GOOD CONCRETE THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES GIFT Good Concrete A Manual For The Rational Use of 'Portland Cement Riverside Portland Cement Company Los Angeles 1914 Copyrighted 1914 by Riverside Portland Cement Co. Los Angeles, Cal. Printed by De Wit & Company Los Angeles. Cal. Engineering Library TA PREFACE. In Portland Cement - Concrete the world has an ideal structural material whose possibilities are limited only by the skill and ingenuity of the user. Its widespread and ever increasing use is exerting a profound influence in making our cities and towns safer and more sanitary. The fire risk has by its use already been reduced enormously, and millions of dollars are being saved annually in insurance. It is doing much to beautify our cities by the ease with which it lends itself to the artistic treatment of our homes, business buildings, sidewalks and streets. It has given to building operations an air of permanence which heretofore they did not possess. Once properly built a concrete structure becomes a thing of per- manence. It will not deteriorate with age, it becomes, so to speak, a part of the geology. There are few structural operations to which concrete in some form cannot be economically applied. Portland cement is sometimes abused. The seeming simplicity with which it can be worked has often led the uninitiated to attempt its use without regard to the laws that govern its proper use. This hand-book is written to present to the cement-user in con- cise form the general and detailed operations necessary for the full realization of the value of Portland cement as a material of con- struction. Contents Concrete Axioms CHAPTER I. Portland Cement CHAPTER II. Concrete. CHAPTER III. Proportioning Concrete 37 CHAPTER IV. The Properties of Concrete 53 CHAPTER V. Portland Cement Sidewalks 73 CHAPTER VI. Portland Cement Curbs and Gutters 101 CHAPTER VII. Concrete Roads HI CHAPTER VIII. Specifications for Concrete Roads with Asphalt Oil Wearing Surface 123 CHAPTER IX. Cement Pipe 151 CHAPTER X. Cement Sewer Pipe 1 65 CHAPTER XI. Some Suggestions for Care and Return of Empty Sacks 171 Appendix 1 79 CONCRETE AXIOMS. Concrete construction does not belong to the class of iDork that can be done by unskilled labor. Definite laws govern the use of concrete as well as all other struc- tural materials. Good rock, sand and cement will not make good concrete in the hands of inexperienced workmen. Don't guess at proportions measure them. The cement in a concrete is the smallest of its ingredients. Don't make it smaller than the specifications require. Cement is the only ingredient in a concrete or mortar that has been scientifically and accurately made. It is a finished product as it comes on the market, in the preparation of which great care and pains have been exercised, whereas the sand and rock, which constitute more than 80% of the total, are natural products and have been collected at random. Use clean materials. Cement cannot bind sand and rock to- gether if clay coats them. Concrete cannot be any stronger than its weakest ingredient. There- fore, use sand and rock whose individual strength is sufficient for the purpose. Don't use very fine sands, or those containing much quicksand. Test all your materials for strength and fitness for the purpose to which they are to be put. Cement needs water to properly harden. If it is robbed of any of the necessary water its strength suffers. Too much water is as bad as too little. Learn to use the right amount. Protect fresh concrete from drying out. Don't lay concrete in cold weather. Cold retards and warmth hastens the hardening of a concrete or mortar. Don't blame cement for poor work before you have considered every factor that might have contributed to the failure. Men and materials are just as liable to be wrong, and more so, than the cement. Portland Cement CHAPTER I. The term "Portland" as applied to cements is used to distinguish the superior artificial hydraulic cements from the inferior natural ones. Portland Cement is not so-called because it was first made in What is Portland, Ore., or Portland, Me., but to the fact that in 1824 when Portland John Aspden made his first artificial cement, its color resembled the Cement? Portland stone much used at that time in England for masonry. The definition of Portland Cement will be found under the "Standard Specifications" of the Am. So. C. E. given below. STANDARD SPECIFICATIONS FOR PORTLAND CEMENT. AMERICAN SOCIETY FOR TESTING MATERIALS. The term "Portland Cement" is applied to the finely pulverized Definition product resulting from the calcination to incipient fusion of an inti- mate mixture of properly proportioned argillaceous and calcareous materials, and to which no addition greater than 3% has been made subsequent to calcination. The specific gravity of the cement shall not be less than 3. 10 on a Specific sample ignited at low red heat. gravity It shall leave by weight a residue of not more than 8% on a Fineness No. 100, and not more than 25% on a No. 200 sieve. It shall not develop initial set in less than thirty minutes, and must Time of develop hard set in not less than one hour, nor more than ten hours, setting 12 GOOD CONCRETE Tensile The minimum requirements for tensile strength for standard strength briquettes shall be as follows: NEAT CEMENT 1 day in moist air 1 75 Ibs. 7 days (1 day in moist air, 6 days in water)... 500 Ibs. 28 days (1 day in moist air, 27 days in water)... 600 Ibs. One Part Cement, Three Parts Standard Sand. 7 days (1 day in air, 6 days in water) 200 Ibs. 28 days (1 day in air, 27 days in water) 275 Ibs. Constancy A neat cement pat 24 hours old exposed to steam over boiling of volume water in a loosely closed vessel must not check, warp or disintegrate. A pat 24 hours old placed in water at 70 deg. F. for 27 days must remain sound. A pat left 28 days in air must remain sound. Sulphuric add The cement must not contain more than 1.75% of sulphuric and magnesia anhydride and must not contain more than 4% magnesia. We will now consider the various items of the standard specifica- tions, their meaning and use in judging a cement. Specific By this term is meant the ratio between a given volume of the gravity substance (cement) and an equal volume of pure water. In short, when we say a cement has a "Specific Gravity" of 3.12, we mean that a given volume of it (solid) is 3.12 times heavier than an equal volume of water. The specific gravity of Portland Cement is higher than that of natural cements, due to the high degree of heat used in burning the former. This test is used to determine whether or not the cement has been 5 * properly burned. The specific gravity of a cement is lowered by long storage due to the absorption of water from the air. For this reason it is necessary to thoroughly dry the sample before it is tested. This test is made to determine how fine the cement is ground. The test is made with the 200-mesh (40,000 holes per square in.), GOOD CONCRETE 15 and the 100-mesh (10,000 holes per sq. in.) sieves. It is essential that the sieve be standardized, otherwise the results of the tests will be of no value. When Portland Cement is mixed with the proper amount of water. Setting a plastic paste is produced, which, after a few hours, hardens to a time stone-like mass. The time taken to produce this result is termed the "setting time." The setting time is divided into two arbitrary periods, i. e., the initial and final setting time. Initial set is that point in the stiffening of the cement paste where Initial it will bear a needle 1/12" in diameter and weighing 1/4 Ib. set This point can be approximately determined by observing the point at which the test piece will bear slight pressure with the thumb nail. Final set is attained when it will support a needle 1/24" in diam- Final eter weighing 1 Ib. Final set is completed approximately when the $ef test piece will take strong pressure with the thumb nail. Mix up about 4 oz. of cement with 1 /5 its weight of water, work field test with a trowel for five minutes until a smooth paste is obtained, roll / O r setting into a ball and place on a clean piece of glass V X A", flatten out time into a circular pat and taper to a feather edge toward the circum- ference. Place in a cigar box lined with wet blotting paper and try every ten minutes as directed above. Riverside Portland Cement will get its initial set in from 1 J/ to 2'/2 hrs., the final in from 3 to 5 hrs., depending on the temperature of the air. It will be faster when warm and slower when cold. This test is very important to the proper handling of the cement. Use of test On it depends the size of the batch of mortar or concrete that can be safely worked up and used before it takes its initial set. A batch of concrete that has begun to set should not be used. If the set is disturbed, the strength is greatly reduced. The practice of adding more water and retempering the partially set concrete is one that cannot be condemned too strongly. 14 _ GOOD CONCRETE Tensile Although cement is never used to take a tensile strain, the tensile strength strength gives a convenient method of comparing different lots of cement and noting the progress of hardening. The strength is usually measured at the end of 1 , 7 and 28 days for the neat and at 7 and 28 days for the 1 :3 sands. The logical test would be to determine the compressive strength, but this procedure is both tedious and more expensive than the tensile test. Constancy T m ' s test j s commonly known as the "Boiling Test" and is made of volume to determine the absence or presence of any dangerous expansion in the cement. 7^ determination of this item serves as an index to the amount anhydride o f gy psum that has been used as a retarder. Generally: Aside f rom ^ setting time tegt) ^ testjng of cement Js ft tec h n j_ cal matter that should be entrusted only to persons expert in this branch and who have the proper laboratory equipment for carrying out the work. The conditions under which the tests are made must be kept uniform in order to get results that will not be misleading. HARDENING. The "set" of cement must not be confused with its hardening. Between Setting is a purely arbitrary period, as has already been explained. set ai d The hardening of a cement, however, is a definite chemical stage, '* and begins after set has taken place. Hardening takes place either in water or in a'ir in fact, the process takes place more uniformly under water than in air. The hardening is due in part to a process of crystallization, which takes place in certain of the elements of the cement. hardline *" T f ^ IatCSt researches on Ac hardening of a cement, it is established that the process is not really as simple as crystallization itself. Michaelis, Sr., attributes the hardening of a cement to the formation of a mineral glue, which is termed the hydrogel, and to the formation of minute crystals of the hydro-aluminate of lime. The hydrogel is composed of a combination of hydro-silicic acid and GOOD CONCRETE 15 lime; that is, hydro-silicate of lime. No definite chemical com- pound is, however, formed, as the composition of this lime hydrogel is constantly undergoing changes by the adsorption of lime. Now, the formation of this mineral glue, or hydrogel, is controlled by two factors first, the temperature; second, concentration, or the relative amount of water present to the amount of available lime in the cement. The formation of this hydrogel is greatly facilitated by agi- tation (mixing). The critical temperature below which the hydrogel will not form has been found by Michaelis to be 40 deg. F. This limiting temperature is, however, theoretic. For practical operations a minimum temperature of 55 deg. is the limit beyond which the proper hardening cannot take place without the application of arti- fical heat. At temperatures lower than 55 deg. F. the "gel" forms but imperfectly, and the mass is more likely to crystallize in inferior flat forms, which do not allow the hardening to progress to the best advantage. When a cement hardens by crystallization alone, it can attain a Crystallization fair degree of strength if kept in air, but such a hardened cement or mortar would soon disintegrate when placed under water, owing to the relative solubility of the crystals. Again, if too much water is used in gauging a mortar or concrete, the cement is decomposed into "laitance" (cement milk). This laitance does not set up, but dries out to a soap-like mass devoid of any strength. CHAPTER II. CONCRETE. Concrete may be defined as a skeleton of rock bound together by Definition a sand and cement mortar. It may with propriety be considered of concrete uncoursed rubble masonry in which the stone ranges from J/4" up to 3", the whole consolidated into a monolithic mass by the binding mortar setting up. The advantages of concrete over coursed masonry lie in its adaptability to any form at the will of the operator, and its ability to yield, in setting up, a monolithic mass. The strength of any concrete is necessarily dependent upon its constituent materials rock, sand and cement. The mortar must, in a plastic state, be sufficient to not only fill the voids in the rock, but to also coat each surface. The rock must be possessed of sufficient strength in itself, and the mortar must be of such strength as to thoroughly cement the rock together. It is evident, therefore, that the mortar is the vital constituent of a concrete. The proper proportioning of the mortar, and its mixing with the rock, constitute the "Knowing how" of concrete. The rock and sand constitute the chemically inert portion of a concrete and are termed the aggregate. Difference between "Rock" and "Sand." Any mineral detritus Difference finer than %" is called sand, and that portion coarser than %" between is called rock (or gravel). rock and sand 18 GOOD CONCRETE ROCK. Kinds Under the head of rock will be considered all of the aggregate, of rock be it artificially crushed or natural, which is coarser than %". The "Rocks" most usually crushed for concrete aggregates are: Trap, limestone, granite, sandstone, basalt and conglomerate. Slates and shales are not adapted to the purpose on account of their lack of strength. Trap and Limestone of dense textures are considered the best materials for the purpose, as they are strong and crush to more or less cubical fragments. Granite and basalt are not so well suited for aggregate as they are likely to break into spawls or flat pieces, which become trouble- some in tamping the concrete due to their tendencey to "arch" and produce pockets. Sandstone is rather too porous to be classed as a first class aggre- gate. Conglomerate, if possessed of a cubical cleavage, makes a good aggregate. Cinders and old brick are in some cases used as aggregate. The cinder must be free from unburnt or partially burned coal and reason- ably free from sulphur. Old brick, if thoroughly wet before using with the sand and cement, can be used to good advantage where no great loads are to be carried. Both cinder and old brick are considerably lighter in weight than rock and are well adapted to use when lightness with reasonable strength is required. The selection of a rock for the aggregate will, of course, be gov- erned by local conditions, by what the locality offers, and the im- portance of the work. In the majority of Southern California locali- ties stream gravel is available in almost unlimited quantities. // proper/]; screened, this material makes an excellent coarse aggregate. GOOD CONCRETE 19 The practice of using the natural gravel and sand just as it comes Danger of from the stream is an exceedingly poor one. Whereas the gravel "' and sand may be in themselves of excellent quality, they are seldom, "' if ever, found in exactly the proper proportions. Furthermore, the proportion of sand and gravel are different for nearly every foot of depth, so that it is nearly impossible to get two successive wagon- loads that are the same. SIZES OF ROCK. The largest size of rock allowable in concrete will depend en- Cyclopean tirely upon the nature of the work. For massive work, such as concrete foundations, dams, etc., 3J/i" for the concrete proper, and it is customary and good practice to imbed in the concrete stone up to 1 cu. ft. in size as "displacers." This is termed "Cyclopean Con- crete." In some very large dams "displacers" of one ton weight have been successfully used. For reinforced concrete 1" is the largest size allowable. EFFECT OF SIZE OF ROCK UPON THE STRENGTH OF CONCRETE. From a purely theoretic standpoint it would seem that the larger Effect of the rock in a concrete the greater the strength, as there is less sur- size of rock face to cover while the percentage of voids remains practically the u P n strength same. But practical considerations of placing and compacting the concrete considerably modify this view. If the stone is too large trouble is experienced in properly tamping. General Gillmore at the Watertown Arsenal made a series of tests to demonstrate this point. 20 GOOD CONCRETE TESTS OF 1:1:3 CONCRETE MADE OF DIFFERENT SIZES OF ROCK. Size of Rock Age, Days Weight per cu. ft. Compressive Strength Ibs. per sq. in. W Trap 32 146.4 2800 %" Trap 32 148.3 3200 1 "Trap 34 160.9 4917 1M"Trap 41 161.2 4562 2K" Trap 32 161.4 4140 #" Gravel 34 147.0 2992 IK" Gravel 29 151.5 3817 3 "Gravel 41 153.6 4200 CRUSHED ROCK vs. GRAVEL. Crushed Much has been said and written about the relative merits of these rock or two materials as coarse aggregates for concrete. Some engineers gravel contend that crushed rock made of hard, unweathered and durable stone is far superior to gravel, basing their contention on the fact that crushed rock has a rough crystalline surface, which greatly increases the adhesion of the mortar to the rock particles, while gravel presents a round and smooth surface. Aside from any preconceived preferences, the choice of the two materials can safely be left to their cost. There have been as many notable concrete structures built of crushed rock as there have been of gravel.^ Gravel by the nature of its occurrence is the "Survival of the fittest"; it represents the most refractory portions of the rock from which it has been derived. On close examination of any of the Pacific Coast gravels it will be seen that the surface is covered with minute "pit marks," which can safely be relied upon to give all the necessary adhesion between it and the mortar. GOOD CONCRETE 21 Either material must be free from surface coatings of foreign substances. SAND. Sand is an unconsolidated debris resulting from the weathering and decomposition of rock. It is composed of grains of varying size and shape. It can be derived from any rock and will therefore possess charac- ,/Vo two teristics as widely different as those of the rocks from which it origi- sands natcd. are alike All sands therefore will not be of equal value as aggregate. Sands which to the eye may seem identical can be found upon testing to be greatly dissimilar in their value as ingredients of mortar or con- crete. In fact, sands from the same pit show enormous variations in sizing of grains. Sands are distributed in nature by rivers and streams. The size of grains that can be transported by flowing water is a /^j'ver function of its velocity. A torrent will carry coarse sand and gravel ana until its velocity is suddenly checked, as by an abrupt bend in the Creek channel, at which point it deposits the coarser particles while the finer sands ones stay in suspension. As the velocity of the moving water grows less, finer material is deposited until in slowly moving streams only silt is dropped. It is in the bends of old stream channels that "Gravel Pits" are found. Bank sands are deposited at periods of high water along the Bank banks and stream terraces. Such sands are usually quite uniform in sands their sizing, but under some circumstances carry a large percentage of foreign matter. On the other hand, sands taken from the beds of streams in the All sands dry season show great variations in the sizing of their grains. In van; in localities where stream beds furnish the supply of sand and gravel composition many of the failures of concrete work are attributed to the cement used, when in reality the sand is responsible. 22 GOOD CONCRETE It is evident that a stream that goes dry at some season must at others carry a great volume of water with varying velocities which will deposit layers of very dissimilar sized sand. It is the indis- criminate use of these different sized sands that is responsible for a great deal of the wretched work done in our small towns. Sands Sand cannot be properly judged by simply looking at it. It must must be be examined by the proper method to establish its value for the in- tested tended purpose. Hol to To establish the characteristics of any sand, it is examined for: test sands (1) Strength of grains (2) Cleanness or freedom from clay, loam, dirt and organic matter. (3) Sizing of particles or Mechanical Analysis (4) Weight per cubic foot (5) Per cent of voids. Grain (1) A mortar cannot be any stronger than its weakest cora- strength ponent. It is necessary, therefore, to select a sand whose grains are of sufficient strength. Sands whose grains can be easily crushed by rubbing between the palms of the hands or by slight pressure are not fit for use. Sands that soften when placed in water or impart to it a perma- nent turbidity are to be avoided. To this class belong those sands derived from chalks and shales. Quartz sands as a general rule are preferable to all others. They contain less decomposed mineral matter and have great grain strength. Sands derived from dense crystalline limestones are also considered excellent material. Artificial sand or screenings made in crushing a durable crystalline limestone are by some authorities considered su- perior to all other sands if they do not contain too much fine dust. Dirty (2) Sands containing clay, loam, dirt and other organic matter sands should be avoided. Such sands might be improved by washing, but this procedure may be more expensive than getting a clean sand from some ether locality. GOOD CONCRETE 23 In working up a mortar made from a dirty sand, the clay and Dirty loam "slimes" and envelops the sand grains, thus preventing a bond sands are between the grains and the cement grout. dangerous These foreign substances also exert a marked influence upon the Dirty sands setting of the mortar. They greatly retard the hardening, and can, affect the in fact, under some circumstances entirely prevent it. hardening The following simple methods are very effective in determining the cleanness of a sand: Rub some of the sand between the palms of the hands. If they Hov> to are badly discolored the sand is "dirty." tell a Into a pail full of clear water drop a handful of the sand. If dlrt ^ sand the bottom of the pail is visible at the end of two minutes the sand is considered clean. Take a quart fruit jar, fill it one-quarter full of sand, then pour in water until three-quarters full, screw on the top and shake vigor- ously for a minute and allow to settle. If a layer of mud settles over the sand, it is "dirty" and should not be used without being washed. The presence of organic matter is usually in the form of soil humus, Soil decayed vegetable matter and mould. These substances form a soap- humus like compound with the lime in a cement and produce disintegration, in sands (3) Sizing of Particles: Of decided influence upon the strength Sands of a mortar is the sizing of the sand grains. It is a well-known fact must that coarse sands give stronger mortars than fine ones. The reason have for this will be apparent if we consider the following: If we assume, proper for the sake of calculation, that each sand grain is a sphere, then sizing each sphere of the same diameter will have a definite surface area. f To separate a sand into various sizes, all that is necessary is to pass it through a given sieve. For instance, if we pass a material through the sieve having 200 holes per linear inch (40,000 per sq. in.), the average diameter will be 0.0027". Now to count the number of sand grains in a cubic yard of 200 mesh material we simply divide GOOD CONCRETE 36" by .0027 and cube the quotient. Then by applying the factor of surface area we have the total surface of grains in a cubic yard. Carrying out the computation for the No. 200, No. 1 00, No. 50, No. 20, No. 1 and No. 4 sieves, we get the relative surface area in a cubic yard of each of these sizes. The results thus obtained are rather surprising. TABLE I. SHOWING RELATION BETWEEN DIAMETERS AND TOTAL SURFACE AREAS IN ONE CUBIC YARD OF MATERIAL: Diameter of Grain Sieve Number Surface to covet in 1 cu. yd. .0027 200 41,500sq.yds. .0045 100 25,1 30 sq. yds. .011 50 1 0,500 sq. yds. .034 20 3,325 sq. yds. .073 10 l,620sq. yds. .22 4 5 18 sq. yds. Why a fine From the above table it is very evident why a fine sand cannot be sand is as stron S m a mortar mixture as a coarse one, when mixed with the not good same percentage of cement. Consider a 1 :3 mortar made of \'\" grains. Such a mortar has 518 sq. yds. of surface per cu. yd., while one made of sand of the No. 1 size has 1 620 sq. yds. of surface to cover with cement grout in a cubic yard. In other words, the No. 1 sand will, according to our calculations, take nearly three times as much cement to produce a mortar of the same strength as the 1 :3 No. 4 mortar. In practice, however, we cannot figure as close as this, as no sands are composed of one size, but of a great many different ones. There is, however, a very close connection between the figures produced and the results obtained in practice. GOOD CONCRETE 25 TABLE II. TESTS SHOWING EFFECT OF SIZE OF GRAIN ON STRENGTH OF MORTAR. Mechanical Analyses: Per Cent Passing Given Sieve Compressive Strength Lb*. PerSq. In.of 1:3 Mortar at 2 Mot. No. 4 100 10 20 46 30 33.5 50 21.0 60 100 200 1 79 1.7 0.8 .0 3627 2 100 99.5 98.5 96.7 82 75.5 30.0 3.1 844 Sand No. 1 is a bank sand from near Yuma, Arizona, used on the Laguna Dam. Sand No. 2 is from the Colorado River near Laguna, Arizona. Mechanical Analysis: The separating of a sand into various sizes by means of different sieves is called "Mechanical Analysis." TABLE III. TABLE OF SIEVES AND THEIR MESHES: How the Sieve No. 4 16 0.22 10 20 30 40 50 100 200 the grains Opening, per tq. m. Size of opening 100 0.073 400 0.034 900 0.024 1600 0.017 2500 0.014 10000 0.0055 40000 IS ^ e ' erm ' ne ^ 0.0027 For this test a set of sieves, Nos. 4, 1 0, 20, 30, 40, 50, 1 00 and 200, is necessary. The sieve numbers give the number of holes per linear inch. The sieve should be about 8" in diameter. They can be had from any "Assayer Supply" house. To make test: Weigh out any even number of Ibs. of sand (sand must be dry). Place on No. 4 sieve, shake until no more passes, weigh what has passed and record weight in ounces. Take this portion that has passed the No. 4 and sieve it through a No. 1 0. 26 GOOD CONCRETE Weigh passed portion and record in ounces. Repeat this for each sieve, taking the portion that passed the previous sieve. Wt. passing that sieve (in ozs.) Then % passing any No. sieve - - X 1 00 Wt. taken for test (in ozs.) If the metric system of weights is used the computations will be eliminated; the weighing will give the per cent direct if 1000 grms. of the sample are used for the test. The strength In order to compare different mechanical analyses it is a great of a convenience to plot the results in a curve or diagram. Squared paper concrete is used, laying off on the horizontal lines the diameter corresponding to is controlled sieve openings, and on the vertical lines the % of the material passing by the any given sieve. The points thus established are joined by straight sizing of lines, and the figure thus produced is called the "Mechanical Analysis grains Curve," or M. A. Curve. These curves are very useful in the appli- cation of the "Concrete Lav>." The form of the M. A. Curve is an index to what may be expected from a given sand as to compres- sive strength. GOOD CONCRETE 27 ^ 2- 2^ *! COCNCNGOt^COTCO sO OO f"^ ON c^ r*^ in ^~ cNCN-f'^rininr^i^ cooOsOcO O vO O fN CO CN 8888 . r^ GO -O rx o O O ao m t> ON i< & r^ ^ CO ^" CO CO CO CO CO n CT^ O oq O CN ^~ ^^ CN CO CN CO CO O co O ON O OO ^f ^^ "^" ON l^x CO in NO co CO CN CN ON CN CO GO ^~ f*^ OO co od co \d co in od CN ^ CN CN CN OO c<^ CN CO O ^ t^ *" in co co co CN \O NO ^- CO CN NO co CN - r\ O vn O r^ CN J ^-^ZZ'^*''^ ___^ -^; "^ ^ t ^- ^^ ^ 1^ r s/' -TVfrr Caacae. Bnk Sjuul . I 'mp Str Jlo. prrsa!,, T - 755* . .... J . *fl B 7/r?r Medanical Analyses of /^/wcs Jw^ 5ho*>iny Relation of M.A- Curves <5- Compress ive Strength of /.-3 Morters GOOD CONCRETE 29 Plate E I ^_______-^" * r * " ^^^ ^^-^ / ^^ A T / ^^ * . / 2. ._L .