that velocities between these limits are obtained. The lower velocity is necessary to prevent the deposit of solid matter in suspen- sion and the higher velocity to prevent excessive wear on the material composing the surface of the conduit, as the abrasive power of water flowing at high velocities is very great. It is partly for this reason that conduits under pressure where the water moves at a high velo- city are generally built of steel or iron, the further reason being that the high pressure exerted on the walls would be fatal to ordinary masonry. Reinforced concrete, however, has now come into favor even in high-pressure conduits, and many of the tunnels of this character are being designed on the new Catskill . waterworks for the City of New York. Dimensions of Sewers. The size of the sewer or conduit is fixed by the amount of material to be carried and the grades ob- [283] Handbook for Cement and Concrete Users tainable; the smallest size consistent with the limiting velocities is usually adopted. The size and the shape having been determined, the thickness of the top, sides, and bottom are to be fixed. There is no special method or formula for proportioning these parts as the conditions are so variable. The depth below the surface, the character of the material, the foundation, etc., must be considered. Experience has, however, fixed certain standard dimensions which may safely be employed for various sizes both in plain and reinforced-concrete FIG. 95. Standard Section in Plain Concrete. New York Rapid Transit System. sewers, and these are given below. It will be noticed that these dimensions point to a very simple rule for finding the thickness at the crown of circular sewers; i.e., the thickness at the crown in inches is equal to the number of feet in diameter + i, the minimum thickness being 4 inches. The amount of steel in reinforced-concrete sewers and conduits must be sufficient to take care of the bursting strain due to the hydrostatic pressure of the water or sewage. This quantity may be determined by the simple formula: of steel. [284] Concrete in Sewerage and Drainage Works p = Internal hydrostatic pressure in Ibs. per sq. in. d = Internal diameter in inches. / = Allowable working stress, for steel, in Ibs. per sq. in. Jlo" /<*-) C/r. 6". . ! S" ,. T" ' .. /o ML FIG. 96. Standard Sections: Reinforced Concrete Sewers. New York Rapid Transit System. A = Area of steel required for each longitudinal foot of con- crete. [285] Handbook for Cement and Concrete Users Construction of Sewers. The construction of sewers follows the general methods already described in mixing and placing concrete. The special features that accompany sewer work are: 1. The construction of the trenches to the proper depth. These should be somewhat wider than the actual width of the masonry, to allow working room, the excess being later carefully backfilled. 2. The trenches must be adequately braced so that no sliding of material will occur during the progress of the work. In shallow cuts with a firm material very little bracing is required, but in soft material heavy tongue and grooved sheet-piling is employed and interlocking steel sheet piling is now coming into extensive use for this purpose. 3. The bottom of the trench should be properly prepared; loose and poor material being removed and replaced by sand or con- crete and the slope of the bottom should be made parallel to the finished slope of the sewer. 4. In case the conduit or sewer is constructed in yielding soil, special means must be taken to secure good foundations, and for this purpose piles are frequently driven and the sewer constructed on a timber platform built on these piles. 5. The excavation having been completed and the foundation prepared, the concreting begins; a mixture of 1:3:5 being suitable to the heavy portions of the work and a i : 2 : 4 should be employed around the reinforcement and at the crown. 6. The forms for building concrete sewers may be made of wooden lagging supported at 5- to 6-foot intervals by specially cut timbers resting on posts or sills, or one of the many forms of collap- sible steel forms may be employed. These forms are especially desirable where long sections of sewers of uniform diameter are to be built, as the use and constant reuse of same results in a consider- able saving in form labor. 7. In laying concrete pipe sewers having hubs, special excavations must be made under the joints of the pipes to provide room for the enlarged ends, and particular care should be taken that the pipes are properly bedded, as any unevenness in the bed may result in open joints and broken pipes. 8. After the concrete has been deposited and has hardened, the forms are removed to be used over again, and sections of the com- [286] Concrete in Sewerage and Drainage Works -S5SS |-.| ?IS 5SP o < zx - ~ o w y *- , z w o tiSII 85: i .-- sSHll! H5 5 o Of- .-M 5 ^ 3 T3 o Q c ^ 6 UjO h U I T-( I I u [287] Handbook for Cement and Concrete Users pleted sewer are backfilled uniformly from both sides so as to eliminate eccentric strains on the roof. In placing the backfilling, care should be taken that no heavy stones are poured or rammed against the completed sewer concrete that would be likely to injure it. Sewers and conduits are frequently constructed in tunnels where the concrete work must necessarily be done under trying conditions. The construction of tunnels is perhaps the most difficult of all engineering undertakings and the accomplishments in this field during the last twenty-five years have been marvelous in the ex- treme. This is particularly the case in subaqueous work where life and limb are in constant danger both from the threatening waters on the outside and the air on the inside, which is highly compressed to keep the water out. Under the cramped and difficult conditions met with in tunnel work, the placing of the concrete is slow, and special forms of mixers and conveyors are frequently employed to accomplish it. It is, however, here that cement finds a large field of usefulness in other ways than mere concrete-placing, for after the concrete has been placed, there remain numerous crevices, and holes near the roof of the tunnel which can not be filled up in the ordinary way and here liquid concrete or grout is employed and pumped in under high pressure as described in Chapter XXXI. Quantity of Flow in Sewers. In the "separate" system the amount of sewage to be taken care of is equal to the water supply, as it is figured that the entire water supply sooner or later will reach the sewer. This amount in any extensive system is taken generally as 100 gallons per day per head of population tributary to the sewer. This total quantity is proportioned irregularly throughout the day, the maximum flow being possibly 10 gallons per person per hour. This is converted into its equivalent in cubic feet per second which is the unit of quantity in all calculations of flow. The amount of water reaching the sewer from storms is a very uncertain quantity owing to the variability of the factors involved. The amount depends upon: 1. The rate or intensity of rainfall. 2. The variation in rate. 3. The length or duration of the rainfall. [288] Concrete in Sewerage and Drainage Works 4. The condition of the surface particularly as regards its power of absorption. 5. The slope of the surface. 6. The shape of the surface and its area. 7. The presence of obstructions to flow, such as vegetation. 8. The proximity fo the sewer inlets. 9. The carrying capacity of the sewer. A great many studies have been made to determine the probable amount of storm water for which the sewer should be designed, but no satisfactory rule applicable to all conditions has ever been formulated; the one most commonly employed being the formula: Q = C y v" 6^ in which Q equals the number of cubic feet reaching the sewer per second, for which the conduit is designed. C = a constant depending upon retentive power of surface. 3.50 = for ordinary prairie land. 5.00 = for paved, rock, or frozen surfaces. 2.00 = for wooded land. y = rate of rainfall in inches per hour. S = slope of receiving surface in feet per 1,000. A = area of receiving surface in acres. CULVERTS AND DRAINS Culverts are employed to carry a stream or watercourse under- neath an embankment constructed for highway, railroad, or other purposes. Drains are employed wherever the carrying off of surplus water is required. Siphons are employed to carry a stream of water across a hill or valley, the water in such cases flowing under pressure. In all these works, concrete, both plain and reinforced, is now extensively employed, brick work, iron, and steel being largely abandoned. Since the purpose of culverts and drains is to carry off surplus water and thereby prevent injury to embankments or foundations, it is necessary to know approximately the maximum amount of water that may have to be taken care of during times of extreme flood. 19 [289] Handbook for Cement and Concrete Users There are several ways in which the required area of a culvert opening may be obtained. i st. The area of the stream at narrow points along the water- course during freshet periods may be measured and the required area thus obtained. 2d. The high drift marks along the banks may be examined and the area between the bed of the stream and the high-water line determined. 3d. Culvert openings at other points along the same stream when they have been found ample, may be taken as a safe guide to proportioning the new culvert. 4th. Where none of these means for determining the area of the waterway can be employed, resort has to be made to some empirical rule or formula which has been established by comparing existing culverts with the area of land which they drain or "drainage area." Perhaps the simplest of these is Myer's formula: Area in square feet = \/Drainage area in acres. Thus, for 100 acres area required is 10 sq. ft. or a 3 1/2 foot culvert. For 900 acres, 30 sq. ft. would be required or a 5 X 6 culvert. The carrying capacity is also, of course, affected by the grade or slope and this is usually fixed by the relative surface elevations for the entrance and exit. As steep a slope as possible should be given. Types of Culverts. The area of waterway having been deter- mined, the type of culvert may be selected. There are three types in general use, depending largely on the area of waterway. i st. The pipe culvert is available where the area of waterway does not exceed 10 sq. ft., which requires a pipe 36 inches in diameter or the maximum size of concrete pipe made. Manufactured concrete pipes below this size are economical and very satisfactory for culvert construction. 2d. Box culverts having rectangular waterways are extensively employed from the 2' X 2' size up to almost any size required. They are easy and cheap to build and are employed for the smaller sizes where shipment of ready-made pipe is not desired, as the box culvert can be built from materials and cements in almost any locality. 290] Concrete in Sewerage and Drainage Works 3d. The arch culvert is employed for the large openings where appearance is of more importance than the question of cost, as the construction of arches is more costly than plain rectangular work. In very large culverts, however, the arch is somewhat more economi- cal in material for a given area of waterway. The larger culverts, both box and arch types, may be reinforced and it is good practice and economical to do so, as it enables much lighter sections of concrete to be employed. The concrete for culvert construction may be a 1:3:6 mix, a somewhat richer mixture, however, being employed about the rein- forcement. Otherwise the construction follows the usual method SIT** I 7*/r* iacea to 'b FIG. 98. Forms for Square Concrete Culverts. of concrete work. The particular point to be mentioned about culvert work is, the protection of the inlet to and outlet of the waterway against any scour by the flowing water. Water finding its way underneath the floor or around the ends will either under- mine the culvert or erode the banks and both of these must be prevented. The method of prevention consists in a substantial stone or concrete pavement laid on the floor of the culvert to con- fine the water to its proper channel, and parapet walls to prevent erosion of the embankment. The construction of culverts may become a difficult matter when a large amount of water is to be taken care of. The best method of procedure is to excavate a temporary channel or provide [291] Handbook for Cement and Concrete Users a temporary flume near the culvert site and divert the course of the stream through the temporary waterway. The culvert can then be constructed in the dry, and when completed, the stream diverted into the culvert, the temporary channel being removed. Imperviousness of Sewers and Conduits. Sewers, particularly in the separate system, shoul^ be as .impervious as it is possible to make them. There are three important reasons for this, as: i st. The necessity for excluding ground water from the sewer. The infiltration of ground water is a serious matter where the sewage must be purified before being disposed of, and records show that millions of gallons of ground water find their way into leaky ! n. Lagging FIG. 99. Arrangement of Forms for Arch Culverts. and defective sewers, entailing a great burden and expense on the purification plant for which they were never designed. Further- more, the leakage of sewage through the lining of sewers has a contaminating influence on the ground, is very unsanitary and may indirectly give rise to epidemics of disease. Another important reason for imperviousness of sewers is the protection of the concrete from possible destructive action of sewer gases which has been discussed in Chapter IV. The importance of waterproofing treat- ment in extensive sewer projects is beginning to be recognized and in one of the largest projects, the Bronx Valley Sewer, in New York State, the entire length has been protected by an exterior shield [292] Concrete in Sewerage and Drainage Works of 2 -ply coal tar felt and pitch, following the method described in the chapter on waterproofing. A dense concrete, properly rein- forced, and to which has been added a small percentage of a good waterproofing compound, or the interior surface of which has been treated to two coats of a durable and impregnating waterproof paint, will answer the purpose very well. Water-carrying conduits likewise must be impervious, as other- wise there will be not only a large, loss of water, but ground water, often polluted, may filter in and cause trouble. When expense is a secondary consideration, a coat of waterproof cement may be applied to the interior surface in accordance with the specifications for. the Integral Method as given in Chapter XXX. Impervious concrete may be obtained by scientific proportioning of materials, as described in Chapter VI, but a good waterproofing treatment is usually advisable. TABLE XXVI. AMOUNT OF MATERIALS FOR ARCH CULVERTS, f MATERIALS FOR CULVERT FOR IO-FOOT ROADWAY EXTRA MATERIAL FOR EACH ADDITIONAL FOOT WIDTH OF ROAD. Screened* Screened Span of Culvert. Feet. Cement. Bags Barrels. Sand.* Double Load. Gravel or Stone. Double Cement. Bags. Bbls. Sand. Double Load.* Gravel or Stone.* Double Load. Load. 5 50 or 12$ 3 6 2 or i i 8 80 or 20 4l 9* 3 or f 3A6 i 10 115 or 28f 7 14 4 or i i * * A double load of sand or gravel is taken as 40 cubic feet or about ij cubic yards. f From "Concrete Construction About the Home and on the Farm," published by Atlas Portland Cement Co. 293] CHAPTER XXVI CONCRETE TANKS, DAMS, AND RESERVOIRS Uses of Concrete Tanks. How to Build Tanks. Reinforcement for Tanks. Concrete Dams. Small Reinforced Concrete Dams. Concrete Reservoirs. THE construction of waterworks has received a new impetus with the development of concrete, plain and reinforced. Its durability, adaptability to any condition, and economy have made possible the erection of any number of works which would have been impossible if more expensive and less permanent material had to be employed. Concrete has thus contributed not a little to improved sanitary conditions in water supplies. In the collecting and storage systems, as well as with distributing systems of all modern waterworks, concrete plays an important part and will continue to do so more and more as its many advantages over other constructive materials become better known. In the smallest of wells, springs, and watering-troughs, as well as in the largest tanks, reservoirs, dams, and conduits, concrete can be advantageously employed and a volume alone could be written on this branch of the subject. The smaller structures used about the farm are discussed in that chapter, and the question of pipes and conduits has also been discussed in other parts of the book. We must therefore confine ourselves here to the discussion of such typical structures as tanks and water towers, reservoirs, and dams. c CONCRETE TANKS* Various Uses. Concrete tanks have been built as receptacles for such a variety of substances that it is impossible to name them all. We naturally think first of a tank as a receptacle for water, * For complete directions see "Concrete Tanks," published by American Associa- tion of Portland Cement Manufacturers, Land Title Building, Phila., Pa., from which this description is partly condensed. [294] Concrete Tanks, Dams, and Reservoirs but this is only one liquid for which a concrete tank is suitable. Manufacturers of oil, wine, milk, molasses, pulp, glue, and a variety of other materials are now using concrete in the construction of their tanks (or vats) , both for the finished product and in the course of manufacture. Vegetable oils are said to have a deteriorating effect upon concrete, but through the use of the very excellent waterproofing compounds now available, concrete can be used in the construction of tanks for these oils. Very naturally, the use we will discuss most fully is that of water, as probably nine-tenths of the tanks built are for the holding of water. For other substances, where the use is a new one, careful experiments should be made to determine the chemical effect upon the concrete of the substance to be held. Concrete tanks are also extensively built to hold dry ma- terials, such as sand, stone, coal, and grain. Choosing the Location, Size, and Shape. Tanks may be gener- ally divided into two classes: viz., those above the ground surface, and those below, and in choosing the proper design the tank location must be first selected. The next step is to decide the shape of the tank. Tanks are built in many shapes, but the convenience of use usually decides the shape selected. How to Build the Tank Rectangular Tanks. Laying Out the Ground. After the size has been decided upon, select a site near the water-supply if possible, and mark off the ground. In selecting the size, remember that 71/2 gallons make one cubic foot, and that a barrel holds from 49 to 54 gallons. Put four nails in the ground in the shape of a rectangle, to mark the outside line of the tank walls, and stretch strings from nail to nail. Excavate inside the space thus marked to a depth of 6 or 8 inches. If the soil is good stiff material, the bottom of the tank may be placed directly on this ground. If the ground is soft, dig a trench just inside the strings one foot deep and one foot wide to secure additional foundations. The ground under the proposed tank should be thoroughly tamped (beaten down), with as heavy a tamper as one or two men can handle. A block of wood, square or round, 12 or 14 inches across, with handles for lifting, makes an excellent tamper. [ 2 95] Handbook for Cement and Concrete Users Amount of Reinforcement in Bottom of Tank. The thickness of bottom will be made in all cases 6 inches; for tanks of this depth reinforcement must be placed 2 inches from the bottom of the slab, and this reinforcement must run each way. Placing Reinforcing. By referring to the accompanying tables, we find it necessary for a tank 6 feet deep to use in the bottom one J-inch round steel rod every 14 inches. If the tank is to be five feet square, these should be cut in lengths of 5 feet each. Lay them on the ground spaced properly, the rods in one direction resting on the rods in the other. Then cut the rods for the vertical reinforcement of the wall. Also we find that for a tank 6 feet deep we require J-inch round rods spaced 5 inches apart. Fifty-two of TABLE XXVII. FOR SPACING OF RODS IN BOTTOM OF TANK. Depth of Tank. Spacing of f-inch Round Rods. Spacing of ^-inch Round Rods. Spacing of f-inch Round Rods. 3 feet 10 inches 4 8 " 1 6 inches 5 7l " *5 " 6 7 " 14 " 7 61 " , 13 " 8 6 " 12 " 24 inches 9 5 " 10 " 20 " 10 4 8 " 16 " these will be required. These rods should be cut 7 feet long. Make a hook at each end of these bars. This can be done by placing the end of the bar between two heavy spikes nailed in a block of wood and bending by moving the other end of the bar. The length of these bars after they have been bent should be about 6 feet 4 inches. Rods should also be bent for the horizontal re- inforcing. From Table XXVIII, we see that for this sized tank J-inch round bars spaced 10 inches apart are required. Seven of these will be needed on a side. The i /2-inch rods with hooks at each end are placed in position by hooking the lower end of all the bars on one side under the rods in the bottom reinforcing, coming about 2 inches outside the line of the form which has been erected. After having placed these [296] Concrete Tanks, Dams, and Reservoirs vertical i/ 2-inch round rods'in the correct positions, the next step is to place the horizontal reinforcement for the walls. This we have previously seen consists of i/ 2-inch round bars spaced 10 inches apart. Where the bars lap, they should be firmly wired together. TABLE XXVIII. SHOWING SIZE AND SPACING OF RODS IN WALL. SPACING OF SPACING OF SPACING OF SPACING OF Depth Thick- I-INCH ROUND RODS. J-INCH ROUND RODS. I-INCH ROUND RODS. I-INCH ROUND RODS. of ness of Tank. Wall. Verti- Hori- Verti- Hori- Verti- Hori- Verti- H6ri- cal. zontal. cal. zontal. cal. zontal. cal. zontal. Feet. Inches. Inches. Inches. Inches. Inches. Inches. Inches. Inches. Inches. 3 5 5 IO 10 20 4 5 4 8 8 16 16 3 2 5 Si 3 6 6 12 12 24 6 6* 2| 5 5 10 10 20 18 36 7 8 3 6 7 14 15 3 8 9* 2* 5 5 10 II 22 9 10$ 5 10 10 2O 10 12 4 8 8 16 TABLE XXIX. DIMENSIONS FOR CIRCULAR TANKS. (') Depth. (2) Diameter. Thickness of Concrete (4) Diameter of Horizontal Q (5 > bpacmg Horizontal Rods at (6) Spacing Horizontal Rods at (7) Diameter Vertical (8) Spacing Vertical in Wall. Rods. Bottom. Top. Rods. Rods. Feet. Feet. Inches. Inches. Inches. Inches. Inches. Inches. 5 5 6 i 8 18 i 36 5 10 6 i 6 12 i 3 10 10 8 f 6 18 I 36 IO *5 8 | 4 18 i 36 J 5 10 12 1 4 18 1 3 15 15 12 i 6 20 1 3 We will illustrate the method of using Table XXIX in building a tank 15 feet deep and 10 feet in diameter. From the table we see that the thickness of concrete in the walls of the tank is 10 inches; that the size of reinforcement to be used is 3/8-inch rods, that is, round rods 3/8 of an inch in diameter; for the first foot these rods should be spaced 4 inches apart, and the vertical rods should be [297] Handbook for Cement and Concrete Users placed 30 inches apart. The table calls for the spacing of the hori- zontal rods 1 8 inches apart at the top of the tank, and the inter- mediate horizontal rods will therefore be spaced distances varying from 1 8 inches to 4 inches; thus in the second foot from the bottom the horizontal rods will be 5 inches apart; in the third foot, 6 inches apart; in the fourth foot, 7 inches apart; in the fifth foot, 8 inches apart; in the sixth foot, 9 inches apart; in the seventh foot, 10 inches apart ; in the eighth foot, n inches apart; in the ninth, 12 inches apart; in the tenth, 13 inches apart; in the eleventh, 14 inches apart; in the twelfth, 15 inches apart; in the thirteenth, 16 inches apart; in the fourteenth, 17 inches apart; and in the fifteenth, 18 inches apart. / CONCRETE DAMS Concrete is now being extensively employed in the construction of dams of every conceivable shape and size. They are al), how- ever, of three general types, the solid or gravity type, the arched type and the hollow reinforced type. The fundamental principles' in the design of gravity dams are much the same as those underlying the design of retaining walls, the main difference being that the dam must not only be strong enough to be safe against a full head of water in the reservoir, but also in the case of very high dams it must be safe against the weight of masonry in the structure itself. Furthermore the external pressure of the water can be determined with scientific exactness while the pressure of earth on walls is subject to many uncertainties. The amount of water pressure per square foot against a dam at any depth is found by the simple rule P = 62.5 H. and against the surface one foot wide. P = 31.25 H* P = Pressure in Ibs. at any depth H in feet. Table XXX gives the pressures at different depths: Gravity dams may be constructed of solid concrete or of concrete in which is embedded large blocks of rubble. The latter type which is called " Rubble Concrete," or " Cyclopean Masonry," is by far the most economical as the amount of cement required is reduced to a minimum. Small Dams. The construction of small dams under six feet [298] Concrete Tanks, Dams, and Reservoirs high may be undertaken without special engineering advice as follows : * "If possible, dig a temporary trench so as to carry the water around the dam while it is being built. If this cannot be done, run the water through a wooden trough in the middle of the dam, and after the wall each side of it is finished, carry the forms across the opening, and make these tight enough so that the water is quiet between them; then place the concrete. "Dig a trench across the stream slightly wider than the width of the base of the dam, carrying it down about 18 inches or 2 feet below the bed of the brook, or if the ground is soft, deep enough to TABLE XXX. HYDROSTATIC PRESSURES. Hydros tatic^Head. Feet. Lifting Pressure per Square Foot. Lbs. Average Pressure per Square Foot on Vertical Surface. Lbs. -S 31.2 15-6 I .0 62.5 31.2 2 .O 125 .0 62 .5 3- 187-5 93-7 4.0 250.0 125 .0 5- 312-5 156.2 6.0 375-o i87-5 8.0 500.0 250.0 10. 625 .0 3i 2 -5 12 .0 750.0 375 - *5-Q 937-5 468.7 20.0 1250.0 625.0 25 .0 !5 62 -5 781.2 30.0 1875.0 937-5 4O.O 2500.0 1250.0 60 .O 375 -o 1875.0 80.0 5000 .0 2500.0 100. 6250.0 3 I2 5- reach good, hard bottom. In case the earth is firm enough for a foundation, but is porous either under the dam or each side of it, sheet piling consisting of 2-inch tongued-and-grooved plank can be pointed and driven with a heavy wooden mallet so as to prevent the water flowing under or around the dam. Build the forms so as to * From "Concrete Construction About the Home and on the Farm," published by Atlas Portland Cement Co. [ 2 99] Handbook for Cement and Concrete Users make the wall of the dimensions shown in the table. Wet them thoroughly, then mix and place the concrete. "Use proportions one part Portland cement to two parts clean, coarse sand to four parts screened gravel or broken stone. "Take special care to make the concrete water-tight by using a wet mix. If possible, lay the entire dam in one day, not allowing one layer to set before the next one is placed. If it is necessary to lay the concrete on two different days, scrape off the top surface of the old concrete in the morning, thoroughly soak it with water, and spread on a layer about 1/4 inch thick of pure cement of the con- sistency of thick cream, then place the fresh concrete before this cement has begun to stiffen. "If the forms on the lower side of the dam are well braced, the forms on the upstream side may be removed in three or four days, and the pond allowed to fill. The forms on the down-stream face should be left in place well braced for two or three weeks. No finish need be given to the surface." Reinforced-Concrete Dams.f Reinforced concrete is particularly adapted to the construction of dams. When so used there is a TABLE XXXI. DIMENSIONS FOR SMALL DAMS AND QUANTITY OF MATERIALS FOR DIFFERENT HEIGHTS OF DAMS. Proportions: i Part Portland Cement to 2 Parts Sand to 4 Parts Gravel or Stone AMOUNT OF MATERIALS PER FOOT Height Above Bed of Stream. Depth Below Bed of Stream.