Asphalts, their sources and utilizations

Contents

Chapters

I. — Discovery and Early Use of Asphalt.

II. — Rock Asphalt Mastic or Asphalt Coule.

Preface

TIS book was suggested by a series of articles that appeared some years ago in Architecture and Building. Since the numbers containing these articles ran out of print, there has been a continuous call for them, and the request was made that they be issued in book form.

The great advance of late in the asphalt industry has called for a complete manual on the subject. This the author has endeavored to furnish, so that architects, engineers and students in the technical schools and municipal officers having charge of road construction may have a reliable reference book on the subject.

As will be seen, many new features in the exploitation and utilization of asphalt have arisen during the first eight years of this century; and undoubtedly the greatest demand yet known is still to come for the purpose of surfacing dustless roads. This line of work is very fully treated of, and, to the author's mind, is the question of the day.

I have endeavored, without fear or favor, to give credit to all producers of asphalt in every country and clime and to give to all their due. I have made no comparisons of asphalts as against other materials, although some of my sources of information may have incidentally given statements showing the superiority of asphalt over other materials for waterproofing, etc.

This book is the result of thirty-six years of active life among asphalt mine owners, refiners, importers, exporters, manufacturers and contractors, and, as will be seen, has taken me to many countries, in all of which I have endeavored to glean information from all interested, from presidents of corporations to the humblest stirrer of an asphalt kettle.

To give due credit to all to whom I am indebted for information would well nigh call for an additional volume. At the risk of seeming ungrateful to the many, I wish to record special obligations to the late Leon Malo, C. E., and his coadjutor W. H. Delano, C. E., to the "Good Roads Magazine," "Municipal Engineering," and other technical journals; principally to the efficient, painstaking officials of the Bureau of Public Roads of the Department of Agriculture, whose work in helping the people of the United States to utilize their opportunities for building "goods roads" in the various sections of the country cannot be too highly spoken of; and last, but not least, to my worthy publisher, W. T. Comstock, and to my son, Kitchell Monckton Boorman.

T. HUGH BOORMAN.

New York. Sept. 14, 1908.

Preface To Second Edition

Since the first edition of "Asphalts" went to print, there have bee» three International Conventions on Road Construction, held respectively at Paris, Brussels and London.

Conventions of National, State and minor sections have been too numerous to mention; the knowledge disseminated at these many meetings has been extensive and interesting. The general tenor of the discussions has created a heavy demand for asphalts of all descriptions and the commercial interests involved are now very heavy. Some of the older known asphalts have become discredited to a great extent and the user of asphalt* has now many opportunities of purchasing materials, capable of meeting any specifications drawn by conscientious engineers.

I have been frequently asked if I made any statements in the 1908 edition which I should wish now to modify. I am glad to state that I can stand today for everything I wrote that year.

Along the line of road work many developments have taken place, and in the five new chapters of this edition I have striven to give some of the new methods of construction evolved since 1908.

I have endeavored by attending conventions, college and engineering society's lectures, and by careful reading of the technical journals, and by revisiting England, to keep in touch with all improvement in street and road construction which have been developed since the time of the first edition.

In the immense amount of treatises and papers on bituminous construction presented before conventions, engineers' associations and colleges, it is lamentable to find how few can be received as from unbiased sources. This is the day of astute advertising, and in addition to their regularly paid employes, such as consulting engineers, chemists and salesmen, the large corporations subsidize to an immense extent the daily and technical press so that the unsuspecting layman seeking information on asphalt, is apt to be misled through statements of merits of individual brands of asphalts, emanating from such clever salesmen with their various titles ranging from college professors to daily news reporters. The most flagrant advertising dodge was that of an asphalt company who offered a premium of $100 to be awarded to the highway college student who produced the best treatise on asphalt.