^L t^L A Camp Sir /A< prr tj 'in - AO7Z "il 2 B, : 4a54i_ ^ ^z^ 11 **' & 1^-" > ""^ -~ 4^^ ^ ' ^^-"'^ r "~ ^^^^ ^ ^^ C Limestone Scn>cnin/j& t . ^^ D * * 1 1 C. Gimp Sh- Uu. fitr so in , G^OO -l/t ft ' * ' m f,ZZI i 5 , * ^^^ (P ^^ c ^^ ,5 I" ^^-^ v "^^ 6 Gran tip ^trrcitinos r ~ ^X" /' JJ , ^^ f- ^ * t " t O > ' i ; ^ =ss ^-^" \ -^sss;*^^" ^^^'^ ^^^j;^^ ^ -'" f Limestone. Sfrftninaa ^^^ F ' ^ ^^ E! Camp Str /A< Pfrxq m - 7J94- /. Z^ /r . . . \. T . .7,/, e r i. * I J r Mechanical Analyses of Various Rock Screenings Showing Relation of M.A.Curves to Compress! ve Strength oj /--3 Mortars 30 GOOD CONCRETE The data in Table IV. is arranged from an elaborate series of test on sands and screenings by the U. S. Geological Survey (Bui. 331). The mechanical analyses are plotted in Plates I and II by the method explained above. These M. A. curves, or diagrams, are worthy of close study. Starting with the M. A. Curve of sands 1 and 2 and going to sand No. 8, there are represented eight types of sizing. Fine sands have a characteristically sharp curve like Nos. 1 and 2, and as the coarseness of grain increases the curve becomes flatter. Thus sands 3 and 4 have flatter curves than sands 1 and 2 ; Nos. 5 and 6 are flatter than 3 and 4, and 7 and 8 are flatter than 5 and 6. The compressive strength of 1 :3 mortar from each of these sands at three months is shown en each diagram. Screenings It will be noticed that the compressive strength increases as the follow a curves flatten out. It will also be noticed on inspection of the 50- different mesh column of Table IV that generally the less the percent of grains rule of passing the No. 50 sieve the greater the compressive strength. This sizing fact holds only for sands, and not generally for screenings. It must be borne in mind that sands usually have round grains, and screenings more angular ones. The M. A. Curve is a diagram showing the size of grains and the percent of these sizes ; and each material will have a typical M. A. curve. In fact, these principles have been worked out so generally that from them is derived the "Concrete Law," which will be con- sidered at another place. Screenings Sand vs. Rock Screenings: Screenings from crushed rock are an make good artificial sand. The use of this material in place of sand is universal fine aggregate in some portions of the U. S. and quite general in Europe. There are quite a number of factors that make screenings superior to sand. Principally the sizing of the grains, and their angularity make it possible to obtain a greater density of mortar, although as a GOOD CONCRETE 31 general rule screenings contain more voids than sand. Limestone and trap rock screenings are far superior to screenings from any other rocks. The grains of these materials are more nearly cubical. Other rocks are likely to give flat grains that will not compact well. The prejudice against rock screenings by some constructors and engineers is based on sound reasons, namely that the screenings con- tain all the quarry "dirt" that occurs in the seams of the rock in place and also a great deal of the "muck" that is shoveled up with the rock in the quarry and passes through the crusher and the screens. Aside from these objections it can safely be said that clean screen- ings are a worthy competitor of sand. In screenings there is usually a higher percent of "fines" (material "Fines" in finer than 50 mesh) than is found in good sands. Applying the gen- screenings eral rule for sand, that fine material is objectionable, screenings would be discredited. Experience and elaborate tests have shown that this is not the case. The reason that the "fines" in the screenings are not detri- mental is probably a chemical one. It is a well-known fact that limestone and trap rock dust will bind together macadam, acting as a cement, and it is probable that in a mortar made of screenings we have the strength of the cement plus the strength of the binding action of the screenings. Plate II shows the M. A. curves of seven types of screenings. These results are contained in Table IV and are from the same series of tests by the U. S. Geological Survey as those mentioned above. The U. S. Reclamation Service has used rock screenings on a number of their projects with excellent results. To Determine the % of Voids: The voids in a sand or rock Voids may be defined as the amount of space between the grains. A short, and but not very accurate, method to determine this is to see what amount hon> to of water the sand will absorb. The chief objection to this method determine is that water will shove the sand grains apart, and thus give too high them a percent of voids. GOOD CONCRETE Solid The most accurate method is to find the difference in weight be- rock tween a cubic foot of solid rock of the same specific gravity as the sand or rock and its weight per cubic foot in the loose state. Since the specific gravity of a substance is its weight compared ta the weight of an equal volume of water, then the weight of, say, a cubic foot of rock solid, will be the weight of a cubic foot of water (62.3 Ibs.) multiplied by the specific gravity of the rock. The average specific gravity of sand is 2.65. Now to compute the voids in a cubic foot of sand proceed as follows: Make a box 12"x12"x12" and weigh it. Fill it with sand and weigh it. From this weight subtract the weight of the box and call it the net weight of the sand. Then 62.3 X2.65=165=wt. of cu. ft. of solid rock, (wt. of cu. ft. of the sand) Then 1- 165 X 1 00 % of voids. TABLE V. TABLE OF SPECIFIC GRAVITIES AND WEIGHT OF 1 Cu. FT. SOLID. Sand Gravel Limestone Trap Granite Spec. Gr. 2.65 2.66 2.60 2.90 2.70 Wt. per cu. ft. solid 165 Ibs. 165 Ibs. 162 Ibs. 180 Ibs. 168 Ibs. Table V will be found convenient in computing the % of voids of sands, gravel, crushed rock and crushed rock screenings. GOOD CONCRETE 33 TABLE VI. VOIDS FOR DIFFERENT WEIGHTS PER Cu. FT. Per Cent of Voids Wt. per cu. tt, loose (1) Sand Grave! Limestone Trap Granite (2) (3) (4) (5) (6) 75 Ibs. 55 55 54 59 55 801bs. 52 52 51 56 52 85 Ibs. 49 49 48 53 50 90 Ibs. 46 46 46 50 47 95 Ibs. 42 42 41 47 44 100 Ibs. 39 39 38 45 41 105 Ibs. 36 36 35 42 38 110 Ibs. 33 33 32 39 35 115 Ibs. 30 30 29 36 32 120 Ibs. 27 27 26 31 29 125 Ibs. 24 24 23 28 26 130 Ibs. 21 21 20 25 23 135 Ibs. 18 18 17 23 20 Table VI gives the voids corresponding to the weight per cu. ft. of sands, gravels, crushed limestone, trap, granite and their screen- ings. These figures are based on dry material; they do not hold for damp or wet conditions. If the material is damp and wet it should be spread out in the sun to air dry before taking the weight per cu. ft. Example: In the first column are given the weights per cu. ft. Suppose a sand was found to weigh 95 Ibs. cu. ft. In Col. 1 find 95, and opposite it, under column headed "Sand," will be found the % voids, which for this particular case will be 42%. The same procedure is followed for crushed rock and screenings. GOOD CONCRETE Density Density of a Mortar: By this term is meant the degree to which the voids in a sand are filled with cement paste. If, for example, a cubic foot of sand was found to weigh 1 1 5 IBs., then from Table VI we know that it contains 30% voids, or 0.3 of a cu. ft. of spaces that are to be filled with cement paste, to make it as dense as possi- ble. If a mortar has all of the voids filled it is said to have a density equal to 1 .0. If all the voids are not filled, then the density will be less than I. If the voids are more than filled the density will be greater than 1. Cement Cement Paste: Dry neat cement has no binding pou>er.... It must paste first be converted into a paste before it becomes capable of cementing and sand grains together. Now in converting a cu. ft. or one sack of rater-tighlness cement into a paste by the addition of the proper amount of water and thoroughly mixing, it will be found that a shrinkage of about 15% takes place. A cubic foot (1 sack) will therefore yield about .85 of a cubic foot of paste, and in the proportioning of mortar it is the amount of cement paste and not of dry cement that should be used to determine the densest mixture. This fact is of the utmost importance in making watertight or impermeable mortar. Consider, again, a sand weighing 1 1 5 Ibs. per cu. ft. with voids equal to 30%. Then 1 cu. ft of the sand contains 0.3 cu. ft. of voids. Now to make the densest mortar we will not need 0.3 cu. ft. of dry cement, but will need 15% more cement. That is, instead of 0.3 cu. ft, (0.3 0.3 x 0.15) = 0.345 cu. ft of dry cement will be needed. How Yield of Mortar: The cement user is of course interested in much knowing how much mortar a given quantity of sand and cement mortar will make. One cubic foot of cement and two cubic feet of sand will not give 1+2=3 cu. ft. of mortar, but considerably less. Under "Density of Mortar" it has been explained what relation the voids have to a mortar. The following table is computed on the basis that 1 sack of cement gives .85 cu. ft. of cement paste: GOOD CONCRETE 35 TABLE VII. AMOUNT OF PLASTIC MORTAR FROM 1 SACK OF CEMENT. Proportion Voids in Sand Cement Sacks Sand Cu. Ft. 25% 30% | 35% 40% 45% 50% Cubic Feet 1 1.60 1.55 1.50 1.45 1.40 1.35 IH 1.97 1.90 1.83 1.76 1.69 1.62 2 2.35 2.25 2.15 2.05 1.95 1.85 2H 2.72 2.60 2.48 2.36 2.24 2.12 3 3,10 2.95 280 2.65 2.50 2.35 3 1 A 3.47 3.40 3.12 2.90 2.77 2.55 36 GOOD CONCRETE Plate ILL Illustrating the Grading of Jf'zes in a Concrete a = Very poor -5izinq *- Ufter * C = exce//e/rf CHAPTER III. PROPORTIONING CONCRETE. Concrete has already been defined. The methods of proportion- ing will now be considered. The proportions are usually stated as so many parts cement to How is so many parts sand to so many parts rock or gravel. Thus a 1-2-4 concrete mixture means 1 part cement to 2 parts sand and 4 parts rock or proportioned gravel. To arbitrarily specify the proportions, as 1-2-4, 1-3-6, etc, for any particular work without regard to the voids in the sand and rock and gravel and to the grading of their sizes, is. to say the least, a very primitive method. Crushed rock and sand vary widely in their percent of voids and the grading of the sizes of their particles. In order to properly balance the cement, sand and rock, the factor of voids and sizes must be considered. Three methods of proportioning are now used: ( 1 ) Proportioning by taking into consideration the voids in the sand and rock. (2) Proportioning by trial, varying the parts of sand and gravel, until the densest mortar is obtained. (3) By the "Concrete Law" which takes into con- sideration the grading of sizes. 38 GOOD CONCRETE (0 Proportioning by Voids: The voids in the rock are determined either by observing the amount of measured water that a given vol- ume will absorb, or by taking the weight per cubic foot and using Table VI to find the voids. The voids thus determined plus 10% will be the volume of mortar necessary to fill all the voids in the rock and produce a dense concrete. The voids The amount of cement necessary for the mortar will of course must be depend upon the voids in the sand, and the purpose for which the fitted concrete is to be used. The proportion of cement should never be less than the voids in the sand. Other things being equal, the strength of a mortar will vary directly as the percent of cement in it For work requiring great strength it is customary to use mixture of 1 cement to 1 sand. This is par- ticularly the case in reinforced concrete columns. It must be borne in mind that the strength of the mortar is the factor that determines the strength of the concrete. Rule for Where no great accuracy is required a convenient rule for pro- finding portioning is as follows: best (a) Take a clean bucket and determine its volume by pouring mix in a measured amount of water. (b) Fill the bucket up level with rock; pour in a measured amount of water until the water comes to the surface. (c) The measured amount of water plus 10% will be the amount of sand necessary. (d) Take one bucket of rock and mix with it the amount of sand determined in (c) ; place back into the bucket this mixture. (e) Pour in a measured amount of water on the mixture until the water comes to the surface. The amount of water taken will be the volume of voids left in the mixture, and this volume plus 15% will be the amount of cement to use. GOOD CONCRETE 39 The proportion determined by this rule will be found to give an excellent concrete, providing the sand and rock conform with the requirements of good materials as set forth under "sand and rock." (2) Proportioning by Trial: This method has for its object the de- termination of the best mixture that can be made from a fixed pro- portion of cement to aggregate. For example, let a specified proportion of 1 cement to 6 aggregate be considered; that is, 1 :6. The proportion of 1 :6 can mean a number of different proportions Hoiv of sand to rock. much sand Thus it can mean :l:5 : 1/2:41/2 :2:4 :2'/ 2 :3'/2 or :3:3 The sum of the sand and rock adding up to 6 in each instance. Which one of these mixtures, then, will give the best concrete? It has been well established by many tests on large construction projects that: For any fixed proportion of cement to aggregate that combina- Best mix tions of sand and rock, which, with the fixed amount of cement, give for a given the smallest volume of plastic concrete, will give the densest mixture, proportion and incidentally the strongest, easiest compacting and quickest hard- ening. Take a piece of steel casing 6" in diameter and 1 0" long, plugged at one end. Lay off on a stick the clear inside depth. Divide this length into as many equal parts as there are units in the sum of cement and ag- gregate. Thus if the specified proportion is 1 :6, lay off (1+6) =7 equal divisions on the length. GOOD CONCRETE Then make up a trial unit, say, of 1 cem. 1J/2 sand, 4]/z rock, by measuring out the quantities in the cylinder, by means of the divided stick. Convert this mixture into a concrete by first thoroughly mixing dry and then adding enough water to give a consistency of soft "puf/p." Tamp this concrete into the cylinder and measure its volume by means of the stick. Note this volume. Then make up another mix, say, of 1 :2:4, and so on, converting each mixture into a concrete of the proper consistency and measuring the volume of each in the cylinder. That proportion of sand and rock which will give the smallest volume will be the proper proportion to use. This method is much used in large work, and is very well adapted to work requiring great density and easy casting qualities. This method was introduced into this country from France, and was first applied in this country by A. E. Schutte of Warren Bros. Coast. Co. The method technically is known as the "Volumetric Synthetic Method." (3) The The Concrete Law By this method, which is by far the most scientific scientific, the sizing of particles and the sizes of the voids are taken grading into consideration. It will on a moment's reflection be evident that the of sizes mere percent of voids will not be sufficient to determine the size of material that will fit into the rock voids. Plate III will illustrate the principle. The "Concrete Law" is not a theoretic "vision," but a law of the greatest practical importance and use. For example, in building the new water supply for New York City, Mr. W. B. Fuller devised and used this method day in and day out. By short laboratory tests on average samples of the sand and stones in lots as delivered on the work he determined the proportion and was enabled to construct watertight thin walls and effect a saving of many thousands of dollars. GOOD CONCRETE 41 The Concrete Law presupposes a knowledge of the sizes of the particles entering into the make-up of concrete. This knowledge is gained from the mechanical analysis of the sand and rock. No at- tempt will be made here to go into the mathematics by which the law was deduced, but the proven law and its factors will be stated. It has been found that by so proportioning the sand and rock that Curve of the mechanical analysis gives a curve of definite form the densest greatest mixture is obtained. This curve is called the curve of greatest den- density sity t or "Parabola of Maximum Density": Plate IV shows the shape of the curve of greatest density for each size of material. It will be seen on inspection that the curves vary according to the size of the "largest stones." It is the grading down from the largest size to the smallest in such a manner that the smallest particles fit into the voids between the larger ones. Table VIII gives the quantities by weight necessary for each size when the "largest stone" is 2^", 2", 1 '/$", 1", %" and Y 2 " ', re- spectively. It must be borne in mind that in the actual practical grad- ing the material will not always in fact, seldom proportion exactly so as to give the curves as regular as those in Plate IV, but they will approximate them quite closely. The concrete law may be stated as follows: To find the percent of any size of aggregate necessary The for a concrete of greatest strength and density: Divide the diameter concrete of the size sought by the diameter of the largest stone in the aggre- law gate. Extract the square root of the quotient, and multiply by 100. Expressed as a formula, the above will be, if D=diameter of largest stone in aggregate d = diameter of size sought P = % of the size sought P= 100 (Square root of ^ J 42 GOOD CONCRETE The Table VIII should now be closely studied. It will be seen that largest the size of the "Largest stone" plays a most important role. Upon it slor.e will depend all the percentages of the various sizes necessary to pro- duce the densest mass. The amount of sand is directly dependent upon the size of the "largest stone." Consider, for example, an aggregate whose "largest stone" is 2]/2 rr - Table VIII on the line marked 2^/2." will give the percent of various sizes and the figures under the column marked No. 4 will give the % of sand, which for the rock under consideration will be 29%. The amount For 2 " slone the % of sand U be 33.3% of sand For ' Vl" slone the % o f sand will be 38.4% depends on For ' " stone tne % of sand will be 47.0% the "largest For 24" stone tn % of sand will be 54.0% stone" For Vi" stone the % of sand will be 66.5% The percent of sand grows larger as the size of the "largest slone" decreases. GOOD CONCRETE 43 .1 3 1 5 I i o S g CM 44 GOOD CONCRETE Now as to the practical application of the "Concrete Law": The reader has, perhaps, looked with skepticism upon the above formula and figures as too "Theoretic" for a "practical man." The so-called "practical man" is usually devoid of the theoretic founda- tion of the principles he unwittingly applies in his daily work, and is very fond of hiding this lack of knowledge behind a veil of scoffing at all things theoretic. Even the most ignorant cement worker will not deny that the densest concrete is the strongest and that it is well to mix coarse and fine aggregate. In so doing he is unconsciously applying the principle of the concrete law. By making himself master of the principle involved in the law the sidewalk, pipe and block maker will be enabled to greatly im- prove the quality of his work. To APPLY THE CONCRETE LAW: 7s/: Determine the size of the "largest stone" by screening through a set of sieves. For example, if a weighed quantify will all pass a 2" sieve and remain partly on a /J/z", then the "largest stone" is said to be 2". 2nd: Make a complete mechanical analysis for the various sizes of the rock eves (down to ]/ 4 "), as explained on page 25. 3rd: Compare this analysis with that of the same size of the "largest stone" found in Table Vlll. 4th: Figure the actual percent of each size by subtracting the successive amounts of the percent passing each sieve for the mechan- ical analysis of the "curve of the greatest density." For example, if the "largest stone" is 2", then from Table VIII we get the percent of each size as follows: 100.0 86.6 = 1 3.4% by weight of 2" size 86.6 70.6 = 16.0% by weight of 1|/ 2 " size 70.6 61.2 =. 9.4% by weight of 1" size 61.2 47.0 = 14.2% by weight of %" size 47.0 33.3 = 13.7% by weight of !/ 2 " ze And 33.3% by weight will be sand. GOOD CONCRETE 45 Now repeat this operation for the mechanical analysis of the aggre- gate under consideration and compare the percent of each size with the corresponding amounts above and the difference between the two will indicate the amount to subtract or add to each size to produce the densest concrete. 5th: Amount of cement to use: The amount of cement ivill have to be such as to fill the voids in the sand with cement paste as explained on page 34. For example: If the "largest stone" is 2" then Table VIII gives Hv> much the percent of sand as 33.3 by weight Find what volume of sand this corresponds to and figure the amount of cement necessary to fill the voids with "cement paste," using Table VI to determine the voids. It must be borne in mind that all the percentages in the concrete law are by weight. The weights are readily converted to volumes by the weight per cubic foot of each of the sizes. This data is very readily obtained by the methods already enlarged upon. UNITS OF MEASUREMENTS IN PROPORTIONING. In proportioning concrete the materials are not usually weighed. The sack f but measured by volume. The sack of cement is taken as a unit of measurement. For all i i .. i i r r ii measurement practical purposes its volume is taken as I cu. ft. as it comes from the manufacturer. The cement should not as a rule be measured loose. If measured loose the "cubic foot" measure must be such as will contain 94 Ibs. of cement The sand and rock are measured in cubic feet If, for example, a specified proportion of 1 :2 :4 is to be mixed and a two-sack batch of concrete is wanted, then the cement will be 2 sacks, the sand 2x2=4 cu. ft. and 2x4=8 cu. ft. of rock. Or two cubic feet of cement in 12 cu. ft. of aggregate. CONSISTENCY OF THE CONCRETE AND MORTAR. Hotv The average worker in cement either uses too much water or goes mu< to the other extreme and uses too little. n>a/erP 46 GOOD CONCRETE A dry mixture such as is used for pipe and blocks, should contain just enough water to make it stick together when squeezed between the hands, or such an amount that vigorous tamping will be necessary to flush water to the surface. In using a dry mixture it is important that certain precautions be bserved. The mortar or concrete must be protected from drying out before it is placed in the forms and after. For this reason dry mixtures should never be worked in the direct sunlight or in even gentle draughts. The work should be performed under cover and great care exercised to keep the moulded work damp by a judicious and adequate application of water. Cement Wei Mixtures: By the term "wet" is not meant inundated. If scum too much water is used with cement it decomposes it, forming a milk- like scum called "Laitance" "Laitance" has no capacity to "set up," but dries out to a talc- like substance. "Laitance" always appears on the surface of a drowned concrete and prevents a proper bond between two consecutive layers of the concrete. For this reason if it is formed proper provision should be made for draining it off. A "wet" mixture is of such con- sistency that it cannot be tamped without quaking. It must be a stiff jelly sufficiently mobile to flow easily without a segregation of the aggregate. Rule for Amount of Water: No definite rules can be laid down for the computing the amount of water necessary for a mortar or concrete. amount TI j of voter * Cariy varying amounts of water as "moisture" that must be taken into consideration. If the sand is perfectly dry then a convenient rule to follow to determine the approximate amount of water to produce the desired consistency of the concrete will be as follows: Multiply the parts of sand by 8, add 24 to the product and divide the total by the sum of the parts of cement and sand. GOOD CONCRETE 47 Example: What amount of water will a 1 :2 mortar need? 2'x 8=16 +24 3)40 13.3% water by weight. That is 13.3% of the combined weight of the sand and cement will be the amount of water necessary. This will then reduce to gallons if the weight by sand and cement to a batch is known and remembering that 1 gallon weighs 8.4 Ibs. Example: What amount of water will be necessary for a 1 :3:6 concrete? 3 x 8=24 +24 4)48 12% by weight of the cement, sand and rock. The concrete worker should make trial mixtures to determine the proper amount of water to use for any size batch and set his water measure accordingly. It will be noticed during the day that, particularly in the summer, the amount of water necessary to produce the same consistency will vary from morning to noon and from noon to sundown. This fact must be considered in pouring reinforced concrete work. EFFECT OF THE CHEMICAL COMPOSITION OF THE MIXING WATER UPON THE STRENGTH OF THE CONCRETE. Little or no attention is usually paid to the nature of the water to be used in mixing the concrete. 48 _ GOOD CONCRETE Effect There have been some notable failures in concrete construction of the that were directly traceable to the chemical composition of the water mixing water utc d. , . All water contains dissolved salts. It is the chemical nature of these salts that will determine the fitness of any water for use in concrete. Sea water or even brackish water greatly retards the "setting up" of a concrete if used in mixing. Hard waters have a varying effect according to salts producing the hardness. If the hardness is due to sulphate of lime and sul- phate of magnesia, the water should not be used, as they can so retard the "setting up" as to allow the normal evaporation to rob the concrete of the water or moisture necessary for hardening before it can be combined chemically with the cement. Waters from mineral and hot springs should be avoided as they are usually highly charged with salts that may attack the con- crete and greatly impair its strength. Water from swamps is particularly deleterious in its action upon the concrete. Usually stream and city main waters are perfectly safe. The above is written to caution the cement worker doing work in places where good water is not to be had. MIXING. The properly proportioned cement and aggregate is not yet a concrete. Work is It becomes concrete upon being thoroughly worked up and mixed important with the necessary amount of water. ingredient To 3^0^^ this ca , u for a definite expenditure of work ehher ncretc muscular or mechanical. We may then define concrete as a mixture of cement, aggregate and water plus work- GOOD CONCRETE 49 Concrete is mixed either by hand or machinery. Machine mixing is by far the best method. A leaner mixture, machine mixed, is usually stronger than a richer one mixed by hand. In the past few years machine concrete mixers have become highly perfected so that today there are mixers to fit the needs of the smallest job. In the hand mixing of concrete the measured aggregate must be Handmixing manipulated on a water-tight and rigid platform placed perfectly level. The first consideration is the thorough mixing of the sand and cement in a dry state, converting it into a plastic mortar by the proper application of water, and then incorporating the rock. In the application of the water to the mixed aggregate and cement. Applying an excellent opportunity is had for completely ruining the concrete, the water If the water is violently thrown on, the cement is washed away from the sand. Another very easy way to accomplish the same result is to "squirt" the water on with a strong stream from a hose. Water should be sprinkled gently on the aggregate and cement mixture and worked into it by turning the mass. A lawn sprinkler nozzle on a hose will be found well adapted to the proper application of the water. If buckets are used the water should be gently poured into a crater formed in the mass and allowed to absorb. A good method of hand-mixing is to prepare a mortar box large A good way enough to accommodate the sand and cement for a particular batch to mix by of concrete. The sand and cement are thoroughly mixed dry, and hand then the water added and the whole worked up to a moderately stiff mortar. The measured rock is then spread out on the mixing platform in a layer about 6" thick, and on it is shoveled the mortar prepared in the mortar box, and worked into it by turning the mass 50 _ GOOD CONCRETE over. Before placing the mortar on the rock the rock should be thoroughly drenched with water. By this method an average of about 2 cu. yds. per ten hours per man can be mixed. The practice of mixing the cement and aggregate together dry and then applying the water does not give as good results as the above method, and it will be found that more turns are necessary to give a uniform concrete. In turning the material the laborer should acquire the "trick" of twisting the shovel as he dumps it. About three turns dry and three wet will usually be sufficient to give a good mixture. Above all things the cement grout must be kept in the mass and not allowed to lealf MACHINE MIXING. Machine concrete mixers are of two general types. ( 1 ) Continuous mixers, in which the cement, aggregate and water are charged into the machine continuously by automatic proportion- ing devices and the concrete discharged in a steady stream. (2) Batch mixers, in which the materials