* Thickness at Base. Thickness at Top. OF LENGTH OF DAM. Cement. Sand. Gravel or Stone. Feet. Feet. Feet. Feet. Bags. Cu. Ft. Cu. Ft. H. G. B. T. I l| I I i I ij 2 ij I I i ij 3 3 4 2 l| if 4 8 4 2 2 *l 2 I 5 10 5 2 2 i l 3* 6| 13^ 6 2 3 i 4* 8J i7l * Make deeper if necessary to get a good foundation. Note. A large single load of sand or gravel is about 20 cubic feet. A large double load of sand or gravel is about 40 cubic feet. f This discussion is arranged from "Concrete, Plain and Reinforced," by Homer A. Reid. [300] Concrete Tanks, Dams, and Reservoirs great saving in material, and on this account a reduction in cost of, in some cases, as much as 20 per cent. Again, the space under the apron may be utilized for storage or power-house purposes, as for the location of turbines, electric generators, etc. Another advantage is that of securing a practically impervious curtain face wall, with- out any of the dangerous leaks so troublesome to locate in some masonry structures. If sufficient number of reinforcing rods are used and run in every direction there will be little or no danger of cracking in the deck concrete. The design of steel dams is that^of a triangle with the upstream face so flatly inclined that the water pressure is made to give in- creased stability by its weight, and this basic principle has been the leading feature in the development of dams of reinforced concrete, FIG. 100. Design for Small Dam. which were first introduced in the Eastern States about the year 1902 by the Ambursen Hydraulic Construction Company, of Boston. About 30 dams varying in height from 10 to So feet, some over 1,000 feet long, have been erected during the last 8 years, many of them attracting marked attention by the engineering profession. The design of these dams illustrates very strikingly the adapta- bility of reinforced concrete to new conditions. The principle followed in the design is that the vertical pressure of the water is utilized to firmly hold the dam down on its foundation. [301] Handbook for Cement and Concrete Users With the usual type of gravity dams, the up-stream face is verti- cal or nearly so. The pressure of the water is thus exerted horizon- tally, tending to overturn the dam, which must therefore be made heavy enough to prevent same from occurring. In the reinforced-concrete dam, the slope of the water face may be so fixed that the pressure on the foundation is controlled by the designer, and the safety factor is made at least five. The usual type of reinforced-concrete dam consists of an in- clined slab of reinforced concrete extending from the heel to the crest, and spanning between and supported by transverse buttresses of concrete, resting upon the foundation. Another inclined slab may or may not be used to form an apron or spill-way. The deck Rot/way FIG. 101. Curtain Type of Reinforced Concrete Dam. is usually increased in thickness from the crest to the heel on account of the increase in pressure as the water deepens. The principles governing the design of reinforced-concrete dams are the same as those used for the design of masonry dams as far as the external pressures are concerned. However, as reinforced-concrete dams are usually of triangular cross-section, they have a much wider base than masonry structures, which greatly increases their resistance to overturning. This resistance is further increased by the weight of the water above the face or deck, which usually has an inclination of from 30 to 45 with the horizontal. An increase in the height of the water flowing over a masonry or solid dam increases the pressure thereon and causes the line of press- [302] Concrete Tanks, Dams, and Reservoirs ure to rise, thereby greatly increasing the overturning moment on the dam without in any way increasing the resisting moment to the same. CONTRACT NO. 3 SHEET NO. 15 j! SHEETS IN..SET, 58 i! - =Cp== --- = =? e = = ==== =&--r^.-_-.iT==A-_--^_-= EgS3HBJf:53!j SElffiHr!?!;!. tE^as - Concrete masonry EITHER FACE AT ROCK FOUNDATION Inspection gallery Flow line Concrete drainage blocks Drainage DOWNSTREAM FACE I t . UPSTREAM FACE ARRANGEMENT OF FACE BLOCKS 10 2 6 10 14 18 22Ft Concrete gutter El. 460 insp ecrion_ gallery Assumed line of excavation MAXIMUM SECTION FIG. 102. Ashokan Dam of the New Water Supply System for the City of New York. One of the Largest Dams in the World. In a triangular dam, however, with a broad base, as in the hollow reinforced-concrete dam, when the head of water flowing over the dam is increased, the lines of pressure become more nearly vertical, [303] Handbook for Cement and Concrete Users the overturning moment is actually reduced, and the stability is in no way endangered.* Owing to the reduction in weight it may be necessary sometimes to fill hollow dams with sand, earth, or gravel to increase its resistance to sliding. Reinforced-concrete dams are particularly fitted to poor founda- tion conditions on account of the broad base and consequent low unit pressures. This will often enable a large saving in cost. Concrete Reservoirs. The construction of reservoirs of concrete present but few features not already discussed in the sections on walls and dams. The principal difficulty encountered is in obtaining a watertight bottom, as extensive areas of shallow concrete are subject to cracking on account of settlement, shrinkage, and ex- pansion. The best means to avoid this cracking is by having a double lining. The under lining is laid in a continuous sheet and covered with a sheet of a good asphalt ic material, and over this is placed concrete, in sections ten feet square, the joints between the sections being filled with an asphaltic material. [304] CHAPTER XXVII CONCRETE SIDEWALKS, CURBS, AND PAVEMENTS Advantages of Concrete Sidewalks. Materials, Equipment, and Forms. Construction of the Sidewalk. Coloring and Protection. Tables of Dimensions and Materials Required. Concrete Curbs and Gutters. Concrete Roads and Pavements. Table of Offsets for Crowning Roads. THE class of work in which the value and adaptability of concrete has been brought most intimately to the attention of laymen and municipal authorities is cement sidewalk construction. Being one of the oldest forms in which cement has been employed, its use in this connection has grown so rapidly that no important community is without its miles of well-paved walks; and what had formerly been a luxury employed only by large towns and cities, has now become an e very-day necessity in all progressive communities. In fact, it is due to the introduction of the cement walk, that many hundreds of communities have been enabled to provide themselves with walks at all; for the cement walk possesses all the merits of the older forms of wood, brick, and stone, and few of their defects, and the low cost and maintenance charges place it within the reach of almost any up-to-date home. The beauty, convenience, noiselessness, durability, and economy of well-constructed walks have always had a highly beneficial in- fluence on property values wherever they have been constructed. Concrete as a material for curbs and gutters is just as advan- tageous as for sidewalks, and its adaptability for the roadway of streets is now becoming quite generally recognized and will continue to be more so in the future. The question of its use as a paving material is taken up later in this chapter. Materials for Sidewalks. Sidewalks should be constructed only of Portland cement, as the natural and slag varieties are unfitted for constant exposure to the elements. A good sand or screenings and a clean, hard, and durable stone should be employed and the same well graded. Five per cent of clay may be allowed. The 20 [ 305 j Handbook for Cement and Concrete Users same principles should be followed in selecting these materials as have been outlined in Chapter V. Tools and Equipment. The tools and equipment employed by the sidewalk builder are shown in the accompanying illustration and their use is there indicated. Forms. Forms for the sides are made of sound wood, at least two. inches thick by five inches wide, while the cross forms and pro- tection strips may be of metal. The forms must be firmly secured by stakes driven at frequent intervals (about 2 feet) and placed upon proper lines and grades. Specially designed metal forms are economical and very desirable on any large work. Construction. The foundation of the sidewalk is, as in all other structures, the most important element upon which the lasting qualities of the structure depend. To assure a good founda- tion, the soil underneath it should be well drained by means of broken-stone trenches, tile pipes, or other suitable means depending upon the character of the soil and local drainage facilities. The soil should be brought to the required elevation of the subgrade either by excavation or fill as the original surface may require. If in excavation, all spongy and bad spots must be re- moved and replaced by sand or other good material. If in fill, the material should be wetted and tamped in layers not more than 6 or 8 inches thick. The fill should extend far enough (at least 2 feet) on either side to allow the material to assume its natural slope without danger of running from under the walk. Preparing the Sub-Base. The subgrade should be at least 12 inches below the finished surface and sJope toward the curb at least 1/2 inch per foot for drainage. The foundation or sub-base should be at least 8 inches thick, made of hard cinders, slag, gravel, crushed stone, or broken brick, grading from 1/4 to 4 inches in size. Concrete Base. In placing, the under bed of concrete should be well tamped until its upper surface is at the required height, about 3/4 inch below the finished surface of the sidewalks. At . all driveway crossings, increase the thickness of sub-base 2 to 3 inches, and of the top 1/2 inch. Do not remove cross forms until concrete is well compacted and set, and in laying adjoining sections, see that old surface is clean and free from loose mortar. Concrete Sidewalks, Curbs, and Pavements Leave expansion joints at least every 50 feet, about 1/8 inch wide. This is done by the insertion of expansion strips which are later removed and replaced by paving pitch or good sand. No block should contain more than 36 square feet, and no dimension should be more than 6 feet. Never leave the work with a slab partly finished, as breaks will be bound to occur at such points. Wearing Surface. The wearing surface should be smooth but ROTARY JOINTER For use in places too small for ordinary style DATE STAMP For marking walks, artificial stone, etc. BRASS JOINER For finishing joints In walks. FLUTED ROLLER BOUND CORNER SIDEWALK EDGES For finishing walks SMOOTHING TROWEL ete> For finishing corners in gutters etc. NAME PLATE For stamping names of makers on walks, artificial stone, etc. SQUARE CORNER SMOOTHING TROWELS For finishing inside or outside edges of circles TAMP For tamping con- crete foundations, etc. RADIUS TOOL JOINTER CENTRE KNIFE For finishing joints For cutting the sur- In cement walks, etc. face of cement walks into f 1 HAND BRASS JOINTER For finishing joints in cement. ROUND CORNER SMOOTHING TROWEL INDENTING ROLLER For indenting the surface of walks. DRIVEWAY IMPRES- SION FRAME For marking cement driveways. FIG. 103. Principal Tools Employed in Building Cement Walks. not slippery and of uniform dull color. Mixture i part cement to i or i i / 2 parts crushed granite, slag, grit, or sand. The top surface may be " tamped" or " floated." The tamping may be applied to the top 3/4 inch, which may be a specially rich mixture. The thin mortar will work to the surface which may then be trowelled smooth. The tamping method will produce a better bond with the base [307] Handbook for Cement and Concrete Users and cause less delay. When the floating method is used the mortar should be mixed thin and worked to a true and smooth finish. Special pains should be taken to obtain a good bond of top surface to base. The latter should be clean and the top surface placed as soon as possible after the base is tamped. Should the base have already hardened, it should be drenched and cleaned and prepared by a thin film of grout before the top layer is placed. The methods described to secure good bond in Chapter XXX, are likewise applicable to sidewalk work. The wooden trowel gives a good finish and is somewhat free from the excessive smoothness and checking caused by the steel trowel. While the surface is still green a grooved roller or brush may be run over it to remove the smoothness and give a better foothold for pedestrians. Coloring. The coloring of sidewalks follows in a general way the coloring of other cement work, as described in Chapter XII. Certain facts have been brought out by experience, however, which it is well to state here. The color of a walk will be affected by : 1. The consistency of the mortar and character of cement and aggregates. 2. The steel floating trowel gives a darker color than the wooden one. 3. The finishing tool. 4. Weather conditions. 5. The protection of the surface. 6. The interval of time between placing and finishing. Trowel- ling on partly hardened surface produces blotches. 7. Sunshine will give lighter color than shade. It is therefore important that the work be done under as uniform conditions as possible to obtain uniform color effect. Protecting the Walk. The walk should be protected against: 1. Rain and sun, which will cause pitting of surface. This may be effected by a layer of sand, tar paper, canvas, or boards secured from displacement. 2. Frost. The method of laying concrete in freezing weather and its protection described in Chapter VII, applies as well to side- walk construction. ' [308] Concrete Sidewalks, Curbs, and Pavements 3. Against displacement by growing roots of trees. This should be done by allowing a clearance of at least six inches all around. 4. Against walking on it or other interference until thoroughly set. TABLE XXXII. DIMENSIONS OF CONCRETE SIDEWALKS FOR RESIDENCE DISTRICTS. Width. Thickness. Length of Block. Area of Block. 4 Feet 3lto 4 " 5 Feet 20 sq. ft. 4i " 3* to 4" 6 " 27 5 " 4" 5 " 25 " " 6 " & 5 " 30 " " 6 " 5" 6 " 36 " TABLE XXXIII. -MATERIALS FOR CONCRETE SIDEWALKS.* BAGS OF CEMENT TO 100 SQUARE FEET OP SURFACE AREA OF CONCRETE BASE OR OF WALL. BAGS, OF CEMENT TO 100 SQUARE FEET OF MORTAR SURFACE. Thickness. Inches. Proportions. Thickness. Inches. Proportions. i : 1^:3 1:2:4 1:3:6 i: i i:ii i : 2 3 8* 61 4! | 3l 2f 2l 4 "I 8f 6 1 5 4 3l 5 Hi ii 7l I 7 5* 4l 6 i6| 13* 9l *4 8 i 61 5t 8 22f 18 12 J l 10 8 61 10 28f 221 I 5l If 12 9* 7i 12 34J 26^ 18* 2 14 ii 9 No. of Square Feet of Concrete Laid with No. of Square Feet of Mortar Surface Laid 4 Bags (i bbl.) of Cement. with 4 Bags (i bbl.) of Cement. 3 47 60 83 | 114 146 178 4 36 46 66 1 80 100 1x8 5 27 36 52 i 57 73 89 6 24 3 41 J i 48 60 70 8 17 22 33 J l 40 50 59 10 14 18 26 if 33 43 5 2 12 12 15 21 2 29 36 44 * From " Concrete in Highway Construction," published by the Atlas Portland Cement Co. See also bulletins of Universal Portland Cement Co. and Vulcanite Cement Co. on Cement Sidewalk Construction. [309] Handbook for Cement and Concrete Users Cost. A gang of six men can lay about 700 sq. ft. of 6 ft. walk per day, having a 4" base and a 3/4" top coat, at a cost of from 10 to 14 cents per sq. foot, depending upon the local price of labor and material. CONCRETE CURBS AND GUTTERS Curbs are usually 6 to 8 inches wide and 12 to 14 inches deep, 6 to 7 inches of which extends above the surface of the roadway. The exposed surface of the curb is slightly inclined and corners rounded off with a i-inch radius. As in the walk, the curb should be underlaid with an 8- or zo-inch layer of cinders. The gutter Curb form Fig. 104. Concrete Curb and Gutter. should be i i / 2 to 3 feet wide, slope toward the curb and have 7 or 8 inches of concrete overlying a cinder base. Several patented devices have been introduced for reinforcing curbs against injury by wheels of vehicles, and these have proved very efficient. The construction of curbs and gutters should follow the same principles as to excavation, fill, concreting, etc., as outlined for walks. The following detailed directions should be given careful attention: Rules for Construction of Cement Curb and Gutter. i. The drainage of foundations should be of the same materials as described for sidewalk paving, and similarly placed, using the methods and instructions as previously described. Concrete Sidewalks, Curbs, and Pavements 2. Place in position forms to receive the concrete. These forms are held in place by stakes set by an engineer at points necessary to accurately designate the line and grade of the proposed curb and gutter. 3. For forms use i 1/2 to 2-inch rough planks. Dimensions to be according to the height of the curb and thickness of the gutter, or special metal forms may be employed. 4. Place forms in position and deposit the concrete base. 5. Cut curb and gutter entirely through every six feet. A convenient and sure method is to use a piece of quarter-inch sheet iron the same form as the concrete base of curb and gutter. Fill in the cuts thus formed with dry sand. f * f s Jty+ 1 ^[w^m^a^f wye r 2 '*y 6 ' Gvrrap&OHMG fonifz Fig. 105. Combined Concrete Curb and Gutter. 6. After each batch of concrete is laid, it should immediately be covered with a top coat or wearing surface. 7. Slope the gutter to meet the requirements of drainage by increasing the thickness of the top coat on the side nearest the street. Work to an even surface with a straight edge laid parallel with the curb. 8. The upper face corner of curb and angle between curb and gutter should be rounded with a radius of i to i 1/2 inches. 9. After getting a good surface, float with plasterer's float until [311] Handbook for Cement and Concrete Users a smooth, even surface is obtained. This surface should be wet or very moist. ic. Dust this surface while it is still wet with granite dust and Portland cement mixed half and half, dusting to take place before the surface water has been absorbed. Immediately smooth down with a trowel, and do not let too great an interval elapse between floating and trowelling. Use a curved trowel for top corners of curb and angles between curb and gutter. 11. After trowelling, finish with a soft brush; an ordinary hearth brush or whitewash brush will do. If the top is too dry sprinkle with water. The brush will take out the trowel marks and give an even texture and color to the finished work. Cut top coat directly over the cuts made in the concrete base, levelling the edges of the cuts with a jointer. 12. Protect the work as previouslv described under Sidewalks. CONCRETE ROADS AND PAVEMENTS The first true concrete pavement was laid in Bellefontaine, Ohio, about 1893. The base was 4-inch concrete, i to 4 and 2-inch wearing surface i to i. The pavement was laid in 5 -inch strips longitudinally starting at each curb and cut into 5-foot squares. During the last 10 years, a great number of concrete pavements have been laid, most of which have been either the " Hassan" pavement or the Blome Grantwood Block, both of which are patented. Mr. J. H. Chubb in an interesting paper read before the National Association of Cement Users, refers to the systems of concrete pave- ments in this country, and the following is quoted from his paper: " A study of the pavements, and of the conditions under which they were laid, makes it quite evident that a first-class pavement may be constructed of concrete at a reasonable cost. Such a pave- ment must, however, be properly laid with suitable materials, to insure satisfactory construction. "A concrete pavement is easily and economically cleaned, and from a sanitary and aesthetic point of view is an ideal pavement. Where properly laid, such a pavement offers a good foothold for horses, is very little, if at all, more slippery than brick or stone Concrete Sidewalks, Curbs, and Pavements block, and certainly less so than asphalt or wood block. , Its resist- ance to traction is probably less than for any other pavement, and while it is not as noiseless as asphalt or wood block, is superior to brick and stone blocks in this respect. " Such pavements are probably not adapted to the heaviest traffic of our largest cities, but may be considered as suitable in all places where brick, wood block, or asphalt would be proper; and adapted to all conditions of traffic except those demanding stone block. Concrete is the ideal material for the paving of residence streets, of alleys, courts, and squares, and in general makes an excellent inter- mediate pavement, as to cost and durability, between the stone- block pavement of heavy travelled streets and the macadam of our country roads." Concrete pavements have been laid by contract at a cost of from 99 cents to $2.92 per square yard. The former figure is un- doubtedly too low for first-class construction even under the most favorable conditions, and $2.92, the cost per square yard of the New Orleans pavement, is high, owing to local conditions. Con- sidering the cost of material and labor and the method of construc- tion, the estimated cost of $1.95 per square yard for the pavement proper as laid in Bozeman, Montana, is probably more representa- tive of the cost of this type of pavement ; if anything, it is a little high. The expensive part of a brick block or asphalt pavement is the wearing surface. In the construction of a concrete pavement a comparatively cheap but satisfactory material, and one that costs much less to lay, is substituted for these expensive wearing surfaces, which explains why this pavement can be constructed at a much less cost than for those now in general use. The saving in cost is in the wearing surface, for practically the same concrete base answers for each type of pavement. GENERAL HINTS FOR BUILDING CONCRETE PAVEMENTS Grading. The entire width of the roadway should be graded to a depth sufficient to lay the required thickness of pavement. The subgrade when properly compacted should be parallel to the finished surface of the street and constructed in the same general Handbook for Cement and Concrete Users way as described for sidewalks; that is, bad spots should be removed and replaced and fills made in 6-inch layers. Heavy rollers and tampers should be employed for compacting the material. Drainage should be provided for in all cases where natural drainage does not exist. Sub-Base. In clayey and other water-holding soils, a 6- to 10- inch sub-base of cinders, gravel, or stone should be laid, the material ranging in size from 1/2 inch to 4 inches. This sub-base is wetted and rolled to a uniform surface, parallel to the final roadway. Pavement Proper. The pavement should be made of a 4- to 6-inch base and a 1/2 to 2-inch wearing surface depending upon the extent of the traffic. A wet mixture should be used for the concrete base, but not too wet to creep under light tamping. This concrete should be deposited across the entire roadway and well tamped with 8-inch hand tampers, weighing at least 18 pounds each. Expansion joints should be provided at the curbline 1/4 inch wide, and every 50 feet across the street 1/2 inch wide, formed by means of wooden or metal strips set in place. These are removed and replaced by paving pitch. Wearing Surface. The wearing surface should be placed within an hour of the base before the lacrer begins to harden much, and the laying follow right along after the completion of the base. A mixture sufficiently wet to allow floating without tamping should be employed. It should be finished with a wooden float and brushed with stiff brooms before completely hardened and may be cut into any desired grooves or blocks to provide good foothold for horses. Protection. The pavement should be protected from the weather until thoroughly set, be kept well sprinkled for 3 days at least, and not put into service in less than a week and longer if weather con- ditions have not been favorable to proper hardening. Patented Pavements. -The essential features of the "Blome Granitoid " Pavement may be stated as follows: 1. The subgrade is prepared 7" below the finished surface. 2. A 5 1/2 inch base of 1:3:5 concrete is then laid in sections extending the full width of street. 3. A i 1/2 inch cement mortar wearing surface made of i cement, 3 parts clean, crushed stone is laid on the green concrete base. [3H] Concrete Sidewalks, Curbs, and Pavements 6. The wearing surface is grooved into 4X9 inch blocks, the length of the blocks being perpendicular to the curb. The grooves have rounded edges and are about 1/4 inch deep and 1/2 inch wide. 7. Before final hardening, the wearing surface receives treat- ment with stiff brushes to eliminate what may otherwise be ob- jectionable smoothness. 8. To eliminate danger from temperature changes, expansion joints are placed 50 feet apart and filled with paving pitch. W/'cffh of ^/reef l/ar/ab/e foundation //? ca^e of c/a FIG. 106. The Blome Granitoid Concrete Pavement. The Hassan pavement is constructed as follows: 1. The street is excavated to the required depth of about 6 inches below grade line. 2. A layer of 11/2 to 2 1/2 inch crushed stone is then placed upon the subgrade properly prepared. 3. This is rolled until top is within 2 inches of finished surface. TABLE XXXIV. OFFSETS FOR CROWNING STREETS OF VARIOUS WIDTHS. From " Concrete in Highway Construction," by Atlas Portland Cement Co. Width of Distance Distance Roadway Between Crown. from Centre of Vertical Offset. from Centre of Vertical Offset. Curbs. Roadway. Roadway. Feet. Inches. Feet. Inches. Feet. Inches. 24 3 4 i 8 ** 30 4 5 4/9 10 i 7/9 36 5 6 5/9 12 2 2/9 48 6 8 | 16 ! 60 8 10 8/9 20 3 5/9 [315] Handbook for Cement and Concrete Users 4. A grout mixture of i part cement to 3 parts fine sand is then poured in the stones and rolling and grouting continued until an even surface is obtained and all voids filled. 5. A 2-inch wearing surface of trap rock is then laid, rolled, and grouted with a i to 2 grout. 6. A finishing coat of i cement, i sand and i pea size crushed trap rock is poured on and brushed over the surface. 7. The pavement then receives its final rolling, and is allowed to harden for a week before being open to traffic. 