REESE LIBRARY OF THK UNIVERSITY OF CALIFORNIA. 0/7 AJ STEEET PAVEMENTS AND PAVING MATERIALS. A MANUAL OF CITY PAVEMENTS: THE METHODS AND MATERIALS OF THEIR CONSTRUCTION. FOR THE USE OF STUDENTS, ENGINEERS, AND CITY OFFICIA LS. BY GEO. W. TILLSON, C.E., * ^President Brooklyn Engineers' Club, Mem. Am. Soc. C. K., Mem. Am. Soc. Municipal Improvements, and Prin. Anst. Engineer, Department of Highioayt, Brooklyn, N. Y. FIRST THOUSAND. NEW YORK: JOHN WILEY & SONS. LONDON : CHAPMAN & HALL, LIMITED. 1900. Copyright, 1900, BY GEO. W. TILLSON. ROBERT DRUMMOND, PRINTER, NEW YORK. PREFACE. IN presenting this work to the public the author does so in the hope that it will answer some questions that have been presented to him during the past, and whose solution was only obtained by actual experience. Fifteen years ago there was probably less literature extant upon the subject of street pavements than upon any other one branch of the engineering profession. Such great advance has been made in pavement construction during that period that works of that day are practically useless at the present time, except as records of what has been done. An active participation in the construction of municipal pub- lic works, particularly in pavements, during the past twenty years has seemed to justify the author in producing this book in order to show not only what is being done at the present time in pavement construction, but also the evolution of the modern city street from the rude roadways of centuries ago. Much time has been spent in historical research, and in Chap- ter I will be found a collection of facts that makes a fairly well- connected history of pavements and roads. It would be useless to enumerate all the works that have been consulted in the preparation of this volume, as they include ency- clopedias, dictionaries, scientific works, technical journals, society and official reports, special reports of consular agents and official committees, magazines, popular publications, and in fact all litera- ture that would furnish information on the subject. Unreliable statements have either been rejected or given for what they were worth. The author is greatly indebted to consular agents and city of- iii IV PREFACE. ficials, who have cheerfully furnished him with valuable and inter- esting facts. Much of the information contained in the chapter on Stone has been obtained from different geologies, and the reports of the U. S. and State Geological Surveys. The entire chapter has been revised by Professor Leslie A. Lee of Bowdoin College, Brunswick, Me., who has thus placed the author under great obligations to him. The chapter on Asphalt has been prepared from the writings of Clifford Richardson, Professor S. F. Peckham, and others, as well as from personal investigations, trade publications, etc. Much of the information relative to the payments for pave- ments by street-car companies was obtained from a report made to the Massachusetts Legislature by a committee appointed to investi- gate the relations between cities and towns and street-railway companies. The main idea of the work has been to have it practical, so that an engineer unacquainted with the subject could obtain sufficient information to prepare specifications for, and intelligently supervise the construction of, pavements. G. W. T. BROOKLYN, N. Y., Sept. 1, 1900. TABLE OF CONTENTS. CHAPTER I. PAGE THE HISTOBY AND DEVELOPMENT OF PAVEMENTS 1 Introduction Ancient Roads Roman Roads Mexican and Peruvian Roads French Roads Spanish Roads Pavements of Rome Paris Pavements Early London Pavements Pompeian Pavements First Paris Pavements Mexican Pavements Pavements of New York, Boston, Philadelphia, Chicago, San Francisco, New Orleans, Cleveland, St. Louis, and Albany. CHAPTER II. STONE. 14 Formation of Earth's Crust Mineral Composition of Rocks Quartz Feldspar Amphibole Pyroxene Mica Granite Gneiss Syenite Porphyry Diabase Basalt Analyses of Granite Annual Produc- tion of Granite Analyses of Trap-rock Sand Sandstone Hudson River Bluestone Medina Sandstone Potsdam Sandstone Berea Sandstone Colorado Sandstone Limestone Marble Bedford Oolitic Limestone Trenton Limestone. CHAPTER III. ASPHALT 40 Derivation of Word ' ' Asphalt " Early Use of Bitumen Definition of Bitumen and Asphalt Maltha Origin of Asphalt Chemistry of Asphalt and Bitumen Methods of Analyzing Asphalt Trinidad As- phalt Description of Pitch Lake Composition of Pitch Lake Asphalt California Asphalt Maltha Composition of Different California Asphalts European Asphalts Theory of Formation Analyses of Rock Asphalts Mexican Asphalt Bermudez Asphalt Kentucky Asphalt Texas Asphalt Utah Asphalt Indian Territory Asphalt Montana Asphalt Cuban Asphalt Barbadoes Asphalt Asphalts of , Turkey Egyptian Asphalt. V VI TABLE OF CONTENTS. CHAPTER IV. PAGE BRICK-CLAYS AND THE MANUFACTURE OF PAVING-BRICK 80 Formation and Composition of Clays Kaolin Characteristics of Clay Shales Fire-clays Definition of ' ' Vitrified "Early Clay Products First Brick-kiln in United States Production of Paving- brick Manufacture of Paving-brick Crushing the Clay Screening Pugging Moulding Repressing Drying Burning Changes of Clay in Burning Annealing Sorting. CHAPTER V. CEMENT, CEMENT MORTAR, AND CONCRETE 96 Definition of Lime and Cement Early Cements Portland and Nat- ural Cements Fineness of Cement Variation in Cement Tests Stand- ard for Tests Cement Specifications Requirements for Cements Ce- ment Mortar Effect of Salt Water in Cement Mortar Effect of Frost on Mortar Concrete Early Use of Proportions for Concrete Mixing Amount of Material per Cubic Yard of Concrete Voids in Broken Stone Proper Consistency of Concrete Relative Value of Hand- and Machine-mixed Concrete Concrete-mixers Manufacture and Consumption of Cement in United States. CHAPTER VI. THE THEORY OF PAVEMENTS 135 Value of Pavements Methods of Payment Forms of Pavements Paving Material Properties of a Pavement Cheapness Durability Traffic Easiness of Cleaning Slipperiness Maintenance Favorable- ness to Travel Sanitariness Consideration of Different Pavements Conclusion as to Best Material Application of Principles Deduced Annual Cost of Pavements Pavements of Leading Cities Openings in Pavements. CHAPTER VII. COBBLE AND STONE-BLOCK PAVEMENTS 177 Roman Stone Pavements Shape of Early Stone Blocks Cobble- stone Pavements Quantity in American Cities Cost of Cobblestone Pavements Size and Shape of Blocks Cost of Belgian Pavement Granite Pavements Quality and Size of Blocks Specification for Blocks in Different Cities Preparing Foundation Laying Blocks Joint-fillers Cross-section of Pavements Concrete Base Cost of Granite Pavements Medina Sandstone Pavements Cross-walks Granite Pavement in Vienna. TABLE OF CONTENTS. vil CHAPTER VIII. ASPHALT PAVEMENTS ............................................... 211 Early Asphalt and Coal-tar Pavements in United States Grades for Asphalt Pavements Character of Asphalt for Pavements Asphaltic Cement Penetration Test Sand for Asphalt Pavements Wearing Surface Binder ^Foundation Method of Laving Cracks in Pave- ment Action of Illuminating Gas on Asphalt Condition of Pave- ment at End of Guaranty Rock Asphalt Pavements Asphalt Pave- ments in London Repairs and Maintenance Cost of, in Different Cities Noiseless Manhole-covers Cost of Asphalt Pavements Asphalt on Bridges American Asphalt in Europe Asphaltina Asphalt-block Pavements. CHAPTER IX. BIIICK PAVEMENTS ................................................... 2C8 Early Brick Pavements Requirements of Paving-brick Abrasion Test Absorption Test Cross-breaking Test Crushing Test Hard- ness and Specific Gravity Application of Results of Tests Size and Form of Bricks Foundation for Brick Pavements Joint-filling Rumbling Laying the Brick Requirements of Different Specifi- cations Amount of Brick Pavement in United States Cost of Brick Pavements in Different Cities Amount of Material per Square Yard of Brick Pavement Estimated Cost of a Brick Pavement. CHAPTER X. WOOD PAVEMENTS .......... ........................................ 293 Early Wood Pavements London Pavements Australian Wood in London Specifications for London Pavements Wood Pavement in Ipswich, Glasgow, Dublin, Paris, Montreal, and Quebec Early Wood Pavements of the United States Wood Pavements in Washington, St. Louis, and Brooklyn Cedar-block Pavements Chicago Specifi- cations San Antonio Wood Pavements Redwood Pavements Des Moines Pavements Specifications for Des Moines Pavements Aus- tralian Pavements Chemical Treatment for Wood Early Methods Kyanizing Burnettizing Creosoting Zinc Process. CHAPTER XI. BHOKEN-STONE PAVEMENTS .................... . ...................... 329 First Broken-stone Pavement Telford Macadam Merits of Mac- adam and Telford Construction of broken-stone pavement Founda- tion Wearing Surface Binding Rolling Quantity of Stone Re- viii TABLE OF CONTENTS. quired Crown Cementing Properties of.Stone Sprinkling Specific- ations of Different Cities Macadam Roads How Built New Jersey Roads Construction of'Macadam Roads Drainage Width Character of Stone Massachusetts Roads Abrasion Tests for Stone Cost of Macadam Roads Specifications of Different States Maintenance of Streets and Roads Ruts Sprinkling Width of Tires. CHAPTER XII. PLANS AND SPECIFICATIONS. . . 376 Object of Plans and Specifications Prepared by Experts Should be concise Should be Plain Alternative Bids Instructions to Bid- ders Certified Checks to Accompany Bids Bond Guarantees Un- balanced Bids Sample Specifications General Requirements Re- quirements for Asphalt, Granite, Medina Sandstone, Brick, and As- phalt-block Pavements ; CHAPTER XIII. THE CONSTRUCTION OF STREET-CAR TRACKS IN PAVED STREETS 421 Early Construction Amount of Pavement Maintained by Railway Companies Location of Tracks Forms of Old Rails Forms of Modern Rails Recent Construction in Different Cities Life of Rails Rail-joints Recommended Forms of Construction Mileage of Street Railways in American and European Cities. CHAPTER XIV. WIDTH OF STREETS AND ROADWAYS, CURBS, SIDEWALKS, ETC 459 Width of Streets Width between Curbs Location of Sidewalks Curbing Specifications for Dressing in Different Cities Foundation Concrete Curb and Gutter Estimated Cost Sidewalks, Stone, Brick, and Cement Specifications for Sidewalks in Different Cities Gutters Street Grades How Established and Recorded. CHAPTER XV. ASPHALT PLANTS 487 Capacity of Plant Location Work of Plant Asphaltic Cement Stone Dust Mixing Cost Portable Plants. LIST OF TABLES. TABLE NO. PAGE 1. Analysis of trap-rock from New Jersey 27 2. Crushing strength of different granites 27 3. Crushing strength of Colorado sandstone 34 4. Analysis of Bedford limestones 87 5. Analysis of Trenton limestones 38 6. Analysis of limestones and resulting limes 38 7. Analysis of different limestones 39 8. Analysis of different asphalts 54 9. Analysis of Trinidad asphalt 60 10. Analysis of rock asphalts 68 11. Analysis of Mexican asphalt 69 12. Mechanical analysis of porphyry 86 13. Chemical analysis of porphyry 86 14. Analysis of Portland cements 99 15. Analysis of natural cements 100 16. Requirements for fineness of Portland cements 101 17. Strength of cements of different fineness 102 18. Strength of ordinary and finely ground Portland cement 102 19. Strength of coarse and fine Rosendale cement 102 20. Strength of same cement from different laboratories 103 21. Showing importance of sand tests for cement 104 22. Strength of cement with long- and short-time tests 105 23. Strength of cement with long-time sand and neat tests 106 124. Requirements of tensile strength for cements 107 25, 26. Showing material required for one cubic yard of mortar 110 27. Showing strength of mortar when immersed in salt water Ill 28. Showing strength of mortar when immersed in and mixed with salt and fresh water 112 29. Showing strength of Portland-cement mortar when immersed in and mixed with salt and fresh water 112 30. Showing strength of mortar when mixed with salt water 114 31-33. Showing effect of freezing and subsequent thawing on mortar. 114, 116 34. Showing effect of freezing and subsequent thawing on concrete cubes 117 ix x LIST OF TABLES. TABLE NO. PAGE 35. Showing strength of mortar after second mixing 118 36. Showing strength of briquettes made at different times after the mix- ing of the mortar 119 37. Showing volume of concrete from certain mixtures 12i> 38. Showing voids in stone, gravel, and mixtures of both 121 39. Showing voids in certain sands, stone, gravel, etc . . 124 40. 41. Analysis of proposed material for Portland cement 133 42. Showing imports and home products of Portland cement Hi3 43. Showing product and consumption of American cement 134 44. Showing methods of paying for street pavements 138 45. Showing average life of pavements in Europe 156- 46. Showing result of traction experiments at Atlantic Exposition 157 47. Showing tractive force required to draw one ton on different streets according to Prof. Haupt 1 oK 48. Showing effect of size of wheels and width of tire on tractive force. . . 158 49. Showing tractive force per ton according to London experiments 159 50. Showing tractive force per ton according to different authorities 159 51. Showing accidents to horses on London streets 161 52. Showing accidents to horses on different London pavements 161 53. Showing accidents to horses on different London pavements under different conditions 162 54. Showing relative value of different paving materials 167 55. Showing comparative costs of different pavements 172 56. Showing increase of pavement mileage in different American cities. . . 173 57. Showing sizes of granite blocks used in American and European cities. 191 58. Showing sizes of stone blocks used in European cities 192 59. Showing crowns for street pavements *. 202 60. Showing methods of laying out cross-section of pavement.' 218 61. Showing sizes of certain sands, 226 62. Showing sizes of sands used in different pavements 227 63. Showing cost per yard of repairs to asphalt pavements in different cities 246 64. Showing cost per yard for each year after expiration of guarantee in different cities 247 65. Showing analysis of different bricks 260 66. Showing loss by abrasion to bricks of different degrees of hardness. . . 266 67. Showing water evaporated from different bricks 271 68. Showing water absorbed by different bricks 271 69. Showing results of different tests upon different bricks 275 70. Showing condition of hard-wood pavements in London 298 71. Showing mileage of street-car tracks in American and European cities. 458 72. 73. Showing analyses of different asphalts 495, 496. LIST OF ILLUSTRATIONS. FIGURE PAGE 1. Possible formation of rock asphalt 67 2. Machine for mixing concrete 127 3. Plan of old Roman road 178 4. Cross-section of old Roman road 178 5. Cross-section of old Roman road . 178 6. Plan of pavement, Catania, Italy 179 7. Cross-section of a cobblestone pavement. 183 8. Cross-section of a Belgian block pavement 186 9. Plan of granite intersection, old method 193 10. Plan of granite intersection, improved method 194 11. Plan of granite intersection, modern method 195 12. Cross-section of granite pavement on concrete base 199 13. Example of steep grade on asphalt-paved street in Pitteburg 217 14. Cross-section of asphalt pavement 235 15. Showing plan and section of noiseless manhole-cover 249 16. Showing expansion-joint in asphalt pavement on Denver viaduct 252 17. Cross-section of a brick pavement 284 18. Cross-section of a broken-stone pavement 347 19. Early form of street-car rail 430 20. Same type used on curves 430 21. Modified form of Fig. 19 431 22. Original grooved rail 431 Centre- bearing rail 481 Side-bearing rail with renewable head 432 ' 25. Grooved rail with renewable head 433 26. Centre-bearing girder rail 433 27. Side-bearing rail 434 28. The Trilby rail 435 29. Modified form of Trilby rail 435 30. West End rail, Boston 436 4 81. Boston subway rail. 437 32. Ordinary T rail 437 33. Improved track-construction in Buffalo 438 xi Xii LIST OF ILLUSTRATIONS. FIGURE PAGE 34. Another form of track-construction in Buffalo 439 35. Tie-construction of track, Department of Highways, Brooklyn 441 36. Concrete-beam construction, Department of Highways, Brooklyn 441 37. Toronto track-construction 441 38. Sioux City track-construction 441 39. Third Avenue Railway construction, New York 443 40. Detroit railway construction ... 445 41. Cincinnati railway construction 445 42. Rochester iron-tie construction 446 43. Rochester concrete-beam construction 447 44. Clamp used in Rochester construction 447 45. Yonkers construction 448 46. Minneapolis constructiou 448 47. Track-construction recommended in granite pavement 453 48. Track-construction recommended in asphalt pavement 453 49. Track- construction recommended in brick pavement 455 50. Method of making grooved rail in old track-construction 457 51. Curb set in concrete, asphalt pavement 466 52. Cy rb set in concrete, granite pavement 467 53 Section of concrete curb 470 54. Plan of stone sidewalk 476 55. Plan of brick sidewalk 477 56. Another plan of brick sidewalk , 477 57. Herringbone plan of brick sidewalk 477 58. Section of cobblestone gutter 481 59. Section of cement-concrete gutter. 481 60. Diagram of grades at a street-intersection 485 STREET PAVEMENTS AND PAYING MATERIALS. CHAPTER I. THE HISTORY AND DEVELOPMENT OF PAVEMENTS. PRIMEVAL man had no pavements nor any use for them. His wants were few and easily satisfied. He knew of nothing outside of his own range of vision. Knowing but little, his desires were few and in almost every instance could be satisfied by the fruits of the soil or the results of the chase. But this could not continue; as the race increased and scattered over the then known world the different divisions settled down into communities or became nomadic tribes. Different localities pro- duced different articles, and in their wanderings and communica- tions with each other they became acquainted with their different products, and the spirit of interchange and commerce sprung up among them. Feelings of rivalry arose, producing wars, and there is no doubt that the commercial and warlike interests were most powerful in promoting exchanges between tribes and later between nations. At first tracks were established across the country, but as time went on these tracks grew to be paths, and the paths roads, and the roads developed into our modern highways, paved streets, and mag- nificent system of railroads. All of this, however, consumed a vast amount of time, and many centuries elapsed after the building of the first road before much similar work was undertaken or the modern boulevard completed. While war-chariots are mentioned in 2 STREET PA YEMENIS AND PAVING MATERIALS. history as existing at as early a period as war itself, commercial commodities were transported in ancient times almost entirely on beasts of burden,. Hence the slow growth for a long time of the demand for roads. All records of work done in the early life of the human race are indefinite, and much that ought to be history and founded upon fact is only conjecture. It is said that a little to the east of the Great Pyramid remains of a stone causeway a mile long have been discovered. This is sup- posed to be a portion of a road built by Pharaoh for the purpose of conveying stone or other material across the sand for the construc- tion of the pyramid. As this pyramid is generally considered to have been built in the fourth dynasty, or about 4000 B.C., it is undoubtedly, if authentic, the oldest road on record. Another ancient boulevard is mentioned by historians which must have been built soon after, as these times are now considered. The city of Memphis is. said to have been connected with the pyramids by a broad roadway, two leagues long, having a paved and well-kept driveway lined on both sides with temples, mau- soleums, porticoes, monuments, statues, etc. In fact, according to descriptions it must have been the modern boulevard with all the accessories that the times and unlimited wealth would allow. The Carthaginians, however, are generally given the credit of "being the first people to construct and maintain a general system of roads. This African city had sprung up about 600 B.C. and by its growth and enterprise became a rival of the Roman Empire across the Mediterranean. Rome endured this rivalry for a time, but at last she issued that famous edict, Carthago delenda est, which resulted in the invasion of Africa and the destruction of Carthage B.C. 146. The Romans without doubt appreciated the benefit of improved highways for the rapid mobilization of troops, for they immediately took up the practice of the Carthaginians, and road-building was always one of the features of their subsequent conquests. It is claimed that in Great Britain alone they constructed 2500 miles of roads. The Appian Way was built by Appius Claudius about 300 B.C., and the Flaminian Way some years later. These roads were prac- THK HISlOllY AM> DEVELOPMENT OF PAVEMENTS. 3 tically examples of solid masonry laid in cement mortar and some- times several feet thick. A traveller in one case reports having crawled entirely across a road under the pavement where the earth had been washed away and the masonry had been self-supporting. Such roads lasted a long time. The Appian Way was said to have been in good repair eight hundred years after it was built. But it must be remem- bered that the traffic it sustained was of such a nature and amount as to produce a very slight abrasion on the roadway. The stone used was irregular in size and shape, but laid in such a manner as to make a solid roadbed impervious to water. Prof. John Beekman of the University of Gottingen states in his "History of Inventions and Discoveries" that the streets of Thebes were regularly cleaned, and thatjhe Talmud says the streets of Jerusalem were swept every day, and accordingly concludes that they must have been paved. A consular report from Palestine states that the pavements of Jerusalem laid by the Romans over two thousand years ago are still in fair preservation, but adds: " They are indeed hidden from sight, and are many feet beneath the rubbish of the city." It is easy to understand how a stone pavement might last centuries under such conditions. Mexico and Peru, although not countries where much transpor- tation was ever carried on by vehicles, built in ancient times many foot-roads of great excellence; those of Peru alone extended for more than a thousand leagues. In the special consular reports it is stated that more than one thousand years before Columbus discovered the New World, the province and fclso the city of Genoa boasted of fine roads and streets. In France all travelling was done on horseback until the latter part of the sixteenth century. In 1508 Louis XII. appointed offi- cers to inspect and report upon the condition of all roads; to repair those under the care of the king, and to enforce the repair of the others by the proper authorities. Other rulers followed his ex- ample, but little good was accomplished, as these officers were often appointed and almost immediately discharged so as to create vacancies which might be filled upon the payment of a certain fee, 4 STREET PAVEMENTS AND PAVING MATERIALS. thereby creating a considerable revenue by the sale of appoint- ments. This fact would seem to show that corruption existed in the carrying out of public work in ancient as well as in modern times. In the latter part of the sixteenth century Henry IV. appointed a " Great Waywarden of France." This is probably the earliest record of the appointment of a public official with a specified title to have systematic supervision over the public roads. These different actions, however, do not seem to have accom- plished much, as it is recorded that as late as 1789 the country roa'ds of France were generally in a state of nature or worse. It is, however, stated that in 1556 a stone road was built from Paris to Orleans, the portion improved being 15 feet, although the entire width was 54 feet. The first highway constructed in Sp'ain, after the Roman regime, was built by Fernando VI. in 1749 from Santander to Reinoso, the labor being performed by soldiers. In 1761 regula- tions were made for the classification, construction, and repair of highways in general, but no definite results were obtained. In 1794 the matter was delegated to a special bureau of the government, but with no better success. And it was not till 1834, when an engineering school was established, graduating its first class in 1839, that any real good was accomplished. From that time roads were built according to the condition of the public treasury. The first Highway Act for the improvement of roads in Eng- land was passed in 1555. The above facts relate to roads rather than pavements proper, and it is interesting to note to what size European cities grew before any particular attention was given to street pavements, and how many years it required to arrive at any satisfactory results. Alexander Dumas said after a visit to Russia, in answer to a question as to how he found the streets and roads, that he had scarcely seen any, inasmuch as during the winter season they were covered with snow, and during the summer they were in process of repair. The streets of Rome were paved in the fourth and fifth cen- turies after the founding of the city. The first pavements in Paris were laid during the reign of THE HISTORY AND DEVELOPMENT OF PAVEMENTS. 5 Philip Augustus about 1184, the square of the Chatelet and the streets of St. Antoine, St. Jacques, St. Honore, and St. Denis being the first improved. The population of Paris at that time must have been little less than 200,000. Cordova, Spain, although a small place, is said to have had paved street's in 850. The Strand, London, was ordered paved by act of Parliament in the fourteenth century, and streets outside of the city in the sixteenth, although it is said that the first regular pavements were laid in 1533, when the city had a population of 150,000. Holborn had some pavements in 1417. Square granite blocks were intro- duced by acts of Parliament for Westminster in 1761, and for London generally in 1766. When the Forum Trajanum was cleaned by the French in 1813, the old Roman pavements were found on an average of 12 feet below the then surface. The stones in these old pavements were polyangular in shape, containing from 4 to 5 square feet and 12 to 14 inches deep, laid with close joints. More modern blocks- in Rome were about 2 cubes long, and on being set up endwise had an area of 10 square inches. This would give a block about 7 inches long, 3 inches deep, and 3 inches wide. They were set on 12 inches of cement concrete. A recent novelist, speaking of London in 1516, says: " There were great mud-holes where one sank ankle-deep, for no one paved their streets at that time; strangely enough preferring to pay the sixpence fine per square yard for leaving it undone." How often this fine was imposed was not stated. Speaking of London in 1685, Lord Macaulay says: " The pave- ment was detestable; all foreigners cried shame upon it. The drainage was so bad that in rainy weather the gutters soon became torrents." Walter Besant in his " History of London " states that in the Elizabethan period carts only were allowed on the street, and their number was restricted to 420. Merchandise was carried on pack- horses. Also: "In the streets the roads were paved with round pebbles they were cobbled; the footway was protected by posts placed at intervals; the paving-stones, which only existed in tHe principal streets, before 1766 were small and badly laid; after a 6 STREET PAVEMENTS AND PAVING MATERIALS. shower they splashed up mud and water when one stepped upon them/ 3 In a pamphlet written by a Colonel Macirone of London in 1826, when the city had a population of 1,400,000, the author says: " Florence, Sienna,, Milan, and other Italian cities have pavements with especially prepared wheel-tracks. These tracks are three feet in width, made of large and particularly well-laid stones. They are about four feet apart, and the space between paved with smaller stones." He further states that these pavements, as well as those of Borne last mentioned, are the best that he has ever seen, but that they would be too expensive for London. Also : " There is no species of pavement that I have ever seen or heard of to the application of which tfl the streets of London there would not be many and great objections. . . . However true it may be that an observant traveller cannot fail of being struck with admiration at the excellence of the turnpikes and other roads throughout this country, he must at the same time be very much surprised at the badness of the carriage-pavements, even of the principal streets of this metropolis." These were the observations of an engineer who had travelled and examined the European pavements of that time, and they ought to express fairly their condition. This was about the time of Macadam and Telford, and soon after this considerable broken-stone pavements were laid in Lon- don. A pavement consisting of broad, smooth, well- jointed blocks of granite for wheel-tracks, with pitching between for horses, was laid in Commercial Koad, London, in 1825. In 1839 there were 1100 square yards of wood pavement in London, which in 1842 had increased to 60,000, when, according to a statement made in the City Council by an alderman during a controversy as to the relative merits of wood and stone pavements, there were 600,000 square yards of the latter, probably nearly if not all macadam. These two items without doubt represented the total amount of pavements in a city of nearly 2,000,000 people. In 1825 Telford recommended the use of stone blocks 4J to7| inches in size for street use; and 3x9 inches granite sets were laid on Blackfriars Bridge with mortar joints in 1840. This was probably the first attempt at a modern stone pavement. Eock TEE HISTORY AND DEVELOPMENT OF PAVEMENTS. T asphalt was laid in London on Threadneedle Street in 1869, and in 1873 there were 60,802 square yards or 4.25 miles of this pave- ment, and 12,238 square yards of wood, in the city. This would indicate that wood, as first laid, was discontinued, and was not used again till laid in its improved form. Concrete was first used in London as a base for pavements in 1872, and the custom was general in 1875. In Liverpool granite blocks were first laid in 1871, and wood in 1873. Tar and gravel joints for stone pavements were adopted in Lon- don in 1869, and in Liverpool in 1872, though they had previously been in use in Manchester. Glasgow first used granite block and wood for pavements in 1841, and asphalt in 1873. Recent excavations show that the streets of Pompeii were paved with lava from Vesuvius. The pavement must have been laid some time previous to its destruction, as the blocks in many places show an appreciable wear, although the traffic must have been very slight when compared with modern times. Sienkiewicz in his historical novel " The Deluge " says that the capital of Lithuania was paved with stone in 1655, and adds that this was something extraordinary for that time. A history of Spanish times in the West Indies, after describing a visit of the pirates to Porto Bello, Venzuela, in 1668, says: " Hav- ing stripped the unfortunate city of almost everything but its tiles and paving-stones, the sea-rovers departed." Although Paris had some pavements before London, it was many years before its streets were in even a decent condition. Martin Lister, writing of Paris in 1698, says: " The pavements of the streets are all of square stones of about eight or ten inches thick; that is, as deep in the ground as they are broad on top, the gutters shallow and laid round without edges, which makes the coaches glide easily over them." On another page he says the material was a very hard sandstone, and that all the streets and avenues were paved. Aaron Burr in 1811 thus describes their condition in a letter to a friend: "No sidewalks the carts, cabriolets, and carriages of all sorts run up to the very houses. Most of 8 STREET PAVEMENTS AND PAVING MATERIALS. pun., up--to--t4ie ve^Jimises. Most of the streets are paved as Albany and New York were before the Eevolution, some arched in the middle, and a little gutter on each side very near the houses. It is fine sport for the cabriolets or hack-drivers to run a wheel in one of these gutters, always full of filth, and bespatter fifty pedestrians who are braced against the wall." A sample of asphalt macadam was laid on the road between Bordeaux and Eouen in 1840. This was a mixture of asphalt rock and ordinary stone, and was probably the first bituminous roadway laid on a public highway, although about the same time asphaltic rock was used for sidewalks on some of the streets of Paris. In 1837 a Mr. Claridge obtained a patent for using Seyssel asphalt for paving purposes in the Departement de VAin. In 1854 the Eue Bergere was paved with compressed asphalt, followed by the Eue St. Honore in 1858, from which time the suc- cess *of asphalt pavements has been assured in Paris. In the ruins of the ancient city of Palenque, Mexico, pave- ments of cut-stone blocks have been discovered which must have been laid at a very early period. In the city of Mexico, from a very early date, cobblestones were used for pavements, and their use was continued till 1884, when a portion of the principal avenue of the city was paved with stone Hocks. The stone being of a poor quality, the result was not satisfactory and the attempt was not repeated. Some five years later wooden blocks were tried, but the expansion was so great that the surface was deformed, and the experiment failed. Lumber being so expensive in Mexico, no further attempt was made with wood. In 1889 some coal-tar pavement was laid, resulting in the usual failure, it being entirely torn up a year later and asphalt blocks substituted. Up to 1899 some 148,000 square yards of this material had been used upon a cobblestone and sand base with "very satisfactory results. Practically all the pavement in the city except this is cobblestone. In the United States pavements of cobblestone were laid in New York and Boston at about the same time. Of the former city Mrs. John King Van Eensselaer in her popular novel " The Goode Vrowe of Manahatta " says that in the early days of New York the Dutch built several breweries on the THE HISTORY AND DEVELOPMENT OF PAVEMENTS. 9 road lying between Broad and Whitehall streets, since called Brower Street. The good housewives, annoyed by the dust raised by the heavy brewery wagons, made frequent complaints to the city authori- ties, who finally paved the roadway with small round stones. This created the greatest interest, and many visitors came to see the " stone road," which finally came to be and is now known as Stone Street. This was about 1656. In Mrs. Lamb's " History of New York " it is stated that De Hoogh Street, now Stone Street, was paved in 1656; that the second was Bridge Street, in 1658; and that in 1660 all the streets most used were paved with cobblestones, the gutter being in the centre of the street, but no attempt was made to lay side- walks. A Swedish traveller, writing of New York in 1751, says: " The streets do not run so straight as those of Philadelphia and have sometimes considerable bendings; however they are very spacious and well built, and most of them are paved except in high places, where it has been found useless." In New York cobblestones were almost the only paving material until 1849, although some experimental wooden blocks were laid on lower Broadway as early as 1835. On this same street " Russ " blocks were laid up as far as Franklin Street in 1849. These blocks came from Staten Island and were from 2 to 3 feet square. In 1855 the blocks on the grades were grooved to give better foot- hold to the horses. This pavement was replaced by the so-called Guidet blocks in 1868 or 1869. A detailed report of the Council of Hygiene and Public Health made January 1, 1865, says that practically all of the New York pavements of that date were cobblestone or Belgian block. There was some Euss and a small piece of cast-iron block on Cortlandt Street. Belgian blocks were first .laid on the Bowery in 1852, and came into very general use after 1859. They made the improved pave- ment of the times. The present-shaped granite blocks were first used in 1876 or 1877, though the Guidet patent blocks had been used a few years previously. This latter had also been adopted to some extent in Brooklyn, but never came into very general use. Its principal 10 STREET PAVEMENTS AND PAVING MATERIALS. difference from the present pavement was in the size of the blocks, they being very large. Some of them measured on Atlantic Avenue, Brooklyn, in 1899 were 5 and 6 inches wide and 18 and 20 inches long. The Dock Department used tar and gravel joints for a granite pavement on a sand foundation on Pier A, North Kiver, in 1881, while the first concrete base for stone was regularly used in 1888 in the city streets. A small piece of asphalt was laid near the Battery in 1871. A general scheme for the improvement of the pavements of New York was adopted in 1889. This was made possible by the legislation obtained the previous winter authorizing the issue of bonds for that work. The first street paved in Boston was probably Washington Street, about 1650, the material being " pebbles/' A portion of State Street was paved previous to 1684, and quite an amount of pavement was laid in the latter part of the seventeenth century. Many of the original paving petitions are now on file in the City Clerk's office, one bearing the date of 1714. Drake's " History of Boston " says that on March 9, 1657, the General Court ordered " the paved lane by Mrs. Shrimpton's to be laid open and no more to be shut up." This is the year following the laying of the first pavement in New York, and would indicate that Boston began the work of paving as soon as, if not sooner than, New York. Speaking of Boston in 1673: " Yet for several years after this there were no streets paved excepting a few sections of some of the principal ones, and those of a few rods in extent." On April 19, 1704, 100 was voted for paving " such places of the streets as the selectmen should judge most needful, and therein to have particular regard to the Highway near old Mrs. Stoddard's "house." On March 29, 1706, 100 was voted "for paving the Mayn street towards the Landing to the south end of the Town, and 50 for paving at the lower end of the Town house." In 1719 the General Court authorized the town to raise $2100 by a lottery towards paving and repairing the Neck, and soon after- wards authorized another to raise funds for paving the highway THE HISTORY AND DEVELOPMENT OF PAVEMENTS. 11 from Boston line to Meeting House Hill in Roxbury. Winter Street was paved about 1743. ShutlifFs " History of Boston " says: " In the year 1758 the townspeople began to pave the streets leading to the Neck partly at the expense of the town and partly by private subscription." Baltimore paved its first street in 1781, using the ever-present cobblestones, which in 1899 composed about 75 per cent of its entire pavement. Philadelphia. In 1726 a Friend relates that he saw paved streets near the court-house and Market House Square. Second Street from High to Chestnut Street was the first one regularly paved. In 1719 a gentleman writing to his brother in England says: "As to bricks, we have been upon regulating our pavements of our streets, the footway with bricks and the cartway with stones, which has made our bricks dear." About the same time the minutes of the City Council state that, as several inhabitants have paved the streets with pebbles, an ordinance is recommended restraining the weights of loaded car- riages passing over them. In 1761-2 an act was passed " Regu- lating, pitching, paving and cleansing the highways, streets, lanes, and alleys &c within the settled parts of Philadelphia." Curbstones were first adopted in 1786. Philadelphia claims to have had macadam, or broken stone, streets or roads two hundred years ago, and was probably the pio- neer in this country in that respect. Several streets were paved with hemlock blocks in 1839 and 1840, but with little success. In 1884 Philadelphia had 535 miles of pavements, of which 93 per cent was cobble, 6J per cent granite, and 2 j per cent asphalt. The granite, however, was not the present-shaped blocks, but prac- iically like Belgian. In that year a special commission of experts was appointed to report on the best material for street pavements, and the era of im- proved streets in that city began with the adoption and carrying out of the commissioners' report. Chicago. In Chicago all street improvements previous to 1844 consisted in keeping the earth roadways in as good a condition as possible. From 1844 to 1855 the roadways of the most important 12 STREET PAVEMENTS AND PAVING MATERIALS. streets were planked. In 1855 1.72 miles of actual pavement was laid, but of what material the reports do not state. San Francisco. In the big fire that occurred in San Francisco in 1850, many planked streets were set on fire and consumed. Roads constructed for short distances of natural asphalt in southern California had been known for a long time prior to 1870. New Orleans. New Orleans constructed her first pavements of cobblestones in 1817, when the population of the city was about 41,000. Previous to this time it had not been deemed practicable to lay a pavement successfully on the soft yielding soil of the city. A general paving ordinance was passed in 1822, and under its provisions streets were improved with shells, cobble, square blocks, and irregular flat stones. In 1837 an ordinance ordered certain streets paved with the " gunnels " of flat boats, although they had been used previous to- that time. In 1838 a portion of St. Charles Street was paved one-third with stone blocks, one-third with curbstones laid flat, and one-third with hexagonal pine blocks. The stone and wood blocks were sat- isfactory, and their use was continued. A bituminous pavement of some kind was laid an Gravier Street in 1880, but proved a failure. Asphalt was first laid on St. Charles Street in 1885. From 1889 to 1896 a number of streets were paved with gravel concrete, but the material did not give good satisfaction. Brick was used in 1894, and chert in 1895. The dimensions of granite blocks were 14 x 10 x 88 inches. Cleveland. The first stone pavements of Cleveland were con- structed between 1851 and 1854, of Independence sandstone. The blocks had a surface of 8 or 10 by 12 inches and were from 8 to 12 inches deep. Medina sandstone was first used in 1856, 'and the streets then paved were in good condition in 1880. Nicholson pavement was laid in 1866. In 1873 an experiment was tried by laying a mixture of coal-tar and roofing-gravel to a depth of three inches on six inches of broken stone. The results- were not good. THE HISTORY AND DEVELOPMENT OF PAVEMENTS. 13 St. Louis. Main Street in St. Louis was paved with stone in 1818. The blocks were roughly dressed, irregular in shape, from 3 to 12 inches thick, 6 to 14 inches long, and 6 to 10 inches deep, and set on 6 inches of sand. In 1842 the specifications called for a regular block 4 to 5 inches thick, 7 to 12 inches long, and 10 inches deep, set on 7 inches of gravel. Macadam was adopted in 1832. Wood has been experimented with in St. Louis to a great ex- tent. In 1851 and 1852 many streets were planked. In 1867 Burnettized cottonwood was used. This pavement lasted about seven years, when it was replaced with untreated pine, which had about the same life. Cobblestones were tried in 1855, but never came into general use. Granite and asphalt blocks were adopted in 1873, and sheet asphalt in 1883. Albany. In September, 1704, the City Council passed the fol- lowing resolution : " It is also ordered that ye streets be paved before each inhabitant's door within this citty, eight foot breadth from their houses and lotts before ye 25th of October next ensueing, upon penalty of forfeiting the summe of 15s. for ye behoofe of ye Sheriffe, who is to sue for ye same." In connection with the visit of Peter Kalm in 1749 it is stated that "the streets are broad and some of them are paved/' In 1764 it appears from Mrs. Grant's "Memoirs of an American Lady" that State Street was only paved on each side, the middle being occupied with public edifices. Active paving work was not begun till about 1791, when Broadway was paved and complaint was made about the quantity of stones required, as " it swallowed up thousands of cartloads." Cobblestones were the only material used for years, dimension granite blocks having been not adopted until 1873. CHAPTEK II. STONE. THE rocks that once formed the crust of the earth were com- posed almost entirely of nine elements, oxygen, silicon, magnesium, aluminum, calcium, iron, sodium, potassium, and carbon, the whole making 97.7 per cent of the earth's crust. These elements combining in different ways formed minerals, and these minerals make the different rocks according to the num- ber and quantity of their components. Rock can be defined as any material forming a portion of the earth, whether hard or soft. Rocks are divided into two general classes, stratified and unstratified. Stratified rocks are more or less consolidated sediments and are of aqueous origin. Unstratified rocks, having been more or less completely fused, are crystalline in form and of igneous origin. The igneous rocks, while not all granite in the strictest sense, may be called granitic, for they are granular and made up gener- ally of the same substances as the granites, varying in their propor- tions and structure. The minerals forming these rocks are generally considered as being divided into essential parts and characterizing and micro- scopic accessories. These terms are self-explanatory, the essential parts making up the body of the stone, the characterizing accessory defining its exact variety, and the microscopic being those con- tained in very minute quantities. The important minerals that make up these rocks are quartz, feldspar, amphibole, pyroxene, and mica. Quartz. Quartz is a pure silica, composed of silicon and oxygen; its specific gravity is 2.65 and it is a hard and brittle mineral. It is 14 STONE. 15 always found of the same composition and hardness, although, the shape of its particles varies considerably. It is practically indestruc- tible by the forces of nature, which accounts for its forming so large a proportion of all sands. Those found on the seashore axe nearly all quartz. When absolutely pure, quartz is colorless, but sometimes it contains impurities enough to give it a color, when it is known as rose quartz, smoky quartz, etc., according to its appear- ance. When it is in a metamorphic state with its crystals cemented together with quartz, it forms a rock called quartzite. v Feldspar. Feldspar is an anhydrous silicate of alumina together with soda, potash, or lime. It is generally softer than quartz, with a specific gravity of from 2.4 to 2.6. There are several varieties of feldspar; the principal ones being orthoclase, microcline, albite, oligoclase, and labradorite. It is also divided into two groups ac- cording to its crystallization, the monoclinic and the triclinic. The former contains principally silica, alumina, and potash; the latter with the exception of microcline, which chemically is almost the same as the monoclinics, has no potash, but in its stead sodium and lime. According as the above constituents vary in quality and quantity, the feldspars vary in hardness and color, and when they are in appreciable quantities they have an important "bearing on the resulting rock. It is susceptible to the action of the elements, all clays being formed by the decomposition of feldspar. Amphibole. This mineral is sometimes called hornblende, which term really belongs to but one variety, of which there are two, the aluminous and the non-aluminous. The former contains about 45 per cent of silica, 17 of magnesia, 10 of alumina, 12 of lime, and 16 of iron oxides; the latter 57 per cent of silica, 26 of manganese, 14 of lime, with small amounts of oxide of iron and manganese. Hornblende belongs to the aluminous variety. Hornblende is hard and tough and imparts these characteristics to all rocks of which it becomes a part. It is found in some metamorphic rocks. Its color is gen- erally a brownish green. 16 STREET PAVEMENTS AND PAVING MATERIALS. Pyroxene. Pyroxene is more brittle than hornblende and consequently not so desirable a constituent for a rock. Its principal variety, augite, is an essential ingredient of diabase and basalt and also an acces- sory. It is dark-colored and composed approximately of silica 50 per cent, alumina 6 per cent, magnesia 15 per cent, lime 23 per cent, and iron oxides 6 per cent. Mica. This is the mineral so well and popularly known as isinglass. There are several varieties, but the two found in granite rocks are muscovite and biotite. They are always found in thin sheetlike forms and are important factors in the make-up of rock, both as to color and structure. They are influential disintegrating agents, as, on account of their laminations, they often allow the entrance of moisture, which is an important element of decay in any mate- rial. If the mica is deposited in different layers or planes, the rock readily splits along these planes. If muscovite is the variety present, the rock is generally light-colored, while the black biotite imparts its color to the stone, often giving it a speckled appearance. Mus- covite is a silicate of potash and alumina, and biotite of alumina,, iron, and magnesia. Having somewhat hastily examined these mineral constituents of the granite rocks, it will now be in order to take up the rocks themselves. They are complex in their composition and structure, having been formed at different times and under different condi- tions; some containing but few and others many minerals, often grading into each other so imperceptibly that it is sometimes al- most impossible to determine where one variety ends and the other begins. For this reason, and on account of the different definitions given to the same variety by equally good authorities, it seems- proper to treat these rocks as one class, each according to its characteristics, and not attempt to make any arbitrary class dis- tinctions. The group of rocks which it is proposed to study in this con- nection may be defined as silicious, holocrystalline, granular rocks. Their essential constituents are quartz and feldspar, and the char- acterizing accessories hornblende, pyroxene, and mica, with some STONE. IT other less important minerals. Microscopic accessories occur, but in such small quantities that they will not be taken up. In some varieties hornblende and pyroxene are considered essential. Granite, according to Dana, consists of quartz, feldspar, and mica. Under this definition, no stone could be a granite unless it contained mica, but as the term is used 'commercially it includes syenite and gneiss and often porphyry. The order of the consolida- tion of rocks is an important factor in their structure. As a rule, in granite the minor accessory minerals crystallized first, taking their natural form. According to some authorities the ferro- magnesian minerals came next, followed by the feldspars, and lastly by the quartz flowing in, filling all the interstices, making a com- plete and solid rock. Occasionally, however, quartz and feldspar are found completely intermingled, indicating that they crystallized at the same time. While the character of a granite is determined principally by its essentials, the accessories have much to do with its quality. The color is generally fixed by the feldspar, but the mica is often a governing characteristic, the presence of muscovite making a granite light, while biotite has always the opposite effect. A large amount of quartz will make a granite hard and brittle, while too much feldspar renders it softer and tougher, but more liable to decomposition. The susceptibility to polish and its ability to resist the action of the elements depend greatly upon the accessory com- ponents. Hornblende is a mineral which permits a granite to take a high polish, while pyroxene, being very brittle, often breaks out when a stone is being hammer-dressed, giving a pitted appear- ance to an otherwise smooth surface. Iron is detrimental, as by the action of the weather iron-rust is formed, and rains washing it over the surface of the stone produce stains upon any structure built of stone containing iron. The size of the particles of the minerals is important. The smaller the grains and the more evenly they are distributed, the better the stone will cut and be polished. The finer the grain the better satisfaction the granite will give in cut work. A fine-grained stone is compact in texture, excluding air and moisture, two agents that are constantly at work to destroy all minerals. Granite is divided into varieties according to the presence of its varying accessories. 18 STREET PAVEMENTS AND PAVING MATERIALS. Muscovite granite is so called from the mica being of the musco- vite variety. It is not found in large quantities in this country, but is produced to some extent from the quarries of Barre, Vt. Biotite granite is similar to the above except that the muscovite is replaced by biotite. On this account, while the former is always light in color, the latter varies from light to dark according to the quantity of mica or the color of the feldspar. This class of stone is often red, owing to the red feldspar. As a rule the stone is hard and tough. Good samples of it are found at Westerly, R. I., and Dix Island, Me. Muscovite Hotite granite stands between the two last described, having both varieties of the mica, and differing from them only in that respect. It is found at Concord and several other places in New Hampshire. Hornblende granite is a variety in which the characterizing accessory is almost entirely hornblende. Biotite is, however, gen- erally found upon a microscopic examination. When the mica can- not be discovered by the unaided eye the name " hornblende " is given to the variety. Examples of this are found at Peabody, Mass., and Mt. Desert, Me. Hornblende-biotite granite is distinguished from the above in that it contains as essentials quartz and feldspar with both horn- blende and biotite. This combination gives a dark and sometimes an almost black granite, capable of receiving a fine polish. Examples of this stone are found at St. George, Me., Cape Ann, Mass., and at Sauk Rapids, Minn. One important property that is possessed by all granites is that of splitting more easily in one direction than another, so that it is easy to get out blocks large or small with practically parallel sides. This property is generally called rift or cleavage. It was caused by pressure before the rock was consolidated. The rift is always perpendicular to the line of pressure. When a stone is resting upon a face parallel to its cleavage plane it is said to be lying on its bed, and the face at right angles to the bed is called the edge. Rift is governed by the amount of pressure and the grain of the stone, so that while all granites have a rift they do not have it in the same degree. The finer-grained granites have the best rift, decreasing as the grains increase, so that a coarse-grained STONE. 19 variety is apt to be bunchy and requires considerable dressing to bring the faces of the block to a plane surface. This fact is well known to quarrymen, and an experienced hand will easily and quickly tell the character of the rift by the general appearance of the stone. Although it has been said that granite breaks more easily in one direction than another, on account of its peculiar structure it can be broken into blocks of almost any shape by skilled workmen with a stone-hammer, or with proper wedges and lewises if a large and irregular block be required. By this method the dividing force is exerted in whatever direction desired by inserting the wedges and lewises into holes drilled for the purpose, when by lightly driv- ing the wedges in succession the quartz which is holding the other crystals together is easily fractured and the granite breaks as de- sired. On account of this fact it is particularly adapted for paving- blocks and curbing, as it is cheaply and rapidly formed into the proper size and shape. Often a stone is barred from use as a pav- ing material for the reason that so much work is required to get it down to specification size. Gneiss is a variety of granite which differs from that just de- scribed only from the fact that its rift is caused by the greater por- tion of its mica being gathered in parallel planes so that the stone is easily broken along these planes. This is purely a physical dif- ference, as chemically and mineralogically it is the same as granite proper. This 'arrangement of the mica weakens the stone appreci- ably when set on edge, a fact which is not true of the granites. Dana defines gneiss as consisting of quartz, feldspar, and mica, and possessing cleavage planes. Syenite, according to Dana, consists of feldspar and hornblende with or without quartz. It will be noticed that the mica of granite and gneiss has disappeared and hornblende has taken its place. This latter mineral is hard and compact, varying considerably in its composition, but made up principally of silicate of magnesium and calcium, with some alumina and iron. It has its cleavage in two planes and is easily brought to a fine polish. In 1787 Werner adopted the definition quoted above from Dana, but later German geologists have used the term syenite to designate rocks without quartz, differing only from granite in that 20 STREET PAVEMENTS AND PAVING MATERIALS. respect and consisting mainly of orthoclase feldspar in company with one or more minerals of the amphibole (hornblende) or pyrox- ene group. This combination has seldom been used or found in this country. Porphyry. The mineral and chemical composition of the quartz porphyries is essentially the same as that of the granites, from which they differ mainly in their " porphyritic " structure. That is, the quartz has cooled first, thereby gaining -a crystalline form so that the rock presents to the eye a dense compact mass of stone in which can be seen crystals of quartz alone or quartz and feldspar together. This structure characterizes all the rocks of this type. The ferromagnesian minerals are often confined to the elements of the earlier period of crystallization, while the original quartz is found in the acid types only, and is generally restricted to the ground-mass. This change of structure prevents the formation of the rift so characteristic of the true granites. In composition it is generally about two-thirds silica. Diabase (Trap-rock). The essential constituents are plagioclase, feldspar, and augite, with nearly always magnetite and apatite in small proportions. The accessories are hornblende, biotite, olivine, etc. It is holocrystalline in form, but not often having perfect crystal outlines, as they are more or less distorted on account of interference during the process of formation. The feldspar gen- erally crystallizes before the ferromagnesian constituent, the former being often found wrapped around by the augite. As a rule it is finer-grained than the granites. It varies in color according to its constituents from a dark gray to almost black. The rock is hard, compact, and tough, but not easily broken into regular shapes. It occurs in dikes, where the material in a melted state poured into the fissures already created and, cooling, there divided masses of the same character into separate and distinct parts. This is often seen in limestone formations in Maine. The best illustra- tion of trap-rock in this country is probably the Palisades of New Jersey, although it is also found in Connecticut, Pennsylvania, and Virginia. It has a specific gravity of from 2.8 to 3.2. Basalt. This rock does not differ materially from diabase, but STONE. 21 is of more recent origin. The essential minerals are augite and plagioclase feldspar with olivine. The accessories are different varieties of iron and apatite with sometimes quartz, mica, etc. Structurally it varies from the glassy to the holocrystalline. Chemi- cally it is composed of silica 50 per cent, alumina 14, lime 10, magnesia 6, oxide of iron and manganese 12, and soda 4 per cent, with small quantities of potash, etc. In the United States it is found principally west of the Mississippi, and especially in Cali- fornia and Oregon. It is generally finer-grained than trap-rock. It was used very generally by the early road-builders of the old country, being carried great distances to form the surface of the roads on account of its fine wearing qualities. Sioux Falls Stone. This is a red quartzite or metamorphic sandstone. It contains 85 per cent of quartz-. Its color is due to oxide of iron. It is said to be the hardest stone in the country. It weighs 162 Ibs. per cubic foot and has a crushing strength of 28,000 Ibs. per inch. On account of its hardness it is not much used for building purposes, but has been to some extent in Western cities for pavements. It wears smooth with a glassy surface. ANALYSIS OF GRANITE FROM PORT DEPOSIT, MD. Per cent. Silica 73.690 Alumina 12.891 Ferric iron 1.023 Ferrous oxide 2.585 Lime 3.737 Magnesia 498 Potash 1.481 Soda 2.811 Water 1.060 Total 99.776 The mineral composition of this rock was calculated from the above analysis, but nothing more than an approximate result could be expected because the exact composition of the minerals is not known. It was supposed to be: STREET PAVEMENTS AND PAVING MATERIALS. Per cent. Biotite 9.7 Feldspars 46.4 Quartz 40.0 Epidote 3.9 100.0 Itfi crushing strength was 21,180 Ibs. per square inch. GRANITE FROM WATERFORD, CONN. Per cent. Silica 68.11 Alumina 14.28 Ferrous oxide 2.63 Lime 1.86 Magnesia 68 Sulphur 34 Oxide of potassium 5.46 Oxide of sodium 6.57 Total 99.93 An average of the tests made of this stone showed a crushing strength of 23,715 Ibs. per square inch. GRANITE FROM BLUE HILL, ME. Per cent. Water 0.27 Silica 74.64 Ferric oxide 1.56 Alumina 14.90 Lime 39 Magnesia Trace Potassium oxide 6.88 Sodium oxide 41 99.05 Prom this analysis the mineral composition was calculated to be: Per cent. Mica 35 Feldspar 10 Quartz 55 100 STONE, 23 GRANITE FROM NORTH JAY, ME. Per cent. Silica 71.54 Titanic oxide and iron peroxide 0.84 Alumina 14.24 Ferric oxide 74 Ferrous oxide 1.18 Lime 98 Magnesia .34 Soda 3.39 Potash 4.73 Water 61 Sulphur and carbon dioxide Trace 98.59 This rock is described as an even-grained white granite com- posed of white feldspar, quartz, biotite, and muscovite, with a small grain of red garnet. Its name is biotite muscovite granite. It showed a crushing strength of 16,310 Ibs. per square inch. A red granite from the same place had a strength of 22,367 Ibs. per square inch. PINK GRANITE FROM MILFORD, MASS. Per cent. Silica 76.07 Alumina 12.67 Ferric oxide 2.00 Oxide of manganese 03 Lime ' 85 Magnesia 10 Potash 4.71 Soda 3.37 99.80 Its compressive strength was 20,883 Ibs. per square inch. DARK GRANITE FROM BARRE, VT. Per cent. Silica 69.56 Ferric oxide 2.65 Alumina 15.38 Manganese Trace 24 STREET PAVEMENTS AND PAVING MATERIALS. Per cent. Lime 1.76 Magnesia Trace Sodium oxide 5.38 Potassium oxide 4.31 Loss on ignition 1.02 100.06 This specimen is described as a fine, even-grained typical granite containing both biotite and muscovite with quartz and feldspar. Its specific gravity is 2.672. It had a crushing strength of 17,254 Ibs. per square inch, weight applied perpendicular to the rift, and 19,957 Ibs. parallel to rift. GRANITE FROM PETERSBURG, VA. Per cent. Silica 64.12 Alumina 20.91 Oxide of iron 2.96 Lime 1.98 Magnesia 66 Sodium oxide 4.57 Potassium oxide. . 4.82 100.02 Its composition was: Per cent. Mica 15 Feldspar 60 Quartz . 25 100 Its crushing strength was 25,100 Ibs. per square inch. GRANITE FROM QUINCY, MASS. Per cent. Silica 75.14 Alumina 15.57 Ferrous oxide 2.49 Lime 1.85 Potash 54 Soda 4.41 100.00 Its mineral constituents are principally quartz, hornblende, and feldspar. The stone is very hard and capable of receiving a high STONE. 25 polish. Its crushing strength was found by Gillmore to be 17,750 Ibs. per square inch, and its specific gravity 2.669. GRANITE FROM EXETER, CAL. Per cent. Silica 75.35 Oxide of iron 3.94 Oxide of aluminum 13.69 Oxide of calcium 2.97 Oxide of magnesium .06 Oxide of sodium 1.14 Oxide of potassium 2.85 100.00 This stone has a shearing strength of 2419 Ibs. per square inch and a coefficient of expansion of 0.00000461 per inch. Granite from Millbridge had a coefficient of expansion of 0.000004 between 32 and 212 F. The total value of the granite output of the United States for the years 1896 and 1897 is $7,944,994 and $8,905,075 respectively. Of this amount nearly one-half was furnished by the States of Massachusetts, Maine and Vermont. The value of the paving-blocks for the same years was'$l,231,736 and $1,140,417. In 1896 Maine furnished $344,101 worth, Massachusetts $324,784, and Georgia $94,390; while in 1897 Georgia supplied $295,005 worth, Massa- chusetts $243,750, and Maine $172,637. This great falling off in values in New England is attributable to the increased use of asphalt for pavements in cities which in former years drew largely from the New England quarries. This use of asphalt not only de- creased the quantity of granite used, but also the value per thousand of the blocks themselves. VALUE OF GRANITE PRODUCT 1890 TO 1897. 1890 $14,464,095 1891 13,867,000 1892 12,642,000 1893 8,808,934 1894 10,029,156 1895 8,894,328 1896 7,944,994 1897 8,305,075 * * One-fourth for building. 26 STREET PAVEMENTS AND PAVING MATERIALS. ANALYSIS OF TRAP-BOCK FROM MERIDEN, CONN. Per cent. Silica 52.37 Aluminum oxide 15.06 ferric oxide 2.34 Ferrous oxide 9.82 Titanium oxide .21 Manganous oxide .32 Magnesium oxide 5.38 Calcium oxide 7.33 Potassium oxide 92 Sodium oxide 4.04 Water . , 2.24 100.03 This stone had a crushing strength of 34,920 Ibs. per square inch and a specific gravity of 2.965. TRAP-ROCK FROM MONSON, MASS. Per cent. Silica * 52.59 Ferric oxide 14.55 Alumina 23.42 Lime 9.05 Magnesia 28 Manganous oxide 09 99.98 Specific gravity 3.01. BIRDSBOROTJGH TRAP-ROCK, PENN. Per cent. Silica 46.87 Alumina 13.36 Ferrous oxide 2.71 Ferric oxide 9.79 Calcium oxide 14.70 Magnesium oxide 4.35 Sodium oxide 4.64 Potassium oxide 2.01 Titanium oxide. . 1.98 100.41 STONE. From the above and microscopic examinations the mineral con- stituents were found to be plagioclase, feldspar, pyroxene, and horn- blende, with 4.56 per cent of magnetite or .magnetic iron. This is a stone similar to that forming the Palisades of the Hudson in New Jersey. TABLE No. 1. ANALYSIS OF TRAP-ROCK FROM NEW JERSEY. Per cent. 52.29 14.30 16.68 9.35 Per cent. Silica 50.61 Iron 13.91 Alumina 18.34 Lime 7.01 Magnesia 6.73 Potash 0.08 Soda 1.60 Water . 1.72 4.58 0.48) 2.80) Per cent. 50.03 16.81 18.20 11.10 1.02 1.03 Per cent. 51.20 11.12 20.88 12.50 2.17 1.03 100.00 100.48 New Jersey Report, 1898. TABLE No. 2. 1.80 100.00 1.10 100.00 RESULTS OP TESTS MADE OP CRUSHING STRENGTHS OF DIFFERENT GRANITES. Locality. Position. Authority. Bed. Edge. 23013 23049 I. H. Woolson, Col. College Do 22548 21699 Do Do. 31881 30996 Do. Barre Vt 17254 19957 Wm. C. Day Swarthmore Col Do 16412 15845 Do. 26880 Watertown Arsenal Stone Mt., Ga North Jay Me white 28953 16310 Do. Do Do red 22367 Do. Westfield Mass 16091 Do. Exeter, Cal 21104 Do. Milford, Mass 20883 Do. Port Deposit, Md 21180 Booth, Garrett & Blair Phil Brandywine Granite Co.* Mount Airy, N. C 25075 20000 Do. Richie Bros., Phila. 23715 I. H. Woolson, Col. College Graniteville, Mo 24749 J. B. Johnson Wash Univ * Gneiss. Sandstone. Sand is formed by the decomposition or disintegration of rocks. It is a common occurrence to find pockets of sand in beds of earth or limestone. These are the result of boulders being surrounded 28 STREET PAVEMENTS AND PAVING MATERIALS: when these deposits of clay or stone were first made. Long after- wards the boulders decayed, and in their places are discovered pockets of sand. Its composition depends upon the minerals con- tained in the original rocks. When large deposits of stone decay, the particles of quartz, being indestructible, are borne away principally by two agencies, water and the winds. At this time the different products are often separated and the quartz, being heavier than the decomposed min- eral, is kept, by itself, as in the case of the sands of the seashore and those of a desert. Large grains are as. a rule affected more than small ones. Sea sands are less sharp than those of rivers and lakes, on account of the constant action of the waves and tides; while those of a desert or any place subject to the action of the winds are most rounded of all. It is only in desert sands that the smallest grains show any great effect of attrition. Sandstone is formed by grains of sand being deposited in beds by some agency and afterwards compacted. The sand proper is almost all quartz, as this mineral is indestructible from the ordinary action of the elements, while the cementing portion of the original rock has generally been decomposed and a new substance formed. The solidification of the stone is caused by great pressure, partial solution, fusion of some of its own parts, or by the infiltration of some cementing material, such as silica lime, or the oxides of iron. It is generally found in layers of variable thickness separated from each other by some softer material. The thickness of these layers probably depends upon the time one force acted continuously upon the sand, the softer deposits being made during the intervening period. The texture of the stone varies according to the sizes of the sand-grains, some being so fine as to be barely discernible, while others are very coarse, with every gradation between them. Mica and feldspar are sometimes ingredients, and upon the composition, as well as the cementing material with which it is held together, depends its value as stone. Sandstones are of many colors, the most common, however, being gray, yellow, and red. These colors are determined by the different combinations of iron; the red being due to peroxides, and STONE. 29 the yellow to hydrous peroxides. Some varieties will change color upon exposure to the air or the application of heat, on account of the oxidation of the iron. When the rock is solidified by any of the methods mentioned above, except pressure, the cementing substance must be considered as having been formed in place, and upon its complete formation the rock may be said to have entered upon a new era in its. his- tory. When the cement is calcareous, it has generally been deposited as mud or pulverized shells, but it has no binding properties until it has been partially dissolved and redeposited in a somewhat crys- talline form. This cement is sometimes mixed with red oxide and brown hydrated oxide of iron. In the hard and tougher sandstones the cement is generally silicious. If the grains have not been much rounded and are of irregular size, the interstices are very small and the silica is of no great amount and often hard to discover, as it may be hidden by dust or iron-stains. When the spaces are comparatively large the silicious cement is often deposited around the quartz-grains, increasing their size and completing the rock by a regular growth. Red sandstones are sometimes found to be easily disintegrated on account of the iron oxide separating the original grains from the cementing material. In street construction sandstones are used for curbing, cross- walks, flagging, and for paving the roadway of the street. Those most commonly used for these purposes in this country are the so- called Hudson River bluestone, Medina sandstone, Berea grit, and Colorado sandstone. The Medina stone and that from Colorado are the only ones of these used in pavements proper. Hudson River Bluestone. This variety is not generally considered to be a sandstone, but is known commercially in the localities where it is used as " blue- stone." It is very hard and durable and is used almost entirely for curbing, flagging, and cross-walks, for which purpose it is so well adapted on account of its great transverse strength. It is also very evenly bedded, so that its surface is smooth, making it espe- cially desirable for sidewalks. 30 STREET PAVEMENTS AND PAVING MATERIALS. This formation extends about 100 miles in New York from the southwestern towns of Albany County across Greene, Ulster, Orange, and Sullivan counties to the Delaware Eiver. The land along this line is of little worth for any agricultural purposes, its value being governed by the amount and quality of the stone it can produce. The different quarries vary much in the number and thickness of the quarry-beds, as well as the amount of the overlying earth. The beds range in -thickness from an inch up to three feet, and irf a few cases to six feet, the thinner layers being near the surface. The strata can generally be split in places parallel to the bedding and to the required thickness, the size -of the pieces being deter- mined by the vertical joints. Stones sixty by twenty feet have in some instances being obtained. The product of the different quarries varies somewhat in color as well as hardness and texture, and consequently in value. The texture ranges from the fine shaly or argillaceous to the silicious and even the conglomerate rock. The best is fine-grained, not very plainly laminated, and is composed almost entirely of silica cemented together by a silicious paste. It is therefore very hard and durable. It is so compact that it absorbs but little mois- ture and dries off quickly after a rain. A representative specimen had a specific gravity of 2.751 and contained 4.63 per cent of ferrous and 0.79 per cent of ferric oxide. It absorbed 0.82 per cent of water. At a temperature of from 1200 to 1400 F. its color changed to a dull red, and the piece was slightly checked and its strength impaired. Stone very similar to the Hudson River variety is found in Luzerne County, Penn. A sample of this being analyzed showed: Per cent. Silica and insoluble matter 94.00 Ferric oxide 1.98 Lime 1.10 Magnesia 1.00 Water and carbonic acid (volatile at red heat) 1.92 Alumina Trace 100.00 Its specific gravity was 2.656. STONE. 31 Medina Sandstone. This stone is found in New York State, extending from Oneida and Oswego counties on the east along the shores of Lake Ontario westerly to the Niagara Kiver. It also continues on into Canada, and is found to some extent in Pennsylvania and Virginia. It is of the Upper Silurian formation. It is generally a deep brownish red in color, though sometimes light and yellowish, and in a few localities gray. The coloring-matter is oxide of iron. In some instances where the red stone joins the gray, the iron has pene- trated the latter to quite an extent. It is both fine- and coarse- grained in texture, the latter being of a deeper color as the iron cement more easily penetrates the interstices between the larger grains. The gray stone often contains marine shells, but these are rarely found in the red. The metals in composition are copper and iron pyrites, oxide of manganese and iron, and carbonates of copper. Alternate freezing and thawing produce but little change in its strength. At Fulton, Oswego County, it forms the banks and falls of the river, and is noticeable for a half mile below, being formed in layers about two feet thick. At one quarry near Lock- port layers are found varying in thickness from an eighth to a quarter of an inch up to several feet, and in another from a few inches up to six feet. These layers are easily separated from each other, as they are partially covered with oxide of manganese. On the Niagara Kiver the stone is nearly white, but on going east it becomes tinged with red, and at Medina the layers are very strongly colored, and sometimes spotted red and white. The principal mineral constituent is quartz associated with some kaolinized feldspar. The cementing material is mainly oxide of iron with some carbonate of lime. It is evenly bedded, and the strata dip to the south. The beds are divided into blocks by sys- tems of vertical joints, generally at right angles to each other, greatly facilitating the work of quarrying. While quarries have been opened in many counties, the principal ones are located between Brockport and Lockport in Monroe and Niagara counties. At Medina the stone is hard, with oblique laminations in the bed. The gray stone is nearly all used for 32 STREET PAVEMENTS AND PAYING MATERIALS. paving-blocks, although other colors are so used as well as for flag- ging and cross-walks. A sample from Albion, Orleans County, had a specific gravity of 2.60. It had 0.51 per cent f ferrous and 0.06 per cent of ferric iron and absorbed 2.37 per cent of water. One from Oswego Falls had a specific gravity of 2.62 per cent, contained 0.59 per cent of ferrous and 1.71 per cent of ferric iron, and absorbed 3.73 per cent of water. Potsdam Sandstone. This formation is the oldest of any in New York in which sand- stone is quarried. It is found in several counties in the State. It is grayish, yellow, brown, and sometimes red in color, according to the amount and kind of iron in composition. It varies from a strong compact quartzite to a loosely coherent granular mass. The largest quarries are near Potsdam, hence its name. This stone is hard and compact, evenly grained, and reddish in color. It is largely used as a building-stone and also for pavements. It was used to some extent in the Columbia College buildings. It consists almost entirely of quartz, the grains being very clear, many of them showing a secondary enlargement. The cementing material is almost wholly silica. It absorbed 2.08 per cent of water, and has a specific gravity of 2.6. Under the heat test its color was unchanged. No checks appeared, and its strength was but little impaired. Berea Sandstone. This stone has an area in Ohio alone of about 15,000 square miles, and it also extends into four adjacent States. It is a well- defined deposit, moderately coarse-grained, from forty to sixty feet thick. It is generally gray in color, but sometimes spotted with iron stains, and in some localities a light buff or drab. It is quarried in great quantities at Berea, Ohio, whence it derives its name of " Berea grit." At that place it is covered by the Cuyahoga shale and by drift clay. At Peninsula, however, the formation is from thirty to sixty feet above the canal, making the quarrying work very easy. It is of great value for building-stone, as it is STONE. 33 easily gotten out into regular shapes and is cut without difficulty. It is the best grindstone grit in the country. It is sufficiently por- ous below the surface to carry petroleum, gas, etc. It is too soft for paving purposes, but is used very generally for curbing and nagging. The formation is supposed to represent an old shore-line, as much of the surface is ripple-marked and shows many signs of worms. An analysis of an average sample gave: Silica 96.90 Iron oxide . 1.68. CRUSHING STRENGTH. Lime .55 Potash and soda 55 Bed 17,500 Carbonic acid, water, etc 32 Edge 14,812 100.00 Heated to 1200 to 1400 F. its color changed to red and its strength was entirely gone. Gillmore found the crushing strength of sandstones- to vary from 4025 to 17,725 Ibs. per square inch. Colorado Sandstone. In Boulder County, Colorado, are several deposits of sandstone that furnish stone for building and street-construction purposes. The products have been used principally in Denver and Omaha, but are scattered about in many smaller towns in both States. The stone varies in color from a gray to a light red according to the composition of the iron compounds. It is generally found in layers from j inch to several feet in thickness at an angle of about 30 with the horizon. It splits easily along the cleavage planes, and breaks readily at right angles, so that it is formed into flagging, curbstones, and paving-blocks without difficulty. It is hard and tough and wears well and smoothly in a pavement. Its grain and texture are such that, al- though smooth, it is never slippery, and, when laid on an un- yielding base, after a little wear it forms a smooth and pleasing pavement, very similar to one made of Medina stone. STREET PAVEMENTS AND PAVING MATERIALS. The following table shows the results of tests of Colorado sand- stone, made for the State Capitol and given in '" U. S. Mineral Re- sources" for 1886: TABLE No. 3. Locality. Color. Position. Crushing Strength per sq. in. Specific Gravity. St. Trains Light red j Bed 11505 2.393 1 Edere 17187 Fort Collins Gray j Bed 11707 2.252 / Edge 10784 Do Light red jBed 12740 2.432 ( Edge 17487 gtout Dark crrav j Bed 10514 2.263 "j Edge 12585 Grayish white ( Bed 18573 2.379 i Ed g e 17261 ANALYSIS OF COLORADO SANDSTONE. Stout. Per cent. Silica 95.50 Iron and alumina 0.78 Calcium oxide 0.88 Magnesia 1.45 Carbonic acid and water 1.18 99.79 Buck Horn. Per cent. 96.45 1.90 1.06 0.64 0.00 100.05 Limestone. Although limestone as well as sandstone is a sedimentary rock, it differs from it very much in its formation. Water flowing down from a rough mountainous country carries with it a large amount of matter both in solution and suspension. As the stream reaches any large body of still water its velocity gradu- ally decreases and that portion in suspension is deposited, the coarser and heavier near the shore and the finer farther out. Calcareous matter as a rule, being soft, is generally fine and is borne from a distance and finally deposited as silt. All waters flowing as above contain a considerable quantity of lime in solu- tion which, being in part precipitated, serves to consolidate the silt. From this same source certain marine animals derive their supply f UNIVERSITY STONE. 35 for their shells. Upon the death and decomposition of the animal life the shells and corals axe left and, breaking up, in time form calcareous banks which later on become beds of limestones of more or less fragmental nature. The theory of the formation of oolitic varieties is somewhat different. It is supposed that certain fragments of calcareous mat- ter have been deposited upon the bottom of some ancient sea, and that they were kept in motion by the action of the waves or some other force, preventing their solidification. If, then, the lime in solution should from any cause become too much for the absorption of the marine animals, it would be precipitated, and would form around the fragments, which, being in motion, would become ap- proximately spherical in shape. But as the precipitation continues the interstices become filled and beds of solid stone are formed having the appearance peculiar to this variety. Both of the above formations are generally in well-defined beds nearly level when not disturbed by any subsequent force. When, however, as often happens, the strata are found at all angles with the horizontal, they have been acted upon by some of the forces so frequent during the formation of the earth's crust. In the course of time some of these beds may be broken up into fragments comparatively small and after having settled into a permanent position and again consolidated by the further de- posits of lime or iron oxides in the interstices of the fragments. It is thus that the metamorphic limestones are formed. Limestones differ greatly in structure from the variety highly charged with fossils to the hard compact rocks denser and heavier than granite. They also vary in color according to the iron and carbonaceous compounds that may be present. As calcite crystallizes so readily, few limestones are entirely amorphous, but range gradually from the amorphic to the holo- crystalline. Few limestones are pure calcium carbonate. Impuri- ties are easily mixed with the lime during the formation. Mag- nesium is often found in considerable quantities, when the variety is called magnesian. When this amount exceeds 45.65 per cent the stone takes the name of dolomite. Dolomite has a specific gravity of about 2.9. 36 STREET PAVEMENTS AND PAVING MATERIALS. Silica and clay are often found in composition, and when they exist in quantities exceeding 10 per cent the stone is said to be hy- draulic. That is, upon being burned and ground it can be made into mortar that will harden under water, a property not belonging to ordinary limestones. A specimen of this variety from Kondout, N. Y., analyzed according to Dana: Per cent. Carbonic acid 34.20 Lime 25.50 Magnesia 12.35 Silica 15.37 Alumina 9.13 Sesquioxide of iron 2.25 98.80 Marble is a name given to certain crystalline limestones that are of such a character as to be capable of receiving a high polish and so become of value for building purposes. Certain dolomites are also called marble. Bedford Oolitic Limestone. This stone is properly a calcareous sandstone or freestone, dif- fering from sandstone in having its grains composed of carbonate of lime instead of quartz, and in the grains being small fossils in- stead of sediment transported by water from some former rock- mass. It differs from other limestone in its granular texture and freestone grain. It occurs in a bed varying from 25 to 100 feet in thickness. The greater portion of it is free from laminations or bedding seams. In almost every quarry or natural exposure there is at least one system of vertical joints, but they are rarely so numerous as to prevent the occurrence of the stone in large dimensions. It is a granular stone, and both the grains and uniting cement are carbonate of lime. In the common sandstones the grains are hard and approximately angular; in this stone the grains are al- ways soft and either round or rounded. In the silicious sandstones the grains are harder than the cement, in the Bedford the cement is harder than the grains. These grains are nearly all small fossil forms, but when they are large, that portion of the stone containing them is thrown away and not used, the finest-grained being much STONE. 