A recent clipping from an unknown source affords an interesting if not instructive statement of the use of asphalt in "ye olden tymes" :

There was nothing slow about the ancient Romans. They used a cement the formula for which many a manufacturer would be glad to have. They built roads so costly as to make the modern politician green with envy. They even were acquainted with asphalt and bitumen. Tacitus, writing about 55 B. C, describes this material as follows:

"At a stated season of the year, the lake throws up bitumen. Experience, the mother of all useful arts, has taught men the method of gathering it. It is a liquid substance, naturally of a black hue, and by sprinkling vinegar upon it, it floats on the surface in a condensed mass, which those, whose business it is, lay hold of with the hand, and draw to the upper parts of the vessel; thence it continues to flow in and load the vessel, till you cut it off. Nor could you cut it off with brass or iron. It shrinks from the touch of blood." * * *

T. HUGH BOORMAN.

Nsw York, April 25, 1914.

Chapter I. DISCOVERY AND EARLY USE OF ASPHALT

CONSIDERING the importance of the subject little has been published in regard to the material known by the generic name of asphalt. A few books and many short papers read before engineering societies, prepared for technical journals or for the circulars of asphalt companies, comprise, generally speaking, the literature on the subject. These have been written almost exclusively by engineers in the employ of special companies or others financially interested in particular asphalt deposits or mines, and so necessarily have dealt with the subject within a much confined limit.

It is proposed in this book to discuss the various kinds of asphalt and their adaptability for different methods of construction. In the first place all disputes on the nomenclature of asphalts must be avoided and the fact conceded that the hydro-carbons, viz., asphalt, bitumen, and maltha, are synonymous, while differing in chemical composition. I am the more anxious to take this ground, as in going back to the earliest times in which asphalt is known to have been used it is necessary to refer to the mineral pitch, or bitumen, as being the material quoted. The first use of asphalt spoken of was the cementing in the erection of the Tower of Babel ; next we read that Noah pitched the Ark within and without, "bituminabis cum bitumine," says the Vulgate, and also in Genesis we read, "Et asphaltus fuit eis vice cimenti." The great law-giver, Moses, was preserved from death at the suggestion of the Egyptian Princess, in a basket rendered waterproof by bitumen.

Felltham wrote in the beginning of the 17th century of the "Bituminated walls of Babylon;" the source of its supply, the fountains of Is, on a tributary of the Euphrates, still yields asphalt.

Xenophon in his Anabasis speaks of the Median Wall as being

ASPHALTS. [chap. i.

built of "Burnt brick laid in asphalt." Diodorus Siculus describes the process of laying the walls of Nineveh with material from the same source. He says : "In order to bind the bricks they were covered with a layer of asphalt, instead of simple tempered clay, and were arranged in courses, and between each thirteenth course a bed of reed canes was introduced." Diderot's Encyclopedia attributes the burning of Sodom and Gomorrah to the accidental ignition of petroleum or bitumen, but the word petroleum not having been known to ancient writers, the legend probably refers to maltha or bitumen. Other ancient authors mentioning asphalt were Herodotus, Aristotle, Strabo, Pliny and Homer.

The Egyptians made extensive use of bitumen; it was spread upon the bandages wound around their mummies, and its wonderful preservative properties can be seen in our museums, where so many of their illustrous dead now have their abiding place. Asphalt was also used by the Egyptians in the foundations of the Pyramids, and for the coating of the external and internal walls of the ground floors of houses, and in the construction of cisterns, silos and other work where waterproofing was necessary. Therefore, from before the time of the Deluge, asphalt has been used and referred to, and it is no new subject to be considered.

During the Middle Ages we read nothing of its use, and not until 1 72 1 do we hear of a treatise on asphalt being written by Eyrini d' Eyrinis, professor of Greek, doctor of medicine, in which he wrote in a half serious, half-humorous manner of its uses for building purposes, and claimed it as a panacea for almost every sickness. This treatise, I understand, was reprinted by M. Leon Malo, C. E., the most able exponent of the Rock Asphalt industry, and to whose works I shall have to refer frequently.

The asphalt beds, or mine, which were discovered by Dr. d'Eyrinis in 1710 were those of the Val de Travers, in the Canton of Neuchatel. The doctor recommends the material, describing it as "Peculiarly suitable for covering all kinds of construction, to protect wood and stone work against decay, worms and the ravages of time, rendering them almost indestructible, even when exposed to wind, wet and extreme variations of temperature."

d'Eyrinis succeeded in using it with good effect for the lining of cisterns and walls, as a cementing material, and for the flooring of warehouses, etc.