8. Expansion joints i inch wide filled with tar are provided for at the curbs and about every 100 feet longitudinally. CHAPTER XXVIII CONCRETE IN RAILROAD CONSTRUCTION* Foundations and Retaining Walls. Bridges and Trestles. Train Sheds and Plat- forms. Signal Towers. Power Houses. Shops and Warehouses. Coal and Sand Pockets. Ash Plants. -Round Houses. Turntables, Pits, Tank Supports, and Bumping Posts. Concrete Ties and Roadbed. Posts and Fences. Tele- graph Poles. Tunnels. Docks. Reservoirs. Elevators. IN railroad construction perhaps more than in any other branch of engineering has concrete shown its versatility. Not only is it replacing steel in construction, but to an even greater extent it has taken the place of stone and brick masonry, not merely for founda- tions, but also for various railroad structures above ground. The classes of railroad structures in which concrete is now extensively employed or in which its use is extending, are in part as follows : (1) Foundations, retaining-walls, piers, and abutments. (2) Bridges and culverts. (3) Depots, signal-towers, shops, and other buildings. (4) Coal and sand stations, roundhouses, and turntable-pits. (5) Tank supports, bumping posts, ties, and roadbeds. (6) Posts, fences, telegraph and power poles. (7) Tunnels and tunnel lining. (8) Wharves and docks. (9) Storage reservoirs. (10) Grain elevators. Many of these classes of construction are described with more detail in other portions of this work. In this chapter only such mention can be made of each as will best serve to illustrate the special rdle of concrete in connection with railroad economics. Foundations. Concrete has been used for foundations in rail- road construction for many years. It was first employed to encase * The matter in quotations in this chapter is reproduced by courtesy of The Atlas Portland Cement Co., from " Concrete in Railroad Construction." [317] Handbook for Cement and Concrete Users the tops of wooden piles and form a level platform on which to start the masonry, thus forming the foundation courses of bridge piers and abutments, buildings, etc. Within recent years reinforcement has been introduced, which distributes the stress, prevents settle- ment, and saves material. Retaining Walls. Both plain and reinforced concrete is in general use for retaining walls. As explained in a previous chapter plain concrete walls are made heavy enough to withstand the earth pressures by virtue of their weight alone while reinforced walls consist of a thin, vertical slab attached to a horizontal base, and either braced by counterforts on the back, or else designed as a cantilever anchored to the base slab which also has a front pro- jection, the whole section being in the form of an inverted T. Piers and Abutments. Concrete is employed for bridge piers either as filling for ashlar or cut stone masonry, or for the entire pier, in which case it may be either plain or reinforced. When of plain concrete, the sizes and general proportions are practically the same as for stone piers. If reinforced concrete is used a great saving in cost can be effected either by reducing the size of the pier or by building it hollow with reinforced walls. Abutments are built generally of plain concrete although rein- forced abutments are also coming into use, and consist essentially of a buttressed retaining wall, supporting a heavy reinforced slab, which forms the bridge seat. Bridges and Trestles. One of the most important applications of concrete to railroad construction is in the building of bridges and trestles. In addition to its freedom from rust and decay the use of concrete represents a large saving in maintenance charges, since such a structure requires no paint or repairs. A concrete bridge is free from the excessive vibrations often experienced in steel bridges and from disagreeable noise. Track is easily maintained on such a structure, since the ordinary track ties and ballast take the place of the more cumbersome and expensive track timber of a steel structure. In the construction of a concrete bridge there is no obstruction of traffic from swinging booms as is the case when setting stone of large dimensions in masonry bridges, nor so much difficulty in securing the necessary skilled labor during times when the building Concrete in Railroad Construction trades are active. The materials used can generally be obtained in the immediate vicinity of the bridge site, while the cost is con- siderably less than that of a stone structure of the same capacity. Owing to the deteriorating influence of locomotive gases upon the under surface of bridge floors the construction of overhead highway crossings is one of the greatest problems which the railroad engineer is called upon to solve. Steel girders when unprotected have to be painted very frequently. To do away with this expense, old structures are being encased in concrete, and new ones are being built either of reinforced concrete or of structural steel encased in concrete. Bridges thus constructed are absolutely unaffected by ordinary rust, rot, or fire, and can be designed economically along artistic lines. Stations and Train Sheds. "Railroads throughout the country are adopting the use of concrete in the construction of railway stations of every class, in many cases for the entire structure and in others for integral parts, such as foundations, platforms, smoke ducts, stairways, and often for architectural features, such as cornices, belt courses, and platform columns. Its permanence, fire- resisting qualities, and adaptability to architectural .treatment render it a most satisfactory building material for both large and small stations. "The train shed for the new Lacka wanna passenger terminal at Hoboken, N. J., is an entirely new departure from the hitherto considered standard type of structure for this purpose. Instead of comprising a series of high arches, which in the common type of train shed are continually enveloped in a haze of smoke and 'gases from the locomotives, it consists essentially of a system of low- arched, short span, longitudinal sections, just high enough to clear the largest locomotives in use on the line, with smoke ducts of rein- forced concrete through which the locomotive gases are discharged directly into the open air. In addition to the smoke ducts, the plat- forms, pedestals and footings are of concrete construction. " Platforms. While plain concrete has been used for many years in the construction of low platforms at main stations, the adoption of high platforms on rapid transit and suburban lines during the past few years has opened up a new field for reinforced concrete. [319] Handbook for Cement and Concrete Users "The Brooklyn Rapid Transit Company, which operates elevated railroad lines in Brooklyn, has recently completed a number of stations in the Flatbush section. At these stations the platforms on either side of the track are about 240 feet long and 8 feet wide and are constructed of a reinforced-concrete slab carried on girders of the same material which are in turn supported by concrete piers placed at 20-foot intervals. " Expansion joints are provided every 60 feet by separating the construction entirely with tarred paper. "The outside edges of the platform are equipped with patent bulb nosing. "The fences running the length of the platform and forming the guard railings on the outside and ends of the platforms are constructed of cement plaster on metal lath. "In designing the platforms a live load of 150 pounds per square foot was assumed and the concrete was figured at 500 pounds per square inch extreme fibre stress in compression, while the steel was allowed to carry 16,000 pounds per square inch in tension. Signal Towers. "Railroads throughout the country are ex- periencing a period of architectural renaissance. Structures which have in the past been built of temporary construction, apparently regardless of outward appearance, are being replaced by permanent buildings of artistic design. This is particularly true in the case of signal towers, the old unsightly and necessarily temporary wooden structures being superseded either by entire concrete or combina- tion concrete and brick towers of pleasing appearance and per- manent construction. "The standard signal towers of the electric zone of the N. Y. C. & H. R. R. R. are combination brick and concrete structures. In these towers, the footings and foundation walls below grade are of i : 4 : 7 i / 2 concrete, and the walls above grade up to the first floor level are of i : 3 : 6 concrete. All the sills and lintels, the coping, the overhanging bay window and supporting brackets and the cornice are of i : 2 : 4 concrete. In this work an excellent surface finish was obtained by floating the green concrete with water and rubbing it with a mortar brick composed of i part cement to 2 parts sand. The roof and floor construction consists of 1:2:4 concrete slabs, reinforced with 1/2 inch round rods, supported by steel I-beams. [320] Concrete in Railroad Construction Power Houses. "The electrification of railroad systems, which bids fair to be a thing of the near future, will necessitate the con- struction of a large number of power stations along their lines. The N. Y., N. H. & H. R. R., which has electrified its line between New York and Stamford, in the construction of a power house at Cos Cob, about three miles from Stamford, has shown what can be done with concrete in this kind of construction. "The exterior of this power house was designed in the Spanish Mission style of architecture, with very pleasing results. The foundations, column footings, and walls up to the water table were built of monolithic concrete mixed in the proportions of i part Atlas Portland cement, 3 parts sand, and 5 parts 2-inch crushed granite. All exposed surfaces of the walls were given a bush- hammered finish. For the water-table, window arches, coping and window sills, monolithic blocks were used. These blocks were built in special shapes and composed of concrete having the same proportions as the other monolithic work. The facing consisted of a mixture of i part cement to 2 parts sand. "The walls above the water-table were built of hollow blocks, lo-inch by 1 2-inch by 24-inch, composed of a mixture of i part cement, 3 parts sand, and 3 parts 11/4 inch crushed granite, faced on the exterior surface with a mixture of i part of cement to 2 parts of sand, and where the inner surface of the wall is exposed with a mixture of i part cement to 4 parts sand. All the window lintels were cast in place, and consist of 1:3:5 concrete reinforced with two 3/4-inch trussed bars. Railroad Shops and Warehouses. "The same advantages which reinforced concrete possesses over other materials for the construction of power houses are equally enjoyed by it as a material for shop and warehouse buildings for railway purposes." The C. R. R. of N. J. have recently erected a mammoth seven- floor warehouse in Newark, N. J., having a length of 360 feet, a width which varies from 130 to 165 feet, and a storage capacity of about 1,200 carloads of freight. The first floor is devoted to team- ing, the second to the freight tracks, and the basement and four top floors to storage. In general the building consists of a steel frame and concrete walls, with steel columns and girders carrying floor slabs of rein- si [321] Handbook for Cement and Concrete Users forced concrete. Owing to the presence of quicksand, an excep- tionally wide spread of footing was required which resulted in the engineers making the foundation one continuous plate of concrete fifteen inches thick, reinforced with extra heavy expanded metal. The walls, which are embellished with rustications, mouldings, dentils and cornices, are twenty inches thick to the second story, sixteen inches thick to the third story, and twelve inches thick from there up to the top. The reinforcement for the walls consists of expanded metal and 3/4-inch rods laid horizontally about four feet apart. Reinforced concrete is peculiarly adapted to the construction of structures which are to be used for the storage of coal on account of its fire-resisting qualities, permanence, and strength. Coal and Sand Pockets. The combination coal and sand station built for the N. & W. Ry. in 1907, consists of an elevated coal pocket, having a capacity of 260 tons of coal, and a wet sand storage house on the ground with an elevated dry sand bin. The coal is dumped through a 10 X 12 foot track hopper into a reciprocating feeder which delivers it into a steel bucket elevator, discharging into a conveyor trough above for distribution into the pocket. The coal is fed to the engine tenders through hinged gates and over counterweighted coaling chutes. The wet sand passes into a dryer, emptying into a sand pit underneath, where it is scooped up and carried by a sand elevator which dumps it from above into the dry sand bin. From this bin it is fed to the engines through two tele- scopic sand spouts. In the construction of the building, concrete mixed in the pro- portion of one part Atlas Portland cement to 2 parts sand to 4 parts broken stone was used. The side walls were designed on the basis of the computed lateral pressure exerted by bituminous coal weighing forty-seven pounds per cubic foot. This gave a maximum lateral pressure of two hundred and forty-eight pounds at the bottom of the pocket; and a vertical pressure on the bottom slab of nearly one thousand pounds per square foot. Ash-handling Plants. Inasmuch as wood burns and steel corrodes, it has long been a problem as to how to build ash-handling plants capable of withstanding the destructive effect of ashes quenched with water. The advent of reinforced concrete into the Concrete in Railroad Construction field of railroad construction has successfully solved this problem. At the present time most of the plants being built throughout the country consist of a steel framework which support bins constructed of reinforced concrete. Roundhouses. The adaptability of concrete to roundhouse construction is clearly demonstrated in the report submitted on that subject by the Committee on Buildings of the American Railway Engineering and Maintenance of Way Association, before the annual convention of that society held in Chicago, March, 1908. For the purpose of discussion, the roundhouse was considered divided into Foundations and Pits, Roof, Supporting Columns, and Outer Walls; and excerpts from the report are given below in order named. Foundations and Pits. " While in some cases local conditions may favor the use of stone or brick for foundations and pits, it may be stated, as a general proposition, that good practice in roundhouse construction now requires the use of concrete for these parts of the structure. When a solid foundation cannot be obtained within a few feet below the floor level of the building a considerable saving may be effected by the use of reinforcement." Roof. "In economy of first cost, durability and fire-resisting qualities, there is no other fireproof roof construction which is equal to reinforced concrete. Steel except as a reinforcement for concrete, is not a satisfactory material for engine house roof construction." Supporting Columns. "If the roof is of reinforced concrete, it should be supported by columns of the same material in the outer and end walls, as well as in the interior of the building. These columns should be concreted with the roof, the concrete being run into the forms from above. The columns on the inner circle to which the doors are attached should be of some other material than concrete, preferably steel or cast iron." Outer Walls. "For a structure roofed with reinforced concrete, the curtain walls may be of brick, plain concrete, reinforced concrete, or plaster. Concrete will, if properly made, give good service and local costs of materials and labor would ordinarily determine which of the first three styles of curtain walls named above should be built. The plaster curtain wall may be used where it is desirable or neces- sary to reduce the first cost to a minimum. [323] Handbook for Cement and Concrete Users "To build such a wall Portland cement is mixed with enough lime so that it can be worked with a trowel and is plastered on expanded metal. The latter is stiffened with rods and channel irons, which are used to support the window frames. A wall of this character can be built more quickly than a concrete wall, is efficient and should be durable. If damaged by a locomotive or otherwise, it is easily repaired, and alterations can be readily made. Used with concrete columns, it should not crack, and its first cost is but about half that of a brick wall." Cost. "The cost of concrete construction in roundhouses de- pends largely upon the number of times the forms can be used. If follows, therefore, that where the structure is large and the forms for each unit or stall can be used many times in the same roundhouse, the cost per stall is much less than in a small building. Consequently reinforced-concrete construction is more economical in large than in small roundhouses, when compared with brick or frame construction." Turntable Pits, Tank Supports, and Bumping Posts. " In connection with roundhouse construction the subject of turntable pits is of special interest. The facility and cheapness with which concrete pits can be built is so generally recognized that practically all turntable pits constructed to-day are built of concrete. " Owing to its strength, rigidity, and resistance to fire and decay, reinforced concrete is well suited for the construction of water-tank supports." Such supports are octagonal in form and consist of reinforced- concrete columns, strongly braced, and supporting a platform from 20 to 40 feet high. The columns may be reinforced with old rails or with the usual bar and hoop reinforcement. The platform should be about 9 inches thick, and strongly reinforced to sustain the weight of the tank. "A bumping post, to insure safety against rotating or breaking down under constant buffing, should be constructed so as to be anchored in the earth direct rather than attached to the track itself, as is the case with practically all of the patented posts now in use on railways in this country. By the use of concrete, bumping posts can be constructed economically so as to meet the conditions of stability and permanence." [324] Concrete in Railroad Construction Concrete Ties and Roadbeds. One of the most serious and perplexing questions which confront the railroad engineer of to-day is the tie problem. As an evidence of this, during the year 1907, the railroads of the United States used approximately 118,000,000 ties, a very large percentage of which were renewals. This vast inroad upon the limited and rapidly decreasing supply of timber has caused wooden ties to become poor in quality and high in price, with the result that railroad engineers are beginning to realize the necessity of procuring a substitute. Many roads have been experimenting with concrete ties of various designs during the past few years. While none of these have been tested long FIG. 107. The Kneedler. One of Many Forms of Concrete Ties. enough under heavy and high speed traffic to warrant the selection of any one as a proper substitute for wooden ties under all con- ditions the success of some of the ties tested- thus far has been great enough to convince railroad engineers who have given the most study to the subject that a properly reinforced concrete tie with proper fastenings, is both practical and economical, especially for tracks where the speed is low and where conditions are adverse to the life of wood or metal. Without question concrete ties are en- tirely suitable and economical for use in yards and sidings and for this purpose alone there is an enormous field for their installation and use. Concrete ties possess certain natural advantages over either timber or steel inasmuch as dampness, drawn fires, and insects have [325] Handbook for Cement and Concrete Users absolutely no effect upon them. In addition, they are practically independent of the steel and timber market, and can be made along the line of the railroad, and, as compared with the chemically treated timber or the steel tie, at a reasonable cost. Concrete ties have been for about ten years in successful use in Indo-China, where a very peculiar species of ant destroys wooden ties in a few months. At the present time it is estimated that there are over 1,000,000 of these ties in service. They are of an inverted T-section, the flange of which is laid on the ground, the stem being vertical. The rails are fastened by bolts which are embedded in an enlargement of the stem where the rails pass. In Italy concrete ties have been tried with such success that the Italian government has recently placed an order with various manufacturers in Italy for 300,000 concrete ties.' In the design of a successful tie there are a number of important functions that seem to be more or less overlooked in many of the ties thus far built. Cushion blocks, if used, should be removable, and the fastenings should be of such a nature that they will not tend to shake loose. They should also be easily accessible, so that they can be renewed when injured. Inasmuch as automatic block signalling is being extended very rapidly upon practically all of the railroads, it is important that the rails should be insulated, and therefore it is necessary to place sufficient concrete between the metal in contact with the rails and the longitudinal reinforcement. Many long ties have failed from the fact that they were not designed to act as cantilever beams, thus being unable to withstand the severe shocks coupled with the sinking of the tie under passing loads on centre bound track. The difficulty experienced with tie blocks has been in keeping them in longitudinal position and maintaining them so that the vertical deflection of one rail will not greatly exceed that of the other, thereby causing rolling and pound- ing of the equipment. ' Finally, ties should be of sufficient strength to support derailed cars and engines until they are off the ends of the ties and actually into the ditch; otherwise, an ordinary derailment may become a serious wreck. [326] Concrete in Railroad Construction Solid Concrete Roadbeds. While the original cost of a solid concrete roadbed is greater than the ordinary cross-tie con- struction, it is undoubtedly more economical in the end for tunnels and subways; especially if the space be cramped, traffic heavy, and a track cannot be temporarily abandoned; also where the running rails, guard rails, and third rails are attached to long ties (as in the case of electrified lines), it is extremely difficult and very expensive to maintain and tamp up track to surface and make tie renewals. A solid roadbed can also be used to great advantage and economy in rock and earth cuts where there is always a large maintenance expense to keep ditches open and track in good surface. In addition to the question of ultimate economy, the solid con- crete roadbed is especially commendable for tunnel and subway /,:.&: ../' iv ^v : v ::/: 'v ; - :;; " >*.. ''>'*.< '** *-. Vi.'/^;/ . . ..-C^....^,-*^-*^'."- FIG. 108. Concrete in Trackwork: Hudson Terminal Station, New York. construction from a hygienic standpoint; for in most tunnels and subways ventilation is difficult and the accumulation of grease, dirt, and debris, which is readily held by the ballast of the cross-tie track construction, is a serious menace to the health of the passen- gers. This danger can be eliminated in the solid concrete con- struction, as the entire roadbed can be flushed with water and kept in a neat, clean, and sanitary condition. Posts and Fences. The growing scarcity and the increasing cost of suitable timber for posts has brought concrete into quite general use. Concrete posts possess the advantage over wooden ones not only of unlimited life, greater strength, and resistance to action of fire and decay, but also they present a more pleasing appearance. It would seem that the concrete post is particularly adapted to railroad use. Most of the post machines are cheap and portable [327] Handbook for Cement and Concrete Users and the materials employed are in daily use on all roads using concrete. The materials are cheap and easily obtained. The Lake Shore and Michigan Southern Railway use concrete whistle posts, made in moulds like blocks, which are 31/2 inches thick, 12 inches wide, and are set about 51/2 feet above the ground. The letters and signs are cast right in the post and are painted black. In places where a substantial fence is required, ultimate economy, strength, durability, and a pleasing appearance can be attained by the use of reinforced concrete. Two types of concrete fences have been tried with success, viz., solid reinforced concrete and cement plaster on metal lath. The solid type of fence generally consists of a vertical slab of reinforced concrete about 3 inches thick with a rounded moulding like a hand rail on the upper horizontal edge. Telegraph Poles. Owing to the increasing scarcity and inferior quality of wood, which has heretofore been used exclusively for telegraph and trolley poles, engineers have been experimenting with reinforced concrete for a number of years with the result that poles have been designed which are meeting the requirements in every way. Among the advantages of the reinforced-concrete pole, the following are worthy of special mention: (i) Lines thus equipped have practically no trouble from lightning, the reinforcing rods apparently acting as conductors of electricity; (2) the poles require no preservative or paint to protect them from the ravages of the weather, as is the case with wood or steel ; and (3) the material is elastic enough to withstand all ordinary shocks. Tunnels and Tunnel Lining. One of the most common uses of both plain and reinforced concrete is in the construction of tunnels and subways. The term tunnel, as generally understood by railroad engineers, is applied to construction under cover, in which the tunnel bore is advanced by drifting, the surface of the ground above the work not being disturbed. The term subway is applied to open cut construction. A tunnel for heavy and fast railroad traffic should be built with a concrete lining, and for still greater economy the roadbed should also be constructed of this material. The old Bergen Hill tunnel on the Lacka wanna Railroad is lined with brick for a portion of its length, yet fourteen men are at work every night Concrete in Railroad Construction in the year inspecting the lining and repairing the track. This ex- pensive and dangerous maintenance work, which costs annually about $6,000, is practically eliminated in the new tunnel described below, which is built with the entire lining and roadbed of concrete. This tunnel is 30 feet wide in the clear, 23 feet 5 inches high from the base of the rail to the crown of the roof arch, and has a concrete lining of a minimum thickness of two feet. The length of the tunnel is 4,280 feet and at two points located at about one-third the length of the tunnel from each portal it is connected to the old tunnel, which is immediately alongside the new, by an open cut extending across the four tracks, 100 feet long and 80 feet wide. At about the centre of the sections, into which these open cuts divide the tunnel, shafts 10 feet long and 30 feet wide were sunk to the new tunnel. These shafts and open cuts were used to good advantage in moving the waste material from the headings and they also greatly facilitated the work of placing the concrete lining. Docks. Inasmuch as practically every railroad system in the country owns valuable water front the question of dock construction is a most important one. The recent terrible fires with their attend- ant devastation along the water fronts of Hoboken and of Boston, have demonstrated only too clearly the absolute necessity of positive fire protection in structures of this nature. The new piers which the Delaware, Lackawanna and Western Railroad have designed to replace those burned down in the Hoboken fire of 1904 are to be built entirely of concrete construction from the cut-off of the piles. In the tropics where the waters are infested with the teredo and limnoria terebrans, either of which will destroy a wooden pile in a few years, and where the very atmosphere itself eats away unprotected wooden and steel structures, reinforced concrete is especially adapted to the construction of wharves and warehouses. Practically all the docks of any magnitude now being constructed in South and Central America and the Philippines are designed as entire concrete structures. Storage Reservoirs. The advent of power construction into the field of railroad engineering incidentally introduces another problem for railroad engineers in the subject of storage reservoirs for supply- ing these plants with water. [329] Handbook for Cement and Concrete Users Reinforced concrete has been used extensively in the construction of reservoirs, and when properly designed and constructed is a most suitable material on account of its durability and adaptability to lighter design than common masonry. For large or small tanks it is usually cheaper than steel and requires no repairs. Reservoirs are built most economically of circular form, and all the tensile stresses must be taken by the steel hoops. In building water tanks, the materials for the concrete must be very carefully proportioned so as to give a watertight wall, and the stone should be of such size that a good surface can be easily ob- tained. The proportions used to resist the percolation of water usually range from i : 2 : 2 to i : 2 1/4 : 4, the most common mixture being 1:2:4. The concrete should be mixed so that it will entirely cover the reinforcing metal and flow against the form. It is absolutely essential that the concreting for the entire tank should be done in one operation, or else that the surface be specially prepared and treated to make water-tight joints. Grain Elevators. Reinforced concrete is especially adapted to the construction of grain elevators or other structures to be used for the storage of grain on account of its being absolutely proof against fire, water, or dampness, dust and vermin; which are all important and essential qualities of the ideal grain elevator. Grain elevators may be grouped into two classes according to the arrangement of the bins and elevating machinery; viz., elevators which are self-contained, with all the storage bins in the main eleva- tor or working house; and elevators consisting of a working house which contains the elevating machinery and storage bins connected with the working house by conveyors. Reinforced-concrete eleva- tors are commonly built of the latter type, with a working house that ,. is generally rectangular in shape with either square or circular bins connected with the independent storage bins, which are usually circular. Concrete is being used in enormous quantities at the present time by all of the leading railroads in the United States. Prominent among these may be mentioned: The New York Central and Hudson River Railroad in the con- struction of its new passenger terminal in New York. [330] Concrete in Railroad Construction The Pennsylvania Railroad in the construction of its new depot in New York, the tunnels under the North and East Rivers, and the yards at Long Island City. The Chicago, Burlington and Quincy Railroad in connection with its track elevation work in Chicago, and in its work of replacing wooden with reinforced concrete trestles throughout its system. 