37 the better if it is uniform in texture and color. The original color was blue, but it is sometimes found buff and even a mixed blue and buff, according to the chemical changes in the iron compound. It is found in several counties of Indiana and extends across the Ohio River into the State of Kentucky. It takes its name from the village of Bedford, Indiana. A series of tests to determine its compressive strength gave an average of 7000 pounds per square inch with a maximum of 13,200 pounds. Experiments on 1-inch cubes were also made to ascertain its fire-resisting qualities. Heated to 1000 F. and plunged into cold water the samples were not affected. Heated to 1200 and treated in the same manner the cubes crumbled slightly along the lower edges. Heated to 1500 and cooled in the air the cubes retained their form, but were calcined in a marked degree. The principal use of this stone is for building purposes. It is easily cut when taken from the quarry, but hardens upon expo- sure to the atmosphere. It is also used in street construction for curbing and flagging, being easily sawed to any required dimen- sions. TABLE No. 4. ANALYSIS OF BEDFORD STONE FROM DIFFERENT LOCALITIES. .Quarry. Crushing Strength. Specific Gravity. Calcium Carbonate. if 1 si CT3 jl Iron Oxide and Alumina. 1 Bedford Ind 5600 2 47 98 27 84 64 15 99 90 Hunter Valley 4100 98.11 92 86 16 100 05 Romona 9100 2.48 97.90 0.65 1.26 18 99 99 Twin Creek ... . 9900 2 51 98 16 97 76 15 100 04 Trenton Limestone. This deposit takes its name from a township in Oneida County, New York. It is one of the most important in this country, ex- tending from Maine on the east to the Eocky Mountains on the west and from Hudson's Bay to Alabama. By its decay it has formed soils of great fertility. That of the celebrated Blue Grass region of Kentucky is a direct product of the decomposition of this stone. 38 STREET PAVEMENTS AND PAVING MATERIALS. In its original locality it is dark blue in color, verging to black and lying in even beds which are sometimes separated by layers of black shale. It contains well-preserved specimens of the Lower Silurian Age. It changes in color and composition as it extends in different directions, but is easily followed by its distinctive features. It is used for building purposes, burned into lime, and broken up for road-building, according to the wants of any particular sec- tion where it is located. Table No. 5 gives the result of several analyses of this stone. TABLE No. 5. '> ill | 2 S if ii | _o o o> O c c o c / ,& 3 ^r; r: o3 i a ^i-3 ojS III o a "5 o | |i 02 ^ di OD cc c Average of 7 specimens non-mag- 2.698 90.976 1.828 2.155 .489 .453 .470 .265 3.794 Average of 11 specimens mag- nesian .... 2.681 64.323 23.541 3.410 .414 .632 .590 .278 6.078 Table No. 6 shows the analyses of different limestones and their resulting limes. TABLE No. 6 Bridgeport, Penn. Longview, Ala. Barton, Ga. Hanover, Penn. Calcium carbonate. . . Magnesium carbonate Oxide of iron and alu- mina Silica and silicates . . . Stone. Lime.; Stone. Lime. Stone. Lime. Stone. Lime. 55.70 41.97 0.72 1.58 1.35 2.95 99.16 0.75 Trace 0.15 1.50 0.56 0.26 0.37 56.02 38.43 1.50 1.94 83.12 8.23 1.236 7.252 1.622 0.03 0.63 o.oa 0.53 Calcium oxide Magnesium oxide Potassium carbonate 58.33 37.37 97.30 34.070 55.736 92.00 3.55 4.23 7.43 Total 99.97 100.00 100.06 99.99 97.89 99.916 99.44 100.34 STONE. Table No. 7 gives the composition of limestone from different localities. TABLE No. 7. 3 = i u 4J S V 2 S r* ^ a "3 . H ^ M Cg 5 s S T* * s o M S C- E ^3 s 0> Q E" i-? - 3 "Cb C T3 |2 ^o y 3 S3 1" I | 5 s 5 S Howard Co Md 77.82 3 19 5.15 13 60 0.24 91 538 944 1 3:14 O OQ 2 854 Hannibal Mo 98.80 .02 40 06 Ulster Co., New York 97.00 0.40 2.60 95.30 1.25 3 62 Nat ural Bridge, N.Y.*.... Vernon N J 52 45 43.25 0.24 1.34 0.24 2.28 5 45t 6 35J 22.43 29.48 47.73 Columbus, Ohio 93.21 4 70 1.74 West Winfleld, Penn 95.10 1.12 1.00 2.78 Lannon, Wis 52.29 42.27 1.68 3.96 Calumet Co Wis 55 09 43 96 .36 .59 98 29 462 167 533 578 * Dolomite. t Alumina. $ Phosphorus. In five samples of Missouri limestone the calcium carbonate averaged 99.2*. Limestones tested by General Gillmore for crushing strength varied from 3450 to 25,000 Ibs. per square inch. CHAPTEE III. ASPHALT. ASPHALT or bitumen under some name has been in use for many ages. The terms have been used so much synonymously as well as interchangeably that it is often difficult to tell just what varie- ties are referred to. The practice is still kept up to a certain ex- tent, some authorities speaking of asphalt, others of asphaltum, and some of both, while all are practically referring to the same sub- stance. Some specifications have mentioned pure asphaltum. It would be extremely difficult at the present time to establish legally what pure asphaltum is. As one writer has said, asphalt is an occurrence and not a distinct substance. In America natural bituminous pavements are called asphalt; in France, asphalte comprime; in Germany, S tamp f- Asphaltum; and in England, asphalte. In the English translation of the Bible it is stated that Noah was told to pitch the ark with pitch; and in another chapter in Genesis, that when the tower of Babel was built slime was used for mortar; and in Exodus, that the ark of bulrushes in which Moses was found was daubed with slime and pitch. In each of these cases the Latin version renders the words " slime " and " pitch " as " bitumen " except in the case of Moses' ark, both words being used in the same sentence; " pitch " is rendered pice, the ablative form of pix. In the Greek version these words are all rendered acrcfiaTiTos, or from the same root except as above in Exodus, where ao- general use in the different cities of the country. The crude material is refined at South Amboy, N. J. When refined, the asphalt contains of bitumen 97.22 per cent,, mineral matter 1.50, and organic matter 1.28. The bitumen ia 72 STREET PAVEMENTS AND PAVING MATERIALS. composed of petrolene 77.90 and asphaltene 22.10 per cent. The specific gravity is 1.08. * Kentucky Asphalt. This material is found in the Chester group of subcarboniferous rocks along the eastern and southern edge of the western coal-field of Kentucky. It also exists in the conglomerate sandstone of the coal-measure, but under heavy cover. Its principal localities are in Breckinridge, Grayson, Edmonson, and Logan counties. The deposit is really a sandstone impregnated with bitumen. The rock is not found in distinct veins, but more in the shape of pockets of varying area, having a depth at the centre often of 10 feet. The material is mined by stripping off the overlying sand- stone, leaving the bituminous rock exposed and ready for excava- tion. The stone is fine-grained and nearly all silica, carrying on an average some 8 per cent of bitumen, but at times as much as 12 per cent. After the bitumen is extracted, the rock analyzes: Per cent. Silica 96.88 Sesquioxide of iron 0.81 Alumina 0.46 Lime 0.34 Magnesia 0.20 Soda 0.81 Potash 0.20 Combined water and loss 0.25 99.95 In preparing the rock for paving purposes it is first ground in mills consisting of horizontal plates to which raised lugs are at- tached revolving at a high rate of speed. The rock is broken by impact and carried by centrifugal force through a screen surround- ing the mill. After leaving the mill and passing a second screen, the powder is borne by elevators to revolving heaters, where, after being raised to a proper temperature, it is taken to the street and laid in the usual manner. The entire operation of grinding and heating is automatic, the rock not being touched by hand from * From a paper by Marshall Morris. Read before the St. Louis Engineers' Club. ASPHALT. 73 the time it is placed in the elevators to be carried to the mills till it is delivered on the street. Care, however, is required in selecting the rock for the crushing so that the product may contain the required amount of bitumen when placed in the pavement. Portions of two streets in Brooklyn, X. Y., were paved success- fully with this material in 1889. In 1890 a small amount was laid on a sidewalk at the wagon- entrance of the Adams Express Co. in Louisville, Ky. Since that time it has been used with good results in many other cities, but most extensively in Buffalo, N. Y., in conjunction with the German rock asphalts, and also in St. Louie, Mo. It has, however, been successfully used in combination with the limestone asphalts of Texas and Indian Territory. The proportion generally recommended in connection with the foreign asphalts is: Per cent. Kentucky rock 70 to 80 Gterman " 30 to 20 Texas Asphalt. The asphalt deposits of Texas are in Uvalde County. There are two areas of bituminous rock, one in the extreme western por- tion of the county along the courses of the Turkey, Gato, and Olmos creeks, and the other near the Nueces River near the South- ern Pacific Railroad. The first-mentioned lies along these creeks in a continuous area about 4 miles long north and south, and half a mile or more in width. The asphalt occurs as an impregnation of a porous limestone. The principal mining is done at Carbonville, about 6 miles from the Cline station of the Southern Pacific Railroad. The quarries are easily worked, as there is very little overlying material to be removed. The rock is treated on the spot and is sold in two con- ditions, as a mastic and as a gum. The mastic is prepared by grinding the rock to the required fineness, when it is melted and run into moulds, and when cool is ready for shipment. This product is used for pavements and is further treated by the addition of sand, residuum oil, etc., as may 74 STREET PAVEMENTS AND PAVING MATERIALS. be required at the place where it is to be laid. A portion of a street in Houston, Texas, has been paved with this material, and it has also been used to some extent in New York City. The gum, however, is more valuable commercially. This is prepared by dissolving out the bitumen from the rock with, benzine. The benzine is then distilled off and used over and over again with but little loss. The bitumen is obtained in an almost pure state. Two different samples of the rock analyzed as follows: Per cent. No. 1 bitumen 25.18 Organic matter 1.46 Mineral residue 73.36 100.00 No. 2 bitumen extracted by petroleum naphtha (petrolene) . . 6.40 " chloroform (asphaltene) 2.63 Total bitumen 9.03 Mineral, residue . 90.97 100.00 The mineral residue was found to be carbonate of lime with an appreciable amount of oxide of iron and a trace of magnesia. Although the above samples show quite a difference in the amount of bitumen, the average is from 14 to 15 per cent. Nueces Biver Deposits. The bituminous rock in this locality is a sandstone. Its area extends from a point on the Nueces Eiver about 9 miles below the Southern Pacific Eailroad for more than 3 miles. Its width has not been determined. It outcrops in places along the river, and at Waxy Falls a stratum of sandstone bearing some bitumen was found 10 feet thick about 25 feet below the top of the bluff. Next T)elow this is another stratum, 5 feet in thickness, containing so much bitumen that under the heat of the sun it oozes out over the surface. Samples of rock taken from the outcrop near Waxy Falls upon analysis gave the following results: ASPHALT. 75 Per cent. At the surface, bitumen 13.24 Two feet below the surface, bitumen 15.03 Sand 74.03 Oxides of iron and alumina 7.76 Organic matter, water and undetermined 3.18 100.00 Four feet below the surface, bitumen 12.36 Utah Asphalt (Gilsonite). Quite a deposit of bitumen of a very pure quality exists in the eastern part of Utah and the western portion of Colorado. It is called " Gilsonite " from Mr. S. H. Gilson of Salt Lake City. It is mined in the counties of Uintah and Wasatch, Utah and Clear Creek Co., Colorado. Physically it is a black substance, quite hard and very brittle, "breaking with a conchoidal fracture. It has a brilliant lustre and in appearance is much like glance pitch. It occurs in veins of from one-sixteenth of an inch to 18 feet in thickness, and some- times extending a distance of 10 miles. These veins were originally cracks in the rock which in some iray have become filled with the gilsonite presumably at the same time the rupture occurred, as pieces of rock are frequently found entirely separated from the adjacent walls. The theory is that the gilsonite while in a plastic state was forced into the rock-fissure "by some unknown force. No attempt has been made to explain the previous condition of the material. There are six well-defined veins of this material, and the follow- ing estimate has been made of their contents: Tons. Duchesne vein 941,916 Culmer vein .' 410,666 East and West Bonanzas 10,504,000 Cowboy vein 8,888,000 Black Dragon vein 3,000,000 23,744,582 It is easily mined, as it yields readily to the common pick and "breaks freely upon the rock, and requiring no sorting after a depth is reached below the influence of the atmosphere. 76 STREET PAVEMENTS AND PAVING MATERIALS. The above veins are from 100 to 200 miles from a railroad, and, on account of the roughness of the country, the transportation charges are heavy. Gilsonite is used chiefly in the arts and manufactures, but it is sometimes added to other bitumens for paving mixtures. It is wholly soluble in carbon bisulphide, and partially so in ordinary ether, alcohol, petroleum ether, and chloroform. Chemi- cally it is composed of: Per cent. Carbon 88.30 Hydrogen 9.96 Sulphur 1.32 Ash 0.10 Oxygen and nitrogen 0.32 100.00 Since the above analysis was made, Prof. Day says that a further investigation shows the nitrogen to be 1.96 per cent, and he thinks the figures for hydrogen are correspondingly too high. Bituminous limestone has also been found in Utah, but it has never been mined to any great extent. Indian Territory Asphalt. The asphalt deposits of this section are located in the south- western part of the Territory, in the Arbuckle Mountains near the Washita Eiver. They extend over an area of several square miles. The asphalt is found in composition with sand and also as bitumi- nous rock. The former contains 16J per cent and the latter 21 per cent of bitumen. The same asphalt is used in pavements in its natural state. It is heated in a special apparatus and laid in much the same way as the European rock asphalts. To the rock asphalt, however, 50 per cent of sand asphalt is added before heating, when it is laid as before. Nearly all the work in the development of this deposit has been done in the last few years, the charter of the company from which the present company leases it having been granted in 1895. Where the material has been used it has given good satisfaction, though a soft pavement would naturally be expected from one con- taining so great an amount of bitumen. ASPHALT. 77 By a process of refining, a bitumen of about the consistency of maltha is produced when required. It is first separated from the sand by being boiled in water. The bitumen, having a less specific gravity than the water, rises to the surface, when it is skimmed off, and the operation continued as long as desired. Montana Asphalt. A deposit of bitumen generally termed asphalt, but not strictly BO under the definition previously given in this chapter, is found in Montana. At ordinary temperatures it is soft and will pour slowly. Upon being treated with carbon bisulphide, 95 per cent was dissolved. Treated with gasolene 80 per cent was found to be petrolene, the insoluble matter in both cases being leaves, feath- ers, bugs, flies and other insects. The deposit has never been de- veloped commercially. Cuban Asphalt. There are four distinct submarine deposits of asphalt situated in the Bay of Cardenas, all within twenty miles of the city of the same name. The first is in the western part of the bay and is practically pure bitumen. It is used principally in the manufacture of varnishes. It has been mined here since about 1870 by sinking a shaft some 125 feet deep in the bottom of the bay. The opera- tion of mining is very simple. A lighter is moved over the shaft and a long iron bar, pointed at the end, is dropped so that its own weight detaches portions of the asphalt with which it comes in contact. The operation is repeated until a sufficient quantity has been detached, when a diver loads it into nets and it is hoisted to the surface. The other deposits produce a lower grade of material which is suitable for pavements. They are operated in practically the same manner as that just described. The largest of these is about 15 miles from the cit} r , near Diana Cay. It has been operated since 1870, producing some 1000 tons per year without any apparent diminution in the supply. This deposit seems to be inclosed within a circumference of about 150 feet and in water 12 feet deep. 78 STREET PAVEMENTS AND PAVING MATERIALS. There are also deposits of asphalt near Puerto Padre on the north coast of the island, as well as some liquid bitumen near Santiago de Cuba. Barbadoes Asphalt. A variety of bitumen known as " glance pitch " has been known for some time on the island of Barbadoes. It is a hard brittle asphalt, breaking with a clear brilliant fracture. It occurs in veins from an inch to a foot in thickness. It has never been used in, and is not suitable for, pavements, but its output is entirely con- sumed in the manufacture of varnishes, etc. It is almost wholly soluble in carbon bisulphide. Asphalt in Turkey. An important asphalt mine is located near Avalona on the Adriatic Sea. It belongs to the Sultan, but has been leased to a French syndicate. The material is taken out in both a solid and a liquid state and is exported to Europe and America. There are also other mines in the interior of Turkey in Asia belonging to the government and private parties, but they have not been worked to any extent on account of the bad transportation facilities. Dead Sea Asphalt. About the Dead Sea there is quite a quantity of asphalt be- longing to the government. It is not used for any purpose, and persons found collecting it are fined or otherwise punished. It is said that in former times asphalt was frequently found floating on the surface of the Dead Sea, especially after earthquakes. Syrian Asphalt. There are four asphalt mines in Syria, but the one at Hasbaya is the most important. The mine 'has been worked at intervals by different lessees since 1864, but only 1000 tons per annum were taken out when actual operations were carried on. It is the private property of the Sultan, and has not been worked to any extent since 1893. From 1882 to 1892 about $70,000 worth of this material was exported to the United States, and in 1897 $3439 worth. In 1893 the product was worth about $90 per ton. 1 ASPHALT. 79 It is said that asphalt exists in this vicinity in large quantities, and under a favorable government thousands of tons might be mined each year. A sample of the Hasbaya product is thus described: It is black with a bright jetlike lustre, making a blackish-brown streak on unsized paper. It is so brittle that pieces may easily be broken off with the fingers. It is very combustible, but a splinter held in the flames will melt before igniting. Its specific gravity is 1.104. Egyptian Asphalt. No natural asphalt is found in Egypt except in very small quan- tities above Suakim near Abyssinia, where it cannot be worked profitably, and some small deposits on the east coast of the Bed Sea. It is said, however, that two firms in Egypt manufacture arti- ficial asphalt, importing material for their use from Italy, France, and England. What their process was, or to what uses their prod- uct was put, could not be learned. CHAPTER IV. BRICK-CLAYS AND THE MANUFACTURE OF PAVING-BRICK. THE word clay as ordinarily used means any earthy substance which can be worked up with water into a plastic mass that when dried will retain any shape into which it may have been formed. Strictly speaking, the term applies to a single mineral, hydrated silicate of alumina, or kaolin. It is not, however, a natural mineral, but is the product of the decomposition of feldspar. Beds of feldspar have often been found covered by the kaolin formed by the decomposition of a portion of its mass. This occurs when the feldspar is exposed to the action of water containing carbonic acid gas, which acts upon the alkaline base of the mineral and carries it away in solution, leaving the silicate of alumina be- hind. As, however, feldspar is seldom found in large quantities by itself, so deposits of pure kaolin are very rarely found. Com- mercially they are of considerable value. When pure, kaolin is composed of: Per cent. Silica 46.3 Alumina 39.8 Water 13.9 This is represented chemically by the formula Al 2 3 2Si0 2 2H 2 (X It is the base of all the substances known as clays, and as they are formed by the decomposition of rocks, so their chemical composi- tion varies with that of the rocks from which they are derived. Quartz and feldspar are the two minerals found in the greatest abundance in the earth's crust, and, very naturally, it is expected to find sand and clay as the most common of the products of the decomposition of rocks. 80 BRICK-CLAYS MAN UFA CTURE OF PAVING-BRICK. 81 Feldspars are divided into three separate varieties: orthoclase, or potash feldspar; albite, or soda feldspar; and anorthite, or lime feldspar, each of these varieties being minerals more or less com- plex. These, too, are at all times in the same mineral, which must be named by one of the terms used in the classification, the one in greatest abundance giving the character to the compound. All feldspars are acted upon by the atmosphere. The oxygen, carbonic acid, and water contained in it, when taken together, form a solvent that is hard for rocks to resist, especially when supple- mented by soil-waters containing more or less acids derived from decaying vegetable products. Under these influences granites and other rocks containing feldspar, especially the potash variety, are rapidly decomposed. The feldspar having lost its cementing property, the rock falls into pieces. The carbonate of potash is dissolved in the water and borne away. The particles of quartz, mica, and other accessory minerals remain and become assimilated with silicate of alumina from the feldspar, all together making up the product commonly called clay. It can be readily seen that it cannot be a pure mineral and that its composition must vary greatly. Kaolin has a specific gravity of from 1.5 to 2.2 and is white in color. It is soft to the touch when dry, and very plastic when wet. It has two marked chemical characteristics, insolubility and infusibility. It being the product of a soluble body, the former might be expected. It is not affected by ordinary chemical agents, nor by temperatures that have thus far been produced in the arts. It is consequently of greatest value in the manufacture of crucibles and other refractory utensils used in chemical research. While this infusibility is true of kaolin, it is not true of clay. For the addition of different minerals found in nature often forms a compound that is easily fused. These minerals when thus used are called fluxes. Naming them in the order of their effectiveness, they are potash, soda, iron, lime, and magnesia. Very small amounts of one or more of these substances are required in any clay to destroy its value as a refractory material. But on the other hand the finely divided silica of the original rock which is always found in a greater or less amount in most kaolin detracts not at all from its heat-resisting qualities, the silica 82 STREET PAVEMENTS AND PAVING MATERIALS. itself being practically infusible. For this reason free silica is prac- tically the only impurity that is permissible in kaolin without de- tracting from its refractory material. Feldspar and mica are found in nearly all clays, the latter often being discernible to the naked eye. The former, however, cannot be thus distinguished from free silica. These two minerals both contain alkalies in combination with silica and alumina, and so it is understood how alkalies can be discovered in clays by analysis, when it would not be expected to find them existing in a free state in a mineral whose origin was due to the action of water and other solvents. The oxides and other compounds of iron are generally found in clays. The sesquioxide and the protoxide are the most common forms, but carbonates are not uncommon, and sulphides are oc- casional as well as injurious impurities. Iron gives the color to clays. The tints vary from buff to red, and from drab to blue or green, the amount of iron not seeming to determine the degree of color. The effect, too, of iron is very much heightened and changed by heat. The colors produced by burning vary from cream to per- fectly black, with nearly all the intervening tints and shades, though the reds, browns, and greens are most common. A hand- some cream-colored brick is made at Milwaukee, and others of pink color in certain parts of Canada. Organic matter is frequently found in clays, but it is of little importance. It is generally caused by the presence of decomposing carbonaceous matter. It gives a color to the clay, but when sub- jected to even a comparatively low heat it is easily driven off. It is very seldom, therefore, that its presence is detrimental. Clay can then be called a compound of a clay base with sand, feldspar, mica, and other silicates colored by iron oxides or organic matter. The properties of clays by which their values are determined are: plasticity, so that when wet it is possible to shape it into any desirable form; > the maintenance of this form, while it is being burnt, to such a degree that its shape is permanent; and its re- fractoriness, so that it is able to withstand great and long-con- tinued heats without fusing. Plasticity is a property that is shared by practically all Delays. BEICK-CLA YS MANUFACTURE OF PAVING-BRICK. 83 As a rule they all tend towards crystallization, and some kaolins are made up of masses of unattached scales. These are slightly plastic and can be made more so by grinding and kneading in water, when an examination shows that the crystalline structure has been broken up. Naturally, plastic clays do not show this structure, indicating that a clay's plasticity depends upon the extent to which this structure has been destroyed. In several places clays are found that are entirely free from plasticity, even after being ground and treated with water. Frost and the action of water disintegrate them and a fine sand is formed, but a chemical analysis shows them to be almost pure kaolin. Permanence of form in clay ware is caused by heat. In ancient times and in dry climates bricks that were only dried in the sun have lasted for a considerable time, but they could not be called per- manently shaped. Generally speaking, if heat has been applied only sufficiently to drive out the water mechanically mixed, the mass will be porous, somewhat shrunken in form, and readily disintegrated under the action of the elements. If, however, the heat be increased and continued, the clay will shrink farther and harden, until, when the proper point is reached, a new material has been formed which is practically indestructible. If the heat be continued still further, the clay will become harder, more brittle, and often deformed. Other clays will melt and become glassy and lavalike, as is so often seen in arch-bricks of an old-fashioned wood-burning kiln. Argillaceous matter as a whole is divided into two classes, clays and shales. Chemically they are often the same. Physically the shales can be detected by their stratified or laminated structure. They are hard and compact, and require considerable work to pre- pare them for use. Like the different kinds of granite, clays merge into shales and shales into clays, so that the line separating them must be an arbitrary one. Shales must not be confounded with slates, which they very much resemble. Slates have been formed by the action o,f heat combined with great pressure. They are hard and durable rocks, while shales will rapidly disintegrate when exposed to the action of the atmosphere. As a rule shales 'are formed in deeper water than clays. Their 34 STREET PAVEMENTS AND PAVING MATERIALS. laminations are supposed to have been caused by the intermittent deposit of the material of which they are formed, by pressure, or by both. According to their- composition, clays are divided into high- and low-grade clays. The first comprises clays and shales that con- tain in conjunction with not less than 50 per cent of kaolin base little else than finely divided silica. The other constituents rarely exceed 5 per cent and are often as low as 3 per cent. The second division includes all other clays and shales. They may run from 10 to 70 per cent of kaolin base, but always contain a large amount of fluxing material. The alkalies compose from 2 to 5 per cent, while lime, magnesia, and iron add two or three times as much more. As a rule the clays of the first division are refractory, and those of the second fusible. Clays, however, are popularly classified into fire-clays, shales, and mud-clays. The first is a refractory clay of a high grade that cannot be fused at any temperature used in the arts. It is also subdivided into non-plastic and plastic varieties. The former are something of the nature of rocks, but upon exposure to the weather they crumble into fine particles similar to sand. With ordinary grinding they show no plasticity whatever, and would thus seem to want one of the main clay characteristics, but an analysis plainly shows their true character, while continued and repeated grinding develops plasticity. Plastic fire-clays differ from mud-clays in the chemical com- position, which gives them their refractory qualities. Kaolin or pure clay is, as has already been said, practically infusible, but it is seldom found in a pure state. The great mass of clays distributed over the earth's surface is impure, and upon the quantity and qual- ity of the impurities depends the fusibility and refractoriness of the clay. The principal impurity is quartz, which is not fusible at or- dinary temperatures used in manufacturing, so that the fluxing ele- ments of a clay are generally considered to be its impurities except quartz. Lime and magnesia are valuable as fluxes, except when they are present as carbonates in any considerable quantity, as they then lower the melting-point of the clay and a hard, tough brick cannot be produced by the burning. The condition of iron is also BRICK-CL ATS MANUFACTURE OF PAVING-BRICK. 85 important, free oxide being the least injurious. The more evenly it is scattered through the clay the better, so that vitrification may be as regular and even as possible. Just how much of these fluxes can exist in a clay without de- stroying its refractory properties is uncertain. It depends greatly upon the character of the clay as well as upon the nature and number of the fluxes. Generally the finer-grained and less dense a clay is the more easily it is fused. The limit of the fluxes is probably from 5 to 7 per cent. In the Eeport of the Geological Survey of Ohio analyses of fourteen different fire-clays used in the manufacture of paving- brick and sewer-pipe are given. The average of these showed 93.41 per cent of clay and sandy matter, with 5.65 per cent of iron and fluxes. In commenting on this, it is said that this would indicate a clay more fusible than the stone- and yellow-ware clays, but far less fusible than the shales; also that the facts prove this, as the above clays, while vitrifying very well up to a thickness of two inches, are very difficult to vitrify when made into a brick or block. The same authority gives the analyses of ten shales used for paving-brick and sewer-pipe. The average composition of these was: Per cent. Clay and sand 84.78 Fluxes 13.22 98.00 Enough has already been said to show the difference between fire-clays and shales. Their product also, when burned, is very different. The shales, containing so much more of the fluxing ele- ments, can be more completely vitrified. A shale brick is harder, denser, and more brittle than one made of fire-clay. The latter absorbs more water, but is tougher. The advocates of both kinds claim all the virtues for their own product and allow very little to their rivals. It is certain, however, that good pavements have been laid with both varieties, and good results will be obtained if proper judgment be used in the selection, whichever kind is used. In " Mineral Resources for 1897 " the following tables are given 86 STREET PAVEMENTS AND PAVING MATERIALS. showing three stages of transformation of a German porphyry into kaolin, Table No. 12 giving the mechanical analysis and No. 13 the chemical composition of the rock at its corresponding change. No. 1 is the original porphyry, No. 2 an intermediate stage, and No. 3 the resulting kaolin. TABLE No. 12. No. 1. Coarse sand 33.95 Fine sand 36.20 Finest sand 7.90 Clay 9.27 Fine clay 7.46 Finest floating particles 5.22 100.00 TABLE No. 13. SiO 2 . . No. 1. 77 48 A1 2 O 3 17.10 Jte 2 O 8 2.83 MnO 84 CaO 38 MgO . 10 K.,0 1 03 NaoO 13 P,O . . Trace No. 2. 22.56 37.40 12.15 12.26 8.55 7.08 100.00 No. 2. 75.73 21.92 .98 .18 .27 .10 .55 .08 No. 3. 2.48 28.52 18.42 20.51 17.69 12.38 100.00 No. 3. 76.48 21.58 .97 .17 .25 .07 .16 .01 99.89 99.81 99.69 The word " vitrification " is defined in the Century Dictionary as " conversion into glass, or in general into a material having a glassy or vitreous structure "; and " vitreous " as " resembling glass, glassy "; but these same words as applied to brick or sewer-pipe have come to receive a very different meaning. A glassy brick would not make a good pavement. It would be smooth and brittle. As applied to brick the term vitrified means that a chemical action has taken place so that the clay particles have coalesced and become fused by the action of heat, forming a solid new homogene- ous whole, but not that the fusion has been made complete and the entire mass brought to a semi-liquid condition. In some clays the BRICK-CLAYS MANUFACTURE OF PAVING- BRICK. 87 character of the material is such that the proper chemical uoion for vitrification will not take place, so that the brick absorbs water no matter to what heat it may have been subjected, and accordingly will not vitrify in this sense of the word. Many engineers, there- fore, have decided upon the absorption test as the proper one to determine to what degree a brick has become vitrified. A thor- oughly vitrified brick breaks with a smooth conchoidal fracture and has no visible pores. The burned particles and granulated structure so plainly discerned in a half-burned building-brick have all dis- appeared. A clay from which such brick can be successfully and profitably made must be both fusible and refractory. Unless it be fusible the product will not vitrify at all, and yet if it have this property in too great a degree, the clay will melt and lose its shape upon the application of great heat. It should be sufficiently refractory to allow the vitrifying heat to be applied within considerable limits, so that if the temperature be increased a hundred degrees or more after vitrification has set in, the form of the brick will not be in- jured. The more equally refractoriness and fusibility can be op- posed to each other, with neither property being pushed to extremes by the heat used by the average burner, the greater will be the percentage of the finished product of the kiln. The proper amount of plasticity must also be obtained. If it be too small, the clay particles will not assimilate in the new state, so that when burned the material will be porous and have little co- hesive strength. If, on the other hand, it be too plastic, the mud will retain its shape and position to such an extent after being machined that the twist given the clay, especially if an auger machine be used, is often plainly visible in the finished product and laminations are formed with appreciable voids between the dif- ferent layers, thus reducing the strength of the brick. These, how- ever, are mechanical faults and can be easily corrected by a study of the crude material and the application of the proper remedy. Shales as a rule are less plastic than clays and require grinding- before they can be used, and in many cases a mixture of a certain percentage of clay to bring about the proper degree of plasticity. By the proper mixing of clays possessing different degrees of fusibility and refractoriness a combination is often reached that 88 STREET PAVEMENTS AND PAVING MATERIALS. permits the utilization of a great number of clays that would otherwise be valueless for vitrified products. Perfectly satisfactory clays are not often found in a natural state. Burned or dried clay has been in use as pottery or bricks for many centuries. Pottery has been made by all prehistoric races, with the single exception of the cave-dwellers of the Drift period, from the Neolithic. The early specimens were rudely shaped and made by hand, but appliances for forming the clay were gradually discovered, and the Egyptians were known to have used potter's wheels as early as 4000 B.C. Allusion is also made to the wheel in Jeremiah xviii. 3, 4, as well as in several places in Homer. Fragments of pottery have been found in clay-brick used in the construction of the oldest pyramid. Bricks themselves were used in the tower of Babel, as well as in the walls of the city of Babylon. The children of Israel made bricks of clay and chopped straw during their captivity in Egypt under Pharaoh. These were probably baked in the sun, although about that time some bricks were burned by the Egyptians. Samples of enamelled work were found on the walls of the palace of Eameses II. built about 140 B.C. Bricks were also ex- tensively used in the palaces of Babylon and Nineveh constructed some two hundred years later. Some of the pyramids were made of bricks, and upon one of them was found this inscription: " Do not undervalue me by comparing me with pyramids of stone. For I am better than they, as Jove exceeds the other deities. I am made of bricks, from clay brought up from the bot- tom of the lake adhering to poles." This shows that even at that period bricks had been used for a sufficient time to demonstrate their enduring qualities. They were used to a great extent by the ancient Greeks and Romans, the former being said to have brought them to perfec- tion. The walls and temples of Athens, as well as the palace of Croesus, were constructed wholly or in part of brick, though, on account of stone being so plentiful in Greece, they were not in so great a demand there as in other countries. BRICK-CLAJS MANUFACTURE OF PAVING-BRICK. 89 Strabo mentions a floating brick made of a kind of silicious earth that when burned has a less specific gravity than water. M'odern bricks were first used in Suffolk, England, in 1260, though they were not manufactured of good quality until about one hundred years later. They did not come into general use in London till after the great fire in 1660. The first brick-kiln in this country was probably built in Salem, Mass., in 1629, although for some years after the early settlements nearly all of the bricks used here were brought from Holland or England. In old houses in Albany, N. Y., and vicinity some of the original Dutch bricks can still be found. The manufacture of paving-bricks.is of very recent origin. They were first used in this country as paving material in 1870. And not for some time after that did brick-makers realize that a new in- dustry had been opened up for them. But in 1897 it had been developed to such an extent that in that year there were manu- factured in the United States 435,851,000 vitrified bricks, having a value of $3,582,037. Illinois headed the list of States with 87,169,- 000, closely followed by Ohio with 85,665,000. In 1898 the production was 462,499,000, valued at $3,922,642, but Ohio had displaced Illinois for first place with a total of 115,- 104,000, against 71,999,000 for the latter State, the average price per thousand being $6.92 in Ohio and $8.88 in Illinois. A peculiar " blue brick," so called, is made for paving purposes in Birmingham, England. The material used is a very ferruginous shale. After the bricks have been placed in a kiln the heat is raised to the vitrification-point. Salt is then thrown on the fire and, being volatilized by the heat, covers the bricks with a thin glaze. Fresh coal is also added to the fire at the same time, and all open- ings in the kiln tightly closed. This causes a reduction in the iron near the surface of the bricks and a thorough fusing of the particles in this outer crust. The process makes a hard, dense brick with the outer inch or half-inch a bluish black, while the inner portion is a deep red. 90 STREET PAVEMENTS AND PAVING MATERIALS. THE MANUFACTURE OF PAVING-BRICK.* Crushing the Clay. Whether clay or shale is used for paving-brick, it is usually crushed in dry pans, or mills with solid rolls that are about 4 feet in diameter and 12 inches wide, running within a revolving pan 9 feet in diameter, with grated bottom. Two such pans can gen- erally supply the largest-sized brick-machine, as they each crush from 5 to 10 cubic yards of shale per hour. It requires about 2 cubic yards of clay for one thousand brick. Screening. From the pans the crushed material goes to screens with both fixed and shaking riddles. They require the use of knockers to prevent the wet clay from sticking, and at some plants a boy is needed to keep the screens from clogging. In the older plants the sizing was often accomplished by the grating of the dry pans, no screens being employed. This, however, is a mistake, as it reduces the capacity bf the pan and causes very imperfect crushing from the wear and breakage of the bridges to the gratings. As the finer the clay is crushed, the stronger the resulting brick, these coarse particles produce an inferior non-homogeneous product. Most plants are still faulty in not screening fine enough, as 4- to 8-mesh screens are employed, whereas 10 to 15 meshes per linear inch should be used to give the best results. Pugging. The crushed clay or shale is next mixed and worked with water into a plastic mass by the pug-mill, which is a long trough contain- ing a series of wide blades set with a cross-pitch on a heavy shaft. This pugging should be thoroughly done to remove air-inclosures, secure a homogeneous mixture, and reduce the laminations in moulding to a minimum. To accomplish this, the mills should be at least 10 or 12 feet long and have the blades or knives 90 degrees apart. Fire-clays are often pugged in " wet pans " or " chasers," which are small mills with a solid bottom, while the rolls have * Somewhat abridged from Wheeler's "Vitrified Paving- brick." BRICK CLAT8 MANUFACTURE OF PAVING-BRICK. 91 a narrow tread. The clay is both crushed and tempered, or worked into a homogeneous paste in this pan, being kept in it until thor- oughly ground and tempered. The " wet pan " yields a product superior to that of the pug-mill, as it can be retained indefinitely in the pan, or until thoroughly tempered; but as it requires a larger plant and takes more labor and power, it is not usually used for paving-brick. Moulding. ' Paving-brick are generally made by the stiff-mud process, but numerous attempts have been made to use the semi-dry or dry press methods, but they have failed to produce a large percentage of good pavers. In the dry-press systems there is no bond between the clay particles and they merely cohere as a result of the quickly applied pressure, and unless such brick are burned to complete vitrification they fail to give a solid, strong, non-porous brick. The type of machine used for the stiff-mu'd process is usually a continuous working auger which forces the tempered clay or mud through the forming die. This gives a continuous bar of stiff clay, which is placed under an automatic cutter that cuts it into the desired sizes. As the bar leaves the die it is usually sanded to pre- vent the bricks from sticking together in the kiln. Instead of an auger producing a continuous stream of clay, reciprocating plung- ers are sometimes employed which give an intermittent bar, and occasionally steam-cylinders with dry plungers are used similar to the sewer-pipe process. The first method is the cheapest, and this style of machine has been developed to a producing capacity of 12,000 bricks an hour, or 100,000 per day. Formerly dies were made about 4 x 2 inches in size, producing end-cut brick, but of late 9 x 4|-ineh dies are being used, which give a side-cut brick. This form of brick is more shapely and decidedly preferable for a building-brick and for repressing, but as to which will make a more solid brick, a brick with fewer lamina- tions, will have to be settled for each individual clay. The weak point of the stiff-mud process is the laminations that must in- evitably result from pushing the stream of clay through a fixed die. The friction on the sides of the die will cause different speed in the flow of the clay, and these variations in the speed of the outflowing 92 STREET PAVEMENTS AND PAVING MATERIALS. clay must necessarily result in laminations or lines of demarcation between the different speeds of the clay bar similar to the veins of a glacier. If the air has been expelled from the clay by the pug-mill, these lines can be largely closed up again by a properly shaped die,, and first-class brick will result in which the laminations will be inconspicuous and of no importance. But if the air has not been expelled, or the mill and die are not properly designed, there will be an excessive amount of concentric lines that almost divide the cross-section of the brick into a series of shells or concentric cylin- ders that greatly weaken the brick for withstanding blows or frost. The character of the clay also greatly increases these laminations,, as the softer it is tempered, or the more plastic it is, the more serious is this trouble. The clay should be worked as stiff as pos- sible, not only to make it dense and reduce the shrinkage, but also to reduce the laminations. A very stiff clay requires more power to work it, however, and if too stiff is very apt to break down the machine. Repressing. Repressing consists in putting freshly made "stiff -mud brick into- a die-box and momentarily subjecting it to a heavy vertical pressure,, which is usually applied on the flat side. This fills out the angles and edges, making a much more shapely and uniform brick which is slightly denser, but probably also decreases the laminations? Drying. The stiff -mud brick are pilled in a sort of checkerwork on cars- as high as they will bear their own weight, some six or eight courses, high, and dried in long tunnels or drying-chambers, heated by direct fires, steam-pipes, or hot air. On account of the marked difference in the drying properties of clay, the selection and design of the dryer is a very important matter and it must be adapted for the specific clay to be used. Some clays can be readily dried in 18 to 30 hours without checking or injuring, while others need 48 to 60 hours, or longer, to avoid cracking to pieces. This means a great difference in the drying arrangement and expense of oper- ating the drying plant, which too frequently is not appreciated by i BRICK CLATS MANUFACTURE OF PAVING-BRICK. 93 the brick-maker or enthusiastic venders of patented dryers, and generally results in an expensive drying department. Burning. This is a most important part of the paving-brick business, as, no matter how good the clay, or how well it may have been mixed, without proper burning it cannot make Xo. 1 paving-brick. The kind of kiln employed in burning paving-brick is the down-draft rather than the round or oblong, as the up-draft type produces too heavy a percentage of soft and overburned brick. A continuous kiln has also been tried on paving-brick, but has not been very suc- cessful. The improvements that have been made, however, would seem to indicate that this type might at some time be used. It is interesting to note the changes that occur in paving-clays in passing from the condition of mud to a first-class paving-brick. When the moulded brick go into the dryer and the mechanically mixed water is evaporated, the brick shrink from 2 to 11 per cent to a firm earthy mass that admits handling and in which the in- dividual particles of clay are plainly distinguished. On being 'heated to a red heat, or about 1200 Fahr., the chemically com- bined water is driven off, which renders the clay non-plastic and it again begins to shrink and to grow harder and stronger. As the heat is raised above redness, the individual particles of clay may be still easily recognized and the brick are very porous. When the heat is still further raised to about a bright cherry heat or from 1500 to 1800 Fahr., depending on the particular clay, it shrinks an additional 1 to 10 per cent and is very much stronger and much less porous. It has the acquired hardness of tempered steel and the individual particles are no longer recognizable. This is the be- ginning of vitrification. From this stage to the molten mass there is no longer any sharp line of demarcation, and as the heat is in- creased the brick finally become viscous and semi-liquid, and when chilled and broken present a thoroughly glassy appearance. From the point at which the clay particles have so coalesced that they can be no longer recognized to the point of viscous liquidity requires an increase in temperature of 100 to 600 Fahr., according to the kind of clay, and is usually 400 in a clay suitable for paving-brick. Midway between these two points the clay 94: STREET PAVEMENTS AND PAVING MATERIALS. ceases to be porous and stops shrinking, which is the maximum degree of hardness and toughness, and is the point at which the burning should be stopped in order to produce an ideal paving- brick. The burning usually takes from 7 to 10 days, a shale brick re- quiring from 1500 to 2000 Fahr., and those of fire-clay from 1800 to 2300 Fahr. If shale brick are heated too hot, they melt into a more or less solid mass, yet it is usually necessary to bring them to a heat which would cause them to stick together if not prevented by sand that is freely sprinkled between them in setting. At the temperature when they border on the condition of a very viscous fluidity, the lower brick become " kiln-marked " by the weight of the upper bricks forcing the lower bricks slightly into one another, and care is required to prevent this pressure from becoming too great by not setting them too high. Paving-brick are set only 22 to 34 courses high, according to the fusibility of the clay. Coal is used throughout in burning pavers, which do not need the preliminary or water-soaking stage. Oil and natural gas however, 'have been used in some localities and are far superior to coal in reducing labor in burning, and producing a superior quality of brick, from the uniformity of the fire and avoidance of the air-checks that result from chills when cleaning the grate- bars. Annealing. After the kiln has been maintained long enough at the vitrify- ing temperature to heat the bricks through the centre, the kiln should be tightly closed and allowed to cool very slowly. Slow cooling is the secret of toughness, and the slower the cooling the tougher the brick. This annealing stage is often curtailed, on account of insufficient kiln capacity, and the kiln cooled down in 3 to 5 days in order to hurry up the brick, often to removing bricks that are so hot as to set fire to trucks. At least 7 to 10 days should be allowed for cooling to secure tough brick, and those who desire the best article can well afford to pay the extra cast of still slower cooling if quality is the first consideration. BRICK CLAYS MANUFACTURE OF PAVING-BRICK. 95 Sorting. If the kiln is properly burned, it will be found to have from 1 to 4 courses, the top brick, that are burned extremely hard, and which are more or less air-checked by being struck by cold air in coaling or cleaning the fires. The top course is also more or less covered with a film of ashes and dust that has been carried over by the draft. Such bricks are excellent for sewer or foundation work, as they have the maximum resistance to crushing strength and minimum porosity. Beneath the top layer the brick to within 2 to 12 courses of the bottom are No. 1 pavers, or brick that should be perfectly sound, completely vitrified, and have the maximum strength, hardness, and toughness. Beneath these are 2 to 10 courses of brick which 'have not received sufficient heat to com- pletely vitrify them and which are classed as No. 2 pavers, and used as the foundation or the flat courses in paving. Beneath the No. 2 pavers are from 1 to 6 courses of brick which have not re- ceived heat enough to be able to withstand the frost and are called builders, as they are about equivalent in strength, hardness, and porosity to the hard-burned building-brick. With a fire-clay it is possible to produce 90 per cent of No. 1 pavers, as there is no risk from overfiring them, while 80 per cent is a high average for shale. One frequently sees claims by venders of patented kilns of 90 per cent of No. 1 pavers, but such a very high percentage is rarely attained with careful grading, while 80 per cent is a high yield, and most yards do not get as high as 70 per cent of strictly first-class No. 1 pavers. CHAPTER V. CEMENT, CEMENT MORTAR, AND CONCRETE. WHEN a pure limestone has been properly burned or calcined the result is lime, that is, the carbonic acid has been driven off by the action of the heat. When water is applied to the lime it slakes with a great increase in volume, and if more be added it can be formed into a paste, which when mixed with sand will harden or set if exposed to the air. Limestone, however, is very seldom found in a pure state, the principal impurities generally being silica, alumina, iron, and mag- nesia. When these impurities exceed 10 per cent the resulting lime has the property of setting under water and is said to be " hy- draulic." If, however, the rock contains about 40 per cent of silica and alumina, the product of the calcination will not slake upon the application of water, but must be reduced to a powder in mills, when it is made into a paste as with the lime. This product is known as " cement." It differs from lime physically in that it re- quires to be reduced to a powder before being used, and does not materially increase its volume in setting. Cements were known to and largely used by the Romans, and it is said that the workmen excavating in London, England, in 1892 found a natural-cement concrete which was known to have been laid eight hundred years before. During the middle ages there seems to have been little knowledge of limes and cements, as what is known at present dates back to the time when John Smeaton, in seeking for a mortar wijth which to construct the Eddystone lighthouse, discovered the hydraulic character of certain limestones, and that this property was caused by the presence of clay in the original rock. Cements are generally spoken of in this country as " natural " 96 CEMENT, CEMENT MORTAR, AND CONCRETE. 97 or " artificial." The former, as the name implies, is made from the natural rock, while the latter is an artificial mixture, the in- gredients being so proportioned as to bring about the best results. As might be expected, the latter are stronger, more durable, and much more expensive. Artificial cements are also known as ' Portlands " from the fact that they were first manufactured in England, and that when set they bore a strong resemblance to the natural stone found in the island of Portland. In a very few locali- ties limestone has been found which when burned has almost the same composition as the artificial Portlands. On account of this similarity these have been called " natural Portlands." A cement of this character was produced in France in 1802. Portland cement as known at the present time was first manufactured in England in about 1824, although patents for " Portland cements " had been issued several years previously. The following is the description given by the patentee in the first specifications issued: " I take a specific quantity of limestone and calcine it. I then take a specific quantity of clay and mix it with water to a state approaching impalpability. After this proceeding I put the above mixture into a slip-pan for evaporation till the water is en- . tirely evaporated. Then I break the said mixture into suitable lumps and calcine them in a furnace similar to a lime-kiln until the carbonic acid is entirely expelled. The mixture so calcined is to be ground to a fine powder, and it is then in a fit state for cementing. The powder is to be mixed with a sufficient quantity of water to bring it into the consistency of mortar, and this applied to the purposes wanted." In 1796 a Mr. Parker of London patented a process of making a " Roman " cement. This was so called, and properly, on account of the similarity to the cement in use by the Romans so many years before. In this country a cement similar to the above was manufactured at Fayetteville, N. Y., in 1818. Portland cement was first produced in the United States in 1865. At the present time the principal works are situated in Pennsylvania, Ohio, New York, and one in South Dakota. 98 STREET PAVEMENTS AND PAYING MATERIALS. In 1828 a natural-cement rock was discovered at Rosendale, New York, and afterwards similar formations in other portions which, on account of the similarity, were also called " Rosendales," being distinguishable from each other by a special name for each brand. As the country was settled and construction work was undertaken in other sections, more deposits were found, a notable one near Louisville, Ky., and now some authorities call all natural cements " Rosendales," to separate them from the " Portlands." In the new Building Code recently adopted by the city of New York the following is found in relation to Portland and other cements: " Cements classed as Portland shall be considered to mean such cement as will, when tested neat, after one day set in air be capable of sustaining without rupture a tensile strain of at least 120 pounds per square inch, and after one day in air and six days in water be capable of sustaining without rupture a tensile strain of at least 300 pounds per square inch. Cements other than Portland cement shall be considered to mean such cement as will, when tested neat, after one day set in air be capable of sustaining with- out rupture a tensile strain of at least 60 pounds per square inch, and after one day in air and six days in water be capable of sustaining without rupture a tensile strain of at least 120 pounds per square inch. Said tests are to be made under the supervision of the Commissioner of Buildings having jurisdiction, at such times as he may determine, and a record of all cements answering the above requirements shall be kept for public information." It will be seen by the above that the cement is graded by its strength. This standard is, perhaps, as satisfactory as any, if the tests are carried on for a sufficient length of time, but most engineers would hesitate to accept or reject cements of which they knew nothing, from the result of so short a time-test as seven days. Under this clause no cements can be used that develop a strength of less than 60 pounds in one day set in air. Natural and Portland cements can be readily distinguished, however, by their composition. Table No. 14 is made up from analyses of well-known cements and taken from Cumming's " American Cements." CEMENT, CEMENT MORTAR, AND CONCRETE. TABLE Xo. 14. PORTLAND CEMENTS. Brand. ej j OQ Alumina. Q !2 X C j Magnesia. Potash and Soda. is f 3 Carbonic Acid, Water, and Undetermined. K B & S 19.75 7.48 5.01 60.71 1.28 0.75 1.64 3 38 24.90 8.00 3.22 59.38 0.38 0.50 1.46 2 16 19 35 7 00 4 50 63 75 5 40 Gerinania 21.14 6 30 2.50 66.04 1.11 2 91 22.91 8 00 1.90 61.76 2.70 2 63 Giant 23.36 8 07 4.83 58.93 1.00 0.50 85 2 46 Alpha 22.89 8.00 2.44 63.38 2.30 99 Natural, Boulogne, France 20.42 12.00 1.87 63.13 0.58 2.00 Average 21.84 8.11 3.28 62.12 1.17 2.74 Mr. Launcelot Andrews, Ph.D., in an article on cements in Clay Record says that an ideal Portland cement should be com- posed of: Per cent. Lime 62.2 Silica 28.2 Alumina 9.6 but adds that about a third of the alumina may be replaced by ' ferric oxide, which would correspond to the composition: Per cent. Lime 61.7 Silica " 27.4 Alumina 7.5 Ferric oxide 3.4 He also gives 3 per cent of magnesia as the maximum to be allowed, a larger amount having a tendency to cause the cement to swell and crumble. Table No. 15 shows the composition of several well-known American cements, also taken from Cumming's " American Ce- ments." 100 STEEET PAVEMENTS AND PAVING MATERIALS. TABLE Xo. 15. NATURAL CEMENTS. Brand. I p a j3 Iron Oxide. 3 1 a a 03 1* jll Utica 34.66 5.10 .00 30.24 18.00 6.16 4.84 23.16 6.33 .71 36.08 20.38 5.27 7.07 Louisville, " Four Leaf " . . Louisville, " Hulme Star".. 26.40 25.28 27.30 6.28 7.85 7.14 .00 .43 .80 45.22 44.65 35.98 9.00 9.50 18.00 4.24 4.25 6.80 7.86 7.04 2.98 Norton High Falls ... 27.98 7.28 .70 37.59 15.00 7.96 2.49 28.43 6.71 .94 36.31 23.89 1.80 0.92 27.60 6.67 1.51 38.01 16.25 5.21 4.74 It will be noticed that the two brands of Louisville very quick- setting cements are high in lime and correspondingly low in mag- nesia, that there is a difference between the naturals and Portlands in every essential ingredient, and that it is so marked that the one can always be distinguished from the other. Fineness. Besides its composition, there is another property of cement which has an important bearing upon its value in mortar, and that is its fineness. It costs materially more to grind a cement so that 75 per cent of it will pass a sieve of 40,000 meshes per square inch than to pass one of 10,000, so that the tendency is to leave the product as coarse as possible and get ,satisf actory results. Gillmore says: "The capacity of a cement to receive sand, other things being equal, varies directly with its degree of fineness." As cements are always used in practice mixed with a certain amount of sand, this matter is of great importance. The author just quoted says that not more than 8 per cent of a cement should be rejected by a sieve of 6400 meshes to the square inch. Mr. Andrews, previously referred to, says that all grains so large as not to pass a sieve of 75 meshes to the linear inch (5625 per square inch) should be considered as inert or wholly passive constituents, and CEMENT, CEMENT MORTAR, AND CONCRETE. 101 that they should not constitute more than 20 per cent of the total weight. Mr. E. W. Lesley in examining different specifications upon this point found the requirements as shown in Table No. 16 (the results being given in a paper read before the Engineers' Club of Philadelphia). TABLE No. 16. PORTLAND CEMENTS. Brand. Percentages to pass Screens of the following Meshes per Square Inch. 2500 3GOO 6400 8000 10000 40000 U. S. Army 954 95 84 70 U. S Navy . . 97 90 District of Columbia 95 97 95 97 85 89 69 Six street and steam railways 80 A number of bridge companies Average of 71 specifications 96 A.N CKS 85 69 AMEKIC IENTS. Average of 38 American specifica- 92 85 79 U. S. Army 91 85 724 *Tf In prosecuting the Boston Main Drainage Works, Mr. Eliot C. Clarke made some very elaborate experiments to 'show the effect of fine grinding on cements. In Tables Nos. 17 and 18 are given some of his results. The figures represent the tensile strength in pounds per square inch. In Table No. 18 the same brand was used in both cases, but one sample was taken from the ordinary delivery, and the other from a lot that had been ground in accordance with a special con* tract. Another test was made by taking the average of these brands of finely ground with the same number more coarsely ground, with the results shown in Table No. 19. These tables show conclusively the value of fine grinding, and, as far as investigations have been carried, that the finer the cement 102 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 17. Brand. Age of Specimen. Percentage retained on a No. 120 Sieve. Parts of Sand to one part of Cement. 2 3 4 5 43 86 English Portland. . . . French Portland. . . . 7 days do. 37 13 319 318 125 205 89 130 59 114 TABLE No. 18. Parts of Sand to one part of Brand. Age of Specimen. Percentage retained on a No. 120 Sieve. Cement. 3 5 Ordinary Portland 28 days 35 403 105 68 Finely ground Portland 28 days 12 304 180 96 TABLE No. 19. Brand. Age of Specimen. Percentage retained on a No. 50 Sieve. Parts of Sand to one part of Cement. IX 2 16 25 Coarse Kosendale . . . 7 days 7 days 17 6 98 92 29 41 Fine Rosendale . . . is ground the more strength it will have when mixed with sand. On account of the great cost of extreme grinding, it is not economi- cal to carry it too far. From the figures previously given, it would seem that the authorities had decided upon a sieve of 200 meshes to the linear inch as the limit to be required. Concerning the tests to be made of cements to determine its real value or its special fitness for any particular work, there is much to be said. Different engineers have different requirements when seeking for the same results, and different laboratories differ very much among themselves in their methods, and consequently their results vary materially even when cement from the same barrel is used. The best illustration of this is shown in Table CEMENT, CEMENT MORTAR, AND CONCRETE. 103 Ko. 20, taken from a paper by Prof. J. M. Porter of Lafayette College. Prof. Porter had ten samples taken from the same num- ber of barrels of Portland cement, thoroughly mixed, and then divided into ten smaller portions which were sent to ten different persons with a request that a seven-day tensile test, one cement to three sand, be made according to the standard of the American Society of Civil Engineers. TABLE No. 20. Tensile Strength in Pounds. Range in Pounds. Ratio of Range to Maximum. Ratio of Average to Last. Water,per ct. 1 2 3 4 5 6 : ;i 153 Aver- age. 75 102 114 133 140 153 163 176 225 247 R. W. Hildreth & Co., New York.. Prof. J. B. Johnson, Washington University, St. Louis H. R. Fahr, City Engineer, Easton, Pa Prof. W. H. Burr, Columbia Col- ( lege, New York { Chas. F. McKenna, New York Prof. F. P. Spalding, Cornell Uni- versity Ithaca ... .... 68 77 106 125 126 148 155 171 220 240 72 94 112 126 132 150 160 177 224 246 74 108 123 130 138 151 164 177 226 249 78 110 82 122 14 45 17 19 27 12 17 8 8 12 17.1 36.9 13.8 13.2 17.7 7.5 9.9 4.5 3.5 4.8 30.4 41.8 46.5 54.0 56.8 62.0 66.0 71.4 91.2 100 13 Not given 10.4 10 8 12 Not given 11 10 12 10.8 137 144 155 166 178 228 250 140 150 160 172 179 o. JS 252 Prof. J. N. Porter, Lafayette Col- lege, Easton Clifford Richardson. Washington. Booth Garrett & Blair, Phila Average 153 117.9 12.9 62.0 These results would seem to indicate that such tests are of little value when a report from one laboratory would cause the cement to be rejected without hesitation under ordinary specifications, and as unhesitatingly accepted according to the report of another equally reliable, and when a special effort has been made to have all conditions as nearly alike as possible. This is hard to explain. But on account of these variations tests of cement must not be given up, but continued with more care, and perhaps on different lines. It is rarely possible to give the cement used in any large and important work sufficient tests to demonstrate its absolute fitness. It must be done analogically. It is necessary, however, to fin-1 a brand of cement before the work is begun that either by experience or long-time tests has been proved to be all that is required. If the former, a series of tests should be made extending over a sufficient 104 STREET PAVEMENTS AND PAVING MATERIALS. period of time and comprising enough individual samples of the cement to establish a rigid standard for that particular brand. It should include neat tests and also those mixed with every propor- tion of sand that is liable to be used on the work, to ascertain as well what mixture of sand will produce the requisite strength. During construction work cement is liable to be delivered in such quantities that it is not possible to make long-time tests without working a hardship on the contractor. If, however, a standard has been established, and it is definitely known that a certain strength neat in seven days will develop into a certain other strength in thirty or ninety days mixed with the specified amount of sand, a very accurate and satisfactory conclusion can be arrived at. Each cement, however, must have its own standard, and the operator who makes the original tests should be retained to carry them on during the prosecution of the work. No new cement should be accepted on short-time tests. They are often very deceptive. Unless it has been used and gained a reputation, careful and elaborate tests should be made as detailed above. The briquettes should be mixed neat and with the propor- tions of sand determined upon, the same day and by the same per- son, using the same sample of cement for both neat and sand briquettes, so that the loss of strength occasioned by the added sand can be accurately determined. Long-time tests are absolutely nec- essary, as a few cements with a moderate amount of sand will give practically as great a strength as when tested neat. As it is long- time results that are desired in construction, the importance of this can be readily seen. Table No. 21 clearly illustrates this. TABLE No. 21. Age of Specimen. Neat. One Part Cement, Two Parts Sand. 24 hours 40 7 days 107 46 28 days ' 254 162 2 months 346 245 3 months 388 311 6 months 450 436 CEMENT, CEMENT MORTAR, AND CONCRETE. 105 The above is the average of five briquettes, and the cement is a natural product well known in the New York market. Thirty per cent of water was used in the neat mixture and 14 per cent in the sand. Mr. E. B. Noyes, in Journal of Engineering Societies for June 1896, gives a case in point ; when a good cement was rejected and a poorer one accepted on comparatively short-time tests without apparently any previous knowledge. Table No. 22 gives his results. TABLE No. 22. 7 Days. 28 Days. 6 Months. 12 Months. 1 19 41 210 518 2 12 24 136 530 3 42 115 202 334 4 71 182 283 260 The cement was an American brand, and the briquettes were mixed one part cement to one part of sand. Nos. 1 and 2 were not used on account of their poor showing in their first tests, while at the end of the year their superiority was clearly demonstrated. No. 2 was certainly a remarkable specimen, and any engineer would be justified in rejecting it upon the six months' test without having had any previous knowledge of its wonderful recuperative powers. In many works, too, it could not be used notwithstanding its great strength in one year, as its development during the first six months is very slow. Sample No. 4 actually receded in strength, though so little that it might have been caused by some individual briquette. It would seem to be a fair inference that it had practi- cally reached its limit in six months. The author several years ago had some tests made of the princi- pal American] cements tributary to the city where he was then located, practically on the lines as indicated above. The results were very satisfactory, demonstrating the necessity of such action, and in this particular case bearing out some action that had been taken in rejecting certain cements. Table No. 23 gives the results att-iined. 106 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 23. CEMENT MIXED NEAT. Briquettes 2 hours in air, remainder in water. 24 Hours. 7 Days. 15 Days. 30 Days. 90 Days. 6 Months. 9 Months. 1 Year. 1 109 112 145 155 250 241 289 227 2 214 228 219 325 387 366 421 316 3 114 186 293 290 282 291 347 339 4 87 197 ^37 264 267 220 367 288 5 46 131 1!>9 279 298 322 402 410 6 206 248 348 I 348 334 355 372 402 CEMENT 1 PART, SAND 2 PARTS, REMAINDER IN WATER. Briquettes 1 day in air. 1 35 80 167 216 199 197 229 9, 40 79 122 143 155 112 161 3 38 70 114 75 89 89 82 4 5 74 26 99 53 134 95 140 141 146 153 153 145 137 142 6 81 103 138 106 81 69 84 This shows that No. 1, which was the weakest at the end of a year neat, was the strongest when mixed as it is generally used; and that Nos. 3 and 5, which were two of the 'highest neat, were but one-half the average strength of the other at the end of the year when mixed with sand. Some engineers in making cement specifications go very elabo- rately into the component parts of the material, exacting a certain percentage of one substance and ruling out more than a certain amount of another. This practice is dangerous, unless one is per- fectly sure of his standing, or the limits are so elastic as to be of no value. It is really encroaching on the prerogative of the manu- facturer. The engineer wishes results, and it is the maker's busi- ness to produce a cement that will give them. The manufacturer will have no difficulty in meeting any requirements, but at what cost to the long-time test he alone might be able to tell. Then the products of different mills differ so that a slight excess of one ingredient might be neutralized by that of another. It is well known that many excellent brands of cement are made. It is better to obtain a perfect knowledge of the peculiarities of each CEMENT, CEMENT MORTAR, AND CONCRETE. 107 and, after specifying certain of these, make sure that each delivery is kept up to the standard. In the case of an excessive demand when the output is small, manufacturers are liable to put on the market a product that in the rush has not received sufficient attention, and which ordinarily would not be sent forth or it may happen without their knowl- edge. It is the object of the tests to detect this or similar defects in standard brands. In the paper by Mr. Lesley previously referred to, he gives the requirements for tensile strength as found in different specifications and shown in Table No. 24. TABLE No. 24. PORTLAND CEMENTS. 24 Hours Neat. 7 Days. 28 Days. Neat. 1 to 3. Neat. ItoS. U. S Army 131 402 383 462 388 319 384 119 85 547 600 189 U S Navy. Cit> specifications 161 115 134 134 538 483 529 201 Railroads Average of a number of specifi- 118 189 NATURAL CEMENTS. ' j Hours 7D ays. 28D ays. Neat. Neat. 1 to 2. Neat. 1 to 2. U. S. Army 40-70 90-125 25-50 100-200 65-200 City specifications 50-100 100-200 150-300 Cement specifications generally specify a time within certain limits for the initial and final sets. When this is done, and in fact the time of setting is generally noted in all tests, it is neces- sary to define what is meant by these terms. A standard was first adopted by General Totten at his work at Fort Adams, R. I., previ- ous to 1830. This was that when the mortar would sustain a wire 108 STREET PAVEMENTS AND PAVING MATERIALS. of Vi2 inch diameter weighted to V 4 pound, it should be said to have received its initial set, and its final wheni it would sustain a wire of */2 inch diameter bearing a one-pound weight. The actual setting-point must be obtained by frequent trials. This standard was accepted by Gillmore and others, and is the one in general use at the present time. While many more and elaborate tests can be and are made en cements, those for fineness and tensile strength on the lines herein indicated will give good and safe results for general work. For general specifications,, then, it would seem to be in accord- ance with best practice to make the following requirements for fineness: PORTLAND CEMENT. 95% to pass a sieve of 2,500 meshes per sq. inch. 85% " " " 10,000 " " " " 70% " " " 40,000 " " " " NATURAL CEMENT. 92% to pass a sieve Of 2,500 meshes per sq. inch. 85% ' 80% " 6,400 10,000 FOB TENSILE STRENGTH PER SQUARE INCH. Portland Cement. Natural Cement. 24 Hours. 7 Days. 28 Days. ' 24 Hours. 7 Days. 28 Days. Neat Ito2 Ito3 175 400 200 125 550 300 200 50 120 50 200 120 It is not necessary, however, that all cements should reach these figures. But it should be provided that a quick-setting cement should increase a certain per cent over its 24-hour strength in 30 days, and that a slow-setting cement should not be less than a specified minimum at that time, and particular attention should be given to its strength with the sand mixtures.. Just what requirements should be called for in special cases de- CEMENT, CEMENT MORTAR, AND CONCRETE. 109 pend upon the conditions under which it is to be used. It can be readily understood that it is not good engineering to insist upon, a cement conforming to certain standards in all cases when at one time, for instance, it may be used as a foundation for a street pave- ment in dry work, and at another be laid in running water. In one instance a quick-setting cement is absolutely necessary, and in the other one that is moderately slow in taking its initial set is better. What should be done is to ascertain what the requirements of the work are and then use a cement that, as it is generally manufactured, comes the nearest to meet- ing these requirements. Tests should be continually made to ascertain if it is being kept up to its standard. One principle should be strictly adhered to in making tests of any kind of ma- terial: have the conditions governing the tests conform as closely as may he to those under which the material is to he used. Eliminate as much theory and uncertainty as possible, and spend neither time nor money in attaining a requirement that will never be of any benefit to the work. In actual construction cement is almost never used neat. It is first mixed with sand and is then called mortar. The common proportion for a natural cement is one part cement to two parts of sand by volume. This is, of course, purely arbitrary, but it seems to have come into general use from the fact that this mixture seems to be strong enough for the more common uses to which cement mortar is put. When a greater or an immediate strength is wanted a brand of Portland is adopted with varying proportion of sand. Some engineers indeed think that Portlands run more evenly than the naturals, and that where only a moderate strength is required the latter should be used, reducing the expense by in- creasing the proportion of sand. Ag it is the mortar that is to be used, whether in regular masonry or concrete, it is important and necessary to know the resulting volume from the mixing of cement and sand in different propor- tions. It should be specified', also, whether the cement is to be measured as originally packed or as poured loosely into the measuring-box. Tables Nos. 25 and 26 give the results of experiments made by L. 0. Sabin, U. S. Assistant Engineer, to ascertain the amount of 110 STREET PAVEMENTS AND PAVING MATERIALS. sand and cememt required to make a cubic yard of mortar under different conditions. TABLE No. 25. B&rrds Barrels Cement. Barrels Cement. Cement. 300 Ibs All Sand Parts of Sand to one of Cement. 265 Ibs. 71 Ibs. per cu. ft. Cement packed 3.73 cu. ft. Cubic Yards Loose Sand. 280 Ibs. 75 Ibs. per cu. ft. Cement packed 3.73 cu. ft. Cubic Yards Loose Sand. per bbl'. 80 Ibs. per cu. ft. Cement packed 3.75 cu ft. weighed 100 Ibs. per cu. ft., voids 37^} percent. Cubic Yards Loose Sand. per bbl. per bbl. per bbl. 1 4.45 0.61 4.32 0.60 4.17 0.58 2 2.83 0.78 2.79 0.77 2.75 0.76 3 2.04 0.85 2.03 0.84 2.00 0.83 4 1.65 0.89 1.60 0.88 1.57 0.87 TABLE No. 26. SAND AND CEMENT, BOTH LOOSE. Cement weighs 60 Ibs. per cubic foot. 1 2 3 4 By Volume, Barrels of Cement. By Weight, Barrels of Cement. 265 Ibs. 280 Ibs. 300 Ibs. Cu. Yds. Sand. 265 Ibs. 280 Ibs. 300 Ibs. Cu. Yds. Sand. 4.08 2.49 1.77 3.86 2.36 1.68 3.60 2.20 1.57 0.67 0.81 0.87 5.21 3.66 2.72 2.15 4.93 3.46 2.57 2.03 4.60 3.23 2.40 1.90 0.51 0.72 0.80 0.84 The above, while being very valuable as showing actual amounts of mortar to be obtained from the different mixtures of cement and sand, also emphasizes the importance of the unit to be used; as, taking the barrel of cement at 265 Ibs. and the proportion of one part cement to two of sand, the tables give the following weights of cement for a cubic yard of mortar by each of the dif- ferent methods: Pounds. By volume, cement loose 660 By volume, cement packed 750 By weight 970 CEMENT, CEMENT MORTAR, AND CONCRETE. in The second method requires 13 per cent and the third almost 50 per cent more cement than the first. The plain and true infer- ence is that the only sure way of knowing just how much cement is being used is to determine proportions by weight, or to specify that a cubic yard of mortar shall receive so many pounds of cement. This is particularly important now when so many manufacturers deliver their cement in bags by weight, and allowing a certain num- ber of pounds for a barrel. When heavier cements, as the Port- lands, are used, it is evident that there will not be so much differ- ence in the methods employed. Cement mortar is often used in sea-water, and in preparing it considerable extra expense would be incurred in providing fresih water for the mixture. Quite a number of experiments have been made at various times and by different persons to determine the action of salt water, if used in mixing, and also when the mortar is immersed in it. Gen. Gillmore made some rectangular parallelepipeds of mortar 2x2x8 inches in vertical moulds under a pressure of 32 pounds per square inch until set. These were broken on supports from a pressure from above midway between the supports. The specimens were kept in a damp place for twenty-four hours, when they were placed in sea- water, where they remained' ninety-four days, till broken. Table No. 27 gives his results. TABLE No. 27. Conditions. Breaking Strength in Pounds. No. Broken. Neat cement mixed with fresh water 499* 8 ' " " sea-water 3794 8 Cement 1 sand 2 by volume mixed with fresh water 3191 5 10.? Cement 1, sand 2, by volume mixed with sea-water, concen- trated by heat 25 per cent 195 165 2 In the report of Mr. E. C. Clarke previously referred to Table No. 28 is given, showing the results of his investigations on this question. 112 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 28. Figures indicate tensile strength per square inch. ROSENDALE. ] Cement, 1 Sand. PORTLAND. 1 Cement, 2 Sand. Mixed with Fresh Fresh 40 126 247 310 Fresh Salt 48 135 250 253 Salt Fresh 50 114 243 224 Salt Salt 61 126 224 217 Fresh Fresh 151 213 314 342 Fresh Salt 122 191 245 231 Salt Fresh 152 203 277 310 Salt Salt 149 *00 264 Immersed in 1 week 6 months Mr. A. S. Cooper in a paper published in the Journal of the Franklin Institute, October, 1899, details some experiments made by him, shown in Table No. 29, to determine the effect of salt water. The briquettes were the American Society of Civil Engi- neers' forms, the proportions being determined by weight. They were stored, in moist air for twenty-four hours and then in an immersion-tank till broken. The figures represent tensile strength per square inch in pounds. TABLE No. 29. PORTLAND CEMENT. STANDARD SAND. 1 Part Cement, 1 Part Sand. 1 Part Cement, 2 Parts Sand. 1 Part Cement, 3 Parts Sand. Mixed with... Immersed in. . 7 days Fresh Fresh 544 574 671 833 846 Fresh Salt 568 709 670 708 625 Salt Fresh 585 621 801 820 819 Salt Salt 618 631 660 610 318 Fresh Fresh 487 560 584 627 587 Fresh Salt 477 586 600 637 471 Salt Fresh 458 507 580 630 614 Salt Salt 492 554 583 589 478 Fresh Fresh 278 335 438 444 431 Fresh Salt 329 376 392 397 282 Salt Fresh 303 880 391 408 344 Salt Salt 270 348 400 408 3a*> 28days 3 months 6 months 1 year... NATURAL CEMENT. STANDARD SAND. 7 days 266 320 237 298 147 177 134 188 65 92 87 110 28 days 310 331 297 384 250 256 218 243 107 150 120 164 4 months 385 369 400 414 296 322 335 325 223 228 230 232 6 months 377 388 370 368 298 325 332 334 221 223 238 237 1 year 305 299 356 275 235 170 207 191 200 162 173 140 While the actual figures given by Mr. Clarke and Mr. Cooper vary much as to the actual strength, owing doubtless to the char- acter of the cement and the method of manipulation, they are rela- tively the same, there being a marked decline whenever the briquettes 1 are immersed in salt water, especially the long-time tests with the Portland cements. Where 'the mixing is done with salt CEMENT, CEMENT MORTAR, AND CONCRETE. 