After some time the material fell into disuse; the quarries of

DISCOVERY AND EARLY USE. II

\ al dc Travcrs were even forgotten, and it was not till the year 1832 that the material was again prominently and successfully reintroduced; the credit on this occasion being given to the Count Sassenay, and in 1838 the first asphalt sidewalks were laid in Paris. The rock asphalt seems to have been used in its mastic form for sidewalks and floorwork up to the year 1854, when M. Vaudry laid the first compressed rock asphalt roadway in Paris. The earliest knowledge of the adaptability of asphalt for this purpose seems, from M. Malo's account, due to the perspicuity of a Swiss engineer, M. Merian, who, in 1849, found that in summer the pieces of rock that fell from the carts in traversing the road between the mine and the mastic works at the village of Travers compressed under the wheels ; he put this lesson to profit by constructing a macadam road of crude rock asphalt, which was compacted with a roller. In spite of the instability of its foundation and the irregularity of its maintenance the road was reported by M. Malo as in good order in 1866. From the Rock Asphalt Mines, therefore, it may be considered that there was started the great industry of asphalt street pavements, which add so much to the appearance and health of our modern cities. Under these circumstances it seems only right to first take up the subject of Natural Rock Asphalt. It was, I believe, first brought prominently before the notice of the American Engineers by Mr. Edward P. North, C. E., who, in a paper read on April 16, 1879, before the American Society of Civil Engineers, on "The Construction and Maintenance of Roads," gave his impression from observation and information acquired by him on the subject of asphalt streets in London and Paris.

Compressed Neuchatel rock asphalt was, however, laid in New York, in Union Square, in 1872, the writer having taken part in the actual work of laying it. This pavement, however, owing to a lack of heavy traffic, did not prove a success, and some ten years later it was replaced with asphalt mastic, which was partly manufactured from the old rock pavement. The original company laying the work became financially embarrassed and went into the hands of receivers, and it was under orders of the latter that four blocks of Natural Rock Asphalt streets were laid on Pennsylvania avenue, Washington, with Neuchatel rock in 1876. This pavement, however, not having any company to look after its maintenance, was repaired with Trinidad asphalt mixture, with which material eventually it was entirely resurfaced.

12 ASPHALTS. [chap. i.

Three or four years later the Neuchatel Asphalt Company, of London, owners of the. Val de Travers' concession, sent over as their representative the late Captain Henry R. Bradbury, who supervised the laying of Neuchatel rock pavement in front of the Brevoort House and Hotel Victoria, on Fifth avenue, New York; his successor in the American management, Mr. Robert Butcher, found that the prices attainable for the work here did not compare favorably with those obtained in European cities, and has not followed up street pavement work.

In 1892 the Compagnie Generate des Asphalte de France established a model rock asphalt plant at Long Island City, and under the management of the author from 1895 to I 9 00 some 28,000 square yards of compressed asphalt were laid in New York, and about 15,000 square yards in Brooklyn. During this period a large amount of rock asphalt was also supplied from the Seyssel and Ragusa mines for use on streets in Philadelphia, Boston and Montreal.

The generally recognized standard European rock asphalts are those of Seyssel, in the Department of Ain, France, and the Val de Travers, in the Canton of Neuchatel, Switzerland. Important deposits are now being operated at Ragusa, Sicily; four companies are working adjacent mines, viz. : The Val de Travers Asphalt Paving of London, the United Limmer & Vorvohle Rock Asphalt Co., the Societa Sicula per L'Explotazione Dell Asfalta Naturale Sicilians, Palermo, and H. & A. B. Aveline Catania, exporting large quantities to Europe and America, their shipping ports being Mazzarelli, Syracuse and Catania — other deposits are found at Mons, Department of Gard, France; Lobsann, in Alsace; Limmer, near Hanover, Germany; San Valentino, Province of Chieti, Italy; Maestu, in Spain, and in several parts of the United States, which, of late, having become quite an important feature in the asphalt industry, will be considered in full in a subsequent chapter. Mr. W. H. Delano, of Paris, in his "Twenty Years' Practical Experience of Natural Asphalt and Mineral Bitumen," published in 1893, gives the analysis of natural rock asphalt as follows: As mined, the rock should be of a chocolate color, fine in grain, evenly impregnated with bitumen, free from sulphur, pyrites, clay, sand and of other extraneous matter. When examining with microscope always look at a fresh fracture. Rich Val de Travers rock, containing, say 11 to 13 per cent, bitumen, should be mixed with equal