1 331] CHAPTER XXIX THE UTILITY OF CONCRETE ON THE FARM* Advantages of Concrete for the Farmer. Concrete Types Found on the Farm. Posts. Troughs. Tanks. Farm Drainage. Cisterns. Cess Pools. Stalls. Silos. Miscellaneous. Useful Hints for the Farmer. Advantages of Concrete for the Farmer. Concrete, both plain and reinforced, has provided the farmer with an entirely new build- ing material. Indestructible, economical, and fireproof, it offers, under most conditions, features of advantage over every other type of construction. Concrete has long been recognized as the ideal building material for heavy construction and is now looked upon with equal regard for the purpose of the lighter forms of construction found necessary on the progressive and up-to-date farm. During the past few years the price of lumber has advanced to almost prohibitive figures, and therefore it is natural that a sub- stitute material which is both cheap and durable, sanitary and beautiful, should gain the recognition which it deserves. The cost of concrete work is variable with the conditions under which the work is performed. It is generally cheap for the farm structure, because the work can be done by the farmer at odd times, with comparatively cheap help, as it is unnecessary to employ masons or carpenters. The lumber for the forms is expensive, but it can be used again, generally, for other purposes. Contractors in concrete construc- tion figure to save 30 per cent of the form lumber for subsequent use. If the farmer hires carpenters and laborers to do the work, his concrete structure will have a larger first cost than wood construc- tion, but it will neither decay nor burn and will be the cheapest in the end. * Partly condensed from " Concrete about the Home and on the Farm," pub- lished by Atlas Portland Cement Co. See also bulletins on Concrete Tanks and Concrete Silos published by American Association of Portland Cement Manufacturers. [332] The Utility of Concrete on the Farm Concrete Types Found on the Farm. A competent engineer or architect should always be employed or consulted in the preparation of plans for houses, barns, or other structures of any magnitude; but by carefully following authentic rules and specifications, the inexperienced farmer can safely undertake reinforced-concrete construction of simple structures. Concrete is found on the farm in the following forms: Posts of all kinds, troughs and tanks for various purposes, walls of all de- scriptions, blocks of all styles, steps and stairs, side-walls, curbs, and gutters, drains, floors, stalls, and pens, silos, corn cribs and grain elevators, houses, barns, and cellars, and in many miscellan- eous forms too numerous to mention. Fence Posts. Concrete fence posts may be considered as typical of post construction. They are generally made with a square or rectangular cross-section, the length depending upon the height desired above ground. The amount to be placed underground depends upon the depth of the frost line which is sometimes 3 or 4 feet. It is customary to make them slightly larger than the wooden posts which would be used for the same purposes, the average cross- section being about 25 square inches. The making of fence posts has already been described in Chapter XV. Hitching Posts, Clothes Posts, Horse Blocks. Hitching posts and clothes posts may be made in a similar manner, round if desired, and reinforced with 3/8" iron rods if more than 7 feet long. Horse blocks are so heavy that they are generally cast in place. An ordinary box form will serve the purpose. It is best not to plaster the top or sides, for it is apt to crack or peel off. Trowel the surface when the concrete is first laid. Care should be used in the preparation of a foundation to prevent unequal settlement. Concrete Watering-Troughs. A concrete watering-trough is one of the easiest and simplest tanks that can be made of concrete, and will never rot. They are frequently built not only in the barn- yard or near the house, but, where large numbers of stock are pastured, they are built in the fields, to hold water from a small spring which would not otherwise be available. Watering-troughs may be made with or without reinforcement, the difference being that between a 5- and 8-inch wall. Typical [333] Handbook for Cement and Concrete Users dimensions are 10 ft. long, 2 ft. wide, 2 ft. deep, 5 in. thick, which may be varied at will. The reinforcement may be done by placing a 2 1/2 inch layer of concrete in the form, and immediately after placing and before the concrete has set, place a sheet of woven fence wire or some other wire fabric over the concrete, bending it up so that it will come to within one inch of the top of the forms at the sides and ends. Place 21/2 inches more of the concrete in the bottom and ram lightly to bring the mortar to the surface and smooth it off evenly. Have the inner form all ready and as soon as the base is laid and before it has begun to stiffen set it, taking care to keep it at equal distances FIG. 109. Watering-trough, Forms, and Bracing. from the sides, and then immediately fill in the concrete between the outer and inner forms to the required height. Small troughs have been built at as low a cost as $5.00. Dipping Tanks, Hog Troughs, Slop Tanks, Fertilizing Tanks. Dipping tanks for disinfection, hog troughs for feeding, slop tanks for heating food in cold weather, fertilizing tanks for containing fertilizing fluids, have all been made of concrete and have given satisfaction. Methods of procedure in such construction will readily suggest themselves. Barn and cellar floors may be made after the manner of side- walks, the barn floor requiring a porous sub-base from 6 to 12 [334] The Utility of Concrete on the Farm inches thick while the cellar floor can be laid directly on the earth which should be evened off and tamped hard. Waterproofing is sometimes desirable. Feeding floors of concrete have been found advantageous for the spreading of fodder. Farm Drainage. Farm drainage is an important problem and concrete its most practical solution. Drains may be made in place by digging a trench with sufficient grade to flush well, and setting forms of the shape of the inside of the drain, so that the concrete will be from 3 to 4 inches thick. If a tile drain is preferred, they may be made from concrete in the following manner: Use i part P r ^Al 1! ! *5/tf'f''ST>6 ?0>f \/n 1 -Ofc =i -c.-.rir 1 _- ! FIG. ii r^If fi : n" "* > / / / / 3 w -< ^LvX^ it'eoe/f* /"*? I wmtzzz^ D. Forms for Watering-trough. Section through Centre. of cement to 3 of clean sand. " One or two sets of forms with four or six tile each may be made so that they can be filled every morn- ing, and in this way enough tiles can soon be on hand to drain a large acreage of land. The concrete tile should be made with a circular bore, and may be either circular, or square on the outside." "Use ordinary stove pipe of the required diameter for the inside mould; this should project far enough above the top of the wood form so that a good grip can be had on it in order to remove it from the concrete. If desired, holes can be punched through the stove- pipe near the top and a rod placed through these holes in order to [335] Handbook for Cement and Concrete Users more easily withdraw the pipes. To keep the pipes in place when pouring the concrete for each tile, drive four nails in the floor or platform on which the tile are to be cast, leaving them projecting so as to locate the end of the pipe and keep it from getting out of position but yet not hindering its removal. The stove pipes must be thoroughly cleaned and greased each time they are used, and must not be dented or have any irregularities on them to make them catch." "The time to remove the stove pipe core varies with the wetness of the mix and the temperature, but it should be pulled as soon as FIG. in. Forms for Square Trough. the top of the concrete begins to harden, which generally is from one-half to one hour; if left too long it is very hard to get them out. The outside forms can usually be removed after two or three hours, or may be left until the next morning. To remove the wood forms, pull the protruding nails with a claw hammer, and carefully turn the whole tier on the side. Next draw out the other side with the partitions attached. If any of the forms stick, they can generally be started by tapping them lightly with a hammer; this applies as well to the stove pipe cores. Scrape the form carefully, re-oil, attach the long side and they are ready for a second filling." Cisterns, Cess-Pools. Concrete cisterns and cess-pools are of similar construction. "Make a circular excavation 16 inches wider [336] The Utility of Concrete on the Farm than the desired diameter of the cistern, or allow for a wall two- thirds the thickness of a brick wall that would be used for the same purpose, and from 14 to 16 feet deep. Make a cylindrical inner form the outside diameter of which shall be the diameter of the cistern. The form should be about 9 feet long for a 1 4-foot hole, and ii feet long for one 16 feet deep. Saw the form lengthwise into equal parts for convenience in handling. Lower the sections into the cistern and there unite them to form a circle, blocking up at intervals six inches above the bottom of excavation. (Withdraw blocking after filling in spaces between with concrete and then fill holes left by blocking with rich mortar.) Make concrete of one part Portland cement, two parts clean, coarse sand, and four parts broken stone or gravel. Mix just soft enough to pour. Fill in space between the form and the earth with concrete, and puddle it to prevent the formation of stone pockets, using a long scantling for the purpose and also a long-handled paddle for working between the concrete and the form. To construct the dome without using an expensive form, proceed as follows: Across top of the form build a floor, leaving a hole in the centre two feet square. Brace the floor well with wooden posts resting on the bottom of the cistern. Around the edges of hole, and resting on the floor described, con- struct a vertical form extending up to the level of the ground. "Build a cone-shaped mould of very fine wet sand from the outer edge of the flooring to the top of the form around the square hole and smooth with wooden float. Place a layer of concrete four inches thick over the sand so that the edge will rest on the side wall. " Let the concrete set for a week, then remove one of the floor boards and let the sand fall gradually to the bottom of the cistern. When all boards and forms are removed they can be easily passed through the two-foot aperture and the sand taken out of the cistern by means of a pail lowered with a rope. This does away with all expensive forms and is perfectly feasible. The bottom of the cistern should be built at the same time as the side walls and should be of the same mixture, six inches thick. " Box Stalls. Box stalls of concrete are found to be warmer in winter and cooler in summer and so are held in high favor. Con- crete barns with hollow walls are readily ventilated by utilizing the air spaces for that purpose. 22 [337] Handbook for Cement and Concrete Users Dairy. The sanitary features of concrete make it an especially appropriate material for use in dairy construction. Being a non- conductor of heat concrete can be used to advantage when it is desired to build an ice box as a part of the building itself. Concrete Silos. During the past decade silos have come into universal use upon the American farm. A good silo must be air- tight, water-tight, smooth on the inside, and maintain an even temperature. A concrete silo meets all these requirements with the additional advantage of being vermin-proof and indestructible. There are three kinds of concrete silos, Solid .Wall Monolithic, Hollow Wall Monolithic, and Concrete Block. The first type re- qi4res the least material, the second prevents freezing of silage in FIG. 112. Handy Road Roller of Concrete. cold climates, the third requires no forms to build. The relative cost will depend largely upon local conditions. Having selected the type of silo to build, the size is next considered. The diameter of the silo depends upon the number of cattle to be fed daily, the height upon the number of days for which a supply of fodder is required. Ten head of cattle will consume thirty-six tons of silage in 180 days, requiring a silo of 10 feet in diameter and a height of 25 feet. Seventy head will consume 252 tons in the same time and require a silo 19 feet in diameter and 40 feet high. Intermediate dimensions may be estimated proportionally. These figures pro- vide for 40 Ibs. per cow per day, at least two inches in depth of silage being consumed daily. The diameter of a silo should never exceed 20 feet, and is better too small than too large. [338] The Utility of Concrete on the Farm "The concrete-block silo is built of circular hollow blocks laid in cement mortar, and reinforced with steel hoops which fit in between every second or third course. When finished the silo is usually painted both inside and out with a cement mortar to insure air tightness. The block silo, like the hollow silo, has a dead air space in the walls which tends to prevent freezing. The principal advantage of the concrete-block silo lies in the ease with which it can be constructed. "The hollow wall monolithic concrete silo is constructed much the same as the solid wall except that two walls are built instead of FIG. 113. Wooden Form for Concrete Roller. one with an air space of 4" between them. The inner wall is rein- forced." The only reason for the outer wall is to form the air space which prevents the silage from freezing. The solid -wall silo is cheap and easily built and fulfills all the requirements of a perfect silo. This type is the one most frequently adopted. Its cost is about 25 per cent less than hollow-wall con- struction. The average dimensions of a silo are 10 feet inside diameter and 25 feet in height. It is built in the following manner: Ex- cavate to a depth of 4 or 5 feet and dig a circular trench one foot deeper for the foundation walls. Fill the trench with a i : 3 : 6 mix- [339] Handbook for Cement and Concrete Users ture and spread 4 inches more over the entire foundation. The earth under the footing should be dry and firm and the excavation well drained. If the foundation is poor the concrete base should be reinforced in the same manner as the walls. After the founda- tion and floor are complete, the remaining operations take the fol- lowing order: FIG. 114. Forms and Staging for Concrete Silos. 1. The building and petting of forms. 2. The placing of the reinforcement. 3. The mixing and placing of concrete. 4. The removal, hoisting, and resetting of the forms. The wall forms are circular and are placed six inches apart to give the proper thickness to the wall. Their height is generally three feet, which enables three feet of silo to be built without shifting the forms. After each three-foot section is complete the forms [34o] The Utility of Concrete on the Farm are loosened by means of adjusting bolts, raised by levers and reset by the bolts, this operation being repeated until the structure is complete. The forms consist of 2" X 6" plank cut circular and held together by i" X 4" cleats, forming 2 complete circles held apart by i" X 4" studding. The inside surface is then covered with sheet steel, No. 24 gauge or with i" tongued and grooved boards. Both outside and inside forms are constructed in the same manner. Screw bolts are used to pull together and separate the forms. Reinforcement for Silos. "The concrete reinforcing of the silo walls with small steel bars or steel wire must be done with accuracy and care, as the strength of the silo depends on the correct use of steel in the walls. The silo walls are reinforced in two directions; vertically, to prevent failure due to wind pressures, and horizontally to prevent failure due to the pressure of the silage. Silage is a heavy material and is estimated by the various State experimental stations to exert a side pressure of no Ibs. per square foot for every foot in depth. ' ' Since the pressure in a silo increases with the depth, it is neces- sary to make the walls much stronger at the bottom than at the top. "In no case should the horizontal wires or bars be placed over 18" apart or the vertical more than 36" apart. The horizontal reinforcement should be cut in one length, if wire, and the ends looped together and twisted back. If bars are used, the ends should be bent around each other at each lap. The extreme ends of the vertical reinforcement should be tied by bending around four extra strands of the largest wire used, two wires being placed 2" below the top of the silo wall, and the other two in the centre of the silo footings. "The vertical rods should be placed in short lengths, as it is very hard to handle the forms with rods running the entire height of the silo. These short lengths can be twisted or spljced together, as the wall is built up. "In starting the vertical reinforcement in the footing use only 2' 6" or 3' o" lengths, taking six inches to twist around the two horizontal tie rods or wires placed in the centre of the footings. This will leave i' 6" to 2' o" to stick above the finished footings. [34i] Handbook for Cement and Concrete Users "The next section of vertical reinforcement is tied to these short lengths, and they will not interfere with the setting of the concrete forms." A roof should be made of 2" X 6" rafters set at a good pitch, and covered with i" sheeting; this in turn may be covered with galvanized iron, tin, or shingles. A hollow-wall silo is constructed in the same way, except that the forms are placed one foot apart and circular boxes used to form the air space as the concrete is placed. TABLE XXXV. DATA FOR REINFORCED-CONCRETE SILOS. (Including 6-inch Floor.) Height. Inside Diameter. Thickness of Wall. HORIZONTAL REINFORCEMENT. Cement, i Part. Sand, 2 Parts. Stone or Gravel, 4 Parts. Size. Spacing Feet. Feet. Inches. Inches. Inches. Bbl. Cu. Yd. Cu. Yd. 10 5 6 y< 12 6y 2 2 4 10 10 6 X 12 15 y 2 4 8 15 5 6 % 12 gy 2 3 6 15 8 6 H 12 i$X 4 8 15 12 6 H 12 24 6y a 13 20 8 6 H 12 19 X 5 10 2O 12 6 H 12 29 y 8 16 2O 15 6 X 12 38 10 20 2 5 10 6 x 12 27 y* 7 X 15 2 5 15 6 X 12 45 12 24 2 5 20 6 % 12 62 i6y 2 33 3 IO 7 X 12 37 IO 20 3 15 7 X 12 58 15* 31 30 2O 7 y* 12 80 22 y a 45 40 15 8 % 12 80 22 y, 45 40 2O 8 H 12 114 30 x 61 40 25 8 K 12 147 38 M 77 Place vertical rods same size as horizontal, 2 M feet apart. A cubic yard is about i K single load or K of a double load. Concrete is also found in many other useful forms upon the farm, such as: well curbs, ice-houses, root and mushroom cellars, hen houses, green houses, flower boxes, cold frames, wind mill foundations, lawn rollers, porch steps and lattice, and chimney caps. Convenient uses for concrete in such domestic construction will occur to the builder's mind as necessity arises. [342] The Utility of Concrete on the Farm Useful Hints for the Farmer. i. Always use the best Portland Cement obtainable. 2. Store your supply of cement in a dry place until ready to use. 3. Use sand that is both clean and well-graded. A large pro- portion of the grains should measure from 1/32 to 1/4 of an inch in diameter. If fine sand must be used, increase the amount of cement ; that is, use a richer mixture. 4. If the sand is dirty, wash it. 5. If the gravel is dirty, wash it. 6. Before using the product of a gravel bank, screen through a i /4-inch sieve and remix, using about twice as much stone as sand. 7. Use gravel or broken stone up to 2 1/2 inches in diameter for foundations and thick walls but limit the size to 3/4 inch diameter when reinforcement is to be used. 8. Avoid the use of soft stones in the aggregate. 9. Use clean water, free from alkalis. 10. Use enough water to give the concrete the consistency of heavy cream. 1 1 . For ordinary work use a i : 2 : 4 mix. 12. For forms, use white pine, fir, yellow pine, or spruce and green timber if possible. 13. Grease the inside of the forms with soap, linseed oil, lard, and kerosene, or petroleum. 14. Omit the greasing if the surface of the concrete is to be plas- tered, in which case, wet the forms just before placing the concrete. 15. Lay sheathing or form boards horizontally. Place studs 2 ft. apart for i in. sheathing and 5 ft. apart for 2 in. sheathing. 1 6. Brace the forms securely. 17. Do not drive the nails all the way home, but let the heads project so that they may easily be withdrawn. 1 8. Keep forms from bulging or separating by the use of bolts or wire. 19. Place concrete in forms in layers from 6 to 12 inches thick. Spade and tamp. 20. After removing the forms, concrete which is exposed to the sun should be soaked with water each day for a couple of weeks. 21. In laying the concrete in hot or freezing weather, use the precautions outlined in Chapter VII. [343] SECTION VI IMPORTANT MISCELLANEOUS DATA ON CONCRETE CONSTRUCTION CHAPTER XXX THE WATERPROOFING OF CONCRETE STRUCTURES The Necessity for Waterproofing. Modern Methods of Waterproofing. General Conditions of the Work. Principles to be Followed. The Membrane Method in Detail. The Integral Method in Detail. Waterproofing by Means of Surface Coatings. Tabular Outline of Modern Waterproofing Processes. The Necessity for Waterproofing. In many of the forms of construction work to which concrete is so admirably adapted, its use brings with it one inherent fault a fault for which remedies have long been sought, but which, until recent years, have not been found in a practical form suited to all the varied needs of modern construction. This striking fault of concrete work is its great thirst for water, a fault which varies in its gravity according to the propor- tioning and mixing of materials and to the nature of the structure, it frequently being the cause of extremely serious difficulty. Of all the opposing forces which constructors have had to combat from time immemorial, none has exceeded in its power for evil the unwelcome intrusion of water, and building materials which in their nature favor such intrusion must suffer in value to the extent of their per- meability or absorptive power. The fact that in practice, concrete is frequently found to be porous and permeable has been one of the leading checks in its rapid development. Volumes have been written on how the in- gredients might be mixed to produce a watertight concrete, but we might as well seek to solve the problem of perpetual motion as to try to mix cement, sand, and stone so as not to absorb water. [344] The Waterproofing of Concrete Structures If we could examine a section of concrete under a powerful microscope, it would appear to us like an immense sieve through which fine particles of water flow with more or less freedom. We have seen water rise up through concrete walls for many feet, and it will rise until the weight of the water absorbed is equal to the capillary attracting force. As already stated in Chapter VII, if concrete is mixed rich and mixed wet, a high degree of impermeability can be secured. Mixing rich imposes greater barriers to the passage of water; mixing wet minimizes the formation of blowholes by displacing much of the extrained air, but neither mixing rich nor mixing wet destroys the "capillary positive" property of the concrete mass. Its absorptive capacity has been largely decreased, but its attraction for moisture has, however, not been eliminated; thus the water-tightness secured by rich and wet mixtures, however theoretically correct the propor- tions might be, is one of degree only, a degree sometimes approach- ing ideal but never reaching it. We cannot expect that a 'mixture made of cement and stone, each of which is in itself " capillary positive," or water-attracting, can become absolutely proof against the absorption of water by the mere act of mixing, unless, indeed, the operation had produced some phenomenal change in the very nature of the constituent materials. By care and diligence, a mixture may be produced which is sufficiently close-grained to prevent the free transmission of water, prevent it sufficiently, in fact, to be all that is required in many forms of construction work. But where water absorption, besides water penetration, is to be absolutely prevented, no degree of mixing, no richness of mixture, will altogether answer the purpose; and yet in many of the forms in which concrete enters our modern buildings, it is resistance to water absorption that is required. Not merely water-tightness in the ordinary sense of the word, but resistance to the ceaseless en- deavors of atmospheric moisture to find its way by capillarity through porous bodies. Some counteracting influence to this tendency of ordinary concrete to take up water by capillarity, is, therefore what is required when dampness is to be eliminated. It is true that concrete exposed to the free passage of water be- comes after a time so clogged up by fine silt present in the water that the permeability is greatly reduced; and Hagloch states that [345] Handbook for Cement and Concrete Users concrete-block buildings exposed to the weather become water- tight in from three to twelve years, a fact which we must likewise ascribe to the clogging of the surface of the blocks by atmospheric dust deposited by rain, and which remains after evaporation. Modern engineering or architectural practice should certainly not sanction a practice of waiting for the erratic and uncertain hand of time where it is essential to secure water-tightness and damp- proofness in concrete structures, and in the meantime to incur the annoying consequences that always accompany damp and leaky structures; and yet this is precisely what is being done in numberless instances by those who refuse to realize the importance of water- tightness in concrete work, or while realizing it, are willing through motives of false economy, to gamble with the future nearly always at their loss. The number of mistakes made by inadequate provision for waterproofing, and their costly consequences, running into thou- sands of dollars, should serve as object-lessons to those who have the design of concrete work in hand and the same degree of attention and study should be given the subject of water-tightness as that given to other details of construction. The importance of the subject and the scarcity of literature concerning it has induced the author to cover the subject in greater detail than would otherwise be necessary.* Method of Conducting the Work. Work Under Contract. Waterproofing work should be done, if possible, under contract by a specially skilled waterproofer, or by the concern making or supply- ing the material. In a large proportion of cases, the actual construction is left largely to a contractor, sometimes under a more or less loose guaran- tee; often under no guarantee at all, and frequently without the least supervision being exercised on the part of the owner. In case of trouble after the completion of the work, the owner may consider himself fortunate if he happens to have a guarantee from a respon- sible contractor who values his reputation for good work as much as he does the cost of remedying the trouble. It is usually not a difficult * Much of this chapter has already appeared under authorship of Myron H. Lewis in Cement Era for 1909-1910, at whose special request the material was pre- pared and is here rearranged with their permission. [346] The Waterproofing of Concrete Structures matter for a contractor to disclaim responsibility and endeavor to shift the burden, particularly where the cause of the difficulty cannot readily be ascertained, and where several independent contractors were at work on various parts of the job at the same time. Any interference or injury to the waterproofing by any but his own men, and without his knowledge, will naturally tend to absolve the water- proofer from direct responsibility. Any deviation from the plans and specifications forming the basis of the contract, failure to lay protecting masonry when re- quired, necessary openings made for pipe passages through walls without the knowledge of the waterproofer, will likewise relieve the latter from his contract in case of future trouble. This division of responsibility has often been the cause of endless annoyance, delays, and expensive litigation. A competent inspector who would look after all the details of the waterproofing from the time preparation of the surfaces begin until final completion of the work, would avoid a great deal of such trouble. If a record is kept of all the work as it progresses, the responsibility for any future trouble may then be traced with some degree of certainty. Without such record, which is more often omitted than kept, establishment of direct responsi- bility is a difficult matter. Work Not Under Contract. A great deal of waterproofing and dampproofing work must of necessity be done, not by con- tract, but by the purchase of materials and using same accord- ing to directions. Where the work to be done is not large, and where the services of an experienced waterproofer are not available, this method must be employed, although, as a rule, it is not so advisable as having the work done by contract, owing to the unfamiliarity of the purchaser with the material and method of application. In all waterproofing work a great deal of judgment and patience must be exercised if good results are to be obtained, and where materials are not applied by the manufacturer or by one specially familiar with same, the purchaser or owner should see that the material purchased is delivered, and that it be used in accordance with full and explicit directions furnished by the manufacturer or dealer. Conditions on different jobs of waterproofing vary so much that the trade literature accompanying materials can- [347] Handbook for Cement and Concrete Users not be expected to give sufficient information to cover all con- ditions, and consequently the purchaser in ordering material should describe to the dealer in detail the character of the waterproofing work he has in hand, and request that material and directions be sent specially adapted to that particular work. The usual vagueness and indefiniteness of such descriptions always gives rise to unnecessary delays, errors in shipments, and often in failure of the work. Importance of Adequate Inspection. Thorough inspection is particularly essential in the bituminous shield or membrane method, where the waterproofing is to be covered or backed up by protecting masonry or other material, and thus cannot be readily reached for repairs. In dampproofing exposed walls of buildings by application of an asphaltic coating on the interior surface of the walls, inspection should also be particularly rigid as failure means the removal of the plaster covering. Furthermore, the difficulty in tracing sources of leakage when the waterproofing is covered up makes the repair work more uncertain and costly. On large works particularly, materials specified for waterproofing purposes should be subject to the same degree of inspection and tests as other construction materials. There is nothing easier than the substitution of poor materials for good ones by irresponsible contractors or dealers, particularly when the price is much below the standard price for like materials. So many of the coal tar and asphaltic preparations look alike, that the quality of the material delivered can be ascertained only by subjecting them to specified tests, fixed according to the character of the work in hand. Water- proofing felts and other fabrics should also be examined for defects, and powders and other materials to be introduced as a part of con- crete work should be tested and compared with samples obtained, to see that the material ordered is actually delivered. So many instances of failures due to various causes have occurred that it might be well before proceeding to the detailed consideration of various systems of waterproofing, to review briefly the important points 'to be considered in general to obtain permanency and efficiency. The following general principles, if carefully followed, will result in an economical, durable, and efficient work: [348] The Waterproofing of Concrete Structures GENERAL PRINCIPLES TO BE FOLLOWED IN ALL WATERPROOFING i st. In deciding upon a system of waterproofing for any par- ticular structure, study the individual conditions of the problem in hand. Consider the location, climate, service, nature of soil, founda- tion, and all other pertinent data and adopt a plan best suited for the necessities of the case. The "Tabular Outline" at the end of this chapter will materially assist in deciding on the method to employ under given conditions. 