are proportioned out- side of the machine, charged into it, mixed and discharged as batches. Continuous mixers are made in all sizes from a portable machine that can be drawn by one man up to those requiring a span of horses. In this type of mixer great care must be exercised in operating to see that the proportioning mechanism does not fail to feed the material uniformly, otherwise a streaky concrete results. Batch mixers are of two types, the tilting and stationary. In the tilting batch mixer the mixing drum is tilted to discharge the con- GOOD CONCRETE 51 crete. In the stationary type a movable chute or spoon dips out the material. The reader is referred to the trade literature of the manufacturers for a further description of each type. In using either type of the batch mixer, the sand and cement should be charged into the drum dry, the machine allowed to make a few revolutions to mix the cement and sand, and then charge in the rock and water. This will give the best mixing possible, and at the same time it will not take any more time than charging in the cement aggregate and water together. In the stationary type of batch mixer it will be well to call alien- tion to a very imporlant point. The spoon that dips out the mate- concrete and rial very often will deliver rock devoid of grout, and then the grout ^ on> * on discharging. This difficulty is done away with if the discharged avm " l * concrete is allowed to fall into a hopper and drawn from it to be transporled lo ihe work. This segregation of the rock and mortar is more likely to take place when the mixture is too wet. DEPOSITING THE CONCRETE. The size of the batch of concrete should not be larger than can Size of conveniently be placed before initial set takes place. batch Concrete should be placed within thirty minutes after mixing. The forms must be properly aligned, wetted and braced before Placing the concrete is deposited. concrete The deposited concrete, in layers not exceeding 6", is then com- pacted by slicing the mass with a spade or slicing tool. Concrete of the proper consistency cannot be tamped with a tamper as it will quake. It is compacted by working a spade or slicing tool up and down in the mass and next to the forms. By this method the air is ex- pelled and the concrete compacted much better than by the old method of using "dry" concrete and vigorously tamping it. 52 GOOD CONCRETE A convenient slicing tool is made by riveting a flat piece of boiler plate |4" x 3" x 8" to a piece of Yz" pipe of convenient length. For transporting the concrete from the place of mixing to the place of disposition wheelbarrows or the familiar concrete carts are used. In wheeling a concrete in this manner it will sometimes happen that the sand and rock will settle and pack on the bottom of the vehicles. This is, by the uninitiated, often called "setting," and as a rule is promptly blamed upon the cement used. This occurrence is but an evidence that the mixture is oversanded and too wet. It is readily remedied by proportioning the mixture by the "cylinder method" (page 39). The densest mixture de- termined by this method will not pack or settle and will give a free casting concrete. In pouring or casting work that is to come up exactly to an established level, as for instance, a column, the shrinkage which takes place in setting up must be taken into consideration. The work should be allowed to stand for a few hours to let the settlement take place, before it is brought up to the prescribed level. This is of particular importance in reinforced concrete construc- tion where a girder is to be cast directly onto the column. Bonding one Jap's work *>*& another: The concrete should always be run in horizontal courses, and not in vertical ones, and allowed to slope off at the ends. Appearance alone would condemn this procedure. How to In stopping a day's work the first consideration should be to leave slop a the upper surface of the concrete in such shape as to facilitate the Jap's work bonding of the next day's work to it The laitance and scum that works to the top should be drained off and the surface roughened and covered with wet sacks or sand. Before starting the next day's work this surface should receive a thin coat of sand and cement mortar and scrubbed in with a stiff broom or brush. CHAPTER IV. THE PROPERTIES OF CONCRETE. The properly prepared cement and aggregate, when converted into a more or less plastic mass by the addition of water and an expendi- ture of work, will after a short time harden into a stone-like mass. This hardened mass (concrete) possesses characteristic properties which distinguish it from other materials ; just as a block of wood has properties which distinguish it from a block of iron or stone. A proper understanding of the properties of any material is essential to its intelligent use. Concrete does not attain its full strength as soon as it is made. Strength The process of hardening is one that takes years. For practical purposes the vital point of course is to know how soon it will be strong enough to take the strain for which it is intended. The rapidity with which the early hardening takes place will Hardening depend principally upon the temperature. Concrete hardens much depends on slower in cold than in warm weather. The temperature of the the weather aggregate, mixing water and the air will control the early stages of hardening or "setting up." In cold weather the aggregate is chilled, the water and air are cold and the concrete "sets up" very slowly, making it necessary to leave the forms on the work a much longer time than in warm weather. 54 GOOD CONCRETE So marked is the influence of temperature that it becomes uneco- nomical to attempt to lay or pour concrete when the temperature is lower than 40 F., unless the aggregate and water are heated. Con- Frozen crete should not be laid or poured in freezing weather. Frozen concrete green concrete will not set up because the cement cannot get the necessary water for hardening when it (the water) is solid. Frozen concrete will "set up" upon "thawing out" and attain a fair degree of strength, but will never withstand constant exposure to water The surface of the concrete will, however, blister or flake off under the action of the frost. This effect, however, is only superficial. Effect of Low temperature affects only the early strength of a mortar or cold on concrete. When once the hardening has begun, the progress is but strength slightly influenced by temperature. It is therefore important to of concrete have favorable conditions of temperature at the time of making. The prevailing temperature at the time of making will control the time in which the forms can safely be removed from the mass. TABLE IX. COMPRESSIVE STRENGTH OF AVERAGE CONCRETE MADE AT U. S. ARSENAL, WATERTOWN, NEW YORK. Prop. AGE 7 days 1 month 3 months 6 months 1:2:4 1:3:6 1565 1311 2399 2164 2896 2522 3826 3088 CHANGES IN VOLUME. Expansion Hardened concrete, like metal, expands and contracts with a rise and fall of temperature. Careful experiments have been made to determine the amount of this change of volume. It has been estab- lished that average concrete expands and contracts almost exactly as much by a change in temperature as does iron and steel. GOOD CONCRETE For every 1 F. rise in temperature, concrete will expand .000006 times its length. So that, for example, a wall 100 feet long will expand with a rise in temperature of 50 F: 100 x (.000006 x 50')=0.03'=0.36" It is this expansion by heat that is primarily responsible for the familiar cracking of concrete work. Aside from the change of volume due to temperature there are Shrinkage other changes that are not so well recognized. That neat cement, sand-cement, mortar, concrete as well as most structural stones (in- cluding brick) show a change of volume when stored in air or in water, is a fact that is now well established by many careful re- searches. Generally a mortar or concrete will show a shrinkage in air and an expansion in water. This change of volume is greatest during the early hardening, and grows less with age. The degree of the change is proportional to the amount of cement in the mass. Neat cement changes more than a 1 :3 mortar and a 1:2:4 concrete less than a 1:3 mortar. TABLE X. SHOWING NORMAL CHANGES IN VOLUME. INCHES PER 100 FT. OF LENGTH. Mixture Shrinkage in Air Expansion in Water 1 month Iyer 2 years 1 month 1 year 2 years Neat Cement 1.9" 2.4" 2.7" 0.98" 1.75" 1.82" 1:3 Mortar 0.492" 0.63" .78" 0.618" 0.276" 0.288" 1:2:4 Concrete 0.312" 0.300" 0.312" 0.104" 0.110" 0.107" Table X. is based upon the experiments of Considiere and Schumann. This shrinkage in air and expansion in water must not be confused with the changes in volume due to temperature. The figures in Table X. are based on a constant unchanging temperature. 56 GOOD CONCRETE In building a structure of concrete this change of volume must be taken into consideration and provided for. It is a common observation that plastered surfaces, sidewalks and walls will crack when only a few days old, and again old work will badly craze upon the surface. These are but manifestations ot shrinkage. In a continuous piece of work (monolithic) this shrinkage in hardening will induce strains that produce cracks. If the hardening takes place in a sheltered place with uniform temperature the cracks are less likely to occur. Draw A freshly placed mortar or concrete in strong sunlight and draughts cracks will show "Jrau? cracks" upon setting up. These draw cracks are due to shrinkage. They result from the top layers of material shrinking faster than the interior of the mass. If the mortar of concrete contains a great deal of very fine sand, this effect becomes particularly conspicuous. The excess of water necessary to bring a fine sand up to a desired consistency, upon being expelled in setting up, leaves the space it occupied void. These voids greatly facilitate the shrinkage and " cracks" result. To insure the permanency and appearance of concrete surface these factors must be taken into consideration. The effect of shrinkage is less for dense than for porous concretes and mortars. Rich mixtures shrink rnore than leaner ones. Crazing The "crazing" of finished surfaces is a result of shrinkage. Sur- faces should therefore never be finished with neat cement. Perhaps the most effective means of preventing "crazing" is to use a mortar containing not less than \Y 2 parts of sand to 1 part cement and to not over-trowel the surface. GOOD CONCRETE 57 It is a well-known fact that "pebble-dashed" or rough finished surfaces do not show "craze." If a concrete surface is over-troweled the neat cement is drawn to the surface. In proportioning concrete by the "volumetric synthetic" method (as explained on page 39), if each of the trial mixtures are moulded into cylinders and allowed to harden the shrinkage of each mixture can 1 very readily be measured. It will be found that the mixture giving the smallest volume (i. e. the densest) will show the smallest shrinkage upon hardening. In large and important structures shrinkage becomes an impor- tant factor and elaborate provision must be made to reduce its effect. IMPERMEABILITY OR WATER-TIGHTNESS. It is a common belief that concrete is by nature not watertight. Porous concrete is, however, but the result of the "hit or miss" proportioning of the aggregate. Watertightness is a relative term. A concrete may be watertight for low or moderate pressures and freely allow the passage of water for higher ones. Watertightness depends upon the density of the mass, the con- sistency, the care with which the concrete is placed and compacted and upon the absence of pockets and shrinkage cracks, and in a measure upon the amount of cement in the mass. Thin watertight walls have, however, been constructed by scientifically grading the aggregate according to the "concrete law." It is a very simple matter to compute the density of a concrete and Measure- mortar. Density is the sum of the volumes of solid material con- rnent of tained in the mass. Thus if we have a cubic foot of sand which density weighs 100 Ibs. we know from Table VI (page 33) that it contains 39% of voids or 1.000.39 or 0.61 cu. ft. of solid material. 58 GOOD CONCRETE How to N OVV the weight of any loose substance divided by the weight per cu. ft. of that substance in the solid state will give the volume of solid mat erial. Thus for the sand just considered, if the weight per cu. ft. loose is divided by the weight per cu. ft. solid, i. e. : 100 =0.61 will be the density or the volume of solid material in 1 1 65 cu ft. of loose material. To compute the density of a concrete proceed as follows: Wt. of cement , Wt. of sand , Wt. of rock , Wt. of water 193 165 f Wt. solid per cu. ft. f 62.3 and this value divided by the volume of concrete will be the "density." Consistency Consistency: The consistency of the concrete should be that of a stiff jelly that will "puddle" easily. Placing Placing: The concrete should be placed continuously and with- out interruption and thoroughly compacted by puddling to remove all the air. Large masses should not be dumped into place suddenly, but the material should fall in a moderate stream. Care of placing: It is obvious that if pockets are formed or shrinkage cracks allowed to develop the mass cannot be watertight. Generally a concrete increases in watertightness with age. Dur- ing the process of hardening the crystallization and other changes that occur tend to fill the voids. For high pressures at early age the concrete surfaces must be treated with some kind of impervious and elastic material, such as a diaphragm of bituminous material. Water- Waterproofing compounds are added to the concrete in mixing. proofing Their effect upon the strength will be considered elsewhere. They compounds are as a general rule not very efficient and their use is of doubtful value. GOOD CONCRETE 59 Watertightness can be most cheaply and expeditiously obtained by properly proportioning the aggregate. RESISTANCE OF HARDENED CONCRETE TO CHEMICAL IN- FLUENCES. Hardened concrete is more resistant to chemical action than any of the building stones. It will not weather, under the chemical action of the gases of the atmosphere, as will marble, granite or sandstone. Carbonic acid (carbon dioxide) which results from the combus- Concrete tion of organic substances, the decay of vegetable matter and the endures breathing of plants, animals and human beings, has only a beneficial effect upon the hardened concrete. Concrete is the only structural material which gains strength with age. The action of water and carbonic acid upon marble, granite and sandstone is perhaps too well known to need mention. If, however, a concrete is porous and freely allows the percola- tion cf water, some of the products formed during hardening will be leached out and the concrete will suffer accordingly. If, how- ever, the concrete is dense such an action will not take place. Pure distilled water will attack the surface of concrete, as it has a greater solvent action than ordinary water. This action has been noticed in cisterns for distilled or rain water. A thin scum is formed on the surface which consists of silica and iron compounds derived from the cement. It was found that if this scum was not removed, no further action took place. But when the scum was periodically removed the surface was affected by the water. Sewage and stable drainage are without effect upon hardened con- Sewage crete, which fact makes concrete peculiarly suitable for sewer pipe and drainage systems. Ail acids attack concrete, as do soured milk and fermenting Acids liquids. 60 GOOD CONCRETE Concrete intended for use where it will be subjected to the action of such substances should be coated with asphalt. All sulphate salts will after a longer or shorter time produce dis- integration of porous concrete, if left in contact with it. Magnesium salts are particularly active in attacking such con- crete. All other salts (chloride, carbonate, etc., etc.) are without effect upon the hardened concrete. Oils Light vegetable oils attack concrete. Mineral oils do not. Con- crete tanks for oil storage have proven themselves well adapted to the purpose in the California oil fields. Recently it has been discovered that in certain portions of the arid west, concrete in contact with certain soils has after a few years disintegrated. This action has been attributed to the magnesium and sodium sulphate present in the soil. In the cases observed it has been established that the porosity of the concrete has absorbed the salts, which have reacted on the interior of the mass, forming compounds which upon crystallization expanded in volume, thus tearing the concrete to pieces. The localities in which sufficient of these salts exist in the soil are very limited, being confined to the several small areas on the eastern slope of the Rocky mountains. Terra cotta pipes are also attacked under these conditions. Remedy The obvious remedy for the evil is to make the concrete so dense as to make it incapable of absorbing the salts. Behavior of Concrete Towards Metals: Iron and steel imbedded in concrete are permanently preserved. Recently some very old foundations for gun carriages were removed by the U. S. A. on the coast. Anchor bolts of iron which had been in place for forty years were found to be in a perfect state of preservation. In fact, the surface next to the concrete was found to be as bright as if it had been burnished. GOOD CONCRETE 61 The preservative action of cement on iron is now so well known Steel and that mixed with linseed oil it is used as a paint for iron. Concrete iron attacks and destroys lead and zinc. These metals should therefore receive a coating of asphalt when they come in contact with con- crete. This is particularly important in plumbing fixtures and in Lead and telegraph and telephone cables, covered with lead, which are very zinc often placed in contact with concrete. THE EFFECT OF SEA WATER UPON HARDENED CONCRETE. The effect of sea water upon hardened concrete is a matter which has provoked much discussion in the technical world, without, however, producing any unanimity. There have been, it is true, some notable failures of concrete structures in sea water, but these have been by so far in the minority as compared to the total number of structures built that their percentage is negligible. We can, with perfect justice, ask what were the causes contributing to these fail- ures. Were they due to an inherent general property of cement to disintegrate, or were they due to faulty cement or to faulty aggregate, or, finally, to the method of placing the concrete in this environment? There are two general methods of placing concrete in sea water. The one consists of depositing the material through a tube called a tromie, and the other consists of moulding the structural members on land, allowing them to harden in air and then placing them into their final position in the sea. It can be said generally that all of the failures that have taken place in concrete structures in sea water have been in those constructed by placing tha fresh concrete directly into the sea. The action of sea water on concrete is attributed to the presence of magnesium sulphate in the sea water, which forms with the lime and alumina of the cement a double salt of sulphuric acid, alumina and lime. This salt, called by Michaelis "sulpho aluminate of lime," on crystallizing undergoes a great increase in volume, and the ex- pansive action resulting from this change is sufficient to destroy the cohesion of any mass in which it might be formed. The action of 62 GOOD CONCRETE this particular salt, and the possibility of its formation, can be ques- tioned, but it can be said, in view of all the recent work done in Europe and by the Bureau of Standards of the United States, that the infiltration and crystallization of any salt on the interior of the concrete mass can produce, by purely mechanical means i. e., ex- pansion a disintegration of the mass. This effect is by no means confined to concrete alone. It holds generally for all natural stones and brick, terra cotta, etc., etc. in fact, in any mass which is at all porous, and which will allow a growth of crystals in its interstices, we may expect disintegration to take place from the expansive force exerted during crystallization. This phenomena is very well illus- trated by the expansive force of water freezing. For instance, we know that water in freezing will crack a boiler containing it. The ancients used this method of quarrying their rock. They would fill a crevasse full of water and allow it to freeze. REMEDIES PROPOSED TO IMPROVE PORTLAND CEMENT FOR USE IN SEA WATER. In view of all the authoritative tests that have been conducted in Europe and the United States during the last ten years, we may safely state that Portland Cement, by itself, needs not to be im- proved for use in sea water. The improvement must take place en- tirely in the making of the concrete. In short, it is not a question of better cement, but of better concrete. Perhaps the most comprehen- sive series of tests upon the action of sea water upon concrete are those instituted by the Scandinavian Association of Portland Cement Manufacturers, co-operating with the Harbor authorities. These tests are entitled to careful consideration, inasmuch as they were carried out on a large scale under very severe conditions. The test pieces consisted of large blocks two feet by four feet exposed to the rise and fall of the tide, frost and atmospheric influ- ences at a number of localities on the Baltic Sea and the coast of Jutland. The result of the ten years' tests have just recently become available. These tests were made with Portland Cement and with GOOD CONCRETE 63 Portland Cement with additions of trass, infusorial earth, santorian earth, puzzolane, slag and fine sand, mixed and ground with the cement. The conclusions so far as they are possible to be drawn from the ten years' exposure may be summarized as follows: Much depends upon the compactness of the mortar. A loose mortar, by allowing salts to penetrate to the interior of the mass, is rapidly disintegrated. A rich mortar must be used. A mortar con- sisting one part of cement to three parts sand is not rich enough, as the majority of the one to three mortars disintegrated, while the one to two mortars did not. Any good Portland Cement not exces- sively high in alumina appears to be suitable for sea construction. The main agency of destruction is not chemical, but is due to the alternate saturation, drying, freezing, etc. The destruction takes place sometimes by cracking, sometimes by scaling and sometimes by softening. The addition of finely ground silicious material is of doubtful value. The addition of an infusorial earth gave very in- ferior results. The destructive action of the sea being mainly physical and me- chanical and not chemical, tests by mere immersion in still sea water are of very little value in determining the behavior of a concrete in massive engineering work. A mixture which disintegrates under these tests is certainly useless, but a mixture which passes this test may disintegrate under the more stringent conditions of practical usage. As long a period as practical should be allowed for the hardening of the concrete in air before placing in the sea. From the many successful structures that are today resisting the action of sea water, coupled with exhaustive researches made into the effect of sea water upon concrete, there seems to be no room for a reasonable doubt that the success of concrete in sea water is de- pendent principally upon better concrete, rather than any modifica- tion of the chemical composition of the cement to be used. 64 GOOD CONCRETE SUMMARY OF TEST ON EFFECT OF ALKALI AND SEA WATER ON CONCRETE. The United States Bureau of Standards has within the last three and a half years investigated the effect of alkali and sea water on concrete. The whole matter has been summed up in Technologic Paper No. 1 2 of the Bureau of Standards, and below is given a com- plete verbatim summary of the result of these investigations: "The conclusions must be limited by the scope of this investiga- tion, and since the physical tests reported cover a period of exposure not exceeding 3J/2 years the conclusion should be considered as some- what tentative. 1. Portland cement mortar or concrete, if porous, can be disin- tegrated by the mechanical forces exerted by the crystallization of almost any salt in its pores, if a sufficient amount of it is permitted to accumulate and a rapid formation of crystals is brought about by drying; and as larger crystals are formed by slow crystallization, there would be obtained the same results on a larger scale, but in greater time if slow drying were had. Porous stone, brick ^nd other structural materials are disintegrated in the same manner. There- fore in alkali regions where a concentration of salts is possible a dense non-porous surface is essential. 2. While in the laboratory a hydraulic cement is readily decom- posed if intimately exposed to the chemical action of various sulphate and chloride solutions, field inspection indicates that in service these reactions are much retarded, if not entirely suspended, in most cases, due probably to the carbonization of the lime of the cement near the surface or the formation of an impervious skin or protective coating by saline deposits. 3. Properly made Portland cement concrete, when totally im- mersed, is apparently not subject to decomposition by the chemical action of sea water. 4. While these tests indicated that Portland cement concrete exposed between tides resisted chemical decomposition as satisfactorily THE EFFECT OF EXPANSION AND SHRINKAGE ON SANDSTONE. The spawling of the outer film is caused by the alternate wetting and drying of the surface producing expansion and shrinkage, which together with the expansion ana contraction due to changes in temperature has torn the surface layer of stone from the main body. These same causes grind and crush the mortar pointing of the hori- zontal and vertical joints. 5- .- p w "O O ' "2 *"* (W _C r- w J ,- -* 1 (U j: 1 s| ^|5':o|isp 3 oo0 os5*S ? S wm^rCai^JiSTJ l! 11 I5l^lr s lll . 4 D V v \i ' '*" ^^Sa? ^ *i ? >^ L L 1 i X W* o ,. PS E *. V ' t 02 > -o .S o o OO o^ GO moo CO Illllll III a? ^**,:i i2 ^^^^^^^12 & S> & S .| .5 -g -g -g -g -g I I I ;? f f >s -S .s .s .s .s .s GOOD CONCRETE 69 M m rf GO oo vO rs \O r^ GO \O t>. QO OO c> o o o c> o o *. % J6$ \O r>> rq \O O^ O rr CO CO r)- c^ TT "j- O O O O O O O 31 r>. oo (N ^r (N oo 1 *& \O n ^- ^ CO m Tj- Tj- Tf o o o" o o o o .S -n 31 CN CO vO t'* ^" GO CN oq in so -j- -- o 1 -s to* oo m r^ r>. a^ CN ^t- sO OO O 1^ GO ON O 0000000 | * J=-s g u U I GOOD CONCRETE 75 PREPARATION OF THE FOUNDATION: The foundation must be so prepared that it will not shrink away Foundation from the concrete base. All roots and organic matter should be removed and the foundation excavated to a depth corresponding to the total thickness of the slab. In ordinary firm soils this is readily accomplished. Sand is an excellent foundation if it is confined laterally so that it cannot move out from under the concrete base. The foundation, or sub-base, must be made firm by wetting and tamping and must be wet at the time the concrete is placed upon it. On a sand foundation too much water is objectionable, in as much as a sand super-saturated with water will shrink away from the concrete upon drying. The sand sub-base should, therefore, be just saturated with water, just enough to make it easy to compact by ramming. Fig. 3 shows the correct and incorrect method of laying a side walk on a sand fill. The most troublesome soil the contractor has to contend with is Adobe the adobe of Central and Southern California. Even the most casual soils observer knows that adobe "cracks up" in summer, and closes up in winter. Adobe absorbs water, which shoves its grains apart. Upon drying out a shrinkage takes place that opens up the familiar adobe cracks. As the material further dries out it slakes and falls to a more or less granular mass. This shrinkage is accompanied by a force Adobe sufficient in magnitude to tear apart a sidewalk resting upon it ; in fact cracks adobe has been known to crack and tear apart bodily a heavy masonry wall. This shrinkage extends to a depth of from 4" to 8". If the dry adobe is tamped into place and kept dry, then no shrinkage can take place. If the dry adobe is pulverized and mixed with sand in the Hom> to proportion of /:/, moistened and tamped into place, it will make a treat adobe very serviceable sub-base for a sidewalk. Fig. 2 shows the for a details of these methods. inundation In preparing a sub-base in adobe either of two methods can be used to insure the permanency of the work. ( 1 ) The adobe is broken up into material not much coarser than pea size, is slightly moistened and thoroughly tamped; upon this a layer of from 1" to 2" of damp 76 GOOD CONCRETE Foundation on Filled Ground Foundation on Ordinary Ground Surface c & d Foundations on Adobe Soil Fig. 2. GOOD CONCRETE 77 Foundations on Sand Fills (Shallow Fills) Wooden bulkhead confining a sand fill. Here the life of the sidewalk is limited by the life of the bulkhead. VI- b. The proper method of confining a sand fill. This is a permanent type of construction. Fig. 3. 