113 water and the immersing in fresh, the difference is not so striking. Although these tests show that cement mortar is weakened by the action of salt water, works have been carried on of sufficient time and extent to make it certain that the deterioration is not danger- ous. This becomes important in studying the action of frost on mortars, as it is customary to add salt to the water for mortar-mix- ing, when it must be used at low temperatures. Mr. James J. 11. Croes gives as a rule: " Dissolve 1 pound of rock salt in 18 gallons of water when the temperature is at 32 F., and add 3 ounces for every 3 degrees of temperature." He adds that masonry laid with such mortar stood well and showed no signs of having been affected by the frost. Mr. Alfred Noblo states that a pier was built on the Northern Pacific Railroad near Duluth at a temperature varying from to 20. Portland cement was used for the mortar in proportions of 1 to 1J for face stone and 1 to 2J for backing. Salt was dissolved in the water, and the sand was warmed. The mortar froze very quickly, and several months afterwards was found to have perfectly set and to be in as good condition as that laid in milder weather. Table No. 30 gives ihe result of some of his experiments to determine the effect of salt upon the mortar, and Table No. 31 the combined effect of salt and freezing. The amount of salt seems to make no material difference, al- though the figures are slightly less for the greater quantities, and, as in the previous tables, the salt water gives poorer results than the fresh. These figures show some gain when salt water is used for the mixture and the briquettes immersed in fresh, and decided increase when they were frozen for six days and immersed in water long enough to thaw, but not a sufficient time to gain an additional set. The table would be of more value if it extended over a longer period of time. Table No. 32 is taken from a paper read before the Canadian Society of Civil Engineers in February, 1895, by Prof. Cecil B. Smith of McGill University. Set No. 1 was submerged, after 24 -hours, in water of laboratory tank 114 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 30. Proportions: cement 1, sand 1, volume; cement 21 ounces; sand 23 ounces; water 6 ounces. Figures are tensile strength per square inch. Salt. 7 Days. 30 Days. 90 Days. 6 Months. 9 Months. 12 Months 18 Months 2 Years. Ooz. 155 220 289 311 390 382 402 430 * 139 200 246 288 363 364 423 346 i 139 192 221 289 352 383 392 326 128 189 217 288 343 369 350 334 TABLE No. 31. PORTLAND CEMENT. Mixture: cement 35 oz., water 7 oz., salt as shown. Salt in Ounces. ^ y\ % \s 429 415 394 215 % H 415 392 390 221 % 1 Immersed in test- room when removed from 327 316 336 169 357 378 422 198 375 411 421 167 392 374 399 217 402 405 384 208 388 383 356 221 402 409 387 239 Exposed to air and frozen three days, then immersed in test- room four days Immersed in test-room when removed from moulds Exposed to air and frozen six days, then exposed to air in test-room at 70 one day. TABLE No. 32. 2 2 K 3% 3 3 1 Mixture. Age. No. 1. No. 2. No. 3. No. 4. a on Is* ?i^ pi ,- c Remarks. 33 0*0 !** d X Portland neat 2 Mos. 602 471 282 334 -t-23F. 422F. 1(5 1 to 1 377 276 194 233 _l_ 50 4.310 20 2 to 1 u 168 150 105 111 -* 24 3tol M 104 85 92 97 -5 - 6 24 3 and 4 showed irregular and injured fractures. Natural neat ' 226 221 349 + 2 4- 5 -24 4 completely blown in fragments. 1 tol Neat , t 125 250 229 281 187 159 44 94 4- 8 4-13 +0.6 4- 5 22 24 Some of No. 4 injured. Mixed with water at 122F. 1 to 1 it 129 170 80 117 4 9 20 Mixed with water at 118F. Neat 1 Month 155 278 217 249 +17 +r* JO Mixed with 2# of brine. CEMENT, CEMENT MORTAR, AND CONCRETE. 115 Set No. 2 was kept on damp boards in a closed tank for the whole period, and never allowed to dry out. Set No. 3 was allowed to set in the laboratory, and then ex- posed to the severe frost and left in open air for the whole period. Set No. 4 was exposed in from 8 to 10 minutes to the severe frost and left there for the whole period. The important deductions from the Portland tests are: 1. That mortar immersed in water is stronger than when used in air; 2. That mortar exposed to temperature below freezing and kept there till set is stronger than when allowed to set in air and then ex- posed to frost; 3. That mortar kept in damp air was the weakest of all the different conditions experimented on. It will be noticed from the results of the tests of the natural cement: 1. That, contrary to the Portlands, these cements should not be used if the mortar must be exposed at once to frosts; 2~ That from the neat tests no time deductions can be made of a sand mixture, as in every case when mixed with fresh water the 1-to-l compound was considerably stronger than the neat; 3. That No. in every case but one was the strongest, while with the Portland it was the weakest; 4. That the addition of salt to the mixing water added very materially to the strength of the briquettes when exposed to the frost. Table No. 33 gives the results of some experiments made by Mr. A. C. Hobart and published in The Technograph, No. 12, 1897-98. In all cases the briquettes were frozen six days after having been allowed to set, as shown in the table. They were thawed from 18 to 20 hours and then broken. The upper line of figures for each mortar is the strength in pounds per square inch of the unfrozen briquettes, and the lower is the percentage of the strength frozen to the strength unfrozen. Table No. 34 gives the result of some tests made on 12-inch concrete cubes by Mr. W. A. Rogers, Assistant Engineer of the Chicago, Milwaukee, and St. Paul Railway at Chicago. " Atlas " Portland and Louisville natural cements were used. The propor- tions were: Atlas, 1 cement, 3 gravel, and 4 broken stone; and Louisville, 1 cement, 2 gravel, and 4 broken stone. Eight cubes were made of each cement, two being mixed with water to which 116 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 33. Portland. Age in Hours when Frozen. 2tol Louisville Star neat. 1 to 1 2 to 1 Akron neat 1 to 1 . Brand Dufassey neat Ito 1 2 to 1 3 to 1 Saylor's American neat. . . . 1 to 1 2 to 1 1 j 3 to 1 | Natural. Clark's Utica neat \ 1 to 1 . . . . \ 2 to 1 Louisville Black Diamond neat 1 to 1 . , 2tol 321 68 133 58 33 26 00 00 285 60 144 47 61 55 18 32 120 90 114 88 45 71 145 109 136 132 96 133 108 83 71 79 57 168 116 72 108 94 63 170 337 72 177 77 43 34 00 00 238 50 176 57 81 73 26 46 116 87 118 91 60 95 135 102 139 135 104 144 112 86 69 76 70 206 173 107 152 132 76 205 3 341 73 172 75 62 48 10 8 234 50 173 56 96 86 15 27 127 95 111 86 80 127 148 372 79 172 75 58 45 14 18 268 59 175 57 102 92 33 59 152 114 128 99 83 132 156 | 117 130 164 126 159 106 147 109 84 143 159 83 123 171 184 142 152 167 87 244 256 175 191 109 119 168 173 148 150 79 93 213 251 12 374 80 184 80 79 62 19 25 284 50 179 58 129 116 48 86 163 122 131 102 74 117 151 117 141 137 106 144 156 120 160 176 85 250 223 138 220 191 101 273 24 400 80 186 79 81 63 28 37 248 45 255 79 143 129 54 96 143 107 142 110 43 68 153 115 130 126 69 96 150 114 133 148 80 235 237 138 202 176 120 316 48 352 67 187 75 60 37 47 240 56 260 79 138 120 69 113 135 79 137 105 45 71 150 93 120 114 57 142 103 131 146 80 222 228 132 185 158 104 297 379 69 193 75 103 75 48 58 300 110 271 82 146 108 74 114 140 80 107 80 49 70 133 81 108 97 64 140 105 129 137 72 189 216 126 179 12 r 78 186 168 327 52 296 105 181 100 106 103 590 110 303 68 161 98 87 121 154 70 138 100 69 83 150 81 123 100 80 107 132 93 127 130 65 108 182 104 171 91 69 157 672 100 331 102 209 114 134 93 671 105 391 87 226 128 124 125 199 89 160 81 77 91 153 79 137 92 92 93 150 97 138 115 60 82 163 93 185 93 90 120 one pint of salt to ten quarts of water had been added, and the others with fresh water. Capacity of machine 185,000 pounds, a showed signs of failure, I showed no signs of failure. The cubes kept out of doors were subjected at once to a temperature considerably below zero. During CEMENT, CEMENT MORTAR, AND CONCRETE. 117 TABLE No. 34. Conditions of Cube after having been Made. Asein Days. Kind of Water. Atlas. Louis- ville. 28 Fresh a 185,000+ 43,000 Kept out of doors 28 115 000 33 000 Kept out of doors 28 days and in office 28 days | 56 b 185,000-f 52,500 28 Salt b 185,000+ 35,000 this exposure the weather was the coldest experienced in Chicago for twenty years, but subsequently grew warmer, so the cubes froze during the night and thawed during the day. The deductions the author of the paper makes for the mixture is: "Freezing before setting does not seem to injure the Portland-cement concrete even if, after having frozen hard, the concrete is exposed to freezing and thawing weather. Exposing green Portland cement concrete to a freezing temperature seems to affect its rate of hardening, making it slower, but eventually the concrete will be just as good as if it had not been exposed to the cold. The use of salt seems largely to counteract the effect of cold in causing slow hardening." He also makes the same deductions for Louisville cement, except that he thinks the use of salt seems to have little if any effect on the strength of the cubes exposed to the cold. Mr. Noble describes the construction of an anchor-block of con- crete. This was built during freezing weather, a portion of the time below zero, with about one-half of the mass below water. The mixture was 1 part Milwaukee cement, 2 parts sand, and 4 to 5 parts broken stone. The material and water were heated, a double handful of salt being added to each part of water. Ice formed over the top of the concrete every night until the mass was above the water-level. No attempt was made to protect the concrete from frost, and six months after it was laid it was found to be thor- oughly set. These experiments cover quite a period of time and were made by different people under very different conditions. As a rule the same general deductions can be made from them. That is, that with proper precautions good results can be obtained by the use of cement mortar in cold weather; that a freezing temperature 118 STREET PAVEMENTS AND PAVING MATERIALS. greatly retards the setting of mortar, but does not seriously injure it if properly treated; that it is much safer to use Portland cement in cold weather, especially if the mortar is to be subjected to alternate freezing and thawing. The one exception to the lat- ter conclusion is the experiments of Mr. Hobart. His results would show that the American cements are not only influenced less by freezing than the Portlands, but that their strength is actually in- creased. Mr. Hobart says that this is so different from all the former ideas on the subject that some of the tests, were carefully duplicated with practically the same results. Specifications for work involving the use of cement mortar al- ways provide that it shall be used within a certain time after it has been mixed, generally from half an hour to an hour and a half, according to the character of the work and the nature of the par- ticular cement. This is because it is considered that cement mortar should be in its permanent place before it has begun to set, and that any disturbance after the first set reduces its ultimate strength. Not many experiments have been made to demonstrate this, and it can be readily understood that to be of value tests must be made of each individual cement. A slow-setting cement will of course permit more manipulation and disturbance than one that sets qnicklj, and just what the effect will be can only be known by experiment. Table No. 35 shows the result of some experiments detailed by Gen. Gillmore. The sections used and the methods of constructing and breaking were the same as on page 111, except that the mortar was made of equal parts of natural cement and sand by volume, and the samples were kept in sea-water for 320 days. TABLE No. 35. Breaking Strength. Cement fresh from barrel, average of five ... 767 Ibs. " repulverized after 3 days' set, average of six 236| " ANOTHER BRAND. Cement fresh from barrel, average of four. 631 Ibs. " repulverized after 3 days' set, average of ten 261 " Table No. 36 gives the results of Mr. Cooper as published in the paper previously referred to. The briquettes were made of Portland-cement mortar mixed 1 : 2 and broken at the end of one CEMENT, CEMENT MORTAR, AND CONCRETE. 119 year. The figures represent tensile strength in pounds per square inch, and the different columns show the time of making the briquettes after the mixing of the mortar. TABLE No. 3G. Kind of Sand. Per Cent of Water. Made when Mixed. Number of Hours Made after Mixing. 1 2 3 4 5 6 j 7 8^ Beach 14 9.7 15.3 13.9 232 182 240 244 248 181 230 233 227 172 245 194 211 176 227 ,, 24( 0-)( 258 226 23; 236 liiver . The author of the paper concludes: " In practical working with most Portland cement, if it becomes necessary for the mortar to stand for one-half of a day even, no injury will result, provided the precaution is taken to keep the mortar wet." Another test to which cements are generally put is the one for maintaining its volume. This is sometimes done by placing the mortar in a cylinder of glass. If any expansion takes place in setting, the glass will be broken, and if any shrinkage, it can be easily detected. Mr. Clarke says in the Boston Main Drainage Report that in his tests the cylinders were invariably broken. An- other method is the so-called " hot water " test. The Faija method is to mix a small pat of cement with as little water as possible, and place it on a glass plate in a covered vessel which contains water maintained at a temperature of about 112. The pat is kept in. the moist air for 6 or 8 hours, when it is immersed in water kept at a temperature of from 115 to 120 Fahrenheit for the remainder of 24 hours. If at the end of that time it remains intact with no signs of disintegration, it is ready for use. Manufacturers, however, can overcome the effect of the heat by adding sulphate of lime to the cement. In speaking of hot-water tests, Mr. Cummings in his work heretofore referred to says: " It is safe to assert that of the more than one hundred and fifty million barrels of American rock cements used in all of the great engineering works through- out the country during the past fifty years, and with no evidence of failure, not one per cent would have sustained the boiline; test. A cement, whether natural or artificial, that will crystallize so rapidly as to sustain the boiling test ought to be looked upon with 120 STREET PAVEMENTS AND PAVING MATERIALS. suspicion, as it is either naturally too quick-setting or too fresh and lacking in proper seasoning." Concrete. Concrete can be defined as masonry made up of broken stone, gravel, cinders, or other similar material, joined together by cement mortar. It has been in use for centuries. One of the oldest and most noted examples of concrete construction is that of the dome of the Pantheon at Rome. In early times it was used principally for foundations. But as its value has become recognized and cement has been produced better and more cheaply, its use has been ex- tended until now it is put to practically as many uses as is stone itself. It is used as a monolith and also in blocks. It is particu- larly adapted to foundations of irregular form, as it is cheaply and easily shaped. It is used extensively in foundations for all classes of work, bridge piers and abutments, sidewalks, curbing, sewer-pipe, fire-proof floors, and even as a monolith in arch bridges of quite ex- tensive spans. Stone suitable for concrete is often found in locali- ties where good building-stone is not obtainable, and thus the use of concrete allows masonry construction when the cost of natural stone would have been prohibitive. So it is not strange that it has become popular with engineers, as, when well made, its success has always been as great as its adaptability. One of the best examples of concrete construction of modern times is the Museum building of the Leland Stanford Jr. University of California. The entire building is practically a monolith. In specifying proportions for concrete-mixing, it is customary to regulate them in units of cement. This is not the true way, and there is a growing tendency among engineers to change this and establish instead a certain quantity of mortar as standard unit. The province of the mortar is to bind the pieces of stone together, and when the voids of stone are positively filled, any excess is simply wasted. In deciding, then, upon the proportions to be used in the concrete, the amount of voids in the stone adopted must be first ascertained. This will vary with different kinds of stone and ac- cording to the uniformity with which it is broken. The actual size of the stone does not make so much difference. When the pieces are approximately cubical and of about the same size, the voids will "be about 50 per cent of the stone. By grading the sizes, however, CEMENT, CEMENT MORTAR, AND CONCRETE. 121 from the largest to a permissible minimum, the amount of voids can be materially reduced, thus accomplishing a saving of mortar and increasing the strength of the mixture. In order to insure the complete filling of the voids and making as solid a mass as possible, it is best to specify an amount of mortar, about ten per cent in excess of actual voids, as perfect work is very seldom attainable in prac- tice. The exact composition of the mortar is important. The char- acter of the work must determine the strength required for the concrete. Kecognizing, then, that a concrete cannot be stronger than its mortar, the proportions of the concrete and sand can be decided upon. For a good concrete, stone should be hard, tough, and of such a texture as to permit of strong cohesion between the mortar and the different fragments. But it would not be allowable, or good engineering, to go to great expense to provide a stone that would be appreciably stronger than the mortar matrix. The ideal concrete would have its stone and mortar of equal strength, so that when broken the fracture will extend through mortar and stone alike. Clean gravel and gravel mixed with broken stone have been used with great success. In concrete for fire-proof floors, where weight is an important consideration, clean steam cinders are generally employed. This gives good results, and some of the tests of very flat arches made of this material show that its strength is surprisingly great. After having determined upon the amount and composition of the mortar required for any given amount of stone, the next step is its preparation. The sand and cement should first be thoroughly mixed dry. The importance of this cannot be overestimated. Without good mortar good concrete cannot be obtained. It is not sufficient that enough and good materials are provided, but they roust also be properly applied. Water should next be added in such quantity as will assure the desired consistency, without drowning out the cement, and the entire mass mixed rapidly until every grain of sand is coated with cement, as this acts with the sand in precisely the same manner as the mortar acts with the stone. It is miniature concrete. As it is desirable to have as great cohesion as possible between the mortar and the stone, the latter should be thoroughly wet, so as to wash off all dust or other foreign matter, and then added to the mortar. 122 STREET PAVEMENTS AND PAVING MATERIALS. The resulting mass must then be turned over forward and back- ward until the mortar is scattered evenly among the interstices of the stone, so that each piece is completely covered and the con- crete is finished. The material at all times must be kept on boards or platforms, so that it shall be kept free from all foreign matter. This operation of mixing should be done without delay and as cxpeditiously as possible, as the sooner the concrete is in place the more complete will be its final set. The place of mixing should be near its final location, preferably so that it can be shovelled to it from the boards; but this is seldom possible, and it must be carried in some conveyance and dumped. When used in any great mass it should be spread in layers from 9 to 12 inches in depth and at once thoroughly tamped till the mortar flushes to the surface, and'then left undisturbed till completely set, or till another layer is ready to be placed upon it. In such work it is better to have one layer follow another before the first -has entirely set, so that they can become thoroughly bonded together. Whenever fresh material is placed upon or against old that has become dry and l.ard, .the latter should first be wet in order to aid in this bonding. The amount of materials of the different kinds necessary to produce a given quantity of concrete is important. Enough has already been said to show upon what this is conditioned. Whether it will be economy to mix gravel with the broken stone if that b used, or whether one or the other is to be adopted, depends upon the ease with which they can be obtained and their relative values. It is the business of the engineer to study this question till it can be correctly settled. Having then 'determined upon the aggre- gate, and the amount of voids it contains, the amount of mortar is at once decided upon. Ordinary sand contains loose about 37 per cent of voids. Some tests to determine this, made in the laboratory of the Department of Highways, Borough of Brooklyn, New York City, resulted as follows: Per cent. Street sand: sample No. 1, compact, voids 28.3 sample No. 1, loose, voids 37.6 sample No. 2, " " 35.0 sample No. 3, " " 37.5 Standard sand : compact, voids 44 loose, " 52.75 CEMENT, CEMENT MORTAR, AND CONCRETE. 123 Mortar mixed with No. 3 in the proportion of 1 cement to 2 sand and tamped into a mould till the water flushed to the surface gave a resulting volume of 2.07 parts, showing but little increase over the original bulk of sand. A similar mortar mixed with four volumes of 1-inch broken stone, very uniform in size, in which the voids had been found to be 51 per cent, thoroughly tamped as be- fore, produced a volume of 4.04 parts of concrete, although* it was discernible to the eye that all the voids had not been filled. In Paper No. 855 of the American Society of Civil Engineers will be found much information on concrete. Mr. Geo. W. Rafter made many experiments to determine the actual amount of mortar and concrete obtained with different proportions of sand, cement, and broken stone. The experiments were made with dry, plastic, and excess mortars. The results are given in Table No. 37 for plastic, as that is the consistency which would be the most liable to be used in actual work. Slightly different amounts were ob- tained with different brands of cements, and the mean is given. TABLE No. 37. Parts Cement. Parts Sand. Mortar. Stone. Concrete. Mortar Percentage of Stone. Shrinkage of Stone, per cent. 1 1 1.83 5.51 5.01 33 9.1 1 1 1.66 4.14 3.82 40 7.7 1 2 2.45 7.28 6.62 33 9.1 1 2 2.50 6.28 5.83 40 7.1 1 3 3.30 9.92 8.89 33 10.4 1 3 3.31 8.23 7.62 40 7.3 1 4 4.28 12.94 11.66 33 9.9 1 4 4.35 10.96 10.09 40 8.0 1 5 5.04 15.05 14.29 33 8.3 From these amounts of mortar it would seem that the sand used must have been very compact, containing very few voids, as the 1-to-l mixture increased 83 per cent over the volume of sand, while the l-to-5 even had a slight increase in volume. The resulting volumes of concrete, on the other hand, indicate a large amount of voids in the stone, as in every case there was a material decrease in the original volume of stone used. 124 STREET PAVEMENTS AND PAVING MATERIALS. In a discussion on the above paper, Mr. Wm. M. Hall gives the voids found by him in sand, gravel, broken stone, and the two last combined in different proportions. TABLE No. 38. SAND 31 PER CENT., ITS SIZE BEING AS FOLLOWS : ' Per cent, by Volume. Held by a No. 20 sieve ............................ 11 Passed by a No. 20 and held by No. 30 ............. 14 " " " 30 " " " " 50 ............. 53 50 22 CRUSHED STONE AND GRAVEL AND MIXTURES OF THE TWO. Voids. 100$ of crushed 2^-in. stone 48# 80 " 2 " " 20 of lt-in. gravel 44 70 " 2 " " 30 " 1^ " " 41 60 " 2i " " 40" H " " 38^ 50 " 2i " " 50 " 1 " " 36 100 " H " " 35 TABLE No. 39. Sand. Sand- stone. Boulder Stone. Gravel. Furnace Slag. Per cent. Per cent. 100 Per cent. 100 Per cent. 100 Per cent. Retained on 1-inch, finer 100 100 10.70 23.65 1 10 8 70 2.86 10 " 17.14 45.62 20 " 30 " " 40 " 4.17 12.52 44.44 38.87 21.76 6.49 5.96 5.99 36.92 8.26 3.24 2.00 Voids 41.7 45.3 48.7 34.08 43.8 The dust had been screened out of the stone, and the sand from the gravel. The slight 'difference in voids between the last mix- ture ajid the gravel alone would indicate that the limit of the reduc- tion in voids had been practically reached. Mr. H. Von Schon, in further discussing this same paper, gives among others a table showing voids found in different materials, and how they were graded as to size. This is reproduced as Table No. 39. CEMENT, CEMENT MORTAR, AND CONCRETE. 125 So much attention has been given to voids, as it is absolutely necessary to know the space to be filled by the mortar in order to get the best concrete, as well as to tell how much will be obtained from a given mixture. The amount of tamping it receives will also affect the quantity materially up to the point of filling the voids. The proper consistency for a concrete mixture is a question that has been much discussed by engineers. As it requires much less labor to mix it when an excess of water is used, contractors and laborers always have a tendency to add as much as permitted, and constant restraint is required to restrict them. The general theory is that a medium dry concrete will be stronger than one mixed with more water. This is probably true theoretically, and would most likely be borne out in tests; but it must *be remembered that such a mixture would require much more tamping to become thoroughly compacted than one more plastic, and also that extreme vigilance is necessary in order to obtain it; also that the mixing itself will not be so evenly done if dry. Then, too, if the concrete is spread out in thin layers, as is done in the case of foundations for street pave- ments, a portion of the water will be evaporated before it has had a chance to combine with the cement, and the mortar will simply dry out rather than set. This is particularly the case in hot weather; and although the tendency can be somewhat overcome by keeping the concrete wet by sprinkling, the results will not be as good. The author was brought up in the dry school, but his own experience has taught him that it is safer to have the mixture a little wet rather than a little dry. The immediate result is to retard the setting, but as time passes its strength increases, and it is very doubtful if it be appreciably weaker at the end of a few months. The ratios for strength of the different concretes made by Mr. Eafter were: dry mortar 29.1, plastic 26.6, and excess 25.3, taking the average of ten tests. Concrete is often mixed by machinery, and much discussion has arisen over the value of this method as compared to hand mixing. Much can be said on both sides. Many machines have been devised for this purpose, and varying results will be arrived at with each. In hand mixing the cement and sand should be first measured out in the proper proportions and then carefully mixed 126 STREET PAVEMENTS AND PAVING MATERIALS. dry on a smooth platform. Enough water should then be added to make a mortar of the desired consistency, when the whole mass should again be mixed. The first requisite is to have a good mortar. Whatever the aggregate to be used, it should be free from all dust or sand and thoroughly drenched, so that it shall be clean and damp in order that the mortar will readily cling to it. The mortar should then be spread upon the board and the stone added. Workmen should then proceed with the mixing, working from the bottom and throwing all material from the centre to the sides, turning their shovels downward in so doing. It should then be all thrown back in the same manner, forming a pile in the centre. If this be carefully done, the stones are generally all coated and the concrete should then be placed in its permanent position. If the work is well carried out, .there will be no question but that good results will be obtained. There are several kinds of machine mixers. One is formed of a cubical iron box of any desired size, with trunnions fastened at opposite diagonal corners, and supported by uprights. One side of the box can be easily taken off for loading and unloading. A charge of cement, sand, stone, and water is measured and placed in the box. The loose side is then bolted on and the box revolved by any convenient power until the ingredients are thoroughly mixed. Another which has been used much in Brooklyn on street work is a portable machine s'hown in Fig. 2. The boiler and mixer are mounted on four low wheels and can be moved by a pair of horses as the work progresses, or by the men on the street. It consists of a square shaft running lengthwise of a horizontal semi-cylinder about 28 inches in diameter and 8 feet long. The cylinder is firmly set in a frame. To the shaft are attached cast-iron blades of such length as will give a little space between the ends and the cylinder, and at an angle inclined to the shaft so that as it is revolved the material moves towards the end. If it move too freely, so that it reaches the end before it is thoroughly mixed, a few of the blades near the centre can be reversed, thus checking the forward motion. W r ater is supplied by a perforated iron pipe running along one side and connected by hose to a hydrant, the amount being regu- lated by a stop-cock. A little room is left near the end to allow FIG i.'. 127 CEMENT, CEMENT MORTAR, AND CONCRETE. 129 about a wheelbarrowful of concrete to accumulate, when the end gate is raised and the concrete dumped into the waiting barrow and then wheeled to any desired location. At the other end of the machine the boiler and engine are located. When the machine is operated continuously the boiler requires about one-half ton of coal per day, the same man acting as engineer and fireman. To operate it to advantage, the machine is located in the centre of the roadway and the broken stone dumped upon planks upon one side and the sand and cement on the other. The latter are carefully measured out and mixed dry in a long pile on a con- tinuous platform. Men with shovels are stationed on each side, the number corresponding to the proportion of mortar and stone desired, and throw the material towards the back end of the shaft so that it may have the benefit of all the blades in the mixing. As the shaft revolves the mass moves forward according to the speed of the engine and the pitch of the blades. As the concrete falls into the wheelbarrow an experienced foreman or inspector can readily detect if it be not properly mixed and apply the remedy, so that in a very short time the machine will be operating success- fully. No attempt is made to measure the stone, as it can be told by inspection whether sufficient mortar is present to fill thoroughly the voids, and that is all that is necessary. If too much or too lit- tle mortar is being used, the trouble is remedied by adding to or taking from the men at work on the stone as the occasion requires. This machine has a capacity of about 150 cubic yards of concrete per day when running smoothly under a capable foreman. Another machine is called " The Portable Gravity Concrete Mixer " and consists of a short steel trough filled with numerous rows of steel pins, staggered to mix thoroughly the sand, cement, and broken stone that are to compose the concrete as they gravitate through the trough. At the upper ends of the trough the pins in the first row are spaced nearer together than the pins in the other row, in order that the stone passing the first row will go through the rest of the mixer without clogging. The water is led from a barrel by a l|-inch hose to the spray- pipe. The man at the bottom of the mixer who can best see the concrete operates the water-valve. The water from the spray-pipe strikes the mixer at about midway its length. By this arrange- 130 STREET PAVEMENTS AND PAVING MATERIALS. ment the concrete is mixed dry in the upper half and wet in the lower half. It is claimed for this mixer that concrete in rolling over and over on the bottom of a steel trough ten feet long,, each and every stone being thrown from side to side by each row of pins, is mixed better than it is possible to mix it by hand or steam. The trough delivers the concrete in a wheelbarrow or other receptacle, when it can be removed as desired. It is probable that good results will be obtained by using either of these machines; and which would be the best for any particular work would have to be decided by the conditions. The first or box machine would not be adapted to street work, as it is not easily moved and its action is not continuous. Wherever it is desired to have a special amount mixed, as, for instance, in making a cement sewer-pipe, this plan will insure the proper amount with very little waste, as all ingredients can be measured before being mixed. By the last method it will be noticed that all material must be raised several feet above the place of delivery. This would be well adapted for concrete to be used in basements, as the material would all be naturally delivered at the street-level and must in any event be lowered to where it was to be used; or for work in trenches, or in fact under any conditions where the concrete would be needed several feet below the natural delivery of the material. By either of these two machines the proportions of the different ingredients would probably be more accurately determined than by the second one described. But that has the advantage of being easily and quickly moved (a great desideratum in street work, espe- cially in a narrow roadway) and is in a good position to be changed easily. Its results are certainly satisfactory when under the charge of intelligent workmen; but if operated by careless and unskilled laborers, the material would probably not be as well mixed as by either of the other machines. In other words, it requires more intelligent supervision. As to the question whether concrete mixed by hand is better than that mixed by machine, it can be said that the product of either is good when properly made, and that incompetent workmen will spoil both. Mixing mortar and stone is hard work, and labor- CEMENT, CEMENT MORTAR, AND CONCRETE. 131 ers will shirk it whenever possible; so that if proper systems are adopted for obtaining and applying the right proportions, it would seem that concrete mixed by machinery ought to give more uniform results than that mixed by hand. In the preceding pages some examples have been given of quan- tities of concrete obtained from certain mixtures of cement, sand, and stone in the laboratory, so that it will be of interest to know of some of the results in actual work carried out on a large scale. It must be understood that different-sized barrels, different kinds of sand, and the varying amount of voids in the broken stone used will materially affect final results. In making concrete for dam No. 11 on the Great Kanawha River Improvement, eleven batches, each containing 2 barrels of cement, 15 cubic feet of sand, and 33 cubic feet of broken stone, made 396 cubic feet or 14J cubic yards of concrete when rammed in place. Assuming a barrel of cement to be equal to 3.75 cubic feet, this would make the proportions by volume 1 cement, 2 sand, and 4.4 broken stone, and would give an increase of concrete over broken stone used of 9.1 per cent. The amount of material used for one yard of concrete was \\ barrels of cement, 11J cubic feet of sand, and 24} cubic feet of stone. On a piece of work where 1000 barrels of Portland cement was used and the concrete mixed cement 1, sand 2, and 2^-inch broken stone 4, the average amount obtained was 20 cubic feet per barrel of cement. The broken stone was well graded in size, and the voids, though not determined, must have been small. This would be 1.35 barrels of cement for 1 cubic yard of concrete. On two separate occasions the author had accurate records kept on street work where the concrete was mixed by machine in the proportion of 1:2:4, and in one case 97 barrels of cement made 81 cubic yards, and in the other 106 barrels of cement made 87 cubic yards of concrete, or almost exactly 1.20 barrels of cement per cubic yard. In these particular cases the parts of sand and stone were taken with the loose cement as a unit. The author once laid a quantity of concrete mixed 1:2:5 in a shape and place where it was difficult to get exact measurements, and he was allowed by the engineers in charge ten per cent in ex- cess- of broken stone used. 132 STREET PAVEMENTS AND PAVING MATERIALS. In the discussion of the paper before the American Society of Civil Engineers, "On the Theory of Concrete" previously referred to, Mr. Allen Hazen gives some data on concrete mixed under his direction as follows: One barrel of cement, 30 pounds of water, 11.4 cubic feet of sand, and 19 cubic feet of gravel. The volume produced from the above was 22.7 cubic feet, or an increase in concrete over the gravel of about 20 per cent. On the entire work 15,085 cubic yards of concrete required 18,584 barrels of cement, or 1.23 barrels per cubic yard. The increase in the consumption of cement, both Portland and natural, in the last ten years has been something enormous. This has been caused by two reasons. In the great amount of construc- tion work that has been going on natural cement has taken the place of lime to a great extent, and Portland is now largely used instead of natural. This has been possible on account of the new and improved methods of manufacture, so that both kinds have been sold at largely reduced prices. American engineers, always skeptical, were very loath to try American Portlands, not believing that it could be made in this country equal to the imported. This fact, however, has been plainly demonstrated, and now American Portlands are not only admitted, but are very properly called for, in a great many specifications for important works. As a result, new factories have sprung up, old ones have increased their capaci- ties, and still in the last few years the demand has been far in advance of the supply, and the work of increase is going on. In the bulletin issued by the United States Geological Survey on " The Production of Cement in 1898 " it is said that all indica- tions point to a large increase in 1899 and an enormous one in 1900; also that four factories in the Lehigh Valley region will soon add 1000 barrels per day to the product of each, and it is claimed that one factory, already the largest in the world, will soon reach a pro- duction of 10,000 barrels per day. A new producing region has come into the field of Portland-cement production that of La Salle, Illinois. Table No. 40 contains an analysis of the ingredients proposed to be used by one of the companies now erecting a plant at that place. CEMENT, CEMENT MORTAR, AND CONCRETE. 133 TABLE No. 40. LIMESTONE. Per cent. Calcium carbonate 88.16 Magnesium carbonate 1.78 Silica 8.20 Iron oxide Alumina 1.30 CLAY. Per cent. Silica 54.30 Alumina 19.33 Iron 5.57 Lime 3.29 Magnesia 2.57 Sulphur 2.36 Table No. 41 shows the composition of the ingredients to be used in the manufacture of Portland cement in Kentucky. TABLE No. 41. LIMESTONE. Per cent. Calcium carbonate 97.63 Magnesium carbonate 0.65 Silica 0.49 Alumina Trace Iron oxide 0.22 Sulphuric acid 0.34 CLAY. Per cent. Silica 55.82 Iron oxide 6. 19 Alumina 19.77 Lime 0.70 Loss, alkalies, etc 19.52 Table No. 42 shows the domestic production in barrels, and the imports of Portland cements, for comparison. TABLE No. 42. 1890. 1891. 1893. 1894. 1895. 1896. 1897. 1898. Home product Imported 335,500 1,900,000 2,235,500 454,813 2,988,313 3,448,126 590,652 2,674,149 3,264,801 798,75? 2.638,107 3,436,864 990,324 2,997,395 3,988,719 1.543,023 2,989,597 4,532,620 85,486 4,447,134 2,677,775 2,090,924 4,768,699 53,466 4,715,233 3,692,284 2,013,818 5,706,102 36,732 5,669,370 Total Consumption It can readily be seen how strong a hold American Portlands have on the market, when from 1896 to 1898 the imports fell off 975,779 barrels and the domestic production increased 2,149,261 barrels. The value of the domestic product for 1898 was $5,970,- 773, or about $1.62 per barrel. Table No. 43 shows the amount of American natural cement produced from 1893 to 1898 inclusive, and also the consumption of all kinds of cement for the same time in barrels. 134 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 43. \ American Natural. Total Consumption. 1893 7,411,815 10,676,616 1894 7,563,488 11,000,352 1895 7,741,077 11,728,796 1896 7,970,450 12,503,070 1897 8,311,688 13,080,387 1898 8,418,924 14,125,026 A barrel is assumed to contain 300 pounds of natural or 380 pounds of Portland cement. The total value of the natural product for 1898 was $3,888,728, or $0.46 per barrel. CHAPTER VI. THE THEORY OF PAVEMENTS. LORD MACATJLAT said in his History of England: " Of all in- ventions, the alphabet and printing-press alone excepted, those in- ventions which abridge distance have done most for the civilization of our species." Adam Smith once asserted that " the construction of roads is the greatest of all improvements." While' these remarks Had special reference to communication between towns or villages, they can with equal force be applied to cities and towns themselves. Some one has said: "Tell me the condition of the churches of a city, and I will tell you of the prosperity of that city." If this be true of churches, how much more truly can it be said of the pavements! Probably no one condition in a city strikes a stranger as forcibly as the general appearance of its streets. The clean and improved pavements of New York City during the last few years have impressed the rural visitor more than any one other feature of the city, the tall office-buildings, even, not excepted. The word " pavement " comes from the Latin pavimentum and means " a floor rammed or beaten down "; hence the hard smooth surface of a street can be called pavement. It can be defined as the artificial surface of an improved roadway formed of hard or durable material for the purpose of facilitating travel and forming a presentable surface to a street at all seasons of the year. There has been considerable discussion among engineers as to what really constitutes a pavement. Its importance can be seen when it is remembered that a great many cities compel abutting property owners to pay for the first pavement, but keep it in repair and renew it at the expense of the city at large. The people, know- ing this, often make their first improvement as cheaply as possible, 135 136 STREET PAVEMENTS AND PAVING MATERIALS. leaving to the general public the task of effecting a real and perma- nent improvement. Pavements have been laid of many materials,, both perishable and imperishable, natural and artificial. The experience of one city has not seemed to benefit very greatly any other, but it has seemed necessary for each one to work out the problem for itself. This was especially true in earlier years, when there was less com- munication between city officials and when, too, there was less in- terest taken in the subject. At the present time the ideas of city officers are spread abroad through the medium of official reports, technical societies, and technical journals, so that one can easily know what is being done in outside cities by keeping in touch with these means of communication. But it by no means follows that the decision as to what is the best paving material for one locality will necessarily govern in an- other, however intelligently it may have been reached. There are so many conditions affecting this question that it must generally be decided by their careful study in each particular case. For in- stance, stone may from its proximity and availability be just the material for one city and the cost of transportation make it pro- hibitive for another, and some other material must be used. The value of pavements to a city or a particular neighborhood is positive and immediate. Real-estate owners, than whom no more shrewd or sagacious men are in business, recognize this, and when they wish to put a piece of property on the market at once and at good prices, always pave the streets with the most popular material. The pavement improves the appearance of the streets so much that the lots not only sell more rapidly, but the owner can add to his price more than enough to reimburse him for his outlay. Of how much importance street pavements are in a large city- can be understood only by a knowledge of their cost and extent. In the present city of New York there were 1720 miles of pave- ments on January 1, 1900. Assuming the cost of a good pavement to be $2.25 per yard and the average width of a street to be 30 feet between curbs, the cost per mile, including curbing, will be about $50,000, making a total of $86,000,000 New York City would have invested if her street pavements were all of good character and in good condition. Or assuming that each street must be repaved THE THEORY OF PAVEMENTS. 13T every twenty-five years, to keep the above mileage renewed when worn out will require the laying of 69 miles of street pavement each year. Assuming further that the average cost of repairs to all pavements will be nothing for the first five years, and three cents per yard for the remainder of its life, the total annual expense for maintenance and repairs on the present mileage of New York City's pavements will be $528 per mile, or $690,096 for repairs and $3,450,000 for renewals, or a v sum total of $4,140,096 per annum to keep the present paved streets of New York in good condition. Other cities will have less cost, but this illustration shows the necessity of careful study and investigation. It will be of interest and value to know how these vast sums are raised; and while payments for all public improvements must come from the property owner, the methods of obtaining it vary much in their detail. In a paper called " Theory and Practice of Special Assess- ments" read before the American Society of Civil Engineers by Mr. J. L. Van Ornum, the methods of paying for street improve- ments in fifty cities were given. Table No. 44 is compiled from this paper. When special assessments are made against the abutting prop- erty different methods are adopted for payments. In certain sec- tions of the West the tax is due in instalments, special bonds being issued to raise funds to pay the contractor, which bonds mature as the instalments are paid, and are not considered as a general indebtedness against the city. In other places the entire amount is payable when the work is- completed, tax certificates against the property being issued to the- contractor as payment, and he being compelled to make all col- lections. In the East it is more common to make the tax payable- after work is completed and assessment laid, funds being provided temporarily by the issue of stock of the city. When the amount of money involved is so great, it is not strange- that many inventors have been at work and many experiments made- to determine what is the best material for pavements. As a result streets have been paved with stone in varied forms and shapes,, wood, asphalt, coal-tar, cement concrete, iron, brick, india-rubber,, shells, gravel, slag blocks, and even glass and hay; and many of 138 STREET PAVEMENTS AND PAVING MATERIALS. these in such modified ways as to make entirely different pave- ments. TABLE No. 44. City. Grading, how paid. Original paving, how paid. Repaving, how paid, Atlanta Ga. .... By city at large % by abutting prop- % by abutting prop- Baltimore, Md Boston, Mass All by abutting prop- erty owners All by abutting prop- erty owners, ^ by city at large All by abutting prop- erty owners All by abutting prop- erty owners, \fa bv city at large All by city at large Cincinnati O erty owners 2% by city at large erty owners 2% by city at large 98$ Indianapolis, Ind... Louisville, Ky 98 by abutting property owners All by abutting prop- erty owners All by abutting prop- by abutting prop- erty owners All by abutting prop- erty owners All by abutting prop- when done by spe- cial act of legislature All by abutting prop- erty owners By city at large Milwaukee Wis erty owners All by abutting prop- erty owners All by abutting prop- By the ward except Minneapolis, Minn . . Newark N J. .. erty owners, except intersections, which are for paid for by city at large By the ward All by abutting prop- erty owners, except intersections, which are for paid for by city at large By the abutting prop- erty owners, except intersections, which are paid for by city All by abutting prop- when on concrete foundation, then as original improve- ment By the abutting prop- erty owners, except intersections, which are paid for by city All by abutting prop- New Orleans, La. . . . New York City Omaha, Neb erty owners % by abutting prop- erty, J4 by city at large All by abutting prop- erty owners % by abutting prop- erty owners % by abutting prop- erty owners, J4 by city at large All by abutting prop- erty owners All by abutting prop- erty owners % by abutting prop- erty owners, 4 by city at large By city at large All by abutting prop- Philadelphia, Pa erty owners, &j by city at large By city at large All by abutting prop- erty owners, except intersections, which are paid for by city at large All by abutting prop- erty owners All by abutting prop- erty owners, except intersections, which are paid for by city at large By city at large All by abutting prop- St. Louis, Mo erty owners By city at large erty owners All by abutting prop- erty owners erty owners All by abutting prop- erty owners Durability was thought to be of great importance, and iron was experimented with in several cities. It was once tried in St. Louis, but was soon taken up. Iron blocks laid on Cortlandt Street, New York, about 1865, were roughened on the surface by hexagonal projections about one inch in size, separated by similar depressions. This made a rough and noisy pavement; horses tore off their shoes, slipped and fell frequently; so that after a short trial it was taken up and replaced with stone. In 1885 some one suggested a hollow iron block 4 inches wide t THE THEORY OF PAVEMENTS. 139 and from 10 to 12 inches long, the hollow to be filled with any ma- terial that might seem fit. In 1877 "iron paving" was laid on " Unter den Linden" in Berlin. It remained for quite a number of years, being removed about 1890 at the request of the experimenters. The same people, however, continued their work by paving the intersection of Langen-Strasse and Marcus-Strasse with impregnated wooden blocks capped with steel. The blocks were laid on concrete, and the joints filled with a- bituminous preparation. An inquiry as to this pavement in 1899 elicited the following reply: " The pavement which was laid down in the year 1888 by the United Kb'nigs- and Laura-IIiitte in the Langen-Strasse at the junction of Marcus- and Holzmarkt-Strasse was removed in the summer of the year 1897, upon application of the makers, and has been replaced by asphalt pavement. " Although the pavement had shown itself to be pretty durable in the beginning, it was, after an existence of about eight years, so worn out in its steel-capping in consequence of the heavy traffic, that it required a renewing of the latter, and an entire repavement became necessary. " As from the beginning the building administration on ac- count of the very high price about twice as much as for asphalt pavement doubted the wisdom of granting a further appliance of this wood-iron pavement, the company, who, as the party obliged to keep the pavement in good order, would have had to carry the cost of renewing, asked us to be relieved of this obligation. " This request was granted by us, and as already stated above, after removal of the wood-iron pavement the same was replaced by a pounded asphalt pavement. " It is hardly necessary to mention that the cost of the pave- ment in question would have been considerably increased by the present price of iron, which is almost 100 per cent higher than it was at that time/' Another plan was to set hollow iron cylinders closely together on a firm base and fill all interstices as well as the cylinders with concrete, the idea being that the iron would prevent the wear, and the concrete a general smoothness. It is doubtful if this idea was ever experimented with, even. 14:0 STREET PAVEMENTS AND PAVING MATERIALS. In 1890 a small piece of experimental pavement was laid on a sidewalk crossing in Columbus, 0., at an entrance to a railroad freight-yard. An iron plate was cast with pockets 3 7 / 16 inches square on the upper side. Each plate contained five full, four half, and four quarter pockets so arranged that when set on the street the plates were square and the pockets at an angle of 45 with the length of the street. The plates were bedded on the foundation, and into the pockets were driven oak blocks five inches high and projecting two inches above the pockets. At the end of sixteen months the blocks showed a wear of but J inch, when it is said that macadam within the freight-yard was renewed in ninety days, and asphalt outside was replaced in four months. This pavement would hardly be practicable, however, on a large scale. About 1889 a so-called jasperite pavement was laid in Wichita, Kansas, the process being protected by letters patent. It con- sisted simply of a concrete made of Portland cement and the par- ticularly hard stone found near Sioux Falls, South Dakota. The author talked at the time with the patentee, who was quite enthusi- astic over his contract. The work amounted to several thousand yards, but never was a success, and was not repeated anywhere About 1898 an experimental pavement of compressed marsh- grass was tried in Eichmond, Va. The grass was first treated with a preparation of oil, tar, and resins, and then compressed with hydraulic pressure into blocks about 5 inches square and bound together with wire. The blocks were laid in the usual way on a street where they were subjected to very heavy traffic. The pavement lasted but a few months. A pavement that is somewhat used in England where the traffic is light is called " tar-macadam." A 10-inch bed of hard clinkers and broken stone is well rolled with a 12-ton steam-roller and covered with 4 inches of 2^-inch broken stone well rolled. Upon this is laid a 3-inch course of tar- macadam, consisting of one ton of IJ-inch granite to 12 gallons of tar, 28 pounds of pitch, and 2 gallons of creosote oil. This is well rolled and covered with an inch of limestone screenings mixed with the same cementing material, then covered with fine screenings and again rolled. THE THEORY OF PAVEMENTS. 141 In certain portions of Germany a combination iron macadam is used for roadways. Common iron slag treated so as to lose some of its brittleness is broken into small pieces as nearly uniform as pos- sible. It is then spread over the surface of the road and thoroughly rolled. Bog iron-ore is then scattered over it until it is covered, and the whole mass again rolled to a hard surface. Where the traffic is heavier, broken stone is used over the slag. Artificial stone blocks have been made in Chemnitz as follows: Coal-tar is mixed with sulphur and warmed thoroughly. Chlorate of lime is added to the resulting semi-liquid mass. After being allowed to cool, it is broken into small pieces and mixed with glass or blast-furnace glass slag. The entire mixture is then subjected to a pressure of 200 atmospheres and reduced to whatever form or shape is desired. Its specific gravity is 2.2. Its crushing strength is 143 kilograms to the square centimeter. Its durability is con- sidered to be about one-half of Swedish granite. It makes a pave- ment easily cleaned, and is said not to be slippery. In 1898 an experimental pavement was laid in Lyons, France. It was made of blocks of devitrified glass. The blocks were eight inches square, each one being cut on top into sixteen smaller squares, so that the finished pavement looks very much like a huge checker-board. The treatment consists in heating broken glass to a temperature of 1250 and compressing it into moulds by hydraulic force. The physical transformation of the glass is due to devitrification under the Garchy process. This action, however, is more apparent than real, as a chemical analysis shows that after devitrification the glass has the same composition as before. It possesses all intrinsic qualities of glass except transparency. It will also resist crushing, and heavy frosts, very much better than before treated. In a pavement it is said to have greater resistance than stone, is a poor conductor of heat, so that ice will not readily form upon it, it is easily cleaned, and is sanitary. It is considered to be more durable than stone and just as cheap. Portland cement has been used in street pavements in Belle- fontaine, 0., to a considerable extent. It was first tried there in 1884, and the streets so paved were in a fair condition after fifteen years of service. The City Engineer in writing of them says: 142 STREET PAVEMENTS AND PAVING MATERIALS. " The greatest objection is that they are slippery. Very few people here now advocate their construction, brick and asphalt having the preference." These pavements were laid on a 4-inch base formed of one part of the best Portland cement and four parts of gravel and sand about equally mixed. This was made into a concrete and thor- oughly tamped on the street. Upon this, and before it was set, was spread the top course 2 inches thick, composed of one part of cement as above and one part of sand and gravel sifted to the size of a pea, a very thin layer of neat cement mortar being rubbed into the concrete to insure a good bond between the two layers. Both layers were separated into blocks 5 feet square and the surfaces grooved into 4-inch squares, these grooves being V-shaped and 3 /ie inch deep and 1 inch wide. When completed the entire surface was covered with 2 inches of wet sand and kept in that condition for one week. In New Orleans roadways of streets have been improved with shells. Oyster-shells are first spread over the roadway to a depth sufficient to give 6 inches when consolidated and then thoroughly rolled. Upon this another 6-inch layer of lake shells is placed and also rolled. This gives a nice, smooth, pleasing surface for light driving, but of course would not stand heavy traffic. Another form of improvement is made of chert. Chert is a sort of disintegrated granite common in some parts of the South and possessed of a cementing property, after having been wet and rolled, that makes a hard, smooth surface upon a street. In New Orleans the subgrade is first covered with 1 x 12-inch cypress planks. The material is then spread in a 6-inch layer, sprinkled and rolled. Other layers 3 inches in thickness are added till the re- quired depth of material is obtained. This makes a cheap and good roadway. The object of the planks is to prevent the chert from being rolled into the soft soil, and its moist condition should pre- vent the decay of the wood. In the early eighties an artificial pavement called the Pelletier block was used in Chicago. It consisted of any hard stone, crushed and thoroughly dried, and then mixed with ten per cent of iron slag or low-grade ore. It was then subjected to a thorough in- fusion of a chemical combination of oxide and chloride of iron THE THEORY OF PAVEMENTS. 143 which was intended to act as a perpetual binder, growing harder and firmer with age and exposure to the weather. These blocks were subjected to great pressure during manufacture, and were impervious to water. They were never very much used. In Cairo, Egypt, an attempt was made to form a street surface by pouring hot asphalt over a bed of broken stones. But the re- sults were not satisfactory. Later another experiment was tried by making slabs of bitumi- nous asphalt concrete by mixing natural liquid asphalt with or- dinary broken stone, and then laying a pavement with the slabs. This was but a partial success. Between Valencia and Grao in Spain there has been a stone- paved roadway for some years. About 1890 a trial was made of laying flat steel rails in the wheel-tracks. The rails are laid double in the natural soil with no special foundation. Where they join a slight indentation is made so that wheels will more readily keep the tracks. The rails are kept in gauge by steel cross-bars spaced at proper intervals. After the tramway had been in use for seven years the average annual cost for repairs had been $380, while previously the stone pavements required on outlay of $5470 per annum, or a net saving for repairs of $5090 each year, or for the seven years a total of $35,630, while the entire cost of the iron track was only $28,518. The average traffic on the road was 3200 vehicles per day. A charge of 8 /io of a cent is levied for each vehicle. In 1875 experiments were made in Budapest with a view of making paving-blocks of ceramite. By 1878 they had been pro- duced with a crushing strength of from 27,000 to 43,000 Ibs. per square inch. They were then adopted as a paving material, being 4x4x8 inches in size. The method of laying was to form the natural soil of the street into the desired shape and lay on it flat- wise bricks 3J x 4 x 11 J inches. The joints of this first 'course were filled with cement mortar. A cushion of sand 0.8 inch thick was spread over the entire surface and the ceramite blocks laid upon it. The blocks were laid with 0.4-inch joint filled with a composition of 1 part coal-tar, 1 part pitch, and from 15 to 20 parts of sand according to fineness. The blocks weighed 22 pounds each. No description of the method of manufacturing or material of these 144 STREET PAVEMENTS AND PAVING MATERIALS. "blocks could be 'obtained, but from their name they probably were burned brick of especially prepared clay. The following is a description of a patented noiseless stone pave- ment: Granite blocks 5x3 inches are wrapped, except the upper surface, with waste fibre and an elastic bituminous compound, and the whole brought together while resting on a continuous pad of the same material. The pad is taken to the street and unrolled over the concrete. The blocks are set diagonally and by a power- ful lever pressed firmly together. This was claimed to make a smooth, noiseless, and sanitary pavement. In 1896 a space 9x9 feet was cut out of an asphalt pavement in Topeka, Kansas, and then paved up with blocks of compressed wood pulp six inches square and four inches deep. This was sub- jected to a wear of about 720 vehicles per day. At the end of two weeks the wear was perceptible, but was not very extensive till at the end of four months, when the blocks wore so rapidly that they had to be taken up. On account of the wear, the asphalt was so broken near them that the original space of 9x9 feet had become 11 x 16 feet which required repaving. A few years ago a novel pavement was laid in Oakland, Cal. It was a combination of wood and asphalt. The base was the usual cement concrete 6 inches thick. Upon this foundation were laid redwood blocks 6 inches square and 4 inches deep. The blocks were submerged in a bath composed of 80 per cent of hard asphalt and 20 per cent of liquid flux for about five minutes. It was found that the time of immersion did not affect the penetration of the asphalt as much as the temperature of the bath, which was kept from 350 to 400 to get satisfactory results. Previous to the block-laying, the concrete was given a thin coating of liquid asphalt at a boiling temperature, although it is admitted that it is doubtful if its utility justified the expense. It was done as an extra precaution to keep as much moisture as possible from the wood. 1 The blocks were laid close at right angles to the street. The joints were then filled with a grouting material composed of 80 parts of hard and 20 parts of liquid asphalt and 30 parts of car- bonate of lime, being first mixed with 15 parts of liquid asphalt. The grouting was applied at three different times, so that all the joints should be filled and the blocks covered with about J inch of THE THEORY OF PAVEMENTS. 145 asphalt. A coating of sand about J inch thick is then spread over the entire surface. This sand is gradually absorbed by the asphalt, which thus becomes hard and firm, leaving the wood coated with 4 inch of what is very similar to bituminous rock. The grout when cold is said to hold the blocks together with a strength of 200 pounds per square inch. The asphalt covering is supposed to be only a carpet to carry the load that is really sup- ported by the blocks. Its durability will be according to the traffic, but under conditions in a city like Oakland it is expected to last two or three years, when it must be renewed. The cost of renewal is about 4J cents per square yard. No expansion joints were left, as it was supposed that all absorption of moisture had been pre- vented by the asphalt bath. With proper renewals of the covering this pavement is supposed to last almost indefinitely, as the asphalt treatment of the redwood should prevent decay except after a very long time. The Jetley pavement of London is thus described: "Under this system the wood blocks are compressed and combined very powerfully together by machinery and in such a manner that no block can afterwards move, and it is brought ready made to the street which is to be laid, in slabs 4' 6" x 12" wide, and when the roadway is completed it forms a homogeneous structure from curb to curb so powerful that no block can move and consequently will remain perfectly level." The slabs are laid without concrete, and when worn rough are turned over, giving practically a new pavement. After three years' service a pavement of this character was said to have been as smooth as when first laid. These examples show how varied have been the attempts to find the best methods of improving streets and roads. They cannot all be said to have been failures, nor, if they had, would they be without value. Mankind as a whole, and engineers in particular, should learn by mistakes of their fellows as well as by their suc- cesses. The question as to what is the best material for street pave- ments, and the detailed methods in which it shall be laid, is by no means settled at the present time. Much experimental work is going on now, but much has been accomplished during the past 146 STREET PAVEMENTS AND PAVING MATERIALS. twenty years. At that time Belgian-block pavement was the im- proved pavement, and it composed a large proportion of the paved area of New York City. During the last ten years it has nearly all been replaced by asphalt or granite blocks, although it was in good condition. It makes way for its betters. In Philadelphia, in 1884, 535 miles or 93 per cent of the pave- ments of the city were of cobblestone. Now the cobblestone has al- most entirely disappeared from the streets, and in its place are found granite, asphalt, and vitrified brick. While many materials are now being used in pavements, it is safe to say that stone, asphalt, and vitrified brick are the 'only materials that should be considered to-day for street-paving pur- poses. American cities have not seemed in the past to have profited much by the customs of their fellows. During the past fifty years nearly all of them have laid their first street pavements. In nearly every instance the city officials have worked out the problem for themselves. In some respects it was a new problem in each place. The best material for New York was not necessarily the best for Omaha, nor does it follow that Omaha's selection would be right for cities still further west. Economic conditions must always be considered. A city, like an individual, must be guided to a certain extent by its financial condition. The cost of transportation prob- ably affects a selection more than any other one condition. Wood is cheap at Chicago, Milwaukee, and Detroit on account of water transportation, and, although of short life, is being used in those and some other Western cities long after it has been given up in most places where it has been tried. Stone has long been acknowledged as being the most economical material for Eastern cities that can be easily reached by water, but its cost makes it prohibitive to the large number of places in the Mississippi Valley. Local conditions must always be considered, so that it is not possible to lay down any fixed rule as to what material makes the best pavement. But by a careful study and understanding of what properties are necessary for a good pave- ment, and a thorough knowledge of the materials proposed, an engineer can determine what selection should be made under given THE THEORY OF PAVEMENTS. H7 conditions. Understand the principles first and apply them after- ward. An ideal pavement should be cheap, durable, easily cleaned, present little resistance to traffic, non-slippery, cheaply main- tained, favorable to travel, and sanitary. Letting the perfect pave- ment have a value of 100 by a study of these different properties, it is possible to assign to each its proportional value of the whole. CHEAPNESS. No matter how desirable, or how economical even, any material may be, its first cost is a question of importance in deciding upon its availability. If the property owners cannot pay for it, the question is settled at once. There is no chance for argument. A committee's recommendation is often rejected when its wisdom is not questioned, simply on account of the cost. When the best cannot be taken this phase is developed: with the money available how can the best results be obtained? A person present- ing a new plan or a new material will first be asked as to its cost. And if it be expensive, his will be a hard task to have it receive a fair trial except at his own expense. Cheapness, therefore, has been given a value of 15. DURABILITY. This is also an economic property. Upon this depends ultimate cost, and in this connection must be considered with first cost. If a pavement be cheap, and pleasing even, it can never be a complete success if it has not durability. Americans expect any construction to. care for itself largely. They are not given to economies in repairs. Durability, too, is affected by so many varied conditions that it is discussed with difficulty. It is acted upon principally by traffic and the atmosphere. The effect of the former depends directly upon its quantity, and the latter upon the character of the ma- terial and the climate to which it is exposed. For instance, wood will have only a certain life even if it sustain no traffic whatever, while stone or good brick would last practically forever under the same conditions. Asphalt also is somewhat affected by the air, but not to such an extent as wood. The influence of traffic is modified by five principal conditions, viz., width of roadway, character of pavement, presence or absence of street-car track, state of repairs, and how well the pavement is cleaned. Traffic has been measured in this country by counting 14:8 STREET PAVEMENTS AND PAVING MATERIALS. the number of vehicles passing over a street in a given time, and so arrive at an approximate tonnage without regard to width. In England efforts have been made to arrive at more definite results, and the tonnage per yard of width of roadway per day or year has been taken as the unit. This reduces it all to a common standard, so that the traffic in one city can be easily compared with that of another. In 1885 a series of observations were made under the direction of Gen. F. V. Greene to determine the amount of traffic in several American cities. The figures represent the number of vehicles of all kinds passing between 7 A.M. and 7 P.M. Broadway, New York 7,811 Broad Street, Philadelphia 6,081 Devonshire Street, Boston 5,362 Douglass Street, Omaha 4,752 Fifteenth Street, opp. Treasury, Washington 4,520 Clark Street, Chicago 4,389 For comparison the number of vehicles passing in twenty-four hours in some foreign cities are given: PABIS. Rue de Rivoli 42,035 Avenue de 1'Opera 29,500 Rue Croix des Petit Champs 20,480 Rue'St. Honore 19,672 LONDON. King William Street 26,793 Gracechurch Street 15,585 Queen Victoria Street 16,531 Cheapside 15,206 SYDNEY, AUSTRALIA. George Street 11,960 Width of Roadway. The distance between curbs affects traffic as it tends to scatter or congest it. The wider a pavement is the more even will be its wear. If several lines of travel can be main- tained irregularly, the wear on the surface will be more uniform and a better service received from the pavement. When vehicles are restricted to direct lines of travel, the wheels move in prac- THE THEORY OF PAVEMENTS. 149 tically the same place from day to day, and the result is a rough and uneven surface in a comparatively short space of time. Character of Pavement. By this is meant the detailed method by which any particular material is laid. Asphalt pavements have been standardized, slight variations sometimes being made to meet special traffic conditions. But with stone, brick, and wood it is very different. Foundations vary for all, and the joint filling of each is what the experience or inclination of the particular engineer may suggest. Wood of one variety is used in one locality, and a different kind in another. It is treated chemically in one city, and laid in its natural condition in others, so that the word " wood " alone means very little as to the exact character of the pavement. Presence or Absence of a Street-car Track. A car-track has a great bearing on the action of traffic. On a rough, poorly paved street where the cars run at long intervals, vehicles naturally make use of the track, thus relieving the pavement from a large amount of its natural wear. On the other hand, on a well-paved street where cars run frequently, the traffic is confined to the space be- tween the tracks and the curb, with all the evils of restricted travel. The appreciation contractors have of this is shown by the fact that in 1897 bids for asphalt pavement in Brooklyn, X. Y., averaged $0.98 per square yard on sixty-eight streets free from tracks, and $1.26 on eleven streets where there were tracks. State of Repair. This is of vital importance to a street pave- ment. If holes, depressions, ruts, or any defect in the surface are allowed to remain for any length of time, the material is displaced and consequently is worn abnormally. This fact is not fully ap- preciated by most city officials, but should they watch the effect of travel upon granite blocks loosely paved in a trench, they would soon be convinced. This is especially true of such materials as asphalt or broken stone. Cleanliness. The effect of street refuse on a pavement varies with its character. An imperishable material is benefited by hav- ing a cushion of detritu's upon it. It serves as a carpet to protect the pavement, which when the cushion is heavy enough becomes the foundation only. This fact will often explain why certain materials are seemingly so much more durable in a small city than in a large one. A poor brick pavement, for instance, will often give 150 STREET PAVEMENTS AND PAVING MATERIALS. good results in a small place where the pavements are cleaned only at long intervals, when it would rapidly fail if kept clean under the same traffic. This will not hold good, however, with wood or asphalt streets. Any street debris collects and retains moisture which hastens the action of disintegration and decay in any perishable material. At one of the meetings of the National Brick Manufacturers' Association one member asked if city streets were not kept too clean; if brick pavements would not last longer and be less noisy if they were allowed to become more dirty. Although answered in the affirmative, he was told that in these times city streets would be kept clean despite the effect upon the material of the pave- ment. r . All of the above conditions modify the action of traffic and thus affect the durability of any material. This property of durability has been considered tq have a value of 21. EASINESS or CLEANING. The experience of New York, Wash- ington, Buffalo, and other large cities in cleaning streets has de- monstrated to citizens and taxpayers that it is not only feasible but very desirable to have pavements kept free from natural street detritus. It has been shown so conclusively that it is an accepted fact that it is not alone desirable, but that it is absolutely neces- sary. The expense of street-cleaning is very great, and any device or any street-construction that will reduce it will be gladly wel- comed by city officials. The appropriation for the Street Cleaning Department of New York City for 1900 was $5,031,282. The benefit of smooth pave- ments to this department will be appreciated from a statement made in 1896 by Col. Geo. -E. Waring,' Jr., then Street Cleaning Com- missioner of New York City. At a meeting of the American So- ciety of Civil Engineers he said that if all the streets of New York were paved with asphalt where the grades would permit, and the street-car tracks constructed with grooved rails, the cost of sweep- ing the entire city would be reduced from $1,200,000 per annum to $700,000. That is, there would be a saving annually of $500,000, which capitalized at 4 per cent would amount to $12,500,000 in a city that then had a pavement mileage of 431 miles, of which THE THEORY OF PAVEMENTS. 151 94 were paved with asphalt. A value of 15 is given to easiness of cleaning. RESISTANCE TO TRAFFIC. This is an important item. One of the chief provinces of a pavement is to reduce this, and conse- quently any pavement that can bring it to a minimum is of special value. A mechanical device that would reduce the friction of a machine 25 or 50 per cent would be recognized at once as of great benefit. There is fully this difference in the various pavements, and this must be recognized and considered before deciding on any particular material. If one horse can draw on one pavement a load that would require two horses on another, the truckman at once sees the importance of a proper selection. Light resistance to traffic is valued at 15. NON-SLIPPERINESS. The slipperiness of a pavement depends upon its material and also upon its condition. The efficiency of a draft-horse varies with his foothold. If that be good, he can use his entire strength to draw his load; while if he be in constant danger of slipping and falling, he will accomplish very little. In- stead of using all his power to overcome the resistance of the load, he uses it only to the slipping-point. The condition of the weather and the climate modify this. An illustration of this is shown in a case where observations were being taken on several asphalt-paved streets in extreme winter weather. On the first day the hourly traffic was 225 tons between 11 and 12 o'clock, reaching 270 tons between 3 and 4 o'clock P.M. On the following day the traffic between 11 and 12 o'clock was 305 tons. About 2 o'clock snow began to fall, the mercury being about zero, making the pavement so slippery that the traffic was reduced to 40 tons between 3 and 4 o'clock, and the street was soon practically deserted. The same results were obtained on all other streets where observations were being taken. Non-slipperiness is assigned a value of 7. In the light of the above this value may seem small, but it must "be remembered that these special conditions seldom arise, an$, while effective while they do exist, do not have as much influence as a smaller force acting continually. EASE OF MAINTENANCE. Maintenance is closely allied to first cost, and many engineers think that they should be considered 152 STREET PAVEMENTS AND PAVING MATERIALS. together. To a certain extent this is true, but mainly when the question of ultimate economy is being considered. The cost of re- pairs liable to be incurred to keep a pavement in good condition should be ascertained as accurately as possible in advance. No material can be intelligently adopted without it. What often seems a wise and sound selection is ruled out simply by the cost of repairs. All works constructed by man require constant attention, and a pavement is no exception to the general rule. But that material which needs the least and allows that to be done at the least expense, as well as inconvenience to the public, is the best, other things being equal. This property has been ranked at 10. FAVOKABLENESS TO TRAVEL. By this is meant the ease and comfort that are enjoyed in driving over a smooth pavement, and also the decrease in the wear and tear of vehicles, as compared with one that is rough and uneven. It is difficult to estimate this exactly, but some approximations have been made. The French engineers say that 50 per cent is saved in the wear and tear by having smooth pavements. A London engineer in 1827 stated that good pavements in Lon- don, Westminster, and Southwark would save 140,000 per annum in wear and tear of vehicles and horses. The area included in the above was 3818 acres, but it must be remembered that the streets of London at that time were in a specially bad condition. In a paper read before the Institution of Civil Engineers in 1871 Mr. Geo. F. Deacon said: " Since the new Liverpool pave- ments have been constructed without giving credit for the great reduction of wear and tear of horses and vehicles, there was a sav- ing of 10,000 per year for every mile of the new pavements- now laid on the dock line of the streets of Liverpool." Smooth pavements are a luxury also. It is a pleasure to drive on some streets, and positively painful on others. Wheeled vehicles are equipped with pneumatic tires to make the pleasure as great as possible, but much can be done to aid it in the pavements itself. With the introduction of the automobile, and the possibilities of its extension, this property of favorableness to travel is bound to receive more attention from year to year. At the present time it is valued at 5. SANITAEINESS. Another important requisite of a pavement is THE THEORY OF PAVEMENTS. 153 that it should be sanitary. A great amount of decaying organic matter, house-garbage, horse-droppings, and various kinds of filth must be deposited in the streets despite the utmost care of citizens and public officials. Any pavement that will allow any of this to- collect in joints, or soak down to the surface to the underlying soil, out of the reach of street-cleaners, must be deleterious to the public health. Any material that will readily absorb moisture and give it forth in dry seasons must be considered as unsanitary. Therefore a pavement that has a smooth surface, is impervious to water, and is not made up of organic matter subject to decay will be desirable from the standpoint of the sanitarian. Noise, too, is an important factor. A noisy material prevents sleep, rasps on the nerves of both the sick and the well, and prevents conversation on the street. This is considered of so great im- portance in large cities that in apportioning the funds allowed for repaving New York City special consideration is given to, and a separate sum set aside for, smooth pavements around schools, churches, and hospitals. Sanitariness is rated at 13. Having now studied somewhat in detail the characteristics of a pavement and obtained a value for each, it will be in order to take up the different paving materials themselves, and by careful ex- amination determine how much of each total is to be apportioned to each according as it approaches perfection in each property. The pavements that will be considered are: oblong granite- blocks laid on six inches of cement concrete with tar and gravel joints called granite A; granite blocks laid on a sand base with sand joints, called granite B; sheet asphalt, wearing surface two inches thick and binder one inch, on six inches of concrete; vitrified brick,, also laid on a six-inch concrete base with joints filled with pitch or Portland cement; Belgian trap-rocks on sand; macadam eight inches thick; and cobblestone. Wood is not taken into considera- tion because it is at present being laid in but a few Western cities,, and untreated cannot be considered as a paving material. It has also been laid in so many different ways and of so many varieties that each case would require discussion by itself. It may be said that cobblestone is a material of the past. This is undoubtedly true, but its use illustrates the scope of the table. 