2nd. The portions of the structure to be treated must be so designed and prepared that the waterproofing may be properly applied thereon; allowing sufficient working room for securing good surfaces and providing for adequate drainage where water pressure is to be taken care of during construction. 3rd. Complete, unbroken continuity of the waterproofing stratum must be obtained, being allowed for in the design and in- sisted upon in the construction. Any breaks in the continuity of the work will surely be disclosed in time by leaks. 4th. The material as well as the design should be suited to the individual conditions of the work, and the delivery of the material ordered should be proved by tests and comparison with samples previously submitted. 5th. Where the designer or owner is not .familiar with this class of work, alternative plans and estimates may be called for from several responsible concerns and submitted to an impartial architect or engineer qualified to pass judgment on same. 6th. Where work is to be done by the immediate purchaser of materials, complete and explicit instructions should be obtained from the dealer upon written request and in conformity with the conditions outlined by the purchaser, and these instructions should be rigidly followed. 7th. The labor employed in all waterproofing work should be intelligent and careful and wherever possible experienced. The most satisfactory way is to have materials applied by a representa- tive of the manufacturer under a guarantee and under supervision of a competent inspector. [349] L Handbook for Cement and Concrete Users 8th. On all large jobs a competent inspector should be present from the inception of the work to its completion, and nothing should be done, and no tampering or interference allowed without his knowledge. MODERN METHODS OF WATERPROOFING Numerous methods and materials are now available to keep water and dampness out of almost any structure, and under the most trying conditions, and failure to secure water-tightness at this date must be looked upon as a mistake on the part of some one; either the designer, constructor, or inspector. All the methods may, however, be embraced in three general classes, as follows : 1. The "Membrane" or " Elastic" method; a term introduced by E. W. DeKnight. (See page 350.) 2. The "Integral" or Rigid, a term introduced by Myron H. Lewis, in 1907, while editing the Waterproofing Magazine. Both of these terms have since been widely accepted by leading writers on the subject. (See p. 359.) 3. Surface Coating. (See p. 366.) These methods are defined in detail in the treatment which follows : THE MEMBRANE METHOD OF WATERPROOFING The term "membrane method," as employed by De Knight, refers to an elastic, continuous, bituminous, impervious sheet or membrane which completely surrounds the structure to be water- proofed. This method is adapted principally to waterproofing structures in course of erection, particularly those portions below ground, such as subways, tunnels, building-foundations, retaining- walls, arches, reservoirs, etc. It is not so well adapted to water- proofing structures already erected, or to remedy leaky conditions in same, or to damp-proofing exposed walls of superstructures. Other methods must be adopted for these conditions and these will be considered later. [350] The Waterproofing of Concrete Structures Materials. The materials employed in the membrane method of waterproofing are : 1. Coal tar pitch (applied hot). 2. Commercial asphalts (applied hot). 3. Specially prepared asphalts and compounds sold under various trade names (applied cold) . 4. Asphalt mastic (applied hot). When merely dampness is to be excluded, any of the first three " ft- lt W 1 Brick wall 4 inch**. '. *. ^ Tile block 4 f$ Waterproofing '/ Brick 4 > * Concr,t. 90 n furring .nd pla.r 4 46H - -*'*. Ba5mcnt f!vr *-. -vv , Ljgi n j i \ -< >-i t| O hr bO Di^ 1 p, u. e^S S 6 g 2 fflJlll r? CL, c/3 ^ ^ bO W3 bObObCbCbO " VM s - 1 CJCCCC ||d|ll lllll i|.23'S^ SSSSS QQ.2tfP4 p^p<^^^ uring Con struction. New Work. ' "2 W 1 ^ fefefe ^^fefeUU j3 |- f* pq co - g : J soNiaiing savoa QNV 371] Handbook for Cement and Concrete Users 125 . 3 II j2 I I tj tj lable Ony Du lable Onl Du Q bD Remed o le New Work o e Work. pally to F ccessible SHH "21 |l ^o w c3 . I c/5 c/3 *-> u u |-g O O ojHN >> ^ -, CO o 8-g ' WWW 5 5 fl o d o O ^O ^ O Mann Applic c "c .S 1 I I I s w o 3 *" Solutions of Alu (Sylvester Pr ne in Satu tion. ed Paraffin plied Ho S ii H >> ^ preta pound ail te Co ed te ed C Bit re n P it Me C Masonry or rectly Propo Masonry or C rectly Propo Cement Wa Compound Cement M ortar w pound Mortar nous G Cement m 'S'a^'NJS o.^o 3 5 a, 2 'r CH d -2 < S.S r aw gw aw aw < PQ U O K [372] The Waterproofing of Concrete Structures proofing processes as applied to varying conditions, and to enable one having a waterproofing problem to solve, and not familiar with the subject, to pick out the method most suitable without having to read up the whole subject. As previously stated, the method must be suited to the con- ditions of the problem if good results are to be had. In numer- ous cases more than one method may be employed with good results and in such cases the methods have been given in order of their desirability. Local conditions, however, may make the order of preference different. Use of the Table. The table is divided into 13 columns as num- bered on bottom. Columns 3 and 5 give the methods of waterproofing for the different structures listed in columns i and 2. These methods are listed by key letters as A, B, C, etc., the essential features of which are described in columns 7 to 13. Column 3 gives the method of waterproofing that may be pro- vided for in plans and specifications for new structures or which may be employed before the construction work has advanced too far. Column 5 gives the methods available for the structures already erected and for remedying leaky conditions in such structures. The fact that a method is not listed in column 5 means that it is not ad- visable to use it for old structures. As a practical example in using the table, suppose it is desired to dampproof the walls of a new brick building which is to be erected and also to waterproof the foundation, which is in wet ground. To Find the Method from the Tables. Look up columns i and 2 for exposed walls; methods given are D, B, and C, in order of de- sirability. Now look in column No. 7 and those following for description of the methods D, B, and C. For the foundation to resist water pressure under walls, G, K, L, M, are given in order of desirability, but G is omitted if walls are not reinforced. The remarks point out some special features such as for L and M, " Asphalt not to be used in ground polluted by gas drip, oils, etc., that injuriously affects it. This is an important precaution." [373] Handbook for Cement and Concrete Users It is not claimed that the arrangement of methods will in all cases be decisive or that some methods not listed may not be em- ployed ; but the use of the table will prevent such glaring but frequent mistakes as using a surface coating for sub-surface work or using a wash on the inside of cellar walls, to waterproof against pressure and in other ways prevent the use of wholly unfit methods. APPROXIMATE COST OF WATERPROOFING The following table gives approximate cost of different classes of waterproofing which may be used as a basis for comparing relative economy of the methods selected from the table : A. Sylvester process, 1/2 cent to 4 cents per square foot. B, D. Dampproofing masonry walls, 2 coats applied in place, 2 cents to 4 cents per square foot. C. Melted paraffine, 5 cents to 8 cents per square foot. F. Adds about 10 per cent to the cost of untreated mass con- crete. G. Cement coatings with waterproofing compounds; i in. on floors, 1/2 in. to 3/4 in. on walls, 8 cents to 30 cents per square foot, depending upon conditions. /. Hot coal tar, pitch, and felt. Horizontal surfaces: first ply, $2 to $4 per square (100 sq. ft.); additional plys, $1.50 to $2.50 per square; vertical surfaces add 10 per cent to 25 per cent. J. Cold process, felt or burlap, same as commercial asphalt. K. Pressure work, i ply, $4 to $5 per square. L. Commercial asphalt and asphalt felt, add 15 per cent to 60 per cent per ply, depending upon conditions. L. Special asphalts and felts, add 30 per cent to 50 per cent per ply. M. Asphalt mastic, i in., 15 cents per square foot. 374] CHAPTER XXXI GROUT, OR "LIQUID CONCRETE," AND ITS USES Preparing and Mixing Grout. Mixing Machines. Various Uses of Grout. Uses of Grout. Grout, or "Liquid Concrete," as it is sometimes called, is a thin, watery mortar, composed either of neat cement or of cement and sand mixed in different proportions. Its principal uses are as follows: 1. As a mortar for cementing the joints in masonry, after the stones have been laid. 2. For consolidating loose stones, rocks, or riprap. 3. For depositing concrete under water. 4. For waterproofing tunnels by injection behind the lining. 5. For stopping springs and leaks. 6. As a paint for coating concrete walls, either for surfacing or for dampproofing. 7. As a surface coating in thicknesses of from 3/4 to i inch for beams, walls, slabs, etc. 8. As a wearing coat for sidewalks, curbs, cellars, etc. 9. For bonding new to old concrete. 10. For levelling up the bedplates of engines and other machinery. 11. As a filler for paving blocks. 12. As a protective coating for iron and steel. 13. For surfacing pipes and conduits to decrease their resistance to the flow of water. 14. For cementing anchor bolts into their sockets. Preparing and Mixing Grout. Grout as ordinarily employed is composed either of neat cement or of cement and sand in propor- tions of i : i or i : 2. The best method of mixing grout by hand is first to mix the cement or cement and sand to the consistency of stiff paste on an ordinary mixing-board; then place in a tub or bucket and add water in small quantities until the paste is reduced to the consistency required. To facilitate me mixing, the paste [375] Handbook for Cement and Concrete Users should be well stirred whije the water is being added. To prevent the grout from becoming stiff through partial set and thus becoming sluggish as well as weak, the material should be poured as soon as possible after the mixing. When poured from any height, it is desirable to employ neat cement or rich mixtures, as there is a 2'grout 2 high pnssure plug FIG. 122. Grouting Machine Used by Board of Water Supply, New York. tendency for the cement and sand to separate and form separate layers. The quantity of water required for grout depends upon the class of work in which it is employed. Where the interstices through which it is to be poured are smaH, it must be made thin [376] Grout, or "Liquid Concrete," and its Uses and watery, otherwise it cannot be forced beneath the upper layers of rock. When the interstices are large or the grout is applied under pressure, a thicker mixture can be used. It is always de- sirable to employ as thick a grout as can be forced into the cavity which it is intended to fill, since a thin grout becomes weak and porous after the water has evaporated. Where grout is used in large quantities, machines are employed for mixing, and the grout is forced through pipes under pressure. Grout Mixing Machines. Grout mixing machines are of two general types: (a) tank mixers and (b) paddle mixers. In the tank machine, grout is mixed by blowing in air at the bottom of the tank, and the material is ejected by turning the air in at the top and forcing the grout through a hole in the base. In this type, there are no stuffing-boxes or shafts carrying revolving pad- dles to wear out by the grinding action of the cement. The so-called paddle-mixing machines consist in general of a closed steel box of cylindrical shape, about two feet in diameter. Through the axis of the cylinder a shaft is fitted. The shaft makes about 30 revolutions per minute and carries about six double paddles which thoroughly mix the ingredients. The time of mixing occupies about three minutes. After mixing, air pressure is ad- mitted to the cylinder and the grout is discharged by means of a flexible hose connected with the cylinder. In grouting the dry stone packing between the tunnel and rock of the East River Tunnel for the Rapid Transit Subway between Brooklyn and New York, a pressure of 90 pounds per square inch was employed, the high pressure being required to force the grout against the hydrostatic pressure due to the depth of the working. Cementing Joints. Grout is employed to some extent for cementing the joints in rubble masonry, but for this purpose its use is not recommended. When so employed the interior of the wall is laid up dry. The grout is poured on top of the wall and is expected to find its way downward and fill all voids. The difficulty with thi:- method is twofold. If the grout is made thin, it becomes porous and weak, and if made thick, it fills only the upper portions of the wall. Better results are obtained by inserting pipes into the body of the wall at several points and forcing in the grout under pressure. Grout was formerly employed in this way in the construction of [377] Handbook for Cement and Concrete Users bridge piers, where it was customary after laying the large backing stones in place to fill the vacant spaces with broken stone of various size and then pour in as much grout as would work its way into the voids. Such methods are, however, no longer in vogue for first- class structures, where each stone is thoroughly bedded in cement mortar before the next course is laid. Consolidating Rip- rap. Grout is legiti- mately employed for the purpose of consolidating loose stone or riprap. In order that the liquid mortar may properly fill the voids in the bottom of the pile, pipes should be inserted into the mass and the grout forced in under pressure, or else some special method adopted for obtaining this result. In Engineering-Contracting, for May 6, 1908, is given a description of the methods em- ployed by the U. S. Government in constructing locks and dams on the upper White River in Arkansas. Lock and dam No. i were located about one mile below Batesville, Ark. The locks The were of concrete masonry while the dam was a Wafer Supply' from Force Pump for Jetting ment of Apparatus for Driving. 'rock\ FIG. 123. Clark Steel Pile A . , M . , Filled with Grout tim b er crib structure weighted down with stone, Showing Arrange- and provided with a concrete apron. The lock was at one end of the dam, and a concrete T-shaped abutment was built at the other end to protect the shore end of the structure from erosion. The foundation for this abutment consisted of a timber crib, formed of 10 X 10 in. squared timbers, with interior pens varying in size from 5 X 10 ft. to 10 X 12 ft. These pens were filled with "one-man" stones to weight down the structure, the filling averag- ing ii ft. in depth. The stones were then consolidated by filling the interstices with Portland cement grout. The method of applying the grout was as follows : Before the filling was commenced, open-ended square boxes, [378] Grout, or "Liquid Concrete/' and its Uses 8 X 8 ins. inside dimensions, were perforated with i 1/2 in. holes and placed on end about 10 ft. apart. These were the distribution boxes for the grout. Inside of the distribution boxes, smaller open- ended square boxes made of i-in. boards were placed. These boxes, which were not perforated, measured 3X3 ins. on the inside and were at first just long enough to reach from the bottom to the top of the outside boxes. As the grout rose in the rubble, the inside boxes were raised and shortened to compensate for the depth filled. By feeding the grout through these smaller boxes, which delivered FIG. 124. Arrangement of Pipes for Grouting Rock over Tunnel Roof. it almost intact at the bottom of the large perforated ones, it had to enter the rubble from below upward : and being twice as heavy as water, the filling of all the voids was practically assured. The grout was a i : 2 mixture of Portland cement and sand, and the cost of grouting was at the rate of $3.65 per cu. yd. of stone composing the fill. Depositing Concrete Under Water. The standard methods of depositing concrete under water are by means of a tremie or trough, by depositing in closed buckets, and by depositing in cloth or paper bags. An older method which, however, is not recommended for first- [3701 Handbook for Cement and Concrete Users class work, is to deposit loose stone or riprap, and to fill the in- terstices by forcing liquid grout into the mass by means of a pipe reaching into the interior. The objections to this method are the impossibility of filling the voids on account of the washing away of a large part of the grout, and to the impracticability of forcing it into all of the interstices between the stones. For use in consolidating blocks employed as paving for reservoir slopes, the use of grout is, however, economical and amply sufficient for the purpose. Grout in Tunnel Linings. One of the most useful applications GROUT PIPES AND ALTERNATIVE^ ARRANGEMENT OF WEEPERS IN UNSUPPORTED TUNNEL IN SUPPORTED TUNNEL FIG. 125. Showing Arrangement of Grout Pipes on Catskill Water Works, New York. of grout is for the purpose of waterproofing and increasing the strength of tunnel linings. In tunnelling through rock, the section removed by blasting is in excess of the requirements. When lined with iron rings or concrete, a space is left over the lining which, if left unfilled, would permit the accumulation of water, causing dampness or leaks in the tunnel, and in the case of unstable rock, producing unequal pressures, or endangering the roof lining from possible slides. It is, therefore, desirable to pack the space above the lining with stone, and in submarine tunnels the stone packing is consolidated and rendered im- pervious by forcing in grout to fill the interstices between the stones, [380] Grout, or "Liquid Concrete/' and its Uses In the construction of the East River Tunnel for the Rapid Transit R. R. or Subway between New York and Brooklyn, an iron lining was employed, and the space between the lining and the rock was packed with stone. In each segment of the lining, holes were left and closed by screw plugs. Through these holes Portland 50 ft or less LC: vent pipe '^Weeper ~ Vent pipe- " (Cut-off wall \jroutpipe Grout pipe* FIG. 126. Arrangement of Grout Pipes in Tunnels of Catskill Water Works, New York. cement grout was injected after a section of the lining had been placed. The grout was a i : i mixture of Portland cement and crusher dust and was injected under an air pressure of 90 pounds per sq. in. through a flexible hose, which was connected with the i/ 4-inch holes in the tunnel shell. The grout was mixed by means of a paddle machine. The mixer consisted of a steel cylinder, 21 in. in diameter by 22 in. long and the mixing was done by means of a shaft carrying six double paddles, which were revolved at the rate of 30 revolutions per minute. Handbook for Cement and Concrete Users The mixing was done in batches. Each batch contained three bags of Giant Portland cement and three bags of crusher dust. The time occupied in mixing was i 1/2 minutes, and it required about five minutes for the complete operation of charging, mixing, injecting the grout, and preparing the machine for the next batch. As to the success of this method of grouting, Mr. Robert Ridg- way, who was Division Engineer in charge of the tunnel section, reported that the filling of the interstices in the stone packing with grout was excellent where the tunnel was in rock. Where the tunnel was in sand, grout was forced up through the ground and was found filling minute crevices in the earth all the way to the surface. Stopping Leaks and Seams. Grout has long been employed for filling the seams in rocks and for stopping springs and leaks. In excavating for the purpose of obtaining suitable foundations for bridge piers, dams, buildings or other important structures, and in sinking shafts and tunnelling, seamy rock and water-bearing strata are frequently encountered. In the case of dams, the seams must all be filled before the foundation courses can safely be started, since otherwise the leakage beneath the dam would tend to float the masonry, and thus endanger the stability of the structure. Hence it is customary to excavate until sound rock is encountered, and then to inject grout under pressure into any seams or faults that may present themselves. In the case of ordinary foundations, the chief danger from springs or flowing water is the washing away of the cement which is used in the masonry. It is therefore necessary to take care of any incoming water until the fresh mortar or concrete employed in the construction has had time to set. This is ordinarily done by carrying the water away in pipes. Where the pressure is high the pipes are carried up and the water permitted to flow away while the lower courses are being laid. With a low pressure or hydrostatic head, the downward pressure of the water in the pipe may be sufficient when carried up to prevent any flow. After the masonry has been carried up a sufficient height, the stoppage of the leak is effected by forcing grout into the pipe. When there is no flow from the pipe, the leak can be controlled by filling the pipe with grout, which will then displace the water and on hardening form an effective plug. Where the spring flows from the [382] Grout, or "Liquid Concrete," and its Uses pipe, it is necessary to force in the grout under pressure and to main- tain the pressure until the cement has hardened, since otherwise the flow would wash away the grout. . Where practicable, it is de- sirable to apply sufficient pressure to the grout to cause it to flow into the seams or porous strata as well as to fill the pipe and fill the interstices between the pipe and the masonry. Grout as a Paint. Grout, when used as a paint, is one of the surface finishes applied to mass concrete. When so employed it should be applied while the wall is still green, since after hardening the grout has a tendency to flake off in patches. Grout is also employed as a dampproofing paint, but when so used it should be applied to the water side of the wall, as it is far more effective in keeping the moisture from entering the wall than it is in preventing the egress of moisture that has already entered the mass. Where pressure is encountered, however, the layer of grout is too thin to offer effective resistance to the passage of moisture and under such conditions, the wall should either be made impervious in itself or else surrounded by a bituminous shield or mastic of sufficient mass to be able to withstand the pressure. Surface Finish. Grout is more effectively employed as a surface finish when it is applied in such a way as to become perfectly in- corporated with the mass of the wall. This is ordinarily done by using a wet concrete mixture for filling the forms and causing the grout to flush to the surface by pulling back the coarse aggregate from the face of the wall with a spade or fork. This forms the ordinary finish for beams, retaining walls, and mass constructions. Some waterproof grouts are now on the market which make excellent surface finishes for concrete and which are made in all colors. Grout for Walks, Etc. Grout or mortar forms the ordinary wearing surface for sidewalks, curbs, cellar-floors, etc. In such constructions, the foundation consists of a layer, from 3 to 6 inches thick, composed of cement, sand, and i/ 2-inch broken stone, while the surface coat consists of cement and sand, which is usually 3/4 of an inch thick. To improve the appearance and wearing proper- ties of this coat, granite chips are also frequently mixed in with the mortar or grout. To be satisfactory for this purpose, the chips must be hard and tough, and should be trowelled in such a way as to [383] Handbook for Cement and Concrete Users bring the flat portions of their surfaces uppermost, thus providing a good wearing surface, and affording protection to the cement. Bonding New and Old Concrete. Grout is generally employed in bonding new concrete to old. The surface of the old concrete is first scrubbed with a steel brush and a stream of water, or a jet of steam, or compressed air to remove all dirt and grease; and where a good bond is desired, it should also be scratched, etched with acid or tooled so as to produce indentations that will serve as a key. After preparing the surface, a grout composed of neat cement is rubbed in with a broom. While this is still soft it is covered with a layer of the regular concrete mixture, and the ordinary work of concreting is commenced. Grout in the Machine Shop. In setting up the bedplates of engines and stationary machines, lathes, planers, drillpresses, and other heavy tools, it is customary first to block up the framework to the required height with wooden blocks and wedges and then to bed the framework to the floor or piers forming the foundation by pumping in a rich mixture of Portland cement grout. When used for this purpose, the grout should be mixed as thick as practicable. so that on drying, a strong, durable mortar will be formed, which will easily support the weight and vibration of the machinery without crumbling or settling out of level. Grout as a Paving Filler. One of the most common uses for grout is as a filler for paving blocks. When used for brick or stone pavements, the blocks are laid dry and the interstices between the stones or bricks are filled by pouring in grout to serve as a cement. The materials commonly employed for fillers are asphalt, tar and its compounds, cement, grout, and sand. The principal ad- vantages of grout for this purpose are as follows: (i) cheapness; (2) adequate protection to the edges of the blocks; (3) prevents the blocks from loosening; (4) is watertight; (5) is durable; (6) permits the blocks to be laid close together; (7) is easy to keep clean; and (8) wears uniformly. The disadvantages of grout fillers are: (i) its tendency to crack; (2) to become slippery; (3) affords a poor foothold on grades; (4) is difficult to remove without breaking the blocks; and (5) causes objectionable noise. These objections apply chiefly to brick pavements. Where [384] Grout, or "Liquid Concrete/' and its Uses stone is employed the irregularities of the blocks are generally sufficiently pronounced to prevent them from becoming slippery and to enable the horses to obtain a foothold on grades. Stone blocks are also less subject to injury when removed. Miscellaneous Uses. In addition to the uses which have thus far been briefly enumerated in this chapter, grout is employed as a protective coating for iron and steel, for surfacing pipes and conduits to decrease their resistance to the flow of water and for many other purposes. The distinction between mortar and grout is but one of degree. While the excess of water contained in grout tends to increase its porosity over that of cement mortar, yet for many pur- poses its use is not only legitimate but unexcelled. Grout is not a safe substitute for mortar in laying up masonry or in important constructions under water. It can, however, be forced into cracks and crevices which thick mortar is unable to penetrate, and thus for stopping springs and leaks, rilling voids between the lining and roof of tunnels, filling the crevices in founda- tions for dams and other structures, and for numerous other pur- poses, grout is extensively employed in engineering works; while its minor uses such as surfacing, painting iron, steel and concrete, filling between paving blocks, dampproofing, and levelling of founda- tion areas have extended the employment of this material to many kinds of construction, although other considerations both theoretical and practical have tended to circumscribe its use. CHAPTER XXXII INSPECTION OF CONCRETE WORK A SUMMARY OF ESSENTIAL RULES AND PRINCIPLES OF CON- STRUCTION, FOR SECURING GOOD CONCRETE WORK The Work of the Inspector. Inspection of the Cement, Sand, and Aggregates. Pro- portioning and Mixing. Inspection of Forms, Reinforcement and Placing Con- crete. Rules for Removing Forms. Rules for Surface Finish. Rules for Blocks, Piles, and Castings. CAREFUL inspection is essential in all concrete work. The best design will come to naught unless it be carried out with the aid of careful and skilful workmanship and the use of good materials. Good construction can be assured only when the work is under the control of competent and conscientious inspectors. The Work of the Inspector. The work of the inspector may be divided into the following parts: 1. Inspection of the cement, sand, and aggregate; a. quality; b. storage. 