78 GOOD CONCRETE sand or shale is tamped and is kept moist until the cement base is deposited. (2) By making a mortar, as above mentioned, of 1 part crushed or pulverized adobe to 1 part sand, and working it with just enough water to consolidate it. This mortar can very con- veniently be prepared in a concrete mixer (which is to be thoroughly cleaned after the operation). Upon the adobe-sand sub-base a thin layer of damp sand is spread before the concrete base is placed upon it. FOUNDATION ON FILLS. Foundation In building a sidewalk on a fill, great care must be exercised to see on that the fill has completely settled. A newly made fill will shrink fills about 15% in volume upon standing. On fills that have been made and left to settle through one rainy season, the sidewalk may safely be constructed without any further compacting, apart from the tamp- ing of the sub-base grade. If, however, the fill is made at about the time the sidewalk is to be constructed, then careful soaking with water Side and tamping will be necessary. The side slopes of the fill must slope conform with the natural slope at which the material will stand (angle of fills of repose of the material). The material must be deposited in layers not exceeding 6" in depth, thoroughly wetted and compacted. The top of the fill should be at least 2" wider than the finished sidewalk is to be. Drainage The slopes of the embankment or fill should be sodded or sown to on fills grass ; the mat thus produced will prevent the fill being washed by the rain. If the fill cr.osses the natural drainage, drains must be provided to allow the safe passage of the water through the fill and prevent the water damming up on one side of it. Side slope The sub-base or foundation should slope slightly toward the curb, of sidewalk to facilitate drainage. One-fourth (|4) inch per foot will be suffi- cient for this purpose. GOOD CONCRETE 79 FACTORS TO BE CONSIDERED IN THE CONSTRUCTION OF SIDEWALK. Fig. 1 shows the various parts of which a sidewalk is com- Factors posed, consisting of a sub-base or foundation, a slab of concrete to be called the base, and a top coat or wearing surface. The require- considered ments for the sub-base have already been considered. The base in the and top, which are composed of concrete and mortar, will have to construction be constructed in accordance with definite rules based on the physi- of sidewalk cal properties of concrete and mortar. On pages 55 and 56 the question of a change in volume of the concrete and mortar was considered at length. The reader is referred to it and advised to carefully study the matter. The change in volume resulting from a change in temperature and Changes that resulting from the natural shrinkage are factors of vital im- in volume portance in the construction of sidewalks. These changes in volume irwi^e are responsible for the well-known "cracks" that appear in side- cracks walks, walls, curbs and other concrete structures. These cracks con- stitute the chief annoyance of the sidewalk builder. The occurrence of cracks due to the change of volume is not to be considered as a fault of the Portland Cement, any more than the expansion and contraction of steel, or the shrinkage of clay, are to be considered as faults of these materials. When iron first came into use it was not very long before the iron Cracks worker realized that allowance had to be made in a structure for can be expansion and contraction resulting from changes in temperature, prevented The first clay workers soon discovered that a piece of pottery had to be molded considerably larger than the finished work, to allow for the shrinkage in burning. The science in using any material consists in making due and intelligent allowance for its physical prop- erties. Cracks can and should be prevented by making allowance for expansion and shrinkage. 80 GOOD CONCRETE METHODS OF PROVIDING FOR EXPANSION AND SHRINKAGE: Object of A sidewalk is divided up into the familiar squares by grooved marking Jj nes> no t on ly to improve its appearance but to mask the expansion and shrinkage cracks that will inevitably appear. These grooved lines make planes of weakness. A sidewalk laid without such mark- ings will in the course of a very few days exhibit irregular cracks running lengthwise and across the walk, dividing it into more or less square blocks. That is to say, nature is providing a relief for the expansion and shrinkage of the material that should properly have been provided by the builder. Nature, however, in making these cracks does not use a straight edge, but lets them follow any planes of least resistance, the result being a rather unbeautiful effect. The result of so laying a sidewalk is shown in Plate V. Marking Is Not Sufficient Provision for expansion and shrinkage. Many sidewalk specifications make no provision for expansion, rely- ing entirely upon the uncertainty of the cracks following the marked Cracks grooves with which the surface is blocked off. That the cracks do do not no t always follow the marking is evident in almost any sidewalk. always Jh ey will at times form across the walk, at others they will follow the follow marking a part of the way and then leave it. Plate VI shows such the marking an i ns t an ce. The crack followed the marking until it came to a point where a piece of rock was directly under the mark. It was here deflected to one side, producing the defect as shown. Even when the cracks form in the markings it is evident that the expansion will cause the blocks to "rise," as shown in Plate VIII. The continual working at the point C and D will eventually crumble the edges of the break. The remedy consists in cutting the whole length into separate blocks separated by a space sufficiently wide to allow each block to freely expand without coming in contact with its neighbor. This is most conveniently accomplished by means of a wooden Beaver Board or steel parting strip placed across the forms at definite intervals. PLATE V. A Sidewalk Laid Without Any Markings, Showing How the Expansion and Shrinkage Has Provided its Own Marking. &^^^ Cause: Lack of provision for expansion and shrinkage. Cracks follow natural planes of weakness. < pension joints .. Remedy: Divide surface into blocks and place expansion joints at alternate block divisions. PLATE VI. View Showing that Cracks Will Not Always follow the Marking. iBiir Showing Cause of Crack Leaving Marking. The Stone Directly Under the Mark Deflecting the Crack. A C Showing the Remedy: The joint C-D is cut through the base. Joint made by placing a !/g" steel parting strip across the form at time of laying. PLATE VII. VIEW SHOWING THE METHOD OF USING PARTING STRIPS HOOKED OVER SIDE FORMS. PLATE VIII. View Showing Expansion Cracks formed at Marks. Exaggerated Section Showing Contorted Surface when Cracks are Formed at Markings. GOOD CONCRETE 3! Various Types of Parting Strips Side form notched I ' Strip in place \ Slot in side form ' Steel Side form Steel Smith Patent Rail Clamp X* Steely / ~T~ Zeiser Patent Wedge X 2 GOOD CONCRETE Method Parting strips if made of steel and of types a, b, c or d, Fig. 4. of using act as ties, bracing the side forms. The parting strips must be so parting spaced that they will come at the exact point where a cross mark strips i s to be made. They are placed at every alternate block division, or they can be placed at every third block division. Thus if the side- Fading walk is to be divided into 2' blocks by the marking then the parting strips must strips will be placed A' apart in the first instance, and 6' apart in coincide the second. These parting strips are left in until the concrete base with block and top have been placed and are removed just before the top is to marking be floated with a steel finishing float. Joints must I n finishing over the joint left by the removal of the parting strips, be kept a pointing trowel should be run down into the joint to cut any of the open to p mortar that might be forced into it by ths float; it is then "edged" by means of the "jointing" or marking tool. Other In some localities an expansion joint 1 " wide is placed at every methods of 50 feet of the walk. This method is preferable to "no joints" at all, providing but dees not provide for the shrinkage. A joint 1 " wide every 50' for expansion is rather unsightly. Appearance alone would favor distributing the joints as is done by the use of parting strips. Beaver Board, if used, may be placed every 1 0' and left in the work. It is elastic enough to give the proper relief. The 1" joint is usually filled with asphalt or pitch. The joint left by the parting strips need not be filled with any mastic material. If the contractor, however, deems it necessary to fill them they should be filled only about two-thirds of their depth. This will prevent the asphalt or pitch oozing out. PREPARATION OF THE CONCRETE AND MORTAR. The base is composed of concrete, on top of which is placed the wearing coat of mortar. The base varies in thickness from 3" to 6" and the wearing coat from J4" to %" , depending upon the kind of work. Concrete The first consideration should be density (see page 58). This for the base calls for a balanced mixture of coarse and fine aggregate. The GOOD CONCRETE 83 84 GOOD CONCRETE coarse aggregate is either gravel or crushed rock which refuses a "4" screen and all of which passes a 1 Yi " screen. Stones larger than 1 Yi" for a base less than 4" thick will be found troublesome. It will not tamp or spade readily. The fine aggregate must all pass a YA" screen. Coarse The coarse aggregate must be composed of crushed, durable rock aggregate or a natural screened gravel. Either material must be free from sur- face coatings of clay, loam or other foreign substances (see pages 17-21). Fine It has already been pointed out that the strength of a concrete de- aggregate pends upon the strength of the binding mortar (See page 1 7). The strength of the mortar will of course depend upon the sizing of the sand particles and the amount of cement, (See pages 21-26). The best sands are those in which the particles grade down from coarse to fine, giving a regular Mechanical Analysis curve. Plate 1 shows various types of sands. For the purpose of side- walk construction a sand should have the following sizing: 100% should pass a J4" sieve. Not less than 30% or more than 70% shall pass a No. 20 sieve. Not more than 30% shall pass a No. 50 sieve. Not more than 5% shall pass a No. 100 sieve. Generally the larger the percentage of very fine sand (finer than 50 mesh) the more cement will be necessary to give the requisite strength. The sand must be free from organic matter such as roots, grass, or soil humus. It must not contain more than 5% of clay and the clay must not be present as a coating on the sand grain. Rock Screenings from crushed trap rock or limestone that will all pass screenings a Y*" screen can be used to good advantage in place of sand or as an addition to it (see page 30). The requirements for sizing of particles for screenings are confined only to all of the material pass- ing a YA" screen and freedom from dirt. The large percentage of fine material, as long as it is all rock dust, is no objection, as has already been explained on page 3 1 . GOOD CONCRETE 85 In proportioning the cement, sand and coarse aggregate, the quan- Proportioning tities must be measured by volume, and not guessed at. The pro- the concrete portion of cement to total aggregate should not be greater than I part cement to 8 parts aggregate. It has already been dwelt upon that the arbitrary proportioning Proportion of sand and crushed stone is a very unscientific procedure, since all of fine to crushed rock, gravel and sand does not contain the same percentage coarse of voids. The amount of cement has been already specified and aggregate represents the quantity that has by experience been found to be best suited for this particular purpose. It remains to find the best propor- tion of sand to coarse aggregate. This can be accomplished by either of three methods: ( 1 ) By determining the voids in the coarse aggregate. (2) By the Synthetic volumetric method. (3) By the Concrete law. These methods are described in detail under the heading "Propor- tioning Concrete" (pages 37-42). By whatever method propor- tioned, the object sought is the proportion which will give the densest mixture. Perhaps the most convenient method of determining the proportion of coarse to fine aggregate for sidewalk work will be the method depending on the determination of the voids in the rock, and adding a volume of sand equal to the voids in the rock plus 10% (see page 38). In many communities the sidewalk contractor is accustomed to use Natural a natural mixture of gravel and sand just as it comes from the stream gravel and bed or gravel pit, mixing it with a given quantity of cement Toithoui crusher regard to the proportion of coarse to fine aggregate (see page 19). run The sand and gravel are seldom if ever found mixed in anywhere Natural near the proper proportions. By using such a material without first gravel determining the proportion of fine to coarse and correcting it by the must be addition of that aggregate which it lacks the contractor is taking a screened chance on the ultimate outcome of the work. 86 GOOD CONCRETE How to T^ test to determine whether or not the coarse and fine aggregate determine. m a natural gravel is balanced is so extremely simple that no excuse the balance exists for not making it. The determination of the voids will immedi- f a ately show whether the material is balanced or not. A sieve test natural ^^ t ^ e jvj o 4 s j eve ^JJ gj ve the amount of each material which the mixture mixture lacks A good There must be at least ] /2 <* s much of the natural material pass a rule to y^n screen as n,,7/ remain on it. If less than Yi of the material (by follow vo lu me ) passes the No. 4 sieve then MORE SAND will have to be added to bring it up to Yz- If more than Yi passes the Yt," sieve then more rock will have to be added. Unscreened jf crus hed from clean durable rock, can be used just as is natural crushed rock or grave l jf tne same precautions are observed to see that the coarse and crusher run fine port i ons are properly balanced. The consistency of the concrete for the base is not to be quite as 'tiecolicrefe plastic as that U8ed f r Other claSSCS f WOfk - II sh uld be iust SO for the base wet l ^ at ' l cannot be tamped much before it will "quake." Mixing This is either done by hand or by a machine mixer. Machine the concrete mixing is preferable. For either method the reader is referred to pages 48-50, bearing in mind that the proper and thorough mixing is a most important operation, and one upon which the success of the work will largely depend. PROPORTIONING THE MORTAR FOR THE WEARING COAT. Proportions The proportion of cement to sand will depend largely upon the fineness of the sand. A fine sand will need more cement than will a well-graded coarse sand. On page 56 attention has already been called to the objection of using too rich a mortar. Such a mortar will shrink more than a leaner one, and will develop "craze cracks." With a well-graded, coarse sand, a proportion of 1 part cement to 2 1/2 parts sand is a serviceable mixture and one that will not develop an undue amount of crazing if it is not over-troweled. With a finer and poorer graded sand a proportion of 1 part cement to 1 Yz parts sand will have to be used. GOOD CONCRETE 87 The sand must first of all be screened through a 1/4" screen to Sand remove any oversized material. The sand must be free from nodules of clay or soft material, and the percentage of grains finer than 50 mesh should be as small as possible. Nodules of clay will "dissolve," leaving pit marks in the finished surface. Soft, friable particles are likely to puff and blister the finished surface. Sand, where sizing conforms to that given under sand for the base, with the exceptions above noted, will answer. Upon the method of mixing will depend the ease with which the Mixing top will work under the trowel. The sand and cement are first thoroughly mixed dry to a uniform color, in a watertight mortar box. The mixed materials are then spread out over the bottom of the box and "craters" formed, into which about half of the necessary water is added and allowed to "soak up" for from 1 5 to 20 minutes. The mass is then worked thoroughly, adding the additional water necessary to produce the desired consistency, in a fine spray. The water should be less than what looks to be enough for a given consistency. Upon further work- ing the mass with the hoe, it will be found to become "wetter" and "smoother." This is due to the cement becoming plastic. If all the water is added at once the mortar will work "short," in as much as the cement has not had time to soak up the necessary water to soften it. The cement particles must be converted into the gelatinous condi- tion by contact with the water before it can be expected to work smooth. When a top finish works "sandy" it is usually due to the cement particles not having become gelatinous. The same effect is produced by a large percentage of "quick sand" in the mortar which floats and works to the top under the action of the trowel. The average sidewalk maker makes his top extremely n?e/, so wet Consistency that the cement and sand will segregate if left standing a few minutes. O f the A mortar as wet as this is of course very easy to float on to the base, mortar It is contrary to good and proper practice to make the mortar as "sloppy" as this. It greatly diminishes the resistance to wear of the hardened top and has other disadvantages that will be considered later. 88 GOOD CONCRETE SIDEWALKS. TABLE XV. -QUANTITIES FOR BASE Proportion by Vol. Thickness of Base No. Sq. ft. of Base from 1 cu. yd. Concrete No. sq. ft. of Base per Sack :2:4 6 " 54.0 8.5 :2:4 ' 5 " 65.6 10.4 :2:4 4 " 81.0 12.8 :2:4 3 " 108.0 17.0 :2:4 2K 123.0 19.3 :2^:5 6 54.0 10.9 :2 1 A:5 5 " 65.6 12.5 :2#:5 4 81.0 15.4 :2^:5 3 108.0 20.5 :2#:5 2*" 123.0 23.5 :3:6 6 " 54.0 12.7 :3:6 5 65.6 15.5 :3:6 4 " 81.0 19.0 :3:6 3 108.0 25.4 :3:6 2^" 123.0 27.6 SIDEWALKS-QUANTITIES FOR TOP Square Feet per Sack Proportion Thickness of Top Grill. Sd. X* h* 1.0 1 w 2.0" 1 1 33.12 22.08 16.56 11.04 7.28 1 I* 41.76 27.84 20.88 13.93 10.44 1 2 50.64 33.76 25.32 16.88 12.66 1 2X 58.48 38.98 29.24 19.50 14.62 1 3 67.92 45.28 33.96 22.64 16.98 GOOD CONCRETE 89 The proper consistency of the mortar should be such that it can just be "rodded" without "pulling" and just so wet that it will not "stand up," but will flatten out in a few seconds, so wet that it cannot be shoveled, but will have to be dipped out in a bucket. It must not be wet enough to allow the cement and sand to separate. Cement is considerably heavier than sand and has a natural tend- ency to separate from it in the presence of too much water. If each cement particle is gelatinous it will stick to the sand with great tena- city, thus forming a viscous mass. It is the production of this viscous mass that is the object sought in a mortar for finishing. PLACING THE CONCRETE AND MORTAR. ORDINARY TYPE OF RESIDENCE SECTION SIDEWALK. On the sub-base or foundation which has been excavated to grade Forms and tamped the side forms are placed. The top of the forms should conform to the finished grade as given by the Engineer. The form on the side nearest the curb is placed a little lower, so as to give the walk drainage toward the curb. The forms are usually made of surfaced 2" stuff with the depth corresponding to the total depth of the con- crete base and top. The surface of the lumber must be cleaned of any adhering mortar and wetted before the concrete is deposited. On the top of the side forms marks are made where each block division will come. The parting strips are then placed and the forms lined up true to the established lines and staked. The sub-base is then wetted and the concrete filled into the forms Depositing and tamped, using the "templet" shown in Fig. 1 . The notch is the concrete equal to the thickness of the top. The tamping, should be most thor- ough, so that the concrete surface will present a uniform appearance. The proper consistency of the concrete will produce a mass that will quake very readily under moderate tamping, and one that will spade readily. Next to the form a shovel or trowel should be run down to "turn" any "arched" stones. The concrete should be deposited on both sides of the parting strips and so tamped as to not "bulge" the strips. 90 GOOD CONCRETE j 55 ' -o J V 3 3 CQ -2 g Q s CQ * - :} J ! J U jg m s Q 5 u . -- 'o 1 J i X J = 1 * 3 i . ^ do ^ u 5 J GOOD CONCRETE 91 The batches of concrete should not be mixed larger than can con- Size of veniently be deposited within 30 minutes. After the base has been batch of placed, tamped and brought to the proper level, the top is immedi- concrete ately placed by first spreading it on the base in a thin layer and trowelling it thoroughly to make a bond on the concrete and then pouring and spreading to the top of forms and levelling off with the floating rod (Fig. 1). The floating rod should be given a "back and forth" motion in levelling off the top, and not moved straight ahead. The top must be placed not more than 30 minutes after the con- Placing crete base is in place. If the base dries out before the top is placed the top and worked into it, a poor bond is produced, which will result in a "loose top." If base does % dry out before top is placed it may be sprayed gently with water. After levelling the top by means of the "floating rod" it is left Finishing untouched until the water begins to leave the surface, i. e., at the the top point at which the surface of the mortar loses its gloss, and just begins to stiffen up slightly. It is then gone over with the wooden float and rubbed up. The parting strips are now removed and the surface blocked off into the sized blocks desired by the length and crosswise markings, using a "jointer," and the edges next to the forms are rounded off with the "edging tool." At the joint left by each part- ing strip a pointing trowel is run down to insure the complete separa- tion of the blocks between the parting strips. If a rough finish is desired the surface is roughened inside the block Rough markings, leaving the border made by the "jointer." The "rough- finish in?" is accomplished by brooming or with a wooden float to which a rotary motion is given. This procedure produces a serviceable roughened surface that is rather pleasing to the eye. If an ordinary smooth finish is desired the surface is lightly trow- Smooth eled with the steel float after marking and edging. If a high polish finish is desired the top is allowed to stiffen up well before it is "rubbed up" with the wooden float, marked and edged. The polish is them 92 GOOD CONCRETE obtained by troweling with a steel float. To get a polish the initial set of the mortar is broken down. A polished surface will always craze after a longer or shorter time. It is the least serviceable finish that can be given a sidewalk. Dusting The practice of "dusting" neat cement upon the surface to make it finish easily is one often indulged in by the finisher. Such a pro- cedure, although producing a smooth finish, will cause the surface to craze badly. Effect of All Portland Cement contains a small amount of gypsum, which working * 8 added to control the setting time. The gypsum is relatively soft the top an d light. In grinding the clinker the gypsum naturally is more too wet easily reduced to flour, and will be much finer than the finished cement. Now, then, if the top mortar is worked too wet this gypsum flour will "slime" to the surface under the action of the floating rod. In levelling off with the floating rod a very thin and "slimy" liquid will be shoved ahead of the rod. This liquid contains most of the gypsum and the surface rodded will be deficient in relarder and at the points where the rod is lifted and the thin grout distributed by troweling the surface will have an excess of gypsum, so that the surface first mentioned will set up very rapidly, whereas the other surface will set up exceedingly slowly. This peculiarity is usually attributed to the cement. The occurrence, however, is positive evidence that the worker has worked the top too sloppy. Again, the thin grout resulting from too much water forms "lai- tance" (see page 15), which covers the surface as a thin film. This film does not "set up," but dries out to a soapstone-like sub- stance which wears off under traffic and leaves the surface "sandy" and mottled. Colored If the surface is to be colored the coloring matter is added to the mortar mortar and should never be sprinkled or dusted on the surface just before finishing. The quantities and kinds of color necessary to produce a given color will be found on page 90, table XVI. GOOD CONCRETE 22 The method of laying a sidewalk extending from the building line Laying full to the curb differs only in some details from that used for the ordi- width nary sidewalk. The chief difference being in the laying of guide Sidewalks in strips at right angles to the direction of the walk to facilitate getting business an even surface. These guide strips are placed from 4' to 6' apart sections and are given the grade that the finished surface is to have. They are usually made of 1" or 2" stuff, having a depth equal to the thickness of the base and top. These strips also act as parting strips. They are left in until after the top is floated, then removed and filled with mortar. The strips should be so placed as to come out at block markings. As soon as the mortar has stiffened in the grooves left by the guide strips a cut through to the sub-base is made by means of a trowel guided by a straight edge. A joint at least y%" wide should be left between the curb and the sidewalk. The sidewalk contractor will often be called upon to lay floors Laying on a base of concrete that has been in place some time; There are floors on a certain precautions to be observed in such cases to insure the perma- hardened nence of the work. Such floors will usually consist of an application concrete of mortar to the hardened concrete base. The "finish" should never base be less than 1 J/fc" in thickness. The concrete base is, first of all, thoroughly "roughened" by picking the surface with a gad or other proper tool. It is then brushed clean and thoroughly rinsed with running water. The old concrete must be thoroughly saturated with water before the top is placed. Guide strips are then placed as above, and a thin grout of neat cement is scrubbed into the surface of the old concrete, upon which the top is immediately placed and vigorously troweled into the base. The top is then rodded off just as in sidewalk work, marked and finished after the guide strips are removed and the joints left by them filled with mortar. The marking should be so arranged and laid out that marks will Marking come over the center of all beams and girders. At these points the marks should be cut through to the base (expansion joint), and the 94 GOOD CONCRETE marks cut through to the base in such a manner as to divide the whole floor into separate blocks not greater than 6' on a side. GENERAL REMARKS. In localities that are very dusty and windy in summer the side- walk worker cannot be too careful to prevent dust settling on the concrete base before the top is placed. A film of dust will prevent a proper bond between the top and the base. He should therefore wet down the pile of excavated material lying alongside of the work. The workmen should also be prevented from carrying dust and dirt on to the base in carrying the top mortar for pouring. Se oj The blocks into which the surface is divided by the marking blocks should not be larger than 3' on a side. The smaller the blocks the less danger from cracking. Finishing J n finishing the surface should not be troweled too much, as in so doing all the neat cement is brought to the top by the "suction" of the float. A rough surface is more serviceable than a highly polished one. A rough surface, if properly fringed by the mark made with the "jointer" is as artistic as a highly polished one. Roughing can be accomplished by means of the "float suction," grooving with a toothed roller, or brushed with a stiff broom. In extremely fine work, such as porch floors, a serviceable finish can be made by rubbing the surface with a carborundum brick after the top has hardened for six or seven days. Air In troweling a surface the finisher will often notice the formation bubbles O f "blisters." These are caused by entrained air. They should be punctured and pressed out before set takes place. If not removed they will eventually cause a loose top by the air expanding. Protecting The surface must be protected against premature drying out. the green If the work is done in a strong draft draw cracks will form before surface the top sets up. These draw cracks open up parallel to one another and usually at right angles to the direction of the draft. A low GOOD CONCRETE 95 screen placed to the windward will effectually prevent the forma- tion of these cracks. As soon as the top has taken on hard set, it should be covered Covering with sand or dirt, which is then wetted at least once a day for several the work days to thoroughly "cure" the top. If water is applied direct to the surface it should only be done in the morning. If cold water is squirted on to the top while it is hot or warm, cracks can result from the sudden cooling. Cement is a poor conductor of heat; it warms up slowly and cools Precaution slowly. A cement mass exposed to the sun during the day will in the retain a great deal of heat for many hours after sundown. It prac- use of tically takes it all night lo cool off. Water therefore should only water on be applied to a "green" sidewalk early in the morning. After the green work has aged for some weeks it can safely withstand the shock cement of cold water applied during the heat of the day. If ordinary earth is used to cover the green work it should be free from soil humus. The acid in the humus will permanently discolor the surface. Adobe also has a tendency to discolor the surface where so used. Causes of Defects in Sidewalks Proper Method of Stopping a Days Work Header must be placed even with a block mark Improper method of stopping Fig. 6. PLATE IX. CRACK FOLLOWING THE LENGTHWISE MARKING. CRACK CAUSED BY ADOBE FOUNDATION SWELLING. Remedy: Prepare Foundation as shown in Fig. 2. PLATE X. LOOSE TOP. CAUSED BY POOR BOND BETWEEN BASE AND TOP PLATE XL Effect of Expansion on End of Sidewalk Caused by the Whole Length Creeping, Due to Absence of Expansion Joints. 