154 STREET PAVEMENTS AND PAVING MATERIALS. First Cost. This of course will vary in every locality, and a different apportionment must be made for every change in price. The following figures are based, upon the average prices bid in Brooklyn, N. Y., in 1897 (all per square yard complete): Granite A $2.50 Granite B 1.65 Asphalt 1.75 Brick 2.00 Belgian 1.40 Macadam 0.75 Cobblestone 0.40 Assuming their values to be inversely as their cost, granite A has 2, granite B 4, asphalt 4, brick 3, Belgian 5, macadam 7, and cobble 14. Durability. This, as ; has already been seen, varies greatly ac- cording to many conditions, so that any conclusion must be gen- eral. It must be remembered, also, that there are two ends to all pavements, a physical and an economical end. The former comes when the material is so worn out that it cannot be repaired and must be relaid; the latter when the cost of repairs is so great that it will be economy in the end to relay at once. The former test will generally be applied to stone, brick, or any block pavement, and the latter to asphalt or macadam. When a pavement is made of moderately sized parts of practically the same character, the wear on the parts is about the same amount, and to repair it requires taking up the old material and replacing it with new rather than adding to the material on the street. But when a pavement is made up of parts so small that they must be consolidated into a con- tinuous whole it is different. The physical end of a pavement can be determined by observa- tion as the blocks wear out. Asphalt and macadam wear away by degrees, and can be added to in whatever quantity it may be desired and its physical life thus prolonged indefinitely. The economic test must then be applied .to ascertain when the repairs must be stopped and a new pavement laid. Assume a street to be paved, and the expense of keeping it in THE THEORY OF PAVEMENTS. * 155 repair is so great that the question arises, shall it be repaved or the repairs continued? Let N = life of proposed pavement; C = cost per square yard; I = rate of interest; R = estimated cost if distributed over entire life; A = sinking fund to be paid each year to equal C at end of A T years. r> Then A + CI + T- = annual expense of new pavement. Take, for instance, an asphalt pavement, and let N = 15 years, C = 1.50, / = 3J, and R = 0.40. Then A will equal .0807 and the equation becomes $0.0807 + .0525 + .0267 = $0.1599; or if the street be repaved, it will cost annually $0.16 till it is renewed. Con- sequently if the life of asphalt be correctly assumed at 15 years, it should not be repaved until the annual cost approaches $0.16 per square yard. Assuming the life to be 20 instead of 15 years and applying the formula as before, the annual cost will be reduced to $0.1356 per yard. The author believes that this is the scientific, the engineering, and the only true way of telling when an asphalt pavement should be relaid. The only element to modify this principle is the incon- venience traffic and property owners on the street are put to while repairs are being made. The determination of this must be made in each case. But the principle of the formula is correct, and when cities have had a larger experience with asphalt pavements, and repair accounts are kept in a more intelligent way, there will be, no- difficulty in determining the variables. A series of experiments were made in St. Louis in 1880 to deter- mine the resistance to abrasion of several kinds of paving material. Strips of pavement 22 inches wide were laid of fire-brick, asphalt blocks, granite and limestone blocks. A traffic standard of 50 tons per day per foot of width of roadway was adopted, and a two-wheeled cart with 2^-inch tires loaded 800 Ibs. per inch was rolled over the different strips long enough to equal a traffic of 8J years. The fire-brick lost 9 per cent in weight and a depth of -J inch, with about one-half broken. Asphalt blocks lost 14 per 156 STREET PAVEMENTS AND PAVING MATERIALS. cent, limestone blocks 10 per cent, while the wear on the granite was hardly appreciable. The officials of different European cities give the average life of the different materials as follows: TABLE No. 45. Granite. Asphalt, Years. Wood. Olassrow . 50 6 30 12 to 15 j Redwood 8 Liverpool ... . . . . 30 12 Australian 15 15 to 18 \ 5 to 8 for Baltic deal 30 .......f Australian 12 8 From the above and data collected from American cities the estimated life of granite A is 25 years, granite B 20 years, brick 15 years, wood 10 to 15 years, asphalt 18 years, Belgian 20 years, macadam 8 years, and cobble 18 years. These estimates give to granite A a value of 21, granite B 17, "brick 13, asphalt 15, Belgian 17, macadam 7, and cobble 15. Easiness of Cleaning. Some figures have already been given showing the benefits of smooth pavements when they are to be cleaned. How necessary this is can be recognized from a state- ment made by a committee of the Society of Arts, London, in 1875, to the effect that at that time it was estimated that 1000 tons of "horse-manure was being dropped daily upon the streets of Lon- don. This had to be taken up and removed to avoid being incor- porated into the human system through the respiratory organs. Other refuse of all kinds collects upon our streets, and the pave- ment that uniformly presents a hard, smooth, and even pavement is cleaned at much less expense than one that is rough and uneven. In accordance with this principle, then, granite A has a value of 11, granite B 8, asphalt 15, brick 12, Belgian 7, macadam 5, and cobble 2. Light Resistance to Traffic. Many experiments have been made to determine the force necessary to draw a given lo'ad over roads and pavements of different character. The most of them were made, however, a good many years ago, those of Morin having been carried THE THEORY OF PAVEMENTS. 157 out in 1843, and those of Macneil in 1838. Since that time changes have occurred in the same kind of pavement, one of stone block, for instance, being very different from that of fifty years ago, so that the results arrived at then may not be absolutely correct to- day, but relatively they should not be far from right. Then, too, the actual condition of the pavement must vary results consider- ably. Differences of temperature would change results on asphalt, the traction being appreciably greater in the summer, when the pavement is soft, than in the winter. It is to be regretted that more modern experiments have not been, undertaken on any extended scale with modern appliances to settle this question. At the Atlanta Exposition in 1895 the Department of Agricul- ture experimented to some extent with some roads and pavements that were available at that time and place. Table No. 46 gives the ^esults reached. TABLE No. 46. Pounds. Loose sand (experimental) 320 Best gravel, park road 51 Best clay 98 Best macadam 38 Poor block pavement 42 Cobblestone 54 Poor asphalt 26 Table No. 47 gives the force in pounds per ton required to draw a load over different surfaces as given by Prof. Haupt in a paper published in Journal of the Franklin Institute in December, 1889. In 1893 the Studebaker Brothers of South Bend, Ind., made some experiments on this subject, and a portion of their results is given in Table No. 48. The figures represent force in pounds per ton. These results would seem to indicate that a load is not hauled much more easily on wide tires over ordinary roads than on narrow, and that on stone pavements the narrow tires actually require less traction. This last is probably due from the fact that a stone pavement must necessarily be more or less rough, and that a wide tire will be apt to pass over more bunches than a narrow one, and as the load must be simply lifted over the bunch in either case, 158 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 47. Character of Roadway. Pounds per Ton. Sand 400 Gravel 200 Ordinary earth 200 Dry clay 100 to 66 Good cobble 133 to 66 Ordinary cobble 250 Ordinary macadam 80 to 57 French macadam 40 Stone block 80 Belgian block 50 Belgian block, well laid 33 Asphalt ' 15 Smooth granite trams 12 Iron trams 10 TABLE No. 48. Diameter of wheels 3 ft. 8 in. and 4 ft. 6 in. 4-inch Tire. IJ^-inch Tire. To Start. To Move. To Start. To Move. Block pavement 161 46 142 35 Good sand roads 323 127 343 180 Good gravel roads 276 81 308 83 Muddy roads 369 254 422 237 more traction will be required with wide tires on a hard surface that is not smooth. The committee of the Society of Arts previously referred to ex- perimented on the streets of London in 1875 to ascertain the force required to draw loads over different roadways at varying rates of speed. Table No. 49 gives results. The report added that the asphalt experimented on was not in good condition, and for that reason the force shown for asphalt was undoubtedly higher than it otherwise would have been. These figures, however, are valuable as they give the effect caused on the draft of increased speed. Table No. 50 is made up from the results of different experi- menters, the figures representing the force in pounds to draw one ton at a speed of approximately 3 miles per hour. From all these figures it is estimated, taking into considera- tion the varying conditions under which all tests were made, as well as the improved character of pavements at present, that the force THE THEORY OF PAVEMENTS. 159 TABLE No. 49. r. . f . ,>, Speed in Miles Force in Pounds Character of Pavement. *J er Hom . to move Qne Ton< Gravelly macadam 6.945 44 Do 3.45 39.8 Granite macadam side of tramway -j Do 2.557 10.5 Granite blocks by freshly laid . . \ 4 ' 239 ( 2.775 84.4 Asphalt 5.025 30.8 Do 3.56 24.2 Do 5.687 29.3 Wood 3.932 41.1 Do 3.278 35.6 Do 3.827 34.8 Good macadam 6.65 37.9 TABLE No. 50. Character of Roadway. Pounds. Authority. Ordinary dirt road 200 Bevan Hard gravel 66| Bevan " 66| Minard. " 51 U. S. Qovt. Bad macadam 143 Gordon Old macadam 100 Navier Good macadam, wet 86 to 66f Morin Best macadam 33i to 43 Gordon 28|to46i Morin 44f Rumford 38 U. S. Govt. Ordinary cobblestone 125 Kossack Good cobblestone 62^ Kossack Cobblestone 54 U. S. Govt. Belgian block 47 Navier " 23to44$ Morin " 31 U.S. Govt. " good 33 Rumford Ordinary stone block 80 Minard " 33 Good stone block 40 Rumford London stone block 33 Gordon Poor stone block 42 U. S. Govt Asphalt...* 15 Gordon " poor 26 U. S. Govt. " 15 Haupt " 24 London Experiment 160 STREET PAVEMENTS AND PAVING MATERIALS. expressed in' pounds to draw one ton over the different pavements herein considered would be: granite A 34, granite B 40, asphalt 16, brick 20, Belgian 40, macadam 40, and cobblestone 65. Tliis will give a percentage to granite A of 7, granite B 6, asphalt 15, brick 12, Belgian 6, macadam 6, and cobble 4. The general opinion among engineers is that the tractive force varies inversely as the diameter of the wheels, but some say in- versely as the square root of the diameter. Mr. W. Hewitt in a paper before the Surveyors' Institution of England says: "From experiments made with Eastren and Anderson's horse-dynamom- eter at the Royal Agricultural Show, 1874, a slightly greater ratio than inversely as the diameter was given, and I am inclined to think that inversely as the diameter is the more correct View of the two." Slipperiness. A great many conditions affect this property: conditions of the street, temperature, whether wet, damp, or dry, etc. Mr. Wm. Haywood, Engineer to the Sewer Commissions of Lon- don, made some very extended observations in the London streets in 1873 to determine the liability of horses slipping on asphalt, granite, and wood pavements. The asphalt observed was the ordinary rock asphalt of that time, 2J inches thick on a 9-inch concrete base, with the surface in good condition. The grades varied from 1 in 58 to 1 in 550. The granite pavement consisted of Aberdeen blocks 3 inches wide, 9 inches deep, and from 9 to 15 inches long, laid stone to stone, the joints being filled with stone-lime grout. The pavement as a whole was not in good condition. The grade varied from 1 in 30 to 1 in 1000. Two wood pavements were experimented with. One was formed of fir blocks 3 inches wide, 5 inches deep, and 9 inches long. The blocks were laid touching each other at the ends, but crosswise of the street; the joints were f inch wide, filled in with thin gravel and grouted in with a bituminous composition. The other con- sisted of beech blocks 3^ inches wide, 4J inches deep, and 6 inches long, with J-inch joints at side and ends, filled in with cement grout. The grades varied from 1 in 30 to 1 in 260. The asphalt T?as sprinkled slightly with sand, and the wood four times with gravel. The wood and granite were watered to lay TEE THEORY OF PAVEMENTS. 161 the dust, but the asphalt was not treated. All the pavements were kept as clean as their nature and respective surfaces admitted with the usual amount of labor. All observations were taken between 8 A.M. and 9 P.M. The mean number of horses passing daily in March and April Ashpalt. Granite. Wood, ( Cheapside 12,366 ( Poultry 10,920 j King William Street 8,555 \ Cannon Street 5,350 ( King William Street 21,162 * ( Gracechurch Street 11,484 Table No. 51 shows the total number of horses that fell on the different streets during the fifty days on which observations were taken, as well as the daily <; of iiic'iiutciKUicc 10 10 7 6 6 7 3 2 Fuvorableness to travel. . . 5 3 2 5 4 2 5 Sanitaria ess 13 9 7 13 11 5 5 2 Total 100 69 56 76 67 52 45 44- Making asphalt the standard at 100, the values of the others will be: granite A 91, brick 88, granite B 74, Belgian 68, macadam 59, -and cobblestone 58. This table is original and has been made up after much careful study. It is not supposed to be infallible, nor always exact, as much of it has been determined by individual judgment. What is claimed for it is that it is working on the right lines in attempting to express positively what is generally given in very general terms. By a proper understanding and use of it an intelligent student can apply the principles used in its construction to any particular case that may present itself, and when he comes to a conclusion be able to defend himself with logical arguments. Its working can be illustrated in several ways. Assume, for instance, a street over which the traffic must be heavy and continuous. Ultimate cost is of great importance. It overrules first cost. Light resistance to traffic and foothold for horses are ruling elements, so that a given power may move its maximum load. The items first to be studied are, then: Dura- bility, maintenance, traction, and the non-slippery property. Con* suiting tfhe table and combining the values for these items, granite A has a value of 44, granite B 35, asphalt 40, brick 37, Belgian 33, macadam 23, and cobblestone 26. Granite A has such a decided advantage over this that further study is not necessary to come to a proper decision. But when the 168 STREET PAVEMENTS AND PAVING MATERIALS. figures are as close as the next three, ranging from 40 to 35, a care- ful examination of the remaining properties would be required. In this particular instance granite A ranks so high in the totals,, and so far ahead in the special requisites, that it would seem that no mistake could be made in selecting it for the material to be used. Consider next a residential street, built up with homes whose owners have means sufficient to afford the best of anything they desire, and, while not wishing to be extravagant, do want and ex- pect the best pavement that can be laid without regard to expense. This is an entirely different proposition. Cost, durability, and maintenance, so important before, can be left out of consideration altogether. Easiness of cleaning, non-slipperiness, favorableness- to travel, and sanitariness are the governing characteristics. Working as before, granite A has 29, granite B 22, asphalt 36,. brick 33, Belgian 18, macadam 12, and cobble 9. Asphalt, possessing all the desired properties in so high a degree,, should be selected without much question. It may be said that durability and maintenance are too hastily disposed of, and that by considering them the results would be changed. But this is the point of the selection. The property owners, can afford the best. They would not carpet their parlors with hemp or matting because it would last longer than tapestry, nor furnish their dining-room table with crockery and pewter rather than with china and silver. The problem is to select the best, material under existing conditions. The above conclusions would generally hold good for the best retail streets. Next consider a residence street with very light traffic, where the abutters wish a good but an economical pavement, one that will be durable and as near the best as their financial condition will admit. This requires careful consideration. The destructive action of travel is almost wholly eliminated. Durability will be governed by the action of the elements. Every quality but slight resistance to traffic must be taken into account. This gives: granite A 62, gran- ite B 50, asphalt 61, brick 55, Belgian 46, macadam 39, and cobble 40. Granite A leads asphalt by 1 point, but by a further study of the table it will be seen that it gets its supremacy by its great dura- TEE THEORY OF PAVEMENTS. 169 bility under traffic. Eliminating this property, granite A has 41, granite B 33, asphalt 46, brick 42, Belgian 29, macadam 32, and cobble 25. All but the three leading materials can now be re- jected, leaving for further examination granite A, asphalt, and brick. Now while durability has been eliminated, its value was deter- mined by the action of the weather as well as traffic. In this case the latter can be left out, and when it is remembered that asphalt has a life that is determined by climatic conditions, irrespective of traffic, it will be seen that granite A and brick in this instance can consistently be placed above it. These two have now practically the same standing, but by a further examination it will be learned that granite A gains 4 points over brick on maintenance simply by its superiority under heavy travel. Leaving that out of the total, granite has 31 and brick 36, and the latter is plainly the selection to be made. If the property owners, however, think the price too high, and prefer granite with its inconveniences to the more pleasing brick, then granite B would be the choice, but it must be understood that the decision was reached for financial reasons. Assume next that a country highway is to be improved where the traffic is not heavy, but the road is needed to facilitate the inter- course between towns, or to connect a suburban village with the parent city. Sanitariness, easiness of cleaning, durability (except as to action of weather), and light resistance to travel can be eliminated, sanitariness and easiness of cleaning because on a sparsely settled road many things are unimportant that could not be tolerated in a city; the other qualities because no heavy loads will be attempted. There will remain, then, granite A 21, granite B 18, asphalt 18, brick 19, Belgian 17, macadam 22, and cobble 21. In this case the values are more nearly alike, but the cost of the first five materials will rule them out at once. There can be no question between macadam and cobble on account of the unde- sirability of the latter, even though the former has but one point in its favor. By modifying the foundation for brick under these conditions, it would make a good showing, and in many localities prove the proper material. The above examples illustrate the workings of the table, show- ing how it is possible to analyze the conditions that may arise in 170 STREET PAVEMENTS AND PAVING MATERIALS. any case, and how easy it is to arrive at an intelligent and logical result when a systematic investigation is undertaken. An engineer who has under his charge the maintenance and re- newal of a large amount of pavement will be governed by slightly different principles from those just laid down. He will have a certain sum of money from year to year to be used on this work, and it will be his duty to make the most of it. He is now endeavor- ing to benefit the entire city, not the residents of any one section, as the funds for this purpose are raised by taxation upon the city at large. He should be governed more by ultimate economy than iirst cost. He must take into consideration, too, the interruption to travel by too frequent repair on business streets. A material that might be figured out as economical, even if short-lived, by reason of its cheapness both of first cost and renewal, might re- quire so much attention as to be an actual nuisance on a business thoroughfare. An engineer's appropriation is generally inadequate ior his work, and careful study is necessary to bring about the best Tesults. The smaller the amount the more time should be spent in directing its expenditure. An eminent authority has said that if one has but five minutes in which to perform, a difficult task, three minutes should be consumed in ascertaining how to do it. The engineer who occupies such a position will find himself confronted with an interesting and ever-varying problem. Condi- tions are constantly changing, traffic is divided, and circumstances keep arising that require his faculties to be ever alert. But if he meet the question successfully, and ultimately arrive at the true solution, his satisfaction is as great, perhaps, as in any other branch of his profession. In estimating the life of a certain material to be laid on any particular street, it must be remembered that when any one road is selected to be made into a thoroughfare, traffic will be immediately- diverted to it and the wear of the pavement abnormally increased. Consequently the natural life of the material must not be judged Toy its wear on this particular street. Taking now the costs and lives of the different pavements as herein deduced, the actual annual expense of each for a period as near fifty years as will be convenient for each material can be easily maintained and compared by the formula THE THEORY OF PAVEMENTS. 171 r> A -j- CI + -T r = annual expense. .zv For granite A: (7 = $2.50; / = .035; 72= .60 an amount sufficient to relay the pavement once during life; A = .064; A T = 25 years. Substituting in the equation, $0.06425 + .0875 + ^ = $0.17575 for first period. For the second period, assuming the value of the concrete to be $0.70 per square yard, making the cost of relaying $1.80 per yard, the annual expense is found as before to be $0.13326, or for fifty years an average of $0.154. For granite B : C = $1. 65 ; / = .035 as before; R = 0.25 cost of relaying pavement once during life; A = .05841; JV= 20 years. Substituting, .05841 + .05775 -f .0125 = 0.12866 for first period. For any subsequent period the cost will be the same, as the pave- ment has no appreciable value at end of life. For asphalt: C - $1.75; / = .035; R = 0.72; A = .0714; N = 18 years. Substituting, $0.0714 -f .06125 + .04 = $0.17265 for first period. 172 STREET, PAVEMENTS AND PAVING MATERIALS. For any subsequent period, assuming the cost of repaying to be $1.25 per square yard, the expense will be $0.1345 per yard, and for fifty-four years an average of $0.147. For brick: C = $2.00; / = .035; R = .60; A = .1036; JV = 15 years. Substituting, 0.1036 + .07 + .04 + 0.2136 for first period. For any subsequent period, assuming cost of repaying to be $1.25 per yard, the annual expense will be $0.1485, or an average for forty-five years of $0.17 per year. Table No. 55 shows the above results condensed. TABLE No. 55. Material. First Cost per Square Yard. Expense per Yard for First Period. Expense per Yard for 50 Years. Granite A. . . . $2.50 $0.17575 $0.154 Granite B 1 65 0.12866 0.12866 Alphalt 1.75 0.17265 147* Brick 2.00 0.2136 0.170f * 54 years. 1 45 years. In 1898 the city of Minneapolis, Minn., awarded a contract for asphalt pavements for $2.15 per yard with a ten years' guarantee,, and an additional price of 10 cents per yard per year for the next ten years after the expiration of first guarantee. Assuming the interest charge to be 3J per cent, and the bonds to mature in twenty years, this pavement would cost 15 cents per yard for the first ten years, and 25 cents per yard for the additional period, but with no other charge, except for maintenance, for the remainder of life. Table No. 56 shows the pavement mileage of eight of the prin- cipal cities of the country on January 1, 1900, except Washington, which is computed for July 1, 1899; also the mileage as it existed in 1890 except as noted. This table is given to show the change THE THEORY OF PAVEMENTS. 173 In character, as well as the amount of pavement, during the last decade. This is particularly noticeable in the case of Philadelphia, where the increase has been 328 miles. Asphalt has increased 210.7 miles, stone block 232.6 miles, brick 99.7 miles, and macadam 105.5 miles, while cobble and rubble stone pavements have de- creased 378.8 miles. The actual amount of new pavements laid in nine years was 666.9 miles, not including streets repaved with the same material. While a great portion of this work was done at the expense of the street-railway companies, it is a remarkable record that will probably never be equalled by any other city in the world. TABLE Xo. 56. Brooklyn. Boston. Buffalo. Chicago. 1890 1900 1891 1900 1890 1900 1890 1900 Asphalt 10.85 88.90 289.21 68.82 159.95 236.86 4.65 69.27 5.95 13.80 86.97 1.01 106. as 140.69 222.74 104.50 9.24 23.10 78.60 29.77 Stone block Cobblestone " !07 3.28 "'if.47 3.08 Brick 3.78 78.57 0.35 204.57 0.80 280.57 227.01 29.51 363.40 Macadam 2.81 Coal-tar and concrete Sla^ block Wood 410.29 763.21 4.88 1269.37 Miscellaneous . Total 386.77 284.79 547.97 383.15 250.07 337.79 669.64 New York. Philadelphia. St. Louis. Washington. 1890 1900 1891 1900 1890 1900 1890 1900 Asphalt 16.34 273.75 3.33 162.44 272.73 1.10 43.4 119.6 375.1 115.5 19.8 88.8 254.1 352.2 69.2 43.3 119.5 193.5 3.95 42.46 11.81 50.36 51.80 23.50 11.50 129.27 27.19 11.31 Stone block Cobblestone . ... Bubble-stone Brick 1.10 118.12 14.23 351.92 '"s.w 38.21 0.40 34.39 14.08 Macadam 24.23 290.08 Coal-tar and concrete.. Granolithic 12.8 S'ag block 5.6 Wood 08 5.26 341.75 6.89 435.21 0.30 133.31 216^ Total 1050.2 317.65 550.57 762.2 In the eight cities mentioned, asphalt, stone-block, and brick pavements have increased from 1043 miles to 2,195 miles, or 111 per cent; while stone block has increased from 776 to 1084 miles, or 39 per cent; asphalt has increased from 246 to 942 miles, or 174 STREET PAVEMENTS AND PAVING MATERIALS. 283 per cent, and brick from 20 'miles to 169 miles,, or 745 per cent~ The actual increase in each case is: Miles. Stone 307 Asphalt 696 Brick 149 Another important fact will be observed from this table: the increase in the amount of asphalt pavement. In 1890 there were 246.26 miles of asphalt in these cities, ex- cept, as noted in Boston and Philadelphia, and in 1900 this mileage had increased to 941.58 miles. These figures speak more forcibly than any other words can as to the popularity of this pavement. Wood, it will be noticed, has never been used to any extent in any of these cities, except in Chicago, where it has increased about 350 miles. Brick has had a great increase in Philadelphia, and has been introduced in several others. Openings in Pavements. One of the great sources of trouble to pavements is the fre- quent cuts made in it for repairs and connections to subsurface construction. Fifteen years ago it was thought that when water, sewer, and gas mains, with house connections to each lot, were laid in a street, it would be tolerably free from disturbance for some years. But in the days when telegraph, telephone, and electric- light wires are required to be placed underground, when pipes for heating and refrigerating purposes are being laid in our public/ streets, when changes in and repairs to street-railway construction are constantly going on, it seems as if, in many cases, a pavement is hardly free from the contractor before it is being torn up by the corporation or the plumber. This matter is very difficult to regulate, especially when so many changes and improvements are being made in subsurface construc- tion. It 'would seem, however, that the best way to prevent streets from being torn up is to provide for all underground construction before the pavement is laid, and then give no permits for openings within a stipulated time except in extreme cases. When a street is ordered improved, every householder on the line of improvement, and every corporation having any property at present or in pros- THE THEORY OF PAVEMENTS. 175 pective on the street, should be notified to make all needed repairs or extensions at once, under a penalty of a refusal to grant per- mits for extensions for a term of years. All repairs should be hedged with such conditions and requirements as to make it so ex- pensive that corporations would find it to their interest to make all possible repairs in advance. If a new building be constructed on a paved street, it must have connections to the different street mains. If these sewers have not been previously laid, the pavement must be opened. The city of Kochester has the power to construct sewers with their attendant connections, lay water-services, etc., under the same contract by which the pavement is laid, and assess the cost against the abutting property. Corporations having or projecting subways for any purpose are compelled to construct them in advance of the pavement. It often happens, however, in most cities, that real-estate owners, are so anxious to increase the value of and sell their property that pavements are laid far in advance of any subsurface construction. When the work of pipe-laying comes to be carried out, the pave- ment is badly damaged and in many cases practically destroyed. In the report of the Commissioner of Public Works for New York City for 1896 it is stated that during the year one mile in four of the paved streets was torn up for construction purposes, and that 59,000 separate openings requiring repairs to pavements were made during the year, or one opening for every 40 feet of paved streets. In Brooklyn, K Y., during the year 1896 35,000 openings were made in the streets of the city, or one opening for about every 75 feet of paved streets. In the report of the Street Department of Boston it is said, that for the year ending January 31, 1898, 14,017 separate openings were made in the streets, with a total length of openings of 213.4 miles. These figures are startling, but would probably be duplicated in every large city in the country in proportion to its size. It is true that the repairs are made at the expense of the corporation or plumber rather than at the cost of the city at large, but it must- be remembered that the money, in every instance, comes event- ually from the people, and that with proper precaution a very large 176 STREET PAVEMENTS AND PAVING MATERIALS. portion of it could be saved. When methods of construction have been developed and fully standardized, and when the requirements of modern civilization in regard to public wants and necessities have been fully satisfied, it is to be hoped that this condition of affairs will be greatly improved. In the mean time every effort should be made to have the pavement disturbances as few as possi- ble, and replaced in a good and substantial manner. It is almost impossible, however, to repair any opening in a pavement so that it will be as good as before disturbance. The new work will generally be a little above or below the old surface, and in either case this means abnormal wear. Then, too, however well the pavement may be laid, any settlement in the earth of the xcavation results in a corresponding settlement of the surface unless laid on a base of sufficient strength to span the opening and sustain the load by its transverse strength. It was the practice in Brooklyn, N. Y., for some time to require all cuts made in the im- proved pavements, whatever the original foundation, to be replaced on a Portland-cement concrete base eight inches thick. Settle- ments under this rule were very rare. Stone pavements on a sand base must always be relaid over con- nections with an allowance for future settlement, else a depression will certainly develop over the trench, requiring relaying. In the event of the former method, the ridge in the pavements is objec- tionable until it reaches its permanent position, and, unless the paver be possessed of rare judgment, it will alwa}^s require some re- adjustment. This will increase greatly the wear of the material and, consequently, decreases the life of the pavement. CHAPTER VII. COBBLE AND STONE-BLOCK PAVEMENTS. "WITHOUT doubt pavements originated from the necessity of im- proving low places in roads, which become impassable in wet weather on account of the traffic. This was done successfully, and seemed so desirable that when traffic increased the pavement was extended, and in time it became a necessity over the entire road. To the ancient Romans must be given the honor of being the first to construct roads in Europe on any general system, and to their credit be it said that the work was done in a thorough and sub- stantial manner. These old Roman roads were practically works of solid masonry construction, built of irregularly shaped stones, but finished to a smooth and true surface. A full description of the method of construction of one of these is taken from the French Encyclopedia of 1836. " 1st. A cement of chalk and sand one pouce in thickness. " 2d. On this cement, for the first bed, large stones six pouces thick were placed on one another, and backed by hard mortar. "3d. A second bed, eight pouces thick, of small round stones, mixed with other broken pieces of building material not so hard, and mixed with a binding cement. " 4th. A third bed, one foot of cement, made of rich earth mixed with chalk." An ancient pouce was 1.09 inches, and an ordinary pouce 1.06. Fig. 3 shows the ground-plan of a Roman road on the Septimer, as taken from a consular report. Figs. 4 and 5 show sections of other Roman roads. The Romans constructed these roads all over their conquered provinces, and in after-times the discovery of their remains was taken as proof of former Roman occupation. That the Romans' work was well done is shown by the roads themselves, as the one 177 178 STREET PAVEMENTS AND PAVING MATERIALS. previously described is said to have been in good condition fifteen centuries after it was built. FIG. 4 FEET METRES Gravel bound in rement mixed with Chalk ^ iRiclTEarth n -O^U^HJt*-< l -uw.f > __.. lit? Cemeii FIG. 5. The early pavements, however, were constructed in a different manner, the material being in almost every case what is now termed cobblestone. This was natural, as the cobblestones were the most available, and were known to have great durability. As cities grew, and the needs and desires for better streets increased, the rough cobblestone did not satisfy the people, and improved methods were demanded. Attempts were then made to construct a smoother pavement by forming the stones into rude irregular blocks, at first of no particular shape, but endeavoring to give a comparatively smooth surface. This was the beginning of the COBBLE AND STONE-BLOCK PAVEMENTS. 179 modern block pavement. As time passed on, the blocks were made better and the pavements, consequently, were improved. In Europe, in many cities, the blocks were made several square feet in area, and at first were laid lengthwise of the street, but as traffic increased it was demonstrated that, the long joints being parallel to the wheel traffic wore rapidly, and the pavement soon became rough and uneven. To obviate this, the blocks were made square and were laid as is shown in Fig. G, which shows a recent SIDEWALKS street in Catania, Italy. These blocks are of hard lava, 16 x 20 inches square and 8 inches thick. It was soon discovered, also, that these large blocks were not suitable for heavy traffic. It was difficult to get them so bedded on any foundation that they would maintain their position under heavy loads, and the blocks themselves soon hecame displaced. This caused the blocks to be made smaller still, and the greater portion of the European cities adopted a block about 6x8 inches square, and of depths varying according to traffic. In this country, however, the original pavements were all of cobble. The cities, as a rule, were poor, the cobblestones were available and naturally came into quite common use. They gave very good service, but were necessarily rough, uneven, and very noisy. The Russ blocks spoken of in a previous chapter were probably the only large square blocks that were ever laid in an 180 STREET PAVEMENTS AND PAVING MATERIALS. American pavement to any great extent, though some were used in New Orleans and Boston. Following the cobblestone, and in response to the demand for an improvement on them, came what has always been known in this, country as the Belgian block. The name is given to it because it was first used in Belgium, and it came to be quite generally adopted in Europe. In shape it was a truncated pyramid, with base about 5 or 6 inches square, and a depth of from 7 to 8 inches, the bottom of the block being of dimensions not more than 1 inch different from the top. This was an improvement on the cobblestone, and when well shaped and of proper material made a very good pave- ment. In New York and vicinity it became quite popular soon after its adoption, about 1850. The trap-rock forming the Pali- sades of New Jersey is easily cut into blocks of this shape, and being so near New York, it makes a very cheap and durable pav- ing material. As the blocks became more common, deviations, were allowed from the specifications, and the resulting blocks were too small on the base to allow a solid bearing, and under traffic they soon got out of position, and in consequence the pavement be- came rough. An improvement on the Belgian block was to make the block an exact cube. This was done in the old country, and many cities there at the present time lay blocks that are of that shape. The question of proper paving material became of so much pub- lic importance in Philadelphia that in 1843 a committee of eminent engineers was appointed by the Franklin Institute to ex- amine into the subject and make a report upon the best material for the city of Philadelphia to adopt. After a very careful and thorough investigation of the material being used both in this country and in Europe at that time, the committee made an ex- haustive report to the society. After speaking o-f several experi- ments of different kinds that had been made in the city, and show- ing where they were faulty, they finally made tlhe following recom- mendations for the material to be adopted for the Philadelphia streets. Streets of the First Class. These should be paved with dressed stone blocks laid in diagonal courses to the street, upon a subpave- ment of pebbles. These blocks were to be exactly 8 inches deep and from 7 to 9 inches wide, and 8 to 10 inches long. The estimated COBBLE AND STONE-BLOCK PAVEMENTS. 181 cost of this pavement at that time was $3 per square yard. This pavement was recommended for streets of heavy traffic when the grade was 2 n / 10 per cent or less. Streets of the Second Class. The pavement for these streets should consist of two stone tramways built in each street to accom- modate traffic in both directions, and the spaces between the trams and curbs to be paved with cobble. It was estimated that this would cost for laying transversely on the streets already paved, and repaving the old material, about $1 per square yard over the entire surface between the curbs. Streets of the Third Class, including all Lanes and Alleys. For this the then method of paving with cobbles was recommended, adopting the improvements suggested in the report, which con- sisted of using more regularly formed stones and thus having the average depth 6 inches. The committee reported as the best shape for the cobblestone " that of a prolate spheroid generated by an ellipse, of which the major axis is double the length of the minor." A tramway street similar to that proposed for those of the sec- ond class had been laid in London in 1825 on the Commercial Road, and the Philadelphians had had an opportunity of seeing one that had been made a short time previous to 1843 on Arch Street. How much attention was given to this report can be seen from the fact that in 1884 (forty-one years after it was made) ninety- three per cent of the entire pavements of Philadelphia (535 miles) was then paved with cobblestone, as has been before stated. It did not require, however, many years' experience with Bel- gian blocks to demonstrate to New York City that the proper pave- ment had not yet been discovered, and many experiments were made with a view to improvement. About 1865 a patent was issued by the United States to Mr. Charles Guidet for laying granite pave- ments. The distinctive points of this pavement, and upon which Mr. Guidet based his patent, were: First, stones bounded by six faces, the two opposite faces being parallel with each other. Second, the width of the joints running transversely to the street is comparatively wide. Third, the width of the joints running longitudinally to the street is comparatively narrow. 182 STREET PAVEMENTS AND PAVING MATERIALS. Pavements under this patent were laid in New York, and sev- eral in Brooklyn, about 1869. The cost of those laid by the patentee was about $7 per yard. Not thinking the patent valid or equitable, the city of Brooklyn paved several streets in accordance with this method, without paying any royalty. The patentee brought suit, but was finally beaten in the United States court and the case dis- missed. This was the first attempt made in this country, on any extended scale, to lay pavements of oblong blocks. The different kinds of stone pavement now being used in the United States are the cobblestone, the Belgian block, and the oblong block. Cobblestone. Fortunately for the people who are to come after us, very little cobblestone pa-venient is now being laid. In a few cities, however, where property owners pay the first cost of the pavement and are relieved of any further charge for its maintenance or relaying, its cheapness is a sufficient inducement to cause it to be used. It never gives satisfaction, and is really only a substitute for a pavement. If laid in the manner, and of stone, similar to that described by the Philadelphia committee, a tolerably good pavement would be secured, but all stones of that character have now become so scarce that to secure them would increase the cost to such an extent as to make it almost equal to that of the granite pavements. Cobblestone specifications, too, have been most shamefully abused and violated. As pavements of this class increased and the demand for the stones became so great that suitable ones were ob- tained only at considerable expense and witjh some difficulty, almost anything in shape and size was permitted to be used. The result was that cobblestone pavements were even worse than they would have been had they been properly laid. Cobblestone specifi- cations generally provide that the stones shall be the best selected water or bank cobblestones, of a durable and uniform quality, with round heads and well-shaped large ends. They shall not be less than 4 inches nor more than 8 inches in diameter across the head, nor less than 5 inches nor more than 10 inches in depth; no tri- angular, split, or otherwise ill-shaped stones can be used', nor any which are soft and rotten. The author, once examining a cobble COBBLE AND STONE-BLOCK PAVEMENTS. 183 street, found one stone of such size that he decided to measure it. It was 3 ft. 10 in. long and 11 in. wide, and was probably laid under specifications similar to the above. In another instance, in repaying a cobble street with granite blocks, a boulder was found forming part of the pavement which was so large that it could not be moved without blasting. When the street was paved originally, the boulder found on the street was simply lowered in position until it was at the required grade for the pavement. The cobble- stone pavement has had its day and is rapidly passing away, but it exists at the present time in such quantities that it will require sev- eral years of active work in repaving in some half a dozen cities to entirely do away with it. Fig. 7 represents a section of a cobble- stone pavement. FIG. 7. According to a bulletin issued by the Department of Labor in 1899, Baltimore, Md., had 5,815,610 square yards; New York City, 4,213,616 square yards; Philadelphia, 2,920,664 square yards; Cin- cinnati, 1,213,000 square yards; and Pittsburg, 1,147,415 square yards of cobblestone pavement. In this chapter, and in the entire work, where estimates are given for costs of any kind of pavement, the street is supposed to be graded to subgrade, and any cost of putting it in this condition must be added to the prices herein given. It is customary for pav- ing contractors in and about New York City to deliver paving ma- terial on the street and pile it compactly on the sidewalks before the work of paving is begun. The foundation is prepared and laborers called " stone-chuckers " are employed to carry the stones from the side to the pavers. The organization of a gang for laying cobblestone pavement is as follows: One foreman, four pavers, two rammersmen, four chuckers, two men preparing sand base, and two men spreading sand on the completed work. This gang will lay, under favorable conditions, 400 square yards per day. 184 STREET PAVEMENTS AND PAVING MATERIALS. Assuming the wages as follows: 1 foreman at $3.50 per day $ 3.50 4 pavers " 4.50 " " 18.00 2 rammersmen " 3.50 " " 7.00 4 chuckers " 1.50 " " 6.00 4 laborers " 1.25 " " . 5.00 Total $39.50 for labor for laying 400 square yards of pavement, or 10 cents per square yard for labor. Assuming sand to cost $1 per cubic yard, delivered on the work,, and that 1 cubic yard will lay 5 square yards of pavement, and that the cobbles themselves will cost 40 cents per square yard, the total cost for material will be 60 cents per square yard plus 10 cents for labor, which will make the entire cost of the cobblestone pavement 70 cents per square yard. In making any estimate upon any kind of pavement, it must be remembered that the cost will vary a considerable percentage ac- cording to the contractor, one man making a paying piece of work out of what would perhaps be a losing one to another. The prices, of material, too, vary considerably even in the same city, on ac- count of the length of 'haul, and other local conditions, so that any estimate must be considered a general one unless special conditions for each case are known. A base for a cobblestone pavement should consist of no less nor much more than 6 inches of loamy sand. If too much or too clean sand be used, the stone will become loose and cannot be maintained in position under traffic. From the shape of the stones, there is nothing in themselves which will serve to bind one to another, so they must be set in a material that will pack solidly and remain in position. In a clean sand the stones will roll, and when no other can be obtained it will be necessary to mix it with a certain per- centage of loam in order to get satisfactory results. Belgian Block. This pavement in New York and vicinity has been laid almost entirely with the trap-rock from the Palisades of New Jersey. This rock is hard and durable, but after some wear becomes smooth and COBBLE AND STONE-BLOCK PAVEMENTS. 185 slippery. It is so hard, however, that when properly laid it will probably last longer than any stone that is brought to the New York market. On account of its being so generally, and always at first, made of this trap-rock, all trap-rock pavements have been called Belgian pavements, but when made of the oblong blocks similar to those of the ordinary granite they have been called, in distinction, u specification Belgian." This is a complete misnomer, as the name refers distinctly to the shape and not to the character of the material, as some Belgian pavements have been laid of granite. One great objection to the Belgian pavement is that, on ac- count of the size and shape of the blocks, it will not retain its form under traffic, except upon a very solid foundation. The blocks, too, are of such size as to give a poor foothold to horses, and being square, or nearly so, there is always a considerable length of joints that is parallel to the line of the wheel traffic. This causes the blocks to round off, wear rough, and, at intersections where traffic is very severe, often to be crowded out of position and become rutted. The courses in this pavement, in this country at least, have always been laid parallel to or square with the street. If a square blojk is to be used, it should be laid in courses diagonal to the street so that no joints should be parallel to the traffic. This, how- ever, would cause some extra expense, but would be more than made up in the benefit that would be derived from this method. r n this country the Belgian has been probably laid on a sand base in every instance. The specifications ordinarily recite that tho stone blocks are to be of trap-rock, of durable and uniform quality, each measuring on the base, or upper surface, not less than 6 nor more than 8 inches in length, and not less than 4 nor more than 6 inches in width, and of a depth not less than 6 nor more than 8 inches. Blocks of 4 inches in width on their face to be not less than 4 inehes at the base. All other blocks of transverse measure- ment on the base to be not more than 1 inch less than on the face, but no block on the face shall be ol less width or length than 4 inches. Blocks laid along curbs must in all cases be 8 inches in depth, and at least one-third of the whole number must be of like depth. The faces of the blocks must be smooth and free from all bunches or depressions. 186 STREET PAVEMENTS AND PAVING MATERIALS. These variations allowed in the size and shape of the blocks make it very difficult to get a pavement in which the courses are true and the joints well broken. It requires constant care and watchfulness on the part of the inspector to see that blocks in the same courses are of the same width, so that the courses may run evenly and in straight lines across the street, and at the same time have all blocks face snugly up against each other. After the blocks are laid, they should be covered with sand, which must be swept into the joints until they are filled. The blocks should then be rammed to a firm unyielding bed and to a smooth surface. Wher- ever out of position, the blocks should be trued up and brought perpendicular to the surface of the street and covered with another coat of sand and thoroughly rammed the second time until the number per yard will vary according to the length, and it does not seem as if this variation is important. After the blocks are laid they should be covered with a clean,, sharp sand, free from pebbles, which shall be swept or raked into the joints until they are filled; each course should then be set up perpendicular to the surface of the street with proper tools, and all imperfect blocks removed and replaced with good ones, and then the entire surface should be thoroughly rammed. It should then be covered with a second course of sand, treated as before, and rammed the second time. This part of the work should be done with great care. If any soft spot or, as the rammer expresses it > " soft blocks " are found, they should be thoroughly rammed until they are solid and then taken up and the foundation brought to- proper grade with added sand, and the blocks replaced and rammed as before. Upon the proper ramming of the pavement depends, in a great measure, how well it will keep its form and shape under traffic. The entire surface of the pavement should be covered with one inch of sand and allowed to remain under traffic a sufficient time to permit all of the joints to be thoroughly filled. Concrete Foundation. With this base the subgrade must be treated in the same way as for sand, and the concrete then laid upon it. After the concrete has been completed and set sufficiently so that working upon it will do it no harm, a cushion of sand should be spread over the entira sur- face. The amount of sand-cushion will depend in a great measure upon the uniformity of the depth of the blocks. If the blocks are of variable depths, the cushion must be deepened, as, on account of the irregularities of the concrete itself, at least 1 inch of sand should be allowed between the bottom of the deepest block and the concrete. When a stone-block pavement is laid upon a rigid base, the joints between the blocks should be filled with a substance that will make the pavement, as a whole, water-proof. With a sand base this is not desirable or necessary, as,, whatever the joint-filling, the blocks, being set on sand, would always have sufficient moticn under traffic to permit water to soak through; but with a concrete COBBLE AND STONE-BLOCK PAVEMENTS. 197 foundation a perfectly water-tight pavement can easily be obtained, and is desirable both from the sanitary and the physical standpoint. Joint-filling. Portland Cement. The first filler that naturally suggested itself, in order to make the pavement rigid, was a mixture of sand and cement. This was a mixture of one part of sand and one of Portland cement, and after the blocks were rammed the joints were poured full of a grout made as above. While making a solid and substantial piece of work at first, the chief objection to this filler is that if for any reason a joint becomes broken it always re- mains so, and accordingly it has never been used to any great extent in stone pavements. Ferroid. In 1886 a filler called "ferroid" was used in Buffalo. This was made up of 10 per cent ferroid, 30 per cent German rock asphalt, 25 per cent Trinidad pitch, 15 per cent coal-tar, and 20 per cent sand. The 10 per cent ferroid above was supposed to be composed of iron borings, sal-ammoniac, and sulphur. This mix- ture was never very extensively used. Murphy Grout. Another joint-filler used to a considerable ex- tent in the West is what is known as " Murphy's Grout Filler." It is principally composed of iron slag and carbonate of lime, and when used on a street a certain proportion of clean, sharp sand is added. This is said to produce a mixture which is as hard as gran- ite and which attaches itself closely to the blocks, making them solid and waterproof. Tar and Gravel The general custom, however, in granite pavements of a concrete base is to fill the joints with gravel and paving-cement. This paving-cement in the vicinity of New York City is composed of 100 Ibs. of commercial No. 4 paving-cement, 20 Ibs. refined asphalt, and 3 Ibs. of residum oil. This commer- cial paving-cement is made from coal-tar. When coal is distilled for the purpose of making illuminating-gas, one of the important products of the distillation is a liquid called coal-tar. This is a very complex hydrocarbon, which when further distilled produces what is generally known as pitch. Its consistency and exact com- position depend upon the amount of distillation to which it has been subjected. It is known to the trade also as paving-cement and numbered according to its hardness. It is much like asphalt 198 STREET PAVEMENTS AND PAVING MATERIALS. in its general appearance, but more brittle. It can be readily dis- tinguished from it by its peculiar odor. It is susceptible to heat and cold,, cracking in winter and becoming soft in summer at a temperature which would not affect asphalt. For this reason it is necessary in using it on streets to flux it with a certain amount of asphalt. Granite blocks on a concrete base are not laid with close joints. The idea is not to fill the joints entirely with paving-cement, but leave them sufficiently open so that they can be filled with gravel and then the interstices in the gravel filled with a paving- cement which forms a perfectly tight joint and one which, if broken during the cold weather, will soften and become perfect again at a higher temperature. The joints should be left just wide enough to allow them to be filled with a gravel which will permit the pitch to flow easily through the interstices and thus make a solid joint. A joint | of an inch wide after the blocks are rammed is sufficient to accomplish this purpose. Gravel for such a joint should be screened so that it will all be retained in a screen having J-inch mesh, and will pass a screen of J-inch mesh. If the gravel be finer and allowed to grade down to coarse sand, it will not allow a free flowing of the cement, and the lower part of the joint will not be filled. The pavement should be laid practically in the same manner as described for the sand base except as to width of joints and the ramming, there being so small an amount of sand under the blocks that much ramming is not needed on a concrete base. In all block pavements special care should be taken to break the joints with a lap of at least 3 inches, and preferably in the centre of the block. Where the blocks run of uneven length, the inspector will have to watch pretty carefully to see that this is accomplished. After the blocks have been laid, the gravel, which has been heated to a temperature that will posi- tively insure its being perfectly dry, should be spread over the sur- face and into the joints in such an amount that when the blocks are rammed the joints shall be filled within 3 inches of the top. The paving-cement should be poured into the joints until they are full to the top of the gravel and until it ceases to run off. The joints should then be filled to the top with more gravel heated to a temperature of not less than 200 degrees, when the joints should be again poured with the paving-cement until they are entirely COBBLE AND STONE-BLOCK PAVEMENTS. 199 filled and flush with the surface of the pavement. This part of the work should closely follow that of the pavers, so that when the pavers stop work for the day, the rammers and cement-pourers will require but little time to complete the pavement that is laid. If the gravel, after the joints are filled, becomes wet, it will not properly receive the cement, as any appreciable amount of water always causes it to foam and not form a solid joint. When treated in this manner, a yard of pavement will require about 1^ cubic feet of gravel and 3 gallons of paving-cement for joint-filling. Fig. 12 represents a section of granite block pavement on a con- crete base. It" FIG. 12. Before proceeding with the construction of the base, the cross- section of the street must be determined. This is a question that has been discussed at considerable length by engineers and upon which there is quite a difference in opinion. The best form of the street for traffic alone would be a straight line from one gutter to another, but this would allow the water during any storm to spread out over the entire street, making it difficult for pedestrians to Across, and also, in case of any settlement of the pavement, holes would be more easily formed. The early pavements in this country had gutters in the centre, and all the water was therefore led to this portion of the street. By this arrangement the most valuable part of the street was prac- tically given up to drainage, and the water was delivered to the intersecting street at the centre, where it was difficult to take care of it. The remedy for this was to make the surface of the street convex instead of concave, and just how much convexity should be given is a question for discussion. The object of the crown in the street is twofold: first, to give sufficient slope to the pavement to carry the water quickly from the centre to the gutter; and second, to confine the water, in the case of storms, to as small a 200 STREET PAVEMENTS AND PAVING MATERIALS. portion of the street as possible, so as not to interfere with pedes- trian travel. When a street is first being paved, and nt> permanent improvements of any character have been constructed, the problem of the cross-section is comparatively simple. It only remains to adopt a standard depth of gutter and a standard crown, and noth- ing will interfere with carrying it out. When, however, the street is being repaved and has permanent sidewalks, so that the elevation of the old curbs can be changed but little if any, and one curb is a considerable elevation above the other, the problem is different. A pavement should be laid with its general ^surface as nearly uniform as possible, and with but little slope from one side to the other. When, however, the difference in the elevation of the curbs is great, by making different depths of gutter this trouble can be very materially helped. Two principles govern in determining the depths of gutters. First, they should not be made so deep as to present a high step- for pedestrians, nor so shallow as to present little obstruction to wheeled vehicles and to have little water capacity. Unless for some: special reason, the gutter should not be deeper than 9 nor less than 4 inches. By thus making the gutter on the high side of the street 9 inches deep, and on the low side 4 inches, the difference of 5 inches is overcome at once, so that with a difference of elevation not greater than 5 inches the crown of the pavement can be put in the centre and the two sides will be symmetrical. If, however,, there be a greater difference than 5 inches, the crown can generally be left in the centre, with an increased difference of 3 or 4 inches,, leaving the street with a greater slope on one side than the other. When the difference becomes so great that the upper side of the street is nearly flat, and the lower side correspondingly steep,, the difference can be overcome to a certain extent by changing the crown from the centre to the upper quarter of the street. By giv- ing the crown an arbitrary elevation of 2 or 3 inches, as may be necessary to insure some fall from the crown to the high gutter,, the least possible fall from the crown to the lower gutter will be obtained, and the result is a surface -that is a compound curve, with the lower three-quarters of one radius and the upper one-quarter of another, not necessarily tangent, but so near it that the difference: can never be discovered by the e} r e. COBBLE AND STONE-BLOCK PAVEMENTS. i^Ol When, however, street-car tracks are laid, or to be laid, on a street, the problem presents a different phase. While it is not necessary that both tracks should be at the same elevation, it is necessary that the two rails on the same track should be level; therefore it is not possible to fit a track to a curved surface. When there is a material difference between the two curbs, the track OH the lower side can be set at the maximum difference of 3 inches below the upper. Then by making the high gutter the maximum depth and the low gutter the minimum, the best possible result is obtained. Possibly, however, in doing this it may be neces- sary to run the water from the gutter to the centre rather than from the track to the gutter. While this is not desirable, it is not positively bad, and, under circumstances similar to the above, quite often must be done. If the longitudinal grade is considerable and the distance from the car-track to the gutter small, there is no par- ticular objection to making the pavement level or on a straight line from the track to the gutter. When such an arrangement is nec- essary, the result is often the draining of quite a considerable surface to the tracks where the water runs down to the first inter- section, and at that point a catch-basin should be provided between the tracks to take care of it. Crown. Very few engineers agree as to the exact amount of crown to be given to a street, and it is also varied according to the material. Some engineers vary the crown with the longitudinal grade, having a formula by which the crown can be calculated with the different grades. This, however, does not seem to be necessary. Any crown at all is a modification of the best cross-section of the street for traffic designed simply for the purpose of drainage. If then a light crown will drain the street to the gutter, the minimum amount can be used in almost every case, and there seems to be no necessity for running the amount above the minimum unless it is positively required, when it is remembered that the nearer flat a pavement is the more truly it will serve traffic, which is its true province. Assuming the roadway of the street to be 30 feet wdde, and adopting a crown of 4 inches, which does not inconvenience travel, a fall towards the gutter of the central J / 3 will be 4 / 9 of an inch, or 202 STREET PAVEMENTS AND PAVING MATERIALS. at the rate of 9 inches per 100 feet, which is sufficient for drainage. The fall of the second 1 / 3 towards the gutter is ! 1 / 3 inches, or at the rate of 27 inches per 100 feet, while that of the 1 / 3 adjacent to the curb is 2 2 / 9 inches, or at the rate of 44 inches per 100 feet. Table No. 59 gives the fall from the centre to the gutter of each third of the roadway, with different widths and of different crowns. TABLE No. 59. Fall Fall Fall to Width of Roadway. s_ Crown. towards Gutter in Central Uof Roadway. Rate per 100. towards Gutter in Second Kof Roadway. Rate per 100. Gutter in fc of Roadway adjacent to Curb. Rate per 100. 24 feet 3 inches * inch Scinches 1 inch 2 ft. 1 in. If inches 3 ft. 6 in. 30 ' 4 " i ;; 9 < 1* inches 2 3 ' 2f 3 ' 8 ' 30 ' 6 " 13* ' 2 " 3 4 ' 3| 5 ' 6 ' 3:3 ' 5 " f " 9 ' If " 2 4 ' 3 ' 3 ; 43 ' 6 " f " 8* ' 2 " 2 1 ' 3* 3 ' 6 ' GO ' 8 " 1 " 8f ' ' 2* " 2 3 ' 4f 3 ' 9 ' This table shows ver) r plainly that even on a level grade the water will drain readily from the centre to the gutters, and at the same time the roadway will be such as to be very favorable for travel. Under the heading of Thirty-foot Eoadways, figures are given for the 6-inch crown as well as 4-inch, showing how very materially the side slope increases with the crown, and this side slope, in slippery weather, is much more damaging to horses than a straight horizontal slope. These figures are recommended as the proper crown on all Level streets of improved pavements, except the 6-inch crown on a thirty- foot roadway. The curve of the pavement is in reality a parabola, but in the distance used is practically a circle. It can be best laid out on the crown by stretching a line from curb to curb, and meas- uring the ordinates down from the line at any desired interval according to the width of the street. The length of the ordinate can be determined by the simple formula in which D is equal to the distance from the centre to any point COBBLE AND STONE-BLOCK PAVEMENTS. 203 in feet, # equals | the width of roadway, C equals the crown in inches, and equals the ordinate in inches. When a street has been laid out in this way and the foundation rolled and prepared as heretofore described, the next work is to lay the concrete; and in order to insure the concrete being laid of the proper thickness, rows of stakes some 10 feet apart longitudi- nally should be set across the street at intervals of 6 or 8 feet, according to the width of the roadway, and driven to such depth that the tops will be on the same level as that required for the con- crete, the proper elevation for the stakes being determined by meas- uring down from the line in the same manner as for the subgrade. Concrete. According to Table No. 25 it is seen that it requires 2.79 barrels of cement and 21 cubic feet of sand to make 1 cubic yard of mortar. Ordinary broken stone of uniform size contains about 50 per cent voids, but no commercial broken stone is uniform, as it is more or less graduated in size, so that the voids are generally only 45 per cent. Assuming, then, that the broken stone contains 45 per cent voids, and adding 50 per cent of mortar so as to insure a complete filling of the voids, 1 cubic yard of mortar mixed with 2 cubic yards of stone will make 56.7 cubic feet or 2.1 cubic yards of concrete, and the amount of material necessary for 1 cubic yard of concrete is 1.33 barrels of cement, 25.7 cubic feet of stone, and 10 cubic feet of sand. In mixing the concrete, if it is done by hand, platforms will bo required for the mixing, some 10 feet square, and for an economical organization two boards should be worked together. The proper organization would be: one foreman and four mixers for each board, four wheelers, one rammer, and one man to carry cement and sup- ply water. Eight wheelbarrows will be required. Enough cement should be mixed in one batch to fill two wheelbarrows, which will be not far from one barrel, but as cement is generally delivered in sacks, it can be easily regulated. Assuming that the concrete is to be mixed in the proportion of one part cement, two parts sand, and four parts broken stone, the m en with the wheelbarrows should wheel four barrows of sand upon the first board, and the cement should be added. The barrowme'n 204 STREET PAVEMENTS AND PAVING MATERIALS. should immediately go to the stone-pile and wheel up four barrows of stone, leaving it standing by this board on the barrows, return- ing again for the other four barrows of stone, and by the time they have reached the b^ard the mixers should have the sand and cement thoroughly incorporated into the mortar, when the barrows of stone should be dumped on the board of mortar and then mixed as described in a previous chapter. The barrowmen should then proceed in the same manner to the other board, and by the time they have furnished it with sand and stone, the mixers on the first board should have the concrete mixed and placed on the street, when the operation should be repeated and continued throughout the day. When hand-work is done, the boards should be situated so near the concrete that the mixers can shovel direct from the board to the face of the concrete, when the rammers should grade and ram it thoroughly until the mortar flushes to the surface and no longer. For this work the expense for material would be: 1.33 bbls. of cement at 90 cts $1.20 .95 cubic yards broken stone at $1.25 1.19 .37 cubic yards sand at $1.00 37 Total per cubic yard for material $2.76 Or per square yard, 6 inches deep, 46 cents. FOB LABOR. 1 foreman $3.00 14 laborers at $1.25 17.50 Total $20.50 This organization should lay 240 square yards per day, which at the above figures would amount to 8.6 cents per square yard, ir.aking a total of 54.6 cents per square yard for hand-mixed con- crete. If, however, the machine described on page 129 and shown in Fig. 2 be used, the organization and results are very different. An engineer would be required to run the engine, and a pair of horses to draw the mixer along as the work progresses. Men are required fop- setting grade-pegs as before, shovelling material into the ma- chine and wheeling it to the work, and as it is dumped from the -wheelbarrows into piles it requires to be raked and graded by laborers for that purpose in addition to the rammers used for hand- COBBLE AND STONE-BLOCK PAVEMENTS. 205 work, so that a total of 30 laborers is required for the organization, making the complete outfit: 1 foreman $ 3.00 1 engineer 3.00 1 pair horses 3.50 Fuel and water t 2.00 30 laborers at $1.25.. 37.50 Total $49.00 This gang should lay per day 800 square yards of concrete 6 inches thick, at a cost of 6.1 cents per square yard. After the concrete is laid, if the weather be warm, it should be immediately covered with a cushion of sand, and with ordinary cement the pavement can be laid in from two to three days after- wards, in accordance with the method heretofore described. The particular things which an inspector should watch on a pavement with tar and gravel joints are that the joints are not filled too nearly full with the gravel, and also that the gravel is so ^nearly uniform in size that it will permit the paving-cement to flow freely through it. If the joints be filled pretty nearly to the top, and the gravel contains any appreciable amount of sand, the paving-cement, in- stead of running to the bottom of the joint, will flow into the gravel but a very short distance, and while seeming to be full, the joint contains in reality a very small amount of the cement. In order, too, that the cement should flow freely, it should be heated to a temperature of not less than 300 degrees when poured. It should l>e heated in kettles brought as nearly to the work as possible, so that it will not be cooled in being carried to the work, and that the process of pouring may be done as expeditiously as possible. For work of this character there will be required per square yard of pavement 3| gallons of paving-cement, 1J cubit feet of gravel, and 1J cubic feet of sand. The organization of the gang on a piece of work that was carried out recently was: 10 payers at $4 50 per day $45.00 5 rammers " 3.50 " " 17.50 6 chuckers " 1.50 " " 9.00 20 laborers " 1.25 " " 25.00 Total.. . $96.50 206 STREET PAVEMENTS AND PAVING MATERIALS. This gang laid on an average 650 yards per day on a street 44 feet wide, and it required 22% blocks, according to the New York specifications in Table No. 57, per square yard, so that the cost for material would be: 22 blocks at 5 cts. each $1.24 3 gallons paving-cement at 7 cts 24 1J cubic feet gravel at $1.95 per cubic yard 09f li cubic feet of sand at $1.00 per cubic yard 06 1 square yard of concrete 55 Labor as above 15 Total $2.34i For a granite pavement on sand the organization would be: 4 pavers at $4.50 per day $18.00 2 rammers " 3.50 " " 7.00 3 chuckers " 1.50 " " 4.50 3 laborers " 1.25 " " . 3.75 Total $33.25 This organization laid 280 square yards per day on a street 30 feet wide free from street-car tracks, at a cost of 12 cents per square yard for labor. On another street where there were street-car tracks the pavers averaged 63 yards per day instead of 70 as above. Assuming, then, the sand foundation to be of such depth as ta require 1 cubic yard for 5 square yards of pavement, and that 24 blocks will lay a square yard of pavement, the material would cost: 24 blocks at 5J cts $1.32 .20 cubic yards of sand at $1 20 Labor 12 Total on a sand base $1.64 In all estimates of cost of work, no special pains have been taken to get the exact cost of material, as that must vary very materially with each locality, but the figures used are approximately correct for New York City in 1899. The amount of material required, however, and the amount of work done, are in almost every case the result of actual observation. COBBLE AND STONE-BLOCK PAVEMENTS. 207 Medina Sandstone. The city of Cleveland, Ohio, has probably more, if not better, pavements of Medina sandstone than any other city in the country. It is the only stone pavement in use there at the present time, and gives almost perfect satisfaction. It is said by the City Engineer to have a life of 25 years, which is all that can be asked of granite. The pavement is laid on concrete in a very careful and thorough manner, the blocks being made so as to be smooth and even. After describing the dimension and form of blocks the Cleve- land specifications say: " The paving-blocks as here referred to shall be understood to mean blocks of Medina sandstone, prepared in the proper manner for dressed-block paving, by nicking and breaking the stones from larger blocks as is done in the quarries where such blocks are usually prepared, and not made by redressing and selecting from common stone paving material. The stone to be flat and even at bottom, which shall be parallel to the top- sur- face, with both top and bottom of stone at right angles at least at one end of the stone, so as to set squarely and firmly in space with- out the use of a paving-hammer." While the dimensions of the stone in thickness range from 3J to 5 inches, the blocks are divided into three classes, the 1st class including blocks from 3J to 3J inches, and the 2d class blocks from 3} to and including 4J inches. Class No. 3 embraces blocks from 4 to and including 5 inches. Blocks in class No. 1 are to be marked with red paint, blocks in class No. 2 with blue paint, and those in class No. 3 with black paint, so that when the blocks are delivered on the street each class can be easily recognized and laid by themselves in the pavement. Instead of being set with open joints as is the case with granite on concrete, with tar and gravel joints, these stones in Cleveland are set tight together with- out any gravel or sand being placed on the top. Upon the com- pletion of every course, if necessary, the blocks are driven together and the course straightened by the use of a heavy sledge and wood block placed against the stone so as to insure close work and a straight course across the street. The blocks are rammed three separate times with a wooden rammer weighing not less than 80 Ibs., and the surface brought up 90S STREET PAVEMENTS AND PAVING MATERIALS. to the proper grade by the use of a long straight-edge. The pavement is also rolled when necessary to bring it to a true sur- face. After ramming and rolling, or even during the process, the pavement is sprinkled or washed with water so as to free the joints to their full depth from sand and thoroughly bed them in the sand- cushion. The spaces between the blocks are then filled \vith a composition consisting of asphaltic cement, Pordand-cement filler, Murphy grout, or such other filling as may be. ordered. The asphalt filler consists of 10 per cent of refined Trinidad asphalt, mixed with coal-tar cement, distilled at a temperature of not less than 600 degrees, and the whole mixed with such proportion of still wax as will prevent it from being too soft in warm weather or too brittle in cold. It is used at a temperature of not less than 300 degrees. Portland-cement filler is made of equal parts of the best Port- land cement and clean, sharp Lake sand, mixed with a sufficient amount of water to permit it to flow freely into the joints. The grouting is done by two applications, the lower one-third of the joint being filled with a somewhat thinner grout than for the re- maining two-thirds. The upper space is filled with a thicker grout, and refilled if necessary, until the joints all remain full. This pavement is generally allowed to stand one week before being used. The entire surface of the pavement when completed is cov- ered with a -J-inch coating of clean sand. The cost of this pave- ment in Cleveland is about $3.25 per square yard. The Medina sandstone pavements of Rochester, N". Y., are laid in about the same way as those of Cleveland and under very nearly the same general specifications, except that they do not call for the blocks to be divided into classes according to width, and the blocks are laid with J-inch joints instead of being laid stone to stone, and these joints are filled with gravel into which, is poured hot paving- cement until the joints are filled. Rochester pavements of this character have cost on the average $2.54 per square yard. Cross-walks. At each intersection in stone pavements, cross-walks must be laid to accommodate pedestrian travel. It has been customary in New York to lay cross-walks of Hudson River bluestone in all cob- f" COBBLE AND STONE-BLOCK PAVEMENTS. 209 ble and Belgian pavements, and granite cross-walks where the streets are paved with granite. In the West, where sandstone is used for paving, the cross-walks are made of the same material. 'The bluestone cross-walks in New York consist of two courses of Hudson River bluestone 2 feet wide and from 6 to 8 inches thick, separated by one course of granite or Belgian blocks, their length being not less than -i nor more than 6 feet. The granite cross- walks as at present used in New York are not less than 4 nor more than 6 feet in length, 1J feet wide, and not less than 6 nor more than 8 inches thick throughout. Cross-walks were originally laid with the end joints parallel to the line of the street, as shown at A, Fig. 9. This gives a joint 18 inches or 2 feet in length, accord- ing to the kind of stone, parallel to the traffic. In a few years these joints always wear badly, so that a rut is formed, especially, as is often the case, if the joint was not squared to its full depth. To obviate this the joints were cut diagonally with a slope of about 6 inches in the width of the stone, so that no traffic would be par- allel to the joint. At first they were all as shown at B in Fig. 10, but, as in the case of the blocks laid on the intersection, this was objectionable, as it made the joints parallel to the traffic turning the corner. The proper way is to lay them as shown at C and D in Fig. 11, with a keystone in the centre, so that the joint is al- ways opposed to the traffic. It is customary in most cities to construct sewers with catch- basins for storm-wat: r at the curb-corners of the intersections. This makes it necessary to carry the water over the cross-walk, and if there is an appreciable step from the pavement to the curb, it is better to stop the cross-walk within about 6 inches of the curb and depress the blocks in the intervening space so that the water can run down the gutter at the end of the crossing, unless the fall be too great. A much better arrangement, however, can be had if, instead of one basin at the corner, two smaller basins could be put oack of the cross-walk, as shown at E and F, Fig. 11. This would allow the intersection to be paved almost to a level with the curb, and so that the street would present practically no obstruction to pedestrian travel. When it is considered how much money is ex- pended in the paving of a street in order to make it convenient for the public, it would seem that the little extra expense neces- 210 STREET PAVEMENTS AND PAVING MATERIALS. sary for this improvement would be justified when the results obtained are considered. Granite Pavement in Vienna. Cubes are mostly employed measuring 7J inches. On streets having a grade of 1 in 50 the blocks are laid at an angle of 45 to the line of the street. On grades up to 1 in 40 they are laid at right angles to the street line. If the grade is more than 1 in 40, cubes measuring about 5 inches are used, also set at right angles to the street. But if the grade is more than 1 in 33, the smaller blocks are grooved to provide a foothold for horses. The blocks are laid on a foundation of 6 inches of gravel, upon which is a sand-cushion of 1J inches. Generally the joints are filled with sand, but on heavy traffic arid built-up streets an asphalt filler is used for the joints. This asphalt filler increases the cost about 30 cents per square yard. The average price of the pavement is from $2.60 to $3 per yard. CHAPTER VIII. ASPHALT PAVEMENTS. THE early history of asphalt pavements in Europe was pretty generally given in the chapter on the history of pavements. In the United States, previous to 1866, sidewalks and cross- walks had been laid in Lock Haven, Pa., of coal-tar mixed with gravel, broken stone, coal-ashes, etc., under a special patent issued to a Mr. Scrimshaw, from whom the name of the pavement was de- rived. In 1867 a small portion of the roadway of one of the drives in Prospect Park, Brooklyn, was paved with the same material. So successful was that experiment that the following year a similar pavement was laid on Diamond Street, now Lenox Road, Flatbush, L. I. The foundation consisted of a course of 2-inch broken stone 5 inches thick, mixed with sand, coal-ashes, and tar. The wearing surface was similar to the foundation, except that no stone was used greater than 1 inch in any dimension. This made a pavement that lasted for more than twenty years, and when the street was repaved in 1896 some of it was found intact and served as a foundation for the new asphalt pavement. This street was probably the first one regularly paved with a bituminous material in the United States. Such pavements gave good satisfaction' as long as a good quality of tar could be obtained, but on account of the large amount of volatile oils contained in the tar it was necessary to close a street to travel for about thirty days after its completion, and with some tars fifty and even sixty days. This was objectionable, and the difficulty was obviated in 1871 by a combination of roofing-pitch and creosote, or dead oil, which combination was patented in March of that year by a Mr. B. Abbott. With this material a better pave- ment was laid, and one that could be used the following day. This was known as the Abbott patent. Streets were paved under this 211 212 STREET PAVEMENTS AND PAVING MATERIALS. patent in Brooklyn and Washington which were in good condition* for fourteen or fifteen years. Some of the old Brooklyn pavements, are found even now when some of the older asphalt pavements are "being relaid. As coal-tar pavements failed, asphalt was laid over the tar as a foundation In 1878 Delaware Avenue, Buffalo, was paved with Trinidad asphalt, fluxed with still wax, or wax tailings. This still wax was a waxy oil, dark green in color, being the last product of the distilla- tion of petroleum before coke is reached, and was free from all oils that would be driven off at a temperature of less than 600 degrees. According to the report of the Board of Public Works in Buffalo,, this street cost for repairs a total amount of $515 until it was re- laid in 1892. In the Delaware Avenue pavement sand was not used for a. matrix, but instead a hard broken stone, screened to exclude all above \ inch in size and to permit smaller stones even down to- dust. Before long, however, chemical research had discovered other and more valuable uses for the wax, and it became too ex- pensive for street use, and recourse was had to residuum oil. In the mean time coal-tar streets of different mixtures had been, laid in Washington soon after 1870. They were laid under a good many different patents, of as many different mixtures, receiving their name generally from that of the patentee. The base was gen- erally made up of broken stone 4 to 6 inches thick, cemented to- gether with coal-tar and covered with a binder coat about 1 inch thick composed of pebbles, fine broken stone, and coal-tar. The difference in the pavement was in the wearing surface, which varied according to the patents, but coal-tar was the cementing material. Some of these failed very quickly. Of 187,271 square yards of the Evans pavement laid in 1872-3 at a cost of $3.20 per yard, over- 150,000 yards were resurfaced within two years. Others stood much better, some not being resurfaced for six or seven years, and quite a number lasted even ten and fifteen years. In the report of the Engineering Department of the District of Columbia, in 1887, Captain Griffin says: " Tne mean average expense for maintenance of 745,305 square yards is 5.5 cents per square yard for fifteen years. That a durable coal-tar pavement can be laid is proven by the fact that the vul- _ ' ASPHALT PAVEMENTS. 