2. Proportioning, measuring, and mixing of the ingredients. 3. Inspection of forms, arch-centres, column moulds, etc. 4. Placing of the reinforcement. 5. Placing of the concrete. (a) General rules. (b) In reinforced work. (c) In hot weather. (d) In freezing weather. 6. Bonding new to old work. 7. Removal of the forms. 8. Surface finish. 9. Moulded blocks, piles, ornamental castings, etc. Inspection of the Cement. Cements are subjected to laboiatory tests to determine their : (a) Fineness. (b) Time of set. 386 Inspection of Concrete Work (c) Soundness. (d) Specific gravity. (e) Strength. (a) Fineness is determined by passing the cement through sieves of various meshes and noting the percentages retained. (b) Time of set is found by making pats of the cement and noting the time required to resist the penetration of wires of specified weight. (c) Soundness is tested by noting the condition of the edges of the pats; also by subjecting pats to a steam bath and observing whether they blow, swell, or crack. (d) Specific gravity is determined by weighing a given volume in air and noting the loss of weight when immersed in a liquid of known specific gravity, such as alcohol, which does not act on the cement. (e) Strength is determined by moulding briquettes of i sq. in. sectional area, permitting them to remain in air and under water for specified periods, and then breaking in testing machines, and noting the breaking loads. Cement should be stored in its original package, until ready for use. It should also be kept in a clean, dry place. If stored in a damp place, the cement will partially set and become valueless for construction purposes. Inspection of Sand and Aggregates. Sand for impervious con- crete should be silicious in character, of graduated size, and with coarse, rounded grains. Sand should also be clean, but excessive cleanliness is not essential as an admixture of clay in amounts up to 10 per cent results in no material reduction in the strength of mortars. A small percentage of clay also tends to increase the imperviousness of the concrete. When specifications call for sharp sand, the grains should be angular. Sharp sand was until quite recently always required by engineers, on account of its binding properties. Recent experiments, however, indicate that sand with rounded grains is less liable to fracture; and when graduated, so that the. smaller grains fit between the larger ones without wedging them apart, is far more impervious when used in mortar or concrete. The best aggregates for concrete are trap rock and gravel. [387] Handbook for Cement and Concrete Users Hard limestones and granite are also good. Soft limestones, sand- stones and schists are less durable, while slate, shale, and cinders are poor materials to use. The size of the aggregate is of importance. In massive work, the stone should pass through a 2 1/2 inch ring, in reinforced concrete beams, the diameter should not exceed 3/4 of an inch. Rules for Proportioning, Measuring, and Mixing. American engineers proportion concrete mixtures by measure, thus: a 1:2:3 concrete is one composed of i volume of cement, 3 volumes of sand, and 6 volumes of aggregate. The duty of the inspector is to make certain that the specified proportions are accurately and uniformly adhered to. This requires : (a) That definite measuring units be employed. (b) That the accuracy of the measure boxes, hoppers, etc., be verified. (c) That the filling of the measuring boxes, hoppers, etc., be exact. (d) That when two or more boxes or hoppers, filled with sand or stone, go to make up a batch, the exact number be employed for each and every batch. Cement differs in volume when measured loose, and when packed in the barrel; cement barrels also vary in capacity. Hence the engineer, contractor, and inspector should reach an agreement as to: (a) Whether the cement is to be measured loose or packed. (b) What the cubic contents of a barrel or bag of cement shall be called. The measures used should be tested to make sure that each holds the amount intended. This can be very simply done by using a known measure to fill the measuring box employed, or the volume of the box can be mathematically computed. When automatic measuring devices are used to proportion the cement, the inspector should see: (a) That they are regulated to give the proper proportions. (b) That the materials do not clog, choke, or arch in the feed hoppers. (c) That the feed hoppers are kept amply supplied with mate- rials. [388] Inspection of Concrete Work Concrete is mixed by: i. Hand turning with shovels and hoes; 2. Machine mixing. Rules for Hand Mixing. Rule i. The batches should be of such size that they can be proportioned without using fractions of mea- sures. Rule 2. Mix the cement and sand dry with hoes or shovels. Rule 3. Over the dry sand and cement mixture spread the broken stone which has been previously wetted and on top of the stone apply water evenly. Rule 4. Finally turn the whole the specified number of times with . shovels. Rule 5. The quantity of concrete in each batch should be not greater than can be mixed and deposited before the cement begins to set. Rules for Machine Mixing. Concrete mixers are of three types: (a) Batch mixers. (b) Continuous mixers. (c) Gravity mixers. In batch mixers the materials are charged, mixed, and discharged in batch units; in continuous mixers the materials are discharged in a continuous stream; and in gravity mixers the materials are caused to mingle by falling through specially constructed troughs, tubes, or hoppers. Rule i. The mixer should be of an approved type, and operated in such a manner as to mix the materials uniformly and efficiently. Rule 2. If a batch mixer is used, the batch should be (a) com- posed of the proper proportions, (b) thoroughly mixed, and (c) completely dumped out as a unit. Rule 3. When a continuous mixer is used, the materials must be (a) fed evenly into the mixer in the proper proportions; (b) the automatic measuring devices must work accurately, and (c) the material must not "bridge" or " choke," and so cease to feed into the mixer drum. Rule 4. The mixer must be given the requisite number of turns for each batch, as determined by trial. Rule 5. The concrete in discharging from the mixer should not drop any considerable distance. Rule 6. The mixer should be cleaned of all adhering mortar or [389] Handbook for Cement and Concrete Users concrete when work is discontinued, as such cakes are liable to break or jar loose and be discharged as an inert body into the next batch. Inspection of Forms. Forms are the moulds in which concrete is shaped, and it is the duty of the inspector to see that they are of ample strength, efficiently braced and in proper alignment. The following rules should also be observed : Rule i. The lumber should be of such quality, size, and finish as to promise absolute stability and reasonably perfect work under the conditions. Rule 2. Forms should be oiled or wetted just before the concrete is deposited to prevent sticking. Oil should be used where a smooth surface is desired. It should not be used where the concrete is to be plastered or whitewashed, as the grease will discolor the work and weaken the bond. Rule 3. White pine, yellow pine, spruce, Oregon pine, and red- wood are suitable for forms; hemlock is unreliable. Rule 4. Forms should be thoroughly cleaned of shavings, chips, sawdust, dirt, or other accumulations just before the concrete is placed. Rule 5. The construction of the forms should be such that they can be removed without injury to the concrete. Rule 6. All forms must be erected in exact alignment, both vertically and horizontally; column and wall forms should be plumb; girder boxes and wall forms without winds or twists; arch and slab centres level : the alignment must be watched during the placing of the concrete, as the loading may distort the forms. Rule 7. Forms should be (a) of ample strength; (b) of sufficient rigidity not to deflect unduly under load, and (c) horizontal forms should be given a camber to prevent them from deflecting below the horizontal. A common camber is 1/2 inch for every 10 feet of span. Rule 8. The carpenter work should be accurate, the lines true and square, the joints close and the finish neat. All forms must be planed where required to produce a smooth surface finish. Rule 9. All joints in forms should be tight enough to prevent leakage of the grout from the liquid mass. Rule 10. Column moulds must be accurately spaced in all directions and set square with the lines laid down on the plans. [390] Inspection of Concrete Work Rule ii. Column moulds should be cleaned with scrupulous care, as they are liable to get the sweepings from girder boxes and other debris. To facilitate cleaning the bottom of the mould should be left open on one side until just before pouring the concrete. Rule 12. The wire ties for wall forms must be in place and drawn taut so as to pull the sides close against the spacers. The spacers must be removed from the forms as soon as they are reached by the concreting. Rule 13. Bolts which can be withdrawn should be used instead of wire as ties for forms where the surface is left exposed, as a rust spot invariably forms on the face of the wall where a wire is cut. Rule 14. Where bolts are used as ties, the bolts must be with- drawn and the holes filled with mortar after the forms have been removed. To facilitate withdrawing, the bolts must be greased. Rule 15. Forms for retaining walls with battered sides, py- ramidal forms for column footings, etc., should be firmly anchored down to resist the up-thrust or floating effect of the semi-liquid concrete. Rule 1 6. Arch centres must be framed, assembled, and erected in a workmanlike manner. Substantial foundations are required; also suitable means for striking or lowering the centre gradually and without shock or jar to the concrete. Allowance should also be made for settlement under load and for permanent camber. The lagging should be of even thickness and planed smooth in order to give a good surface to the soffit of the arch. Placing of the Reinforcement. Concrete is weak in tension but strong in compression. Reinforcement is placed on the tension sides of beams to make up for the weakness of the concrete. The number, size, and spacing of the bars must be in exact conformity with the engineer's plans, otherwise the structure may be materially weakened. The position of the bars in the form is of no less im- portance than their proper number and size, as they are designed to be in the position where they will most add to the strength of the construction. The following rules should also be observed : Rule i. Where the steel is received, it should be checked, assort- ed, and stored in such a way as to be reasonably protected from rust, dirt, oil, and paint. Handbook for Cement and Concrete Users Rule 2. In the assembling of the reinforcement, the exact number, size, form, spacing, and location of bars, stirrups, ties, spacers, etc., called for by the plans must be strictly adhered to. Rule 3. The steel should be free from paint, scale, dirt, and ex- cessive rust. Concrete which has lodged on the steel and hardened during previous work must also be removed before the reinforcement is finally concreted in. Rule 4. Bars should be bent in such a manner that they do not break or crack at the bend. The bending force should be applied gradually and not with a jerk. Cold bending is always preferable; if hot bending is allowed, it must be done in such a way that the bar is not burned or weakened. Rule 5. Splicing of bars, lapping, wiring, use of sleeves and set screws, etc., must be carried out as directed by the engineer. Rule 6. Protruding ends of bars which are left for splicing should be coated with cement paint to diminish rusting, and guarded against being bent or loosened. Rule 7. All reinforcement must be securely fastened to preserve spacing, location, alignment, etc. Rule 8. The wiring of reinforcement at intersections should be done carefully and strongly, using No. 16 or No. 18 B. and S. gauge soft black wire. Rule 9. In column reinforcement, the reinforcing frame should be concentric with that of the column below, the bars vertical, all ties in place and taut, and all splices made according to specifications. No part of the steel should touch the walls of the form and the space between the steel and form should be uniform. Rule 10. Templets should be used especially at bottom and top of column to insure accurate spacing of bars. Rule ii. Column bars should be spliced as follows: In a butt joint the ends should be square, the bearing uniform, and the joint be held true to line by sleeves or splice bars. If lap joints are allowed, the wire wrappings, cable splices, etc., must be made taut and secure. Rule 12. Beam reinforcement should be placed symmetrically with the axis of the beam, the bottom bars kept at the required height above the bottom of the beam, the proper space maintained between the reinforcement and the sides of the beam, and the re- Inspection of Concrete Work quired connections made at the ends of the beam with the column bars or the reinforcement of abutting beams or walls. All planes and lines should be true and all parts of the reinforcement wired together or otherwise held firmly in position. Placing of the Concrete. Before the practice of reinforcing con- crete came into general use, specifications called for dry mixtures, thorough tamping, and depositing in uniform horizontal layers. In reinforced work, dry mixtures do not flow readily around the bars, while tamping is liable to throw them out of position. Hence in such work wet mixtures are used and puddling or slicing takes the place of tamping. This consists in churning and cutting the wet mixtures with rods or slice bars to work out air bubbles, close up pockets, and settle the materials. The following rules should also be observed : Rule i. Buckets should just clear the work when discharged, as when the materials are allowed to drop, they are liable to jar the forms and displace the reinforcement and at the same time produce separation of the stone from the mortar. Rule 2. In depositing through chutes, care must be taken to detect any separation of the stone from the mortar. Rule 3. Pouring should be done at several points over the area to be filled so as to reduce flowing and spreading to a minimum. Rule 4. The concrete must be poured before it has begun to set. Rule 5. Dry mixtures, when specified, should be deposited in even layers not exceeding 6 to 8 ins. in thickness and thoroughly tamped with rams heavy enough to thoroughly compact the concrete and bring a film of water to the surface. Rule 6. Wet mixtures should be well puddled, so as to work out air bubbles and pockets and bring the concrete into close contact with the reinforcement at every point. Rule 7. In making slabs, the full thickness should be poured in one continuous operation. If possible slab and beam should be made monolithic. Rule 8. Beams should be poured in one continuous operation from bottom to top, the concrete worked closely around the rein- forcement by puddling, and the stone worked back from the sides by spading. [393] Handbook for Cement and Concrete Users Rule 9. When beam and slab are designed to act together as a T-beam, both must be poured in one operation. Rule 10. Columns must be poured well ahead of the beams. The operation should be continuous from the base to the underside of supported beam or girder, and the concrete well puddled by bars long enough to go easily between the outside of the reinforcement and the inside of the form. Rule ii. In concreting arches, the arch ring should be divided into sections of such size that the pouring of each can be made a continuous operation. In longitudinal sections, the concrete should be begun simultaneously at both skewbacks and continued uniformly and continuously to the crown. Where the sections are transverse or across the arch, the better practice is to concrete the crown section first and work towards both skewbacks a pair of sections, one on each side, at a time. Rule 12. In depositing under water, the concrete should be kept as free as possible from wash which will float off the fine cement from the mixture. The concrete should never be allowed to drop through any considerable depth of water. The standard methods of depositing under water are in bags, in closed buckets', and through tremies. Rule 13. In hot weather, great care must be exercised to prevent the concrete from drying out before it has set. The aggregate should be thoroughly wetted, more water used in the mixing, and if necessary, the work should be covered with planks or tarpaulins. Rule 14. In freezing weather concreting should be stopped at the temperature required by the specifications. When salt is added to prevent freezing, the amount should not exceed 10 per cent of the weight of the water. Other methods of protection are heating the materials, housing in the work, covering with tarpaulins, using artificial heaters, and adding calcium chloride in amounts equal to about 2 per cent of the volume of the mortar. Bonding New to Old Work. The surface of concrete which has hardened has a skin or coating to which fresh concrete will not adhere. This skin must be removed and the surface prepared for the new material. The methods employed are, to (a) Prepare the surface by scrubbing, washing, and grouting. [394] Inspection of Concrete Work (b) Etch the surface with an acid wash, and thoroughly remove the acid by washing. (c) Break the surface with steam, air blast or water under pressure. In stopping work over night, the following rules should also be observed : Rule i. In slabs, the concrete should be stopped in a vertical plane at right angles to the span either (a) at midspan, or (b) over the centre of the supporting beam or girder. Rule 2. In beams or girders, the concrete should be stopped in a vertical place at right angles to the length of the beam either (a) at midspan, or (b) over the centre of the supporting column. Rule 3. Columns should be stopped at the level of the bottom of the beam or girder which they support. Rule 4. Walls should be stopped in vertical planes across the wall; if practicable the stoppage should occur where an expansion joint is to come. Removal of the Forms. All forms must be taken down without straining or jarring the freshly placed concrete. The greatest care must be exercised to prevent workmen, who are taking down forms, from dropping a single piece of lumber on the floor. Shores for floors or arches must never be removed in less than two weeks after the concrete is placed. In damp or cold weather, they should remain in place at least four weeks. Centres for long- span arches should remain in place from one to three months. Before removing shores on extra long spans, it is advisable to put horizontal saw cuts completely through the shores. If weakness then develops, it will simply close up the saw cuts and the shores will continue to do their duty. Rule i. Moulds for ornamental or indented castings must be so constructed that they can be removed piece by piece without injury to the concrete. Rule 2. Forms should not be removed until the concrete has hardened sufficiently to carry its load. Forms should remain longer under beams and arches than around columns and walls, and longer under arches of long than of short span. Forms should not be removed until the concrete is hard enough to ring clearly when struck with a hammer. [395] Handbook for Cement and Concrete Users Rule 3. Under average conditions, forms should remain in place for the following periods : Walls in mass work from i to 3 days. Thin walls and columns from 2 to 5 days, according to weather conditions as noted above. Slabs up to 6 feet span, from i to 2 weeks. Beams and girders, from 2 to 4 weeks. Small arches, from i to 3 weeks; large arches from i to 2 months. Rule 4. Forms should be removed gently without chipping "or jarring the concrete. Prying with bars or striking with a sledge should be prohibited. Rule 5. Column forms should be so constructed as to permit of their removal without disturbing the beam or slab forms. Rule 6. Beam forms should be so constructed as to permit of the removal of the sides before the bottom is disturbed in order that the condition of the concrete can be examined. Rule 7.. Beams should be supported by shores for a considerable time after the forms have been removed, or until the concrete has become thoroughly cured. Rule 8. Arch centres must be removed without shock or jar to the arch ring. Centres should be lowered evenly and gradually, so that the ring can settle uniformly. Rules for Surface Finish. Surface finishes are of two kinds: (a) Those in which the moulded surface is treated after the forms are removed. (b) Those in which the moulding is so done that the finish is a part of the moulding process. The following rules should be observed for class (a) : Rule i. If the surface is to be grouted all holes and joint marks must be filled or smoothed down before the grout is applied. Rule 2. When the surface is to be tooled, from 30 to 60 days must elapse before the concrete is hard enough to give a good, clean tool cut. Rule 3. When scrubbed, the scrubbing should be continued just long enough to remove the surface cement and to partially expose the aggregate without loosening it. Rule 4. When etched with acid, the acid must not be allowed to remain too long, and all excess acid must be removed by washing. [396] Inspection of Concrete Work Spaded or mortar finishes are used for class (b). The following rules should be observed : Rule i. Spading is best done with a special flat-bladed spade, having the blade perforated with holes or slots, which will screen back the stones and allow the mortar to pass. Rule 2. In a mortar finish, the facing mortar and concrete back- ing are placed at the same time and are tamped together. The tamping should not be so hard as to force pieces of stone through the facing, but hard enough to bond thoroughly the facing mortar and backing. Rule 3. The preferable method of construction is to use a facing form between the lagging and the backing. Fill between the facing form and the lagging with mortar, then fill behind the facing form with the backing, and finally withdraw the facing form and tamp backing and facing together. Moulded Blocks, Piles, Ornamental Castings, Etc. Three general processes are employed for moulding cast concrete work : (a) A dry mixture is heavily tamped into a mould and the block is immediately released and set aside for curing. (b) A liquid mixture is poured into moulds where the blocks remain until hard. (c) A medium wet mixture is compressed into moulds by hydraulic presses or other means of securing great pressure. The following rules should be observed for Dry Mixture Blocks. Rule i. For dry mixtures the mixing and tamping must be thorough and the water uniformly distributed. Tamping should begin with the first shovelful and should be continued until the mould is filled. Rule 2. Dry mixtures should have a consistency such that the block will part from the mould without sticking, sloughing, sagging, or loss of form. Dryness in excess of these requirements should not be allowed. Rule 3. Moulds must be rigid and adequately clamped. The construction should be such that the green blocks are not injured when removed. Rule 4. After removal, the dry mixture blocks must be stacked in a horizontal position on immovable supports and freely sprinkled with water. A dry mixture block does not have enough mixing [397] Handbook for Cement and Concrete Users water to enable the cement to set and harden perfectly, and this deficiency must be supplied by sprinkling. The sprinkling should begin within an hour after moulding and should continue for at least ten days. While the block is soft, the sprinkling should consist of a gentle spray, that will not wash the concrete. Rule 5. Blocks should be cured for at least 30 days before they are removed from the storage yards for use in construction. The following rules apply to wet mixtures: Rule i. The mixture must be thoroughly stirred and churned to eliminate air voids, prevent arching and fill corners and edges of moulds. Rule 2. The mould must not be removed until the concrete has thoroughly set and is hard enough to do without its support. Rule 3. The block must be true to shape and exact in dimensions, with faces true to plane, and edges true to line. Mouldings and other ornamentations must be perfect. A moulded block should be equal in perfection to cut stone in all particulars of shape and dimensions. Rules for Concrete Piles. Concrete piles are driven (a) by punching a hole in the ground by means of a metal mould and filling with concrete ; (b) by casting the piles in moulds and driving by aid of a water jet. The following rules should be observed for concrete piles in place : Rule i. In driving the shell for new piles, care must be taken that adjacent piles in which the concrete is still green are not jarred and injured. Rule 2. In concreting piles in place, the concrete must be lowered in small buckets or in such a way that the cement is not separated from the stone. Rule 3. The reinforcement must be set parallel to and concentric with the axis of the pile. The best practice is to assemble the rein- forcement into a unit frame, and to place it as a unit. The following should be observed for cast piles: i. Cast piles should be straight, the metal points, when used, firmly attached and the pile should be without cracks or chipping. None of the reinforcing metal should be exposed. If cored for sinking by water jet, the cores must be open and unobstructed. If fluted on the sides to provide passages for the rise of [398] Inspection of Concrete Work water used in jetting, the flutes or corrugations must not be obstructed. 2. Moulds should be straight and kept true to line and level. 3. The reinforcement must be kept parallel to and concentric with the axis of the mould. 4. The concrete should be poured at several points along the mould to prevent flowing and segregation. 5. The driving should be done in such a way that the pile is not fractured in the body. The head should be protected by a cushion cap to take the direct blow of the hammer. If the driving is done by a water jet, the pile should settle to a firm bearing. 