73 Here the length of A-B was sufficiently strong to not crack on being thrust up as shown. The curb C being buried prevented any horizontal movement in the direction of the arrow, making the walk lift itself. A 73 m P ':Q:-'O- , ' 0.'. (>.'- - O ' >> :.D " ' 'p': '. '!'.'' -&\ o 0'? 't>"-'0. : 'o *? ! Remedy: Cut through the base by parting strips at points A-B and at each alternate block division. PLATE XII. Example of the Effect of Expansion. Corner Block Shoved Bodily Out of Place. Cause: The expansion from two directions A and B have combined to shove the corner in the direction C. Remedy: Provide ] /$" expansion joints every alternate block division along A and B. Make the corner entirely separate, pro- viding '/4 " joints cut through the base at D-E. PLATE XIII. The Effect of Expansion on Corner Blocks of Combined Sidewalk and Curb. vr. Cause: Lack of provision for expansion. Remedy: Make corner entirely separate from the rest of the walk. Keep curb and walk separate. H ^ .-S o - c l l!P ^ 5 s fe' I! Curbs and Gutters CHAPTER VI. CURBS AND GUTTERS. The same general principles governing the use of cement for side- walks apply to the construction of curbs and gutters. From the nature of the construction, more provision for expansion Expansion and shrinkage is necessary in a curb than in a sidewalk. A curb and has about J/2 of its mass buried. As the street side of the curb acts shrinkage as a gutter, the gutter will usually be more or less moist. In this moist environment concrete will expand instead of shrink (see page 55). That is, one half of the curb will be shrinking while the re- mainder will be expanding. This condition produces stresses in the concrete, which inevitably causes more or less vertical cracks at intervals of from 8 to 12 feet. For work done in cool weather the combined thermal expansion, shrinkage and normal expansion, can with the advent of warm weather produce most destructive ef- fects, as shown in Plates XV-XVI. To provide for these factors the curb or curb and gutter must be Provision for separated during construction into separate blocks by means of part- expansion ing strips. and shrinkage Figs. 7 and 8 show the details of such construction for all of the types of construction. The following specifications will be found to give excellent work if closely followed: 102 GOOD CONCRETE SPECIFICATIONS FOR CONCRETE AND GUTTER. MATERIALS. Cement T^ e cement shall be Riverside Portland and meet the require- ments of the Standard Specifications for Portland Cement of the American Society for Testing Materials. Fine The fine aggregate shall consist of sand, crushed stone or gravel, aggregate screenings, conforming in composition and grading of particles to the requirements set for sidewalk work on page 84. Coarse Coarse aggregate shall consist of inert materials graded in size, aggregate such as crushed stone or gravel, which are retained on a screen hav- ing one-quarter (|/4) inch diameter holes, shall be clean, hard, durable and free from all deleterious matter. Aggregates consisting of soft, flat or elongated particles shall be excluded. The maximum size of the coarse aggregate shall be such that it will not separate from the mortar in laying and will not prevent the con- crete from filling all parts of the forms. The size of the coarse aggregate shall be such as to pass a one and one-quarter ( 1 '/4 ) inch ring. Natural Natural deposits of sand and gravel, usually being out of balance, mixed s ^ a ^ be screened and remixed to agree with the proportions specified aggregates n inch. Troweling When required, the surface shall be troweled smooth. The application of neat cement to the surface in order to hasten the harden- ing is prohibited. Color When coloring, matter is required it shall be mixed dry with the sand and cement, which have been previously mixed dry, until the mixture is of a uniform color. The quantity and quality of the coloring shall be such as not to impair the strength of the wearing surface. Protection When completed, the curb and gutter shall be kept moist and pro- tected from traffic for at least one ( 1 ) week. Combined Curb ana Gutter Form Fig. 7. CO &b PLATE XVIII. EXAMPLES OF THE EFFECT OF EXPANSION ON CURBS. EFFECT ALONG CURB. X S> x 6 tj -J n __ u UJ I H U. O 3 BU 5 < 5 PLATE XXI. EXAMPLES OF GARDEN WALLS. PLATE XXII. EXAMPLES OF GARDEN WALLS. PLATE XXIII. EXAMPLES OF GARDEN WALLS. CONCRETE ROADS CITRUS AVENUE, LOS ANGELES COUNTY, CONCRETE BASE WITH ONE-HALF INCH BITUMINOUS WEARING SURFACE. CHAPTER VII. CONCRETE ROADS. INTRODUCTORY. A good road should provide a permanent, even surface for the travel of vehicles. The creation of an even surface is in itself an easy matter, but the maintenance of such a surface, once created within the bounds of economy, is not an easy matter. The water-bound macadam road until about ten years ago repre- sented the best type of highway construction. It embodied the total accumulated knowledge of the road-building art. With the coming of the motor-vehicle, defects soon developed which clearly indicated the inadequacy of this type of construction to serve the demands of the new traffic. Efforts were made to increase the resistance of the macadam road by various surface applications. In every case such measures failed to give a permanent remedy. The road builder was soon brought to the realization that past experience offered no suggestions for the saving of the waterbound macadam road from rapid destruction by motor traffic. Highway Engineers in all parts of the world, pressed by the urgent demand for a better road for the changed traffic conditions, set about to determine the factors in road construction that make for ]2 GOOD CONCRETE permanency. The past decade has witnessed more experimental work in the construction of highways than any other period of the world's history. The first problem to be studied was the cause of the rapid destruction of macadam by rubber-tired wheels. It was once believed that the "suction" of pneumatic tires removed the binder from the road. A rapidly moving automobile will raise a cloud of dust which, it is true, may be composed of the binder, but this is not the result of any suction on the part of the pneumatic tire, but in fact the effect of the air currents set up by the automobile plowing through the air. That the binder of the road was being destroyed and removed was perfectly obvious; the cause of this dis- integration, however, was not immediately understood. Cause of It has now been established that the destruction of macadam roads destruction is the result of crushing forces which are in excess of the compressive of strength of the binder. With the high unit loads imposed by mod- macadam ern vehicles upon the road surface, the binder is crushed and the large stones, being no longer bound together, are pounded into the sub-grade and ruts are developed; the loosened binder meanwhile is swept away by each passing vehicle and breeze. The destruction of this type of road, then, is due primarily to its lack of strength. Without this important attribute the body of the road cannot distribute the loads over the sub-grade, and each imperfection and irregularity of the sub-grade is soon reflected upon the surface of the road. Rigid A sub-grade, however well prepared, is far from having a homo- foundation geneous character. Almost invariably it is in a cut or a fill and necessary will settle unevenly. If then, a smooth road surface is to be main- tained, the body of the road must be composed of a rigid material which will equalize the irregularities of the sub-grade. Portland cement concrete is the only material that we possess which is endowed with sufficient compressive and tensile strength to fulfill the modern requirements of a road material GOOD CONCRETE 133 The development of the sheet asphalt pavement clearly illus- trates this fact. Attempts which were once made to cover a non- rigid road foundation with a wearing surface of asphalt were never successful, and today it is invariably constructed upon a foundation of Portland cement. The acknowledged supremacy of this type of pavement for city streets is to be attributed to the rigidity of the concrete base and its ability to distribute the loads over ihe sub-grade. This fact has long been under observation by highway engineers and its adaptation to country road building was only deferred by the high cost of Portland cement which prevailed until four or five years ago. About five years ago concrete roads were constructed simultaneously in at least eight different States; the data obtained from the observation of these first roads is largely responsible for the present enormous extension of the use of cement in highway making. There is as yet no general single standard for the construction of concrete roads. Three types, each of which has its advocates, are in general use. One-course concrete, Two-course concrete, One-course concrete with a wearing surface of bituminous material. In this form of construction only one layer of concrete is placed One-course directly upon the properly prepared sub-grade. The total thickness concrete of the concrete after compacting is somewhere about seven inches. In this type of construction an adequate base of concrete is first Two-course placed, followed by a wearing surface of richer concrete from two concrete to three inches in thickness. A wearing surface of cement-sand-mortar has not been found to give satisfactory results and its use has been abandoned. In this type of construction, which seems peculiarly adapted to One-course Pacific Coast conditions, a layer of concrete, the thickness of which concrete with a is usually controlled by local conditions, is placed on a properly bituminous prepared sub-base and covered with a wearing surface of bitumen wearing surf ace 114 GOOD CONCRETE and sand from Yi," to f" in thickness. This class of road has been adopted by the State Highway Commission and by the Los Angeles County Highway Commission. Each of these types gives excellent service. There are, however, a number of factors for and against each, which should be carefully considered before deciding what type will best serve a given purpose. Quality oj The all-concrete road, when properly constructed, gives a wearing concrete surface that is the last word for hardness and toughness. Such a necessary surface, however, requires careful and elaborate provision for the protection of the edges of the expansion and shrinkage joints. Again, provision must be made for the eventual wearing out of the concrete surface. Careful measurements indicate that concrete will wear down at the rate of 1 / 1 6" per year, so that a 2 " surface finish will have a life of thirty-two years. Owing to the serious problem involved in bonding a new wearing surface upon an old concrete base, perhaps the best practice will be to replace the wornout concrete surface with a bituminous wearing surface. It is an important fact to remember that a concrete road of whatever type affords a permanent foundation upon which any form of wearing surface may be placed after the original surface dressing is worn out. FUNDAMENTAL REQUISITES FOR CONCRETE ROAD CONSTRUC- TION. In applying concrete to the construction of roads and highways the cardinal point is to fully realize what demands will be made upon thp material. Strength in concrete is a matter of degree ; it can be varied between wide limits at will. The toughness and resistance to abrasion can likewise be controlled by the selection of a properly endowed coarse aggregate. Wear of In the construction of concrete roads the engineer should and must concrete be satisfied only with the very best concrete that can be produced from roads the materials at his command. GOOD CONCRETE 115 If one considers the infinite pains and attention to detail expended in the proportioning of such a low-priced commodity as sheet asphalt, there certainly can be no excuse offered for the loose methods of pro- portioning, mixing and placing concrete now in general use. With a given specification the production of good concrete is not a matter of additional expense, but simply one of intelligence. In the construction of concrete roads the factors that make for per- manence will be: 1. A sub-grade well rolled, compacted and drained. 2. A concrete which has a mortar of sufficient strength to prop- erly bind the coarse aggregate together and enable it to resist the shock and wear of the traffic. 3. A coarse aggregate that is tough, durable, clean and entirely free from all soft or decomposed particles. 4. All the wear is to be taken by the coarse aggregate, and the mortar shall serve only to rigidly hold the coarse particles in place. 5. Methods of placing and curing the concrete which will be such as to permit the concrete hardening to the best ad- vantage. 6. Adequate provision for taking care of shrinkage and expan- sion and the proper protection of all such joints to prevent frazzling. PROVIDING FOR EXPANSION. The question of providing for shrinkage and expansion is one Expansion for which there seems to be more than one solution. It is now a ana well-established fact that average concrete has about the same co- Shrinkage efficient of expansion for every degree of change in temperature as steel has; but aside from these changes in volume, due to changes in temperature, we have the changes in volume due to normal shrinkage and expansion. Concrete which is hardening under water 116 GOOD CONCRETE or in a damp environment expands constantly up to a certain point. This expansion, due to hardening in water, or in a moist environment, will amount to 0. 1 " for every hundred feet at the end of two years. When concrete is allowed to harden in air, or in a dry environment, a contraction or shrinkage takes place, which amounts for a 1:2:4 concrete to 0.3" for every hundred feet at the end of two years. The amount of this expansion and shrinkage is, however, greatly influenced by the amount of water used in mixing. An extremely wet mixture will show more shrinkage in air than one that is just about plastic. It will also be influenced by the amount of sand present in a concrete. An oversandsd concrete will always shrink more than a properly balanced one. EXPANSION AND CONTRACTION DUE TO CHANGES IN TEM- PERATURE. The co-efficient of expansion of average 1:2:4 concrete is .0000055, which can very conveniently be remembered as "five naughts and a five," so that for every 50 deg. F. rise or fall in temperature this change will amount to about 1 /3" per hundred feet; so that shrinkage in air during hardening is just about equal to the expansion due to a change of 50 deg. in temperature. It is upon this fact that some engineers advocate laying the concrete road without any provision for either expansion or contraction. As we have shown above, there is a theoretical justification of this attitude, but in allowing nature to provide its own reliefs for changes in vol- ume she will not usually produce these reliefs in geometrical lines. The cracks may, and are likely to be, very irregular. Instead of traversing the road at right angles to its length, they are just as likely to form partly at light angles and partly in the same direction as the length of the road. A crack parallel to the line of traffic will receive more wear than one at right angles to it. If the concrete surface is supplied with a bituminous wearing surface, it will be a matter of indifference in what direction these cracks are formed; but if the road is to be supplied with a concrete wearing surface, the GOOD CONCRETE H7 matter of making provision for expansion and shrinkage becomes a very vital one. The first all-concrete roads built have demonstrated the fact that the life of a road will depend upon the provision for expansion and shrinkage and the protection of these joints. The proper protection of these joints adds materially to the cost of con- struction. Perhaps the most satisfactory method yet devised is that used in Wayne County, Mich. The joint is protected by a patented steel plate called the Baker plate, which is, in substance, a curved steel plate conforming to the crown of the road, which protects both sides of the expansion joint and is separated by either several layers of tarred paper or by a bituminous compound. These plates wear uniformly with the concrete and do much to prevent the formation of little irregularities at each expansion joint. THE PROPER INTERVAL FOR EXPANSION JOINTS. The amount of expansion which can produce cracks will vary Interval for with the season of the year in which the concrete is laid. If concrete expansion and is laid in Summer, the development of expansion cracks will be very shinkage small, because the concrete is at its maximum volume on account of joints the heat. In such work contraction cracks will inevitably develop. The interval at which relief is provided varies from 25 to 75 feet. This holds only for roads with concrete wearing surfaces. The Los Angeles highway engineers, as well as the highway engineers of the State of California, who have adopted as their standard the one-course concrete road with a bituminous wearing surface, make no provision for either expansion or contraction, as the wearing surface will automatically flow into and take care of any cracks that are formed. The specifications for concrete roadways of Wayne County, Mich., require an expansion joint for each 25 feet. Those of Mason City, la., one every 37J/2 feet; the Illinois Highway Commission require one every 50 feet, while those of the Maryland State High- way Commission require one every 60 feet. In all of the cases above 118 GOOD CONCRETE cited the roads are all provided with a concrete wearing surface. The proper interval for any locality will depend upon local condi- tions and is one that the engineer will have to determine for himself. How MUCH CROWN FOR CONCRETE ROADS? There can be no argument against crowning a macadam road, as in this type of construction the life of the road depends upon its being rapidly and well drained. Concrete, on the other hand, when properly made, is an impermeable material whose strength is not impaired by contact with water. The matter of crown and its degree will be of minor importance in a concrete road, and need only be such as will make travel in wet weather more convenient, by permitting the drainage to take place laterally instead of longitudinally. Flatter There certainly can be no justification for adherence to the old crown for precedents established for the water-bound macadam roads when concrete it comes to crowning a concrete road. It is now generally recognized roads that a concrete road needs less crown than does a water-bound mac- adam one in fact, some constructors prefer to give the road no crown at all, simply building the surface as an inclined plane sloping in one direction only. The crown need not be in the form of an arc of a circle, but can be composed of two planes sloping to each side from the center. Excessive crowns in concrete roads are a fruitful source of longi- tudinal cracks. Such excessive crowns have the additional disad- vantage that they concentrate all the traffic at the center of the road, while a flatter crown distributes the traffic over the entire surface, thus providing a uniform wear. The crown of the sub-grade is usually made to conform to that of the finished road surface. The crowns for concrete roads vary from J/g" to ^4" P er ft- of width. CONCRETE. Proportioning Whatever type of concrete road a community may decide upon. the concrete attention to the proportioning, mixing and placing of the concrete will GOOD CONCRETE 119 be the cardinal point. We have already made mention of the neces- sity of proportioning and making a concrete of such physical proper- ties as will resist the unusual wear to which the work will be subjected. The sand, first of all, must be clean it need not be sharp. The word "sharp" in specifications for sand is a relic of Mediaevalism. The sand will need as much attention to determine its quality as will the cement. We have already considered in the chapter dealing with sand and its physical properties the various items which determine the quality of a sand. Perhaps the safest and most expedient way of testing sand will be, first of all, a determination of the amount of silt, and, secondly, its tensile strength. For the purpose of road con- struction the sand used with a concrete shall show a tensile strength in pounds per square inch not less than the tensile strength of the same proportion of standard Ottawa testing sand when made up according to standard methods and tested with the same cement to be used on the work. The coarse aggregate must be, first of all, composed of a tough Coarse and durable rock perfectly free from any soft or disintegrated parti- aggregate cles. The rock is depended upon to take the wear of the traffic, and if there are soft places, these will be worn away in a short time and leave a cavity in the surface which becomes the nucleus for wear, and a rut will soon result in much the same manner as one soft brick in many hard bricks in a brick pavement will start the destruc- tion of such a type of wearing surface. The coarse aggregate may be either a crushed rock or screened gravel. Gravel is usually composed of the toughest particles of rock which have resisted erosion. They represent the most refractory por- tion of the rock from which they were derived. Natural screened gravl, however, will sometimes carry quite a proportion of shale boulders, which would unfit them for the intended use. The proportion of cement to total aggregate should never be less Proportioning than 1 :6. Perhaps the most glaring defect that one finds in the concrete majority of specifications is the arbitrary fixing of the proportion of sand to rock. For example: A 1 :6 mixture is usually construed as 120 GOOD CONCRETE meaning one part of cement, two parts of sand and four parts of rock. This may be the best proportion of sand to rock for some mixtures. The scientific way of determining the best and strongest mixture would be by the volumetric synthetic method, as explained on page 39. Bearing in mind that that combination of sand and coarse aggregate for a fixed proportion which gives with a fixed amount of cement the smallest volume of plastic concrete will be the strongest and densest mixture. It would be well at this point to emphasize that the strength of a concrete depends upon the strength of its cement and sand mortar. The tendency is, if a concrete does not work smooth enough in laying, to add more sand. In doing this the constructor is deliber- ately weakening his concrete. It apparently never occurs to him that the proper thing to do would be to decrease the rock- DETERMINING THE BEST PROPORTION OF SAND AND ROCK BY THE VOLUMETRIC, OR CYLINDER METHOD. If, for example, the specified proportion of cement to aggregate is fixed as 1 :6, the procedure would be as follows: Construct a cylinder about 6" in diameter, plugged at one end, and mark on a stick the inside clear depth of this cylinder. Divide this length into as many equal divisions as there are parts of cement and total aggregate. For a 1 :6 mix the distance on this stick would be divided into seven equal parts. Then measure by means of this stick various proportions of sand and coarse aggregate, such as, for example: 1 part of cement, 1 J/2 parts of sand and 41/2 parts of rock 1 part of cement, 2 parts of sand and 4 parts of rock Convert each mixture into a plastic concrete and ram it into the cylinder. Then that mixture which gives the smallest volume will be the proper mixture to use. For further details the reader is referred to the chapter on Proportioning Concrete. Mixing The logical way to mix concrete is to first prepare the sand and cement mortar of proper consistency, and to add to it the wet aggre- gate. In machine mixing this is done without any inconvenience GOOD CONCRETE 121 whatsoever. The sand and cement are charged into the mixing machine and the machine allowed to make several revolutions. The water is then added, and as soon as the mortar becomes uniformly mixed the rock or coarse aggregate is charged into it. By this method of mixing much is done to obviate the tendency of a concrete to draw crack that is, to open up into short parallel cracks. These cracks are due to the cement absorbing water from the sand. A cement particle, as minute as it is, is a very hard and refractory material. It needs a certain definite time to soften in contact with water, and if it is not allowed this time it will do so after it is placed into the work and give the concrete the appearance of "setting up." The sub-grade upon which the concrete is to be deposited must be Depositing saturated with water, otherwise the concrete will be robbed of the the concrete water which is so essential to its proper hardening. The concrete, after it is in place, must be protected from direct Protection sunlight and draft. The practice in the Middle Western States is to of the cover the freshly laid concrete, as soon as it has taken initial set, concrete with a large canvas. This canvas is allowed to remain for 1 2 to 24 Qjtcr hours, after which the surface of the concrete is thoroughly wet and kept wet for seven days. Where a sand or other proper material is available, it may be placed on the wetted concrete surface and saturated with water. If the road surface is to be finished with a bituminous wearing surface, the properly cured concrete must be thoroughly cleaned and dried before the oil and sand can be applied. \22 GOOD CONCRETE _s m 3 cs s (S a i-O 1^ f^ .-xj c^ ^f O^ 1 I"^N <\i uO CN| < ^ OQ UJ _: _: cs G vi _: fXJ ^* Q Ci H j 2 CJ fe 3 ? 3 a 1 8 : t d pQ .