213 canite pavements have only averaged 2.9 cents per square yard per annum." So expensive were these coal-tar pavements to maintain that Lieutenant Hoxie, in 1887, estimated that their cost would be 20 cents per yard per annum, so that when the first Board of Commis- sioners appointed under Act of June 11, 1878, came into office, they expressed themselves as follows on this subject: " In determining the class of pavements to be hereafter laid > the commissioners maintain that each class of pavement must prove its quality under test of actual traffic before being exten- sively laid upon the streets of this city. " While some of the later and better class of coal-tar pavements show good service and give a fair promise of reasonable dura- bility, yet the general condition of this class of pavements in the city is such as to lead to their condemnation as faulty in principle and deficient in vitality. " The use of bituminous bases has also given rise to many per- plexing problems in the grades of streets upon which they have been laid, and as, when properly laid, their cost is as great as, if not greater than, hydraulic concrete, they have been definitely abandoned." In 1886-87 Congress passed a law which provided that no con- tract should be made for making or repairing concrete or asphalt pavements at a higher price than $2 per square yard, of a quality equal to the best laid in the District prior to July 1, 1886, and with the same depth of base. The lowest bid for asphalt pavements re- ceived immediately after the passage of this act was $2.25, which could not be accepted, and the city was obliged to return to coal- tar pavements and those of asphalt block. The specifications for these coal-tar pavements provided that the base and binder should be 4 inches thick and laid as follows: " The base will be composed of clean broken stone that will pass through a 3-inch screen, well rammed and rolled with a steam- roller, to a depth of 4 inches, and thoroughly coated with hot pav- ing-cement composed of the best No. 4 coal-tar distillate, in the proportion of about 1 gallon to the square yard of pavement. The second binder course will be composed of clean broken stone thor- oughly, screened, not exceeding 1J inches in dimension, and No. 4 214: STREET PAVEMENTS AND PAVING MATERIALS. coal-tar distillate. The stone will be heated by passing through revolving heaters and thoroughly mixed by machinery with the distillate in the proportion of one gallon of distillate to one cubic foot of stone. The binder will be hauled to the work, spread upon the base course at least two inches thick, and immediately rammed and rolled with hand and heavy steam rollers while in a hot and plastic condition. The wearing surface will be 1J inches thick when compacted, made of paving-cement composed of 25 per cent asphalt and 75 per cent coal-tar distillate, mixed with other mate- rials as follows: " Clean, sharp sand will be mixed with pulverized stone, of such dimensions as to pass through a J-inch screen, in the proportion of 2 to 1. "To 21 cubic feet of the above-named mixture will be added 1 peck of dry hydraulic cement, 1 quart of flour of sulphur, and 2 quarts of air-slacked lime. To this mixture will be added 320 Ibs. of paving-cement to compose the wearing surface." This material was laid on the street in practically the same man- lier -as asphalt pavement is at the present time. The coal-tar pavements laid in 1887 cost 4.65 cents per yard per year for maintenance for ten years, and those laid in 1888 cost 5.96 cents per yard per year for a period of nine years. At the end of ten years it was found necessary to relay some of them and substitute standard asphalt, and future repairs will be made in the same manner. From a table published in the report of the Engineering De- partment of the District of Columbia, in the fiscal years 1886-87, it is 'shown that the annual expenditure for the maintenance of coal-tar pavements for fifteen years ending July 1, 1886, had been 7.2 cents per square yard. These pavements being laid on a bituminous base become prac- tically a part of the base, and in repaving them it is necessary to take up the entire pavement; while if they had been laid on a !iydraulic-cement concrete base, it would only have been necessary to have renewed the wearing surface. The fact, that these coal-tar pavements did not give complete satisfaction, and were expensive to maintain, led people interested in the subject to make experiments with other material. ASPHALT PAVEMENTS: 215 Mr. E. J. de Smedt, who had taken out several patents and had made many experiments, laid a bituminous pavement in Newark, N. J., in front of the City Hall in 1870, with Trinidad asphalt as the cementing material. This was without doubt the first asphalt pavement laid in the United States. It was followed by another similar one in New York City near the Battery in 1871, and soon -after by another in Philadelphia, and in a few years still more in New York City. These pavements gave such satisfactory results that they attracted the attention of the authorities in Washington, and a special commission was appointed by Congress to investigate -and report as to the advisability of adopting them in Washington. As a result of the commissioners' report Pennsylvania Avenue from First Street to Sixth Street was paved with rock asphalt by the Neuchatel Asphalt Co. in 1876-77, and from Sixth Street to Fifteenth Street at the same time with Trinidad asphalt. These pavements gave good satisfaction, except that the rock asphalt was so slippery that when the street was resurfaced in 1890 Trinidad asphalt was laid over the entire area. The success of asphalt in Washington may be considered as settling to a great extent the ex- perimental nature of the pavement, and from that time on its suc- cess has been assured and its use has continually increased. In many respects asphalt makes a perfect pavement. It will sustain travel without being damaged, and in fact is benefited by quite severe traffic. It is smooth, pleasant to drive over, almost noiseless for carriages, and can be kept absolutely clean. It is im- pervious to water or moisture and, consequently, as a sanitary pave- ment is without a rival. It is considered by some to be expensive, and it is, as compared with some of the coarser rock pavements, but very few who have once used it are willing to give it up, or doubt that they have received the value of their money. Many asphalt pavements have failed, and have required con- siderable resurfacing sooner than they should; but when it is re- membered how new the industry is, how rapidly it has been developed, that there was no precedent for the mixtures, and that the principal mode of treatment, as well as the percentages of materials to be used, had to be determined by actual practice and experiment, the wonder is that not so many but that so few pave- ments have failed. 216 STREET PAVEMENTS AND PAVING MATERIALS. One of the objections made to asphalt is on account of its- slipperiness and the liability of horses falling when they come off from a rough stone surface to the smooth asphalt. There is some reason in this, but as asphalt pavements increase in quantity,, horses will become more accustomed to them and learn to adapt themselves to the smooth surface. Asphalt itself, contrary to the general belief, is not slippery. It is smooth, and any soft substance upon a smooth surface makes it slippery. Asphalt pavements should be kept clean and then there will be less trouble on account of horses slipping. Asphalt is much less slippery when dry than when slightly damp or moist. It is well known to truckmen that horses travel on a smooth pavement much more easily during a heavy rain than in a drizzle. A certain amount of street detritus, must collect on any smooth pavement, and when rain falls in a quantity sufficient to wet it only rather than wash it clean, it must be slippery to a certain extent. The question as to what is the steepest grade on which it is safe to lay asphalt has received a great deal of study. When the material was first introduced grades of 4 per cent were considered prohibitory, and very little was laid on those exceeding 3 per cent,, but practice soon showed that this was too conservative a view, and as a result pavements have been laid successfully and quite fre- quently on grades as high as 7 and 8 per cent, and in Scranton, Pa.,, there is a portion of one street that has a grade of 12 J per cent. It was said to have been placed on this particular block for the sake of preventing traffic, but, strange to say, it has not done so, and the City Engineer says that after several years' use no great trouble has- been experienced with it. Fig. 13 represents a profile of a portion of Bates Street, Pitts- burgh, Pa. This shows that the elevation of the grade increased from 188.21 at the property line to 209.63 at a point 200 feet dis- tant, making an average rise of 10.7 per cent. Instead, however, of making a uniform grade, these points were connected by a vertical curve, making in one section a grade of 17.1 per cent, and in the first 80 feet the minimum rate is 12.4 per cent. This street is paved with sheet asphalt, and without doubt has the steepest grade of any street in the world paved with that material. As a rule, however, asphalt should not be laid on a street that ASPHALT PAVEMENTS. 217 will be subjected to any material amount of traffic on grades ex- ceeding 6 per cent, for there must be certain times of the year when they can be used but little and with considerable difficulty. On resi- dence streets, however, where traffic is light, the people are willing in many cases to put up with the inconvenience of the slippery streets on a comparatively few days of the year for the sake of hav- 209.63 2096 208.70 208.13 207.49 206.74 206.02 205.19 204.28 203.31 202.28 >OQ.OQ 198.76 / 197.45 / 136.08 19464 I93.I4 191.56 / I89.92/ T^Y PROPERTY UNB 187.79 BOUQUET ST. CURB LINE FIG. 13. ing smooth, clean, noiseless pavements for the remainder of the time. In New York City, where a street has been paved on a 6 per cent grade with asphalt on the sides and granite in the centre, as a rule the traffic seeks the smooth asphalt with its ease of traction, rather than take the granite. Asphalt pavements are now in use upon grades in different cities as shown on page 218. 218 STREET PAVEMENTS AND PAVING MATERIALS. Per cent. New York City 6 Omaha, Nebraska 7 to 8 Brooklyn, N. Y 4y 2 Syracuse, N. Y 7 Scranton, Pa ' 12y 2 The crown of pavements has been thoroughly discussed in the chapter on Stone Pavements, and the remarks made there will apply with equal force to asphalt. Table No. 60 shows the method adopted by the Department of Highways in the Borough of Brooklyn, New York City, for laying TABLE No. 60. CKOSS-SECTIONS TO BE USED IN LAYING ASPHALT PAVEMENTS ; SHOWING MEASUREMENTS FROM A LINE DRAWN FROM CURB TO CURB TO THE FINISHED PAVEMENT. Measurements to Finished Surface. Curb. % K from, from Centre. M from. % from. Curb 4" GUTTERS. Centre 2" above line (6" crown) " 1" " " (5" " ) even with " (4" " ) 4" V 9tf f ' f 154" ab. V^" above J 2" above 1" above 1M" ab. j-^" above f 4" 4" 4" 4" X 5" GUTTERS. Centre 1J^ above line (6^' crown) f" below " (4" " ) 4 // 1 WH 1" above 'n I" ab. H" above 34" above H7 ^' 2^" 5" 5" 6" 4" x 6" GUTTERS. Centre 1" above line (6" crown) " even with" (5" ) " 1" below " (4" ) 4" 4" 4" \" $?' W above r \" above 1" 1" w 2^4" 3" 3V^" 6" 6" 6" 4" x 7" GUTTERS. Centre \y above line (6" crown) || W f ' f below || (5JJ || ) 4" 4" 4" s J4" above %" W above l^ /: ' %" above! 3^" l^ y/ f" 2^1" IS" 7" 4" X 8" GUTTERS. Centre even with line (6" crown) " 1" below " (5" " ) y, , fa ) 4" 4" 4" w w l x/ 1%" 1" 2" 1^4" a^" 3^ 4" ^" 8" 8" H" 4" X 9" GUTTERS. Centre U" below line (6" crown) " 1V$" " " (5" " ) " 2!4" " " (4" " ) 4" 4" 4" jr 2H" f " 1&" 2^" 2" 3" S" e"" 9" 9" 9" 5" GUTTERS. Centre 1" above line (6" crown) " even with " (5" " ) 1" below " (4" " ) 5" 1 1^" 5" 2^" 5" |2%" J4" above ^ 1" above 1" H x ' above ]^' W 2^ 7/ 294" 5" 5" 5" 6" GUTTERS. Centre even with line (6" crown) " 1" below " (5" " ) " 2" (4" " ) 6" 6" 6" W *W 3%" i 1" 2" i 2%" 3>/2" 3%" 6 X/ 6" 6" ASPHALT PAVEMENTS. 219 out the cross-section of asphalt pavements with different depths of gutter, the surfaces being obtained in the same manner as with stone pavement, by measuring down at stated intervals from a line stretched from curb to curb. Character of Asphalt. To make a first-class pavement, asphalt should be of a good character, properly mixed with the right materials, and well laid upon a good foundation. Whether untried asphalt will or will not make a good pavement can only be settled by actual use. A chemist can analyze it, tell what are its component parts, give its physical properties, as well as his idea as to what it ought to do, but cannot tell positively how it will act in a pavement. The asphalt on Eighth Avenue, New York City, laid in 1890, probably has received more notice than that laid on any other street in this country. Stephen- son Towle, at that time Consulting Engineer of New York, in speaking of this pavement in his report to the Commissioner of Public Works in January, 1895, said: " This asphalt was submitted to and approved by experts and chemists before the contract was entered into. Soon after the pave- ment was laid, and before its completion [it has never been ac- cepted], it showed unmistakable evidences of disintegration. This failure was exceptional, and the experts and chemists who had ap- proved of the asphalt could not account for it. My own belief was that the asphalt was inferior or lacking in some essential property unknown to chemists." While all asphalt contains bitumen, all bitumen will not make a good pavement, no matter with what it is fluxed. Certain varie- ties of asphalt will be brittle and not possess the cementitious properties necessary to hold the sand together. An asphalt pave- ment is really an asphaltic concrete in which particles of sand are held together by the cementing properties of the asphalt, and if for any reason the asphalt loses the cementing properties, the pavement must disintegrate and fail. Some asphalts, however, while not suitable for pavements in themselves, can, by being mixed with proper quantities of other bitumens by people who understand the nature of the material, be made into a valuable cementing' sub- 220 STREET PAVEMENTS AND PAVING MATERIALS. stance. A poor asphalt treated by an expert is liable to make a bet- ter pavement than good material handled by poor and inexperienced workmen. A new asphalt should be laid two or three years at least before it is safe to pass an opinion upon it as to its durability. If laid, as it generally is, in the summer, the winter season subjects the material to a severe test. The cold weather causes it to con- tract, and if laid too hard, it is apt to crack and, if the cold con- tinues, crumble to a certain extent. In a previous chapter reference has been made as to the proper method for the chemist to examine new asphalts. Asphaltic Cement. Very few asphalts now on the market, and probably but one, are fit to be used in pavements after they are refined. Used as they come from the refinery, the resulting pavements would soon disin- tegrate. Consequently they must be mixed with certain fluxing materials which will dissolve the asphaltine and cause the whole mass to form a soft, tough cementing material. This is called asphaltic cement. The early asphalt pavements and the greater part of those in use at the present time were laid with asphaltic cement formed of refined asphalt and petroleum residuum. In later times, since the discovery of asphalt in California, and bitumen in a softer state, such as maltha, and in even a still lighter form, quite a considerable amount of the refined product has been fluxed with maltha and asphaltic oils. Considerable controversy has arisen as to the relative values of these different fluxes. Mr. A. W. Dow, Inspector of Asphalts and Cements in the District of Columbia, and Mr. Clifford Eichardson, chemist for the Barber Asphalt Co., have probably investigated this particular subject more thoroughly than any one else, and have arrived at almost diametrically opposite re- sults. In a paper prepared by Mr. Eichardson and published in Municipal Engineering in 1897, after detailing some experiments he says: " The most successful proof of the solubility of the bitumen and asphalt in residuum oil was reached by preparing a pure bitumen of both Trinidad and Bermudez asphalts. This was done by dis- solving each in chloroform and removing everything insoluble by ASPHALT PAVEMENTS. 2*21 subsidation, filtering, and the use of the centrifugal. With this pure bitumen the same percentage of the pure residuum, made as nad been previously described, was mixed as thereafter used in practice, in the proportion of the ordinary asphalt cement. There being no impurities present, it was possible to determine by ex- amination of the resulting mixture under the microscope with a very high-power objective, 1 / 12 homogeneous immersion, whether .solution had taken place or not. In each case a perfectly homo- geneous substance was seen and entire solution had taken place. Whether separation would take place on a reduction of the tempera- ture, or with age, was then determined. When the residuum con- tained much paraffine scale there was a very slight evidence of the presence of paraffine at a temperature below freezing, but ordin- arily nothing separated. After three years' preservation, at ordinary temperatures, the pure asphalt cement was as homogeneous and uniform as when first made. The solution still remained com- plete/' Summing up, among his conclusions he says: " Residuum oil is perfectly miscible with and a satisfactory solvent for asphalt. It does not separate from asphalt cements when they are properly made. It remains of very soft consistency, and of value as a fluxing agent, even after heating for many hours at high temperatures." In speaking of maltha and asphaltic oils he says: " They have been proved to be most unsuited and unsafe for use as fluxing agents, because they are gradually changed in con- sistency in heating at temperatures at which asphalt cement is usually held when melted. They are finally turned into glassy glance pitch, having no fluxing value. They are composed of un- stable and easily volatile hydrocarbons. They are neither fluxes nor asphalts for forming cement which can be maintained of any constant consistency, and it generally goes into the work upon which it is employed either too hard or too soft." On the other hand, Mr. Dow, in speaking of some experiments which he had made with Trinidad asphalt and residuum oil, says: " From the above it is very evident that there is a marked dif- ference in the bitumen that filtered through and that left -in the iilter. In taking this result and its proper microscopic examina- 222 STREET PAVEMENTS AND PAVING MATERIALS. tion of the filtrate, we are led to the conclusion that a bitumen Trinidad asphalt is not completely soluble; that it is more soluble in hot residuum than in cold; and that the extra amount that enters into solution on heating separates out on cooling." After making a number of experiments with mixtures corresponding to those used on the street and giving their results in a table, he- further says: " On examining these results, we find in the case of the two cements made with petroleum residuum that several per cent of the asphalt bitumen has been rendered insoluble by the addition of the residuum,, and that this insoluble bitumen is held in sus- pension and will settle out as so much inert material. It is im- possible to even approximate the amount of insoluble bitumen, but it must be quite some more than has settled in these experi- ments. It is only reasonable to believe that proportionately less of it would settle than of the mineral ingredients, and there are still quite some of these held in suspension. Combining with all these what we learn in the previous experiment [that more of the asphalt bitumen was soluble in hot residuum than in cold], the- quantity of this residuum insoluble in the residuum at normal temperature must be considerable. In the case of a cement of asphaltic oil we find that even though there was quite as much mineral matter subsidized, yet the bitumen is a uniform composi- tion throughout the tube, showing a complete solution. Judging- from the physical properties of petroleum residuum and its chemi- cal relation to asphaltic bitumen, it is not a desirable flux, but it should not be judged too strongly in the absence of physical tests carried on with the asphalt cement made with it." When two such diametrically opposite opinions are given by experts who are honestly seeking truth, it only remains for the- engineer to take what he is satisfied will give good results, and leave fine questions of distinction to be decided by chemists. What is positively known is that good pavements have been made with both petroleum residuum and maltha and asphalt oils as fluxes. It seems a radical statement to say that a flux that has produced such pavements as the asphalt pavements of the last fifteen years is not the proper material to be used. Whether it is the best or not is another question. Until that is definitely determined, the advo- ASPHALT PAVEMENTS. 223 cates of both will continue the use of the one that is most con- venient to them. When petroleum residuum is used as a flux it is sometimes first mixed with a so-called asphalt, often termed " Pittsburg flux." The Washington reports say that a pavement was improved by this process, and that the asphaltic cement was made by mixing 100 Ibs. of refined asphalt, 14 Ibs. residuum, and 11 Ibs. Pittsburg flux. Pittsburg flux is manufactured by heating petroleum residuum with sulphur, the sulphur combining with portions of the hydrogen of the petroleum and escaping as hydrogen sulphide gas, leaving the product as a residue. The usual amount of residuum used to flux Trinidad asphalt is about 18 Ibs. of oil to 100 Ibs. of refined asphalt. When maltha and asphaltic oils are used, the amount must be determined both by the character of the flux and also of the re- fined asphalt. Whatever the character of the crude and refined asphalt, it is the asphaltic cement upon which the success of the pavement de- pends. The asphaltic cement should be tough and elastic; should be adhesive so as to hold the particles of sand together, and co- hesive so as not to disintegrate. It should be capable of resisting changes of temperature of over 30 below zero and 140 above, as. it will in many instances be subjected to these temperatures in pave- ments. Observations taken in Washington when the temperature of the air was 104, about 2 feet above the pavement, showed the asphalt itself to be at a temperature of 140, while the tempera- ture of macadam at the same time was 118. In St. Paul, Minn.,. and Omaha, Neb., pavements in the winter will be subjected to temperatures of 30 below zero, although not very often. It would be quite safe to predict that an asphaltic cement that would com- ply with the conditions as given above would make a good pave- ment. In order to establish some standard for asphaltic cement, in 1888 Prof. Bowen, who was then chemist for the Barber Asphalt Paving Co., devised an apparatus for determining the softness, or viscosity (as chemists prefer to call it), of asphaltic cements. The object of this machine, and the principle on which the standard is based, is to determine how far a needle will penetrate the asphaltic cement at a standard temperature in a given time. The STREET PAVEMENTS AND PAVING MATERIALS. needle is weighted with a 100-gram weight and allowed to pene- trate the cement for one second. The needle is inserted in the end of a weighted lever. This lever is suspended by a thread from a, spindle around which it is wrapped. At one end of the spindle a pointer is fastened which indicates on a dial the distance, up or down, moved by the lever-arm to which the needle is attached. On the spindle there is a small drum,, around which the thread is wound supporting the weight, which acts as a partial counter- balance to the weight of the lever. This counterweight keeps the lever-thread tight, and when the lever-arm is raised it returns the pointer to the dial. The viscosity of the sample is determined by placing one end of the needle, which is then lowered upon its point, so as to just touch the surface of the asphalt. The position of the pointer of the dial is noted, the clamp released, and the needle allowed to penetrate into the sample for a fixed time. At the end of the time the clamp is closed and the distance the needle has penetrated can be read from the dial, which for convenience is divided into 360 equal parts, and the number of these parts which the needle has moved represents the penetration of the cement. This is an arbitrary standard, but it has been used successfully in some twenty-five or thirty laboratories or paving-yards. Before testing the samples, they should be kept at a standard temperature for a sufficient time to allow them to attain the de- sired temperature. The temperature which has been generally taken as the standard is 77 Fahr., and the simplest way to main- tain the sample at the proper temperature is by immersing it in Crater which is .kept at that temperature. Mr. Dow has adopted a somewhat different method of testing the viscosity by a machine that is somewhat complicated. His standard is the distance expressed in hundredths of a centimeter that a No. 2 needle will sink or penetrate into the asphalt paving- cement in 5 seconds when weighted with 100 grams, the cement and apparatus being at a temperature of 25 C. This makes an absolute and positive standard, but requires a delicate apparatus for the measurement. Under the Bowen standard the penetration of the asphaltic cement used in Washington by the Barber Co. in 1897 was 85, and by the Cranford Paving Co. 77; in 1898 by the Barber Paving Co. 91, and by the Cranford Paving Co. 83. In 1889, when ASPHALT PAVEMENTS. 225 Mr. Dow used the standard just described, the penetration of the paving-cement by the Eastern Bermudez Paving Co. was 45, and by the Cranford Co. 36, showing that in absolute figures the latter standard gives a less result than the former, but it must be remem- bered that the Bowen standard was wholly arbitrary, while that of Mr. Dow is absolute. When it is remembered that only about 10 per cent of the so- called asphalt pavement is made up of bitumen, it can be readily understood that it is necessary to select the best possible material for the remainder. Whatever this material may be, it must sustain the traffic to which the pavement is subjected. Stone in some form has been settled upon as the best material, but there has been more or less controversy always as to the size of the particles, and also as to how they should be graded. A hard material is abso- lutely necessary, and the particles must not be too large, else under the action of the horses' shoes the stone will pick up and leave -appreciable voids in the pavement which will cause it to crumble and wear away. As has been said before, quite large stones have been used, but the experience of the last twenty years has demon- strated very satisfactorily that a, hard silicious sand is the best material than can be obtained. In a paper read before the Ameri- can Society of Municipal Improvements, in 1898, Mr. Dow went very carefully into the character and size of sands that should be used. He first demonstrated that asphalt cements are liquid, and basing his argument upon the fact that fine beach-sand, when wet with water, is almost solid, while the coarser sand is soft. He goes on to say: " Looking at asphalt cement as liquid, we should expect to find analogous results when paving mixtures are made with these two sands, using with each the same asphalt cement; that the mixture made with the finer sand would be harder than that made with the coarser (this is what we find in practice), while by using a much softer asphalt cement with the finer sand and with the coarser equally hard mixtures are produced. The cause of this is ex- plained by the fact that the voids of the finer sand are much smaller in size, which means that the sand-grains are closer to- gether. It is a well-known fact that the smaller the space betwepri two solid bodies that are held together by the attraction of a liquid 226 STREET PAVEMENTS AND PAVING MATERIALS. between them, the greater the adhesion. There are two grades of sand that have small voids; one is composed of very fine grains,, and the other is a sand with the grains so graded from coarse to fine that all of the large voids are filled with smaller grains and their voids in turn filled with still finer. The latter is the most desirable sand, for several reasons. Among them are: It is very easily handled in the manufacture of the pavement, and it re- quires less asphalt cement, not alone because the per cent of fine is less, but the total surface area of the sand-grains is smaller." It will be noticed in this conclusion of Mr. Dow that he argues in practically the same way as one might in relation to cement concrete, and really the principle is the same. The wearing sur- face of the asphalt pavement is a concrete in which the bituminous substance is the cementing matter rather than the hydraulic cement. Mr. Dow further goes on to illustrate the differences in result when different sizes of sand are used by referring to the pavement in Washington laid in 1894, which he said marked as much, if not more than, those laid in 1897, and some of the former cracked in cold weather. The asphalt cement, however, with which the 1897 pavement is laid was found to be 20 harder than that used in 1894. Consequently he inferred that the difference must be due to the sand. Upon a trial, the sand was found to be graded as follows: TABLE No. 61. 1SP4 1897. Retained on 20 mesh per linear inch. . 4.5 2.5 40 " " " " .. 40.0 21.0 60 " " " " .. 32.0 35.0 80 " " " " .. 9.5 8.5 100 " " " " .. 6.0 10.0 Passing 100 " " " " . . 8.0 24.0 He also refers to the well-known fact that the European rock pavements, the durability of which, without doubt, is greater than that of the American pavements, is made up of a limestone powder, cemented together by asphalt so soft that its flow is perceptible at a temperature of 75, which is three times softer than any asphalt cement used at present in American pavements. It is also well known to all persons engaged in asphalt paving that the European rock asphalts are much harder on the street at the same air-tern- ASPHALT PAVEMENTS. 227 perature than the pavements in this country. He also says that angular and not rounded sand should be used, as the angular sand packs much more solidly and gives a correspondingly harder pave- ment. All of the sand used, of whatever sizes, should be hard and solid. Table No. 62 shows sands used in different cities. TABLE No. 62. SHOWING SIZE OF DIFFERENT SANDS USED BY VARIOUS ASPHALT PAVING CONTRACTORS. Contractor. City. ! Percentages Retained by Sieves. 10-mesh. I | 60-mesh. ! .G 1 *15 *13 *24 *19 *26 *18.5 *15 *.53 *23.19 *21.95 3.51 18.70 10.26 32.65 *18.70 Passing 200-mesh Barber Paving Co.. . . ranford Paviug Co. Barber Paving Co. ... Cranford Paving Co. Eastern Bermudez Paving Co Washington Brooklyn M Toronto, Can. Brooklyn 1897 189? 1SJJS 1898 1899 1899 1898 1896 1896 1896 1898 1898 1898 1>99 1888 7.39 0.5 2.18 2.87 0.9 0.36 13.25 2.5 3.5 2.5 3.5 2.5 3 12 16.98 8.95 10.52 13.22 2.61 6.74 .24 18.21 24.5 27 21 29 20 26.5 25 27.26 26.68 27.1? 29.07 11.26 20.93 2 69 24.34 31 32.5 35 33 31.9 38.3 20 18.87 29.16 26.58 27.23 16.30 27.04 11.80 16.15 16 15 8.5 7 8.3 7.0 10 5.80 9.95 9.54 6.47 7.38 7.99 10.85 3.68 11 10 10 8 10.8 6.5 18 1.17 2.02 2.06 7.25 24.24 10.04 24.72 5.60 10. 3S 19.42 16.64 17.05 Cranford Paving Co. Recommended by Mr. Dow ranford& Co Eastern Bermudez Asphalt Paving Co. Brooklyn Alcatraz Asphalt Co CJrantord & Co .... Eastern Bermudez Asphalt Paving Co. Brooklyn Alcatraz Asphalt Co * Passing 100-mesh. Wearing Surface. The wearing surface of the asphalt pavement should be abso- lutely impervious to water. Unless it is so, in wet weather the moisture will soak into the material and the oxygen in the water will oxidize the asphalt, changing the petrolene into an asphaltene and thus causing premature disintegration. In order to make this more certain, it has always been customary to mix with the sand a certain amount of mineral matter. As carbonate of lime was first used, it was thought that there was some chemical action be- tween the bitumen and carbonate, and for that reason it should be 228 STREET PAVEMENTS AND PAVING MATERIALS. used rather than any other fine material, but this idea is pretty well exploded at the present time, and paving experts generally believe that a pulverized silica is as good as, if not better than, car- bonate of lime. Carbonate of lime has a tendency, especially if used in excess, to make the pavement hard and slippery, and in fact to some extent of the nature of a rock asphalt, while a silicious, powder will make the resulting pavement less slippery, and in the last two or three years a great many pavements have been laid with this rather than with pulverized limestone, with invariably good results. It would have been used even more if it could have been obtained as readily and as cheaply. The wearing surface, then > of the asphalt pavement is made up of asphaltic cement, sand, and pulverized mineral matter. If these materials have all been selected and manufactured with care, the next thing to be considered is the proportion in which they should be mixed. The powdered mineral matter should be of such degree of fine- ness that 16 per cent of it by weight will be an impalpable powder,, and the whole of it should pass a No. 30 screen. The exact quantity to be used must be determined by the gradation of the sand, as the object of the mineral matter is to fill the voids in the sand so as. to make the total voids as small as possible. The amount gener- ally used is from 4 to 8 per cent. The amount* of paving-cement re- quired depends, first, upon the character of the cement, and, second, upon the voids in the combined sand and mineral powder. Refined Trinidad asphalt contains about 55 per cent bitumen,, refined Alcatraz about 80 per cent, and refined Bermudez about 90 per cent. So that whatever the nature of the fluxes by which asphaltic cement is made from either of these asphalts, the re- sulting cement must vary greatly in the amount of bitumen con- tained if the same amount of asphalt is used. It is admitted at the present time that the wearing surface should contain, speaking generally, about 10 per cent of bitumen, and at all events not less than 8-| or 9 per cent, although in some ex- ceptional cases good pavements have been in existence for some years where the analysis showed not more than 7 per cent bitumen. Consequently, in order to obtain 9 per cent of bitumen in any mix- ture, more Trinidad cement will be required than Alcatraz, and more Alcatraz than Bermudez. One asphalt company in giving direc- ASPHALT PAVEMENTS. 229 tions for the determining of the actual amount of asphaltic cement says: " Take the known weight of the sand and powdered carbonate of lime, previously deprived of water and thoroughly mixed in the proportions determined upon. Place same in a large tin or iron bucket; add water until no more can be absorbed and until the voids are all filled with water, and no more. The resulting increase in weight will of course give the weight of water necessary to fill the voids of so many pounds of sand and powdered limestone. Multiply the weight of the water thus obtained by the specific gravity of the asphalt, and the result will be the least amount by weight of asphalt cement required to fill the voids of the known weight of sand and mineral matter." In illustrating this they say: " Let us suppose, for example, that 50 Ibs. of sand and 6 Ibs. of powdered limestone were found to absorb 5 l / 2 ^ s - f water. In that case, since 5 1 / 2 times 1 1 / 10 (the specific gravity of that particular asphalt) equals 6 5 / 100 , the resulting mixture should be: 50 Ibs. sand 6 Ibs. carbonate of lime 6 5 / 100 Ibs. asphaltic cement Total, 62 5 /ioo lbs - Or, reducing these figures to a percentage basis, we have practi- cally: 80 parts by weight of sand 10 parts by weight of carbonate of lime 10 parts by weight of asphalt cement 100" Thickness of the Wearing Surface. After determining upon the composition of the wearing surface, it will next be proper to decide upon its thickness. A certain amount of the paving material, of whatever kind, must always be wasted when a pavement is relaid. It is never possible to get the entire amount of wear out of the whole surface, so it is not economy to lay a greater thickness than can be used to advantage. If the thickness of the wearing surface be too great, it will not be possible 230 STREET PAVEMENTS AND PAVING MATERIALS. to give it proper compression under the roller, and consequently the entire amount of material will not be used, and in fact the pave- ment will be more likely to fail than if the portion actually com- pressed was laid upon a solid base rather than the softer asphalt which was not compressed. In actual practice it has been found that a compressed asphalt of 2 inches gives the best satisfaction. This requires the material to be spread loosely, as it is brought upon the street, to a depth of about 2J inches. In light-traffic streets the surface is sometimes made 1-J inches thick, but, on the principle laid down above as to the economical wear of the entire amount laid, it would seem that, even if the travel be light, it would be true economy to lay a pavement of such thickness as could be thoroughly compressed. Methods and proportions for mixing will be discussed later on. Binder. The first asphalt pavements were laid 2J inches thick, with a so- called J-inch cushion-coat laid first and rolled upon the concrete, and a top coat 2 inches thick laid upon that. If the concrete con- tained any appreciable amount of moisture when the hot cushion- coat was laid upon it, the moisture was evaporated into steam and bubbles formed, raising the cushion-coat in small places from the concrete. It was also found that it would be difficult to prevent the cushion-coat from sliding on the base and at the same time to get a thorough bond between the top and the cushion-coat, so that it was deemed best to change somewhat the method of construction, and for the cushion-coat to substitute a so-called binder, made up of coarse stones held together by asphaltic cement. This binder has been laid of different thicknesses, sometimes 1-J or even 2 inches. Its object, however, is simply to serve as a medium between the wearing surface and the concrete. The binder will take a firmer hold upon the concrete than the finer top surface would, and the top surface will form a perfect union with the binder, so that in this way a better result is obtained than by the old method. As the province of the binder is simply to serve as this connecting link, there seems to be no necessity for making it any thicker than what is required to make a solid course, and the thickness of 1 inch seems ample for this purpose. ASPHALT PAVEMENTS. 231 The stone of which this binder is composed should be hard, angular, and somewhat graded in size. It should all pass through a screen of 1-inch mesh and be retained by a No. 10 screen. It should be so hard that it will not break up under the roller, and should be free from all decomposed or soft material. The binder is to be cemented by asphaltic cement, but need not, and in fact should not, have the voids filled. Only enough cement should be used to insure the holding together of the stones. If too great a quantity be used, in a short time it will gradually work up into the wearing surface and, by increasing the amount of bitumen, make the pavement too soft and cause its failure. This happened upon one street in Brooklyn, and the analysis of the wearing surface showed an excess of 50 per cent of bitumen. Foundation. Of whatever material the asphalt pavement may be made, or with whatever care it may be laid, it will always be a failure unless it is laid on a good foundation. This statement is true of almost every work of construction, but it is particularly so of asphalt, be- cause the asphalt itself simply acts as a carpet to receive the traffic, but the weight must be borne by the foundation. Asphalt has no inherent strength. It does its work by its elasticity, simply trans- ferring the loads to the foundation. Mention has been made of a bituminous base used in the early -days in Washington. In South Omaha, Neb., in 1891 an asphalt pavement was laid on a bituminous base somewhat differently con- structed than those of Washington. It was made of broken stone .and gravel 6 inches deep, and the entire portion thoroughly mixed with asphalt so that the base itself was a concrete cemented by asphalt. Upon a good foundation this makes a good base, but it has not much strength in itself, and when the pavement comes to be relaid it is generally necessary to take up the entire base. The best base is made of broken stone and hydraulic cement concrete. Its thickness depends upon the traffic of the street, but it is almost invariably laid with a depth of 6 inches. Some time after the success of asphalt pavement was fully assured, an attempt was made to reduce its cost and allow it to compete more successfully with 232 STREET PAVEMENTS AND PAVING MATERIALS. other pavements by varying its character and thickness according to the amount of traffic. A foundation of 6 inches of broken stone was laid upon a prepared subgrade and thoroughly rolled. Upon this was scattered coal-tar in quantity approximating 1 gallon per square yard. The asphalt was then laid upon -the stone. This base is even more objectionable than the one .spoken of in South Omaha, as it has absolutely no strength in itself, will settle with every inequality of the ground upon which it rests, and unless the sub- grade has been made absolutely solid and compact, the surface of the pavement must become rough and uneven. With proper care, how- ever, in preparing the subgrade and by rolling the broken stone in somewhat the same manner as is done for macadam pavements, a foundation can be obtained which, if not disturbed by plumbers or for any subsurface construction, will give good and satisfactory results, but its cost in that case would be almost as great as if laid with hydraulic cement. In 1899 such a base was being used in some instances in Phila- delphia, but probably not in any other city in the country to any extent. When an old stone pavement is being replaced with asphalt, it is often desirable to lay the new pavement over the old and thus, save the cost of a new foundation. This has been done to quite an extent in many cities. Notably so in New York and Brooklyn. Many of the old cobblestone streets in Brooklyn have been covered with asphalt. There 'would be almost no objection to this practice if the street were to remain undisturbed by plumbers, and the old pavement were laid with the proper cross-section desired for the new, but in almost every case it is necessary to relay at least one- half and sometimes the whole of the old cobblestone in order to- get the desired cross-section. This gives a foundation which must necessarily be more or less unstable, and when the entire surface is relaid the cost would be fully one-half that of the hydraulic- cement-concrete foundation. There are also a great many holes- and inequalities in a cobblestone pavement which must be filled up or repaved. In such a case, where the old cross-section will admit, a most satisfactory result can be obtained by filling in all of the inequalities with broken stone and rolling them to a true surface across the entire street and laying the pavement upon it. Asphalt ASPHALT PAVEMENTS. 23& lias also been laid very successfully over granite and Belgian block pavements. There has been a great amount of this work done in Xew York City. There the pavements in almost every instance were taken up and relaid at a lower elevation than originally, so- as to bring the surface of the new pavement approximately equal to that of the old. When this is done the blocks are laid with quite open joints, filled to within about 1 inch of the top with, sand, leaving room for the binder to fill up the remainder and so obtain a firm hold upon the new surface. Asphalt has also been laid over old macadam roads, and where the pavement is to be un- disturbed no possible objection can be made to this practice. Laying the Pavement. With good materials, well mixed, and in proper proportion, it is very easy to produce a poor pavement by bad manipulation and inexperienced workmen on the street. After the foundation, of whatever nature, is ready for the pavement proper, the binder should be brought to the street and spread to such a depth (which can easily be determined by practice) as will give it a thickness of 1 inch after being compressed. If the foundation is cement con- crete, and has not had sufficient time to become thoroughly set, it should be covered on one side with planks for the trucks to drive over, especially if the blocks are long. It is also often better, when the blocks are of extreme length, to begin laying the binder in the centre rather than at one end, so that the trucks will not be obliged to drive over the foundation for more than half the length of the block, thus saving, if the planks are used, half the amount of material and preventing any damage to the foundation. The same rule will hold good in laying the top, as, however good the binder may be, it is liable to be injured by too much driving if the blocks- are of extreme length. The laying of the wearing surface should follow the binder as quickly as possible. Should the weather be* good, this is not so essential; but in wet weather, or in the latter part of the season, the binder, being porous, is liable to be acted" upon by the moisture and become brittle and disintegrate under a small amount of traffic if it has remained exposed for any appreci- able length of time. In such weather, where possible, it is good 234 STREET PAVEMENTS AND PAVING MATERIALS. practice to lay the binder in the forenoon and cover it with asphalt in the afternoon, although if the following day should be pleasant this would not be actually necessary. In preparing for the wearing surface, a line should be marked along the curb at the height of the finished surface, so that it can always be ascertained whether a sufficient depth is obtained. The surface of the concrete having been laid in the same manner as that described for stone pavements, by means of ordinates, the thickness of the asphalt at any point on the street can be determined by stretching a line from curb to curb and measuring down at any desired point. The material for the wearing surface should be brought upon the street, in carts protected from the weather, at a temperature of not less than 250; and if the weather be cold, 275 or even 300 is preferable. After being dumped upon the binder it is spread out into its approximate depth by shovellers, and then graded off by experienced workmen with rakes. Several devices have been used for determining the proper depth of the loose material, such as having rakes with teeth of a certain length, etc., but after a little experience, an intelligent laborer soon learns the required depth, and easily tells by his eye whether or not a particular place is too high or too low. As soon as the material is spread out to the required depth by the rakers, it should receive its preliminary compression by hand-rollers, after which hydraulic cement should be lightly broomed over the surface and then rolled by a steam-roller weighing about five tons. This roller should be followed in a short time by one weighing not less than ten tons, or 250 Ibs. per inch of roller. The object of the three rollers is to allow the asphalt to be compressed without being pushed forward. If a heavy roller is used at first, before the material has had the preliminary compression, the tendency will be in many cases to push the material at times rather than compress it vertically, and thus cause inequalities in the surface which are very hard to be rolled out. This rolling should follow the distribution of the ma- terial closely, so that it shall not have time to cool before the final compression is obtained. Some asphalts have a certain amount of natural set in themselves, and consequently require more care in rolling than others; for if this set takes place before the final ASPHALT PAVEMENTS. 235 compression is reached, no amount of rolling will produce a true and impervious surface. The state of the weather also is an element to be considered. If a strong wind be blowing, the material, spread out as it is, over a broad surface only 2 or 3 inches thick, will cool much more rapidly than on a calm day when the temperature is considerably lower. On the other hand, when the weather is hot there is no necessity of following up the rakers so closely. The roll- ing should be continued without any cessation until the asphalt has received its ultimate compression. If the street be wide enough, the rolling should be done crosswise as well as lengthwise on the street, and in any event the rolling should be done at as great an angle as possible, so that any little inequality which might be caused by .the roller moving lengthwise may be taken out by this cross- action. The amount of rolling required depends upon circum- stances greatly, but in general two such rollers as above described should roll 2000 square yards of wearing surface in ten hours. Fig. 14 represents the cross-section of an asphalt pavement. FIG. 14. When the mixture for the wearing surface is dumped upon the binder all lumps should be carefully broken up and spread out, and the material taken up clean from where it was dumped upon the binder, lest if any appreciable amount be left it will cool and be- come hard before it is covered up by the top, and so not receive the required amount of compression, and eventually wear away and fail at this place. In making the connection with the pavement that has been laid at any appreciable time before, care should be exercised to make a. perfect joint with the old work by heating the edge or painting it, with asphaltic cement. In some asphalts it is necessary to cut the joint down vertically; otherwise if it is chamfered off, it will after- wards scale under traffic. Where asphalt pavement joins a street-car track, stone header, or any 'unyielding surface, it should be laid about one -eighth of an 236 STREET PAVEMENTS AND PAVING MATERIALS. inch above it, as wheels coming from the hard iron or stone to .the softer asphalt will compress the latter, so that soon a depression will be formed, eventually becoming a hole under the blows from the wheels. Gutters. In most cities it is customary to lay the asphalt up to the curb. In such cases special care should be exercised to thoroughly com- press the material in the gutter; and as it is often difficult to roll this thoroughly, it should be tamped by hand with irons especially prepared for this purpose. A straight-edge some 12 or 14 feet long should be used, so that the -gutter may conform to the exact grade of the curb and be free from any slight depression. For a distance of 12 inches from the curb the surface should be painted with asphaltic cement and ironed in with hot smoothing-irons. This should be done immediately after the tamping, before any foreign matter has gathered upon it and when the pores are comparatively open. The object of this is to saturate the material thoroughly with asphalt and prevent any subsequent absorption of moisture which would lead to disintegration. The smoothing-irons used should not be too hot. Iron does not show any heat by color until it is at a temperature of about 1000 or 1200 Fahr., and this temperature would be detrimental to the asphalt and liable to burn it sufficiently to cause disintegration. It is claimed by advocates of Bermudez and Alcatraz asphalts that the water does not injure either material, and for that reason this work is not necessary; but at the present time it is customary to treat all asphalts in this manner where the material is laid from curb to curb. On account of this effect of the water, however, stone, brick, and sometimes cement are used for gutters in some cities. In the city of Washington the officials have decided to use vitrified paving-brick for this purpose. This material has been in use there for some years, and has given satisfaction, as it presents a smooth surface to traffic- and is not acted upon by the water. Where either stone or brick is used, the concrete should be depressed sufficiently so that it shall have the same amount under the gutter as under the pavement proper, and the blocks should be set in mortar on the concrete, not on the cushion of sand, so that they ASPHALT PAVEMENTS. 237 shall be perfectly rigid, and the joints poured either with Portland- cement grout or asphaltic cement. Temperature for Laying. It has long been a mooted question at what temperatures the laying of sheet asphalt should be discontinued. Where it is not definitely stated in specifications, it is generally stipulated that it shall cease at a temperature below freezing, but this is very seldom done in actual practice. It is certain that better results can be obtained by laying the asphalt in warm weather than in cold, as a more perfect anc 1 even compression can be obtained. That this is important was demonstrated on a street where the work was com- pleted at a low temperature and opened for traffic. It soon began to pick up under the impact of the horses' feet, and quite a portion of it had to be repaired, and at one time it looked as if an entire "block would require relaying. Eventually the weather grew warm again, and in a few days the action of the traffic had obliterated all signs of the picking up, and the compression required was obtained by travel, and no further trouble occurred from that source. In another instance, a street containing some 12,000 yards was surfaced at a temperature of about zero where the haul from the plant was about 1J miles. Nearly half of the work was performed under these conditions. The street picked up considerably under travel during the winter, and the indications were that quite a portion of it would require to be resurfaced in the spring; but fortunately there was only slight travel on the street during the winter-time, so that not much damage was done, and the traffic during the coming summer put the street in such a condition that only about $500 was expended upon it during the guarantee period of five years. The practice of doing work under these conditions, however, is not to be commended, as it is in exceptional cases only that good results are obtained. In order to be sure of good work, the wearing surface should not be laid at a temperature below 20. Cracks. One of the principal ways in which asphalt pavement has failed in cities subjected to great extremes of temperature is by the form- 238 STREET PAVEMENTS AND PAVING MATERIALS. ing of cracks. These are thought by some engineers to be caused by the pavement cracking through the base, but a careful study of the subject does not seem to bear out this view. In one instance a pavement laid in one. of the Southern cities was subjected soon after completion to a rapid change of temperature of about 40% but even then it was but little below the freezing-point, and not enough to cause any contraction in the concrete base, but the asphalt surface showed a great many fine cracks, demonstrating conclusively that these cracks were formed in that particular in- stance, at any rate, by the contraction of the wearing surface itself. Many specifications in detailing 'how the wearing surface should be laid say that the material shall be such as to form, a pavement which shall not be too soft in the summer, nor crack and disin-, tegrate in- the winter. This is a simple proposition in the specifi- cations, but not so easy to carry out. The engineer generally wishes. a pavement to be laid as hard as possible without cracking. The contractor, on the other hand, has as his standard one that will be as soft as possible and not mark or rut too much in hot. weather. It is well known that a pavement hardens as the volatile- oils evaporate and the asphalt becomes oxidized, so that the softer the pavement is laid the longer it will probably last, and the aim of the con- tractor is to lay it as soft as possible without bad results the first season. Very frequently complaints are made of new pavements cutting up and becoming rough under the action of travel when laid in hot weather, which after the first summer give no trouble whatever. As material is laid soft and in hot weather, allowance must be made for the changing temperature to come, and to meet this successfully the skill of the contractor is taxed. A pavement that is laid soft will seldom give trouble by cracking except after it has been laid a long time. In Western and Northern cities, where the range of temperature is great, it is probably impossible to lay sheet-asphalt pavements that will not crack in extremely cold weather. In the vicinity of New York City very little trouble is experienced by cracking. In some cities engineers have sought to remedy this trouble by making an expansion- joint crosswise of the street at frequent intervals. The theory of the expansion- joint in any structure is that the material is free to slide upon the base upon which it rests. This is certainly not true of a well-constructed ASPHALT PAVEMENTS. 239 asphalt pavement, as it is hardly conceivable that a binder with this superimposed pavement could slide any appreciable distance on the concrete. An expansion-joint will certainly cause a crack to form, wherever it is made, at a change in temperature, while really the contraction of the material might be entirely taken up by the elasticity of the asphalt. At all events, the most that it could accomplish would be the formation of the cracks at regular intervals, which is neither desirable nor of any particular advan- tage. These cracks form sometimes from the centre towards the gutter and sometimes from the gutter towards the centre, but always in the line of the least resistance. As the pavement becomes older more cracks, appear diagonally and lengthwise of the street, dividing the pavement into irregular areas. When these become small and the cracks large the pavement must be relaid. These cracks often appear in a pavement without doing any particular amount of damage, especially if there is considerable traffic on the street. If, however, there is not traffic enough to consolidate the pavement after the weather becomes warm, the moisture enters the cracks and hastens disintegration. The best method of taking care of the cracks is to prevent them, or where not possible to do that entirely, to devise, by a study of the conditions, a composition that will withstand changes of temperature to the best advantage. If a pavement is laid too soft and the traffic is heavy, the result is that an uneven surface soon forms, the top pushes under traffic, either upon itself or upon the binder, or the whole upon the concrete, and holes appear long before they should in such cases, and the soft surface must be taken up and relaid with harder material. This trouble may be caused by too much flux in the asphalt cement, or by an excess of bitumen being used in the wear- ing surface. Effect of Illuminating-gas. The action of illuminating gas, as it sometimes escapes from leaky mains, is very detrimental to asphalt pavements. Pavements have failed in many instances from causes for which no explanation could be given at first, and the surface was relaid without any question; but in one instance the pavement failed so frequently 240 STREET PAVEMENTS AND PAVING MATERIALS. that a careful examination was made and the odor of gas detected, and when the asphalt was all taken up sufficient gas was found to give a perceptible flame when lighted, although the base was 6 inches of cement concrete. An examination of the gas-main at this point disclosed a large leak. In other cases also when this failure has been noticed broken gas-mains 'have been discovered. The action of gas is generally made manifest by the appearance of a great many cracks or checks in the pavement, lengthwise of the street, which under traffic soon become soft and the pavement disintegrates. Whether the gas companies shall make such failure good, whether they shall be repaired by the contractor who has the pavement under guarantee, or whether the expense shall be borne entirely by the city, is an interesting problem, but one which has not been satisfactorily solved at the present time. Damage by Fires. Another cause of damage to asphalt pavements is the building of fires upon them. While this should never happen, as a matter of fact it does, and from the report of the water-purveyor of New York City it is seen that during the year 1896 alone 8654 square yards of asphalt were destroyed by fire, at an expense to the city of over $30,000. In 1894 the asphalt so destroyed amounted to 3410 square yards, and in 1895 to 3692 square yards. The probable reason for the excess in 1896 was the fact that it was a presidential year, and the youth of New York consider it proper to celebrate the victory by building bonfires upon the pavement, without re- gard to its effect. Standard for Condition of Street at End of Guarantee Period. In the early contracts for asphalt pavements there was in- serted a clause requiring the streets to be kept in good repair for a term of years, and turned over to the city in such condition at the end of the specified time. The words " good repair " are in- definite, liable to mean one thing to the engineer and something else to the contractor. So much controversy has arisen over this point that present specifications attempt to make clear what is expected and* required. Specifications for asphalt pavement in New York City contain the following clause: ASPHALT PAVEMENTS. " Just previous to the expiration of the guarantee period the entire work shall be inspected, and any bunches,, depressions, or unevenness in the surface of the pavement that shall show a varia- tion of of an inch under a four-foot straight edge or template, or any crack wider than J of an inch, or any portion of the pave- ment having a thickness of less than 1^ inches, shall be immedi- ately repaired upon the order of the Commissioner of Highways by the heater process, or by removing the entire pavement from the concrete and replacing it in the same manner as when originally laid, provided that when more than 50 per cent of the surface of any one block requires repairing according to the above conditions, the entire block shall be taken up and relaid. When any defects are caused by the failure of the concrete the entire pavement, in- cluding foundation, shall be taken up and relaid in accordance with the specifications." Rock Asphalt. The rock asphalts of Europe have been made entirely of bituminous limestone. Generally the stone had become impreg- nated in some manner with bitumen so that it became almost one substance. Some bituminous limestone has been found in this coun- try, as well as a sandstone bearing asphalt, and also in California beds of sand which contained asphalt, and of which many of the early California asphalt pavements were made. These pavements were laid in a very crude manner, with but little knowledge of the material or the subject, and a great many of them failed in a short time, as might have been expected. These failures, however, should not have been charged up to California asphalt or to asphalt pave- ments, as experience has demonstrated that with the proper treat- ment a good pavement can be laid of this material. Buffalo, N. Y., probably has more rock asphalt pavement than any other city in the United States; some of it has been laid with imported foreign asphalt, and quite a large amount by a combina- tion of the foreign with the Kentucky rock asphalt. The first Kentucky rock pavement was laid In Buffalo in 1890 as a sample, since which time nearly 10 miles have been laid. Successful pave- ments have been laid with an asphaltic sand rock of Indian Terri- tory, although they have not been developed to such an extent as the Kentucky asphalt. ^ 242 STREET PAVEMENTS AND PA VINO MATERIALS. Wearing Surface of American Rock Asphalt as used in St. Louis, Mo. Upon the foundation thus formed shall be placed a wearing surface as follows: A mixture of American bituminous rock, which shall be pre- pared and laid on said concrete foundation as follows: The wear- ing surface shall be composed of bituminous sandrock from the Chickasaw Nation or Breckinridge County,, Ky., 50 per cent to 66f per cent; bituminous limerock from the Buckhorn mines in the Chickasaw Nation, 33^ per cent to 50 per cent. The rock of both materials shall be ground finely and thoroughly mixed, and nothing shall be added to or taken from the powder obtained by grinding the bituminous rock. This powder shall be heated in a suitable apparatus to a temperature of from 150 to 200 Fahr.; it shall be brought to the street in suitable carts, and spread with rakes to an even thickness of such depth as will insure a uniform thickness, of 2 inches after having received its ultimate compression. The surface shall then be compressed by tamping and rolling, after which a small amount of hydraulic cement will be swept over it, and then it will be thoroughly compressed by a steam-roller weigh- ing not less than five tons. Method of Laying. The bituminous sandrock shall contain from 9 per cent to 12 per cent of pure bitumen. The bituminous limerock shall be as nearly as possible a pure carbonate, thoroughly and evenly impreg- nated with asphalt, having no more impurities than the standard German rock asphalt of Limmer or Vorwhole, and shall contain not less than 7 per cent and not more than 12 per cent of bitumen, according to the richness of the bituminous sand used. The method of laying the European rock asphalt is entirely different from that of the ordinary sheet asphalt. The material is taken from the mines and shipped to the city where it is to be used in its natural state. The products of the foreign mines vary in the amount of bitumen contained, some having too little and others too much, so that it is generally necessary to mix the dif- ferent products so as to get the required amount of bitumen in the pavement, which is approximately 10 per cent. . After these proportions have been determined and the material ASPHALT PAVEMENTS. 243 mixed, it is first crushed with rollers at the plant and then reduced to a fine powder by being passed through disintegrators, after which it is sifted through a sieve to separate any lumps that might otherwise get into the pavement. This powder is then heated in a cylinder which is kept constantly in motion to allow the air to circulate freely among the particles, and kept for about two hours at a temperature from 300 to 325 Fahr. The material is then carried in carts to the street and spread upon the prepared base to a depth that will give the required thickness when thoroughly com- pacted. The binder course is not generally used with rock asphalt, al- though it is sometimes. Over the powder spread upon the street a light roller is run to give the surface its initial compression, when workmen, each with a round iron rammer some G or 7 inches in diameter, carefully go over the surface, one following the other, all striking blows, in unison, on the asphalt until it is thoroughly compacted. A coat of hydraulic cement is then spread over the surface, when it is ready for the final rolling, which should be done by steam, and preferably with an arrangement inside the roller for keeping it hot. About twelve hours after the rolling is completed and the material has become cold, the street can be thrown open to travel, which continually adds to the compression already given. It has been found in several instances, where a pavement has been laid and subjected to heavy traffic for a number of years, that while it has decreased very materially in thickness, its weight has not correspondingly decreased, showing that compression has been continually going on. Eock asphalt very seldom gives any trouble by cracking. In a report upon rock asphalt pavements made to the corpora- tion in 1900, the City Engineer of London names sixteen streets that were relaid at the end of the guarantee period. The original contract provided for free maintenance for two years and a specified sum for 220 + 1000 325 - D 10 278 STREET PAVEMENTS AND PAVING MATERIALS. Formulas 1 and 2 are based on the following mean numerical values deduced from the St. Louis tests: R = 16.5 per cent; RG = 4.7 " " A = 1.25 " " T' = 3300 pounds; C = 13,000 " In deducing mean values for formulae 3 and 4 a study was made of tests from various parts of the country, from which 262 were selected for use, and they gave the following: R = 8 per cent; A =2 " " T = 2200 pounds; C = 10,000 " D =2.25 #=6.5 In which V = the required value; RG = the rattler loss in terms of granite; R = the rattler loss in percentage of the weight of the hrick; A = per cent of absorption of the weight of the brick; T = modulus of rupture per square inch; T" = the crushing strength per inch width; C = crushing strength per square inch; D = specific gravity; IT = hardness by Mohs' scale. Where the four factors, R, A, T, and (7, only are used, Mr. Wheeler assigns the value of 60 per cent to the rattler test and 50 per cent where all the above factors are known, while Prof. John- son assigns 50 and the Board of Public Improvements of St. Louis only 30 per cent. It is probable that the value of the rattler test is of even greater value than that assigned by Mr. Wheeler, and might reach 75 per cent, as no engineer would be willing to lay any brick in a pavement that had not passed a good test in the rattler. Mr. Wheeler published a table in the book heretofore men- tioned in which he shows the comparative ratings of two well- known paving-brick by the formulae here given, in which the necessity of assigning the proper percentages to each factor is very clearly demonstrated to any one having a knowledge of these brick. BRICK PAVEMENTS. 279 In Columbus, Ohio, it has been the practice to take one or more samples from each street of all brick used and test them by the rattler test as specified by the National Brick Manufacturers' Association, calling as loss by abrasion all pieces of one pound weight, and less, aiming to admit on the streets only such brick -as would show a loss of less than 27.5 per cent by abrasion under this test. A record of one test was for blocks selected in order as deliv- ered by the contractor: charge No. 1, loss 18.55 per cent; charge No. 2, loss 17.9 per cent average 18.22 per cent. At the same time, blocks which were slightly fire-cracked and which the inspector had rejected as unfit for use were tested with the following results: charge No. 1, loss 25.5 per cent; charge No. 2, loss 24.25 per cent average 24.87 per cent. Which is a somewhat better showing than was generally obtained, the best single charge being: loss 15.4 per cent, average 17.07 per cent; and the highest being: loss 36.65 per cent, average 33.56 per cent. Size of Bricks. Paving-bricks have been made of very different shapes and sizes by different manufacturers. Other things being equal, the same principles laid down for establishing dimension of granite "blocks would apply to sizes of paving-bricks; but it must be re- membered that while the material of which the granite blocks arc made is natural, that composing the bricks is artificial. Conse- quently new conditions arise, and in determining dimensions con- sideration must be given to the method of manufacture. If the brick is made too long, it is liable to warp either in the preliminary drying or while it is being burned in the kiln. If it is too thick, so that the clay in the interior is vitrified with difficulty, it is probable that when sufficient heat has been applied to insure proper vitrification to the central part of the brick, the outside will have been damaged and the brick not of uniform texture texture throughout, so that in determining the thickness the same rule will not apply to all clays, as some clays will vitrify more readily than others. But a thickness must be adopted for any particular clay which will admit of complete vitrification at a tem- perature which will not injure any portion of the brick. 280 STREET PAVEMENTS AND PAVING MATERIALS. Then, too, apart from the physical conditions governing the size, the economic reasons must be considered. If brick are made of an unnatural size as compared to building-brick, underburned brick, which are always found in greater or less extent in every kiln of paving-brick, will be almost a total loss, as they can be used to very little advantage for any other purpose; while if of about the standard size of building-brick, the soft brick can always be disposed of to builders without loss. Bricks have been made, however, and used in pavements, hav- ing dimensions as large as 4 x 5 x 12 inches, but for the above and other reasons their use has been discontinued, and at the present time smaller sizes are adopted. Many manufacturers make two sizes, the smaller being practically 2J x 4 x 8-J inches, and the larger 3x4x9 inches. These latter are generally termed blocks in distinction from the smaller size. Form of the Brick. Whether the bricks should be made rectangular in shape or whether the corners should be rounded off is a mooted question. The argument used by the advocates of the round corner is that if the brick are laid with square edges, the impact of the horses' shoes soon wears them off practically to the round corners, leav- ing them in a rougher and much worse condition than if they had been originally made round. There is considerable merit in this ar- gument, and if the joints are to be filled with sand or some unstable filler, it is probably the best shape; but if the joint-filler is rigid, like Portland cement or some similar filler, so that the joints can be filled solidly to the top and so maintained, it would seem that the square-edged brick would give better results. With the rounded corner and the joints filled only to the top of the brick a thin edge of the filler must be made at each side of the joint, which is maintained with difficulty under traffic. It has not been definitely determined by manufacturers which is the better method. Different devices have been adopted for keeping the bricks at a certain distance from each other in a pavement, so that the space may be left sufficiently wide to admit of enough filling material to make a good and substantial joint. Some blocks have a projection t , ' BRICK PAVEMENTS. 281 on one side to maintain the distance, and a groove on the other side to receive the joint-filling material. It is a well-known fact that, whatever the material composing blocks for pavements, the smaller the amount of joint-space the better. It would seem, therefore, that it was hardly necessary to provide any special ar- rangement for keeping the brick apart. It has been the author's experience that where the brick were apparently laid tight in the work, when they came to be rammed or rolled sufficient space would be found to receive the proper amount of joint-filler. Upon this question of size and shape the Philadelphia specifications say: " The bricks or blocks must be vitrified clay, repressed, especially burned for street-paving, and not less than 9 inches long, 4 inches wide, and 3 inches thick. The bricks or blocks must have two or more ribs or projections upon one of the vertical sides extending from top to bottom. On the opposite vertical side of the brick or block [there should be] a groove or channel extend- ing longitudinally from end to end of the brick or block, and con- necting with the like transverse groove extending across each end, thus serving by contact with the flat side of an adjoining brick or block to secure a separation, so that cementing material may effect a practical encircling of each brick or block, flowing into the grooves, thus keying or locking together the entire pavement. The Department of Public Works is authorized, however, to ac- cept proposals for street-paving with other vitrified brick, pro- vided they shall be in quality not inferior to those herein described." St. Louis specifications say: " The brick shall not be less than 8 inches nor more than 9 inches long, not less than 2J inches nor more than 4 inches wide, not less than 4 inches nor more than 4^ inches deep, with rounded edges of a radius of f of an inch. Said brick shall be of the kind known as repressed brick, and shall be. repressed to produce a mass free from internal flaws, cracks, or laminations." Foundation. The foundation of a brick pavement, like that of all others, is very important. As has been shown before, blocks of any kind wearing from abrasion wear much more rapidly if they are 28:3 STREET PAVEMENTS AND PAVING MATERIALS. not exactly level. Thus if the blocks are set and maintained with a smooth even surface, so that the wear is directly on the top rather than on the edges or corners, the abrasion is reduced to a minimum and the life of the pavement correspondingly increased. This is particularly important in a brick pavement, because the blocks are necessarily small and the number of joints and corners correspondingly increased, so that to get the best results the foundation should be such as will allow the brick to be placed in position and ^so maintained under traffic. Unfortunately for the good name of brick pavements this principle, if understood, has not always been carried out in practice. Brick pavements have been laid upon foundations of sand alone, a combination of boards and sand, a combination of sand and bricks laid flat, and on a foundation of broken stone and cement concrete. For reasons specified above, it can readily be understood that a foundation of sand alone cannot be expected to give good re- sults. The weight of a vehicle coming upon any particular brick is transferred to the' foundation beneath, and if the foundation be sand, and the underlying earth unstable, any amount of heavy traffic is bound to make such pavement soon appear rough and uneven. The wear then quickly becomes abnormal, and the pave- ment wears out and is replaced long before it should have been. The early pavements in some places were laid on a foundation of 3 inches of sand, upon which were placed oak boards 1J inches thick which had been previously soaked in coal-tar, and this cov- ered with a cushion-coat of 1 inch or 1J inches of sand. This foundation gave very good results for light traffic, but could not be expected to sustain the heavy travel of business streets. Another method adopted was laying the bricks flatwise on a bed of sand, rolling and ramming them thoroughly. They were then covered with a cushion-coat of sand, and the surface brick set on edge. This construction has been used to considerable ex- tent in the Central West and with good results. It commends itself to cities located at any distance from stone-quarries, for two reasons: the stone necessary for this foundation, whether used with or without cement, is expensive, and because it gives an opportunity for the economical use of the underburned brick, BRICK PAVEMENTS. 283 which are not suitable for the wearing surface, but have been burned sufficiently to give satisfaction in the lower course. It can be seen that in a locality where brick are readily available and the cost of freight is correspondingly low, and where broken stone is expensive, this would be an economical foundation; but if the brick are to be carried to such a distance that freight is an important item, it might prove to be expensive. The proper plan must be determined upon in each case. Broken Stone. In many parts of Illinois where paving-brick have been used to a considerable extent, limestone can be obtained easily and cheaply. Consequently foundations of broken stone, thoroughly rolled and compacted, have been used in many cities with excel- lent results. With this material, however, care must be taken to roll and compact the stone thoroughly to a hard, firm surface, so that when the cushion-coat of sand is applied and the pavement laid, the traffic will not cause the sand to mix with the stone in the foundation, thus causing a settlement in the pavement and allowing it to become rough and uneven. Several brick pavements have failed from this cause. If, however, the stone be rolled as for a macadam road and thoroughly compacted and made solid, it cannot fail to give good satisfaction if undisturbed. Cement Concrete. The best foundation, although its expense in every case may not be justifiable, is cement concrete, such as has been heretofore described. It should be made in the same manner as for asphalt or stone, but care should be taken to have the surface as smooth as possible, so that there will be no danger of any brick resting upon a projecting piece of stone and so getting an unequal bear- ing, and perhaps breaking under a heavy load. The object of the . sand cushion is simply to give the brick a firm bearing, and the smoother the surface of the concrete the smaller the quantity of sand necessary, and the smaller the quantity of sand the less liable is any individual brick to settle out of place. 284: STREET PAVEMENTS AND PA VINO MATERIALS. Fig. 17 represents a cross-section of a brick pavement on a con- crete base. FIG. 17. Joint-filling. The material for filling the joints of the brick pavement is practically the same as that used for stone, with the exception of gravel combined with tar. All have been used in different sec- tions of the country, but it is not yet a settled fact which is the best. The City Engineer of Minneapolis in his report for 1898 states that when, during the year, the city asked for bids from manufacturers for furnishing paving-brick, with a guarantee of fifteen years, allowing the bidders to designate the filler which they preferred should be used, one bidder specified sand, and dis- tinctly stated that unless it were used he would not guarantee his brick. It is generally considered, however, that when brick are laid on a solid foundation, a rigid, or at least water-tight, joint- filler should be used. Of these, the three principal ones are Port- land-cement grout, Murphy grout, and paving-cement. Engineers, however, do not agree as to which one of these gives the best re- sults. The two former are rigid, and when the joints are once broken they can never be made tight and are no better than a sand joint, while a pitch joint once broken will become solid again at a warmer temperature. At a meeting of the American Society of Municipal Improve- ments, held in Toronto in 1899, it was stated by one engineer, in a discussion upon this subject, that he had examined nearly all of the brick pavements laid in this country with a Portland-cement joint, and had come to the conclusion that they were failures. Further on in the discussion another engineer of equal experience stated that it was his belief that a brick pavement well laid with a Portland-cement joint would last five years longer than a similar pavement laid with sand joints. This testimony was corroborated by that of another engineer of considerable experience. The prin- BRICK PAVEMENTS. 