6. Cast piles should not be dragged along the ground or other- wise roughly handled. Ornamental Castings. In ornamental castings, great care must be taken in the moulding, handling, and setting in place to preserve the true lines, flutings, and other ornamentations. When white cements, stainless mortars, or other special materials are required, the inspector should take particular pains to insure the use of the proper ingredients. The general rules for cast blocks and piles apply with additional force to all ornamental work. [399] CHAPTER XXXIII COST OF CONCRETE WORK General Cost of Main Classes of Work. Elements of Cost. Cost of Materials. Cost of Mixing. Cost of Placing. General Expenses. Summary of Costs. Cost of Mortar. Actual Examples of Cost. Building Blocks. Paving. Removing Efflorescence. Stucco. Forms. Cost of Buildings in Terms of Cubical Con- tents. Cost of Residences. Cost of Sewers. Concrete Pipes. Bridge Piers and Bridges. Piles. Trestles, Sidewalks, Curbs, and Gutters. Fence Posts. Poles. Roofs. Tunnel Lining. Waterproofing. Cost of Concrete Dams. THE cost of concrete construction is made up of the combined cost of materials and labor. The cost of materials for any given class of work is readily determined from the dimensions of the structure and the market prices of cement, sand, broken stone, timber, steel, etc.; the labor cost, however, is dependent not only upon the prevailing rate of wages, but also upon the efficiency of the men employed, the amount of form work, and the character of the construction. The cheapest construction is obtained when the concrete is deposited in large masses and when the transportation, mixing, and depositing in place is performed by machinery. When laid in thin sections, as in tunnel linings, small arches, thin walls, etc., the use of forms and of hand labor per cubic yard of concrete is very largely increased, which greatly augments the unit cost of the construction. General Cost of Main Classes of Work. Where Portland cement can be obtained at $1.50 per barrel, sand at 80 cents per cubic yard, and broken stone at $1.50 per cubic yard delivered on the work; and where the cost of form timber does not exceed $25.00 per M; while the rate of wages for carpenters is $3.50, laborers, $1.75, and teams $3.75 per ten-hour day, the cost of concreting, including interest and depreciation on plant, but with no allowance for profits, will run about as follows: Heavy mass constructions, as large dams, reservoir -v walls, pavements, heavy foundations, abutments, rubble [ $3.50 to $5.oo per cu. yd. concrete, etc. [400] Cost of Concrete Work Foundation footings and difficult mass construction. 6.00 to 8.00 per cu. yd. Thin rough walls, sewers, and culverts 8.00 to 10.00 per cu. yd. Thin tooled or reinforced walls and heavy buildings "1 and bridges, difficult pneumatic and submarine construc- ... , . , , . , , r 10.00 to 15.00 per cu. yd. tions which are subject to delays, remforced-concrete re- taining walls, etc. Light reinforced-concrete buildings having thin walls, \ slabs, and columns, light reinforced-concrete bridges, > 15.00 to 20.00 per cu. yd. arches, etc. Elements of Cost. The various elements which enter into the cost of plain and reinforced concrete may be summarized as follows : 1. Cost of cement, aggregate, and reinforcement at the work. 2. Cost of loading the materials into barrows, buckets, or cars, and of their transportation to the mixer and dumping. 3. Cost of mixing: (a) Hand-mixing; (b) Machine-mixing. 4. Cost of loading the concrete into barrows, buckets, or cars, and of its transportation to the work. 5. Cost of bending, placing, and wiring the reinforcement into position. 6. Cost of dumping, spreading, slicing, spading, and ramming. 7. Cost of forms: (a) Timber, nails, wire, and other materials; (b) Carpenter's labor. 8. Cost of plant, storage house, runways, etc. 9. Cost of engineering, inspection, time-keeping, and general expenses. 10. Interest on the investment, repairs, depreciation of plant, etc. 11. Profits. Cost of Cement. The cost of cement depends upon the class, brand, quantity, kind of package, freight-rates by rail or water, and cartage. At New York, the prices in large lots delivered alongside of the docks are at the time of publication as follows for large lots: Natural cement *o.8o per barrel Portland i-43 " Imported 2 -4 2 At the mill Portland cement can be obtained in bulk at $1.00 per barrel. On many of the irrigation projects in the West, where the haul 26 [ 4oi ] Handbook for Cement and Concrete Users from the nearest railroad is considerable, the cost of cement varies from $2.50 to $3.00 per barrel delivered; at a dam recently com- pleted at Hume, Cal., the cement cost a little over $5.00 per barrel,* the high cost being due to the location of the work, which necessitated a great deal of hauling and handling. Cement when ordered in wooden barrels costs 10 cents more per barrel than in bulk ; when ordered in cloth sacks, a charge of 10 cents per sack is made, but on return of the sacks, a credit of 8 to 10 cents per sack is allowed; when ordered in paper bags the cost is 5 cents more per barrel than in bulk. Hence a barrel of cement, costing $1.40 in bulk and containing four bags to the barrel, will command the following prices, depend- ing upon the package in which it is sent : 1. In wooden barrels $i .40 + . 10 = $i .50 2. In cloth sacks i .40 4- .40 = i .80 3. In paper sacks i . 40 + . 05 = i . 45 4. In cloth sacks, which are returned $i .40 to $1.48. Cost of Sand. The cost of sand varies from 20 cents to $1.00 per cu. yd., depending upon the need of washing and the length of haul. Standard grades of Long Island washed sand are quoted at 35 cents alongside the docks at New York; white quartz sand at 60 cents; and white quartz grit at 75 cents per cu. yd. for full cargo lots of 500 cu. yd. Cost of Gravel. The cost of gravel varies from 50 cents to $1.50 per cu. yd. Washed gravel alongside of dock at New York sells at 75 cents in cargo lots and white quartz roofing gravel at $1.30 per net ton. Cost of Broken Stone. The cost of broken stone varies from 60 cents to $1.50 per cu. yd. Alongside of the dock at New York the prices are 90 cents to $1.00 for i-i/2-in. stone; $1.00 to $1.10 for 3/4-in. stone, and 90 to 95 cents for screenings. The contract for furnishing the Department of Docks, City of New York, with 15,000 cu. yds. of stone was awarded recently at $1.04 to $1.06 per cu. yd., including the services of men to load the buckets and empty them on the dock, the city furnishing the power. Cost of Steel for Reinforcement. At the mill plain bars 3/4 * Engineering Record, Jan. 15, 1910. t 432 ] Cost of Concrete Work inch and larger vary in price from $1.25 to$i.8o per cwt., and smaller bars from $1.50 to $2.30 per cwt. Twisted bars are held at an ad- vance of from 10 to 25 cents per cwt. over plain bars, while the prices of other deformed bars vary according to the shape, but are in gen- eral higher than those of twisted bars. Expanded metal varies in price from 2.80 to 8.30 cents per sq. ft. at New York, according to the mesh and weight; triangular mesh, from .67 to 2.55 cents per sq. ft. in carload lots; expanded lath from n 1/2 to 14 cents per sq. yd., at mill for black, and from 18 1/2 to 21 cents per sq. yd. for galvanized, and diamond lath from 14 to 20 cents per sq. yd. at New York for black. Total Cost of Materials. This varies according to the proportions of cement, sand, and stone or gravel, and the price of each ingredient. With cement at $1.50 per bbl., sand at 80 cents, and broken stone at $1.20 per cu. yd., the quantity of materials and their cost for different mixtures would be as follows: PLAIN CONCRETE, COST OF MATERIALS per cubic yards, with Cement at $i . 50 per barrel. Sand " . 80 per cubic yard. Stone " 1.20 " " " 1:2:4 Mixture. i : 2^:5 Mixture. i: 3 : 5 Mixture. Cement 1.46 bbl. at $1.50 . . . Sand .41 cu. yd. at 80 $2.19 .33 i. 20 at .4.2 at $1.50 $1.80 $. 80 . .34. 1.13 at .4.8 at Si. 50 .80 $1.70 7Q Stone .82 cu. yd. at 1.20. . . . Cost of materials per cu. yd .98 $?. CQ .84 at Cost. 1. 2O I.OI .80 at Cost 1. 2O . .96 Cost of Loading into Barrows, Buckets, Etc. Under average conditions, one man should be able to load 17.5 cu. yds. of aggregate into a barrow in 10 hours. With wages at $1.75 per day, the cost per cu. yd. of materials handled would be 10 cents. For the 1:21/2:5 mixture the cost of loading per cu. yd. of concrete would be : Sand .42 cu. yd. at ro cents 4.20 Stone .84 cu. yd. at 10 cents 8.40 Cement .17 cu. yd. at 10 cents 1.70 Total for i cubic yard 14-30 [403] Handbook for Cement and Concrete Users Cost of Transportation and Dumping. This depends upon the grade and length of haul and will vary from 5 to 10 cents per cu. yd. of concrete. Mr. H. P. Gillette, in his "Handbook of Cost Data," gives the following rules for the cost of transportation of materials to the mixing board : 1. With barrows: "To a fixed cost of 4 cents (for lost time), add i cent for every 20 ft. of distance from stock pile to mixing board if there is a steep rise in the runway, but if the runway is level add i cent for every 30 ft. distance of haul." 2. With a horse and cart: "To a fixed cost of 5 cents (for lost time at both ends of haul), add i cent for every 100 ft. of distance from stock pile to mixing board." Cost of Hand Mixing. This will vary from 25 to 40 cents per cu. yd., according to the efficiency of the labor and the number of times the materials are turned over with shovels. With wages at 17.5 cents per hour, and men turning over mortar and concrete at the rate of 3 cu. yds. per hour, the cost per cu. yd. would be 5.8 cents for each turn. The cement and sand for each cu. yd. of concrete will measure about .45 cu. yds. If 6 turns are given to this mixture, the cost of turning the mortar will be .45 X 6 X 5.8 cts. = 15.7 cents. If the stone and mortar are turned 3 times, the cost of mixture will be 3 X 5.8 = 17.4 cents. Hence the total cost of turning is 15.7 + 17.4 = 33.1 cents per cu. yd. of concrete. Cost of Machine Mixing. The labor cost of mixing will vary from 2 to 8 cents per cu. yd., and the cost and maintenance of the mixer from 6 to 15 cents, according to the size and kind of mixer and the percentage of time which the machinery is idle. If a 3/4 yd. batch mixer is employed, 200 cu. yds. are readily mixed in one day with three men to attend to the machinery. The cost of oil, fuel, and labor per day will total about $7.00; or 3.5 cents per cu. yd. of concrete. In the Engineering Record of May 21, 1910, is given the actual maintenance cost of four mixers owned by the Aberthaw Construc- tion Co., of Boston, who run a ledger account for each mixer. In this article, it is shown that the highest maintenance cost was 13.95 cents per cu. yd., the lowest 5.4 cents, and the average of the four mixers 8.94 cents. I 404 ] Cost of Concrete Work Taking an average cost of maintenance at 9 cents, and the cost of mixing at 3.5 cents, the combined cost or the cost of machine mixing will total 9 + 3.5 = 12.5 cents per cu. yd. for a batch mixer of average size in steady use. Cost of Loading and Transporting to Place. When loaded by hand into barrows, the cost is less than that of loading the raw materials, since the volume of the concrete is less than that of the unmixed ingredients and should average about 12 cents per cu. yd. When mixed by machinery, the concrete is dumped directly into barrows or cars without cost of handling. The cost of transportation by barrows or carts will be about the same as that for hauling the raw material, or from 5 to 10 cents per cu. yd. When conveyed by means of a hoist or cableway, the ex- penses for power, labor, and maintenance will total from 3 to 8 cents per cu. yd. Cost of Dumping, Spreading, Ramming, Slicing, Spading, Etc. These will vary with the character of the work and the consistency of the mixture. In mass work with a wet mixture the cost will average 15 cents per cu. yd. If a dry mixture is used, the expense of tamping may increase this amount to 30 or 40 cents. In building construction the cost of slicing to cause the material to flow around the reinforcing bars and of spading to pull back the coarse aggregate from the surface will total from 25 to 35 cents per cu. yd. Cost of Forms. White pine, yellow pine, spruce, and Oregon pine are used for surface forms. Hemlock, although unsatisfactory, is used in rough constructions. Prices of timber in sizes and grades suitable for form construction are as follows at New York at the time of publication. Spruce boards, i in. thick in car lots $25.00 per M ft. B. M. Spruce studding, 2 in. thick in car lots .... 25.00 to $30.00 per M ft. B. M. Hemlock boards i in. thick 18.00 per M ft. B. M. Hemlock studdings, 2 in. thick 20.00 per M ft. B. M. North Carolina Pine, 2 in. thick, 20.00 per M ft. B. M. Long Leaf Yellow Pine, dimension sizes . . 30.00 to $40.00 per M ft. B. M. The labor cost of framing, erecting, and removing forms will run from $5.00 to $20.00 per 1,000 ft. B. M., and the cost of form work per cu. yd. of concrete in place will depend upon : (i) The size of the walls, slabs, arches, etc., since a thin wall [405]' Handbook for Cement and Concrete Users requires more form work per cu. yd. of concrete in place than one of massive construction. (2) The number of times each form can be used in the course of the construction. (3) The salvage value of the material after the work is completed. In ordinary walls, arches, piers, etc., which can be erected without elaborate false work, the cost of form work will run from 20 cents to $1.00 per cu. yd. of concrete in place. In reinforced- concrete buildings, forms will cost in place from 5 to 20 cents per sq. ft. of surface in contact with concrete, or in general from $2.50 to $10.00 per cu. yd. of concrete in place. Cost of Reinforcement in Place. In ordinary beams, slabs, columns, retaining walls, etc., from 0.70 to 1.25 per cent of rein- forcement is used. Where i per cent of steel is employed, the volume of steel per cu. yd. of concrete will be 0.27 cu. ft., and the weight .27 X 490 = 132 pounds. The cost of handling, bending, and assembling steel reinforcing bars will run from $5.00 to $15.00 per ton, or from 1/4 to 3/4 cents per pound. Where plain bars are used at a cost of i 1/2 cents per lb., at the mill, the cost of freight and wagon haul to the work 1/4 cent per lb., and the cost of handling and wiring in place, 1/2 ct. per lb., the total cost of i per cent of reinforcement in place would be i 1/2 + 1/4 + 1/2 = 2 1/4 cents per lb., or 2 1/4 X 132 = $2.97 per cu. yd. of concrete. General Expenses. These include: (a) cost of plant, storage buildings, runways, etc.; (b) engineering, inspection, time-keeping, and (c) interest on the investment, repairs, depreciation of plant, etc. In a well-equipped organization the general expenses, after deducting the salvage value of the plant should not exceed 15 per cent of the cost of materials and labor. When work is done by contract, and the preliminary surveys, plans, and specifications are so complete and fair as to reduce the chances of loss to a minimum, a reasonable profit to the contractor would be 15 per cent of the cost in addition to the interest on his investment. When, however, there is much uncertainty as to the probable cost for materials or labor, or where the specifications are unduly severe, the contractor will be likely to raise his bid to an amount 20 or even 30 per cent above the estimated cost of the work. [406] Cost of Concrete Work Summary of Cost. The cost of mixing and placing concrete where no expense for forms is incurred, as in a street-paving job, may be estimated as follows : Cost of loading cement and aggregate Hand Mixing. id. Machine Mixing. Wheeling 60 ft. in barrows (4+3 cts.) .... O7 Mixing u / Loading concrete into barrows 66 12 Wheeling 60 ft. in barrows (4+3 cts.) O7 0*7 Spreading and ramming T C .u/ T X J L b General expenses, 15 per cent $0.88 1 3 $0.67 Total cost of labor $i .01 $o . 77 Cost of materials for a f Cement at 81.50 per bbl. \ i :2 1/2:5 mixture < Sand " .80 percu. yd. > $3.15 ^S-^-S with ' Stone " 1.20 per cu. yd. ) Net cost per cu. yd $4.16 $3.92 When the work is done by contract, add from 15 to 30 per cent for profit. ( For mass work from $0.20 to $1.00. Where forms are required, add per cu. \ _ . .... , . i For building construction, from $2.50 yd. concrete in place. / I to $10.00. Where reinforcement is used, add for ( ^ . . \ For mass work, $2.00 to $4.00. each i percent of steel per cu. { _ ,.,,. / For building construction, $2.25 to $4.25. yd. of concrete in place. In building construction, tunnel-lining, thin walls, arches, etc., where much spading and slicing is required; also where very dry mixtures are used, necessitating much ramming, the cost of spread- ing and ramming will be increased to from $.20 to .50 per cu. yd. In difficult, pneumatic, submarine, and other work subject to delays in transporting and placing, the cost of mixing and placing concrete will be increased from 25 to 100 per cent. In general, heavy mass work will cost from $4.00 to $7.00; heavy arches from $7.00 to $10.00, heavy building construction from $10.00 to $15.00 and light reinforced buildings from $15.00 to $20.00 per cu. yd. for concrete in place. Cost of Mortar. This depends upon the proportions of cement and sand and the cost of each ingredient. With sand containing 45 per cent of voids, and a barrel of cement holding 3.8 cu. ft. the [407] Handbook for Cement and Concrete Users quantities of each per cu. yd. of mortar would be as follows, accord- ing to Gillette:* Proportions of Cement to Sand. i to i i to ij I tO 2 I tO 2^ i to 3 i to 4 No. of bbls. of Portland cement No of cu yds of sand 4-3 2 o 60 3-6i o 80 3-10 O QO 2.72 I OO 2.16 I OO 1.62 i .00 With cement at $1.50 per bbl., and sand at $0.80 per cu. yd., the cost of i cu. yd. of i to 2 mortar would be as follows: For materials 3.10 X 81.50 = $4.65 .90 X 0.80 = .72 *5-37 Labor, transportation, and mixing i.oo Total cost $6.37 To the above must be added the cost of placing, whether for plastering, grouting, laying up masonry, etc. SOME ACTUAL EXAMPLES OF COST OF CONCRETE WORK In the remaining pages of this chapter, the actual costs of placing concrete in recently erected structures of different types are pre- sented. In each instance the authority is stated and a brief descrip- tion is given, including, wherever possible, a summary of the elements entering into the cost. Cost of Grouting. In Engineering-Contracting for May 6, 1908, the cost of grouting a rock-fill dam recently constructed on the Upper White River, in Arkansas, is given at $3.65 per cu. yd. of loose rock in place. Cost of Concrete Building Blocks. In a paper read before the Iowa Cement Users' Association in 1905, Mr. L. L. Bingham states that the average cost of materials and labor for mixing, moulding, and curing concrete blocks in Iowa with average wages at $1.83 per day, is 10 1/3 cts. per sq. ft. of face of wall for lo-inch walls. This is made up of 2 cts. for sand, 41/2 cts. for cement at $1.60 per * Gillette's " Hand Book of Cost Data.' Cost of Concrete Work bbl., and 34/5 cts. for labor. General expenses, including interest, depreciation of plant, and profits combine to double this amount, so that the selling price is about 21 cts. per sq. ft. of wall. Cost of Concrete Paving Blocks. In a paper read before the National Association of Cement Users, in 1910, Mr. Geo. C. Wright * gives the following data as to the cost of 2 -inch cubes made of Portland cement, sand, and i/ 2-inch gravel, as used for a roadway pavement by the New York State Highway Commission on 1,600 ft. of experimental roadway near Rochester, N. Y. u The cost per square yard of the cubes laid was as follows: Cement, 0.088 bbl., $0.1 21 ; cost of factory, $0.107; labor of manu- facture, $0.161; gravel at 50 cts. per cu. yd., $0.024; carting, $0.027; l a y m g> $0.072; total cost per sq. yd. laid, $0.512. There were placed on shoulders 219 cu. yds. of gravel covering i, 800 sq. yds., and costing $2.12 per cu. yd. rolled in place, or 26 cts. per sq. yd." Cost of Surfacing. According to Ransome, Gillette, and Neher, a concrete face can be bush-hammered by an ordinary laborer at a cost of from i 1/2 to 2 1/2 cts. per sq. ft., wages of common laborers being 1 5 cts. per hour. In Engineering-Contracting, Dec. 9, 1908, Mr. Linn White, Engineer South Park Commission, states that the cost of etching 3,466 ft. of 2 5 -ft. cement walk in Chicago was at the rate of i 2/3 cts. per sq. ft. This produced an excellent finish. Cost of Removing Efflorescence with Acid. Mr. H. P. Gillette f states that the cost of removing efflorescence on a concrete bridge at Washington, D. C., by scrubbing with a solution of i part hydro- chloric acid and 5 parts of water was at the rate of 20 cts. per sq. yd. for plain walls, and 60 cts. per sq. yd. for the entire bridge, in- cluding the balustrades. Cost of Tooling Surface. In Engineering News, Jan. 14, 1909, Mr. L. C. Wason gives the actual cost of tooling the concrete surface of a mill at Attleboro, Mass., as at the rate of 5.6 cts. per sq. ft. of area. In a paper presented to the National Association of Cement Users, at their annual convention in 1907, Mr. Henry H. Quimby, M.Am.S.C.E., states that the cost of tooling concrete surfaces by * Engineering Record, March 5, 1910, p. 277. f " Hand Book of Cost Data." [409] Handbook for Cement and Concrete Users means of a bush hammer or axe, operated by hand or pneumatic power, without subsequent cleaning with acid, was found to be from 3 to 12 cents per sq. ft., according to the character and extent of the work and the equipment. Mr. Quimby also states that the cost of scrubbing with wire brushes is trifling if done at the right time. A laborer may wash, say, 100 sq. ft. in an hour if the material is green, or the same area, if it has been permitted to get hard, may take two men a whole day to rub into shape. Cost of Applying Stucco. The cost of applying Portland cement stucco to frame houses by the use of expanded metal, or similar fabric nailed to the studding strips, will run from $1.10 to $1.40 per sq. yd. Cost of Reinforced-Concrete Building Construction. Mr. Leonard C. Wason,* M.Am.Soc.C.E., in a valuable paper presented to the Fifth Annual Convention of the National Association of Cement Users in 1909, gave the following actual costs of forms and concrete in place as compiled by the Aberthaw Construction Co., Boston, Mass., from their office records: f [See Table on page 412.] Cost per Ton. Cost of bending, fabricating, and placing ( Highest $16.47 of steel in dollars per ton, omitting < Lowest 2 54 the first cost of the material. ( Average of 21 ... 8.52 Deductions from Table. The following deductions from Mr. Wason's figures by the authors, while not scientifically exact, are nevertheless sufficiently accurate to roughly approximate the average cost of constructing reinforced-concrete buildings in terms of the number of cubic yards of concrete employed. Averaging the mean costs for each class of construction, gives the following unit costs: Forms $.111 per sq. ft. of area, or assuming that each sq. ft. of area cor- responds to 1/54 of a cubic yard of concrete, the cost would be per cu. yd. of concrete in place, $. 1 1 1 X 54, or $6 . oo Concrete per cu. yd., $3.04 X 27, or 8.21 If i per cent of steel is used, the weight of steel per cu. yd. of concrete in place will be 132 pounds. At a cost of i K cts. per Ib. delivered at the work, the cost of the reinforcement per cu. yd. of concrete would be $.175 X 132, or 2 .31 16.52 * President Aberthaw Construction Co., Boston, Mass. f Engineering News, Jan. 14, 1909, page 43. Cost of Concrete Work Brought forward from previous page $16.52 At a mean cost of $8.52 per ton, the cost of placing this reinforcement would be $.00426 per lb., or $.00426 X 132 per cu. yd. of concrete, or 0.56 Average cost of concrete work in buildings containing i per cent of steel per cu. yd. of concrete in place $17 .08 Cost of Buildings in Terms of their Cubical Contents. At the annual meeting of the Association of Cement Users in 1907, Mr. Emile G. Perrot, in a paper on "Comparative Cost of Reinforced Concrete Buildings," gave the following costs for concrete buildings built by his firm in terms of their cubical contents : Warehouses and factories 8-1 1 cts. per cu. ft. Stores and loft buildings 11-17 cts - P er cu - ft- Miscellaneous, such as schools and hospitals 15-20 cts. per cu. ft. These costs include the building complete, omitting power, heat, light, elevators, and decorations or furnishings. In "Reinforced Concrete in Factory Construction," published in 1907, by the Atlas Portland Cement Co., it is stated that the cost of reinforced-concrete factories finished complete with heating, lighting, plumbing, and elevators, but without machinery, may run under actual conditions from 8 to 12 cents per cubic foot of total volume, measured from footings to roof. The former price may apply where the building is erected simply for factory purposes with uniform floor loading, symmetrical design, which permits the forms to be used over and over again, and with materials at moderate prices. The higher price will usually cover buildings located in restricted districts, where the appearance both of the exterior and interior must be pleasing. The cost does not, however, in either case include interior plastering or partitions. Cost of Concrete Residences. The following comparative building costs of different systems of buildings are based upon an average frame dwelling costing $10,000 complete, located in the vicinity of New York : (a) $10,000 Frame. (&) $11,000 Brick outside walls, wooden inside. (c) $10,250 Stucco on expanded metal, wooden inside. (d) $10,500 Hollow terra cotta blocks stuccoed, wooden inside. (e) $12,000 Hollow blocks stuccoed: fireproof throughout except roof. (/) $14,000 Hollow terra cotta block walls faced with brick, fireproof floors and roof. (g) $15,000 Brick walls, fireproof floors and roof. [411] Handbook for Cement and Concrete Users o l O M M O W Ttf^-O -T^O fO O) CO "^ W 00 O O w ON ^O t^ OO CN M O "I- ON O Tj-^O O r~^ 10 10 ON O O j o > oou -OOMOOOOOOOOMOOMQOOOO Bi H s 6vpoo'c>t>66oegspj>o" cS vo rot^io^O t^-rfQ\OO VOONW rhO t^csrvoo M q i 8oo qoooqoooo > ooo :> oooo M M to O *O t^* vO OO ^O t-* ^" ON 10 ^O ON OO ^O *O ^O OO OO OO t^ CO i^* *O M M O M OO ^" ON t^* t^> w ON ^O O ON w ON ^OMMOMMWMMOOMOMMQMMOO J^^, u^J^JOW^'^'-'^wwvjv-'wO 1 ^ f\I co O l>* i>* 1 O ON t"^ OO M (N Ol ro ^O ^O CO 6 OOOMOOOOOOOOOOOOOOOOO" CO [412] Cost of Concrete Work The above figures are based on an average taken from two architects and two builders, who have had experience with the methods of construction designated and have been compiled by The National Fireproofing Co. Cost of Constructing Concrete Sewers. In Engineering News, for Feb. 3, 1910, Mr. Frederick R. Charles, City Engineer, Richmond, Ind., gives the following table, showing the costs per lineal- foot for materials and labor employed in placing the concrete for sewers ranging from 42 to 54 ins. in diameter, which were re- cently constructed in Richmond, Indiana: Cost per Linear Foot of Concrete Sewers at Richmond, Indiana. Diameter of sewer 54 ins. 48 ins. 42 ins. Thickness of shell 5 ins. 5 ins. 4 ins. Total cost, exclusive of machinery, and superintendence $i-349 $1.083 $0.911 In Engineering Record for April 4, 1908, the cost of building a 53 X 54 in. arch sewer with cement at $1.53 per bbl., sand at $0.50 and broken stone at $1.10 per cu. yd., is stated to be at the rate of $2.97 per lineal foot or $8.02 per cu. yd. of concrete. Data on Cost of Concrete Pipe. The following figures are given in the March Bulletin of the U. S. Reclamation Service for 1908, and relate to the cost per lin. ft. of constructing concrete pipe. Cost of cement, $3.05 per bbl.; of sand, $1.40 per cu. yd.; and of labor, $5.00 per day for foremen; $3.00 per day each for two men; and $2.75 per day each for two men. The concrete was made of i part cement and 3 parts sand. The unit costs were as follows: Diameter of Pipe. Inches. Thickness. Inches. Weight per Linear Foot. Lbs. Number of Feet Made. Cost per Foot. 12 I H 56 144 So- 25 18 IK 94 248 37 24 2 143 56 57 36 3 366 54 i-i5 Cost of Large Concrete Pipes. In the Reclamation Record for June, 1908, the cost of constructing 63 1/2 in. concrete pipe at Ballantine, Montana, is given at $6.90 per lin. ft., and the unit cost at $11.64 per cu. yd. Handbook for Cement and Concrete Users Cost of Reinforced-Concrete Culverts. In Engineering-Con- tracting for July i, 1908, the cost of constructing a 7 -foot reinforced- concrete box culvert with flat roof slabs at Huntley, Montana, is given at $17.41 per cu. yd.; while the cost of the steel was $0.0327 per pound in place. Cost of Concrete in Bridge Piers. The following costs for materials and labor used in placing concrete used to construct the piers and abutments of the Chattahoochee River Viaduct near Atlanta, Ga., in 1907, were given by Mr. John W. Ash in the Engineering Record, for Aug. 29, 1908. These costs do not include excavation or cofferdam construction: Total cost of materials $20,555.83 Total cost of labor , 4,515.39 5,024 cu. yd $25071.22 = $4.99 per cu. yd. The total cost of the work, including excavation, cofferdams, pile driving, etc., was about $45,000. Cost of Reinforced-Concrete Bridges. The approximate total cost of reinforced-concrete highway bridges, including excavation, falsework, and all other charges, is from $2.50 to $10.00 per sq. ft. of roadway area. The following are actual costs of recently built structures: Mulbury Street reinforced-concrete viaduct, Harrisburg, Pa., which is 1,841 ft. long and consists of 19 arches, varying in span from 36 to 93 ft. in the clear, cost $2.60 per sq. ft. of roadway area. This bridge is fully