^ -^ CO ro> fv] CO -r - 1 n *- oq -i Gal. per Sq. Yd. * as Thicknets of Wear- ing Surface X i k 8, s 5 I CM to o i CN t o^ CO CO ^ CN * O Co ^T t O B UJ 3C .DWAY I CN E CO O CO 8 i ^ i k r> sO fx ? C^4 u. ^\ in lO CM i CO CM V GO Thickne of Concrete if! 5 1| Specifications for Concrete Roads with Asphaltic Oil Wearing Surface CHAPTER VIII. SPECIFICATIONS OF THE CITY OF GLENDORA For the Construction of PORTLAND CEMENT CONCRETE PAVEMENT WITH ASPHALTIC OIL WEARING SURFACE, By FLOYD G. DESSERY. The work herein provided for is to be done in accordance with Genera/ the plans, profiles, detail drawings and cross-sections for the work requirements on file in the office of the City Engineer of the City of Glendora, and all work shall during its progress and on its completion, conform to the lines and levels which may from time to time be given by said City Engineer. ( 1 ) To excavate or fill in the area upon which the pavement The work herein provided for is to be constructed on the Street, Avenue, Alley to be done or Roadway, to such extent as may be required by the plans, profiles, is as follows. detail drawings and cross-sections and these specifications. (2) To construct and lay thereon the pavement hereinafter specified. (3) To furnish all materials and labor necessary to perform said work and construct the same. 126 GOOD CONCRETE (4) And to do whatever else is required by these specifications to be done. Sub-grade The surface of the compacted sub-grade for the roadway shall be such distance below the finished surface of the Street, Avenue, Alley or Roadway as shown on the above mentioned plans, profiles, detail drawings or cross-sections. Grading Grading shall include the removal of all earth, stone, loose rock, cement, hardpan, boulders, solid rock and all other materials which may be encountered in preparing the sub-grade, and shall include also all filling, trimming, shaping, packing down, refilling, surfacing, roll- ing or other work which may be necessary in bringing the surface of the roadway to the required sub-grade. When required by the plans, profiles, details drawings or cross-sections, the area back of the curb line shall be graded to conform to the grade shown on the said plans, profiles, detail drawings or cross-sections. When mud, sand, vegetable, or other soft material is encountered, it shall be removed to a depth of twelve (12) inches below sub-grade, and the space filled with good gravel or earth, which shall be rolled with a self-propelled road roller weighing not less than ten, (10) tons, until the surface of the foundation ceases to sink under or creep in front of the roller. In places where filling is necessary to bring the street to the re- quired grade or sub-grade, all brush and rubbish shall be removed and the fill shall be made with good sound earth. The embankment shall be carried up of full width in layers not to exceed one ( 1 ) foot in thickness, and the teams shall be made to travel as evenly as possibly over the whole surface of each layer, both coming and going. If there should be an excess of smooth or rounded stone, rock or boulders in or upon the material forming the sub-grade, the same shall be removed and good earth or gravel shall be substituted in place thereof. GOOD CONCRETE 127 The formation of well-defined ruts is especially prohibited. No material of spongy nature shall be used in filling. After each block or section has been graded as above specified the surface shall be thoroughly watered, and shall then be rolled with a self-propelled road roller weighing not less than ten (10) tons, until the surface is smooth and unyielding. Depressions made by rolling shall be leveled up with good earth, thoroughly sprinkled and rolled again. Such portions of the street as cannot be reached by the roller, and all places excavated below the sub-grade and refilled and all pipe trenches and other places which cannot be properly compacted by the roller, shall be tamped solid, and in case of wet weather or soft and muddy ground making the use of the roller unsafe or impracticable, the rolling shall not be undertaken until the ground has become sufficiently dry. The surface of the compacted sub-grade shall be so finished that it will not vary at any point more than one-half ( Yi ) inch from its intended position. The Contractor shall notify the Street Superintendent when the sub- grade shall have been prepared as above specified and no further work shall be done upon it until it has been examined and a certificate of acceptance has been issued by said Street Superintendent. Upon the sub-grade prepared as above specified shall be laid a Concrete concrete foundation of the thickness, width and form shown on the foundation plans, profiles, detail drawings or cross-sections. Proportions: The cement concrete shall be composed of: One Concrete (1) part of Portland Cement, Two (2) parts of sand or broken stone screenings, and Four (4) parts coarse gravel or broken stone. Gravel, broken stone or crushed rock forming the coarse aggregate shall not exceed in its greatest dimension three- fourths (24) of the thickness of the concrete foundation to be constructed. Measuring and Mixing: All proportions shall be obtained by actual measurement in boxes and no material shall be used which has not been thus measured. All mixing shall be done in suitable boxes or upon tight platforms or in mixers of an approved type. In 128 GOOD CONCRETE the process of mixing the concrete, the broken stone, gravel or coarse aggregate shall be spread in a regular layer not over ten (10) inches in depth on the platform; upon this coarse aggregate shall be uni- formly spread the proper amount of sand or fine aggregate; and upon the fine aggregate shall be spread the required amount of cement. The whole mass shall then be mixed by turning at least three (3) times dry, sufficient water shall then be added in a fine spray to pro- duce a concrete of a consistency which will require light tamping to flush mortar to the surface, after which the whole mass shall be turned two (2) times wet. If a machine is used for mixing, it must be of a standard or ap- proved type and the concrete so mixed shall be at least equivalent to that mixed by hand, as above described. No concrete shall be used that shows evidence of having set or that has become unfit for good work from standing too long or from any other cause, and no remixing of concrete will be allowed. Placing After the concrete has been mixed as above specified, it shall be handled rapidly and successive batches deposited in a con- tinuous operation completing each individual section. Under no circumstances shall more than thirty (30) minutes elapse between the mixing and placing of the batch of concrete. The upper surface of the concrete shall be finished parallel to and three eighths ( ^ ) of one ( 1 ) inch below the grade of the finished pavement by thoroughly hand tamping until the mortar flushes freely to the surface. After the concrete has been thoroughly tamped, it shall be immediately brought to a smooth and even surface by the use of a flexible wood float formed to truly fit the curve of the crown and extending entirely across the pavement, after which no disturb- ance of any character of the surface will be allowed. The earth foundation or sub-grade shall be thoroughly sprinkled immediately before placing the concrete. All concrete shall be placed at once after mixing. As soon as the surface of the concrete has been finished as above specified it GOOD CONCRETE 129 shall be protected from the direct rays of the sun and from rain and wind by spreading a wetted canvas over it. The canvas shall be allowed to remain at least ten (10) hours over the fresh concrete, during which time it shall be sprinkled at least once, after which time the canvas shall be removed and the surface of the concrete shall be sprinkled with a spray (and not a jet) of water at intervals of not exceeding three (3) hours between each application of water. This sprinkling shall continue over a period of not less than ten (10) hours, after which the surface of the concrete shall be covered with a layer of earth or soil to a depth not less than one ( 1 ) inch when wetted and compacted. The earth or soil covering shall then be immediately sprinkled until water runs from all the surface. This manner of sprinkling shall be performed at least three (3) times each day and continue for fourteen (14) days after the placing of the concrete. No traffic of any nature whatever shall be permitted to pass over the concrete for a period of thirty (30) days after the concrete has been placed. Expansion and contraction joints shall be constructed in accord- Expansion ance with and where shown on the plans, profiles, detail drawings or and cross-sections. They shall be carefully contructed and where templets contraction are used to form the joints, the templets shall be removed in such a joints manner that will not break, crack or injure the edges of the concrete forming the joint. The filler for joint space formed by the removal of the templets shall be made with the same material that composes the wearing sur- face hereinafter described. This space or joint to be filled shall be filled prior to the application of any asphaltic oil, screenings or sand to the surface of the concrete and care shall be exercised that the screenings or sand and asphaltic oil are well mixed and incorporated and that no surplus asphaltic oil or sand shall be applied, but after properly filling the space or joint the top of the same shall be level with the top or surface of the concrete base. When required by the plans, profiles, detail drawings or cross-sections, joints extending the full length of the roadway shall be constructed. These joints extend- BO GOOD CONCRETE ing longitudinally shall be formed by the use of a necessary amount of tarred paper (depending on the thickness of such paper) to make the joints conform to the dimensions shown on the plans, profiles, de- tail drawings or cross sections. All joints shall extend through the full depth or thickness of the concrete and shall be well aligned and made in a neat and workmanlike manner. Unless otherwise provided for in the plans, profiles, detail drawing or cross-sections, the portion of the pavement adjoining the curbs and forming the gutters shall be constructed for the full length of the work before any other portion of the pavement shall be constructed. Fofrm, Forms for all concrete work shall be free from warp, or other de- fects and of sufficient strength to resist springing out of line when properly staked, they shall be securely staked or otherwise held to the established lines and grades and extend to the full depth of the con- crete and their upper edges shall conform to the established grade of the pavement. All wooden forms shall be thoroughly wetted or oiled and metal forms oiled before any material is deposited against them. All mortar and dirt shall be removed from forms which have been previously used. Cement The cement used shall be Portland Cement and shall conform to the following conditions and be subject to the following tests: The tests shall be made by the methods and under the conditions pre- scribed by the committee of the American Society of Civil Engineers and shall be open to the Contractor. Not less than ninety-two (92) per cent of the weight of the cement must pass through a sieve of one hundred ( 1 00) meshes to the inch and not less than seventy-five (75) per cent by weight must pass through a sieve of two hundred (200) meshes to the inch. Time of Setting: The initial set of the cement shall be in not less than thirty (30) minutes when mixed neat with the smallest possible amount of water at the temperature at which it flows from the tap in the testing room provided ty the City of Glendora, but hard set GOOD CONCRETE j 3i must develop in not less than one ( 1 ) hour nor more than ten (10) hours. Tensile Strength : Briquettes one ( 1 ) inch square in section shall attain at least the following tensile strength and shall show no retro- gression within the periods specified: After twenty-four (24) hours in moist air neat, one hundred fifty (150) pounds per square inch. After seven (7) days (Briquettes to remain in moist air one (1) day, in water six (6) days, neat, four hundred fifty (450) pounds per square inch: three (3) parts sand to one (1) part cement, one hundred fifty (1 50) pounds per square inch. After twenty-eight (28) days briquettes to remain in moist air one ( 1 ) day, in water, twenty- seven (27) days, neat, five hundred fifty (550) pounds per square inch, three (3) parts sand to one (1) part cement, two hundred (200) pounds per square inch. Soundness: Test pats of neat cement about three (3) inches in diameter, one-half (Yz) mc h thick at the center and tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. They shall then be exposed in a steam bath, above boiling water, in a loosely closed vessel for five (5) hours. At the expiration of this time, the pats shall remain firm and hard and shall show no signs of distortion, checking, cracking or disintegrating. Samples of the cement proposed to be used upon any piece of work shall, upon re- quest, be furnished to the City Engineer for test, and any cement the samples of which do not come up to the required standard shall be immediately and permanently removed from the work. Fine Aggregate: The fine aggregate shall consist of an approved Sand, material of silicious, granitic or igneous origin, hard, durable and free stone, from mica in excess of five (5) per cent by weight. It shall be free screenings from oil or organic matter, and must not contain more than six (6) and broken per cent by weight of clay, silt and other material passing a No. 1 00 stone Standard Sieve. It shall all pass a No. 4 Standard Sieve, and at least fifty (50) per cent, but not more than eighty-five (85) per cent by weight, shall be retained on a No. 30 Standard Sieve. 132 GOOD CONCRETE Coarse The coarse aggregate shall be sound gravel or broken stone, having aggregate a specific gravity of not less than 2.6. It shall be clean and free from all foreign matter, uniformly graded, and shall range in size from one-fourth (!/*) inch up to three (3) inches. Water The water used in mixing the concrete shall be clean, free from oil, acid, alkalies or vegetable matter of any nature. Asphaltic When the concrete foundation has been thoroughly cleaned of all oil tearing dirt by sweeping and flushing with water and after it has thoroughly surface dried, the entire surface of the concrete foundation shall be covered with heavy asphaltic oil of the quality hereinafter specified. The oil shall be applied under pressure by means of an approved spraying machine, at the rate of one-half (|/2) gallon per square yard of sur- face covered. Immediately after the asphaltic oil has been applied, the entire oiled surface shall be covered with a thin layer of broken stone screenings in quantity sufficient to absorb the oil. Wherever free oil shows on the surface, additional screenings shall be applied to absorb the oil. After the oil applied as above specified has been covered with screenings for at least three (3) days the entire surface shall again be covered with asphaltic oil of the quality and in the manner above specified at the rate of one-fourth (J4) gallon per square yard of sur- face covered. Immediately after the asphaltic oil has been applied it shall be covered with a thin layer of broken stone screenings or coarse, screened sand, in quantity sufficient to absorb the oil, and wherever free oil shows through the surface of screenings or sand thus applied addi- tional screenings or sand shall be applied to absorb it. The surface of the roadway thus prepared shall be maintained for at least ten (10) days, after the last application of asphaltic oil, and no traffic of any nature will be permitted to pass over it until the expiration of such time. The completed pavement shall present a uniform bituminized ap- pearance, with a true and even surface free from irregular patches of screenings or excess oil. GOOD CONCRETE 133 No gravity machine shall be used in applying the asphaltic oil and the Contractor shall exercise great care in applying the oil in uniform quantity, and if the class of machine or apparatus for applying the oil is such that the curbs will become spattered or coated with the oil when being applied to the pavement, then the Contractor shall use such means as may be necessary to prevent the oil from depositing on the curb or curb face. No asphaltic oil shall be applied on the concrete foundation until at least twenty-one (2 1 ) days have elapsed after the concrete foundation has been completed. Broken stone screenings and sand for asphaltic wearing coal Broken stone screenings shall be that portion of crusher run that passes through a circular screen opening one-half (j/2) inch in diam- eter and from which all fine dust has been removed. The broken stone screenings shall be hard, tough, sound, of irregular cleavage and of uniform quality, from which substantially all dust has been removed. All sand shall be clean, coarse screened sand, all of which will pass through a circular screen opening one-half (J/2) inch in diameter and from which all fine sand has been removed. Oil: The oil shall be a heavy asphaltic oil prepared from Cali- Asphaltic oil fornia products, and shall be free from admixtures with any residues obtained by the artificial distillation of coal, coal tar or paraffine oil and shall conform to the following requirements: Water: It shall not contain more than one-half (Yz) of one (1 ) per cent of water by volume. Sediment: It shall not contain more than one-half ('/z) of one ( 1 ) per cent of sediment by volume. Volatility: When twenty-five (25) grammes placed in a No. 13 brass spherical dish, with a radius of four and two-tenths (4.2) centi- meters, inside measurement, is evaporated in a Blackmar or Richard- son type of Asphalt Oven, maintained at a uniform temperature of two hundred and twenty (220) degrees Fahrenheit for one ( 1 ) hour, it shall not lose more than seven tenths (7-10) of one ( 1 ) per cent. 134 GOOD CONCRETE Solubility In Carbon Di-Sulphide : It shall, when freed from water, be sol- uble to at least ninety-nine and five-tenths (99.5) per cent in pure carbon di-sulphide. In CS 2 Bromine Solution: The Bitumen soluble in carbon di- sulphide shall be soluble to the extent of at least ninety-nine and eighty-five one hundredths (99.85) per cent in a solution composed of one hundred and thirty-five (135) milligrams of bromine to one hundred ( 1 00) cubic centimeters of carbon di-sulphide, when twenty- five (25) cubic centimeters of the solution are poured on two (2) grammes of the oil in an Erlenmeyer Flask, which is then shaken in the dark for three (3) minutes, the solution being immediately filtered through a Gooch Crucible using a suction equal to a column of mer- cury not more than eight (8) inches high. When the solution has all passed through the crucible, the crucible shall be washed with pure carbon disulphide, dried at two hundred and twelve (212.0) to two hundred and twenty (220.0) degrees Fahrenheit and weighed. The amount of bromine in the carbon di-sulphide solution is deter- mined by adding to twenty-five (25.0) Cubic Centimeters of the solu- tion, about twenty-five (25) cubic centimeters of water and an excess of Potassium Iodide crystals and then titrating by decinormal solution of Sodium Thio sulphate. In Casoline: The asphalt, prepared as hereinafter specified, having a penetration between seventy-five (75.0) and eighty (80.0) degrees District of Columbia Standard, shall be soluble in California gasoline (hereinafter specified) to the extent of at least eighty-five and five-tenths (85.5) per cent when one hundred and fifty (150.0) cubic centimeters of gasoline are poured on five-tenths (0.5) of one gramme of the asphalt in solution in one (1.0) cubic centimeter of carbon di-sulphide and shaken ocasionally for ten (10) minutes. This test shall be made at about 77 degrees Fahrenheit. Gasoline: The gasoline herein specified shall be between sixty (60.0) and sixty and six-tenths (60.6) degrees Baume at 60 F. GOOD CONCRETE 135 Between fifty-eight (58.0) and sixty-one (61.0) per cent shall distill and pass out of condenser at two hundred and twenty-five (225.0) degrees Fahrenheit. Not less than three (3.0) nor more than four (4.0) per cent shall remain in the still at three hundred and thirty (330.0) degrees Fahrenheit. The rate of distillation shall be not less than one (1.0) nor more than two (2.0) drops per second. The amount taken for test shall be two hundred and fifty (250.0) cubic centimeters. After being freed from water, it shall contain not less than Asphalt ninety-five (95) per cent of asphalt, having a temperature of seventy-seven (77) degrees Fahrenheit a penetration of eighty (80.0) degrees District of Columbia Standard. The percentage of asphalt shall be determined by heating twenty-five (25.0) grammes in a No. 1 8 brass spherical dish with a radius of four (4.0) and two tenths (0.2) centimeters, inside measurement, in a Blackmar or Rich- ardson type of oven maintained at a uniform temperature of four hundred and thirty (430.0) degrees Fahrenheit until it has reached the proper consistency, when the weight of the residuum is determined and the per cent calculated (the temperature of the oven shall be taken with the bulb of the thermometer resting on the bottom thereof). The ductility of the asphalt as above prepared having a Ductility penetration between seventy-five (75.0) and eighty-five (85.0) de- grees District of Columbia Standard shall be not less than one hun- dred and ten ( 1 1 0.0) centimeters. This test to be made by im- mersing the asphalt in water which is kept at a uniform temperature of seventy-seven (77.0) degrees Fahrenheit for at least thirty (30.0) minutes, using the "Dow" asphalt mould and pulling apart at a uniform rate of speed of five (5.0) centimeters per minute. All oil shall be delivered at the point of application at a tempera- Thermal ture or not less than three hundred (300.O) degrees Fahrenheit, nor readings more than four hundred (400) degrees Fahrenheit. 136 GOOD CONCRETE Corrections In determining the quantity of oil delivered the correction Thermal for expansion of heat shall be as follows: From the meas- ured volume of oil received at any temperature above sixty (60.0) degrees Fahrenheit, an amount equivalent to three-tenths (0.3) of one (I) per cent for every ten (10) degrees above said sixty (60) degrees Fahrenheit shall be subtracted as the correction for expansion by heat. For the purpose of measuring this oil, a tem- perature of sixty (60) 'degrees Fahrenheit shall be deemed normal temperature. All of the oiling hereinbefore specified shall be done only when the atmospheric temperature is above sixty-five (65) degrees Fahren- heit and only when the sun is shining. No oiling shall be permitted unless the surface to be covered is thoroughly dry. SPECIFICATIONS OF THE LOS ANGELES HIGHWAY COMMISSION. CONCRETE PAVEMENT WITH BITUMINOUS WEARING SURFACE. Before the concrete pavement is laid, the roadbed shall be graded Shaping to a true cross-section, conforming to the grades given by the engineer roadbed and the section called for on the plans. It shall then be watered and rolled with a roller weighing not less than ten (10) tons until the sur- face is hard and unyielding. The width to be rolled shall include not less than one foot on each side of the pavement to provide satisfactory support for the forms. Depressions shall be filled with fresh material and the watering and rolling continued as before. Where a uniform and unyielding surface cannot be otherwise obtained, the surface shall be cultivated and again rolled until a uniform, smooth and firm foun- dation is secured. No concrete pavement shall be laid or material deposited upon the roadbed until it is in a condition acceptable to the engineer. After the roadbed has been prepared as hereinbefore specified, Forms forms shall be constructed, satisfactory material for which shall be furnished by the contractor. The proposed concrete pavement is to be supported on each side by two inch by five inch (2"x5") redwood lumber, planed straight on two edges. The forms are to be set true to the lines and grades given by the engineer and held in place by 138 GOOD CONCRETE stakes, of such size and length and set at such intervals as may be necessary to insure rigidity. The stakes shall be flush at the top with the side strips and the entire form work constructed in a substantial and workmanlike manner. The forms are not to be removed, but are to remain as part of the completed work. Concrete Cement: All cement for the concrete pavement will be furnished pavement by the County. It shall be Portland Cement, conforming with the Standard Specifications for cement adopted in August, 1 909, by the American Society for Testing Materials. The cement shall be suitably protected from the weather and piled so as to permit of access for tally, inspection and identification of each shipment. It will be delivered in the original package with the brand and the name of the manufacturer plainly marked thereon. The contractor shall be held responsible for the proper protection and safety of the cement after delivery by the County. He shall also collect and make prepaid return shipment of empty cement sacks, and all shortage of cement or sacks shall be charged to his account. The concrete shall be composed of broken stone or screened gravel and sand all of which shall be clean, hard, durable, well graded and satisfactory to the engineer Portland Cement and fresh, clean water. Othet The sand shall be of such size that all of it will pass through a materials screen having four (4) meshes per linear inch, and at least forty (40), but not more than eighty-five (85), per cent by weight will be retained on a sieve having thirty (30) meshes per linear inch. Not more than seven (7) per cent weight shall pass through a sieve having one hundred ( 1 00) meshes per linear inch. The broken stone or gravel stones shall vary in their longest dimen- sions from one-half ('/z) of an inch to two and one-half (2'/2) inches. Composition Concrete materials shall be proportioned as follows: One (1 ) cubic foot (95 pounds) of cement, two (2) cubic feet of sand, and four (4) cubic feet of broken stone or screened gravel, and water which GOOD CONCRETE 139 shall be added in such proportions as the engineers may from time to time determine. If the concrete is mixed mechanically, a mixer shall be used which Mixing and is satisfactory to the engineer, and into which the materials, including placing the water, can be precisely and regularly proportioned. Hand-made concrete shall be mixed on a tight, level platform, as follows: The cement and sand shall first be thoroughly mixed dry in the proportions specified. Clean water shall then be added and the materials thoroughly mixed and deposited on the broken stone or screened gravel, which has been previously drenched with water. The ingredients shall then be thoroughly mingled and turned over until each stone is covered with mortar. The batch shall be carefully de- posited without delay and thoroughly rammed until the water flushes to the surface and all the voids are filled. Should defective work be discovered it is to be removed and the space refilled with fresh material as directed by the engineer. No allowance shall be made for any materials or labor necessary on account of water. The concrete is to be brought to a true and uniform surface con- forming to the grade and cross section of completed roadway as shown on drawings, by means of templates and such other implements as may be necessary. While the concrete is still plastic, it is to be finally finished with steel floats and given a granolithic surface, which shall be free from any unevenness. During warm and dry weather, and whenever the engineers may direct, all newly-built concrete shall be kept shaded from the sun and well sprinkled with water. All concrete shall be measured in accordance with the dimensions shown on the plans and cross sections. Concrete pavement will be paid for at the unit price per square yard for concrete pavement in place complete, which price shall in- clude the furnishing of all materials, all labor, tools, implements, forms and all work on same, and everything incidental and necessary to the completed work, except as herein otherwise specified. 140 GOOD CONCRETE Bituminous After the concrete pavement has been constructed as hereinbefore wearing specified, all dust, mud, earth or foreign material of any kind which surface may have accumulated upon it shall be removed and the surface flushed with water. When it has become sufficiently hard and dry, and in the opinion of the engineer is ready to receive it, asphaltic oil wil be furnished and applied by the County. It will be put in one (1) application of approximately one-third (1/3) of a gallon to the square yard. All the work hereinbefore and hereafter provided for shall be performed by the contractor except the application of as- phaltic oil. Directly after the oil has been applied, stone screenings of the commercial size known as Number Four (No. 4) shall be uniformly spread upon it in sufficient quantity to combine with the oil without leaving any excess screenings on the finished road surface. The stone screenings are to be spread in a direction parallel with the road and never crosswise. If necessary, from time to time additional screen- ings shall be spread, as the engineer may direct, to cover any oil which may come to the surface, until the final completion and accept- ance of the work. The stone screenings are to be furnished and spread by the contractor and must be of a quality, size and spread in a manner satisfactory to the engineer. Protection The contractor shall exercise due precaution to prevent damage of pavement to the work during the various stages of construction. He shall, when- ever necessary, construct fences or barriers to prevent travel from passing over the concrete pavement until it has been in place at least seven (7) days, or over the oiled surface before the pavement is completed. Any dust, mud, earth or foreign material carried or de- posited upon the concrete pavement which is to be oiled, or upon any oiled surface, shall be removed by the contractor at his own proper expense, and the surface thoroughly cleaned before further work progresses. GOOD CONCRETE 141 g ri \ i (2 :- \ - s \ \ s \^ \ \ Ul \ \ u \ v > CO \, \ \ H Ul \ V g \ U \ i i I O 1 \ X V 1 X \' 1 t 1 . | CO S \ ' \ s i x 1 , H i I \ \ \ , \ L 1 t 1 ^-2 -.