285 cipal objection that is made to the use of the cement-grout joint is on account of the rumbling noise that is heard when driving over such a pavement. This does not always happen, but has occurred in a great many instances and is certainly very objectionable. The rumbling must be caused by cavities that exist between the brick and the concrete. Just what causes these cavities is not so well known. In discussing this subject in a convention of the National Brick Manufacturers' Association, held in Pittsburg in 1898, it was thought by many of the manufacturers that these cavities were caused by a slight shrinkage of the concrete, and their remedy was not to have the brick laid until the cement had become thor- oughly set and dry. Other people, and perhaps those who have studied the question more, think it is caused by expansion; that the curbstones acting as abutments support the arched pavement, and that it expands with the heat and rises from the concrete. To obviate this it was recommended that an expansion-joint of 1 inch or 1J inches be left next the curb and filled with asphalt or paving- cement; also to lay expansion-joints filled with the same material across the street at regular intervals. It would seem, however, that if this trouble was caused by expansion, it would have taken place longitudinally along the street, as the width of the street is slight as compared to its length. This has occurred in one or two in- stances. It is reported that at Easton, Pa., when the temperature was 94 in the shade, a brick pavement was heaved to such an extent that it broke with a loud noise. The rupture formed an arch with a nine-foot span and an eight-inch rise extending from curb to curb, a distance of 42 feet. An occurrence somewhat similar to this took place in Newark, N. J. Very few instances, however, have been reported, and in Brooklyn, N". Y., there is one street laid continuously with brick with a Portland-cement joint, a distance of mile, where no trouble of this kind has occurred. In 1895, however, two blocks of brick pavement were laid with the Mack block and Portland-cement joint. After the bricks were laid and had been rolled, the weather turned so cold that it was impossible for a while to do the grouting. When the weather became warmer, in attempting to roll further, it was found that 286 STREET PAVEMENTS AND PAVING MATERIALS. the bricks were so solidly imbedded in the frozen sand that many of them broke under the roller and the rolling was discontinued. An attempt was made to thaw out the frozen sand with hot water, but how thoroughly it was accomplished is uncertain. After the pavement had been laid for some time, a great deal of rumbling was observed when teams were driving over it, and many com- plaints were made by property owners. The bricks were cut out for a distance of 1^ inches along the curb on both sides, to see if that would relieve it, but no difference was noticed. A fifteen-ton macadam roller was run continuously over one block during an entire day in an attempt to press the brick down to a firm, bearing. This caused no impression whatever upon the pavement, and the noise still continued as loud as before. So many and persistent were the complaints that the brick was finally taken up and re- placed with asphalt. The other block, however, was not quite so noisy and is still in use, and no complaints are made by the prop- erty owners, and it seems as if the noise had decreased. The theory of the city authorities was that there were slight, local cavities existing between the brick and the concrete, caused by the frozen sand melting and shrinking somewhat. It is prob- able that an air-space of -J of an inch, and perhaps even less than that, would cause this rumbling, and it would seem in this case as if the above were the proper solution. The argument against the expansion theory is that in many cases the noise is reported to have been greater during cold weather than warm. There seems to be no question but that a brick pavement with its joints filled with a good cement grout will last materially longer than one with a less rigid filler, and if the pavement is laid during warm weather and care is taken to have the bricks thoroughly rolled and bedded in sand, there should be no trouble from abnormal noise. No trouble from noise has ever been experienced when sand or paving-cement has been used as a filler. If the foundation is not solid and is liable to settle unevenly, it would be a waste of money to use a rigid filler. One objection to the rigid joint is the difficulty with which cuts- are made in the pavement. Many bricks are broken in taking them up, and the expense of cleaning before relaying is considerable. BRICK PAVEMENTS. 287 It is also hard to keep traffic off a small patch while the cement is setting. A very large proportion of the brick pavements in the West have been laid entirely with sand joints, and experience there has shown that good brick will wear well under such conditions, but the pavement will not be impervious to water. When that is required a solid filler must be used; and if the engineers are afraid of noise from Portland-cement, a paving-cement filler can be used to advantage. If sand is used, it should be fine, silicious, and per- fectly dry, so that it can be swept readily into the joints, so as to fill them completely and thus maintain the bricks in the position in which they are placed. The paving-cement should be applied at a temperature of from 250 to 300, and if possible during the warm portion of the day when the bricks themselves are warm, so as to allow the cement to flow readily and completely fill the joints. This filling is some- times applied by pouring the cement directly into the joints from buckets made for that purpose, or by spreading it indiscriminately over the surface and sweeping it into the joints with brooms. The objection to this latter method is that a certain amount of the cement is wasted and the entire surface of the pavement covered, which is liable to be sticky during the hottest part of the day. To obviate this last trouble, as soon as the joints are filled the pave- ment should be covered with a thin coating of sand, which under traffic will take up the cement and clean the surface to a certain extent. If the first covering should not do this satisfactorily, a second can be applied. This will also probably be necessary if the joints are filled from the buckets. The grout, when Portland cement is used, is made by mixing equal parts of Portland cement and fine, sharp sand with sufficient water to give it such a consistency that it will readily flow into all the joints. Great care is necessary in this mixing both of the cement and sand, and also when the water is added, so that the grout shall be uniform in quality and not leave one joint in the bricks filled with almost pure cement and another with almost clear sand. The grout is generally mixed in large boxes, taking one barrel of cement at a time, and, after being thoroughly mixed, poured out upon the pavement and thoroughly broomed into 288 STREET PAVEMENTS AND PAVING MATERIALS. the joints. The street should be closed to traffic until the mortar of the joints is absolutely and entirely set,, which will probably require a week and perhaps more; but it is very important that it be thoroughly hardened before any traffic is allowed upon it. Laying the Brick. After the concrete has become sufficiently set it should be covered with a sand cushion, care being taken to see that the sand is entirely free from any small stones or pebbles that might cause the brick to be supported unequally. The sand is brought to the exact shape desired by means of a template which has been cut to the required crown, resting on the curbs if the roadway be nar- row, or, if too wide for that method, with one end resting on the curb and the other on a scantling buried in the sand at the cen- tre. After one side is brought to the desired shape the template can be reversed and used on the other side. No walking on the prepared surface, or disturbance of it of any kind, should be al- lowed. The pavers, unlike stone-pavers, should stand on the completed pavement, working from themselves. The courses should always be started with a half-brick, so as to break the joints evenly across the street, and when finished they should be set up tightly with an iron bar so that the end joint shall be as close as possible. This is important, whatever the joint-filler is, as these cross- joints come directly in the line of travel. The courses should be kept square with the street and trued up every four or five feet. It is customary generally to have one man working at the side of a street where the courses are completed, cutting the brick to be used as closers. After the brick have been laid, the surface should be swept off clean and, if a steam-roller is to be had, should be thoroughly rolled until all the brick are brought to a firm and even bearing. If the brick run unevenly for hardness, it may be desirable, just previous to rolling, to wet the pavement thoroughly with a hand-hose, so that the soft bricks can be detected. This is a sure test, as the soft brick absorb the water readily, and when the harder ones dry those retaining the moisture can easily be seen and should be removed and others put in their places. If a steam-roller cannot be had, good results can be obtained BRICK PAVEMENTS. 289 by ramming, when a plank should be laid on the surface parallel to the curb-lines, and the pavement rammed by striking the plank with an iron rammer. If the planking is used crosswise of the street, the pavement is liable to be rammed unevenly. The prin- ciples laid down in the stone pavement for the position of the bricks and direction of the courses, both between streets and at intersections, are perfectly applicable to brick. The method shown in Fig. 57, called the herringbone plan, is sometimes used. This, however, is not desirable, as between the streets it brings the line of cross-joints lengthwise to the travel of the street, which permits a weak spot in the pavement, and at intersections it brings a great many of the brick lengthwise of the traffic turning the corners. This method has never been used to any great extent. Brick pavements, especially when laid with a sand filler, generally show considerable wear during the first few weeks, especially if laid with rectangular bricks rather than those with rounded ejlges. This is because the traffic quickly finds any inequalities in the sur- face, and also because the horses' shoes soon round off the edges of the softer brick; but in a short time this abnormal wear ceases, and from then on the observable wear is slight. Brick specifications vary principally in the tests that shall be required, joint-filling, and foundations. The following is taken from the specifications of St. Louis: " To secure uniformity in bricks of approved manufacture, de- livered for use, the following tests shall be made: " 1. They shall show a modulus of rupture in cross-breaking of not less than twenty-five hundred pounds per square inch. " 2. Specimen bricks shall be placed in the machine known as a ( rattler,' twenty-eight inches in diameter, making thirty revo- lutions per minute. The number of revolutions for a standard test shall be eighteen hundred, and if the loss of weight by abrasion or impact during such test shall exceed thirty per cent of the original weight of the bricks tested, then the bricks shall be rejected. An official test to be the average of two of the above tests. " No bid contemplating the use of rejected brick shall be enter- tained. " Samples may be submitted by manufacturers, in which case 290 STREET PAVEMENTS AND PAVING MATERIALS. the bidder proposing to use brick of such manufacture will not be required to submit samples. The quality of brick furnished must conform to the samples presented by the manufacturers and kept in the office of the Street Commissioner. " The Street Commissioner reserves the right to reject any and all bricks which, in his opinion, do not conform to the above speci- fications. " Any brick may have a proper shrinkage, but shall not differ materially in size from the accepted samples of the same make, nor shall they differ greatly in color from the natural color of the well-burned brick of its class and manufacture. " No bats or broken bricks shall be used except at the curbs, where nothing less than half a brick shall be used to break joints. The bricks to be laid in straight lines, and all joints broken by a lap of at least two inches, to be set on edge on the sand as closely and compactly as possible and at right angles with the line of the curb, except at street-intersections, where they are to be laid as the Street Commissioner may direct. " The pavement to be thoroughly rammed two or three times with a paver's rammer weighing not less than seventy-five pounds. The pavement to be surfaced up by using a long straight-edge and by a thorough rolling of the pavement with a road-roller weigh- ing not less than three nor more than six tons, and when com- pleted to conform to the true grade and cross-section of the road- way. " All joints in the pavement shall be completely filled with Portland-cement grout. The cement to be of brand approved by Street Commissioner, to be fine ground; eighty-five per cent shall pass through a sieve having ten thousand meshes to the square inch. All cement shall be capable of withstanding a tensile strain of five hundred pounds per square inch of section, when mixed neat, made into briquettes and exposed twenty-four hours in air and six days under water. All cement shall be put up in well- made barrels, and all short weight or damaged barrels will be re- jected. Cement without manufacturers' brand and other certifi- cate will be rejected without test." " The grout shall be mixed in portable boxes in the proportion of one part cement to one part sand. The cement and sand to be BRICK PAVEMENTS. 291 thoroughly mixed together dry, then sufficient water to be added to make a grout of proper fluidity when thoroughly stirred. " The grout shall be transferred to the pavement in hand- scoops,, or as the Street Commissioner may direct, and rapidly swept into the joints of the pavement with proper brooms. " Teams, carts, and wagon traffic and wheeling in barrows, ex- cept on plank, will not be allowed on the pavement for at least seven days after the grout is applied. " The surface of the pavement, when completed, shall be cov- ered with one-half inch of clean, coarse sand of approved quality, which, with all dirt, shall be removed from the pavement and sewer-inlets, by or at the expense of the contractor, at such time, before the final acceptance of the work, as the Street Commis- sioner may direct." The following are extracts from the Philadelphia specifications: " The bricks or blocks must be set vertically on edge in close contact with each other, in straight rows across the street excepting at intersections, which shall be paved at an angle of forty-five de- grees to the lines of the intersecting roadways, and those in adjoin- ing rows so set as to regularly break joints. No bats or broken bricks or blocks can be used except at curbs, where half-bricks or blocks must be used to break joints. The bricks or blocks, having been set, must be rolled with the above-mentioned steam-roller. " After being rolled, the surface of the roadway must be true to grade, and show no continuous lines of unequal settlements pro- duced by the roller. " After being thoroughly rolled, the bricks or blocks shall be grouted with Portland-cement grouting until the joints are filled flush with the surface of the bricks or blocks. The grouting to be composed of one part fresh-ground Portland cement and one part clean bar sand, and mixed with clean water to a consistency that will readily permeate the joints between the bricks." While brick pavements have been in use in this country for only about twenty years, according to the bulletin of the Depart- ment of Labor issued in 1899 there were 18,665,000 square yards in cities having over thirty thousand inhabitants, Philadelphia liaving- the most, with 1,777,123 square yards, Des Moines, la., being next, with 1,509,195 square yards, Columbus, 0., third, with STREET PAVEMENTS AND PAVING MATERIALS. 1,505,015 square yards, Cleveland, 0., with 800,000 square yards, and Louisville, Ky., with 659,733 square yards. The following are the lowest bids received for brick pavements at different places in the spring of 1900: Hampton, Va., May 3 $2.25 Olean, N. Y., April 25 1.80 Norfolk, Va., April 25 2.17 Bellefontaine, O., April 24 1.36 Paterson, N. J., April 16 2.10 Gloversville, N. Y., April 16 1.45 Columbus, Ga 2.00 Rome, N. Y., May 9 1.79% Cohoes, N. Y., May 9 2.47 New Haven, Conn., May 18 1.92 Cambridge, O., June 2 1.15 Binghamton, N. Y 1.95 Glens Falls, N. Y 1.91 Bay City, Mich 1.76 Peoria, 111 1.3234 Bridgeport, Conn 2.19 MATERIAL PER SQUARE YARD OF BRICK PAVEMENT. Size of brick 2y 2 X 4 X 8y 2 inches Size of blocks 3 X4x9 inches Number of brick per square yard 58 Number of blocks 44 Yards of pavement per barrel of Portland cement for joint-filling 45 Gallons paving-cement per square yard 1% ESTIMATED COST. 58 bricks at $14 per M $0.81 Joint-filling Portland cement 10 Joint-filling paving-cement 16 Sand : 05 Labor laying 06 Concrete base 55 Total Portland-cement joints $1.57 Total paving-cement joints $1.63 CHAPTER X. WOOD PAVEMENTS. WITHOUT doubt the crudest and probably the earliest form of a wooden roadway was that which is generally known as the corduroy road. This was constructed roughly by laying logs cut to the desired length across the roadway in close contact with each other. This construction was used at low places in roads across swamps, and, while being very rough and uncomfortable, was fairly serviceable and made many of the roads passable which, without this, could not have been used for a considerable portion of the year. This form of roadway is in use now to a limited extent on wood roads in certain parts of New England. In Alpena, Mich., roadways, and even entire streets, have been graded with sawdust, while in other parts of the State roads have been constructed of charcoal. The method was to pile logs along the road two or three feet high, and burn them in practically the position in which the material was to be used. After the coal was burned, it was raken off and graded down to the required width and depth of the road. This construction gave very good satisfaction, and in 1845 the Commissioner of Patents in his report stated that at the season when the mud in an adjoining road was half-axletree deep, on the coal road there was none at all, and the impress of the feet of horses passing rapidly over it was like that made on hard-washed sand as the surf recedes on the shore of a lake. Russia, however, is reported to have had the first real wooden pavements, as hexagonal blocks are said to have been in use there several hundred years ago. They could not have been used to any great extent or for any great length of time, as no detailed record is obtainable of them. In .London, Eng., the first wooden pavement was laid in 1839. 294 STREET PAVEMENTS AND PAVING MATERIALS. This consisted of hexagonal blocks of fir, some 6 to 8 inches across and 4 to 6 inches deep. They were laid on a foundation of gravel that had been previously compacted. The blocks were either bevelled on the edges or grooved on the face to afford foothold for the horses. These first pavements were not. very successful, but others soon followed. Mr. Hayward, the engineer of the Sewer Commission, stated in a report made in 1874 that, counting the size of blocks as constituting the difference, there must have been more than two dozen different kinds of wood pavements experimented with in the city previous to that time. Another system known as Carey's consisted of blocks 6J to 7-| inches wide, 13 to 15 inches long, and 8 or 9 inches deep, the sides and ends having projecting and re-entering angles, locking the blocks together to prevent unequal settlement. Pavements of this kind were laid in 1841 and 1842. They required renewing every three or four years. The dimensions of the blocks were afterwards modified and finally reduced to a width of 4 inches and a depth of 5 or 6 inches, and the re-entering angles were also discarded. Another system, known as Improved Wood, was first adopted in 1871. On a subgrade a bed of 4 inches of sand was laid, and upon that two layers of inch deal boards, saturated with boiling tar, one layer across the other. The blocks were 3 inches wide, 5 inches deep, and 9 inches long. They also were dipped in tar and laid on the boards with the end joints closed, but the transverse joints were f of an inch wide, the space being maintained by pieces of boards nailed to the foundation and also to the blocks. The joints were filled with gravel, rammed, then a composition of pitch and tar was poured in until the joints were completely filled, when the surface was also covered with tar, gravel, and sharp sand. This foundation was somewhat elastic and maintained the even surface of the pavement as long as it was in shape, but when the pavement became pervious to water it settled and became rough and uneven. This was probably the first use of the tar and gravel joint for pavements of any description. In 1872 a cement-concrete foundation was first used for a wood pavement. The concrete was 4 inches thick and was laid by the Ligno Mineral Co. The blocks were of beech, mineralized by a special process, 3J inches wide, 4J inches deep, and 7J long, with . WOOD PAVEMENTS. 295 the ends cut to an angle of 60. They were laid with the ends inclining in opposite directions in alternate courses. In a few jears, however, this form of block was abandoned for the rectangu- lar, and fir was used instead of beech. The blocks were bedded in Portland cement and laid with joints J inch wide, partly filled with asphalt, and then grouted with mortar. It was thought after a few years' experience that the laying of the blocks directly upon concrete made so rigid a construction that the blocks wore more rapidly under traffic than they otherwise would. There were sev- eral means devised for overcoming this and making the pavemenjt more elastic. The Asphalt Wood Paving Co. laid -J inch of asphalt upon concrete, and formed also the lower part of the joint with the same material, and the upper part with a grout of Portland cement and gravel. In addition to the elasticity, it was claimed that this also gave a perfectly water-tight joint. One objection to this method, however, was that the asphalt softened under blocks when the weather became hot, allowing them to settle un- evenly under traffic, making the pavement generally uneven and consequently causing abnormal wear. Still another system was what was known as Henson's. In this method the blocks were laid close, with a strip of roofing-felt from 1 / 16 to 1 / 8 of an inch thick, cut to the same width as the depth of the blocks, laid between each course. The joint was thus closed as completely as possible, leaving only the actual fabric of the felt, the material support of the blocks saving them from the rapidly destroying action of spreading at the edges. The pro- tection of the wood was further enhanced by a layer of similar felt over the whole surface of the concrete foundation upon which the wooden blocks were cushioned. Another object of laying the felt between the blocks was to take up any longitudinal expansion that might occur on account of the changes of the atmosphere. It was thought that the felt would be thick enough to provide for the expansion of any one course of blocks. The results justified this method, which was somewhat expensive, but the endurance of the blocks was said to be increased from one-half to two-thirds by this freedom from the joining of the blocks- and the mutual support of the edges. In order to provide for the transverse ex- pansion a space of 1 or 1J inches was left along by the curb and 296 STREET PAVEMENTS AND PAVING MATERIALS. fi]led with asphalt, sand, or gravel. In some cases, however, the- row of blocks next to the curb was left open until the greatest amount of expansion had taken place, and then filled in. The kind of wood used in London at that time was generally Swedish deal, and the blocks were generally laid without any chemical treatment, as that was considered of doubtful ad- vantage, as they wore out under traffic rather than failed from decay, and it was not thought that creosoting or similar treat- ment would benefit the wearing qualities. In 1874 Mr. Wm. Haywood made an extensive report to the Commissioners of Sewers of London upon the comparative merits, of wood and asphalt pavements. At that time there were but 12,238 square yards of wood pavement and 30,802 square yards of asphalt, quite a portion of the area previously laid with wood having been replaced with asphalt. In a table which he presented at that time he gave the actual life of wooden pavements that had been laid at different times, since 1841 as varying from five years and five months to nineteen years and one month. The pavement having the longest life, strangely enough, was the first one laid of those in the table. The average cost per square yard during life, including repairs, varied from Is. 5^d. to 3s. 4d., which last pavement had a life of twelve years and three months. He gave the average life of the pave- ments in the three streets of the largest traffic as nine years, and those of the least traffic as eleven years and three months. His conclusions on the whole were more favorable to asphalt than to wood, although the experience with asphalt at that time extended over a period of only five years, but later experience has justified his conclusions. London at the present time is using wood as a paving material practically for the same reasons as those given for Paris because it is less noisy than stone and less slippery than asphalt. On London Bridge, King William Street, blocks wore 2f inches in three years and two months, the traffic being 12,000 vehicles per yard for twelve hours. Mr. Haywood estimated in general that the wear of wooden pavements would be from 2 / 10 to 3 / 10 of an inch per year, under traffic of from 300 to 660 vehicles per yard for twelve hours. WOOD PAVEMENTS. 297 In 1884 the wood pavements in London consisted generally of blocks 3 inches wide by 6 inches deep by 9 inches long, although the dimensions of length and depth varied somewhat. Swedish deal blocks laid on concrete with a cushion-coat of asphalt cost $3.08 per square yard and had an average life of seven years and cost $0.209 annually for repairs. Creosoted blocks, lime joints, cost $2.95 per square yard, with an average life of eight years, and cost $0.204 per year for repairs. Creosoted blocks with asphalt mastic joints cost $3.55 per yard, with an average life of eight years, and cost $0.24 per year for repairs. Pitch-pine blocks cost $2.91 per square yard, with cement joints, with a life of eight or nine years, and were maintained at an expense of $0.088 per square yard per year for repairs. The life of these foreign pave- ments is estimated for the traffic standard of 750 tons per yard of width per day. The cost of repairs varies very much with the method of mak- ing them. A contract was made to keep Piccadilly and part of Kings Road in repair for fifteen years for 3s. per yard per year, when the engineer estimated that its cost would not be more than 2s. The annual cost per square yard for a plain deal, spread over fifteen years, ran Is. 3|d., with a traffic of 279 tons, to 3s. 2d. for improved pitch-pine, with a traffic of 558 tons per yard per day. These figures were made in 1884. In 1893 a portion of the Euston Eoad was paved with wood 63 feet with yellow deal, 62 with Karri, 49 with yellow deal, and 63 with Jarrah. After three years' time the wear was found to be J inch on Jarrah and Karri, and If inches on the deal. From observations taken, the traffic was found to be 575,544 tons per yard of width per anjium. On another por- tion of the same road the wear was inch per annum with a traffic of 411,318 tons. Tottenham Court Road, which was paved with Jarrah blocks, showed only J inch of wear after three years, with greater traffic than Euston Road, and on the Westminster Bridge Road after nearly seven years of wear the Jarrah blocks had worn from 1 1 / 1Q to 1V 8 inches, with a traffic of from 233 to 334 tons per foot of roadway in twelve hours. Table No. 70 gives information relative to hard-wood pave- ments in London. 298 STREET PAVEMENTS AND PAVING MATERIALS. TABLE No. 70. First Cost ... . ^ and Cost of a] Renewal. OS 0) , Parish Kind t* A *" ii 1 or of "^o S a oo ^ * o 3 * Remarks. District. Wood. w oj <-* _. o o o *^3 ^^H IS III ll ^0 a !! l|i ill II |l 0.0} S9 )pE| M U fe > 3 > E^ M K -Jj 8450 2.75 l^TS l>t St. Pancras.. -j Jarrah, Karri, BlueGum i 110000 (2.62 -j to (2.87 [.... -i Hardwood will probably be ex- tensively used in this parish. Wands worth < Jarrah, Karri, -r rt __ V j- 18000 4.12 9 7 I It is not proposed to increase the use of hardwood to any great extent. Kensington . . -j Jarran, Karri j- 3509 Not satisfactory. Hardwood paving has not been sufficiently long in use to judge accurately as to its life under varying conditions, but generally it would appear to last about twelve years. The Council in granting loans of this kind allows a period of ten years for the repayment thereof. For heavy traffic the material is likely to be extensively used, although in several districts Baltic deal is still employed in preference, the average cost of the latter being $1.68 per square yard, and the life from five to eight years. NOTE. The above information concerning hardwood pavements in London was fur- nished the author by the Clerk of the Councif in 1899. London Specifications. Hard-wood Pavements. The surface is to be laid to such, curva- tures, currents, and inclinations as may be needful to enable the water to run off with, the best selected Karri or Jarrah blocks 3" x 9" x 5" deep, sawn true and free from shakes and gum-holes and thoroughly seasoned. The blocks are to be laid close with the grain, vertical, in transverse rows at right angles with the channel- ' WOOD PAVEMENTS. 299 courses; the channel to be formed of three rows of blocks laid parallel with curbs. These channel-courses are to be dipped in a mixture of boiling tar and pitch in the proportion of four to one, and laid close and well in advance of the general work, an expan- sion-joint one inch wide to be left next to the curbs and to be filled in with sand. A mixture of boiling tar and pitch mixed in the proportion of five to one is to be poured over the entire surface of the wood pavement and worked into the interstices between the blocks and cleaned over with squeegees; the surface is then to be floated with cement grout brushed over same until every in- terstice is perfectly filled up, and a coating of clean, sharp Thames sand to be immediately thereafter spread over the surface. Soft-wood Pavements. No tender for blocks less than six inches in depth will be accepted. The blocks are to be of the best yel- low deal and are to be creosoted; the creosoting used is to be of the best creosote oil free from adulteration and heated to a tem- perature of 220 Fahr., and forced into the blocks under a pres- sure of 144 Ibs. to the square inch, the steam generated being first withdrawn from the creosoting-cylinder by means of an air-pump. The creosote as described is to be forced into the blocks as specified to the amount of 12 Ibs. to the cubic foot of timber, which must be ascertained by weighing the wood before putting it into the cylinder and weighing it after it has been taken out. The blocks are to be laid on the concrete foundation with, grain ver- tical, in transverse rows at right angles with the channel-courses, the joints to be close. The channels are to be formed with three courses of blocks laid parallel with the curbs, an expansion-joint at least one inch wide being left next the curbs. The joints of the pavement are to be grouted and filled up solid with a mixture of blue lias lime and sand, and the surface to be dressed with a layer of fine hoggin or gravel. The Surveyor for the Board of Works for the Strand District, London, says (Feb., 1900): " The system of laying wood pavements during the past twenty years has little altered, and the best pavement is considered to be the soft wood [Baltic timber] creosoted and laid with small jo'nts run in with bitumen and grouted with Portland cement and sand,. 300 STREET PAVEMENTS AND PAVING MATERIALS. the whole laid on a Portland-cement concrete substratum. This pavement has given excellent results on steep hills with heavy traffic, where granite setts were found very trying to the horses; the wood, however, has to be kept very clean to give good foot- hold." The average cost of maintaining 114,215 square yards in the parishes of St. Margaret and St. John for the year ending March 25, 1899, was 5.2 cents per square yard. The Surveyor to the Works Committee of Paddington says in a report dated November 4, 1899: " As the traffic now is so enormous, I am of the opinion that very little advantage is gained by having deal blocks creosoted, certainly not to warrant the entire expense; they are, perhaps, more sanitary the first two years, and prevent a certain amount of soaking into them, but you do not in any way add to the life of the wood, for it is perfectly plain that all descriptions of wood paving after four or five years' wear become wavy and rough; then numerous complaints are made that the roadway is bad and worn out, when such is not the fact, there still being three to four inches in depth of good wood/ 7 In a paper read before the Association of Municipal and County Engineers of Great Britain in the summer of 1899, Mr. Edward Buckham, Borough Engineer of Ipswich, gave a descrip- tion of the wood pavements laid in that city, which is a good sam- ple of the way such pavements are laid in England at the present time. The blocks used in the first pavements were of fir, 5 inches deep, and laid on a base of 6 inches of lime concrete. Later, how- ever, the depth of the blocks was reduced to 4J inches, which is the present standard. An experimental length of pavement was laid on a 1-inch bed of gravel without any concrete. The advocates of this plan urged that the gravel base would afford a better drainage than the con- crete and that consequently the blocks would last much longer. Experience, however, showed just the reverse, as the moisture, instead of soaking away, worked up through the gravel and the lower pottion of the blocks decayed. Consequently concrete was adopted as a base for all wood pavements. In the place of the WOOD PAVEMENTS. 301 "6-inch lime base, however, a bed of Portland-cement concrete 3 Inches thick was used. The concrete was mixed in the proportion of one part of Portland cement to one part of sand and four parts of gravel. Upon the concrete was spread a half-inch coat of -cement mortar, mixed with one part of Portland cement and three parts of sand. Upon this the blocks are laid, with ^-inch joints, regulated with a lath between them. The laths are afterwards taken out'and the joints filled with a grout composed of one part of Portland cement and two parts of sand. This is swept into the joints until they are entirely filled. After the cement of the joints is set, fine gravel and coarse sand are sprinkled over the surface, and the travel allowed to come upon it. The particles of stone are crowded into the surface of the blocks by the action of traffic, and the surface is made much harder in consequence. The early pavements were laid with plain wood, but when they came to be renewed creosoted blocks were used. The life of these pavements has been from eight to ten years for plain wood, while the only street paved with the creosoted blocks for any length of time has l>een down thirteen years and will probably last fifteen. It is estimated that creosoting adds 50 per cent to the life of a pavement. Wood pavement was first laid in Glasgow in 1841. Beech tim- ber was used, but instead of being sawed into square logs, round timber was cut into short lengths and placed on end. The wood soon decayed, however, and had to be removed. Wood paving was again tried in 1874, when a portion of one street was paved with yellow-pine blocks. The blocks were laid on a foundation of plank and sand, the joints being filled with cement. This pavement lasted only until 1877, when it was repaved by the same company. In 1881 it again required extensive repairs, and in 1885 the entire pavement was removed and a new system of laying blocks adopted. This pavement was laid on a Portland-cement concrete base, and the joints were filled with bitumen. Side streets have since been paved in this manner, and Australian wood has been used to a cer- tain extent, but stone has always remained the principal paving material. In his report dated October 30, 1897, the Master of Works in Glasgow says: "In regard to the durability of timber as a pav- 302 STREET PAVEMENTS AND PAVING MATERIALS. ing material, the soft varieties, in my opinion,, are not at all suited for our city. For the first two years they wear well enough, but after that time give way rapidly. No doubt carbolizing has a fav- orable effect in preserving to some extent from the effect of mois- ture. So far as regards the durability of the hard timbers, it cannot yet be stated how age will affect them, but, so far as can be judged from the blocks put down in Buchanan Street, J;he extent of the wear of the material since laid down seems to be compara- tively light, while the substance or fibre of the wood does not show any appearance of being shattered as it does in the soft varieties." About 1872 wood pavements were laid in Edinburgh with Bal- tic redwood blocks, but they did not give satisfaction and were taken up after eight or ten years and replaced with stone. The blocks were practically of the same dimensions, and laid in the same manner as those of London. Dublin, Ireland, also has some wood pavements. The blocks are of beech or pine, 3 inches wide, 5 inches deep, and 9 inches long. These blocks are generally creosoted before laying, 10 Ibs. of creosote being used on an average for one cubic foot of wood. The foundation consists of 6 inches of cement concrete, and the joints are partially filled with hot pitch and creosote oil, when the remaining space is filled with a mixture of one part of cement and six parts of gravel, partly to solidify the pavement and partly to protect the pitch and creosote from the action of the sun. This pavement is said to have an average life of ten years. Wood pavements were also laid about the same time in Berlin, some of American cypress, and others of Swedish pine. It is said that in 1883 a pavement laid in 1879 in Oberwall Street had be- come so much damaged that half of it had to be relaid, and the other half the following year. In another street a pavement laid in 1879 was replaced by asphalt in 1884. In 1891 Consul-General Edwards translated from the Berlin Journal as follows: " It is reported that the wood pavement which was laid in many parts of Berlin has worn so badly that the Munici- pal Street Commission has decided to entirely stop using this material for paving purposes. Every sort of wood which has yet been tried has rotted in a comparatively short time, and its upper surface has become so much injured that repairs are hardly^ pos- WOOD PAVEMENTS. 303 sible; also horses fall upon it more easily than upon asphalt pave- ment." Paris did not adopt wood as a paving material until after the earlier improvements in London, and not until it had been de- monstrated about what the pavement was capable of. It was used, not as a cheap or durable material, but as one that would give results that would be much less noisy than stone and much less slippery than asphalt. The decaying properties of the material were not seriously considered, because it was expected, as proved to be the case, that the pavement would be worn out by the severe traffic of the streets before any action of decay would set in. The blocks are about 3^ inches wide by 4J inches high and 6 inches long, and are set directly upon the foundation, the surface of which is made perfectly smooth to receive them. The blocks are set in courses at right angles to the street, with a space of 7 / 16 of an inch between them. Some pavements have been laid with J- and J-inch joints, but this is not the custom. The blocks are kept the proper distance apart by strips of wood 1 to 2 inches broad and about 5 feet long, which are laid obliquely between rows, with the ends projecting above the surface, so that they can be readily withdrawn when half a dozen or more rows have been laid. As soon as they are taken out, hot coal-tar is poured into the joints, so as to fill them to a depth of about 1 inch. The remaining space is filled with a grout made of Portland cement and sand. The surface of the pavement is covered with a thin layer of clean, sharp gravel, so that it may be ground into the surface of the block by traffic, making them harder and more durable. To provide for expansion a joint is left next to the curb about 2 inches wide, which is filled with sand. Norway spruce and fir were used at first, but later pine from the southern part of France and some pitch-pine from Florida have given better results. Still later experiments have been made with the Australian woods, which will be taken up later on. The average life of the pavements has been from eight to nine years upon heavy-traffic streets. The blocks in some instances have been worn down to half of their original depth. The wear on some ten of the principal streets has varied from .0746 to .2908 of an inch per year. The average cost of wood pavements in Paris has been 304 STREET PAVEMENTS AND PAVING MATERIALS. about $3.47 per square metre, and the cost of maintenance 29 cents per square metre per year. In January, 1897, Paris had 1,339,520 square yards of wood pavements. In 1890 the city of Montreal laid a pavement of tamarack blocks made from 3-inch planks of the following dimensions: 3 inches thick, 5 inches wide, and 6 inches deep. The blocks were creosoted and then laid closely together on concrete, and a coating of hot coal-tar and pitch poured over the entire surface until the blocks and joints would absorb no more, when the entire pave- ment was covered with fine roofing-gravel about 1 inch in thick- ness. Tamarack blocks have also been laid in Quebec, being first used there in 1855. The following description of the pavement is taken from a consular report: " The street is excavated to a depth of 2 feet, properly graded, and rolled with a horse-roller. Then a foundation is made of wooden flooring of IJ-inch boards laid longitudinally and crossed at right angles by a second flooring of inch boards so as to con- form more readily to the crown of the roadway. These are laid with J- or f-inch spaces between so that should any surface-water penetrate it will not remain and freeze, but run through and be absorbed by subsoil, after passing through a layer of sand which is strewn over the flooring to the depth of \ inch, thus prevent- ing the blocks coming in contact with the flooring. This double flooring is the means of distributing the weight of passing loads over the extent of area, and also prevents any local settlement of the surface. On the flooring are laid blocks of red tamarack about 12 inches long, as sawn from the log, about 10 or 15 inches in size, and placed on end. In the spaces formed around the blocks small pieces of wood are forced, thus filling in and tighten- ing the mass. The interspaces remaining are then filled with a grout made of sand, cement, and tar, or a mixture of finely-sifted coal-ashes and cement. The surface is evenly rolled and covered with sand, which is allowed to remain until every cavity is filled, when the street is swept clean on the block. " These roads are very durable. Pavements laid thirty-five years ago were recently taken up and the tamarack blocks had not shown any signs of decay, but had worn down to about half their WOOD PAVEMENTS. 305 original length. The surface was as hard as stone, and it is said that there is more resistance to these surfaces practically than stone, because stone, under the influence of water and constant teaming, wears away like a grindstone. The vertical pores of the wooden blocks fill with grit, and the fibres of the wood, like the bristles of a brush, sway to and fro with the traffic of opposite directions without breaking. The blocks are used in their green state, with bark on, which prevents the wood from coming in con- tact with the filling, and the bark lasts for many years, as precau- tion is taken to cut down the trees in the proper season after the sap has all been reduced to fibre and before the spring sap begins its ascension through the pores of the wood. The cost of this pavement is from $1.50 to $1.75 per square yard. In the older part of the city a number of the streets are planked with 3-inch pine deals. These streets are very narrow, the entire width being only from 8 to 12 feet." Any extended writing about the wooden pavements of the United States must of necessity be principally history. While during the last thirty years many millions of yards of wood pave- ments have been laid, at the present time very few cities are lay- ing them to any extent. Just when wood was adopted as a paving material in this coun- try is uncertain. In a report of the Committee on Paving Mate- rials to the Franklin Institute, made in September, 1843, and referred to in the chapter on Stone Pavements, extended mention was made of the wood pavements of Philadelphia. The following quotations from that report will give the standing of wood pave- ments at that time: " The hexagonal hemlock pavement laid some years ago in Chestnut Street, between Fourth and Fifth, cost $2.50 per square yard, and was decayed to such an extent as to require renewal within three years." " The squared-block wooden pavement in Third Street, of Northern spruce, cost about $2.25 per square yard, and after three and one-half years' use the hemlock portion of it is very much decayed and needs renewal, while the heart yellow-pine portion is still in apparently good order, although presenting strong symp- toms of decay. This pavement was laid in September, 1839, and 306 STREET PAVEMENTS AND PAVING MATERIALS. the hemlock will probably require removal in the course of the present year [1843]." " The wooden pavement of white cedar formed of oblique prisms, dowelled together on the Count de Lisle's plan, which was laid in Walnut Street in 1840, cost $1.75 per square yard and is. still in good order." " The cubical hemlock pavement in front of the State House > laid in July, 1839, has so extensively decayed that it has this year been replaced by a cubical pavement of stone laid upon the diagonal plan." " The squared hemlock-block pavement laid in Spruce Street cost about $2 per square yard in November, 1839, and although exposed to very little travel, it now exhibits unequivocal symptoms. of speedy destruction. The hemlock which has been chiefly used in Philadelphia for wooden paving is certainly the most unsuitable timber that could have been employed for such purpose. Never- theless its very rapid decay showed but too clearly the great lia- bility of wood in general to rot under such circumstances." The Gommittee instanced one example of a wooden pavement laid with chemically-treated blocks, which they stated were much decayed at that time, but did not give the date of laying. They add, however, that it was stated that the blocks were somewhat rotten prior to being boiled in the solution of the sulphates of copper and iron. They conclude their deductions as follows: " Finally, in consequence of the slippery nature of their sur- face, their deficiency of durability when of ordinary timber, of their expense in the ultimate, and in view of results of experience as far as they have become known to us, we are reluctantly im- pelled to the conclusion that, though their use may be proper in some detached situations, wooden pavements ought not at this time to be recommended as part of the general system of paving by the city of Philadelphia." They also added that since the report was written they had learned that the authorities of New York had determined to take up their decayed wooden pavements and relay them with stone; also that they had learned with regret that the experience of Bos- ton had been practically the same as that of Philadelphia and New York. WOOD PAVEMENTS. 307 While only history, the above is interesting and important, as it shows the conclusion arrived at at that time to be practically the same, as relates to this particular material, as would be found by a committee of engineers appointed for the same purpose at the present time; and if this conclusion had been accepted by the cities of the country as a whole, a large amount of money would have been saved that has been wasted in experimenting with wood pavements. Probably no city in the country has had as great a variety of pavements laid with this material as the city of Washington. When the Board of Public Works of that city was appointed in 1871, the pavement question was far from settled, and a great many experimenters were in the field. Previous to this date there had been a little over 100,000 square yards of wood pavement laid in Washington and Georgetown. Just what kind this was is not known, but probably quite a proportion of it was the Nicholson, as that was laid in many cities previous to 1870. Subsequent to 1871, and under the authority of the Board of Public Works of the first Board of Commissioners, there were laid in Washington 1,087,738 square yards of wood pavements, under twelve separate patents. These had cost from $2 to $4.20 per square yard. They soon began to decay, and after two or three years began to be replaced, and between 1875 and 1878 over 315,000 square yards had been removed. From this time on they were gradually replaced by other material, until in 1887 about 18,403 yards were left, and the last was removed in 1889. In a re- port to the Engineering Department in 1887, the Commissioner says, when speaking on this subject: " Cedar-block pavements Tised so extensively throughout the Northwest are cheap $1 to $1.30 per square yard but deteriorate rapidly, are objectionable on sanitary grounds, and are anything but smooth for street wear. Creosoted wooden blocks, with a hydraulic-cement foundation, when closely laid, approach nearest to the ideal block pavement. Those in the form of the blocks of the Ker Pavement Co., New York, are a fair example of this class. These are laid with creo- soted wooden blocks, 6x9x3 inches in dimension. The wood iibre is placed vertically to a depth of 6 inches; f-inch joints are left which are filled, 1 inch with hot asphalt and 3 inches with 308 STREET PAVEMENTS AND PA VINO MATERIALS. Portland-cement grouting. The resulting pavement is clean,, noiseless, smooth, and not slippery." Very little information can be obtained concerning the early wood pavements of New York and Boston, but they were in use- in both cities previous to 1839, and the statements of the Com- mittee of the Franklin Institute no doubt expressed the conditions fairly. St. Louis also had some experience with pine and cottonwood pavements, some laid plain and others treated chemically, but with the same results as the other cities mentioned. Between 1860 and 1870 a large amount of wooden pavement was laid in many cities in this country under the Nicholson patent. The best description of this pavement can probably be obtained by quoting from the Brooklyn specifications in a contract made in 1869: " The wooden blocks of the Nicholson pavement are to be of sound white pine or Southern yellow pine, sawed so as to be 3 inches thick and 6 inches long; the blocks for paving the kennel to be sawed to a uniform level so that a channel-way for surface- water will be formed outside the curb-lines. The flooring for blocks, and the pickets to be used between each traverse course of blocks, to be of sound common pine boards, conforming to 1 inch thickness, the whole 2 inches wide and 1 inch thick. The foundation or sand bed which is prepared is to be brought to a proper crown and width to the street edge and then covered with sound common pine boards of the dimension described, paved lengthwise to the line of the street, the ends resting on similar boards laid transversely from curb to curb; the flooring to be well and thoroughly tarred on both sides with hot coal-tar brought to the proper consistency with paving-cement, so as to be tough and fibrous and not brittle when cool. Upon this floor of plank the blocks are to be set on end in parallel courses, transversely with the line of the street; each block before laying to be dipped to half its height in hot coal-tar and paving-cement prepared as de- scribed; each course to be separated by a course of pickets placed on the face of the blocks and to be properly nailed; the space be- tween each course of blocks about the pickets to be filled with clean roofing-gravel and hot coal-tar, and then the cement thor- WOOD PAVEMENTS. 309 oughly mixed and compactly rammed by means of a paver's ram- mer and an iron blade made to fit the interstices or spaces be- tween the blocks; the gravel to be very thoroughly dry and warm,, so as not to chill the tar; the coal-tar in all cases is to be boiled down and so thickened with paving-cement and shape of the stone, and the character and amount of binder used. Keferring to the principle of Macadam that a road will wear out more quickly with a solid than with an elastic foun- dation, it is equally true, and for the same reason, that a macadam road will be consolidated much more quickly if the subgrade is. unyielding. In such cases the action of the roller is direct upon the stone and its work is much more quickly accomplished. This, is often seen when macadam is built in part upon an old roadbed and in part upon an ordinary earth base. The difference in the. amount of rolling required on each is very marked. The character of the stone itself, however, is an important factor, as the softer the stone the quicker it consolidates. Lime- stone, for instance, with a binder of sand or limestojne screenings- will become compacted under less than one-half the amount of rolling required with trap-rock of the same size. The size and shape of the stone also have an important bear- ing upon the labor of consolidation. If the pieces be cubical and of approximately the same size, they wedge closely with each other and become thoroughly compacted; whereas flat stones will continually tip under the roller and be compressed without being bound together. The proper material for binding has been discussed to a con- siderable extent. When it is considered that the object of the binder is only to serve as a cementing material to hold the pieces of stone together, and at the same time make the surface water- tight, it would seem that the material which would serve this pur- pose with the least amount of rolling would be the best, because the cheapest, if the first cost of each should be the same. Sand, limestone screenings, and trap-rock screenings, as well as certain kinds of clay and loam, have all been used in different places and by different engineers as binding material. Ordinarily sand is. the cheapest, as it can generally be found nearer to the work than the stone of which the pavement is composed, but it produces a road that will be very dusty under traffic, as, in order to possess any cementing properties, it must contain a certain amount of loam. Clean, sharp, fine sand will give no binding effects, as the pieces of stone will simply roll in the sand without consolidating. BROKEN-STONE PAVEMENTS. 341 Limestone screenings give excellent results, as they possess in themselves first-class cementing properties and give a hard and smooth surface to the road. If, however, the wearing surface is composed of trap-rock, most engineers wish the binding material to be composed either of trap-rock screenings or a mixture of trap-rock screenings and sand. Mixed in the proportion of 3 of screenings to 2 of sand, good results can be obtained. Trap-rock in itself has very little cementitious value. If the binder be composed entirely of this material, it will require a great amount of rolling and a free use of water, but the result will be a hard, compact, durable road. It will not be so elastic as the limestone, but more durable. It will also require much more roll- ing. The different qualities of limestone vary much in the amount of rolling required. The so called Tomkins Cove limestone, of which a great amount is used in the vicinity of New York City, has a wonderful cementing value and is easily made into a smooth, compact road. It breaks with a very nearly cubical fracture and is an almost ideal stone for a light-traffic road, as it always wears smoothly and presents a pleasing surface to vehicles; but from the very fact that it is easily bound and wears smoothly, it wears more rapidly than the other stones and consequently is not as durable upon heavy-traffic streets. The amount of rolling that has been actually given in the con- struction of different streets varies greatly. Mr. Rockwell, in his work previously referred to, says that, assuming a layer of stone to be 3 inches thick and that a 10- or 12-ton roller is used, it is sufficient, with ordinary limestone, for the roller to pass over the surface 50 times, with granite 50 to 75 times, and with porphyry or trap 90 to 100 times. He adds that the amount required in- creases with the thickness of the layers, but not in proportion to the thickness, and that it is more if the stones are rolled dry than, if they are wet. American engineers, in specifying the amount of rolling re- quired, generally say that the street shall be rolled to the satisfac- tion of the engineer in charge. In France the engineers have attempted to be somewhat more specific and have sought to measure it by the number of ton-miles per square yard; ranging 342 STREET PAVEMENTS AND PAVING MATERIALS. ordinarily from 0.4 to 0.6 ton-mile per yard. This, however, while it takes into account the weight of the roller, does not con- sider its speed; that is, a 10-ton roller passing over a street at the rate of 4 miles an hour would, according to that rule, have twice the efficiency of one moving at the rate of 2 miles per hour, but it is hardly probable that in practice that result would be obtained. At the same time, a roller moving at the rate of 4 miles an hour would probably do much more effective work than one moving at the rate of 2 miles, but there seem to be no specific data whatever to be obtained on this particular point. A standard, however, can- not be set up that will be satisfactory without taking into consid- eration both the speed and weight of the roller. In a piece of work containing about 18,000 square yards of macadam, composed of two courses each 4 inches in thickness, a careful account of the rolling was kept, and the average amount rolled per day was almost exactly 200 square yards, the material being limestone for the first course and trap-rock for the second, with trap-rock screenings for binding material. Wherever, as in this case, the wearing surface and binding material 'are both com- posed of trap-rock, the binder must be practically a flour when the road is being finished. If it be coarse, the stone will not be cemented together; but if thoroughly rolled and wet so that the trap-rock flour is flooded, it will form a paste which, when dried out, will make a smooth, solid, and impervious surface. If the traffic on such a street be light, the pavement will probably pick up slightly under travel at first; but if it be rerolled in a short time after being opened to traffic, it will take its final consolidation and prove very satisfactory. A certain road in Morris County, N". J., was built 12 feet wide of trap-rock, in two courses of 2J and 1J inches in thickness re- spectively, and finished with trap-rock screenings. This was com- pacted at a rate not to exceed 200 square yards per day. In a discussion on road-building before the American Society of Civil Engineers in the latter part of 1898, Mr. E. W. Harrison of Jersey City, N". J., detailed to some extent the construction of the Hudson County Boulevard in New Jersey. This road was theoretically 12 inches deep with an 8-inch telford base and 4 inches of macadam, all of trap-rock. The macadam was made up f BROKEN-STONE PAVEMENTS. 343 *)f two courses of 2^- and 1^-inch stones that would pass a 2^-inch ring, and the surface was finished with trap-rock screenings, ex- cept in one portion where a small amount of clay was used between two layers of stone. Water was used freely and, according to the records kept of the rolling, the road had been gone over from 100 to 115 times. In a paper on the Construction and Maintenance of Roads,, presented to the American Society of Civil Engineers in 1879, Mr. E. P. North mentioned some repairs on the Southern Boule- vard, New York City, where trap-rock broken to pass a 2-inch ring was laid 6 inches thick in one course, and 38.2 hours' rolling was given per 1000 square yards. He says: "Allowing the speed to have been 1 miles per hour, the work done on it amounted to 0.859 ton-mile per square yard and 5.177 ton-miles per cubic yard. 201 trips were made over the surface. The work was done in July and August, and a little less than 0.6 of a cubic foot of water per square yard was used for compacting and puddling. About J screenings were added." In a consular report it is stated that in Dresden a steam-roller weighing from 10,000 to 15,000 kilograms can compact from 80 to 100 cubic yards per day. The amount of binder required to properly consolidate a road can be approximately estimated. Assuming the voids in the stone, as it is ordinarily delivered .on the street, to be 45 per cent, and that under the action of the roller these voids will be reduced one- half, there will still remain 22.5 per cent voids which should be filled by the binder in order to have the road thoroughly solid and compact. This would give, then, approximately 25 per cent of the amount of stones spread loosely on the street to fill voids. Any amount very much in excess of this would seem to indicate that the road was not thoroughly compacted unless an appreciable ^quantity was left upon the surface. In carrying on the rolling the work should be begun at the sides, working towards the centre. Otherwise the street when completed is liable to be more flat than is desired. 344: STREET PAVEMENTS AND PAVING MATERIALS. Crown. The principle governing the amount of crown to give a macadam street is somewhat different from that governing one of stone or asphalt. While the surface of a macadam road should be made solid and impervious to water, it is not always done, and the street should receive as much crown as possible without hav- ing a tendency to drive traffic to the centre of the street. The element of slipperiness which must be considered on the side slope of a hard-surface street can be entirely eliminated on the- macadam. Then, too, the water should be carried from the road- way into the gutter as quickly as possible to prevent any washing of the surface. This, on steep grades, is very important, as, in a. heavy storm, water running over the surface of the macadam will do much more damage than a great amount of traffic, so that, con- trary to the rule for the stone pavement, the crown of steep grades should be greater than that of light ones. The cementitious properties of stone, while very important, have not received much systematic investigation, especially in this country. The Massachusetts Highway Commission, however, has been making experiments to determine this during the past five or six years. The test which was finally adopted is the impact test, to which briquettes made of the dust of the different kinds of stone to be tested are subjected. These briquettes are made of the dust that has passed through a screen with 100 meshes per inch and is obtained either from the abrasion test or by specially powdered stone. The briquettes are circular in section, 0.98 inch in diameter and the same in height. The dust is placed in a metal die of the proper dimension, and mixing with it enough water to moisten the dust (0.24 cubic inch), a closely fitted plunger is inserted on top of the wet dust and sub- jected to a pressure of 1422 pounds per square inch. The weight of the dust varies with the density and compressibility of the stone, generally requiring about 0.9 ounce of dust to make a bri- quette of the above dimensions. Two weeks should be allowed for the briquettes to dry, at the ordinary temperature of a room. A machine for testing these briquettes consists of a hammer weighing 2.2 Ibs., arranged like a hammer on a pile-driver, on two- BROKEN-STONE PAVEMENTS. 345 vertical guides. The hammer is raised by a screw and dropped automatically from any desired height. It falls on the plunger, which rests upon the briquette to be tested. The plunger is bolted to a cross-head and guided by two vertical rods. A small lever carrying a pencil at its free end is connected with the side of the cross-head by a link motion arranged so that it gives a vertical movement to the pencil six times as great as the movement of the cross-head. The pencil is pressed against the drum, and its movement is recorded on a slip of paper fastened thereon. The drum is moved automatically through a small angle at each stroke of the hammer. In this way a record is obtained of the move- ment of the hammer after each blow. The standard fall of the hammer for the test is 0.39 inch, and the blow is repeated until the bond of cementation of the material is destroyed. The final blow is easily ascertained, for, when the hammer falls on the plunger, if the material beneath it can withstand the blow, the plunger rebounds. If not, the plunger stays at the point to which it is driven. The automatic record which is obtained from each briquette is filed for future reference. The number of blows re- quired to break the bond of cementation, as described above, is taken as representing the binding power of each stone, and is so- used in comparing this property in road materials. Another material that is used in the vicinity of New York City for binding and for surface covering is Koa Hook gravel. This material comes from up the Hudson Eiver and is possessed of re- markable cementitious properties. It is found in sizes that are large enough to make the roadbed complete if desired, and when screened to the desired size makes the finest finishing for any macadam road. It has been used to a great extent on the drive- ways of Central Park, Manhattan, and Prospect Park, Brooklyn r and makes a surface that is probably as good as, if not better than, any other finishing material to be obtained in this country. Be- cause it is easily bound and cemented it wears rapidly, and on account of its actual cost and its rapid wear it makes a doubly expensive material. It is a luxury, and for park driveways or bicycle paths it forms a surface that cannot be improved upon. 346 STREET PAVEMENTS AND PAVING MATERIALS. Finishing the Roadway. The amount of fine material that is to be left upon a finished roadway is something upon which engineers differ. If any ap- preciable quantity remains, it receives the action of the traffic and, acting as a cushion, prevents to a certain extent the wear of the stone; but it will be excessively dusty unless sprinkled, and if sprinkled enough to prevent dust, is liable to form mud. On the other hand, if only enough is left to fill the interstices, the action of the traffic comes directly on the stone, and the wear is con- tinual with the amount of traffic. It would seem better, there- lore, to put on a quantity that will actually cover the surface of the road, and not very much more, and when this amount becomes worn down or blown away renew it. In this way a less amount of sprinkling will be required, the wear on the pavement will be reduced, and as little dust as possible result from the traffic. Sprinkling. After the stones have become compressed and the binder has been applied, the road should be constantly sprinkled with water at the time of the rolling, and continued as long as the rolling is in progress. The water is necessary both to wash the binder into the interstices of the stone, and also to aid it in cementing the individual stones together. If the work can be carried on during a mild rain, excellent results will be obtained; but should excessive rain or excessive sprinkling at any time cause the roadbed to be- come soft and yielding, the rolling should be at once stopped until the subgrade has had sufficient time to dry out; for with a soft roadbed the rolling will not only do no good, but it will absolutely do harm, as the earth under the stones will be formed into mud by the action of the stones in contact with it, and the mud will be gradually forced up between the stones, which will cause the road to be loose even after it is dried out and has been rolled. Continual sprinkling, too, shows whether the road has been made water- tight, as the wave which the engineers generally specify shall form in front of the roller before the rolling shall cease will not be pro- duced if the road is porous and allows the water to soak away. I BROKEN-STONE PAVEMENTS. 347 Gutters. On any street that is paved with macadam, gutters of some sort must be provided, as there is probably no action that will cause more disintegration or greater injury to macadam than w r ater flowing over it; so that a runway for the water must be provided of a different material if the street is paved from curb to curb, or, if no curb is set, to provide a shoulder for the gutter. This matter, however, will be taken up in detail in a subsequent chapter. Fig. 18 represents a cross-section of a macadam pavement. FIG. 18. Specifications. The city of Providence, R. I., has a large amount of streets paved with macadam which have given satisfaction. The stone is purchased by the city' and the construction of the pavement carried out by day's labor. The following is taken from the instructions issued by the City Engineer to the foreman having charge of this work: " If the subgrade is too sandy to admit of rolling, cover it with a thin layer of loom or gravel of sufficient thickness to permit rolling. Pave the gutters in a sand bedding, and back them well with coarse-sized broken stone; the paving and backing to be thoroughly rammed. " Put on the roadway a layer of medium-sized broken stone; this layer is to be so placed as to leave the roadway surface true to section and about 2^ inches below finished surface after com- pacting. " Roll with the steam-roller until this layer is shaped to given section and sufficiently firm to admit of driving over without pick- ing up; then put on the roadway a layer of broken stone of sizes varying from one-half to one and one-quarter inches; this layer tc 348 STREET PAVEMENTS AND PAVING MATERIALS. be so placed as to leave the roadway surface true to section. Roll thoroughly with the steam-roller, the road metal to be kept damp while rolling. If open spaces appear in the stones when finishing rolling, put on sufficient fine stones to just fill the open space. The roadway is to be left true to section when finished." Boston, Mass., is another city which also has a large number of macadam streets, many of them in the heart of the city, and some of them with very steep grades. The following is taken from the Boston specifications for macadam with telford base, as far as relates to the construction of the roadway: " SECT. 6. Telford Base. (a) In the excavation for the road- way is to be laid the telford base, made as follows: Sound, hard stones, four inches to ten inches in width, eight inches to twenty inches in length, and not less than ten inches in depth, are to be placed by hand, vertically on their broad edge and lengthwise across the roadway, so as to form a close, firm pavement; the pro- jections of the stones above an even surface are to be broken off by hand and hammer, and used, with other stones of proper size and shape, as wedges, to firmly wedge the stones of the base in proper position, so that the surface of the base will be parallel to the sub- grade for the roadway and eight inches a^bove it; the base is then to be thoroughly rolled with a steam-roller. " SECT. 7. Macadam Surface. (a) Upon the telford base is to be laid the macadam surface, made as follows: Hard, durable broken stones, which will pass through a screen with 2^-inch round holes, and will not pass through a screen with one-inch round holes, and are free from round or other ill-shaped or improper stones, are to be spread over the whole surface of the base, and thor- oughly rolled and packed with a fifteen-ton steam road-roller of approved pattern, until the surface is one-half inch below the finished roadway; the spaces between these stones are then to be filled with fine screenings or binding-gravel applied in at least three layers; each layer thoroughly worked in by wetting and rolling, as aforesaid before the next layer is applied, and during the operation the surface is to be brought, with the broken stone, to the grade and shape of the finished roadway, and smooth, free from waves or other irregularities; only the teaming necessary for distributing the screenings, and for rolling and wetting, is to be f BROKEN-STONE PAVEMENTS. 349 allowed over the broken stone after it is spread on the base, and no teaming is to be allowed over the finished surface for at least three days after it is finished." Extract from Brooklyn Specifications. " (4) Macadam Pavement. On the foundation for the mac- adam pavement prepared as heretofore described and after thor- ough rolling with a ten-ton steam-roller, there shall be spread a layer of trap-rock or limestone of such size that all of it will pass through a circular revolving screen having holes three inches in diameter and be retained by a similar screen with holes two inches in diameter. " If limestone be used it shall be tough, hard, and uniform in color, and must not contain more than thirty per cent of lime. Trap-rock used in the lower or finishing course must be of uni- form quality, free from sap, seams, and other imperfections. It shall be tough and not too brittle, and approximately cubical in form. Any lot of stone containing a noticeable proportion of stones whose length is more than twice their breadth will be re- jected. " This course shall be of such depth as will provide a thick- ness of four inches when consolidated. It shall then be rolled with a steam-roller weighing not less than ten tons, beginning at the sides and rolling towards the centre, until the stone is entirely compacted and does not move under the roller. " After this rolling a second course of trap-rock and of such size that all of it will pass through a circular revolving screen having holes two inches in diameter and be retained by a similar screen having holes three-quarters of an inch in diameter shall fte spread upon the roadway to such depth as will give a thickness of four inches after thorough rolling, and the surface shall con- form exactly with the section shown on the profile plan. During the rolling of this course screenings of trap-rock and selected -coarse sand or gravel shall be spread upon the stone in small quantities and washed in with a sprinkler. The trap-rock screen- ings shall be free from dirt and other foreign matter, and shall vary in size from one-half inch to dust, and about twenty per cent must 350 STREET PAVEMENTS AND PAVING MATERIALS. be what is known as trap-rock dust or flour. The sand must be> coarse and only of such quality as may be approved by the Com- missioner of Highways. Samples of this sand must be submitted to and approved by the said Commissioner before it can be used. " Not less than six parts of the trap-rock screenings to four parts of the sand shall be used as a binding and filling material. The screenings and sand shall be placed upon the roadway only in such quantities as will fill the interstices, but leave no loose material upon the surface. Should an excess of fine material at any time be placed upon the roadway, it shall be swept off by hand- brooms before the work will be allowed to proceed. The rolling of this course shall be continued until the roadway is perfectly solid and compact. " A finishing course consisting of trap-rock screenings and selected sand in the proportions above described shall then be spread over the roadway so that it completely covers the surface. This course shall be rolled and sprinkled simultaneously until it is brought to proper form and grade and is so hardened and bound that it will not pick up under travel." Roads. Although the question of road-building has been discussed to a considerable extent in this country, for many years only the States of Massachusetts, New Jersey, and New York have under- taken road-building systematically and as a work of the State. In. Massachusetts the first Act was passed by the Legislature in 1893. The work was all under the charge of a Highway Commission ap- pointed by the Governor and which has general charge of approxi- mately all road-building under this Act. A certain amount is appropriated by the Legislature each year, being $600,000 in 1896 and $800,000 in 1897, a portion of which is repaid to the State as follows: " One-quarter of any money expended under provision of this Act in any county of the highway, with interest on said one-quar- ter at the rate of 3 per cent per annum, shall be repaid by the said county to the Commonwealth in such reasonable sums and at such m BROKEN-STONE PAVEMENTS. 351 times within six years thereafter as the State Commission, with the approval of the State Auditor, shall determine. Taking into consideration the financial condition of the county, the Treasurer and Receiver-General shall apply all money so repaid to the pro- portion to be expended by such Commission/' Under this law a great many miles of macadam road have been built, and the general scheme for a good road system throughout the State has been adopted and is being carried out as rapidly as time and money will admit. In New Jersey what is known as the " State Aid Road Law " was passed in 1891. This law placed the superintendence of the construction of the roads built under this Act in the hands of the Commissioner of Public Roads. Section 4 provides: " That one-third of the cost of the roads constructed in this State under this Act shall be paid for out of the State Treasury, provided that the amount so paid shall not in any one year ex- ceed the sum of $100,000. If one-third of such cost shall appear, by the statements filed in any one year with the State Commis- sioner of Public Roads, to exceed the said sum of $100,000, then and in such event the said sum of $100,000 shall be apportioned by the Governor and State Commission of Public Roads amongst the counties of the State in proportion to the cost of the roads constructed therein for such year as shown by the statements of costs filed in the office of the State Commissioner of Public Roads. The Governor and said State Commissioner of Public Roads shall, between December 15th and 31st in each year certify to the State Comptroller the amount to be paid to each county for such year, and the State Comptroller shall thereupon draw his. warrants in favor of the respective county collectors for the sums certified as aforesaid upon the State Treasurer, who shall pay the sum out of any moneys in the State treasury not otherwise appro- priated." The report of the Commissioner of Public Roads in New Jer- sey for the year 1897 states that in 1893-94 there were built, pre- sumably under this law, 74.76 miles; in 1895, 46.27 miles; in 1896, 51.38 miles; in 1897, 66.5 miles. The subject of good roads was discussed in New York with such force that it resulted (March 24, 1898) in the passage of a 352 STREET PAVEMENTS AND PAVING MATERIALS. law to provide for the improvement of the public highways. Sec- tion 9 of this law reads: " One-half of the expense of the construction thereof shall be paid by the State Treasurer upon a warrant of the Comptroller issued upon requisition of such engineer out of any specific appro- priations made to carry out the provisions of this Act. And one- half of the expense thereof shall be a county charge in the first instance, and the same shall be paid by the county treasurer of the county in which such highway or section thereof is, upon the requisition of such engineer; but the amount so paid shall be ap- portioned by the board of supervisors, so that if the same has been built upon a resolution of said board without petition, thirty-five per centum of the cost of construction shall be a general county charge, and fifteen per centum shall be a charge upon the town' in which the improved highway or section thereof is located; and if the same has been built upon a resolution of said board after petition as provided in Sec. 2, thirty-five per centum shall be a general county charge, and fifteen per centum shall be assessed upon and paid by the 'Owners of the lands benefited in proportion to the benefits accruing to said owners as determined by the town assessors in the next section hereof." The supervision of this work is placed in the hands of the State Engineer, and the amount of work which can be performed de- pends entirely upon the State appropriation, which the first year was only $50,000, while the petitions for the time that that ap- propriation was available, if granted, would have involved the con- struction of 356 miles of road, which, at the cost of $10,000 per mile, would have meant an expenditure on the part of the State of $1,680,000, when only $50,000 was provided. Road-construction. Although nearly everything that has been said concerning the construction of macadam on city streets could also be said with the same force about macadam roads, there are a great many other things that must be taken into consideration by the engineer when he is about to build a broken-stone road in a suburban or country district. In the one case, the engineer is generally given the limits i BROKEN-SI ONE PA YEMENIS. 353 of the street on which it is proposed to lay the pavement, and his province is to provide specifications that will give the most satis- factory results for that particular street. The question of cost, while entering to a certain extent, is not the ruling principle. On the other hand, in road-construction the engineer is generally given a- certain amount of money which is to be expended to connect two given points with a satisfactory road at the lowest possible expense, and the engineer who can accomplish this with the best results is the best man for the community. In order to solve this question of getting the greatest amount of value from a given sum, the engineer must study the case from all points of view. He must consider the amount and character of travel, whether a road is desired that will provide the most comfort to those using it, or one that shall be the most useful. Both of these points will have a bearing on the selection of the par- ticular material to be used. As has been said pertinently by an engineer who has given this matter a great deal of study, " a road is valuable for its length rather than for its width and thickness," and the engineer who can build the longest satisfactory road for a specified amount has best solved the problem. The most important questions which he will have to decide in this connection will be the width and depth of the road to be improved, and the character of the material to be used. Drainage. However he may decide these questions, he must provide for a good roadbed. This cannot be accomplished without drainage, and in doing so he must take care of both the surface and subsoil water: the latter so as to prevent the moisture from coming up from below and soaking the subgrade, allowing it to freeze solidly in cold weather, and heave and soften the road metal when it thaws in the spring. If the subgrade be kept free from moisture, this will not happen. This is plainly shown* by the action of the frost in all soils that allow the water to flow freely through them. No better instance of it can be seen than in the alluvial soil of Nebraska, where during severe cold spells it is a common occur- 354 STREET PAVEMENTS AND PAVING MATERIALS. ,rence to see cracks in the road from ^ inch to 1 inch in width, caused by the contraction of the earth, yet on account of the lack of moisture no heaving or disturbance is caused when the frost is coming out in the spring. In that section cottages are often built upon the surface of the ground, the only underpinning being sufficient masonry to level up the surface, and no trouble is ever caused by the heaving of the earth when the frost comes out. The surface-water must be taken care of. Otherwise it will settle on -the road and soften it and cause the trouble already described by the alternate freezing and thawing. This principle, too, was well understood by Telford and Macadam, who always provided for drainage, and their practice has always been followed by engineers since their time. This subject has been considered so thoroughly and so intel- ligently by the Chief Engineer of the Massachusetts Highway Com- mission in his instructions to resident engineers that the following quotation is made from his report for the year 1896: Drains. " 82. Where telfording is used, or where ground-water from a side hill may work injury to the road, you will build drains. " 83. If the road passes through a cut, you will place a drain on each side. " 84. If the road is on a side hill, you will place a drain on the up-hill side only. " 85. All drains must be carried to a proper outlet, either to a culvert, to another drain, or through the bank. "86. Where it is necessary to extend a drain to an outlet be- yond the section needing to be drained, you will lay the pipe with cement joints on such extension, and omit the gravel or stone in the trench. "87. Where a pipe is carried through a bank, the outlet must be protected by masonry, as provided in pipe culverts. "88. All pipe must be laid. true to a line and grade, and no pipe is to be laid on a grade of less than three inches in one hun- dred feet. " 89. If, in laying out a drain, you find the trench is likely BROKEN-STONE PAVEMENTS. 