described in Engineering News, Jan. 13, 1910. Two-span highway bridge near Carlisle, Pa., consisting of two 62 ft. 9 in. arches, was built in 1909 at a cost of $2.35 per sq. ft. of bridge floor. This structure is described in Engineering Record for Feb. 19, 1910. In his paper on " Cost of Concrete Bridges," presented to the National Association of Cement Users in 1907, Mr. Henry H. Quimby, Engineer of Bridges of Philadelphia, said in part : "Of 18 concrete arch bridges recently built in Philadelphia, the concrete price spread upon the span area the clear span by the width varies from $3.11 to $9.74 per sq. ft. The average of the lot was $6.25 per sq. ft. of span area, most of them being single-span bridges with long wings, and all being highway bridges designed to Cost of Concrete Work carry loads of 40 tons on two axles 20 ft. apart. All have ornamental concrete balustrades and washed granolithic surfaces and paved decks, with electrical conduits and manholes, and water pipe and sewer well-holes, and some have pretty deep foundations. If the whole contract price be set against the yardage of the concrete in the structure, the unit costs vary from $8.50 to $11.25 per cu. yd., averaging $9.75." Mr. Quimby also states that in several instances where oppor- tunities for fair comparison occurred, steel plate-girder bridges would have cost 25 per cent, more than the reinforced-concrete bridges, which were constructed. A real money value also attaches to the superior beauty and attractiveness of a decorative arch over that of a purely utilitarian structure. Cost of Constructing Piers on Concrete Piles. Two piers built at Brunswick, Ga., in 1906, one 500 ft. long and 140 ft. wide; the other 900 ft. long and 140 ft. wide, both constructed on concrete piles, cost $1.40 per sq. ft. The piers are described in Engineering News, May 20, 1909. In a similar pier built at Charleston, S. C., described in the same issue, the cost was $2.60 per sq. ft. Cost of Concrete Piles. In a dike recently constructed on the Missouri River at St. Joseph, Mo., and described in Engineering News, Feb. 18, 1909, Cap. Edw. H. Schulz, Corps of Engineers, U. S. A., gave the following data: Total piles driven, 36; total lin. ft., 1,457; length of piles, 32 to 50 ft.; penetration, average, 21 ft. Total cost, $1977.21 or $1.36 per lin. ft. of pile. Cost of Concrete Trestles. The average cost of concrete trestles, used to replace similar timber structures on the Chicago, Burlington and Quincy Railroad, is given by Mr. C. H. Cartlidge, bridge en- gineer for the railroad, in Engineering Record, April 23, 1910. These trestles vary in length from 100 to over 1,000 ft. The bents are spaced from 14 to 16 ft. c. to c. Each bent consists of six i6-in. rolled piles spaced 2 .ft. 4 in. on centres. The cap is 2 1/2 ft. wide, 3 ft. 3 in. deep, and 14 ft. long. The floor is 14 ft. wide, made up of two solid reinforced-concrete slabs each 7 ft. wide and i ft. ii in. in minimum thickness for a slab of i6-ft. span. Parapets 6 in. high are cast on the slab to retain the ballast. The cost of the trestles is said by Mr. Cartlidge to vary from [4i5] Handbook for Cement and Concrete Users $20.00 to $45.00 per lineal foot. For estimating purposes a cost of $30.00 plus a constant of $300.00 was ample for any design. Cost of Reinforced-Concrete Poles. In Engineering-Contracting for Feb. 26, 1908, the cost of constructing reinforced-concrete poles 30 ft. long, and 6x6 ins. in sectional area at the top, and 10 X 10 ins. at the base, is stated to be $7.45. The cost of erecting a pole of this size is said to be $1.00 when proper equipment is provided. In the March 1 1, 1908, issue, of the same journal the following cost data for reinforced-concrete poles, erected at Richmond, Ind., is given : Length. Feet. , Top. Inches. Bottom. Inches. Cost. 2 5 6 IO $6.71 30 6 II 8.63 35 6 12 u-45 40 7 15 I7-05 45 7 16 21.78 50 7 17 2 5-5o 55 7 18 31-93 60 7 J 9 36.60 Cost of Constructing Concrete Sidewalks. The following data relates to the cost of laying cement sidewalks in Chicago, and is condensed from a paper by Mr. N. E. Murray, Superintendent of Sidewalks, for Chicago, 111., which was printed in Engineering News, Feb. 17, 1910. The ordinary concrete sidewalk gang in Chicago is usually composed of six men, paid as follows (for 8 hours) : i finisher at 65 cts., $5.20; i helper at 47 1/2 cts., $3.80; 4 laborers at 37 1/2 cts., $12.00; total $21.00. Such a gang will lay on the average 600 sq. ft. per day of 5 -inch cement walk. The cost per day for materials and labor, including the cost of filling and grading, is as follows: Cinders (allow for 20 per cent shrinkage), 20.83 cu - yds. a * 5 c * s< Base, 4% ins. (i: 2 H: 5) $10.42 Cement, 9.77 bbls. at $1.20 $11.72 Sand, 3.47 cu. yds. at 1.75 6.07 Gravel, 6.85 cu. yds. at 1.50 10 . 28 $28.07 416] Cost of Concrete Work Brought forward from previous page $38.49 Wearing coat, Kins. (2:3): Cement, 5.56 bbls. at $1.20 $6.67 Sand, 1. 17 cu. yds. at $1.75. 2 .04 8.71 Water, at i mill per sq. ft .60 Labor, one gang per day 21 .00 Use of tools, waste of materials, etc., at 2 per cent i .37 Supt. and office expenses at 5 per cent 3.51 Profit at 10 per cent . 7 . 36 Total cost per day $81 .04 Average cost 13.51 cts. per sq. ft. Cost of Concrete Curb and Gutter. The cost of building con- crete curb and gutter is about 40 cts. per lineal foot, including ex- cavation, for a gutter slab 24 ins. wide, and a curb 12 ins. high, both curb and gutter being laid monolithic in 7-foot alternate sections, with a 3/4 in. surface coat of cement and sand. Cost of Concrete Boundary Monuments. The cost of building 103 concrete monuments in post holes five feet deep, the average sectional area being 8X8 ins., is stated by Mr. Leonard Metcalf in Engineering Record, for Jan. i, 1910, as averaging $4.30 for each monument. Cost of Constructing Concrete Silos. Data taken from Hoard's Dairyman, for June 19, 1908, and described in Engineering-Con- trading for Sept. 9, 1908. Cost of concrete silo 10 ft. in diameter, and 31 ft. deep 15 ft. in ground and 16 ft. above. Materials, $75.00; labor, $97.00. Total, $172.00. Cost of Constructing Concrete Roofs for Filters and Reservoir. This should approximate $6.00 per cu. yd. In Engineering News for April 7, 1910, Mr. Thomas H. Wiggin, Assoc. M.Am. Soc. C.E., gives data on the design, construction, and cost of 44 different filters and reservoirs. In these structures, the cost of constructing the groined arch roofs varied from $0.182 to $0.61 cts. per sq. ft., depending upon the span, thickness, and other conditions. Mr. Wiggins estimates the comparative cost of plain concrete groined roofs as $0.25 and reinforced-concrete slab roofs as $0.54 per sq. ft. Cost of Concrete Tunnel Lining. The Gunnison Tunnel, recently completed by the Reclamation Service near Montrose, 27 [417] Handbook for Cement and Concrete Users Colo., is the largest work of its character and purpose. This tunnel has a width of about n ft., a height of 12 ft., and a length of 31,000 ft. The following data as to the cost of lining about 984 lin. ft. of arch and side walls with plain concrete was compiled by Mr. F. W. Hanna, engineer U. S. Reclamation Service and published in Engineering Record, May 30, 1908. The rate of wages was for foremen, $5.00 per day; and for laborers, $3.04. The mixture was in the proportion of i : 2 1/2:5. TABLE SHOWING COST OP CONCRETE TUNNEL LINING IN THE GUNNISON TUNNEL Distribution of Cost. Total Cost. Cost per Linear Foot. Cost per Cubic Yard. Superintendence 187 ?o $0.203 $O 212 Placing steel forms Tearing down forms. . . 275.12 288.80 0-33 o . 307 Q-35 1 O. 321 Mixing concrete 2Q^ ^2 o 33I O 34.S Placing concrete S8^.68 o .632 o .6^0 Hauling concrete 218 02 0.236 O.246 Sand and gravel at $o 637 per cu yd 70? 70 o 8^0 o 807 Cement delivered at $3 oo per barrel 77JQ JC 3CQ2 37CO $5971.49 $6.496 $6.781 During the period in question, 818 linear feet of forms were put into place and 940 linear feet were taken down. Cost of Waterproofing. Hot coal-tar and felt. Horizontal ist ply $2.00 to $4.00 per square (100 sq. ft.). Additional $1.50 to $2.50 per square. Vertical, add 10 per cent to 25 per cent. Pressure work, i ply $4.00 to $5.00 per square. Commercial asphalt and asphalt felt, add 15 per cent to 60 per cent per ply; special asphalts and felts, add 30 per cent to 50 per cent per ply; cold process felt or burlap, same as commercial asphalt; asphalt mastic, i in., 15 cts. per sq. ft. Cement waterproofing compounds. i in. on floors, J in. to f in. on walls, 8 to 30 cts. per sq. ft. Dampproofing masonry walls. 2 coats applied in place, 2 to 4 cts. per sq. ft. In a paper presented to the National Association of Cement [418] Cost of Concrete Work Users in 1907, Mr. H. Weiderhold, Mgr. Vulcanite Paving Co., Philadelphia, Pa., states that the cost of asphalt mastic for water- proofing in the vicinity of New York, when laid in i-inch layers, will range from 15 to 25 cts. per sq. ft. In Engineering Record for Oct. 31, 1908, is given the following cost data for waterproofing concrete-covered bridge floors with felt cemented together with Hydrex compound, as used by the Central R. R. of New Jersey, on their through girder bridges. "The work per square of 100 sq. ft. required 1.66 hours of time for a foreman, 11.71 hours water-proof ers' time, and 7.75 hours of laborers' time. The best record was 750 sq. ft. in one day of 10 hrs., while the average time was 40 per cent longer. The materials cost 2of cents, and the labor i of cents per sq. ft. for a five-ply covering. Cost of Reinforced Concrete in Dam Construction. The Corbett Diversion Dam of the Shoshone Irrigation Project, near Cody, Wyoming, is of the reinforced-concrete buttressed type, having a deck 30 in. thick on the upper side with a slope of i to i. This deck rests on buttresses two feet thick, spaced 14 ft. on centres. The following data as to the unit cost of concrete placed in the structure is condensed from the Reclamation Record of August, 1907. Materials and engineering, $5.00 per cu. yd. Contractors' labor and plant charges, $10.00 per cu. yd. Placing steel, $.035 per Ib. Cost of Rubble Concrete. In Engineering-Contracting for Oct. 7, 1908, is given the following cost data for placing 30,000 cu. yds. of concrete in a rubble-concrete dam near Chicago : Cost per Cubic Yard Concrete in Place. Stone Sr . 26 Sand 0.46 Cement 2.31 Forms o . 62 Mixing o .58 Placing o .69 Total $5 .92 In the canvass of bids opened Aug. 6, 1907, by the Board of Water Supply of New York City, for the construction of the Main Dams of the Ashokan Reservoir, the bid submitted by Messrs. [419] Handbook for Cement and Concrete Users Me Arthur Bros, and Winston, who received the contract, was as follows for concrete construction: Description. Unit. Quantity. Price. Portland Cement Barrels $1 5O Concrete Masonry Cubic Yards 280 ooo 400 Cyclopean Masonry Class A 4.75 OOO 7 AQ Cyclopean Masonry, Class B ; < ,000 "? QO Concrete Blocks 11 64 ooo 1 1 5O Grout of Portland Cement . " Feet 5 ooo O 5O The total bid on all of the estimated quantities for this work, of which concrete represents a large percentage, amounted to $12,669,- 775.00. The actual unit costs to the contractor for concrete may be approximated by deducting 15 per cent from each item. This represents his probable profits for the work. HEAVY TRIANGULAR POSTS. Materials. Cost. Number of Posts. Cost per Post. i yard of rock or gravel $1 OO 2O $ 03 % i yard of sand I OO c8 Ol K i barrel of cement 3 two-ply No. 12 wire cables (weight i Klbs.) 2 men for one hour at 20 cents per hour i boy for one hour at 15 cents per hour 1.50 .025 per Ib. .40 | ir ( 18 i 5 .08 y, .Q\% .11 Total Cost 2Q STRAIGHT SQUARE POSTS. i yard of rock or gravel $1 OO 2C $ 04 i yard of sand . ... I OO CQ 02 i barrel of cement . I ^O 16 oo K 4 two-ply No. 12 wire cables (weight 2 Y* Ibs.) 2 men for one hour at 20 cents per hour i boy for one hour at 15 cents per hour .025 per Ib .40 [ *5 i i 5 .05 K .11 Total cost -J2 X Cost of Reinforced-Concrete Fence Posts. The above data relative to the cost of constructing 7-foot reinforced-concrete fence [420] Cost of Concrete Work posts was published in Bulletin 403 of the U. S. Dept. of Agriculture, issued May 21, 1910. The mixture consists of i part of cement, 2 parts of sand, and 4 parts of crushed rock or screened gravel; a reinforcement consisting of two No. 12 smooth fencing wires twisted into a cable and cut to the necessary length at the factory; concrete mixed by hand; all material delivered at the work, and all labor of men and teams paid for. [421] INDEX ABUTMENTS, 255, 264, 274 Acid for bonding, 362 treating surfaces, 1 1 1 Activity of cement, 18 Aggregates sand, gravel, and broken stone, 36 selected, for surface finish, 112 Alkali, effect of, on concrete, 31, 281 Arches, concrete, 261 backfilling, 271 centres for, 268 construction of arches, 271 definitions of parts, 261 design of, 263 kinds of arches, 262 methods of failure of, 263 crushing, 263 poor foundations, 263 rotation, 263 sliding, 263 reinforced concrete for, 265 types of, 265 removing centres, 269 waterproofing, 370 Architecture, concrete, 3, 78 Asphalt, concrete, 27 for waterproofing, 353 Atlas Portland Cement Co., 162, 163, 184, 259, 279, 293, 300 BANK sand and gravel, 39, 5 1 Batch mixers, 53 Beams and slabs bridges, 273 design of, 169, 195 forms for, 71 in factory and building construction, 223 Blocks, concrete, 118 advantages of, 119 concrete block data, 134 construction details for, 129 cost of, 130 Blocks, inspection of, 397 machines for, 124 making the block, 125 dry process, 125 wet process, 126 facing, 126 curing, 127 coloring, 127 manufacturing processes, 121 materials for, 119 objections to, 131 specifications for, 135 tests for, 137, 138 types of, 121 waterproofing concrete blocks, 128 Blome granitoid pavement, 314 Bonding new to old concrete, 362 Bridges, concrete advantages of, 273 arch bridges, 265 advantages of, 266 general types of, 265 beam and girder bridges, 273 classes of, 274 beam and slab bridges, 275 girder bridges, 276 flat slab bridges, 275 trusses, 277 Building construction advantages of concrete for, 223 construction details for, 224 basement floor, 227 columns, 226 floor slabs, 224 floor system, 228 layout, 229 loading, 228 roofs, 230 shafting, method of attaching, 230 stirrups, 225 walls, 230 Bumping posts, 324 [423] Index CAISSONS, 243 Carving surfaces, 115 Castings, ornamental concrete, 139 Cements, 5 choice of cement, 15 common lime, 5, 16 fat lime, 5 hydraulic cement, 5, 8 hydraulic lime, 5, 6, 16 natural cement, 9, 15 plaster cements, 14 Portland cement, n, 15 puzzuolana, 7 quick lime, 5 slacking, 5 slag or puzzolan, 14, 1 6 slaked lime, 5 testing, 20 Cement coatings for waterproofing, 366 Centring, 268, 278 Cess pools (see Farm) Chenoweth pile (see Piles) Cinder concrete, 26 Clinton wire cloth, 217 Coal pockets, 322 Coal tar pitch for waterproofing, 353 Coatings, cement, for waterproofing, 366 Color of cements, 18 . Coloring, 113 blocks, 127 sidewalks, 208 stucco (see Plasters) Columbian system, 221 Columns design of, 173,190 forms for, 69 reinforcement for, 216 use in buildings, 226 Compounds for waterproofing (see Water- proofing) Concrete, 26 aggregates for, 36 architecture, 78 consistency of, dry, 29 grout or liquid concrete, 29 medium wet, 29, 58 very wet, 29, 58 effect of various agencies on, 27 aggregates, 28 Concrete, coloring matter, 29 gases, alkali, sewage, 31 heat, 31 sea water, 31 water, 29 forms for, 64 inspection of, 386 kinds of concrete, 26 asphalt concrete, 27 cinder concrete, 26 reinforced concrete, 27 rubble concrete, 26 mixing, 47 placing, 58 proportioning, 42 strength of, 33 waterproofing of, 344 Concrete structures, etc. abutments (see Abutments) arches and arched bridges, 261 beams, slabs, and columns, 169 bridges, 265 building blocks, 118 bulkheads (see Retaining Walls) culverts, 289 curbs and gutters, 310 dams, 298 on the farm, 332 fence posts (see Fence Posts), 157 foundations, 233 "liquid" or grout, 378 ornamental concrete, 139 pavements, 312 pipes, 150 railroad construction, 317 reinforced concrete (see also Reinforced Concrete), 27, 165 reservoirs, 304 residences, 82 retaining walls, 245 sidewalks, 305 surfaces, treatment of, 106 systems of reinforcement for, 215 tanks, 294 tiles and other products, 131 Counterforts (see Retaining Walls) Cost of concrete work, 400 elements of cost, materials, handling, etc., 401 general cost of main classes, 400 424] Index Cost of boundary monuments, 417 bridges, 414 bridge pier, 414 building blocks, 408 culvert, 414 curb and gutters, 417 dams, 419 fence posts, 420 forms, 412 mortar, 407 trowelling, 408 paving blocks, 409 piles, 415 poles, 416 reinforced concrete buildings, 411 removing efflorescence, 409 residences, 411 rubble concrete, 419 sewers, 413 sidewalks, 416 silos, 417 stucco, 410 surfacing sidewalks, 409 tooling surface, 409 trestles, 415 tunnel lining, 417 waterproofing, 418 Cracking of surfaces, 115 Culverts, concrete, 289 carrying capacity, 289 drainage area, 289 imperviousness of, 292 types of culverts, 290 arch culverts, 291 box culverts, 290 pipe culverts, 290 Cyclopean masonry, 26 DAMS, cost of, 419 pressures on, 298 reinforced concrete dams, 300 small dams, 298 Dressing of forms (see Forms) EFFLORESCENCE, 366 cost of removing, 409 Elevators, 330 Etching with acid, in Expanded metal, 217 FAILURE, methods of, 263 arches, 263 retaining walls, 246 Farm, concrete on the advantages of, 332 cess pools, 337 cisterns, 336 dairy, 338 drainage, 336 fence posts, 353 hitching posts, 333 horse blocks, 333 silos, 341 data for (see Tables) stalls, 337 troughs, 335 useful hints, 343 watering trough, 333 Fence posts, 157 fastening fences to posts, 162 machines for, 156 manufacture of, 156 moulds for, 155 reinforcement for, 161 Fineness of cement, 19 Finishing concrete surfaces, 106 Fireproof ness of concrete, 166 Floors, concrete, 228 Forms for concrete, 64 beam and slab forms, 71 centring, 73 column forms timber, bolted, and clamped forms, 70 cost of, 76 dressing and lubrication of, 74 panel form, 69 pressure of concrete on, 73 simple braced forms, 65 special forms, 73 studding and matched boards, 68 time to move after placing, 75 wire and bolted forms, 66 Formula for proportioning concrete, 44 Foundations caissons and cribs, 243 concrete footings, 235 concrete for, 235 cost of, 400 importance of, 233 425] Index Foundations in poor soils, 234 piles (see Piles), 237 requirements in construction of, 234 safe loads on, 233 GASES, effect of, on concrete, 31 Grout or liquid concrete, 375 machines for mixing, 377 preparing and mixing, 375 uses of, 375 for bonding new and old concrete, 384 for cementing joints, 377 for concrete under water, 379 for consolidating riprap, 378 for machine shop, 384 for miscellaneous purposes, 385 for paving filler, 384 for stopping leaks and seams, 382 for surface finish, 383 for tunnel linings, 380 for walks, 383 Gypsum cements, 94 HANDMIXING of concrete (see also Concrete) Hennebique pile, 239 system of reinforcement, 218 INSPECTION of concrete divisions of the work, 386 duties of inspector, 386 inspection of aggregates, 387 blocks, 397 castings, 397 cement, 386 forms, 390 measuring, 388 mixing, 388 piles, 398 placing concrete, 393 proportioning, 388 reinforcement, 391 removal of forms, 395 sand, 387 surface finish, 396 waterproofing, 348, 355, 362, 364, 394 Integral method of waterproofing, 362 Internal stresses, 169 Introductory, i JOINTS, cementing with grout, 377 KAHN system, 217 Keene's cement, 95 Keying, 92 LAITANCE, 29 Laths (see also Plaster), 100 Lime (see Cements) Liquid concrete or grout, 375 Literature, concrete, 3 Loads on (see article in question) Lubrication of forms (see Form), 74 MACHINE mixing of concrete (see also Mixing), 52 Martin's cement, 75 Mechanics of the beam, 195 Melan system, 221 Membrane method of waterproofing, 351 Merrick system, 221 Mixing concrete by hand and machine, 47 (see also Inspection) Modelling ornamental concrete, 139 Mortar, 5, 16, 46, 90 Moulds for concrete blocks (see Blocks) for fence posts (see Fence Posts) ornamental concrete, 142 for tiles and pipes (see Pipes) glue, 146 metal, 143 plaster, 144 sand, 147 wooden, 143 Mushroom system, 220 NATURAL cements (see Cements) OILS, effect of, on concrete, 31 Ornamental concrete, 139 methods of manufacture, 139 modelling, 139 moulding, 142 PARAFFINE for waterproofing, 368 Pavements (see Roads) 426] Index Pebble dark finish, 108, 109 Piers and abutments, 264 Piles advantages, 237 concrete, 237 disadvantages, 238 historical, 237 Pipes and tiles advantages of, 150 data and costs of, 156 machines for, 151 manufacture of, 152 moulds for, 151 reinforced concrete pipes, 154 Placing concrete, 58 (see also Inspection) Plasters and plastering, 90 cement plasters, 14 gypsum plasters, 95 Keene's, Martin's, and Parian ce- ments, 95, 96 plaster of Paris, 95 lime plasters, 90 plastering interior, 91 brown coat, 92 exterior lathing and plastering, 100 finishing coat, 93 Portland cement plasters or stucco, 96 scratch coat, 91 applications of stucco, 101 materials for stucco, 105 rules for metal lath, 99 specifications for laths, 98 Platforms, 319 Pneumatic caissons, 243 Poles, concrete, 328 Portland cement (see Cement) Power houses, 320 Precautions and rules for mixing (see also Rules, etc.), 5 6 > 35 6 > 3 6 4, 3 86 Pressure on forms, 73 hydrostatic, 299 of earth, 259 Processes of manufacture (see article in question) Properties of cements, 18 Proportioning materials for concrete, 42 (see also Inspection) Protection of concrete after placing, 60 Protection of waterproofing (see Water- proofing) Puzzuolana (see Cements) RAILROAD construction, concrete in ash-handling plants, 322 bridges and trestles, 318 bumping posts, 324 coal and sand pockets, 322 docks, 329 foundations, 317 grain elevators, 330 piers and abutments, 318 pits, 324 platforms, 319 posts and fences, 327 power houses, 320 railroad shops, 321 retaining walls, 318 roadbed, 327 round houses, 323 signal towers, 320 stations and train sheds, 319 storage reservoirs, 329 telegraph poles, 328 ties, 325 tunnels, 328 turntables, 324 Raymond piles (see Piles), 241 Reid, Homer A., 300 Reinforced concrete, 165 (see also Concrete) advantages, 165 design of beams, 169, 195 design of bond, 188, 209 design of columns, 173, 190 design of slabs, 178 design of stirrups, 187 materials for, 167 rules for design of beams, 173, 175 rules for design of columns, 173, 190 specifications for, 210 systems of reinforcement, 213 (see also Systems) tables for use in design (see Tables) Removal of forms (see Forms) Requirements for cement, 23 natural cement, 24 Portland cement, 25 Reservoirs, concrete, 304 427 Index Residences, concrete, 82 architectural features of, 86 concrete block residences, 83 cost of concrete residences, 89 Edison cast concrete house, 86 kinds of concrete residences, 83 monolithic residences, 84 reinforced concrete, 85 surface finishes for block residences, 83 stucco residence, 84 Retaining walls appearance of, 251 design of, 245 drainage of, 254 earth pressures on, 246 failures, methods of, 246 bulging, 247 overturning, 246 sliding, 246 foundations for, 253 land ties for, 254 relieving arches for, 254 types of, 248 gravity walls, 248 design of, 248 reinforced concrete walls, 249 without counterforts, 250 with counterforts, 251 restrained, 252 construction of, 252 Riprap, consolidating with grout (see Grout) Roadbeds, 327 Roads and pavements, concrete, 310 patented pavements, 314 Blome granitoid, 314 Hassan pavement, 315 Roebling system, 219 Rough cast finish, 108 Round houses, 323 Rubble concrete, 26 Rules for concrete workers (see Inspec- tion) SAND for concrete, 36 broken stone for concrete, 39 gravel for concrete, 40 Scouring, 92, 93 Screeds, 92 Scrubbing surfaces, no Seams, grouting (see Grout) Selected aggregates for surface finish, 112 Sea water, effect of, on concrete, 3 1 Sewage, effect of, on concrete, 31 Sewers, concrete, 281 Sidewalks, concrete, 305 advantages of, 305 coloring, 308 construction of, 306 sub-base, 306 base, 306 wearing surface, 307 dimensions of (see Tables) forms for, 306 materials for, 305 protecting, 308 tools and equipments, 306 Signal towers, 320 Silos (see Farm) Slab bridges (see Bridges), 266 Slacking (see Lime) Slag cements (see Cements) Slap-dash finish, 108 Smooth -float finish, 108 Soundness of cement, 18 Specifications for concrete blocks, 135 Specifications for design of reinforced concrete, 210 Specifications for lathing and plastering, 98 Specifications for waterproofing (see Waterproofing) Strength of cement, 19 Strength of concrete, 33 Stresses in reinforced concrete tension, compression, shear, bending, 169, 170 Stucco and its application, 101-104 Stucco and stuccoing (see Plasterers and Plastering) Stucco finishes (see Surface) Surface coatings for waterproofing, 366 Surfaces artistic treatment of concrete, 106 facing with mortar, 109 imperfections in concrete, 106, 115 methods of finishing, 107 mosaics, carving, etc., 115 panelling, 114 scrubbing and washing, no [48] Index Surfaces, selected aggregates, 112 TABLES : spading and trowelling, 158 xm. stucco surfaces, 108 xrv. pebble dash, 108, 109 rough coat, 108 xv. slap dash, 108, 109 smooth float finish, 108 xvi. tinting and coloring, 113 tooling, 112 XVI A. Surfaces, cost of finishing, 409 Systems of reinforcement, 215 xvil. rods and bars, 215 wire, 216 xvni. expanded metal, 217 spiral reinforcement for columns, 216 xix. special systems, 216 xx. expanded metal, 217 Clinton wire cloth, 217 xxi. Kahn system, 218 xxii. Hennebique, 218 Hinchman-Renton, 218 xxni. Roebling, 219 Turner, Mushroom, 220 XXIV. Merrick, 221 Melan, 221 xxv. Columbian, 221 Unit, 222 xxvi. TABLES: xxvn. I. Outline of process of manu- facture of hydraulic ce- xxvm. ments, 10 II. Ingredients in one cubic yard xxix. of concrete, 45 in. Materials for one cubic yard XXX. of mortar, 46 iv. Materials for two-bag batch xxxi. of concrete, 52 v. Bank sand and gravel re- xxxn. quired for two-bag batch, 53 vi. Pressure on forms produced xxxm. by concrete, 74 vn. Sizes of metal laths, 98 xxxiv. vni. Quantities for 100 square yards of laths, 98 xxxv. ix. Area covered by mortar, 105 x. Materials for coloring mor- xxxvi. tars, 114 xi. Concrete block data, 134 xxxvu. xii. Hollow spaces in blocks, 137 [429] Data for concrete tile, 156 Quantity of materials for fence posts, 162 Quantity of materials for cor- ner posts, 163 Data for design of reinforced concrete beams, .176 Co-efficients for design of rein- forced concrete beams, 204 Depths of beams and squares of same, 181 Weight of reinforced concrete beams, and cost, 182 Properties of steel bars, 183 Dimensions of reinforced con- crete beams, 184 Allowable loads on floors, 229 Earth pressures on retaining walls, 259 Dimensions for basement walls, 259 Dimensions for gravity re- taining walls, 260 Dimensions and quantities for slab bridges, 279 Amount of materials for arch culverts, 293 Spacing of rods in concrete tanks, 296 Spacing of rods in concrete tanks, 297 Dimensions of circular tanks, 297 Hydrostatic pressures at vari- ous depths, 299 Dimensions for small dams and materials for same, 300 Dimensions for concrete side- walks, 309 Materials for concrete side- walks, 309 Offsets for crowning streets, 3i5 Data for reinforced concrete silos, 342 Number of ply ,and thickness of waterproofing, 352 Outline of modern water- proofing processes, 370 Index TABLES : xxxvui. Cost of forms and concrete in buildings, 412 Tanks, concrete, 294 Testing cement, 20, 21 Tiles, concrete, 131 Tremie for depositing concrete under water, 62 Troughs, 334 Trowelling, 93, 94, 108 Tunnel lining, grout for (see Grout) Turntables, 324 Turner mushroom system, 220 UNIT system, 222 VAN DEERLIN, R., on concrete architec- ture, 78 Voids in concrete, 42 Volume of barrel of cement, 43 WATER for tempering cement, 31 Waterproofing, cost of, 374 importance of inspection, 348 general principles to be followed, 349 method of conducting the work, 346 work under contract, 346 work not under contract, 347 modern methods of waterproofing, 350 integral method, 359 addition of materials to the con- crete, 360 compounds employed, 361 powders, 361 waterproof cements, 361 Waterproofing liquids, 361 combinations, 361 membrane method applications of materials, 306 continuity of work, 357 preparation of surfaces, 356 protection of work, 358 materials for, 351 scope and applicability of, 350 specifications for materials, 353 asphalt, 350 asphalted felt, 355 coal tar pitch, properties and tests, 353 necessity for, 344 surface coatings, 366 applicability of, 366 bituminous process, 369 cement grouting processes, 369 materials for, 366 paraffine, cold process, 368 pataffine, hot process, 368 Sylvester process, 367 workmanship, 370 rules for applying coatings, 364 application of coatings, 365 preparation of coating, 364 preparation of surface, 364 tabular outlines of modern processes, 37i waterproof cement coatings bond, 362, 363 continuity, 363 homogeneity of work, 363 soundness, 363 -^J^ [430] RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW 7la DD20 15M 4-02 LD 21-100m-ll,'49(B7146sl6)476 YC 13585 THE UNIVERSITY OF CALIFORNIA LIBRARY