-* 1 SPECIFICATIONS FOR STREET PAVING WITH ASPHALT PAVEMENT IN THE CITY OF Los ANGELES. (Specifications No. 80.) Nolc The following specificfiations cover the materials and meth- ods of preparation for sheet asphalt on a Portland Cement concrete base. The thickness of this wearing surface for very heavy traffic is by the best authorities placed at 2", while for moderate traffic a thickness of \Yi" will be ample. ASPHALT WEARING SURFACE. Upon the binder course, prepared and laid as above described and thoroughly swept free from all rubbish, shall be laid an asphalt wearing surface composed of asphaltic cement, sand and stone dust, the different ingredients being mixed in such proportions that the percentage composition, by weight, of the wearing surface shall be within the following limits: ( I ) Bitumen soluble in carbon disulphide between 1 per cent and 1 2 per cent. (2) Sand, stone dust and other inorganic ingredients, as follows: Passing screen of 200 mesh to the inch, between 1 per cent and 1 4 per cent. GOOD CONCRETE Passing screen of 80 mesh to the inch and rejected by screen of 200 mesh to the inch, between 20 per cent and 28 per cent. Passing screen of 50 mesh to the inch and rejected by screen of 80 mesh to the inch, between 20 per cent and 26 per cent. Passing screen of 30 mesh to the inch and rejected by screen of 50 mesh to the inch, between 1 8 per cent and 24 per cent . Passing screen of 20 mesh to the inch and rejected by screen of 30 mesh to the inch, between 4 per cent and 8 per cent. Passing screen of 10 mesh to the inch and rejected by screen of 20 mesh to the inch, between 2 per cent and 5 per cent . At least ten (10) per cent, and not more than eighteen (18) per cent of the wearing surface shall be stone dust. If the composition contains the ingredients aforesaid, and within the percentages above fixed, it will be accepted as in compliance with this paragraph. PAVEMENT MATERIALS. Asphaltic Cement: The asphaltic cement must be prepared from California products. It shall be a mixture of a refined liquid asphalt with a refined solid asphalt, or be an oil asphalt, and must be free from admixture with any residues obtained by the artificial distillation of coal, coal tar, or parafhne oil. The asphaltic cement must be homogeneous and its consistency at the time of its use must fall within the limits of sixty (60) degrees and eighty (80) degrees penetration by the District of Columbia standard. It must be adhesive and ductile, and also slightly elastic at a temperature of thirty-two (32) degrees Fahrenheit. When twenty (20) gramme are heated in an oven to a temperature of three hundred (300) degrees Fahrenheit for five (5) consecutive hours in an uncovered cylindrical glass dish three and one-half (3}/i) cen- timeters high by five and one-half (5^) centimeters in diameter, it must not lose more than one ( 1 ) per cent in weight, and its pene- GOOD CONCRETE tration must not be reduced, as a result of such heating, more than fifty (50) per cent. It must, when ready foi use, contain at least ninety-nine (99) per cent of bitumen, soluble in carbon disulphide. It must be soluble in carbon tetra-chloride to the extent of at least ninety-seven and one- half (97J/2) per cent, when two hundred (200) cubic centimeters of the solvent are poured on one gramme of the asphaltic cement and the mixture is allowed to stand for eighteen (18) hours at a tempera- ture of twenty-five (25) degrees Centigrade and filtered at twenty- five (25) degrees Centigrade. Not less than seventy (70) per cent, shall be soluble in eighty-six (86) degree naphtha when one hundred and fifty ( 1 50) cubic centimeters of the solvent are poured on one- half O/i) gramme of the finely divided asphaltic cement and the mixture is allowed to stand for eighteen (18) hours at a temperature of twenty-five (25) degrees Centigrade and filtered at twenty-five (25) degrees Centigrade. It shall not contain more than fifteen (15) per cent, of fixed carbon on ignition. When the asphaltic cement is prepared by mixing a solid oil asphalt with a liquid asphalt, the solid oil asphalt shall be prepared by distilling the crude oil until the asphaltic residuum has a penetra- tion not less than fifty (50) degrees by the District of Columbia standard, and shall not be prepared by mixing or fluxing a more solid asphalt with liquid or softer asphalt. The refined liquid asphalt used in softening a solid asphalt must be a stiff residuum of petroleum oil with an asphalt base. It must be free from water and from light oils volatile at less than two hun- dred and fifty (250) degrees Fahrenheit. When twenty (20) grammes are heated in an oven to a temperature of three hundred (300) degrees Fahrenheit for five (5) consecutive hours in an uncovered cylindrical glass dish three and one-half (3 5/2) centi- meters high by five and one-half (5 Yl) centimeters in diameter, it must not lose more than three (3) per cent in weight. It must contain not less than ninety-nine (99) per cent of bitumen soluble in carbon disulphide. GOOD CONCRETE 145 The sand for the wearing surface shall be clean, hard- Sand grained and sharp, and shall contain not more than three (3) per cent of loam, clay or other earthy impurities; it must all pass a ten (10) mesh to the inch screen, and not less than seventy-five (75) per cent of its volume shall pass a forty (40) mesh to the inch screen. The stone dust may be a finely powdered limestone or other Stone dust hard and durable rock or Portland cement, as the Contractor tractor elects, and shall be of such fineness that all of it will pass a fifty (50) mesh to the inch screen, and at least sixty-six (66) per cent shall pass a two hundred (200) mesh to the inch screen. The Contractor shall furnish to the City Engineer by test, Samples whenever called for and free of charge, samples of all the materials entering into the composition of the pavement, the asphalt and asphaltic cement to be furnished in boxes, and said City Engineer shall have access at all times to all branches of the work. All tests shall be open to the Contractor. PREPARING FOR THE WEARING SURFACE. The sand shall be heated in suitable driers to a temperature be- tween three hundred (300) and three hundred and seventy-five (375) degrees Fahrenheit. The hot sand and cold stone dust shall then be thoroughly mixed together in a suitable mixer. The neces- sary quantity of asphaltic cement (previously heated to between two hundred and fifty (250) and three hundred (300) degrees Fahren- heit) shall then be added, and the whole mass shall be mixed until every particle of the sand and lime dust is thoroughly coated with a thin layer of asphaltic cement. In no case, after refining, shall the asphaltic cement be heated above three hundred and twenty-five (325) degrees Fahrenheit. The material so produced must leave the mixer at a temperature between two hundred and fifty (250) and three hundred and twenty- five (325) degrees Fahrenheit and must be fine-grained and capable M6 GOOD CONCRETE of producing a compact pavement. Proper sand and sufficient asphaltic cement and dust must be used in order to secure this result. LAYING THE WEARING SURFACE. The surface mixture, prepared as above, shall be brought to the work in suitable carts or dump wagons, and shall not be colder than two hundred and fifty (250) degrees Fahrenheit or hotter than three hundred and twenty-five (325) degrees Fahrenheit when it reaches the street. It shall at once be uniformly spread over the binder course, with hot shovels and hot rakes to such a depth that, after receiving its ultimate compression, the finished asphalt wearing surface will be of a thickness not less than that shown upon the cross-section adopted for the work, and uniform in density throughout its entire thickness. Rakes used for this purpose shall have strong teeth of a length sufficient to penetrate through the entire thickness of the wearing surface. It shall be immediately compressed by a roller weighing not more than one hundred and twenty-five (125) pounds to the lineal inch width of tire, after which a small amount of hydraulic cement or infusorial earth shall be swept over it, and it will then immediately be thoroughly rolled by a roller weighing not less than 210 pounds to the lineal inch width of tire. This rolling must be continued for not less than five (5) hours for each one thousand (1000) square yards of pavement. All places that are inaccessible to the roller must be tamped with hot iron tampers. The resulting pavement must show a close-grained, even and smooth surface, true to grade and cross-section and free from al' hollows and inequalities. When a straight edge five (5) feet long is laid on the finished surface of the roadway and parallel with the line of the street, the surface shall in no place vary more than one-quarter (|/4) of an inch from the lower edge of the straight edge. GOOD CONCRETE 147 No traffic shall be allowed on the street until the pavement is thor- oughly cooled and set. No binder or wearing surface shall be laid in rainy weather or when the foundation or binder is wet from rain or other cause. All cold joints shall be thoroughly painted with hot asphaltic cement. Where stone, brick or cement gutters are not provided for, the street shall be paved to the curb and the surface for a distance of three (3) feet next to the curb shall be coated with hot, pure asphalt and smoothed with hot smoothing irons, in order to saturate the pavement to a certain depth with an excess of asphalt and make the gutters entirely impervious to water. OTHER TYPES OF WEARING SURFACE. Sized crushed rock bound together with some form of bitumen has also found extensive use as a wearing surface placed upon a Portland cement base. This bituminous concrete is usually made from 1" to 2-H" in thickness and is technically known as "Bitulithic" and as the "Topeka specification". This type of wearing surface is an alternative form of construction to an asphalt wearing surface. CEMENT PIPE CHAPTER IX. CEMENT PIPE. The use of Portland Cement concrete for the construction of water supply and drainage projects is one of the oldest and most extensive applications of the material. The use of a monolithic construction for sewers is and has been for a long time considered the best practice even by those who are prejudiced in favor of brick or like products for this purpose. Yet the use of separately moulded cement pipe as an auxiliary to a monolithic trunk line is condemned by some for no apparent reason other than perhaps that it is a serious competitor for terra cotta pipe. Separately moulded concrete pipe possesses advantages over glazed terra cotta that are apparent to even the most casual observer. A cement pipe is, first of all, a uniform product that is true to die. Advantages A concrete pipe moulded in any given section preserves that sec- f tion upon hardening. It does not warp, and two consecutive pieces of pipe will always fit into one another at the joints. It can be made upon the premises by local labor and materials. It eliminates the cost of hauling a factory-made product from some distant point to the place of use. 152 GOOD CONCRETE Advantage h can be inspected and tested while being made. It is stronger than a terra cotta pipe of the same size. cement pipe When properly made it is more impermeable than a glazed terra cotta pipe. In the manufacture of terra cotta pipe the product of each kiln must be segregated, and there result three or more grades of pipe. In the manufacture of cement pipe the entire product is uniform. IRRIGATION PIPE. The agricultural welfare of the Southwest depends upon the eco- nomic conservation and distribution of water. Water is wealth. The seepage from open flumes and the loss by evaporation is a direct financial loss to the irrigationist. Cement irrigation pipe has been a powerful factor in the develop- ment of the agricultural resources of the Pacific Coast States, and the means of efficiently applying water in irrigation operations. CONTROLLING FACTORS IN THE MAKING OF GOOD CEMENT PIPE FOR IRRIGATION. As in all manufacturing operations, the use to which the product is to be put will control the quality and the quantity of the constituent materials. The large majority of irrigation pipe for tile is made by hand. The equipment is very simple and comparatively inexpensive. Hand made Hand-made tile is usually of the tongue and groove pattern. One cement pipe end of the pipe is formed into an annular groove, the other into a for irrigation tongue. The tongue fits into the groove when the pipe is laid. Bell ends of the type of cast iron water pipe can be also made by hand, but are not as convenient to handle in making or laying. The ordinary pipe mould consists of an outer shell and an inner core. The outer shell is so constructed that it can be expanded by a simple lever for releasing the pipe. The core is so made that it can be col- lapsed by simple mechanical means. The outer shell rests on a pallet GOOD CONCRETE \53 which has the form of the groove. This pallet is fastened rigidly on to the outer shell. The top of the outer shell is fitted with a funnel, and the core is topped by a cone, which serves to guide the material into the mould. The material is tamped into the moulds with iron tampers, and the top of the pipe is formed into the "tongue" by press- ing and rotating a suitable ring on it. The complete mould is then moved to the storage pile. The core is collapsed and withdrawn by giving it a twisting motion to prevent tearing. The outer shell is then expanded and removed, leaving the pipe resting on the pallet. The pallet is not removed until the pipe has become strong enough to handle. The pallets represent the greater portion of the equipment neces- sary in a pipe yard. The pipe-maker will need a supply of pallet rings large enough to handle a given output. The pipe can, as a rule, be lifted from the pallets at the end of two or three days. MATERIAL FOR IRRIGATION PIPE. Irrigation pipe up to the size of 24" is usually made of sand and cement mortar. The corresponding concrete is used when the thickness of the shell will permit. The proportions of sand to cement vary from 3:1 to 4 : 1 for ordinary tile. The quality of the pipe depends largely upon the sand used in its Sand making. The pipe-maker will find that strict attention to the quality of the sand will net him a direct financial return. The cement pipe industry has grown to such an extent within the past few years that competition is now very keen in even the smallest community, which should be the incentive for the highest quality. The influence of the sizing of grains of the sand upon the strength of a mortar made with it has already been considered at length on pages 30-32. The table of quantities for a given size material for the "Concrete Law" should be closely studied. The pipe-maker will, for certain sizes, find it a positive advantage to use as an addi- tion to his sand a sized one-half inch gravel or crushed stone. In 154 GOOD CONCRETE the following table the effect of adding sized gravel to mortar is very strikingly illustrated. The cement and sand in each instance were the same. TABLE XVII. No 1 ^roportion i Proportion of Compressive Sir. Cement Sand Gravel to Aggregate at 28 Days 1 2 :2 21501bs. 2 2 3 :5 2750 " 3 3 :3 1383 " 4 3 5 :8 1620 " 5 4 :4 1060 " 6 5 :5 532 " 7 6 :6 165 " This table emphasizes the necessity of a balance between the sand and rock or gravel. For example, No. 2, which is composed of cement, sand and gravel, has the same amount of cement in it as has No. 6, which is composed only of cement and sand. Yet No. 2 has a strength more than five times as great as No. 6. It is evident that there is a limit to the amount of sand that can be used in a mortar. As the proportion of sand in a mortar is increased, the strength de- creases very rapidly. Quality Different sands, and, in fact, sands from the same locality, show of sands a wide variation in their percent of voids. Referring to Table IV, page 27, it will be seen that the percent of voids in sands is by no means constant. In this particular instance we have a variation from 29% to 40.5%. The tensile and compressive strengths of the 1 :3 mortar is greatest for sands having the least voids. GOOD CONCRETE 155 WEIGHT PER CUBIC FOOT As AN INDEX TO THE PER CENT OF VOIDS. The weight per cubic foot of a dry sand is a ready means for judging its percent of voids, as is shown in Table VI, page 33. The pipe-maker should aim to get a sand whose per cent of voids is as low as possible, and whose weight per cubic foot is as high as possible. By the exercise of a little thought and the application of the principals presented in this book, he will be able to mix two or three sands in such a manner as to decrease the per cent of voids and increase the weight per cubic foot of the mixture, thereby in- creasing the strength and density of his product. The mixing of mortar is usually done by hand. In larger yards Mixing machine-mixing is resorted to. For a sand and cement mortar the only machine mixers that will give satisfactory results are those of the trough and paddle type, in which the material is fed into the horizontal metal trough and mixed by a series of paddles actuated from a central shaft. AMOUNT OF WATER AND SIZE OF BATCH. The amount of water necessary to produce a mortar of the proper consistency is a most important item in cement pipe making. In order that the moulds may be removed as soon as the pipe is formed, the mortar must of necessity be of a "dry consistency." In the Consistency degree of "dryness" lies the secret of making an impermeable pipe, of The consistency of a mortar for hand-made pipe is usually specified mortar as that of "damp sand." This term is, however, not sufficiently specific. It will be more definite to say that the consistency shall be such to just allow the moulds to be removed from the pipe with- out adhering to it, and so wet that the pipe will just stand without sagging. In order to properly compact the sand and cement mortar there Water for must be present, in addition to the water necessary for proper hard- / ening, an amount of water which will serve as a lubricant and allow 156 GOOD CONCRETE the sand grains to become coated with a paste of cement, and to slip on one another into the most compact position. The most common error committed by pipe-makers is to use too dry a mortar. It is only by using the right amount that the full strength of the pipe can be developed. Evaporation The proper degree of water must be maintained, and to this end from * ne s i ze f a batch should be such that the water will not evaporate mortar before the mortar is moulded into the pipe. In Summer it will take but a very few moments to evaporate from 1 to \2% of the water in a mortar. Care should therefore be exercised to prevent this evaporation by providing suitable working sheds under which the work is done. CURING THE PIPE. The green pipe should be protected from strong drafts and direct sunlight. Water is constantly applied in a fine spray to the pipes as soon as they are a few hours old. The pipe should be cured for at least three weeks before placing in the ground. LAYING. The properly cured pipe are laid in a trench excavated to grade. Each joint is carefully cleaned and soaked with clean water. A mortar consisting of 1 part sand and 1 part cement of the con- sistency of putty is then applied to the tongue and groove and the pipe brought together. The exterior is then covered with this same mortar, to cover the joint, and finished by wiping with the gloved hand. The inside of the joint must also be "wiped" smooth. GENERALLY. The bedding of the pipe in the trench is a very important opera- tion and one to which too little attention is usually paid. If the pipe is not carefully bedded by properly back filling around GOOD CONCRETE 157 the entire lower half the earth will arch and leave a portion of pipe unsupported. Any settlement that takes place will then crack the pipe. Proper bedding is important even in cast iron pipe. The pipe line should be supplied with air vent valves at all points where there is a change in the grade. All valves for controlling the flow of the water should be of such design that in closing they do not produce a water hammer. Stand pipes with proper valves should be provided at proper intervals as a relief for any pressure in excess of the safe working strength of the pipe. Hand-made pipe may for lines carrying a high pressure be rein- forced with hoops of wire, which are dropped into the moulds while forming the pipe and spaced about 1 J/2 inches apart. Reinforced concrete pipe should only be made in accord with plans furnished by a competent engineer. UNITS OF MEASUREMENT USED IN MEASURING WATER. The Federal Government uses the cubic foot per second for Cubic feet measuring all water. Engineers generally use the same unit. A P ejr cubic foot per second, or "second foot," is the amount of water that second will flow past a point in a channel having a sectional area of 1 square foot with a velocity of 1 foot per second. In California there is a local unit used termed the "Miner's inch." ' " e m *n er 5 A miner's inch has two values. The old, and most generally used, mc " value is equivalent to 1/50 of a cu. ft. per second. The new value, which was defined by the California Legislature of 1 90 1 , places the equivalent of a miner's inch at 1/40 cu. ft. per second. The old value is, however, most generally used, and in contracts for a water supply, unless otherwise specified, the old miner's inch is the accepted unit. VALUES OF ONE CUBIC FOOT PER SECOND. 1 cu. ft. per second = 50 Old Miners' inches = 8.97 gals, per min. 1 cu. ft. per second = 40 New Miners' inches = 1 1 .22 gals, per min. 1 cu. ft. per second = 448.8 gals, per min. = 646.272 gals, per day (24 hours) 1 cu. ft. per second is approximately one acre covered one inch in depth per hour. 1 cu. ft. per second is one acre covered 1 .98 feet deep in 24 hours. 160 GOOD CONCRETE U O 1 ^ CD CD CD GO CD > * CNOO OO CD co CD m mO xOOco--r^coo^ CD m mO m o CNJ i^ CN CN co QOvDu^aOfNOfOOOmOOOOOOO Oip>Tr\' 31 yiCNC^in >O O O '""S" co OO CNQOO N f^'O^OO v OCNir\^r'^J - cOcocN O ~ OOOoOOOvOOOOOpcOvO^-CNp oOO^t'OO too CNOio cooOO OvOcvjcO^TO OvOaOOO co-3-sOaO ;S d^ \O cvjco ^ O CNCOCNCNCNOCN CNCN CN CN CN CO ao O 1J0001 CNCNCNCNCNCO 162 GOOD CONCRETE 1 cu. ft. of water weighs 62.5 pounds. 1 cu. ft. of water contains 7.48 gallons. I Acre Foot is one acre covered with 1 foot of water. 1 Acre Foot=43,560 cu. ft. To use To Use Table: Let it be required to find the size of pipe neces- table sary to carry 30 miner's inches (old) of water when the pipe line is 2,500 feet long and having a total fall of 10 feet. First reduce the total fall to feet fall per 1 ,000 feet. Thus 10 feet fall in 2,500 feet of line is equivalent to 4 feet per 1 ,000. In the first column of table find "4 feet," and on the same horizontal line opposite find the number under "Miner's inches" which is next larger than 30. This is found to be 34.15, and this corresponds to an 8" pipe. PLAIN CONCRETE PIPE TABLE Size w< pa h. Ti.ickr., of Contents in cu. ft. prr Lin. ft. Pipe per cu. yard Lin. ft. perbbl. Lin. ft. perbbl. Lin. ft. perbbl. Wet Dry Shell Linear ft. Sand&Grav. 1:3 Mix 1:4 Miz 6" 23# 20# IV ,16 138 75 87 100 8" 10" 36 53 31 44 !%- .25 .35 88 62 48 34 56 40 s 12" 70 57 IK" .45 48 26 31 35 14" 88 68 }%' .56 38 21 24 28 16" 103 90 ]%'" .68 32 17 20 24 18" 130 100 \%" .82 26 14 17 19 20" 136 114 \% " .90 24 13 15 17 22" 176 141 2 " .05 20 11 13 15 24" 220 163 2X" .30 18 9 10 12 26" 225 180 2X " .40 16 8 10 11 28" 30" 265 286 208 225 2H" .66 .80 14 12 7 6 7 9 8 32" 333 260 3 " 2.08 10 5 6 7 36" 408 320 3 " 3.55 8 4.7 5 6 GOOD CONCRETE WEIR TABLE Giving Cubic Feet of Water per Minute that will flow over a weir one inch wide and from 1 A to 20% in. deep. For other widths multiply by the width in inches. In. Cu. ft. #in. Cu.ft. #in. Cu.ft. H in. Cu.ft. Kin. Cu.ft Kin. Cu.ft. X'm. Cu.ft. * % in. Cu.fl. .00 .01 .05 .09 .14 .19 .26 .32 1 .40 .47 .55 .64 .73 .82 .92 1.02 2 1.13 1.23 1.35 1.46 1.58 1.70 1.82 1.95 3 2.07 2.21 2.34 2.48 2.61 2.76 2.90 3.05 4 3.20 3.35 3.50 3.66 3.81 3.97 4.14 4.30 5 4.47 4.64 4.81 4.98 5.15 5.33 5.51 5.69 6 5.87 6.06 6.25 6.44 6.62 6.82 7.01 7.21 7 7.40 7.60 7.80 8.01 8.21 8.42 8.63 8.83 8 9.05 9.26 9.47 9.69 9.91 10.13 10.35 10.57 9 10.80 11.02 11.25 11.48 11.71 11.94 12.17 12.41 10 12.64 12.88 13.12 13.36 13.60 13.85 14.09 14.34 11 14.59 14.84 15.09 15.34 15.59 15.85 16.11 16.36 12 16.62 16.88 17.15 17.41 17.67 17.94 18.21 18.47 13 18.74 19.01 19.29 19.56 19.84 20.11 20.39 20.67 14 15 20.95 23.23 21.23 23.52 21.51 23.82 21.80 24.11 22.08 24.40 22.37 24.70 22.65 25.00 22.94 25.30 16 25.60 25.90 26.20 26.50 26.80 27.11 27.42 27.72 17 28.03 28.34 28.65 28.97 29.28 29.59 29.91 30.22 18 30.54 30.86 31.18 31.50 31.82 32.15 32.47 32.80 19 33.12 33.45 33.78 34.11 34.44 34.77 35.10 35.44 20 35.77 36.11 36.45 36.78 37.12 37.46 37.80 38.15 CHAPTER X. CEMENT SEWER PIPE. The attributes of Portland Cement concrete which have found for it such a widespread use as a material for the construction of monolithic sewers would most naturally recommend it for sewer pipe of smaller cross-section. The economies to be affected by the use of separately moulded concrete pipe are such as would certainly entitle it to consideration in competition with pipe of other materials. That there have been a great many wretched cement pipes made in the past cannot be denied, nor can the same be denied for terra cotta pipe. In the early days of the cement pipe industry, Portland Cement was both expensive and uncertain in quality, and the condi- tions were not so favorable for good concrete as they are today. To sweepingly condemn cement pipe on the failures of the first attempts without analyzing the causes of these failures is not only unjust but unintelligent. WHAT Is NEEDED FOR GOOD CEMENT SEWER PIPE. The principles of cement pipe construction for irrigation hold also for sewer pipe. A sewer pipe will be subjected to different service conditions than will an irrigation pipe. Its constituent ma- terials should therefore be so selected as to meet the requirements 166 GOOD CONCRETE of these conditions. A sewer pipe must, first of all, be impermeable, Necessary and the relatively greater depths at which it is usually imbedded strength under the ground surface will necessitate a somewhat stronger mix- ture than is customarily used for making irrigation pipe. Cause of Th fi most common cause of collapse of both terra cotta and cement collapse sewer pipe is the lack of care used in bedding the pipe in the sewer trench. With careless back-filling and tamping, the earth arches and leaves a portion of the lower segment of the pipe unsupported, which, when the depth of fill is sufficient, will cause the pipe to crack. Impermeability Impermeability can only be obtained by using a comparatively depends upon wet mortar or concrete. The pipe may also be given a wash on the consistency the interior with neat cement cream. Impermeability, however, to of the mixture be of a lasting value, must be obtained in the making of the pipe rather than in subsequent treatment. Impermeability will depend upon the degree to which the voids in the sand or the aggregate are filled with cement paste, and upon the use of the proper amount of water in mixing. CEMENT SEWER PIPE IN EUROPE. The manufacture of separately moulded cement sewer pipe has in Europe become a highly organized industry. The European manufacturer of this class of pipe does not confine himself to circular sections, as does the American. For the larger sizes of pipe the section is sometimes egg-shaped, with a flat base to allow the proper bedding. The ease and perfection with which the European cement pipe-maker produces Y's, T's, elbows and siphons of large and small diameter would indicate that the sewer pipe industry in Europe has reached the dignity of an art. The extent to which cement or concrete pipe is used in Germany may be realized when we consider the words of a very prominent German sanitary engineer, who in a recent lecture made a remark that brick as a material for constructing sanitary sewers was only of historic interest! PLATE XXX. SEPARATELY MOULDED CONCRETE SEWER PIPE, KOENIGSBERG, PRUSSIA. GOOD CONCRETE 167 Perhaps the largest sewer in existence built of separately moulded concrete pipe is that in Koenigsberg, in Prussia. The pipe here are 7 feet 3 inches in internal diameter with a shell thickness of 6". MACHINE-MADE CEMENT PIPE. Within the past few years cement sewer pipe has been very suc- cessfully made by machine. The machine-made product possesses marked advantages over the hand-made. The so-called glazed cement pipe machine produces a product whose density and imper- meability leave nothing to be desired. The principle of this machine is a revolving core, which not only serves to compact the mortar, but to give the interior of the pipe a polished troweled surface. It was the product of this machine which recently in San Diego vindicated the cause of cement sewer pipe. The adoption by the municipal authorities of San Diego of cement sewer pipe was so bitterly resented by the competitors in terra cotta that in self-justification the city engineer had to resort to the unprecedented procedure of testing, every single piece of pipe for a length of several miles. RESULTS OF A PUBLIC TEST MADE AT THE SAN DIEGO INDUS- TRIAL FAIR, FEBRUARY 24, 1913. 