355 to exceed five feet in depth below the finished grade, you will immediately report the conditions in writing to the Chief Engineer. " 90. The centre of the pipe in all drains will be placed twelve inches outside of the line of broken stone. "91. When the grade of the finished road is three inches or more to the hundred feet, the bottom of the drain-trench must be three and one-half feet below the finished surface of the road at that part of the cross-section. " 92. The drain-trench will be excavated to a width of twelve inches at the bottom and fifteen inches at the top, and should be excavated only as fast as the drain can be finished. " 93. On the bottom of this trench you will place two inches of gravel or broken stone which will pass through a one-half-inch mesh. " 94. All side-drain pipe will be five-inch salt-glazed vitrified clay pipe, with bell and spigot joint (unless stated to the con- trary in the specifications). " 95. The pipe is to be laid on the grade hereinbefore men- tioned, with open joints and the bell end toward the rising grade. " 96. Gravel or broken stone of the sizes already described will be filled about the pipe and over it to a depth of one foot. This must be carefully tamped about and rammed over the pipe. The remainder of the trench is to be filled with stone which will pass through a three-inch and not through a one-inch mesh. Grea't care must be taken to prevent any sand, silt, or earth from getting into the pipe or the interstices of the stone in the trench. " 97. The subgrade of the road is to have a regular slope to the edge of the drain. "98. The price per linear foot includes the cost of trenching and refilling with gravel or broken stone, the cost of the pipe and laying, as well as all incidental work. "99. No allowance will be made on extra size of pipe in any drain unless the larger pipe has been ordered in writing by the Chief Engineer." Having prepared a base, the next thing w-ill be the determin- ing of the width and depth of the road. In determining upon the width of the road to be improved, the engineer should first decide from the amount of traffic which it is liable to have, 356 STREET PAVEMENTS AND PAVING MATERIALS. whether it is necessary to have the roadway wide enough to accom- modate two lines of travel. If the width for one line is sufficient, it will be a waste of material to make the road any wider than will well accommodate one line of vehicles. Two trucks with 5 feet width of wheel-base and 9 feet width of load meeting can pass on a 16-foot roadway with a clearance of 1 foot, assuming the outer wheels of each to go within 6 inches of the edge of the macadam, so that a width of 16 feet would be ample to allow loaded teams. feet wide to meet and pass without any wheels going off from the macadam. Such a case as this, however, rarely occurs, and if,, as generally happens, the road is in the vicinity of, and tributary to, a large city, the loaded trucks will almost all be going in one direction, when there will be no difficulty in the unloaded ones, turning out and passing outside of the improved portion of the road. So that it would seem that, except in extreme cases, a width of 16 feet would certainly be enough, and generally one of 10 or 12 feet if only one line of traffic is to be provided for. Even then, however, the road should not be too narrow. It should be sufficiently wide to allow traffic considerable lateral motion, so that the wheels will not travel uniformly in the same- lines and thus form ruts; but as the wheel-base of the ordinary trucks does not often exceed 5 feet in width, a roadway 10 or 12 feet wide will be ample in this regard. . The improved portion of the roads as constructed by the Massachusetts Highway Commission is 15 feet wide and upwards. In a report of that Commission for 1898 a table is given showing the width actually travelled on these roads. The average width commonly travelled on forty-six of the roads 15 feet wide was 9 feet 7 inches. It would seem, therefore, that while a width of 10 feet would not have been sufficient to accommodate that traffic,, a width of 12 feet would have been, as any width that is provided and not used is so much loss. The New Jersey roads are many of them only 10 or 12 feet wide, and these have given the best of sat- isfaction. The depth of the road must be determined upon practically on the same principle as that laid down in the construction of street pavements. The foundation must be sufficient to sustain the traffic, and the wearing surface sufficient to bear traffic an BROKEN-STONE PAVEMENTS. 357 economical length of time. It is the practice of some engineers to make the centre of the road thicker than the sides, as the centre naturally takes more traffic than any other portion, and in that way the entire surface of the pavement will be worn out approxi- mately at the same time. In many cases this is good practice. The Massachusetts roads are built with a thickness of 6 inches, after having been thoroughly consolidated and finished to an arbi- trary grade. New Jersey roads vary in thickness from 4 to 1 inches according to the traffic the road is expected to sustain. In Queens County, L. I., the heaviest-traffic roads are built 8 inches thick in the centre and 6 inches on the sides, and for the lighter- traffic roads the thickness is 4 inches spread loose, the contractor being paid per cubic yard for the stone used. Character of the Stone. In determining upon the stone to be used in a country road, the engineer will often find it cheaper to use a poorer grade of stone, which is close at hand, even if it does require more frequent renewal, than to transport a harder and more durable stone from a longer distance. There is one disadvantage, however, in using the ordinary crushed field-stone in highway construction. The different stones vary so much in degree of hardness that the wear of the road is liable to be uneven and cause more frequent renewal and a greater cost of maintenance than if the stone had all come from one ledge and been of uniform material. It must be remembered, however, that certain kinds of con- struction are permissible in country roads that would not be in city streets, for, while not desirable, the amount of dust and mud which would be almost prohibitive in the city can be allowed often on a country road without serious discomfort. So, too, variations in sizes of stone can be allowed, and if the traffic be heavy, larger stone than could be used in a city pavement. The Massachusetts Highway Commission has studied this question very thoroughly and its results are here given: " The State highways are divided as follows, with reference to broken stone (sizes given are in inches): 358 STREET PAVEMENTS AND PAVING MATERIALS. " a. Of trap-rock, bottom course to be 1 J to 2^ inches, top course to be \ to 1^ inches. " b. Of trap-rock, both courses to be 1J to 2% inches. " c. Local stone other than trap, bottom course to be 1^ to 2J inches, top course to be -| to 1J inches. " d. Local stone other than trap, both courses to be ^ to 2^ inches. " e. Bottom course of local stone other than trap, J to 2^ inches; top course of trap-rock, \ to 1J inches. " f. Bottom course of local stone other than trap, J to 2% inches; top course of trap-rock, 1J to 2% inches. " g. All trap-rock. Bottom course to be ^ to 1^ inches, top course to be 1J to 2^ inches. " h. Local stone other than trap, bottom course to be \ to 2% inches, top course to be 1J to 2J inches." These different classes are used on different roads according to the character of the traffic and the stone which is available. It will be noticed that all of the sizes for trap-rock range from 1 J to 2 J, except in one case, and that the local stone ranges from J inch to 2, the idea being that the trap must in almost every case be transported a considerable distance, and consequently none but the best size would be used, while the local stone, being near at hand and easily provided for repairs, is used in as small sizes as J inch, the idea being in this case to utilize the entire product of the crusher, as the finishing course and binder were always formed of the same material as the top course. In this way the most economi- cal results are obtained, and these conclusions certainly show a thorough and conscientious study of the subject. In classes e, /, g, and h it will be noticed that, contrary to the usual custom, the lower course is smaller than the upper. This is where the traffic is heavy and it is not considered desirable to use larger stone than 2J inches, which will sustain traffic better than a smaller size. In order to utilize the entire output of the crusher, it was necessary to make the lower course of the smaller size. This Commission has also made very extensive and scientific tests as to the character of the different kinds of stone which are valuable for use in the vicinity of their roads. BROKEN-STONE PAVEMENTS. 359 The specimen to be tested consists of at least 30 Ibs., to be a fair representation of the stone to be supplied, to contain one piece 3 x 4 inches on each face and to be about 2 inches thick, and the remainder of the stone to be the largest-size stone coming from, the crusher. The tests made have been the abrasion and the cementation tests previously described. The description of the testing-machine for abrasion is taken from the report for the year 1898: " It is constructed entirely of cast iron, which greatly lessens its cost. With this new machine and new methods of obtaining results, two tests a day can be completed, whereas with the old machines it was possible only to complete three in a week. For the .abrasion the machine consists of four cylinders each 7.9 inches in depth. Each of these cylinders is closed at one end and has a tightly fitting cover for the other. They are fastened to the shaft so that the axis of each cylinder is at an angle of 30 with the .axis of rotation on the shaft. The shaft which holds the cylinders is supported by bearings, and at one of its ends is a pulley by which the cylinders are revolved, and at the other a revolution- counter. " The stones employed in making the abrasion test are about the size used in making macadam roads between 2J inches and 1J inches in diameter. In making the test 11 Ibs. of stone of the above dimension and perfectly clean are placed in one of the cyl- inders. The cover is then bolted on and the cylinder rotated at the rate of 2000 revolutions per hour for five hours. Four tests -can be made at once by using four cylinders. At each revolution of the shaft the fragments of stone are thrown twice from one end of the cylinder to the other, which grinds them against one another and against the walls of the cylinder. After 10,000 revo- lutions have been made the machine is stopped, the cylinder opened, and the contents placed on a sieve having -inch meshes. The material that passes through the sieve is put aside for the cementation test. The sieve and remaining fragments of stone are then held under running water until all the adhering dust is washed off. After these remaining fragments have thoroughly dried they are carefully weighed and their weight subtracted from 11 Ibs. original weight of all the stones of the test. The difference 360 STREET PAVEMENTS AND PAVING MATERIALS. obtained is the weight of the detritus under T ^ inch worn off by the test. The percentage of the -inch detritus may be taken, as the coefficient,, or the coefficient adopted by the National School of Eoads and Bridges of France may be used. The latter has been adopted by the Commission and may be obtained by the formula Coefficient of wear = 20 X 7*7 ~yy> where W is the weight in grams of detritus under -^ inch in size obtained from 2.2 Ibs. of stone, used. A table is given showing the results of 221 tests made for abrasion and cementation, and. from the table it is found that in sixteen samples of trap-rock the coefficient of wear ranged from 15.03 to 26.93 with an average of 19.85, and for the cementation value from. 11 to 62, with an average of 29. On forty-four samples- of field-stone the coefficient of wear ranged from 5.43 to 19.19, with an average of 11.70, and the cementation value from 6 to 46, with an average of 17.7. In five samples of granite the coefficient of wear ranged from 8.41 to 17,90, with an average of 13.56, and for cementation value from 5 to 14, with an average of 8.8; while four limestone ranged for coefficient of wear from 8.26 to 17.20, with an average of 11.78, and cementation value from 10 to 23, with an average of 15. In the above instances the cementation value and coefficient of wear are derived from the same stone. The Massachusetts Highway Commission provides that where the subsoil is of impervious clay, telford base shall be used, laid on a gravel foundation. After the top of the telford is formed and the space partly filled up, broken stone is spread over the entire- surface and rolled solidly into the telford. This practice is not sanctioned by many engineers, as they prefer to leave the telford more or less open to provide for drainage; but when, as in this case, it is laid on a gravel base, there can be no objection to it, and it certainly forms a much more solid and compact roadbed than could otherwise be obtained. The method of construction of tha road proper will be the same as that described for the macadam pavement, and the remarks made on construction there can be ap- plied to road construction with full force. BROKEN-STONE PAVEMENTS. 361 Quantity of Material. The amount of stone to be used in any road-construction will depend upon the amount of rolling and consolidation that is given to it. It is generally conceded by the best authorities that ordinary broken stone as used upon the street contains about 45 per cent voids. If we assume that the voids are compacted under the roller to 20 per cent and then filled with binder, the shrinkage caused by the rolling will be the same as the reduction of voids, or 25 per cent. Consequently it will require 10 inches of loose stone spread upon the road to make a thickness of 8 inches when con- solidated, and about 2 inches of binder will be required to fill the voids. As a matter of fact, however, the voids are probably not abso- lutely filled by the binder, as the stone must wear into the base to a certain extent, so that with the above amount of 2 inches sufficient will be left to cover the surface of the road. When the road is finished to an absolute and arbitrary grade, any soft place of the roadbed is liable to increase the amount of stone required, as any loss in the foundation must be made good at the surface. To construct 18,400 square yards of macadam previously re- referred to under " Boiling " required 5400 yards of broken stone and 900 cubic yards of trap-rock screenings. This would give an area of 3.4 square yards of finished surface to 1 cubic yard of loose stone, and J of the amount for binder. This piece of work was conscientiously and carefully done, and these amounts can be con- sidered a fair average of what would be required on similar work. In a discussion on road-making before the American Society of Civil Engineers, previously referred to, Mr. W. C. Foster in speaking on this point said that in some road-construction carried on under his direction the thickness of the loose stone was from 5| to 6 inches on 4-inch work, and from 7J to 7-J inches on 6-,inch work, and adds that the thicknesses were calculated from the actual car measurements and the number of yards laid. These results vary a little from that already given, but the difference is probably no more than would generally occur on roads laid on an earth base. 362 STREET PAVEMENTS AND PAVING MATERIALS. Cost of Construction. The cost of building a macadam road is governed by so many different conditions that the cost in one place cannot be considered as a criterion for that in -another, as the variations are quite great when apparently the conditions are the same. The practice in New Jersey is to have the work done for a contract price per square yard. According to the report for 1897 the average cost of two roads of 10-inch macadam was 56 cents, but the price for one was 70 cents, and for the other 43 cents. The average cost of three roads 8 inches thick was 58 cents, for 6-inch roads 40 cents, and for 4-inch roads 32 cents per square yard: Mr. Henry I. Budd, Eoad Commissioner of New Jersey, stated before the American Society of Civil Engineers that under the first working of the State law roads cost from $7000 to $10,000 per mile. Afterwards they were made somewhat thinner and the cost was reduced to from $6000 to $7000 per mile. In 1897 they cost about $5000 per mile, and in 1898 $4000; while two roads 10 feet wide and 8 inches deep were built for $3000 per mile, and the cost of 90 miles being constructed at that time (1898) was expected to be about $4500 per mile. The rock in many instances was found adjoining the roads themselves, so that the crushers were estab- lished practically on the work, where the haul was reduced to a minimum, and where the small variations in the thickness of the road made no great difference in the cost. In Massachusetts the practice is to purchase the stone by the ton and then have the work carried out by the contractor. The price for stone, as given in the report for 1898, shows a variation in cost for local field-stone of from $1 to $2 per cubic yard, and for trap-rock from $1.20 to $2.20 per cubic yard, and the average cost of the roads built in that State is given at about $5700. In a table given in the latter part of the report for 1898 the cost per standard mile of road 15 feet wide is given for all roads, contracted to date of December 31, 1898, in the different towns of the State. Those for macadam with surfacing and shaping varied from about $3000 to $9174 per standard mile. On the assumption that the roadbed and base have already been BROKEN-STONE PA VEMENT8. 363 prepared, the cost of a macadam road has been estimated as what might be expected under ordinary conditions, and corrections can easily be made for any variations that may occur: 240 cubic yards of stone at $1.50 per yard $360.00 40 cubic yards of binding material at $1.50. ... 60.00 1 foreman at $3 3.00 10 laborers at $1.50 per day . 15.00 2 rollers at $10 per day 20.00 Sprinkling 10.00 Total $468.00 Assuming that one cubic yard of loose stone will lay 3 square yards of pavement 8 inches thick, and that one roller will complete 420 square yards per day, the above material and organization will lay 840 square yards per day at a cost of 56 cents per yard, or mak- ing as the itemized cost per yard: Cents. Stone 43 Binder 7 Labor 2 Sprinkling iy 2 Rolling 2y 2 Total 56 Extracts are here given from the State specifications for road- building from New Jersey and New York, as far as relates to the actual work of road-construction. There are also given the speci- fications of Mr. Jas. Owen of Newark, N. J., who has constructed so many miles of roads in that State. It will be seen that he uses as a binding material a certain amount of cjay, which is contrary to the practice of nearly all of the road-builders in this country. While, in the light of Mr. Owen's results, it would be hardly fair to criticise his work, this practice could hardly be recommended in general, as it is probable that the good results obtained by Mr. Owen have been on account of the peculiar clay in New Jersey and the engineer's. knowledge of the way to use it. 364 STREET PAVEMENTS AND PAVING MATERIALS. New York Specifications. " Kinds and Sizes of Broken Stone. The broken stone shall be of two courses. The bottom course will be four inches thick after rolling and may consist of gneiss, granite, flint, or any of the harder grades of limestone, broken in sizes varying from one and one- quarter inches to two and one-half inches. " The top course will be two inches thick after rolling and will consist of trap-rock, broken in sizes varying from one-half inch to one and one-quarter inches. " Screenings free from all dirt and dust shall be added to fill all interstices that cannot be filled by the rolling or compacting of the other stone. Such screenings will be of the same class of stone as the course into which they are to be rolled, and must be free from earth, sand, loam, vegetable or any foreign matter and contain as small a percentage of dust as is practicable. " Spreading and Rolling. After the earth f oundaton has been completed agreeably to these specifications and has passed the in- spection of the said engineer, a layer of the broken stone of the quality and size herein specified for the bottom course, and of such a depth as will, w'hen rolled, make a course four inches thick, shall be spread evenly over the subgrade; this layer is then to be rolled until the stone is as closely fitted together as practicable, with or without sprinkling as may be directed. Such an amount of screen- ings as can be introduced without separating the stone is to be rolled into each course or layer so as to fill the interstices^ and stone is to be added or removed so as to make the surface practi- cally of the proper height. " The next overlying course will be of stone as hereinbefore described for said course, and is to be spread at such a depth that the surface, when rolled, will be at the proper grade irrespective of the finishing material; this layer is then to be rolled, and dur- ing the process of rolling, if necessary, similar stone is to be added or removed from time to time, so that when the rolling ceases the roadway is truly surfaced to the required grade and crown. Dur- ing the process of rolling the upper course of stone, screenings shall be introduced dry, in such manner and quantity that the BROKEN- STONE PAVEMENTS. 365 Interstices shall be entirely and completely filled with screenings; and after the upper layer has become sufficiently compact, there shall be spread upon the surface sufficient screenings, as specified, to produce a smooth, true surface when rolled. The rolling is to -continue until, by sufficient use of water, a wave is produced be- fore the wheel of the roller. The surface of any course shall be scratched, if required, so as to obtain the proper bond with that next overlying. " The rolling of the stone and screenings shall be done with a steam-roller weighing not less than ten tons. " Each layer of the broken stone and the screenings shall be well and thoroughly rolled, and the rolling on each layer shall be prosecuted until, in the opinion of the Engineer, such course shall have been completed as hereinbefore specified, and until each layer and the finished surface shall be rolled and finished to his entire satisfaction and approval. " The amount of rolling shall not be less than 100 times over cations that all water encountered should be taken care of by the contractor at his own expense, if water should be discovered in other parts of the work the contractor would be entitled to the extra cost of doing the work on account of the existence of the water. This would be a matter very hard for the engineer in charge of the work to adjudicate, and would almost always result in litigation. When a contractor prepares to bid upon any piece of work, he expects to, and it only seems fair that he should, take such steps as will give him all the necessary information about the character of the material to be encountered as will enable him to put in an intelligent and reasonable bid. Lf the corporation re- quiring the work to be done furnishes all information as to where and how it is to be constructed, that would seem to be sufficient in most cases. In some special instances, however, where the work was of a particularly difficult nature, requiring a great deal of pre- liminary work before any knowledge of the material could be obtained, it might be advisable and economical to all concerned for the corporation to furnish all necessary information. It must be understood, of course, that if the contractor makes a large out- lay in a preliminary investigation, it will be added to his bid, and the party for whom the work is to be done will in the end pay for it. Quantity of Work to be Done. With the plans and specifications for street work, and in fact for nearly all kinds of work, should go a statement giving, as nearly as can be determined in advance, the exact quantity of work to be performed. By this is not meant the amount of mate- rial required in any construction, but simply the aggregate quan- tities of the different parts of the work. This should be obtained from a careful survey, and a price called for in the bidding blanks for each item on the list. This method shows to the contractor the amount of work required of him, and it also enables the engineer to determine with certainty the lowest bidder, and to ascertain whether the bid is made out intelligently with a proper price for each item. Lump Sum Bids. Some people, however, advocate the letting of contracts for a lump sum, on the ground that the contractor in looking over the 380 STREET PAVEMENTS AND PAVING MATERIALS. work will be apt to omit or forget something and consequently put in a bid for a less amount than he otherwise would. That is, the intention is to get, if possible, a certain amount of work done for nothing. This is neither honest nor expedient, because, as was said before, where a contractor loses on one part of the work he is very apt to make good his loss on another. It is exceedingly difficult, however close and intelligent the inspection, to watch the contractor at all times, and if by the use of sharp practice on the part of the corporation or individual he has been led into making a contract by which he will lose money, it is not to be won- dered at that he will attempt to recoup himself at the expense of some portion of the work. No individual or corporation can afford to have work done for nothing. Good work is worth a good price, and the information placed before the bidder should be of such nature that he can plainly know everything that will be required of him. Indeterminate Quantities. It often happens that the quantity of certain parts of the work cannot be determined in advance. If, however, a price is asked for each one of these items, a quantity must be fixed in order to deter- mine the lowest bidder in canvassing the bids; but if this quantity be too small or too great, this difference, when the bidding is close, may make a difference in the lowest bid. Then, too, when the quantities are small, the contractors are apt to specify a large price, as the sum total will not much change the entire bid. To avoid trouble of this kind, especially where work is not to be paid for by assessment, a good plan is for the engineer to determine upon and fix in the specifications a price that will be paid per unit for each of these indeterminate quantities. It has been decided by legal authorities that, even if work were to be paid by special assess- ment and as the result of competitive bidding, where it was not possible to determine accurately the amount of different kinds of work called for, it would be legal to specify their price in ad- vance, the theory being that there would be less liability to in- justice with a fair price specified than to allow the contractors to bid on an uncertainty. Extra Work. Another thing that always causes much trouble in all contracts is extra work and claims for extra work. While it often seems im- f PLANS AND SPECIFICATIONS. 381 possible to provide beforehand for everything that will be re- quired, in most cases it can be done, and certainly always should be if possible. Contractors should always be discouraged from making any application for extras. Specifications generally re- quire that all extra work shall be done only upon a written order of the proper authorities. If no price is fixed in a contract for such extras, a written order should always contain the amount to be allowed for the extra work done, so that when a bill for the same is presented by the contractors there will be no question of the amount of remuneration. Where the contractor and the engineer are in harmony, extras are very often ordered in by, and performed under, verbal orders, even when this clause is inserted in the specifications. The im- portance, however, of observing such clause, and in fact all clauses of the specifications, by the contractor as well as the city officials, was seen in carrying out a sewer contract in which the specifica- tions provided that no sheeting left in the work should be paid for unless it was so ordered by a written order from the Board of Public Works. In this particular case sheeting was ordered in verbally by the Engineer of the Board, and a return made of the same by the inspector in charge. When the final estimate was given the Board of Public Works refused to pay for the sheeting, and, in a suit which was brought to settle other disputed points of the same contract, the court decided that the city was not liable for the sheeting because it had not been left in in accordance with the written order as provided by the specifications, although it was ordered in verbally and deemed necessary by the Chief Engineer of the Board. Alternative Bids. It is sometimes the practice in receiving bids to allow con- tractors to make alternative propositions, that is, a proposition to do the work for a certain price if performed with a certain kind of material in a certain manner, or for another price if performed with other material in a certain other manner. This is objectionable, as it makes it possible to have two lowest bidders, depending on the way the work is to be carried out. It also leaves it possible for the contract to be awarded to one bidder at one price, and after the 'Contract is let to substitute the alternative proposition at its price, and so have the work performed eventually by a contractor who 382 STREET PAVEMENTS AND PAVING MATERIALS. was not the lowest bidder. Wherever possible, the conditions should be so studied beforehand as to be able to decide which material is better for any particular work, and call for bids accordingly. Sometimes, however, the question of deciding is an economical one, and the matter of cost is an important element in the decision. In that event, it is permissible to receive alternative bids, but as a rule the practice should be discouraged. General Instructions. Attached to the specifications should be a sheet giving general instructions to bidders, telling what formal requirements are called for and what steps it is necessary to take in order that their bid should be received and be in proper form. In order to facilitate the canvass of bids and to insure uniformity in bidding, blanks should be made out for each bidder, giving estimated quantities upon which bids will be canvassed. In the instructions to the bidder should be inserted a clause telling at what hour all bids are to be in. This time should not be varied from, and as a rule all bids should be opened at the time specified for their reception. It often occurs, if bids are allowed to remain a certain time after they have been received, that one or possibly more may come in between the time of reception and opening. If these should all be high bids, no trouble would occur; but if the lowest bid should happen to be one that was received after" the time advertised for the bids to be in, complications would be very apt to arise. Con- tractors who have complied strictly with all the requirements com- plain, and rightly too, if these requirements are not lived up to by the city, and it seems no more than just that if the city or corporation calling for bids require the contractor to live up to these requirements, it should do so itself. Certified Check. On every work of any magnitude it is customary to have a. certified check accompany each bid, in order to indemnify the city from any loss or damage if for any reason the successful bidder should not be able to enter into the contract. It is also sometimes required, in addition to this certified check, that the bidder give the names of the persons or surety company who will sign all bonds for the performance of the work in case the contract should be awarded to the bidder. It does not seem necessary, and in some cases it works hardship, to require both certified check and the PLANS AND SPECIFICATIONS. 383 names of the bondsmen. A certified check should certainly be sufficient to indemnify the city for any damage, and in case satis- factory bondsmen could not be provided the city would have re- course to the check. The amount of this check should be as small as possible and yet. give the city adequate security. It is generally customary to re- quire a percentage of the amount of the bid. This, perhaps, for a general rule, is as good as any; although in some contracts where it is necessary for the work to be done as soon as possible, the time lost in readvertising would be of considerable value, while in others the delay would be no material damage, so that it would probably be more satisfactory to establish an arbitrary sum for each contract. Five per cent of the amount of the bid is the ordinary re- quirement. Error in Bid. It is often found or claimed, while the bid is being read, that an error has been made in making out same, and an application made for an opportunity to make a correction. To allow this would be to establish a dangerous precedent. The contractor must take certain chances. He takes work by contract so that he may make more than ordinary day's wages, and if an error should occur so that he is compelled to do a certain amount of work for less than the market price, or bids so high on some item by mistake that he loses his contract, he must abide by the letter of the bid,, trusting for his loss in one case to be made up by gain in another. A variation from this rule will open the way for endless trouble,, and for claims of errors where none exist. Withdrawal of Bid. No changes or withdrawals should be permitted after any bids, are opened. If, however, the contractor should tender his bid some hours in advance of the final closing, and wish to make changes in the same, there should be no objection to his having it returned prior to the expiration of the time for the receiving of the bids. Indorsement of Bids. In order that there may be no question as to whose bid any package may contain, all envelopes should be indorsed with the name of the bidder and the work which he proposes to carry out. 384 STREET PAVEMENTS AND PAVING MATERIALS. Bond. Before any contract is executed by the city, a bond should be signed by responsible parties guaranteeing that the contractor will carry out the provisions of the contract. The amount of this bond must be determined by the nature of the work. It should be a fixed amount, decided much upon the same principle as that gov- erning the amount of the certified check, that is, the damage that the city is liable to be put to from the failure or delay in the carry- ing out of the work. It should be large enough to provide for any loss of time on account of the necessity of cancelling the con- tract and readvertising the work, and also to make good any dif- ference in the cost from the original contract price and what was actually required to perform the work. The former must be deter- mined by the location and character of the work, and the latter by the prices for the different items in the contract. Time for Completion. All contracts contain the provision that the work shall be done by a specified time or in a specified number of working days, and generally provide for a penalty to be paid by the contractor for each day in excess of the stated time. It is necessary to insert such a provision in all contracts. Otherwise it would be possible for a contractor to begin a piece of work and, after it was partially completed, to leave it for some other and more profitable contract, or to dilly-dally on the street to the inconvenience and detriment of the public at large. The engineer, however, in determining the time should be sufficiently liberal to enable the contractor to finish within the specified time if he uses reasonable diligence. Penalty. The question of penalty, however, is one that should be taken up with a great deal of care. It must be considered that it requires two parties to make a contract, and if a penalty is required for any excess of time employed, and no bonus given if the work is per- formed sooner than the specified time, it is questionable whether such penalty could be enforced. It would seem, too, if the work was of such a nature that the time of completion was important, that it would be just to both parties to require a penalty if the time limit were exceeded, and to pay a bonus if the work were com- pleted inside of the specified time. This is the general practice on large and very important contracts. If, however, the contractor PLANS AND SPECIFICATIONS. 385 has bid a certain price for agreeing to finish within a certain time, which possibly is higher than that of the bidder who proposes to do it in a longer time, the question is different, for in the latter case the contractor receives extra compensation for early com- pletion, and if he exceeds the limit, a penalty should and un- doubtedly could be enforced. Maintenance. In specifications for street improvements of any kind it is gen- erally provided that the work shall be maintained and kept in repair for a certain length of time. When asphalt pavements were first introduced in this country it was necessary for the con- tractor to agree to keep the pavement in repair for five years in order to have any city adopt them. The material was new and no -city would run the risk of paying the price asked for an unknown and uncertain pavement; so that when the contracts were made they contained a clause binding the contractor to keep them in good repair for five years, whereby the city in each case was cer- tain of a good pavement for a definite period. The conditions, however, at the present time are very different. Asphalt pave- ments are well established and have come to stay, and the ques- tion of guarantee, as to its length and exact meaning, is very important. Payments. The method of paying for the original pavement and of keep- ing it in repair varies in different cities. In some places the original cost is paid by special assessment, and the repairs by a gen- eral tax. In such cases as this the guarantee period must be carefully determined upon. It has been adjudicated in the courts many times, and the established limit has been that a guarantee period of five years can be enforced in a contract for an asphalt pavement the payment for which is derived by general assessment, but that it cannot when the cost of repairs or repaving is defrayed by general tax. In New York City all contracts for asphalt pave- ment requiring payment by special assessment are made with a guarantee period of five years, while in those where the expense is borne by a general tax the guarantee is made ten and sometimes fifteen, years. Guarantee. While the original asphalt pavements were laid with the inten- 386 STREET PAVEMENTS AND PAVING MATERIALS. tion of being kept and maintained, without any expense to the city, for a period of five years, it is questionable, unless specifically defined, just what is meant by the terms " guarantee " and " main- tenance." Cities as a rule consider that it means that they shall be at no expense whatever for the care of these pavements during the guarantee period. The contractors, however, maintain that their guarantee covers simply that the work shall be done in a proper manner and with good materials; that if any unforeseen circumstances arise, causing damage to the pavement, they are not compelled to repair it without special compensation. Fires, settlements of sewers, causing breaks in the pavement, are all cases in point. Specifications, therefore, should clearly define just what is intended, and it would seem that when a guarantee is given that the work will be done properly and good materials furnished, nothing more could be required or expected of the contractor, on the principle laid down before, that the contractor should know- all of the conditions under which he bids, and that the city should, pay the cost of any unforeseen damage to the pavement. As to how long the guarantee shall run is also a mooted ques- tion. For some reason five years has seemed to be taken as the- unit for asphalt pavement, although in many cases contracts have- been made with ten and fifteen years 7 guarantee. Sometimes the- cost of guarantee has been included in the original price per square yard. In other cases the contract has provided for the original price per square yard, the pavement to be maintained without ex- pense for five years, and then for an additional five years for a specified price per year. In 1898 a contract for laying asphalt pavement was made in Minneapolis, Minn., for a certain price per square yard, with a ten years' guarantee, and the additional price of 10 cents per yard per year for a second period of ten years. Newark, N. J., has asked for bids for a five-year guarantee, and has specified an additional price of 5 cents per yard per year for an additional ten years. Other cities have called for stipulated prices per yard for a certain guarantee period, with the option of making an additional contract for a specified price per yard per year. Previous to consolidation New York City required asphalt pave- ments paid for by the general public to be maintained for fifteen PLANS AND SPECIFICATIONS. 387 years. The specifications provided that on the completion of the work TO per cent of the contract price should be paid to the con- tractor. Of the remaining 30 per cent, one-tenth was to be paid each year, beginning five years from the date of final acceptance. The present contracts call for a guarantee of ten years with a re- serve of 20 per cent, one-fifth of which shall be paid each year, beginning, as above, five years from date of completion of the work. The old city of Brooklyn required a five-year guarantee on all asphalt pavement, but made payment in full upon the completion of the work, relying upon the bond wholly for the carrying out of the maintenance portion of the contract. Omaha, Neb., also re- quired five years' maintenance, but reserved 15 per cent of the contract price until the end of the guarantee period. The contrac- tor was, however, allowed to purchase city bonds and deposit them with the city treasurer, in lieu of this reserve, and thus draw in- terest upon the amount withheld. Upon granite, brick, or other pavement, where it can soon be determined whether there are any faults in either material or con- struction, no long-time guarantee is necessary. At the end of nine months any defects from the above causes will have been developed and can be repaired, and there would be no good reason for requir- ing any reserve fund to be longer held. When the work is completed the entire amount should be paid less ten or fifteen cents per yard of pavement, according to the character of the work. When the guarantee period has expired and any necessary repairs have been made, the above amount should be paid the contractor. The specifications for stone pavements of Cleveland, 0., require a guarantee that the pavement be kept in good condition for five years, and provide that any paving-stones at the end, or during the term of said guarantee, which, in the opinion of the Director of Public Works or Chief Engineer, show a greater loss than 10 per cent of their original or specified depth, shall be taken up by or at the expense of the contractor, and good and acceptable ma- terial substituted therefor, and the pavement placed in good and satisfactory condition. To provide for the enforcement of the above 2 cents per square foot is retained for each and every square foot of pavement, flag- 388 STREET PAVEMENTS AND PAVING MATERIALS. ging, and cross-walk. The amount retained from the final estimate is deposited in the city's name in some bank designated by the city, and all interest and dividends accruing become the property of the contractor if the provisions of the contract have been satisfactorily carried out. Details of Work. To just what extent it is proper for any city or corporation to specify the details with which work shall be carried on when it is to be maintained for a specified time is often questioned. The contractor claims that he is under contract to maintain pavement for a certain length of time, and it is for his best interest to do the work in a proper manner, and that he should be allowed to do it according to his judgment. The engineer, on the other hand,, argues that the contractor knew the specifications and requirements before he bid, and if he could not get good results from those speci- fications, he should either have protested before putting in his bid or making his contract, or else refused to have anything to do with the work. The contention of the contractor is hardly valid, for even if he enter into a contract to maintain the pavement for a term of five years or fifteen years, he is also under contract to leave it in good condition at the end of that time, and it is for the city's interest to have it left in such condition at the end of the guarantee period that it will last for as long a time as possible afterwards, with little repair. So that there seems to be no question but that the city has, the right to enforce all the requirements of the specifications. This assumes, however, that the city will, as in fact it must, employ a competent engineer to make the specifications so that no impossible requirements are inserted. Unbalanced Bids. Another source of great trouble to the engineer in the carrying out of contracts is unbalanced bids. When different items are given for the amount of work to be performed and there is any uncertainty as to these quantities, the shrewd contractor often goes over the work in advance of the bidding, in order to verify these quantities and make his own estimate as to the probability of their being correct. If he thinks they are liable to be varied in the carrying out of the work, he will make a high price for one item and a low price for another, so that he will be the lowest bidder on PLANS AND SPECIFICATIONS. 389 the quantities as given, but be higher on the work as completed. While this would do no harm on contracts where the quantities are not changed, it often does cause great trouble if for any reason it is desired to make any changes. It also permits the engineer, if in collusion with the contractor, to change some items, reducing those of small price and increasing those of the higher price, to the great benefit of the contractor. It is not always easy to determine what is an unbalanced bid. Often the conditions may be such that one contractor may be able to do a piece of work, or one portion of it, for a price which would seem to make it an unbalanced bid, when it was strictly legitimate. In some way he might have an advantage over another contractor. But there are cases where it is plain to be seen on the face of it that the bid is unbalanced. In every case of this kind the bid should be thrown out without hesitation, provision having been made in the specifications for such action. One of the best, if not the best, of the methods of overcoming unbalanced bids is that adopted by Jersey City, N. J. It it customary there for the En- gineer, after carefully studying the market, to establish a price for each item that is called for in the work, and require all bidders to bid a certain percentage above or below this standard, and apply this percentage to every item of the schedule. This absolutely prevents any trouble from unbalanced bids, and certainly seems fair to both city and contractor. Combinations among Contractors. Another plan of protecting the city, not from unbalanced bids, but from contractors making combinations among themselves, has been adopted in Toronto, Can. There the City Engineer himself puts in a bid to the city, agreeing to do the work for what he con- siders a fair and reasonable price. If he should be the lowest bid- der, the work Is awarded to him and carried out by the city by day's labor under the Engineer's supervision. The contractors, knowing this is to be done, realize that there is no opportunity for obtaining an extravagant price, and in consequence generally bid with the expectation of a reasonable profit. Plans. The plans for the paving of a street should show first the limits of the contract on the main and on all of the cross streets. It should show the location of all the cross-walks to be laid, and all 390 STREET PAVEMENTS AND PAVING MATERIALS. special work called for. It should show the cross-sections of the finished pavements,, and give every detail of construction. The profile should show the amount of excavation and embankment for the entire length of the street. It should show the existing surfaces of both property lines and. also the centre, so that the contractor would know in exactly what parts the excavation and embankment were located,, and thus be able to determine the dis- tance that the earth would be hauled. The plans should also show the quantities of each kind of work required. After the contract has been awarded, the contractor should sign the plans, which should become a part of the contract, as should also the specifications. The foregoing remarks on the Plans and Specifications are general, although mainly referring to pavement-construction. The specifications which follow are suggested for general use for the original improvement of streets that have never been graded. These specifications are made up mainly of the plans and specifications for New York City, modified according to the ideas of the author and the result of twenty years' experience in munici- pal work. They embody what is considered the best practice of the principal cities of the country. The section relating to Medina-sandstone pavements has been taken almost entirely from the specifications of Cleveland, 0., and that for asphalt blocks from those of the Hastings Pavement Co. While these specifications are general, they are supposed to be so made up that they can be applied and used in any city in the country by making the changes required by local conditions and laws. Some modifications would be required for repaving work, but for the actual work of pavement-construction they are recom- mended for general use. Notice to Bidders. Bidders must satisfy themselves, by personal examination of the location of the proposed work and by such other means as they may prefer, as to the accuracy of the estimated quantities, and shall not, at any time after the submission of a bid, dispute or complain of such statement or estimate of the Engineer, nor assert that there was any misunderstanding in regard to the nature or amount of the work. The quantities given herewith are sup- PLANS AND SPECIFICATIONS. 391 posed to be accurate, and are estimated by the City Engineer for the purpose of determining the lowest bidder, but final payment will be made on measurements made of work actually performed. Each bidder must deposit with the Commissioner of Highways, at least four days before making his bid, samples of the materials he intends to use, according to the character of the work called for, as follows: 1. A specimen of refined asphalt, with a certificate stating where the material was mined. 2. A specimen of the asphaltic cement, with a statement of the formula to be used in the composition of the mixture for the wearing surface. 3. A sample of not less than four pounds of the paving mix- ture as it will be laid upon the street. 4. Not less than twelve bricks which are proposed to be used. 5. A sample block of either stone or asphalt. 6. Additional specimens of all kinds must be furnished as often as may be required during the progress of the work. No bid will be received or considered unless the deposits of material referred to above are made with the City Engineer within the time prescribed. Any bid accompanied by samples which do not come up to the standard required by these specifications will be regarded as in- formal. No proposals will be received or considered unless accompanied by either a certified check drawn to the order of the Comptroller, or of money equal to five per cent of the amount of the security required for the faithful performance of the work. Such check or money must not be inclosed in the sealed envelope contain- ing the proposal, but must be handed to the officer or clerk who has charge of the proposal-box, and no proposal can be de- posited in said box until such check or money has been examined and found to be correct. All such deposits, except those of suc^ cessful bidders, will be returned to the persons making the same after the contract is awarded. If the successful bidder shall re- fuse or neglect, within five days after notice that the contract has been awarded to him, to execute the same, the amount of the deposit made by him shall be forfeited to and retained by the city .. . . as liquidated damages for such neglect or refusal; but if he 392 STREET PAVEMENTS AND PAVING MATERIALS. shall execute his contract within the time aforesaid, the amount of his deposit shall be returned to him. SPECIFICATIONS FOR GRADING AND PAVING WITH PAVEMENT ON A CONCRETE FOUNDATION. (1) The work to he done shall consist of grading the entire width of the street, setting curbstones and heading-stones if re- quired, laying and relaying the cross-walks where so required, and laying - - pavement on a - - foundation on the roadway of- - Street from Street to - -Street. (2) All the materials furnished, and all the work done, which,, in the opinion of the City Engineer, shall not be in accordance- with the specifications shall be immediately removed, and other materials furnished, and work done, that shall be in accordance therewith. Before any materials are placed upon the street the City En- gineer shall approve of the quality and finish of samples of the: same which shall be furnished at his office. These shall include- the samples referred to on page , and also a sample of the paving-blocks to be used in the work. (3) The work under this specification is to be prosecuted at and from as many different points in such part or parts of the streets on the line of the work as the City Engineer may, from time to time, determine, and at each of said points inspectors may be placed on the day designated for the commencement of the work. (4) The right to construct any sewer or sewers, receiving-basins or culverts, or to build up or adjust any manholes, or to reset or renew any frames and heads for sewer or subway manholes, or for water or gas stop-cocks, or to lay gas- or water-pipes, or to con- struct necessary appurtenances in connection therewith in said street or avenue, or to grant permits for house-connections with sewers, or with water- or gas-pipes, or for any other underground or subway construction, or to alter and relay railroad-track, at any time prior to the laying of the new pavement over the line of the same, is expressly reserved by said City Engineer; and said City Engineer reserves the right of suspending the work on said pave- ment, on any part of the line of said street or avenue at any timer PLANS AND SPECIFICATIONS. 393 during the construction of the same, for the purposes above stated, without any compensation to the Contractor for such suspension other than extending the time for completing the work as much as it may, in the opinion of the said City Engineer, ha* T-K been de- layed by such suspension; and the said Contractor shall ***t inter- fere with or place any impediment in the way of any person or persons who may be engaged in the construction of such sewer or sewers, or in making connections therewith, or doing other work above specified, or in the construction of any receiving-basins or culverts. (5) In case there shall be at the time stipulated for the com- mencement of the work any earth, rubbish, or other incumbrance (building material for which a proper permit has been issued is not herein included) on the line of the work, and Hot required by the Department, the same is to be removed at the expense of the Con- tractor. (6) Grading. The entire width of the street is to be regulated and graded, in accordance with the grade as shown upon the profile or map on file in the office of the City Engineer. The carriageway and sidewalks to be shaped as per cross-section shown on the plans. That portion of the street which is above the grade-lines to be excavated, and such parts as are now below the grade-lines to be filled in, in the manner hereinafter provided, and the surplus earth not used for filling to be removed from the street. If, owing to the unfitness of the present material for a foundation, it is con- sidered necessary by the Engineer to remove it to a greater depth and substitute other material, such removal and refilling will be paid for by the cubic yard at the prices bid for excavation and em- bankment, except as hereinafter specified. The slopes in excavation shall be one and a quarter horizontal to one vertical. The embankment shall be formed of good, wholesome earth, sand, gravel, or clean ashes. No house-ashes containing garbage or rubbish, no vegetable matter or debris of any kind will be al- lowed. The slopes of the embankment shall be one and a half hori- zontal to one vertical. No allowance will be made the Contractor in any case for settle- ment, shrinkage, or additional slopes. If any material shall be encountered in excavating which is considered especially adapted 394 8TEEET PAVEMENTS AND PAVING MATERIALS. for the foundation, it shall be placed aside when so directed, and used at the proper time for that purpose. The embankment is to be made from material- excavated on the street where there is a sufficient quantity of such material. Where the amount of excavation is less than the amount of embankment the Contractor must supply the deficient material. The price bid for grading shall be applied to whichever amount shall be in ex- cess. (7) Grading Sidewalks. All stone shall be dug out of the side- walks, to three inches below the finished grade thereof, and the holes filled to the grade of the sidewalks with clean sand or gravel. The sidewalks to have a slope of six inches from the line of the street to the curb. (8) Preparation of Roadbed. The carriageway shall be thor- oughly rolled with a ten-ton steam-roller, all soft spots having been excavated and filled with gravel or other suitable material until the whole roadway has been thoroughly consolidated and finished to the following depths below the surface of the completed pavement: For asphalt nine inches; for asphalt block seven and one-half inches: for granite on sand twelve inches; for granite on concrete fifteen inches; for Medina sandstone on concrete thirteen and one half inches; and for vitrified brick eleven inches. (9) Cross-walks. The cross-walks shall consist of three courses of stone. The stone to be of the same quality as the blocks, the side and ends to be squared and free from all winds, seams, and other imperfections; each stone to be not less than four feet nor more than six feet in length, one and one-half feet wide, and not less than six nor more than eight inches thick throughout, to be dressed to an even face on top, sides, and end. The ends of the stones are to be cut to such curves, when necessary, as may be directed, and all to form close and even joints from top to bottom when laid. Where cross-walks are at right angles to the line of travel all joints shall be cut with a bevel of six inches. The Contractor shall lay one row of stone blocks between the courses of bridge-stones. The cross-walk stones must be firmly bedded on the same foun- dation as the pavement, and set true to line and grade. The courses must be so laid that the transverse joints will be broken by a lap of at least one foot. PLANS AND SPECIFICATIONS. 395 Any old cross-walks now on the line of the street or adjacent fo the new pavement shall be relaid by the Contractor, when so directed, in the manner above described, without any charge there- for. (10) Curbstones. The new curb shall be of the best quality of , hard, sound, and free from seams or any other imperfec- tions. It shall be fifteen inches in depth, not less than five inches in thickness, and the back shall be free from projections of more than two inches; while it shall have a uniform thickness of five inches for at least three inches from the top. The bottom bed shall be roughly squared. It shall be in length of not less than three and a half feet nor more than eight feet. The top shall be axed to a smooth surface with a bevel of one- half inch in five inches, and the face shall be out of wind and be brought to a surface which shall in no place vary more than a quarter of an inch from a true plane. Special care must be taken to cut the joints square with the face, and they shall be close for the full thickness for not less than six inches from the top; while the face shall have close joints for its entire depth. All curb, unless otherwise directed, shall be set in a bed of concrete six inches in depth and shall have a backing of concrete six inches in thickness, extending to within four inches of the top, as shown in detail plan. The concrete bed shall be laid immediately before the curb is set, and the backing put in place as soon as set, and as much of the concrete foundation for the pavement as may be directed, which shall not be less than one foot; the object being to obtain a uniform and well-bonded mass of concrete behind, under, and in front of the curb. When set, the corners of the top shall be in a straight line and the face a plane surface. Should the concrete in front of the curb have set before that on the remainder of the street shall have been laid, the surface shall be carefully cleaned and thoroughly wet before any fresh concrete is placed against it. Whenever curb is set for stone pavements or without concrete, it shall be eighteen inches deep, but in all other respects shall con- form to. the above conditions. (11) Heading-stones. When asphalt or brick pavement joins the pavement of another kind or an unpaved street, heading-stones, 396 STREET PAVEMENTS AND PAVING MATERIALS. not less than five inches thick and not less than twelve inches in depth and in lengths of not less than two feet, shall be set between the new and the old pavement. They shall be set upon and firmly bedded in a bed of concrete six inches in depth. These heading-stones may be of bluestone, granite, or other approved stone, and the grade of the adjacent surface, whether paved or un- paved, shall be adjusted to that of the new pavement without extra charge therefor. The heading-stones will be paid for as pave- ment, and must be included in the price bid therefor. (12) Concrete. All concrete used in the work shall be made of one measure of natural hydraulic cement, measured in the original package, two measures of sand, and four and one-half measures of broken stone, If the mixing is done by hand, the cement and sand shall be thoroughly mixed dry and then made Into mortar with as little water as possible, after which the stone, which shall have been previously drenched with water, shall be added, and the mass thoroughly mixed until all of the stones shall have become coated with mortar, when it shall be promptly placed into position and rammed until the water flushes to the surface. The mixing shall be done upon suitable wooden platforms as may Le directed by the Engineer. If a concrete-mixing machine be used, the cement and sand shall be mixed as above, and precaution must be taken to insure the proper proportion of each of the materials, so that the re- sultant mixture shall be uniform in quality. The cement, sand, and stone must be placed upon board platforms and kept free from dirt. Great care must be exercised to make the surface of the con- crete exactly parallel to and - - inches below the finished pave- ment. The concrete shall be protected from the weather until set. Should the concrete at any time oe considered by the En- gineer to be poorly mixed or not to be setting properly, such por- tion shall be taken up and replaced with satisfactory material. The cement used shall be equal to the best quality of freshly ground American cement. It shall be delivered on the street at least forty-eight hours before the mixing of concrete is commenced, and no cement shall be used until it shall have been tested, and ac- cepted by the Engineer. No exact requirement will be made for the tensile strength of PLANS AND SPECIFICATIONS. 397 the cement. But when the samples are submitted, the City En- gineer will test them according to such a standard as may be adopted for each particular brand; the object being to ascertain and maintain the normal strength of each kind of cement offered and accepted. The sand shall be good, clean, coarse, sharp sand, free from loam or dirt. The stone shall be equal in quality to good limestone, entirely free from dust and dirt, and of such size that it will pass through a screen having holes three inches in diameter, and be retained by a screen having holes one inch in diameter and as evenly graded between the two extremes as possible. No concrete can be used which shall have been mixed more than thirty minutes. No carting or wheeling will be allowed on the con- crete until it is sufficiently set. When connection is to be made with any section which shall have set or partially set, the edge of such section must be thoroughly cleaned and wet so as to insure a .good bond with the new work. Asphalt Pavement. (13) a. The pavement proper shall consist of a binder course one inch in thickness and a wearing surface two inches thick. 6. Binder. The binder course shall be composed of suitable clean broken stone passing a one-and-one-quarter-inch screen, not more than five per cent of which shall pass a No. 10 screen. The stone will be heated in suitable appliances, not higher than 300 F. It is then to be thoroughly mixed by machinery with asphaltic cement made as per sample submitted and as is acceptable for surface cement, at 300 to 325 F., in proportion of about 6 to 7 pints of cement to 1 cubic foot of stone. The mixture will be so made that the resulting binder has life and gloss without an excess of cement. Should it appear dull from overheating or lack of cement, it will be rejected. No cement composed of mixtures of asphalt and tar will be allowed. While hot the binder will be hauled upon the work, spread upon the concrete, to such a thickness that when compacted it will be at no place less than one inch in thickness, and im- mediately rammed and rolled until it shall receive its required com- pression. 398 STREET PAVEMENTS AND PAVING MATERIALS. Should the resulting course not show a proper bond., it shall be immediately removed and replaced by the Contractor,, or, should he fail to do so in twenty-four hours after written notice from the City Engineer, it shall be removed and the cost charged against any moneys which are or may become due him from the city. After compacting,, the upper surface of the binder shall be exactly parallel with the wearing surface of the pavement to be laid. c. Wearing Surface. Upon this foundation must be laid the wearing surface, or pavement proper, the basis of which must be asphaltic cement unmixed with any of the products of coal-tar. The standard paving mixture for the wearing surface shall be composed of: 1. Refined asphalt; 2. Heavy petroleum oil, or other approved flux; 3. Sharp, clean sand; 4. Finely powdered mineral matter. d. Asphalt. The refined asphalt for use in the manufacture of the asphaltic cement for the preparation of the standard paving mixture shall be obtained from the crude natural material, and shall be in all respects satisfactory to the City Engineer. To accomplish this, the crude asphalt must be specially refined, and brought to a uniform standard of purity, quality, and specific gravity; and, after having been so refined, it shall contain not less than fifty-five per cent of bitumen soluble in carbon bisulphide, of which bitumen at least sixty-eight per cent shall be soluble in Pennsylvania petroleum naphtha of a specific gravity of 72 Beaume (boiling-points 80 to 90 centigrade); it shall soften at from 189 to 192 Fahrenheit, and flow at from 200 to 210 Fahrenheit; it shall volatilize from 2J to 3 per cent of oil in ten hours at a temperature of 400 Fahrenheit; it shall have a specific gravity of not more than 1.38, and shall be free from all manner and form of adulteration, After the evaporation of the solvent, the pure bituminous matter soluble in carbon bisulphide shall be adhesive, malleable, and ductile at temperatures ranging from 70 F'ahren- heit to its liquefying-point. It shall soften at 168 Fahrenheit and flow at 180 Fahrenheit. The above properties shall be considered standard, but any asphalt with properties differing somewhat from the above can be used if satisfactory to the City Engineer. e. Heavy Petroleum Oil The oil used in the manufacture of f ' PLANS AND SPECIFICATIONS. 390 asphaltic cement as hereinafter described shall be a petroleum from which the lighter oils have been removed by distillation with- out cracking until the oil has a specific gravity of from 18 to 22 Beaume and the following properties: 1. Flash-test not less than 300 F. (The flash-test shall be taken in a New York State closed oil-tester.) 2. Fire-test not less than 350 F. 3. No appreciable amount of light oils or matter volatile under 250 F. 4. Distillate at 400 F. for thirty hours, less than 10 per cent. (The distillate shall be made with about 50 grams of oil in a small glass retort provided with a thermometer and packed in asbestos.) 5. It shall be free from foreign matter and coke. /. Asphaltic Cement. Asphaltic cement, manufactured from refined asphalt and heavy petroleum oil or other approved flux > agreeing in composition and properties with those described in the foregoing paragraph, shall be prepared in the following manner: To the melted asphalt at a temperature of not over 325 Fahrenheit, the oil, after having been heated to at least 250 Fahrenheit, is to be added in suitable proportions to produce an asphaltic cement equal to the submitted sample. As soon as the flux has begun to be added, suitable agitation, by means of an air-blast or other acceptable appliances, shall commence and be continued until a homogeneous cement is produced. The appli- ances for agitation shall be such as to accomplish this in ten hours, during which time the temperature shall be kept at from 250 to 350 Fahrenheit, and no higher. If the cement then ap- pears homogeneous and free from lumps and inequalities, it may be used. Should it not prove homogeneous, such deficiencies as may exist shall be corrected by the addition of hot flux or melted asphalt in the necessary proportions. Asphaltic cement shall ful- fil tests enumerated under heavy petroleum oil. When asphalt cement is kept in storage, it must be thoroughly agitated when used, as must all dipping-kettles while in use. Samples of asphaltic cement and of the flux shall be supplied to the City Engineer or his approved agents when required, in suitable tin boxes and cans, and he shall have access to all branches of the work at any time. Should ft be determined by experience that the asphaltic cement 400 STREET PAVEMENTS AND PAVING MATERIALS, as submitted does not produce a satisfactory pavement, its propor- tions may be changed with the approval of the City Engineer. g. Finely Powdered Mineral Matter. The powdered mineral matter must be of such degree of fineness that the whole of it will pass a 30-mesh screen,, and at least seventy-five per cent a 100- mesh screen. h. Sand. The sand in use shall be hard-grained, moderately sharp and clean, not containing more than one per cent of hydro- silicate of aluminum. On sifting, the whole of it shall pass a 10- mesh screen, twenty per cent shall pass an 80-mesh screen, and at least seven per cent shall pass a 100-mesh screen. The material complying with the above specifications shall be mixed in the following proportions by weight: Asphaltic cement from 15 to 18 Sand from 80 to 67 Pulverized mineral matter from 5 to 15 The proportions of materials used will depend upon the charac- ter, and will be determined by the City Engineer; but the per- centage of bitumen flux in any paving mixture soluble in carbon bisulphide shall not be less than nine nor more than twelve per cent. If the proportions of the mixture are varied in any manner from those specified, the mixture will be condemned, its use will not be permitted, and, if already placed on the street, it must be removed and replaced by proper materials at the expense of the Contractor. The sand and asphaltic cement shall be heated separately to about 300 Fahrenheit. The pulverized carbonate of lime, granite, or quartz while cold shall be mixed with the hot sand in the re- quired proportions, and then mixed with the asphaltic cement, at the required temperature and in the proper proportion, in a suit- able apparatus, so as to effect a thoroughly homogeneous mixture. Sand-boxes and asphalt gauges must be weighed in the presence of inspectors as often as may be desired. i. Laying the Pavement. The pavement mixture prepared in the manner thus indicated must be brought to the ground in carts at a temperature of not less than 250 Fahrenheit; and if the temperature of the air is less than 50 Fahrenheit, the Contractor PLANS AND SPECIFICATIONS. 401 must prepare suitable apparatus in order to maintain the proper temperature of the mixture. It shall then be thoroughly spread by means of hot iron rakes in such manner as to give a uniform and regular grade, to such depth that after having received its ultimate compression it will have a net thickness of two inches. The surface will then be compressed by hand-rollers, after which a small amount of hydraulic cement will be swept over it, and it will then be thoroughly compressed by a steam-roller weigh- ing not less than five tons, followed -by one of not less than ten tons, the rolling being continued as long as it makes any impres- sion on the surface. In order to make the gutters, which are consolidated but little by traffic, entirely impervious to water, a width of twelve inches next the curb must be coated with hot asphaltic cement and smoothed with hot smoothing-irons, which operations must com- pletely saturate the pavement to a depth of one inch with an excess of asphalt. This must immediately follow the rolling before the surface has become cold or covered with any extraneous matter. j. Liquid Asphalt. Should a liquid asphalt or other softening agent be used as a substitute for a portion or for all of the petro- leum residuum in making the asphaltic cement, such liquid asphalt or other softening agent must fulfil the tests enumerated in para- graph e for heavy petroleum oil; it must contain not less than ninety-five per cent of bitumen, and its acidity in terms of caustic potash must not exceed two per cent. The softening agent shall be such that when added to the refined asphalt in proper propor- tion it will produce an asphaltic cement having essentially the same consistency and the same properties as that made of refined asphalt and heavy petroleum oil, as hereinbefore described, or properties that shall be considered and accepted by the City Engineer as equivalent or superior thereto. k. Rock Asphalt. Should any of the rock asphalts be used, the material shall be a natural bituminous limestone and shall be pre- pared and laid in the following manner: The lumps of rock, after being mixed in the proper propor- tions, shall be finely crushed and pulverized, and the powder shall then be passed through a 20-mesh sieve. Nothing whatever shall 402 STREET PAVEMENTS AND PAVING MATERIALS. be added to or taken from the powder obtained by grinding the bituminous rock. The powder shall contain from 9 to 12 per cent of natural bitumen. This powder shall be heated in a suitable apparatus to 200 or 250 Fahrenheit, and must be brought to the ground at a tempera- ture of not less than 180 F., in carts made for the purpose, and then carefully spread on the concrete foundation prepared as speci- fied for refined asphalt pavement, to such a depth that after having received its ultimate compression it will have a thickness of 2^ inches. The surface shall be rendered perfectly even by tamping,, smoothing, and rolling with heated appliances of approved design. After the completion of the work, and whenever the City Engineer shall so direct, the surface of the pavement must be sprinkled with clean, sharp sand. If rock asphalts are used, the gutters need not be saturated with asphaltic cement. /. General Requirement. The asphalt for use under this con- tract shall be one agreeing in composition and properties with that described in a foregoing section, or one having composition and properties which shall be considered and accepted as equivalent or superior thereto by the. City Engineer; but whatever may be the character of the asphalt used in the manner of manipulation and laying, the pavement obtained must be the same as or equal to that resulting from the use of the standard mixture described in Section h and shall conform to the following general requirements: The pavement when laid shall not be so soft as to be unfit for travel on the hottest days of summer, nor so hard as to disin- tegrate from the effects of frost. When laid it shall be equal in consistency, surface, durability, and other* properties to the stand- ard pavement made as hereinbefore described. It shall contain no water, nor an appreciable amount of light oils, nor matter volatile at a temperature under 250 Fahrenheit. It shall yield, when ex- tracted with bisulphide of carbon and after evaporation of the solvent, not less than nine nor more than twelve per cent of sub- stance which shall have the same properties as the substance ex- tracted in the same way from the above-mentioned pavement made from refined asphalt, heavy petroleum residuum, and mineral matter in accordance with the foregoing specification, or proper- ties which shall be considered and accepted as equivalent or su- PLANS AND SPECIFICATIONS. 403 perior thereto by the City Engineer. The extracted bituminous matter shall have a fire-test of 350 Fahrenheit, and shall not possess any marked acidity to caustic potash. The mineral matter which it contains shall be the same or equivalent in nature and condition to that prescribed in the preparation of the standard pavement hereinbefore described (at least fifteen per cent of which mineral matter shall pass a 100-mesh (per lineal inch) sieve), except in case of the use of rock asphalt, when the mineral matter shall be that which occurs in the natural, product. m. Xo asphalt shall be laid during wet. weather, nor unless the surface of the concrete is perfectly dry. All materials as well as the plant and methods of manufacture shall be subject at all times to the inspection and approval of the City Engineer or of such engineer and inspectors as may be in charge of the work. Granite Pavement. (14) a. Description of Paving -blocks. Stone blocks shall be of granite of a durable, sound, and uniform quality, each stone measuring not less than eight inches nor more than twelve inches in length, not less than three and one-half nor more than four and one-half inches in width, and not less than seven nor more than eight inches in depth, and the stone shall be of the same quality as to hardness, color, and grain. No outcrop, soft, brittle, or laminated stone will be accepted. Around car-tracks and man- holes the blocks may be of other dimensions than above described when specially so directed by the Chief Engineer. No stone shall l>e laid between the rails of any car-track that is more than ten Inches long. The stone from each quarry shall be piled and laid together in separate sections of the work, and in no case shall the stones from different quarries be mixed, or stone of different widths be laid in the same course except on curves. The blocks are to be rectangular on the tops and sides, uni- form in thickness, split and dressed so as to form, when laid, close joints, with fair and true surfaces, free from bunches. All blocks measuring in thickness from three and one-half to four inches, inclusive, shall be considered as one class, and all blocks four up to and including those four and one-half inches 404 STREET PAVEMENTS AND PAVING MATERIALS. thick shall be considered as in another class. These two classes must be kept apart, and brought upon and laid in separate sections, of the work. b. Laying the Pavement. On the roadbed, prepared as herein- before specified, or on the concrete foundation as designated, shall be laid a bed of clean, coarse dry sand, to such depth as may be necessary to bring the surface of the pavement, when thoroughly rammed, to the proper grade. On this sand bed and to the grade and crown specified, shall be laid the stone blocks at right angles to the line of the street or at such other angle as may be directed. ' Each course of blocks shall be laid straight and regularly, with the longitudinal or end joints broken by a lap of at least three inches. All joints shall be close joints, except that when gravel filling is used, the joints between courses shall not be more than three- fourths of one inch in width. c. Sand Foundation. When the blocks are laid on a sand foundation they shall be covered to within three courses of the pavers with sharp, coarse sand, free from stones, which shall be raked until all the joints become filled therewith. Each course of blocks shall then, with proper tools, be set up perpendicular to the surface of the street, and all blocks not uniform in width or properly laid shall be taken out and proper ones set in their places;, the blocks shall then be thoroughly rammed to a firm, unyielding- bed of uniform surface to conform to the grade and crown of street. No ramming shall be done within twenty feet of the work that is being laid. Whenever the pavement for as great a distance as may be deemed desirable shall have been constructed as above described, it shall be covered with a good and sufficient second coat of clean, sharp sand, and shall immediately thereafter be thor- oughly rammed until the work is made solid and secure; and so- on until the whole of the work embraced in this agreement shall have been well and faithfully completed in accordance with these specifications. This second coating of sand shall be left upon the pavement for thirty days. At the end of that time the sand shall be removed and the pavement cleaned at the expense of the Contractor. PLANS AND SPECIFICATIONS. 405 The Contractor shall sprinkle with water the sand placed upon the pavement during the time it is left thereon, as may be directed by the Engineer in charge, and shall then comply with the ordi- nances relating to the dropping of dirt, sand, etc., in the city streets; and if any dirt, sand, etc., shall be dropped upon the city streets, said streets may be cleaned up as often as may be deemed necessary by the Commissioner, and the expense of the same may be deducted from any sum otherwise due the Contractor. d. Concrete Foundation. When the pavement is laid on a concrete foundation, the blocks, laid as above, shall be covered with clean, hard, dry, and hot gravel which shall have been artificially heated and dried in proper appliances placed in close proximity ta the work, and brushed in until all the joints are filled within three inches of the top. The gravel must be entirely free from sand or dirt and must have passed through a sieve of five-eighths-inch mesh and been re- tained by one of three-eighths-inch mesh. The blocks must then be thoroughly rammed, and the ram- ming shall be repeated until they are brought to an unyielding bearing with a uniform surface, true to the given grade and crown. No additional gravel shall be added after the ramming before the first pouring of the cement. The boiling paving-cement, heated to a temperature of 300 F. and of the composition hereinafter described, shall then be poured into the joints, while the gravel is still hot, until the same are filled flush with the top of the gravel. Dry, hot gravel of proper size, which shall have been heated in pans especially provided for the purpose, shall then be poured into the joints until they are filled, when the hot paving-cement shall be again poured into the joints until they are filled and re- main full. The appliances for heating paving-cement shall be sufficient in number and of such efficiency as will permit the pourers to closely follow the back-rammers. All joints of the finally rammed pave- ment shall be filled with paving-cement as noted above, before the cessation of work for the day or any other cause. No horse, cart, or vehicle of any description shall be permitted to stand on or pass over the pavement until the joints have been 406 STREET PAVEMENTS AND PAVING MATERIALS. finally poured with cement as above, and the same has had time to harden. e. Paving-cement. The paving-cement to be used in filling the joints shall be composed of twenty parts of refined Trinidad or other approved asphalt and three parts of residuum oil mixed with one hundred parts of coal-tar pitch, which shall be obtained from the direct distillation of coal-tar,, and shall be the residuum there- from,, and shall be such as is ordinarily known as number four at the manufactory; all proportions to be determined by weight. It shall be delivered in lots at least one week before being used, that the necessary analysis and examination may be made. The Contractor must also furnish a certificate from the manufacturer or refiner that the materials are of the kind specified. The coal- tar, oil, and asphalt must be heated and mixed in the proportions named by weight on the work as needed for immediate use. Medina Sandstone Pavement. (15) a. Blocks. Paving-blocks shall consist of the best quality of Medina sandstone, and shall not be less than three and one- fourth nor more than five inches thick, and not less than six nor more than six and one-half inches deep, and from eight to thirteen inches long. The stones to have parallel sides and ends, with right- angle joints; all roughness and points of stones to be broken off, so that when set in place they shall have tight joints for a dis- tance of at least three and one-half inches from the top down; the area of the bottom of any stone to be not less than three-fourths of the area of the top. Top to have a smooth, even surface. Paving-blocks, as here referred to, shall be understood to mean Hocks of Medina sandstone, prepared in a proper manner for dressed-block paving, by nicking and breaking the stones from larger blocks, as is done at the quarries where such blocks are usually prepared, and not made by redressing or selecting from common stone paving material. Stones to be flat and even at bottom, which shall be parallel with the top surface, with both top and bottom of stones at right angles to at least one end of the stone, so as to set squarely and firmly in place without the use of a paving-hammer. - PLANS AND SPECIFICATIONS. 