8" Vitrified Cla\) Pipe. 8" Glazed Cement Pipe. No. 1. With 15 Ibs. pressure, No. 2. Subjected to 15 Ibs. commenced to seep in 3 pressure for 5 minutes minutes and broke at 55 and broke at 80 Ibs. Ibs. pressure. pressure, with no seepage N. 3. Small seepage in 5 min- utes under 1 5 Ibs. pres- whatever. No. 4. Subjected to 15 Ibs. sure. Broke at 65 Ibs. pressure for 4 minutes pressure. and broke at 1 1 5 Ibs. No. 5. Under 15 Ibs. pressure, showed seepage in 1 minute and broke at 73 pressure, with no seep- age whatever. No. 6. Pressure was held at 1 5 Ibs. pressure. Ibs. for 3 minutes, then slowly run up to 125 Ibs., then in jumping, the pressure to 150 Ibs. the pipe broke. No seepage whatever. 168 GOOD CONCRETE The results of these tests have been given wide publicity and have served to not only justify the Municipal authorities, but to effectually silence the "influences" through whose efforts these tests had to be undertaken. The pipe used in the above tests was selected from "stock" and each manufacturer knew that the specimens were to be used for a public test. The favor with which machine-made cement sewer pipe is regarded by the foremost in the engineering profession will be realized by quot- ing the testimony given before the San Diego City Council in the sewer controversy. The late James Dix Schuyler as a witness was examined by Councilman Adams. Q. (by Mr. Adams) : Mr. Schuyler, what do you think of the pipe you saw being made for the City of San Diego? A. (by Mr. Schuyler) : I think so well of it that I would use it in preference to any vitrified clay pipe. Q. (by Mr. Adams) : Mr. Schuyler, that is a strong statement and you are a man of international reputation. Do you realize that your statements are being recorded and will become public? Would you be willing to stake your reputation on the use of cement pipe for sanitary sewers? A. (by Mr. Schuyler) : If I could get such machine-made pipe as I have seen here, I would. In hand-made pipe there is likely to be more variation, but this pipe is remarkably uniform. Q. (by Mr. Adams) : What is your opinion of the effect of sewer gases on cement pipe? A. (by Mr. Schuyler) : I have not had much actual experience, but have read considerably about it. My opinion is that the gases in sewers cannot affect a dense cement pipe such as this is. Q. (by Mr. Adams) : You say that you would prefer this pipe to vitrified clay pipe? A. (by Mr. Schuyler) : Yes, sir. GOOD CONCRETE Q. (by Mr. Adams) : If you were City Engineer of San Diego, would you use this glazed cement pipe for the city sewers and recom- mend its use to this City Council? A. (by Mr. Schuyler) : Yes, sir ; I would do so without any hesitation. Mr. Schuyler was then examined by Attorney H. J. Stevens. Q. You have had a great deal of experience with cement, have you not? A. Yes, sir; for many years. Q. I believe you built the Sweetwater Dam? A. Yes, sir. Q. Have you ever made any tests yourself in order to bring out the qualities of vitrified clay pipe as compared with cement pipe? A. I have made tests, and very recently. Specimens of vitri- fied clay pipe were procured from an inspector of the street de- partment of Los Angeles. My representative went to a point where a sewer was under construction and procured pipe which had been accepted as passing the Los Angeles city specifications, and which were lying by the side of the trench ready to be laid in place. Care was taken to choose the specimens having a particularly fine glaze. I have been told they were "top" joints, meaning that they were burned in the top tier of the sewer pipe kiln, and, as a consequence, received the most intense heat and the heaviest salt glaze. When this pipe was submitted to the test to determine permeability that is, filld with water under pressure I was astonished to see the water percolate freely through the shell of the pipe at from 5 to 10 Ibs. pressure. At 1 5 Ibs. it shot out in every direction in innumerable fine streams. If you gentlemen had seen this test, your confidence in clay pipe would have been shaken as mine was. The results were shocking, yet I can vouch for the absolute fairness of the test, except- ing that the specimens were considerably above the average in quality. 170 GOOD CONCRETE One or two sections of merely average pipe which had been ac- cepted by the City of Los Angeles were submitted to the test described above. In one case it was impossible to move the needle on the pressure gauge, as the water flowed through the porous shell of the pipe so freely that no pressure could be procured." The various manufacturers of machine-made cement sewer pipe will, to our definite knowledge, guarantee their product to be as im- permeable and as strong as the best vitrified clay pipe, and they will welcome the opportunity of having their product publicly tested against vitrified clay pipe of the same size. CHAPTER XI. SOME SUGGESTIONS FOR THE CARE AND RETURN OF EMPTY SACKS. Like any other commodity, cement makes its special requirement of everyone concerned in handling it, whether it be the consumer, the dealer or the manufacturer. We can appropriately conclude this book on the correct usage of Portland Cement with some remarks upon its peculiarities as an article of commerce. CARE OF SACKS. The sacks in which cement is shipped are perishable property of a Sacks highly valuable nature, employed because of necessity by the manu- are facturer of cement to convey his product to the consumer of cement. Disregard of the business principles underlying the transaction is sure to result in loss and discontent to him who neglects them. The best statement of these principles that we have ever seen was made by Mr. L. T. Sunderland, Vice-President of the Ash Grove Lime & Portland Cement Co., before a meeting of the Retail Lumber Dealers of Kansas on September 15, 1912. We reprint his paper, entitled: SACK LOSSES WHO SHOULD BEAR THEM? "Many cement users contend that worn-out and unserviceable cloth sacks should be redeemed, and the loss incident to wear and tear, losses 172 GOOD CONCRETE abuse and misuse while in service, should be borne by the manufac- turer whose brands such sacks carry. "Such a contention is often based on the erroneous assumption that manufacturers (a) Use cloth sacks for their own convenience. (b) Make a large profit on them; and (c) Merely loan them to the purchasers of cement to be returned when empty. "As not one of these assumptions is correct, such a conclusion must fall. "The facts are: Why a "First. Manufacturers use cloth sacks from sheer necessity, there cloth sack? being no other package that can be substituted without imposing in- creased burdens upon the dealer in, or user of, cement. There are two other kinds of packages that have been used to a limited extent, viz: Wooden barrels and paper bags. Barrels "Wooden barrels are out of the question because of increased cost of packing the cement into them; the large initial cost of the barrel itself (35 to 40 cents each) ; the inconvenience in handling a pack- age weighing 400 pounds, especially on large work; the increased cost represented by freight on weight of each barrel (approximately 25 pounds) ; and the increased cost of the cement to the dealer and user because the barrel cannot be returned. It will be seen, there- fore, that the use of the wooden barrel would entail a direct addi- tional tax on the dealer or user all items considered of approxi- mately 40 cents per barrel. There were 78,000,000 barrels of cement produced in the United States in 1911, and if all had been packed or shipped in wooden barrels the additional cost of that cement to the ultimate consumer would have been $31,200,000 on that one year's production. Paper bags "Paper bags are used to a very limited extent. They cost the manufacturer 10 cents per barrel (four bags to a barrel), and the GOOD CONCRETE 173 additional burden to the dealer and user is represented by this 10 cents per barrel, plus the loss resulting from breakage in transporta- tion and handling, which is large (probably 5 cents per barrel) and very annoying. The shippers will not be responsible for damage to paper bags, which at best are too weak for the load they carry, and, on the whole, paper bags, which cannot be saved or returned, impose an additional and wholly unnecessary burden of approximately 1 5 cents per barrel all items considered on the ultimate consumer, which, when applied to the 78,000,000 barrels of cement produced in 191 1, would represent $1 1,700,000 for one year. "The cloth sack is the only practical package available. It will stand transportation, its size and shape make it convenient to handle, and it is returnable at the option of the dealer. If properly cared for it may be used over and over again many times. "The use of the cloth sack (which, as shown below, places a bur- den on the ultimate consumer of only 5 cents per barrel), when proper/]; handled, is a source of little, if any, loss to the dealer save the cost of bundling and prepaying freight to the mill. (A dealer should not accept from his customer any but serviceable sacks all serviceable sacks are accepted by the manufacturer; therefore if the dealer sustains losses of any consequence it is his own fault.) "Second. Manufacturers do not make a profit on the cloth sacks; on the contrary, they usually sustain serious losses. The price of standard cloth cement sacks today is approximately $100 per thou- sand (10 cents each) in carload lots, and the cost of the material from which they are made is increasing. The best cement manufac- turers have facilities for cleaning and repairing sacks, and give deal- ers full credit for all sacks that may be readily repaired. This is a large expense, borne altogether by the manufacturer; hence it will be seen the manufacturer sustains an actual loss, which at times is quite serious. "Third. When a miller ships flour he sells the package (sack or barrel) with the flour, but the packages are not returnable. Like- 1J74 GOOD CONCRETE wise with lime the barrel (or sack, if hydrated lime) is included in the price. With cement, as with flour and lime, the price includes the packages which are sold with the cement. The sacks are not loaned, but are sold outright. The dealer is under no obligation to return them, but the manufacturer extends the dealer the privilege of so doing if he chooses, at a certain price under certain conditions. "Cloth sacks wear out largely while in consumer's hands, therefore the consumer should bear the loss incident thereto. "If a cloth cement sack can be used eight times, as it may be if properly cared for and returned promptly when empty, the loss or burden imposed upon the ultimate consumer from the use of cloth sacks is only five cents per barrel, which is only one-third the burden imposed by the use of paper bags, and one-eighth the burden im- posed by the use of wooden barrels. "Cheaper cloth sacks than those now used for carrying cement are out of the question, because they are too frail and weak to stand transportation and protect the heavy weight of cement." RETURN OF EMPTY SACKS. Empty sacks Western Classification Exception Sheet provides that all empty must be sacks must be prepaid before acceptance by carriers, and this rule Prepaid will be rigidly enforced in future. The Southern Pacific, Santa Fe, S. P., L. A. & S. L., and Pacific Electric Railway Companies have all taken a firm stand in this regard, and we call your attention to the rule to avoid misunderstanding and consequent delay. The Riverside Portland Cement Company prints a set of rules for the guidance of its customers when returning empty sacks, a copy of which is furnished with every car of cement. The instruc- tions given on the placard are quoted below, and the illustrations reproduced. How TO BUNDLE SACKS. How TO BUNDLE SACKS. D GOOD CONCRETE 175 How TO SHIP EMPTY SACKS. Empty sacks are valuable property and should be handled care- How to fully at all times. It is important that they should be, made up into s/iip empty tight, strong bundles, and tagged with the best grade of linen tags, sacfc completely filled out, so that each bundle in the shipment may be fully identified. All railroads recognize the importance of proper bundling and tagging and have rules providing that bundles which are not properly marked and] bound shall not be accepted for trans- portation. The instructions given below are based on the railroads' rules and it is necessary to follow them for this reason, as well as for your own protection. BEFORE BUNDLING SACKS. Cull out all sacks that have been wet or in which the cloth has Do not ship become weak or rotten. They are not worth shipping. rotten or Cull out all sacks that do not bear the brand of the manufacturer to * whom you are shipping. They will not be credited. Cull out all sacks that show signs of deliberate misuse, such as sacks that have been cut open to remove the cement and sacks that have been soiled by using them to carry other materials, such as clay, lampblack, dry colors, etc. They are not worth paying freight on. How TO BUNDLE SACKS. Lay the sacks out flat, in piles of 50 each. How to Pass a wire or rope, 40 inches long, under each end of the pile, ^ ^ and lay a third wire or rope, 8'/2 feet long, lengthwise on top of the pile, as in Figure A. Rope must be at least 3-16 of an inch thick- Bring the two short wires or ropes up over the pile of sacks and tie them tightly as in Figure B. This will roll or double the sacks over the long rope. Turn the bundle over. Bring the ends of the long rope around the ends of the sacks. Take hitches with the long rope around the two short ropes that already been tied. 176 GOOD CONCRETE These hitches will keep the short ropes from being slipped over to pull any sacks out of the bundle. Then cross the long rope in the middle, as in Figure C, bring it around the middle of the bundle and tie tightly, as shown in Figure D. This will make a bundle that will stand rough handling. It will be light and convenient to carry, so that no one will be tempted to drag it. If the ropes are tied tightly it will be next to impossible to pull any sacks out of the bundle. It is a good practice to put one of your business cards, letter heads or a tag with your name on it inside each bundle, as this will enable the consignee to identify your property even if the tag should happen to be detached. How TO TAG BUNDLES. Tag all Use nothing but linen lags, preferably those furnished by the manu- bundles facturer to whom you are returning the sacks. Fill out all the blank spaces on both sides of every tag. Fasten the tag securely to the bundle, with wire, as shown in Fig- ure C or Figure D. How TO SHIP SACKS. See that the destination on the bill of lading is an exact copy of the destination shown on the tags, and have it written out in full. Do not allow it to be abbreviated or cut short. Prepay the freight. Prepay the Be sure that the amount of freight you pay is shown on the bill freight on of lading. returned sacks , , , , . , . , , Send, to the parly to whom the sacks are being snipped, me orig- inal bill of lading and a letter saying how many sacks are in the shipment. GOOD CONCRETE 1 77 There is a very good reason for every suggestion made above, and we earnestly recommend that you tack up this circular where it can be seen by the people who handle returned sacks. Return sacks to our mill at Riverside if by Southern Pacific Ry. Return sacks to our mill at Riverside if by Santa Fe Ry. Return sacks to our mill at Crestmore if by Salt Lake Ry. You can depend upon getting a square deal from us in all mat- ters pertaining to sacks, but to follow the above rules simplifies mat- ters enormously and saves money for all concerned. OUR METHOD OF LOADING CARS. We weigh each empty freight car to obtain the correct tare. We Correctness load the cement into the car direct from the packing room under a of our checking system which gives us three independent tallies upon the con- weights tents of the car. When the loading is completed a tally sheet is made and fastened to the inside of the car for the consignee's convenience in checking the out-turn of the car. The car is then weighed with the load, which must verify the loading tally, or the car is not al- lowed to go forward. We operate under the Trans-Continental Weighing & Inspection Bureau Agreement No. 30, and our weights are obtained by sworn weighmasters. All chance for error in count of shipments is re- moved before the bill of lading is issued. UNLOADING. We attach a Red Sticker to each bill of lading to furnish con- signees with instructions as to the proper method to follow upon arrival of shipments at destination. A copy of this notice follows: "Please check the contents of this car with the LOAD- ING CARD which is tacked inside the car. The contents have been checked by us and weighed by a sworn weigh- master. Get the RAILROAD AGENT to acknowledge any shortage by a notation on the FREIGHT BILL. No claim for a shortage can possibly be entertained unless both 1_78 GOOD CONCRETE the FREIGHT BILL and the LOADING CARD are sent us bearing the proper notations made by the RAIL- ROAD AGENT. When there is no agent at the destina- tion, any variation from our loading must be verified by two responsible parties, and a record made of the condition of the seals on the car." PAYMENT OF FREIGHT. We sell cement f. o. b. cars at destination conditionally upon con- signees paying the freight charges and deducting the amount from in- voice value of the shipment. We prepay freight charges to prepay or non-agency stations only, and immediately render cash bills to consignees for freight charges thus advanced. CAR SHORTAGES. In periods of car shortage we attach another "Sticker" to bills of lading, which reads as follows: PONT DELAY! DO IT NOW! UNLOAD THIS CAR! CARS ARE SCARCE AND GETTING SCARCER. OUR ABILITY TO FURNISH CEMENT IS REGULATED BY THE RAILROAD'S ABILITY TO FURNISH CARS. ORDER LARGE CARS AND UNLOAD PROMPTLY GENERAL INFORMATION. Our plant is located at Crestmore, Cal., on the line of the Crescent City Railway Company, having direct connection with the Southern Pacific. A., T. & S. F., and S. P., L. A. & S. L. lines. We can make delivery to all points via these lines or their connections. Our office is at 640 Title Insurance Building, in the City of Los Angeles. Our telephone number on the Sunset is Main 5753 and on the Home is 10527. A Private Exchange will connect you with all -ity warehouses as well as with office departments. GOOD CONCRETE 179 APPENDIX. I. OTHER PUBLICATIONS. In addition to "Good Concrete," the Riverside Portland Cement Company issues printed matter upon special subjects which it will cheerfully furnish to applicants at its office on the Sixth Floor of the Title Insurance Building, Los Angeles. Selections can be made from the following list: Bulletin No. 1. Concrete Building Blocks. Bulletin No. 10. Concrete Surface Finish. Bulletin No. 18. Reinforced Concrete Chimneys. Bulletin No. 19. The Use of Cement in Sewer Pipe and Drain Tile Construction. Bulletin No. 20. Mixing and Placing Concrete by Hand. Bulletin No. 21. Concrete Silos. Bulletin No. 22. Cement Stucco. Bulletin No. 23. Concrete Tanks. Bulletin No. 25. Concrete Poles. Bulletin No. 26. Concrete in the Country. Bulletin No. 27. Concrete School Houses vs. Fire Traps. Standard Specifications for Portland Cement Sidewalks. Standard Specifications for Cement Hollow Building Blocks. Standard Building Regulations for the Use of Rein- forced Concrete. Standard Specifications for Concrete Road and Street Pavements. Standard Specifications for Portland Cement Curb and Gutter. Standard Methods of Testing and Specifications for Cement. INDEX Adobe As Sub-base for Sidewalk 75 Aggregate Definition '- 1 7 For Sidewalks 84 For Curb and Gutter t 02 For Roads 119 In Concrete Law 41-42 Materials for 1 8-20 American Society of Civil Engineers Standard Methods for Testing Cement 130 American Society for Testing Materials Specifications for Portland Cement 11-102-138 Asphaltic Oil Wearing Surface I 32- 1 42- 1 46 (See Wearing Surface.) Asphalt Roads Cause of Destruction 1 12 Concrete for Rigid Foundation 112 (See Road and Pavements) Axioms Concrete 8 Basalt as Aggregate- 18 Beaver Board ... 80-82-102 Behavior of Concrete towards Metals 60-61 Bituminous Wearing Surface 1 13 Boiling Test for Cement--- 14 Bonding Concrete 52 Briquette Tensile Strength ... 12-131 Cars, Methods of Loading 177 Methods of Unloading - 177 Shortage 178 Cement Asphaltic .. 143 Cement Paste 34 Covering for Protection 95 182 INDEX Expansion and Shrinkage in 34-79-101 Effect of Sea Water on ... 62 Rules for Use of - 8 Test Pats of .-131 Chemical Influences 59-60 Coloring Cement 92 Concrete Consistency .-45-58-105 Definition 17-48 Effect of Weather 53-54 Mixing - -.48-51-105 Proportioning 3 7-42-85-1 04 Strength 53 Size of Rock ... - 19 Concrete Bonding of Old and New 52 Depositing - 51-52-89-105 Frozen 54 Hardening - 53-54 Tamping 51 Concrete Crazing 56 Effect of Alkali and Sea Water on - 64-66 Expansion and Shrinkage of 54-79-101-115 For Sidewalks 73 Resistance to Chemical Influences 59-60 Concrete Axioms 8 Concrete Construction 8 Concrete Law 26-37-40-42 Application 44-47 Considiere and Shumann - - .. 55 Consistency (see Mortar). Construction of Curb and Cutter 104 Cracks In Sidewalks 79-80 Crazing 56 Crown for Concrete Roads I 18 Curbs and Gutters 101-108 Construction of 1 04 Dimensions 103 INDEX ,83 Expansion and Shrinkage | Q \ forma j Q3 Proportions of Concrete j Q4 Specifications .. 102-104 Sub-grade j Q2 Wearing Surface | Q6 Cyclopean Concrete | 9 Depositing (see Placing). Drainage Of Sidewalks 78 Draw Cracks -- 55 Expansion Joints 1 1 7-1 29 Expansion of Cement 54 In Concrete Road Beds 1 15 In Curbs and Gutters 101 In Sidewalks 79 Fills As Foundation for Sidewalks 78 As Foundation for Gutters 103 Floors Laid on Hardened Concrete Base 93 Forms for Concrete For Cement Sidewalks 89 For Gutter and Curb 103 For Roads ... -.130-137 Treatment of 5 1 Foundation For Concrete Roads 127 For Sidewalks --73-78 Fuller, Mr. W. B 40 Grade for Gutter 102 Grading for Concrete Roads 126 Granite as Aggregate --- 18 Gravel As Aggregate 20-85 Gravel Pits 21 Hardened Concrete Behavior toward Metals ... 60 Mineral Oils 60 Resistance to Chemicals Resistance to Sea Water 61-62 184 INDEX Sewage ; 60 Vegetable Oils 60 Hardening of Cement 14-1 5 Irrigation Pipe I 52 Laitance ... 1 5-46-52 Limestone as Aggregate 18 Screenings 84 Laying Cement Pipe ----156 L. A. County Highway Commission ....114 Macadam (see Road and Pavements). (See Asphalt.) Machine Concrete Mixers .---50-51 Magnesia in Portland Cement ... - 12 Marking of Sidewalks 80 Measurements of Density --- - 57 Mechanical Analysis --25-44 Mechanical Analysis Curve .. 26-30 Michaelis, Sr 14-15 Miner's Inch - - -159-162 Mixing Concrete -- 48 By Hand - 49 For Irrigation Pipe 155 For Roads 120-127 For Sidewalks - 1 87 Machine Mixing 50 Mortar Color 92-106 Consisting of 45-87-155 Density of 34 Expansion and Shrinkage in --- -.--54-79-101 Mixing 87-106 Proportioning for Curb and Cutter - ----106 Proportioning for Sidewalk 86 Strength due to Sand 25 Oil, Asphaltic As Wearing Surface of Roads : 132-140 Specifications -- ---133 Solubility 1 134 Test for Asphalt ... ....135 Temperature 135 INDEX 185 Parting Strips for Sidewalks 82 Pipe, Cement for Irrigation Advantages of | 5 1 Curing 156 Laying 1 56 Specifications 153 Valves 157 Pipe, Cement for Sewer Consistency - | 66 In Europe 1 66 Machine Made 167 Specifications 1 65 Placing Concrete and Mortar 58 For Curbs and Gutters 105-106 For Roads 1 2 1 For Sidewalks 89 Road Foundation 121-128-139 Portland Cement Application of -- 7 Definition 1 1 For Concrete Roada 130- 138 Hardening 14 Neat -- 12 Specific Gravity 12 Standard Specifications - Setting Time - -.13-130 Strength 14 Proportioning Concrete By Voids 35 By Trial --39-40 Concrete Law 40-42 For Curbs and Gutters 104 For Roadbeds 119-127-138 For Sidewalks 87 Methods of .. 37-42 Protection of Concrete For Roads 121 For Sidewalks ... General Rules for 9 186 INDEX Riverside Portland Cement 1 02 General Information 1 78 Publications I 79 Roads and Pavement, Concrete Advantages of 113-114 Bituminous Wearing Surface 1 13 Crown I | 8 Expansion and Shrinkage 1 15-117 One Course and Two Course 113 Quality of Concrete Necessary for 114 Specifications for 1 | 5 Wear of Roads M4 Roads and Pavements, Concrete 117 Aggregate - -.119-131-132 Expansion Joints I 17 Mixing Concrete 120-127-139 Proportions for - 118-177-138 Protection after Placing 121-140 Roads and Pavements, Concrete Asphaltic Oil Wearing Surface Specifications 125-132-142 Forms 130-137 Foundation 127 Grading 126-137 Placing - -.121-128-139-146 Proportions - 127-138 Rock Difference between Rock and Sand I 7 Effect of Size upon Strength of Concrete -- 19 Voids ... 3 1 -33-38 (See Mortar.) For Curbs 1 02 For Roads 132-138 For Sidewalks 84 General Character I 8-20 Sacks Advantages of Cloth - 1 72-1 74 Return of Empty 174-177 Value of 1 7 1 Sand Asphalt Wearing Surface 1 45 INDEX 187 Description of 2 1 -2'6 For Curbs 1 02 For Roads 131-138 For Sidewalk 84-85 General Character 2 1 -25 Irrigation Pipe 1 53 In Asphalt 1 42 Testing of (see Aggregate) 8 Specifications (see Mortar) 46 Voids - 31-33 Sandstone as Aggregate 18 Schutte, A. E 40 Screenings, Rock For Asphaltic Wearing Coat of Roads 133 For Sidewalks 84 Used as Sand 30-31 Sea Water Effect on Concrete 6 1 -64-66 Remedies 62 Setting of Cement Time of 13-130 Shrinkage of Cement 34 In Concrete Road Beds 115-117 In Curbs and Gutters -101 In Sidewalks 79 Sidewalks, Cement ... 73-98 Advantages of 73 Adobe Foundations 75 Air Bubbles - 94 Cause of Defects ... 97-98 Coloring Consistency of Concrete for - Covering for 93-94-95 Drainage of 78 Dusting of Finishing of 92 Foundations for - 73-78 Guide Strips Marking of 80-93-94 On Fills 78 188 INDEX Parting Strips --- ... 82 Placing Concrete and Mortar 89 Placing 91 Preparation of Concrete and Mortar---- ... -82-86 Proportions for 87 Prevention of Cracks in -- 79 Wearing Coat 86-87 Sieves 2*5 Standard Mesh 1 3 1 Sizing of Particles of Sand 23-24 Specifications for Concrete Roads (with Asphaltic Wearing Surface) City of Glendora 1 25 L. A. Highway Com -137 Specifications for Curb and Gutter 102-104 Specifications for Portland Cement 1 I Specifications for Sidewalks 73-98 Specifications for Street Paving, in City of Los Angeles --..142 State Highway Commission I 1 4 Sulphuric Anhydride in Portland Cement -. 12 Tables I. Showing Relation between Diameters and Total Surface Areas in One Cubic Yard of Material 24 Tables II. Tests Showing Effect of Size of Grain on Strength of Mortar 25 III. Table of Sieves and their Meshes 25 Tables IV. Tests Showing Relation of Mechanical Analyses and Strength of Mortar 27 V. Table of Specific Gravities and Weight of One Cubic Foot Solid--. 32 Table VI. Voids for Different Weights per Cubic Foot * 33 Table VII. Amount of Plastic Mortar from One Sack of Cement 35 Table VIII. Table Showing the Sizes Necessary to Produce Densest Concrete -- 43 Table IX. Compressive Strength of Average Concrete Made at U. S. Arsenal, Watertown, N. Y 54 Table X. Showing Normal Changes in Volume, Inches per 100 Feet of Length 55 INDEX 189 Table XII. Weights per Cubic Yards of Different Aggregates 67 Table XIII. Percent of Shrinkage in Rock and Screenings 68 Table XIV. Table of Quantities for One Cubic Yard of Concrete Rammed in Place- 69 Table XV. Sidewalks Quantities for Base 88 Sidewalks Quantities for Top 88 Table XVI. Weight of Coloring Matter per Sack of Cement 90 Table XVII. Barrels of Oil per 100 Feet of Roadway, Cubic Yards Screenings 122 Quantities of Concrete 1 22 Table of Proportions For Cement Irrigation Pipe I 62 Table XVIII. Amount of Water Flowing Through Cement Pipe Running Full 161 Tamping Concrete 5 1 Trap as Aggregate 1 8 Screenings 84 Temperature Expansion and Contraction from I 01-116 Effect on Strength of Concrete 54 Of Oil in Asphaltic Surface . 135 Voids in Sand Rock Determination of Per Cent. 3 1 -33 For Proportioning Concrete 38 Volumetric Synthetic Method 40-5 7- 1 20 Warren Bros. Construction Co 40 Water Chemical Composition of 10Z Effect of Chemical Composition on Strength of Concrete- 47-48 For Concrete Roads -- -130 For Irrigation Pipe -- Methods of Mixing 49 Proportion for Concrete 8-45-47 Units of Measurement for Water Tightness of Concrete Depending on Density 57 190 INDEX For Sewer Pipe 1 66 Waterproofing Compounds 58 Wearing Surface Curbs and Gutters 1 06 Roads 132 Sidewalks 86 Weather Effect on Hardening of Concrete -- 53 Weir Table 1 63 TA Good concrete: a manual.... 681 UNIVERSITY OF CALIFORNIA LIBRARY r}^9 Los Angeles This book is DUE on the last date stamped below. JUL1 Form L9-30m-ll,'58(.8268s4)444 /aK&&jm