407 ~b. All paving-blocks, before being placed upon the streets where they are to be laid, shall be properly assorted, and all stones of greater or less dimensions than above specified shall be rejected; all acceptable stones shall be gauged as to thickness into at least three classifications, and each class marked with oil paint in the following order, to wit: Class No. 1 to embrace all blocks from three and one-fourth to and including three and one-half inches in thickness; Class No. 2 to embrace all blocks from three and three-fourths to and in- cluding four and one-fourth inches in thickness; Class No. 3 to embrace blocks from four and one-half to and including five inches in thickness. Blocks in Class No. 1 to. be marked with red paint; those in Class No. 2 with blue paint; and those in Class No. 3 with black paint. Each and every block shall receive its proper mark, in order clearly to designate to which class the same be- longs. All such assorting, gauging, and marking shall be done under the direction and to the satisfaction of the City Engineer before being delivered upon the street; but it is distinctly understood that such inspection shall not prevent such further inspection and assorting as the City Engineer may deem necessary to obtain good work. The Contractor shall at all times furnish at his own expense a sufficient number, in the judgment of the City Engineer, of careful and proper persons to properly do such classifying and marking of the blocks as here specified. c. After the blocks have been classified and marked as above specified, they shall be kept separate and distinct in hauling to and piling upon the street; each wagon loaded with a particular class of blocks shall be unloaded only at places on the street where stones of a like class are to be unloaded; blocks of the different classes are to be placed on different sides of the street or in separate piles upon the same side, as the City Engineer shall di- rect. In wheeling or placing the blocks in the beds for laying, the same care shall be observed not to injure the surface of any bed or foundation after the same has been properly prepared for the blocks, and also to keep the classes distinct and separate from 408 STREET PAVEMENTS AND PAVING MATERIALS. each other; but if from any cause the classes of blocks have be- come mixed up in the beds before laying, or are so found after being placed in the pavement, or the surface of the foundation disturbed, the City Engineer may order all such blocks removed from the beds or work, and reasserted, gauged, and marked, and the foundation repaired, as heretofore specified, and at the expense of the Contractor. It is understood that all such classifying and marking of the blocks is for the purpose of assuring more uniformity in the construction of the pavement, and by placing before the paver blocks of more uniform depth and thickness to aid in the progress of his work. d. Stones are to be set tight together, in uniform rows, break- ing joints at least two inches and resting against stones, in the same and the adjoining course; those of the same class and thick- ness to be placed together in the same row; rows of similar thick- ness to be placed together, and set directly upon a cushion of one inch of sand spread upon the concrete foundation; no gravel or sand to be placed on top or between the stones as laid. Stones to be set perpendicular to the grade, and in right-angle courses across, the street, except at street and alley intersections, where the courses are to be set at such angle as the City Engineer shall direct. Upon the completion of every fourth course or oftener, as the City En- gineer may direct, the course shall be driven together and straight- ened by the use of a heavy sledge, and wood block placed against the stones as directed. The pavement shall always be laid by the paver standing upon the upper side of his work; the pavement shall then be subjected to the following treatment by the Con- tractor, and in such order and to such extent as the City Engineer shall direct: e. The paving to be thoroughly rammed by courses, three or more times, besides the first and final surfacing, as may be di- rected, with a paver's rammer, weighing not less than eighty pounds, no iron of any kind being allowed on its lower face to come in contact with the paving. The pavement to be surfaced up by using a long straight-edge, and when complete to conform to the true grade and crown of the roadway, as directed by the Chief Engineer. The first ramming of the pavement, if so ordered, to> PLANS AND SPECIFIC A2 IONS. 409 "be done by one man, using a hand-rammer of not more than 36 square inches face and weighing from 25 to 40 pounds, as ordered. Such first ramming to be done only on such paving-stones as may project above the general surface of the other stones, for the pur- pose of evening the surface of the pavement as first laid before using the heavy rammer, as heretofore specified. The pavement after having been laid and rammed, or during the process of ramming, shall be thoroughly rolled to the satisfaction of the City Engineer. f. The pavement after ramming and rolling, or during the process, as may be directed, shall be thoroughly sprinkled or washed with water, to insure the thorough bedding of the blocks, leaving the joints or spaces between the stones their full depth. The spaces or joints shall then be filled with a concrete com- position, consisting of either paving-cement, Portland cement, Murphy grout-filling, or such other composition as the Director of Public Works and Chief Engineer may order or approve, and shall be mixed and used in the following manner: If paving-cement filling is used, it shall consist of the same composition as that specified under Granite Pavement. If either Portland cement or Murphy grout-filling, or both, are ordered or permitted to be used on the street, they shall be of approved quality and used as follows: The Portland cement, if used, shall consist of a cement which, in the opinion of the City Engineer, is equal in tenacity, durability, and hardness to the best American Portland cement. The Murphy cement, if used, shall, in the opinion of the City Engineer, consist of the best quality of that material made by John Murphy, at Columbus, 0. The material, whether of Portland or Murphy cement, shall be fresh, live cement and finely ground, and be subject to the tests and approval of the City Engineer before being used on the work. The cement of either kind used, after having been approved by th'e City Engineer, is to be mixed with clean, sharp lake sand, of approved quality, in the proportion of one to one; the cement and sand to be thoroughly mixed together dry in a box of the proper form "and capacity, and then only a sufficient amount of water 410 STREET PAVEMENTS AND PAVING MATERIALS, added to make the grout of the proper fluidity when thoroughly stirred. The grout shall be prepared only in small quantities at a time, and shall be stirred rapidly and constantly in the box while being applied to the pavement, and no settlings or residue will be allowed to be used. The grout-filling shall be transferred to the pavement in hand- scoops, or in such other way as the Engineer may think most ad- vantageous and best for the work, and shall then be rapidly swept into the joints of the pavement with proper brooms. Unless otherwise directed, the filling is to be done by two applications of the grout; the first one-third in depth from the bottom of the space to be filled, with the grout somewhat thinner than required for the remaining two-thirds; the remainder of the spaces is then to be filled with the thicker grout, ajid if necessary refilled until the joints will remain full to the top; the stones to be well wet, as directed, before the grout is applied. All the teams and wagon traffic, and all wheeling in barrows, except on planks, to be rigidly prohibited on the pavement for one week after the grout is applied, or until, in the opinion of the Engineer, it has become thoroughly set and hardened, so that the bond will not be broken by traffic over the pavement. g. The surface of the paving, when completed as above, shall, when directed, be covered with a half-inch top dressing of clean, coarse sand, or gravel of approved quality, which, with all accumu- lations, shall afterwards be removed from the pavement and from all new or rebuilt catch-basins, by or at the expense of the Con- tractor, at such time before the final acceptance of the work, as the Engineer shall direct, and as hereinafter specified. Brick Pavements. (16) a' Brick. All brick shall be of the best quality of vitri- fied paving-brick made of shale or fire-clay, repressed and especially burned for street-paving purposes. They shall not be more than 3x4x9 inches nor less than 2 x 4 x 8-| inches in size; but only one size or make shall be used in any single contract. They shall be hard, tough, strong, and non-absorbent of water, and shall be PLANS AND SPECIFICATIONS. 411 tested under the conditions prescribed by the National Brick Manufacturers' Association for paving-brick. They shall be rectangular, with parallel sides and straight edges, uniform in size and texture and free from cracks, bunches, or defects of any kind, and equal in all cases to, and from the same place as, the sample submitted with the bid. b. Laying the Pavement. On the concrete foundation shall be laid a bed of clean, coarse, dry sand to such depth as may be neces- sary to bring the surface of the pavement, when thoroughly rammed or rolled, to the proper grade. The sand cushion shall be brought to the exact form and crown by means of a template of the proper shape, resting on the curbs, or with one end on the curb and the other on a scantling imbedded in the sand at the centre. The template shall be drawn forward and backward im- mediately in front of the bricklaying, so that the sand cushion shall be maintained constantly at the proper crown. On this sand bed the brick shall be set on edge at right angles to the curb-line, except at intersecting streets, where they shall be laid at such angles and in such manner as the Engineer may direct. All the longitudinal joints must be broken by a lap of half the length of the brick. The brick shall be laid in close contact with each other by skilled workmen, who shall stand on the bricks already laid, and in no case shall the bed of sand in front of the pavement be disturbed or walked upon after having been smoothed over and brought to the exact crown and grade. After the bricks are laid, the end joints are to be made close and compact by the use of a steel bar applied at the ends next the curbs. At every fourth course, or as often as directed, the bricks are to be closed up, and the courses straightened in a satisfactory man- ner. Nothing but whole brick shall be used, except in starting or finishing a course, or in such other cases as may be specially directed by the Engineer, and in no case shall less than one-half of a brick be used. In all cases the end joints shall be made close and tight. The cutting and trimming of bricks shall be done by experi- enced men and proper care taken not to check or fracture the- 412 STREET PAVEMENTS AND PAVING MATERIALS. part to be used; the joints all to be at right angles to the top and sides. As soon as the block between any two intersecting streets shall have been laid, the brick shall be thoroughly wet by sprinkling with a hand-hose, and any soft bricks which may be thus detected shall be taken out and replaced by good, hard brick. c. Rolling. The pavement shall then be swept clean with brooms and afterward rolled with a roller weighing not less than five tons till all brick are thoroughly imbedded in the sand and brought to an unyielding bearing, making the finished surface of the pavement smooth and even, conforming to the required grade and crown. All bricks that may be broken or chipped in any way by the rolling shall be taken out and replaced with perfect ones. d. Joints. When Portland-cement joints are specified, the surface of the pavement, after rolling as above, shall be thoroughly wet and grouted with a mixture of equal parts of the best American Portland cement, as heretofore required, and fine, sharp, washed sand, mixed with sufficient water to run freely; the grout to be poured over the surface of the pavement and well swept into the joints with stiff brooms until no further settlement is apparent and the cement filling remains flush with the top of the bricks. When required a thin layer of clean sand shall thereafter be spread upon the pavement and the street shall remain closed for seven days, or longer if so deemed necessary by the City Engineer, after which it shall be thrown open to travel. e. If sand joints are specified, the pavement when perfectly dry shall be covered with a thin layer of clean, dry, fine sand (dried upon the street by artificial means, if necessary, immediately before using), which shall be swept into all the joints by stiff brooms. The surface shall then be thoroughly rolled with a roller weighing not less than five tons, after which a fresh coating, treated as before, shall be applied, and again swept into the joints. A coating of one-half inch of the same sand, but which need not be heated, shall then be spread over the surface, and the street shall be thrown open to travel. /. When paving-cement is specified for a filler, the joints shall be slowly poured full with a paving composition as described in PLANS AND SPECIFICATIONS. 413 section e under Granite Pavement, heated to a temperature of 300 F. in such a manner as to cover the surface of the brick with as little pitch as possible. After this first pouring has been allowed to settle away, but not to become cool, the joints shall again be poured until they are full and remain full. The entire surface of the pavement shall then be covered with one-half inch of clean, perfectly dry sand. The sand shall be left on the pavement until ordered removed by the Engineer, when, if any appreciable amount of pitch still remains on the brick, they shall be covered with sand -as before, the same to be removed when directed by the Engineer in charge. The entire operation of pouring pitch and spreading the sand is done only when the pavement is entirely dry, and when the work is done in cold weather, only during the warmest portion of the day. Asphalt-block Pavement. (17) a. Blocks. The size of the blocks, must be four inches ^vvide, three inches deep, and twelve inches long, and a variation of one-quarter of an inch from these dimensions will be sufficient ground for rejecting any block. The blocks must be composed of the following materials: Paving-cement 10 to 14 parts Crushed- trap rock 90 to 86 " The paving-cement must be made from steam-refined, Trinidad Lake, or other equally good asphaltum, and heavy petroleum oil free from all impurities and brought to a specific gravity of from 18 to 22 Beaume and a fire-test of 250 Fahrenheit. Said cement must be composed of one hundred parts of pure asphaltum and eight to ten parts of petroleum oil. 1). Laying. Upon the surface of this concrete foundation shall be spread a layer of cement mortar one-half inch in thickness, which shall bring the thickness of the complete foundation up to five inches. This mortar surface shall be composed of a slow- setting Portland cement and clean, sharp sand free from pebbles over one-quarter inch in diameter, and mixed in the proportion of one part of cement to four parts of sand. This mortar top shall be 414 STREET PAVEMENTS AND PAVING MATERIALS. " struck " to a true surface exactly parallel to the finished pave- ment and three inches below it, in the following manner: On the surface of the concrete shall be set strips of wood four inches wide by one-quarter inch thick, and of a length equal to the width or half the width of the street if practicable; or strips of steel four inches wide by one-eighth or three-sixteenths inch thick and of a convenient length may be used. These strips must be carefully set from curb to curb to the exact crown of the street and imbedded throughout their length in mortar, so that the top surface of the strips shall be three inches below the grade of the finished pavements. An iron-shod straight-edge or " striker "' shall be used on two sets of strips, set as described above, ten or twelve feet apart, to strike the mortar top to a true and even surface. As soon as a bed has been struck up, one set of strip* shall be taken up and carefully filled with mortar with a trowel. Upon this mortar surface the blocks shall be immediately laid with close joints. The blocks must be laid by the pavers standing upon the blocks already laid, and not upon the bed of mortar. The blocks are to be laid at right angles with the line of the- street, with such crown as the Engineer may direct; each course of blocks to be of a uniform width and depth, and so laid that all longitudinal joints shall be broken by a lap of at least four inches and the surface present a smooth and uniform appearance, with proper grade and crown. When thus laid the blocks will be immediately covered with clean, fine sand, entirely free from any loam or earthy matter, perfectly dry, and screened through a sieve or screen having not less than twenty meshes to the inch. This sand shall be swept over the surface until the joints are all filled. The sand as above described will be allowed to remain on the pavement not less than thirty days, or for such a time as the action of the traffic on the street shall have thoroughly ground the top sand into all the joints. The whole operation of laying the blocks and cutting in at the curb shall be performed upon each bed struck up, before the mortar top shall have begun to set. As soon as the mortar top shall have sufficiently set, the street may be opened to traffic. PLANS AND SPECIFICATIONS. 415 In case of car-tracks in the streets a template shall be used, to run on the rails, to strike the mortar top to the required grade between the rails of the car-track. (18) In case any curb, flag, paving, trees, fence or barrier, or other material along the line of the work become broken or in- jured by the Contractor or his agents during the progress of the work, they are, if required, to be removed, and others equally as good placed in their stead, at the expense of said Contractor, and to the satisfaction of the Engineer. (19) Should any sewer manhole or catch-basin heads require raising or lowering to conform with the proper grade, such heads shall be so raised or lowered by the Contractor at his expense. Man- holes or other surface work of any corporation will be adjusted by the company or corporation owning them upon notice from the City Engineer. (20) Clearing Up. All surplus materials, earth, sand, rubbish, and stones, except such stones as shall be retained by the order of the Engineer, are to be removed from the line of the work, block by block, as rapidly as the work progresses. Unless this be done by the Contractor within twenty-four hours after being noti- fied so to do, to the satisfaction of the City Engineer, the same shall be removed by said Engineer, and the amount of the expense thereof shall be deducted out of any moneys due or to grow due to the party of the second part under this agreement. (21) All loss or damage arising out of the nature of the work to be done under this agreement, or from any unforeseen obstruc- tions or difficulties which may be encountered in the prosecution of the same, or from the action of the elements, or from incum- brances on the line of the work, shall be sustained by the said Contractor. In case any injury is done along the line of the work in conse- quence of any act or omission on the part of the Contractor or his employees or agents in carrying out any of the provisions or requirements of this contract, the Contractor shall make such re- pairs as are necessary in consequence thereof, at his own expense and to the satisfaction of the City Engineer; and in case of failure on the part of the Contractor to promptly make such repairs, thev may be made by the City Engineer, and the expense thereof shall 416 STREET PAVEMENTS AND PAVING MATERIALS. be deducted out of any moneys to grow due or to be retained from the party of the second part under this contract. (22) The prosecution of the work shall be suspended at such times and for such periods as the City Engineer may from time to time determine; no claim or demand shall be made by the Con- tractor for such damages by reason of suc'h suspensions in the work, but the period of such suspensions to be determined in writ- ing by the said Engineer will be excluded in computing the time hereinafter limited for the completion of the work. During such suspension all materials delivered upon but not placed in the work shall be neatly piled or removed so as not to obstruct public travel. (23) Whenever the word " Contractor " or a pronoun in place of it is used in this contract,, the same shall be considered as re- ferring to and meaning the party or parties signing the contract or his authorized agent. (24) The work s'hall be commenced on such day and at such point or points as the City Engineer shall designate, and progress therewith so as to be fully completed in accordance with this agree- ment, on or before the expiration of - - working days. (25) Damages for Non-completion. If the Contractor shall fail to complete his contract within the time specified, the City En- gineer shall make a careful estimate of the value of the work to be performed at the expiration of the contract time. When the work shall be finally complete the said Engineer shall deduct from the final estimate, as liquidated damages, 'an amount equal to one- half of one per cent of the value of such uncompleted work ob- tained as above for each working day in excess of the time specified in the contract, provided that the amount charged shall not be less than the actual increased cost of inspection. (26) If at any time any overseer or workman employed by the Contractor shall be declared by the Engineer to be unfaithful or incompetent, the Contractor, on receiving written notice, shall forthwith dismiss such person, and s'hall not again employ him on any part of the work. (27) When each section of the street has been completed, travel is to be allowed thereon, if required by the Engineer; and at the time of completion of the entire work, and before the final pay- PLANS AND SPECIFICATIONS. 41 T merit, the Contractor will be required to make good at every point any defect which is the result of non-compliance with any of the provisions of this contract. (.28) The said party of the second part hereby further agrees that he will obey and conform to all ordinances of the city now in force, or that may be in force, during the progress of such work. ('29) If at any time the City Engineer shall be of the opinion, and shall so certify in writing, that the said work or any part thereof is unnecessarily delayed, or that the said Contractor is wilfully violating any of the conditions or covenants of this con- tract, or is executing the same in bad faith, or if the said work be not fully completed within the time named in this contract for its completion, he shall have the power to notify the aforesaid Contractor to discontinue all work, or any part thereof under this contract, by a written notice to be served upon the Contractor, either personally or by leaving said notice at his residence or with his agent in charge of the work, and thereupon the said Con- tractor shall discontinue said work or such part thereof. The City Engineer shall thereupon have the power to place such and so many persons as he may deem advisable, by Contract or otherwise, to work at and complete the work therein described, or such part thereof, and to use such materials as he may find on the line of said work, and to procure other materials for the completion of the same, and to charge the expense of said labor and materials to the aforesaid Contractor, and the expense so charged shall be deducted and paid by the party of the first part out of such moneys as may be then due, or may at any time thereafter grow due, to the said Contractor under and by virtue of this agreement, or any part thereof; and in case such expense is less than the amount which would 'have been payable under this contract if the same had been completed by said Contractor, he shall forfeit all claim to the dif- ference; and in case such expense shall exceed the said sum he shall pay the amount of such excess to the party of the first part. (30) Guarantee. Asphalt pavements shall be kept in repair, as specified herein, at the expense of the Contractor for the term of five years, and all other pavements for the term of twelve months, from the date of the provisional acceptance of the work, 418 STREET PAVEMENTS AND PAVING MATERIALS. at which time it is to be turned over to the city according to the provisions of Section 34, provided, however, that should the date of final acceptance fall between December 1st and March 31st, the City Engineer shall have the right to postpone said final acceptance until the weather will permit an examination and necessary repairs, to be made. (31) During the performance of said work the Contractor shall place proper guards upon and around the same for the prevention of accidents, and at night shall put up and keep suitable and sufficient lights, and shall indemnify and save harmless the party of the first part against and from all suits and actions, of every name and description, brought against it, and all costs and damages to which it may be put for or on account or by reason of any injury or alleged injury to the person or property of another, re- suiting from negligence or carelessness in the performance of the work, or in guarding the same, or from any improper materials used in its prosecution, or by or on account of any act or omission of the said Contractor; and the whole or so much of the moneys due the said Contractor, under and by virtue of this agreement, as shall or may be considered necessary by the City Engineer, shall be retained by the proper city officials until all such suits or claims, for damages as aforesaid shall have been settled, and evidence to that effect furnished to the satisfaction of the said Engineer. (32) On a street paved with asphalt if, at 'any time during the period of guarantee, the work or any part thereof, or any depres- sions, bunches, or cracks, shall, in the opinion of the City Engineer,, require repairs or sanding, as provided for in Section 13, paragraph fc, and the Engineer shall notify the Contractor to make the re- pairs or do the sanding as required, by a written notice to be served on the Contractor either personally or by leaving said notice at his residence or with 'his agent in charge of the work, the said Contractor shall immediately commence and complete the same to the satisfaction of the said Commissioner; and in case of failure or neglect on his part so to do within forty-eight hours from the date of the service of the aforesaid notice, then the said Engineer shall have the right to purchase such materials as he shall deem necessary, and to employ such person or persons as he shall deem proper, and to undertake and complete said repairs or sanding, and PLANS AND SPECIFICATIONS. 419 to charge the expense thereof to the said Contractor; and the said Contractor hereby stipulates and agrees to pay all such expense to which the said Engineer may have been put by reason of the neglect of the said Contractor to make such repairs or to do the sanding as aforesaid. (33) The Contractor further agrees that he will during the same period lay and restore the pavement over all openings made by corporations or plumbers for making new service-connections or repairing, renewing, or removing the same, and over all trenches made for carrying sewers, water- or gas-pipes or any other subsur- face pipes or conduits, for the building or laying of which permits may be issued by the proper authorities for the contract price per square yard for all openings whatever, the Contractor or corpora- tion making such opening or trench having taken such precautions to prevent settlement of the filling over the same as are deemed necessary by the said Engineer. All materials to be of the same quality and mixed in the same manner as specified in this contract. The Contractor further agrees not to demand additional or further payment on account of repairing any injured or sunken pavement laid over the repairs above described. (34) Just previous to the expiration of the guarantee period on asphalt pavements the entire work shall be inspected, and any bunches, depressions, or unevenness in the surface of the pavement that shall show a variation of three-eighths of an inch under a four-foot straight-edge or template, or any crack wider than one- fourth of an inch, or any portion of the pavement having a thick- ness of less than one and one-half inches shall be immediately re- paired upon the order of the City Engineer, by the heater process or by removing the entire pavement from the concrete, and re- placing it in the same manner as when originally laid; provided, that when more than fifty per cent of the surface of any one block requires repairing according to the above conditions, the entire block shall be taken up and relaid. Whenever any defects are caused by the failure of the concrete or the settlement of the road- ^vay from any source, the entire pavement, including foundation, shall be taken up and relaid in accordance with the specifications. Just previous to the expiration of the guarantee period on stone 420 STREET PAVEMENTS AND PAVING M4TERI LS. or brick pavements the entire work shall be inspected, and any defects caused by inferior material or defective work, or settle- ments from any cause, shall be immediately repaired on the written order of the City Engineer and to his satisfaction. Should the Contractor for any kind of pavement fail to make the necessary repairs within six days after being served with the above order, or to perform the work in a satisfactory manner, the City Engineer shall have the same done and charge the cost thereof to the reserve fund held for that purpose. After all repairs have been satisfactorily made, the City Engineer will issue his certificate- to that effect. (35) Payments. When the amount of the contract is more than $5000, on or about the first day of each month a payment will be made to the Contractor of eighty per cent of the value of the work performed during the previous month upon the issuance of the certificate of the City Engineer; provided that no partial pay- ment will be made after the expiration of the time for the comple- tion of the contract. When the work has been entirely completed, and such com- pletion certified to by the City Engineer, the entire amount due under the contract shall be paid to the Contractor less any pay- ments previously made and any amounts rightly retained under the provisions of these specifications. On all work guaranteed for five years ten per cent of the amount of the contract price shall be retained till the end of the guarantee- period; but the contractor will be allowed to deposit city bonds with the financial agent of the city to the amount of the reserve- due, when the entire balance will be paid. During the guarantee period he will be allowed to draw all interest due upon the bonds,, and upon the final acceptance of the work, and the Engineer's certificate to that effect, the entire amount will be returned to the Contractor, less any amount paid out for repairs. On work guaranteed for twelve months a sum of ten cents per square yard for granite on sand, and fifteen cents for stone or brick pavements on concrete, shall be retained until the final acceptance, when the said retained sum, less any amount expended for neces- pary repairs, will be paid. CHAPTER XIII. THE CONSTRUCTION OF STREET-CAR TRACKS IN PAVED STREE1S AND ROADWAYS. THE problem of how to construct street-car tracks in the best manner in paved streets has been troubling engineers in charge of pavement construction for many years. In the early days of street-railways, when the streets were paved with cobblestones and when street-cars were small and drawn by horses at a speed of five or six miles an hour, this question was not so important. But in the present time of asphalt and other improved pavements, of rubber tires, bicycles and automobiles, and with cars weighing from 10J to 12 tons propelled by electricity along our streets at a speed of from eight to fifteen miles per hour, the importance of good and smooth track-construction, both to the general public and to the street-car company, can hardly be overestimated. There is no doubt that the street-car track is detrimental to. any pavement, but it is a necessary evil, for it is well recognized at the present time that no one thing tends to develop and build up a city as does a good system of street-cars. The problem of the construction of street-car tracks is very different from that of the ordinary steam-railways. The steam- cars run on their own right of way, making stops only at long intervals, and the tracks can be constructed in such a manner as. will give the best results as regards economy of construction and maintenance, with no regard for the wishes of others, except at street or road crossings. Street-cars, however, run through public highways which are being used constantly by vehicles, and crossed often by pedestrians, and their construction must be such as will not only accommodates 421 422 STREET PAVEMENTS AND PAVING MATERIALS. their own cars, but also interfere as little as possible with the ordinary vehicular traffic of the street. It must be remembered, however, in this connection that there are two travelling publics, the one in the cars and the other using private vehicles, and while the former uses the vehicles of the corporations, operated in a public thoroughfare, any action which tends to discommode or interfere unnecessarily with the action of the cars must discommode to a great extent a very large pro- portion of the travelling public. Probably 40 per cent of all the business men in the average American city of more than 100,000 inhabitants depend more or less upon the street-cars for their convenience every day. The authorities of street-railways, and the cities in which they are operated, generally differ considerably in their ideas of what is the proper construction for the tracks. The street-car companies are interested only to perform their work economically. A con- struction that will allow their rolling-stock to be operated with the least amount of wear and tear and will cost the least for original construction, as well as maintenance, is what they desire. On the other hand, the city authorities are not interested to any great extent, either in the cost of construction or maintenance. They wish a construction that can be carried out with little obstruction to the general travel of the street, will require but little interfer- ence with the pavement for maintenance and repairs, and present little obstruction to the general traffic. In early track-construction the railway companies sometimes sought to lay a rail that would be very obstructive to travel. When a track is such that vehicles seek it in preference to the street, the operation of the street-cars is interfered with, and the com- panies seek every means to prevent this. With the -rough stone pavements of twenty-five years ago, the special form of the rail added very little to the general roughness of the street, but railway companies must recognize at the present time that smooth and improved pavements have come to stay, and that they must adopt a method of track construction that will con- form to these pavements. The ideal construction seems to be one in which the track is a part of the pavement itself, and not a separate and definite part THE CONSTRUCTION OF STREET- CAR TRACKS. 423 of the work, and the track and pavement should be studied to- gether as one whole. The time of probable renewal of each part should be taken into consideration, and the design of each made so as best to accommodate these renewals. This, however, is not verv often practicable, from the fact that it very seldom happens that & pavement and a railway-track are constructed at the same time, so that certain modifications or concessions can be agreed upon and the best results for both obtained. The question should be taken up by the railway and city authorities conjointly, as if both were owned and were to be oper- ated by one interest; and after the details which would be best under this arrangement were determined upon, general modifica- tions could be made if desired, so that the interest of either party would not suffer. Street-railway companies, having operated in public highways for so long a time, with an inexpensive construction determined upon by themselves, find it very hard at times to meet the require- ments of modern pavements and the present city officials, but they soon find that it is better economy as well as better policy to adopt a construction that will be both durable and satisfactory to the municipal authorities. The question as to the proper remuneration to be made to municipalities for the use of its highways for the operation of street-cars has never been definitely settled. In some cities it is arrived at by the company's paying a certain amount to the city, sometimes based upon its receipts, the number of passengers carried, or sometimes a lump sum^ determined upon in advance. In some cities, also, the cost of paving is settled in much the same way; but, as a rule, the actual amount of the street to be cared for by the railway company is defined either in its charter or by special legislation. No attempt will be made in tkis connection to treat the question of value from the franchise standpoint, but simply with reference to the care of the pavement. In 1854 an Act was passed by the Massachusetts Legislature incorporating the Dorchester Avenue Railway Co. and requiring it to keep in repair the whole of the bed of any road in the town of Dorchester in which it might lay tracks. In the following year, however, this Act was amended by a repeal of this clause and the 424 STREET PAVEMENTS AND PAVING MATERIALS. ( substitution of a provision requiring only that part of the road occupied by the tracks to be kept in repair,, and denning that portion " to be the space between the rails and so much on each side thereof as shall be within a perpendicular let fall from the extreme width of any car or carriage used thereon, being the space from which public travel is excluded during the passing of said car or carriage." In Baltimore, Md., the street-car companies pave and keep in repair the space between their tracks, and 2 feet on each side. In Buffalo, N. Y., different conditions exist in regard to the paving requirements by the different companies, but in general the maintenance of the street between the tracks and 2 feet outside is required. Although in some locations no paving at all is required from the street-car companies, in New York a bill was passed in- 1895 which provided that one-fourth of the cost of repaying any street in Brooklyn in which was operated a street-railway should be assessed against the company owning such track. A great many streets were paved under this law, but at the present time no tax has been col- lected from the street-car companies. This question, however, will probably be settled by a general New York statute which will be referred to later on. In Chicago, 111., the conditions under which the companies now operate require that they pave and maintain 16 feet in width of the street in case of double tracks and 8 feet in the case of single tracks, with a pavement of as good quality as that of the rest of the street. In Detroit, Mich., the railway company pays no special tax on the gross earnings, is required to do no paving either between its tracks or other part of the street in which they are located, is not required to make pavement repairs if the streets -are dis- turbed for railroad repair work, and the concrete base on which its tracks are laid is put down by the city. In Indianapolis, Ind., a readjustment of the terms of the orig- t inal franchise was made in 1878, when a provision requiring the road to repave between its tracks was changed so as to read " repair between its tracks." On account of this action there is considerable feeling between the taxpayers and the railway company. THE CONSTRUCTION OF STREET- CAR TRACKS. 425 In Xew York City it is held that the different companies are bound by Chapter 676 in Laws of 1892, a portion of which reads as follows: " Every street-railroad, so long as it shall continue to use any of its tracks in any street, avenue, or public place in any city or village, shall pave and keep in permanent repair that portion of such street, avenue, or public place between its tracks or rails of its tracks, and two feet in width outside of its tracks, under the supervision of the proper local, authorities, and whenever required by them to do so, and in such manner as they may prescribe. In the case of neglect of any corporation to make these pavements or repairs after the expiration of thirty days' notice to do so, the local authorities may make same at the expense of such corporation." The street-car companies, however, have not always lived up to this requirement, and it was stated in a paper read before the American Society of Civil Engineers in December, 1896, that bills aggregating more than $700,000 had accumulated against surface railways on Manhattan Island from 1889 to 1895 inclusive. The street-car companies in the city of Philadelphia have prob- ably expended more 'money for pavements in city streets than any other city in the world. In 1892 the streetrrailways changed their power from horses to electricity, and an agreement was entered into between the companies and the city authorities by which the roads agreed to pave and maintain the streets through wTiich they operated, from curb to curb. The streets of Philadelphia being so narrow that in most cases only one track is operated for each street, a large amount of street mileage is occupied by the street- car companies. It is said that on January 1, 1898, there had been expended by the different companies for street pavement since 1892, w Milford, Mass 2g North Jay, Me 23 Petersburg, Va 24 Port Deposit, Md 21 Quincy, Mass 24 Waterford, Conn 22 kaolin 80, 86 lime 3& limestone and resulting limes 3& Bedford 37 from various localities 39 Trenton 38 Maltha 63 Material for cement 133. paving-brick 260 porphyry 86- sandstone, Berea 3& Colorado. 34 shale 85- trap-rock, Birdsborough, Pa 26 Meriden, Conn , 26 Monson, Mass 26 New Jersey 27 Appian Way 2 Artificial-stone blocks l41 Asphalt, analysis of, Endemann's method 53 Linton's method .... 5& Richardson's method 52 Sadtler's method 5 artificial, Day's experiment with 47 Asphalto fluxing 66 refining. 66 Barbadoes, analysis of ,- 496 description of 78- Bechelbronn, analysis of 51 Bermudez, analysis of 7t description of 71 first used in pavement 71 location of "0 California, analysis of 6H bitumen in . 228 description of 63, 6& INDEX. 499 Asphalt, California, first used 62 location of 63, 65 character of 219 comparison of different kinds 55 cost of 250 Cuban, analysis of 495 description of 77 Dead Sea, analysis of 495 description of 78 definition of 42, 44 Egyptian, description of 79 formation of 44,45,49 how tested 220 Indian Territory, analysis of 496 bitumen in 76 description of 76 Kentucky, analysis of 495 analysis of rock containing 72 bitumen in 72 description of 72 preparation of 72 used in pavements 73 location of 56 Mexican, analysis of 69, 70, 496 description of 69 location of 69 Montana 77 petroleum 64 rock of California, description of 66 location of 66 rock of Europe, analysis of 68 bitumen in 68 formation of 67 location 67 Syrian 78 suitable for pavements... 219 terms for 40 Texas, analysis of 74, 75, 495 location of 73 preparation of 73 uses of 74 Trinidad, analysis of 54,60,61 bitumen in 228 how mined 58 location of 57 500 INDEX. PAGE Asphalt, Trinidad, refining of 60, 61 Turkey 78 Utah, analyses of 76, 49fr description of 7~> quantity of 75, value of analyses 55. Asphalt block pavement : advantages of 256 amount of 256 blocks, how made 255 how laid. 256, 413 sizeof 256,413 cork blocks, cost of 257 where laid 257 cost of 256 first laid 255- in Poughkeepsie 164 specification for: blocks, composition of 413 covering for 414 how laid 413 size of 413 Asphaltene, description of , , 51 formula for 52, 54 Asphaltic cement : amount in pavement 229, 250, 490 as a liquid 225 fluxes for 220, 221, 222 hardness, how tested 223 in Washington 224 how prepared 220, 490 Asphaltina : cement, composition of , . 254 description of 253 pavement, cost of 255 mixture 255 specifications for 254 Asphalt macadam, first used 8 Asptialt pavement: American, in Europe , 252 binder for, action of water on 233 composition of 230 object of 230 size of stone for 231 thickness of 230, 397 cost of 250, 251 cracks in 238 caused by what 23S effect of 239 how formed . . . . 239 INDEX. 501 PACK Asphalt pavement : cracks in, how prevented 238 cross-section of 235 table for laying out 218 damaged by fire 240 effect of illuminating-gas on 239 appearance of 240 first laid: London 7 New York 10 Paris 8 United States 215 Washington 215 foundations for: bituminous 231 broken stone , 232 cobblestone 232 necessity of 231 stone block 232 grades of 216^ 217, 218 gutters for, how laid 237 material far 237 how laid against rigid surface 236 in Cairo 143 maintenance of 244, 246, 247 material for 225 method of laying 233, 235 method of rolling 234 amount of 235 objections to 216 on bridges 251 sand for 226 size of, in different cities 227 slipperiness of 216 standard of condition of, at expiration of guaranty. . . . 240 temperature of air when laying should be discontinued 237 temperature of material when laid 234 wearing surface of: aspbaltic cement in. 229 composition of 227 laying 283 mineral matter for 228 requirements of - 227 rolling 234 thickness of . 229 weightof 250 when too soft 239 Asphalt-pavement specifications : binder, asphaltic cement for 39"^ 502 INDEX. PAGE Asphalt-pavement specifications: binder, character of 397 how laid 397 stone for 397 thickness of 397 general requirements of 402 maltha (liquid asphalt), how used 401 properties of ; 401 not laid in wet weather 403 rock asphalt, amount of bitumen in 402 how laid , 401 temperature of 402 wearing surface, asphalt, description of 398 asphaltic cement, how made 399 gutters, how treated 4; 1 how laid 4(0 how prepared 4CO mineral matter, fineness of 400 mixture for 398 petroleum oil, description of 398 proportions of material for 400 rolling 401 sand, size of 400 temperature of 400 Asphalt plant : capacity of 487 cost of 492 location of 488 machinery for 491 portable, capacity of 495 demand for 493 description of ^ 493, 494 province of , 487 work of : asphaltic cement, preparation of 490 sand, how heated 489 stone-dust, preparation of 491 time of mixing 492 Asphalt roads in California 12 Australian wood pavements 320 London 298 New York 321 Baltimore, early pavements of 11 Barbadoes asphalt 78 Basalt, composition of ~1 description of 20 Belgian blocks, description of , 180 INDEX. 503 PAGE Belgian blocks, first used in New York t 180 material for -.-.-. 184 objections to 185 specifications for 185 Belgian-block pavement , 9 cross-section of 186 description of 185 estimated cost of , 187 how laid 186 Berea sandstone, analysis of 33 location of 32 strength of 33 Bermudez asphalt 70 Bids, alternative 381 certified check to accompany 382 not to be changed after opening 383 not to be received after expiration of time limit 382 to be indorsed with name of bidder 383 unbalanced 388 Bidders, blanks to be provided for 382 instructions to . '. 382 notice to 390 Binder, amount of, for broken-stone pavement 343 for asphalt pavement 230 macadam pavement 339 material for 340, 345, 350, 368 Biotite granite 18 Bitumen, amount of, in asphalt 228 asphalt pavements 225, 228, 242, 250 artificial, how discovered 56 as natural gas 44 definition of 40-43 derivation of word 40, 41 divisions of 43 forms of, for pavements 62, 219 origin of ; German theory 46 Malo's theory 45 Mendelejeffs theory 49 Moissan's theory 49 Peckham's theory 50 Torrey's theory 46 Wall and Sawkin's theory 48 Wurtz's theory 50 parts of 51 refining 64 504: INDEX. Bitumen, sand-bearing 53 solvents for 55 transportation of 64 Blank forms for bidders 3 $ Blocks: asphalt, cork, size of 2.~>6 first used 355 size of 25'i Belgian 180, 185 granite 18a first used 5 first used in Liverpool 7 size of, in American and European cities 191 Medina sandstone 207 paving, of Rome, size of 5 stone, for Blackfriars Bridge (> size of, in Catania, Italy 179 European cities 1 92 wood, size of 294, 295, 320 Bondi amount of, in contract 383 Bonus for completion of contract 384 Boston, early pavements of ^0 Boulevard, the first 2 Brick: blue, made in England 89- early use of 88 fire-clay 85- first used in England 89- floating 89 in pyramid 88 kiln, first in United States 8& manufacture of paving. 90- paving, see Paving-brick. shale 85 vitrified 8& clay to produce 87 test of 87 Brick pavements, advantages of 261 amount in United States 291 cost of, in American cities 292 estimated 292 cross-section of 284 first laid in United States '. 259= foundation for, brick laid flatwise 282 broken stone 28& cement concrete , 283 plank and sand 282; INDEX. 505 PAGE Brick pavements, in England 25$ in Holland 258 life of 258 in Japan 258 joint-filling for 284, 286- cement grout ?87 sand 287 temperature of paving-cement for 287 laying, arrangement of brick 289 breaking joints 288 preparing bed "388 rolling 288 testing for soft brick 288 material per square yard of 292 rumbling of 285 causes of 285 examples of 285 how prevented 286 Brick pavements, specifications for : brick, how laid 41 1 how tested 411 in Philadelphia 291 St. Louis 290 joint-filling for 412 size of 410 covering for 413 Brick sidewalks, how laid 477 where laid , , 477 Bridges, asphalt pavement on 25 1 expansion-joint in 252 Broken stone, voids in 120, 124 how reduced 122 Broken-stone pavements, construction of, amount of rolling for. . .338, 341-343 finishing surface 346 foundation course 337 cross-section of 347 crown of 344 drainage for 334 foundation for , 334 thickness of 336 gutters 347 Macadam's theory of 331 Macadam's and Telford's methods compared.. 331, 338 maintenance, cost of, in Glasgow 370 London 370 Marseilles . . 371 506 INDEX. PAGE Broken-stone pavements, maintenance, cost of, in Paris 370 Rochester, New York . . 371 material for 336 objections to t 333 preparation of road-bed 333 roller for '. 338 rolling. 338 size and shape of stone for 330, 336, 337, P41, 349 specifications for Boston 348 Brooklyn 349 Providence 347 sprinkling 346 Telford's method 330 binding for 330 Tresaguet's method . . 329 use of binder for 338 quantity of 339, 343 when first built systematically 329 Broken-stone roads, see Macadam roads. old methods of constructing 332 size of stone for 330, 332 thickness of 3b2 Burnettizing 328, 324 effect of 324 railway ties, cost of 326 California asphalt, analysis of 63 description of 63 first used 62 for pavements 62 location of 63 California, asphalt roads in 12 Carbonate of lime for asphalt pavements 227 Carthaginians, the first road-builders 2 Cedar-block pavement, amount in Chicago , . . 313 in the Central West 311 life of 311 sapless 312 specifications for 313 Cement, artificial 97 consumption of 132 definition of 96 early use of 96 expansion of, in setting 119 test for 119 how tested.. . 104 INDEX. 507 PAGE Cement made in United States 9 T natural 9? analysis of 100 fineness of 101 New York Building Code definition of 98 production of 133 results of tests on 102 strength of 107 value of 134 neat, and sand, tests of 104 Portland 97 analysis of 99 of materials for 133 fineness of 101 result of tests for 102 value of 100 first made in United States 97 first used 97 ideal, composition of 99 magnesia, maximum amount in 99 production of 183 requirements for 396 specifications for 106 specifications of first patent for 97 strength of 103, 107 value of 133 Roman 97 Rosendale, see Natural 98 use of, in cold weather 115, 117 value of long-time tests of 104, 105, 106 Cement curb, estimated cost of 473 material in 472 specification for 47 1 steel edge for 470 Cement gutter, estimated cost of 473 form of 481 how laid 471 specifications for 471 Cement sidewalks, estimated cost of 479 how laid 478 material for 479 specifications for 478, 479 Cementitious value of stone 360 Ceramite blocks 14:i Certified. checks to accompany bids 382 508 INDEX. PAGE Certified checks to accompany bids, amount of 383 Charcoal roads 293 Chert pavement 143 Chicago, early pavements of 11 City engineer to bid on work 389 (/lay, classes of 83 84 colored by 82 definition of 80, 82 fire, analysis of 85 fluxes of 84 amount of 85 non-plastic 84 plastic 84 fusible 84 high-grade 84 low-grade 84 permauance of form in 83 how produced 83 plasticity of 82, 84, 87 preparation of, for paving-brick 90, 91, 92 properties of 82 refractory 84 Cleveland, early pavements of 12 Coal-tar, how discovered in asphalt 56 Coal-tar pavements condemned in Washington 213 cost of repairs to 212, 214 first laid 211, 212 life of 212 specifications for 213 Coal-tar pitch 197 Cobblestone pavement, amount in United States. 183 cross-section of 183 description of 182 estimated cost of 184 foundation for 1 84 how laid 183 repairs to 164 Cobblestones, size of. 181, 183 specifications for 181, 182 Colorado sandstone, analysis of 34 description of 33 strength of 34 Concrete, action of frost on 115, 117 bituminous 212, 213 composition of 121 consistency of 125 INDEX. 509 PAGE Concrete, cost of 204 472 definition of 120 early use of 96 example of 120 hand and machine mixed, relative value of 130 how laid 122 how mixed 121, 122, 126, 203, 396 how protected 205 machines for mixing 126, 127, 129, 130 material per cubic yard of 203 estimated cost of 204 proportions for 120, 122 quantity of material in 123, 131, 472 Concrete base, first used in London 7 first used in New York 10 first used fur wood pavements 294 Contracts, bond for 383 bonus for completing 384 extra work under 380 indeterminate quantities in 380 let for lump sum 380 maintenance clause in 385, 387 penalty for failure to complete 384 time-limit of 384 Cordova, pavements of 5 Cost of asphalt-block pavement 256 asphalt pavement 251 asphaltina 255 Belgian-block pavement 187 brick pavement 292 broken-stone pavement 363 cobblestone pavement 184 granite pavement , 205, 206 macadam roads 362 Medina sandstone 208 wood pavement 298, 305, 309, 318, 321 Courtyards, necessity of 460 width of 462 Creosote oil, amount of, per cubic foot of timber 299, 318 definition of 326 preservative value of , 326 should contain naphthalene 326 Creosoting, definition of 323 Indianapolis specifications for 318 London specifications for 299 value of, to pavement 301 510 INDEX. PAGE Cross-breaking test for paving-brick, method of conducting 273- reasons for 274 value of 274 Cross-section of asphalt pavement 235 Belgian 186- brick " 284 broken-stone " 347 cobblestone " 183 granite " 199 Cross- walks, dimensions of 209, 394 how laid 209, 394 material for 209, 394 Crown of pavements, formula for laying out 202 on side-hill streets 201 principles for determining. 200, 201 table for 202 Crushing-test for paving-brick, method of conducting 275 value of 276. Cuban asphalt 77 Curbing, concrete, see Cement curb. Curbstones, cost of 464, 474 dimensions of 394, 463 foundation for 395, 466 amount of concrete for 466 how dressed 395, 464 how set 464 limestone for 467 material for. . ; 463 object of 462 radius of 465 specifications for : Cincinnati 468 Liverpool 467 New York City 468 Rochester 469 St. Louis 468 Cushion-coat for asphalt pavements, description of 230- objections to 230 thickness of 230 Cypress-block pavement in Galveston 316 in Omaha 311 life of 312, 316 Dead Sea asphalt 78 Diabase (trap-rock), formation of 20 location of 20 Dolomite 35- INDEX. 511 PAGE Drainage of macadam streets and roads 334, 853 Early pavements, construction of 178 cross-section of 199 of Europe 179 Earth, composition of crust of 14 Egyptian asphalt 79 Engineering, School of, in Spain 4 Estimates of cost, how made 184 Evaporation of water from paving- brick 271 Expansion-joint for asphalt pavement. ... 239 asphalt pavement on bridges 252 brick pavement 285 wood pavement 295, 299, 303, 32 1 Feldspar, composition of 15 how destroyed , 81 varieties of 15, 80 Ferroid 197 Fineness of cement 101 specifications for 108 Fire-clay 84 analysis of 85 Fire-clay brick 85 Formula for determining economic life of pavements 155 for determining relative value of paving-brick 277 for obtaining amount of traction on grades 482 Foundation for asphalt pavement 231 Belgian-block pavement 185 brick " 282 broken-stone " 335 cobblestone " 184 granite-block " 191 macadam roads 360 Fusibility of clay 84, 85, 87 Galveston, wood pavements of 316 Genoa, streets of 3 Gilsonite, analysis of 48, 76 Glass'pavement 141 Gneiss 19 Grades, effect of 482 examples of 483, 485, 486 for asphalt pavements 216 formula to obtain traction on 482 how established 484 on business streets 482 steep, at intersections 485, 486 512 INDEX. PAGE Grades, steep, best pavement for 483 Granite, adapted for curbing, and pavements 19 analysis of 21, 22, 23, 24, 25 characteristics of 17 crushing strength of 27 definition of 17 formation of 17 properties of 18 rift of 18 value of anual product 25 varieties of 18 Granite blocks : dimensions of, in American and European cities 191 principles determining 189 first used 5 in Vienna 210 specifications for 190 used as toothing-blocks in street-car tracks 457 wear of 188 Granite pavement : blocks, how laid at intersections 193, 194 how laid in 193 concrete foundation for 196 cross-section of 199 estimated cost of 206 foundation for 191 preparation of 192 in Vienna 210 Granite pavement, joint-filling for ; ferroid 197 gravel, temperature, and size of 198 Murphy grout 197 paving cement, amount per sq. yd.... 199 composition of 197 temperature of 205 Portland cement 197 tar and gravel 197 laying 1 96 material per square yard of 205 organization of gang for laying 205 ramming, importance of 196 repairs to 163 width of joints in 195, 198 Philadelphia specifications for 195 Granite pavement specifications : blocks, classes of 403 description of 403 how laid 404 concrete foundation 405 INDEX. 513 PAGE Granite pavement specifications: gravel. 405 paving-cement, composition of 406 temperature of 405 sand, foundation 404 sprinkling with water 405 Gravel for joint-filling 198 voids in 124 Grass pavement 140 Guidet pavement, 9 description of , 181 size of blocks in 10 Guaranty for asphalt pavement 240, 386 brick " 387 granite " ." 387 how paid for 386, 387 term of, principles determining 386, 387 Gutters, depth of, how determined 200 for asphalt pavement, how laid . . 236, 401 material for 286 for broken-stone pavement 347 forms of 481 how laid 480 materials for 480 Hardness and specific gravity of paving-brick 276 of asphaltic cement, how tested 223, 224 of paving-brick, how tested . . 262 Mohs' scale for 262 value of tests for 270 Heading-stones, dimensions of 395 how set 395 Highway Act, first, in England 4 Holborn, pavements of 5 Hornblende 15 Hornblende granite 1H Hornblende, biotite granite 18 Hudson River blu'estone, composition of 30 description of 2!) location of 2!) Hydraulic limestone, composition of 90 definition of 90 Illuminating-gas, effect of, on asphalt pavements 239 Indian Territory asphalt 76 Instructions to bidders 382 Iron macadam pavements 141 Iron pavements 138, 139 514 INDEX. PAGR Italy, pavements of U Jasperite pavement 140 Jerusalem, streets of 3 Jetley pavement 145 Joint-filling 197, 208 for brick pavement 284, 286, 4ia in Philadelphia , 291 in St. Louis 290 for Medina sandstone pavement 409 for wood; 294, 295, 299, 301, 303, 308, 318, 319- Joints in pavement, tar and gravel first used 7 in New York City 10 Joints in street-car tracks, effect of, on traction 451, 452 how made 451 number of special, in Brooklyn 452. in Chicago 452 Kaolin, analysis of 80, 86 characteristics of 80 chemical formula for > 8u- fluxes for 81 formation of 80, 86. Kentucky asphalt 72 Kyanizing 323 Life of asphalt pavements 156 in London 243, Belgian-block pavements 156 brick pavements 156 in Holland 258 granite pavements 156 Medina sandstone pavements 207 pavements in European cities 156 wood pavements in Chicago 313 in London 296 in Omaha 311 in Paris 303 in Quebec 304 Lime, definition of 96 analysis of 38 Limestone, analysis of .36, 37, 38, 39 Bedford oolitic, analysis of 37 description of 30 effect of heat on 37 strength of 37 dolomite , 35 for macadam pavements 341 INDEX. 515 Limestone, formation of 34 hydraulic, analysis of 30 definition of 36, 96 marble, definition of 36 oolitic, formation of 35 strength of ... 39 Trenton, analysis of 38 location of 37 uses of 37 Liquid asphalt, how used 401 properties of 401 Lithuania, pavements of 7 Liverpool, granite blocks first used in 7 London, early wood pavements of 6 streets of 5 Macadam pavement, see Broken-stone pavement. roads 350 amount built in New Jersey 352 appropriation for, in Massachusetts 350 in New York 352 character of stone for '. . . 357 cost of construction of, estimated 363 in Massachusetts 362 in New Jersey 362 drainage, necessity for 353 rules of Mass. Highway Commissioners for. 354, 355 how paid for, in Massachusetts 351 in New Jersey 351 in New York 352 maintenance of : cost of, in England 370 in France 370 in Europe 371 methods of 369 quantity of material used in 369, 370 quantity of material for 361 questions governing construction of 353 ruts in 371 specifications for : New Jersey 366 New York 364 Owen's 368 sprinkling 372 stone for, in Massachusetts 35S abrasion test of 359 description of test of 359 machine for test of . . . 359 516 INDEX. PAGE Macadam roads, stone for, in Massachusetts, size of 35& width and thickness of, how determined 35ft Macadam's theory of 331 standard for, in Mass. . . 356, 35T N.J... ..*.... 866, 357 Queen's Co., L. I. 357 Magnesia, maximum amount in Portland cement 99' Maintenance: asphalt pavements, Buffalo method 245 Cincinnati method ... 245 Cost of, in Buffalo 246, 247 Cincinnati 246, 247 European cities 248 Omaha 246, 247 Rochester 24$ Washington. 246, 247 Omaha method 244 Washington method 246- how paid for 386, 387 Macadam roads 370 period of 384. 386 conditions governing 385 wood pavements 297, 300 Maltha, analysis of 63 as a flux 223 definition of 43- deposits of 62 description of 62 how obtained 62 Marble 06- Material, quantity of, for asphalt pavements 489, 490, 491 Belgian pavements 187 brick pavements 292 cobblestone pavements 184 granite pavements 206 macadam streets and roads. 361 , 363 maintaining macadam streets and roads . . . .369, 370 Medina sandstone, composition of 32 description of 31 location of 31 pavements, cost of, in Cleveland 208; Rochester 208; description of blocks for 201 dimension of blocks for 207 how laid in Cleveland 20T Rochester 2.08 ! INDEX. 517 PAOK Medina sandstone pavements, joint-filler for 208 Medina sandstone pavement, specifications for : classes of blocks 406- covering for 410 description of blocks 406 how laid 408 ramming 408 joint-filling 409 how applied 410 Mexican asphalt 68 Mexico City, pavements of 8 Mica, description of 16 varieties of 16 Montana asphalt 77 Mortar, action of frost on 113: composition of 109 cost of 472 definition of 10 in salt water Ill strength of Ill, 112 material in 472 mixed with salt water 112 strength of 114 rule for amount of salt in 1 13 time of use after mixing 118, lift unit of measurement of 110 volume of 110, 12$ Mud clays 84 Muscovite biotite granite 18 Muscovite granite 18 Murphy grout 197 Natural gas a bitumen 44 Napthalene, value of, in creosote 326 New Orleans, early pavements of 12 New York, concrete base for pavements first used in 10- early pavements of ft first asphalt pavement in 215 first cobblestone pavement in 8 mortality of 166 Noiseless manhole-covers 249 Noiseless stone pavement 144 Notice to bidders 390 Oolitic limestone / 35, 36 Palenque, Mexico, pavements of S Paris, first asphalt pavement of & 518 INDEX. PAGJS Paris, first pavement of 4, 7 streets of 7 Pavements, annual cost of 171, 172 in New York 136 artificial blocks for 141 asphalt 211 accidents on 161, 162 first in New York -215 first in Paris 8 first in United States 215 in Cairo... 143 slipperiness of 161 asphalt block 255 asphaltina 253 assessments for, how paid 137 Belgian 9, 184 best for steep grades 483 brick 258 broken stone 329 ceramite blocks for 143 chert 142 choice of 136 coal-tar 211, 212 cobblestone. ... 1 82 combination, wood and asphalt 144 construction of, early . . . . 178 crown of, formula for laying out 2( 2 on side-hill streets 201 principles for determining 200, 201 table for 202 definition of 135 derivation of word . . . . , 135 early, of Albany ; 13 Baltimore 11 Boston 10 Chicago 11 Cleveland 12 Europe 179 New Orleans 12 Philadelphia 11 San Francisco 12 St. Louis 13 early wood, of London 6 estimated value of, in New York. 136 experimental wood 140 INDEX. 519 PAGE Pavements, favorableness to travel, discussion of 164 examples, of in Brooklyn 164 London 165 Poughkeepsie 164 for country roads 169 for residence streets 168 glass 141 granite 188 accidents on 161, 162 slipperiness of 161 grass 140 Guidet ft increase of, in last decade : in Boston 173: in Brooklyn 173- in Buffalo 173 in Chicago 173 in New York 173 in Philadelphia 173 in St. Louis 173 in Washington 173 influence of 1 35 iron 138 iron in Berlin 139 iron macadam 141 jasperite 140 jetley 145 joint filling for, see Brick, Stone, and Wood pavements. material used in 137 Medina sandstone 207 method of payment for 138 mileage of, in New York 136 noiseless stone 144 of Catania, Italy 179 of Cordova, Spain 5 of Holborn 5 of Italy 6 of Lithuania T of Mexico City & of Philadelphia 14& of Rome 4, 5 of West Indies 7 openings in, how prevented in Rochester 175 how repaired 1 76 number of, in Boston 17& 520 INDEX. Pavements, openings in, number of, in Brooklyn 175 New York 175 purposes of 174 origin of 177 Pelletier blocks 142 Portland cement 142 properties of an ideal 147 cheapness 147 durability 147 durability influenced by what 147 easily cleaned 150 easily maintained 1 51 favorableness to travel 152 non-slippery 151 resistance to traffic 151 sanitariness 152 relative values of 167 renewal of 170 repairs to cobblestone \ 164 granite-block 163 macadam 163 sanitariness of 166 conditions of 166 examples of, in New York 166 how accomplished in London 165 Scrimshaw... 211 selection of material for 146 shell 142 specification Belgian 186 steel-rails in 143 study of standard 153 annual cost of 155 durability of 154 easily cleaned 156 economic life of 1 55 estimated life of, in American cities 156 first cost of 154 kinds of 153 life of, in European cities 156 resistance to traffic 156, 157, 158, 159 tar macadam 140 value of 136 wood 293 accidents on 161, 162 slipperiness of 161 INDEX. 521 PAGE Pavements, wood pulp 144 Pavement between street-car tracks, how paid for 425-428 how laid 454 Paving-brick, analysis of 260 crushing clay for 90 density of 264 first used 89 form of 280 hardness of, how tested 262 homogeneity of 263 porosity of 264 production and value of 89 relative values of 277, 278 requirements of 261 size of 279, 280, 281 specifications for 281, 289 strength 263 tests for abrasion 266 absorption 270 cross- breaking 273 crushing 275 hardness 262 in Columbus, Ohio 279 toughness of 262 uniformity of 263 wear of 265, 266, 267 Paving-brick, manufacture of: annealing, importance of 94 time required for 94 burning, beginning of vitrification 93 changes of clay in 93 fuel for 94 importance of , 93 kiln for 93 pugging 90 temperature for 94 time required for 94 drying 92 screening clay for 90 machine for 91 capacity of 91 moulding 91 repressing 92 sorting, proportion of different grades 95 Paving-cement, amount per square yard of pavement 199, 205, 292 composition of 197, 319 522 INDEX. PAGE Paxing-cement, temperature of 205, 319 Paving material, report of Philadelphia committee on 180 St. Louis experiments on 155 Pelletier blocks 142 Penalty for failure to complete contracts 384 Pennsylvania bluestone 3O Petrolene 51 formula for 52, 54 Petroleum, asphalt from 64 amount of 65 California 44, 50 Eastern 50 oxidation of , 43- requirements of.. 398 residuum, amount used with Trinidad asphalt 223- as a flux 221 Philadelphia, early pavements of 11 streets of & Pitch, derivation of word 40 Pitch Lake, Wall and Sawkins, description of 48 Pittsburg flux 223- Plans, how much to be shown on 378 object of 37(> should be part of contract 389* should be signed by contractor 389 should show amount of work to be done 379, 389- should supplement specifications 376 when to be prepared by contractor 378 Plasticity of clay 82, 84, 87 Pompeii, streets of 7 Porphyry, analysis of 80, 86 description of 20 formation of 20 Portland cement 97 for joint-filling 197, 291, 301 pavements 141 Potsdam sandstone 32 1 Pottery, early use of 88 Proposals, conditions of 391 Pyroxene 16 Quartz 14 Quartzite 15 Kails of street-car tracks, Boston 436 " subway 437 early form of 430, 431 INDEX. 523 PAGE Rails of street-car tracks, girder, centre-bearing 433 life of 450 renewable heads 432, 433 side-bearing 434 tee 437 Trilby 435 Trilby modified 435 Railway ties, chemical treatment of 324, 325 Refractoriness of clay 84, 85, 87 Repairs, see Maintenance. Repairs to coal-tar pavements, cost of 212, 213 Report on rock-asphalt pavements of London 243 Roads, asphalt, in California 12 charcoal 293 first, in France 4 Rome 2 Spain 4 stone 2 macadam 350 Mexican 3 officials, first, in France 3 Peruvian 3 Roman 177 Russian 4 Roadway of street, how determined 460 width of 460, 461 Rock, definition of 14 stratified 14 study of 16 unstratified 14 Rock-asphalt, California 66 European 67 Indian Territory , 76 Kentucky 72 Texas 73 Rock-asphalt pavement, binder not used with 243 bitumen in 242 Buffalo 241 composition of 241 how laid 242 London report on 243 specifications for, in St. Louis 242 temperature of, when laid 243 Hollers, size of, for asphalt pavements 234 524: INDEX. PAQK Rollers, size of, for broken-stone pavements 338, 348, 349 Rolling, amount for asphalt 235 macadam 338, 341, 342, 34a depends upon what 340 standard for 342 Rome, pavements of 4, 5 Rumbling of brick pavements 285 Russ blocks in New York 9- Ruts in macadam roads , 371 Sample to be submitted 390, 392 Sand, amount of, in asphalt pavement 489 formation of 27 size of, in asphalt pavement 227 voids in 122 Sandstone, Berea 32: Colorado 33 color caused by 28 description of 28 formation of 28 Hudson River , 29 kinds of 29* Medina 31 Potsdam 32 strength of 33 San Francisco, pavements of 12 Scrimshaw pavement 211 Set, initial 107 final , 107 Shale 83 analysis of 85 Shale brick 85 Shell pavement 142 Sidewalks, brick 477 cement 478- specifications for 478, 479 in business sections 474 material for 475 slope of 474 space for, how treated 462 stone. 475 specifications for 479 width of ; 462, 474 Sioux Falls stone 21 Slate 83 Specific gravity of paving-brick 275, 27& INDEX. 525 PAGE Specifications, Belgian blocks 185 Belgian-block pavement 186, 18T Specification, acceptance of work 41$ asphalt pavement 39T asphaltina cement , 254 asphaltena, wearing surface 254 asplialt-block pavement 413 Belgian block 185 pavement 186 brick 410 in Philadelphia 291 in St. Louis 289 brick pavement 410 in Philadelphia 291 in St. Louis 290 broken-stone pavement, Boston 348 Brooklyn 349- Providence 347 catch-basins to be adjusted . . 41 .> cement 396 curbing 471 gutter 471 sidewalks 478, 470 character of work 391 coal-tar pavement 213 competition allowed 377 concise, to be 376 concrete 396 contractor, meaning of word 416 creosoting 327 in Indianapolis 318 in London 299 railway ties 323 cross-walks 394 curbing 394, 468, 469, 471 damages for non-completion 416 provisions for 415 embankment, how made 393 slopes in 39IJ enforcement of 378 excavation, how made 3SJ3 slopes in 393 extra work, provision for 381 granite blocks 190 pavement 403 526 INDEX PAGE Specification, guarantee 417 hard- wood pavement in London 298 beading-stones , 395 injured material, how replaced. 415 injuries, provisions for 415 macadam roads, New Jersey 366 NewYork 366 Owen's , 368 maintenance 384, 418 manholes to be adjusted 415 Medina sandstone blocks 207 pavement 406 Nicholson pavement 308 object of 376 openings to be restored 419 ordinances to be obeyed 417 pavement, maintenance of 418 payments 420 plain, to be 377 roadbed, how prepared 394 rock-asphalt pavements in St. Louis 242 rubbish, removal of 393 sewer-laying permitted 392 sidewalks, cement 478, 479 how graded 393 stone 479 soft-wood pavements of London 299 street to be cleaned up 415 water-pipe laying permitted ^ 392 wood pavements of Indianapolis 318, 319 work, delay of 417 how protected 416 how suspended 416 partial completion of 416 time of 416 workmen to be discharged 41 6 Sprinkling broken-stone pavements 346 macadam roads 372 Steel rails in paved road 143 St. Louis, early pavements of 13 Stone blocks, size of 191, 192 cementitious properties of 344 tests for 344 value of 360 machine for testing 345 INDEX. 527 PAGE Stone coefficient of wear of 360 for macadam roads 357 Stone sidewalks, foundations for 477 size of stone in. 475, 476, 480 specifications for 479 Strand, London, ordered paved 5 Street-cars, weight of 421 Street-car tracks, amount of, in American and European cities 458 in United States 458 construction of : cost of creosoted ties in 456 cost of, in Minneapolis 449 difference in opinion concerning 422 how decided upon 423, 450 ideal 422 improved forms in Buffalo 438, 430 in Brooklyn 440 in Cincinnati 445 in Detroit 444 in Dublin 449 in Minneapolis 448 in Rochester . . .446, 447 in Sioux City. . .440, 442 in Third Ave., N.Y. 443 in Toronto . . 440 in macadam roads . . 456 recommended for asphalt pavement 453 for brick pavement 455 for granite pavement 453 early rails of 430, 431 improved form of rails 432, 433, 434, 435, 436 filling between flanges of 455 joints in, how made 451, 452 location of Beacon street, Boston 429 Canal street, New Orleans 429 city streets 428 country roads 429 pavement in, how laid ,... 454 Glasgow method 458 in old construction 457 " how paid for in Amsterdam 427 Baltimore 424 Berlin 428 Brooklin 424 Buffalo , 424 Chicago 424 528 INDEX. PAGE, Street-car tracks, pavement in, how paid for in Detroit 424 Dorchester, Mass 423 Great Britain 427 Hamburg 428 Indianapolis 424 New York 425 Philadelphia 42") Rochester 42-"> St. Louis 420 Toronto 4',>6- Vienna 428 Washington 42? traction on 451 Street railways, first operated in Boston 429 Glasgow 430 London 430 New York 42& Philadelphia 429 Streets, courtyards in 460, 462 Boston 10 Genoa 3 Jerusalem 3 London 5 New York 9 Paris 7 Philadelphia 9 Pompeii 7 Thebes 3 space of, how divided 4< 1 width between curbs, how determined 460 treated 460, 461 width of 459- Syenite 19- Syrian asphalt 76 Tar-and-gravel joints, construction of 199- first used T in New York 10- Tar macadam pavement 140 Telford's roads 330- Temperature for laying asphalt pavement 237 Tensile strength, natural cement 101 Portland cement 10T requirements for 109* specifications for 108 Texas asphalt 7a INDEX. 529 PAGE; Thebes, streets of 3 Timber, see Wood. Tires, width of 373, 374, 375 effect of 158 in foreign countries 375 New Jersey 37.0 laws concerning, New York 374 Michigan 373 Ohio 374 Rhode Island 373 Traction, experiments on, by Department of Agriculture 157 Studebaker Brothers 158 general table for 159 Prof. Haupt's table for 158 Society of Arts' table for 1 59 Traffic affected by character of pavement 149 how well cleaned 149 state of repair 149 street-car tracks 149 width of roadway 148 in American Cities 148 European " 148 Tramway streets in Italy 6 Philadelphia 181 Trap-rock 20 analysis of 26, 27 for broken-stone pavements 338, 339 Tresaguet's roads 329 Trinidad Lake, description of 57, 58, 59 location of 57 size of 58 Trinidad Lake asphalt, analysis of 54, 60, 61, 495, 496 bitumen in 228 mining of 58 refining 60, 61 Turkey asphalt 78 Unbalanced bids 388 how prevented in Jersey City 389 Values, relative, of paving-brick 277, 278 Vitrification, beginning of, in burning brick 93 definition of 86 Vitrified brick, see Paving-brick. clay to produce t 87 definition of : 86 test for.. 87 530 INDEX. PACK Voids, broken-stone 120, 124, 343 gravel 124 sand 122, 124 stone and gravel mixed 124 Wax tailings 212 West Indies, pavements in 7 Wood, chemical treatment of : best method 328 Burnettizing 323 creosoting 323 early methods of 323 experiments with railway ties 325 kyanizing 323 method for railway ties 323 operations of 326 railway ties in Germany, cost and durability 325 specificationsjor 299, 318, 327 Wellhouse process modified 324 when necessary in pavements 322 zinc creosote process 325 tannin process 324 Wood and asphalt pavement 145 Wood as a paving material 312, 328 Wood pavements, Australia, cost of 321 description of 320 durability of 321 material for 320 wear of 320 Australian, in New York , 321 Berlin 302 Boston 306, 308 buckling of 316, 317 cedar-block 310 quantity of, in leading cities 315 Chicago, foundation for 310 how laid 311 material for 310 cypress-block 310 Dublin 302 early, of Russia 293 experimental 140 Edinburgh 302 Glasgow 301, 302 gravel and concrete foundations compared 300 Indianapolis, cost of 318 description of 317 INDEX. 531 PAG": Wood pavements, Indianapolis, material of 317 specifications for 318 Ipswich, England 300 Ker system 307 London 6 Australian, in Paddington 300 specification for 298 statistics of 298 Strand district 299 Gary system 294 concrete base, first used for 294 cost of 297 cost of repairs to 297 first laid 293 Benson's system 295 improved system 294 life of 291) method of laying 294, 295 report on 296 wear of 296 Miller system, cost of 310 description of 309 life of 310 Montreal 304 New York 806, 308 Nicholson system, cost of 309 life of 309 specifications for t . . . 308 Oakland, California 316 Paris, amount of 804 cost of 304 description of 303 life of 303 material for 303 wear of 303 Philadelphia, conclusions concerning 306 cost of 305 durability of 306 material for 306 report on 305 Quebec, cost of 305 description of 304 life of... 304 method of laying 304 San Antonio . 316 532 INDEX. PAGE Wood pavements, St. Louis 308 Washington, amount in 1871 307 cost of 307 durability of 307 Wooden roads, early . 293 in Michigan 293 Wood pulp pavements 144 INDEX TO ADVERTISEMENTS. PAGE Barber Asphalt Paving Company, The I Commercial Wood and Cement Company 4 Copley Cement Company, The 5 Cranford Company 3 Lawrence Cement Company, The 2 New York and Bermudez Company 2 Ransome & Smith Company 4 Wilson & Baillie Manufacturing Company, The 5 Wiley & Sons, John 4 OF THE UNIVERSITY ASPHALT PAVEMENTS. FOR INFORMATION, CATALOGUES, THE BftRBER ASPHALT PAVING COMPANY 11 BROADWAY, NEW YORK, OR ANY OF THE BRANCH OFFICES. 1 15,000,000 BARRELS HOFFMAN" Cement Have Been Used on Important Work THROUGHOUT THE UNITED STATES. NO OTHEE CEMENT COMPANY CAN SHOW SUCH A EECOED IHEUWiOMUICL Established 1853. E. R. ACKERMAN, Pres....Assoc. Am. Soc. C. E. SALES OFFICE: No, 1 BROADWAY, NEW YORK. NEW YORK AND BERMDDEZ COMPANY For particulars address General Office, BOWLING GREEN BUILDING, 2 5 Owners of the largest ASP HAL T LAKE in the WORLD, situated in the State of Bermudez, Republic of Venezuela, South America. Bermudez Lake Asphalt is the PUREST and is unexcelled by any other for STREET PAVING, RESERVOIR LINING, WATERPROOFING, ROOFING, etc, NEW YORK. J. P. CRANFORD, President F. L. CRANFORD, ^ice-President. W. V. CRANFORD, Secretary and Treasurer. CRANFORD COMPANY, Asphalt Pavements, GENERAL CONTRACTORS, Mechanics Bank Building^ 215 MONTAGUE STREET, Telephone 1180 Bed.ord. BROOKLYN, NEW YORK. Works: 524 St. Harks Ave. 3 "iron oar Portland Cements Manufactured by GLENS FALLS PORTLAND CEMENT CO. Sole Selling Agent: 'Commercial Wood and Cement Co. 156 FIFTH A7E., NEW Y02Z. From James D. Scfiuyler, Consulting Hydratilic Engineer, JMS Angeles, California. " MY DEAR SIR : " Everybody is simply astonished at the performance of the mixers. They are surely the greatest machines for the purpose ever invented. " I have used all kinds of mixers, but these are so far superior to any other device with which I am familiar that I should never think of using any other. " Sincerely yours, (Signed) " JAS. D. SCHUYLER, M.A.S.C.E." Mr. Schuyler employed six of our drum mixers on the Portland water- works, Portland, Oregon. RANSOME CONCRETE-MIXERS. RANSOME & SMITH CO., 17 and 19 NINTH ST., BROOKLYN, N. Y. From Professor S. S. Netvberr'/'s report on Annual Meeting of the Asso- ciation of German Cement Manufact\irers, Eng. News, Feb. 25, 1897. " In building the Munderkingen Bridge, a concrete of I cement, 2)4 sand, and 5 gravel, mixed in a drum mixer, gave a compressive strength of 340 tons to square foot, whilst the same mixture, in same job, mixed by hand, gave a compressive strength of only 184 tons to square foot." Inspection of the Materials and Workmanship Employed in Construction. A reference book for the use of inspectors, superintendents, and others engaged in the construction of public and private works. Containing a collection of memoranda pertaining to the duty of inspectors; quality and defects of materials; requisites for good construction; methods of slighting work; etc., etc. By AUSTIN T. BYRNE, Civil Engineer, author of " Highway Construction." xvi-f 540 pages. 12010. Cloth, $3.00. Order through your bookseller, or copies 'will be forwarded, postpaid, by the publishers on the receipt of the retail price. NEW YORK: LONDON: JOHN WILEY & SONS. CHAPMAN & HALL, LIMITED. T. HENRY DUMARY, President. S, OLIN JOHNSON, Vice- President. E. H. BAILLIE, Secretary. F. B. JOHNSON, Treasurer. The Wilson & Baillie Manufacturing Co. Main Office and Factory, 85-93 Ninth Street, Brooklyn, N. Y. MANUFACTURERS OF ARTIFICIAL STONE. For Sidewalks, Driveways, Copings, Steps, Bailroad Depot Flat form:, Flooring for Warehouses and Apartment Houses, Water-tight Cellar Floors, and Improved Stable Floors. Kosmocrete Steel-Bound Curb, " Wainwright's Patents." The Steel-Bound Curb is su- perior to any natural stone. Laid in ten-foot lengths, with invisible joints, with concrete foundations, is never out of line. Galvanized steel edges cannot rust or break. It is the most beautiful and durable curb laid, and with gut- ter combined is the ideal for as- phalt, brick, or macadam streets. Heavy Concrete Construction A Special Feature of our Business. A natural cement resembling a Port- land in color and texture. ROSENDALE CEMENT The most eco- nomical cement on the market on ac- count of its great sand-carrying ca- pacity. MANUFACTURED BY THE COPLAY CEMENT CO. The favorite brand of natural hydraulic cement for the concrete foundation of street pavements. 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