DISCOVERY AND EARLY USE. 13

parts of fine Seyssel rock containing 7 per cent, of bitumen, which is fixed and invariable, producing thus :

11 + 7

=g per cent, powder, suitable for a climate like that of Lon-

2 don. The same may be done with Ragusa (Sicilian rock), which is rich in bitumen of excellent quality, only the texture or grain of the limestone is loose, whereas that of Seyssel is fine and dense. Mons and St. Jean de Marejols asphalts are similar in structure to Ragusa, but the limestone is much finer.

The rough and ready way of testing rock asphalt is to dissolve a sample of its powder taken from three-ton bulk, in carbon bisulphide, turpentine, or ether. After stirring this well with a glass rod, strain it through a thick paper filter; then let the sulphide evaporate, which it will do at 70 degrees ; weigh the bitumen and the residuum, afterwards washing the latter in hydrochloric acid, which will cause the lime to effervesce, leaving any residue of silica, pfyrites, etc. ; but for an absolute test an analyst accustomed to hydro-carbons should be called in.

In connection with this the following tables, showing the comparative analyses of asphalts, are given on the next page. They were prepared by Col. James W. Howard, B. L., C. E.

The rock asphalt industry may be divided into two branches. The "comprime," or compressed work, and the "coule," or mastic work. For streets the compressed asphalt is used. The rock in its crude condition is placed in a crusher and reduced to small pieces and then passed through a disintegrater and reduced to a powder ; it then passes through a twenty-mesh sieve, nothing being added to or taken from the powder obtained by grinding the bituminous rock. The powder should contain not less than 9 per cent, of natural bitumen. The powder is then heated in a suitable apparatus to 200 degress to 250 degrees Fahrenheit, and must be brought to the street at a temperature of not lss than 180 degrees Fahrenheit in carts made for the purpose, and carefully spread to such depth that after having received its ultimate compression it will have a thickness of two inches. The surface is rendered perfectly even by tamping, smoothing and rolling with heated appliances of approved design. This surface should invariably be laid on a foundation of six inches of Portland cement concrete.

ASPHALTS.

[chap. i.

Table I.

ANALYSES OF CRUDE ASPHALTUM FROM A FEW COUNTRIES, ETC.

California. Cuba.

Bitumen 38 to 85% 24 to 68%

Mineral matter 60 to 8 73 to 26

Organic matter 1 2 to 1

Water 2 to 6 1 to 5

Mexico. 35 to 94% 55 to 4

8 to 2

Venezuela. 45 to 95% 40 to 2

7 to 1

8 to 2

ANALYSES OF ASPHALT ROCK FROM A FEW COUNTRIES, ETC.

California.

Various.

Indian Ter.

Various.

Kentucky.

Various. % 4. to 10.70

Calcium Carbonate 9.10 80.00

Alumina, etc 15.90 0.10 to

Magnesium carbonate

Miscellaneous ... 3.80

1.11

1.86 0.30

0.37

Texas.

Various.

88.32

6.0

0.3

0.29

Utah.

Various.

27.74

2.77

Table II.

♦CLASSIFICATION AND LOCATION OF CERTAIN

COMPOUNDS.

IMPORTANT BITUMENS AND

GLANCE-PITCH, ASPHALTUM, MALTHA. ASPHALT AND BITUMINOUS ROCK.

Pure or Nearly Pure (with Small Per Cent, of Mineral and Organic Matter).

Argentina.

Barbadoes.

China.

Cuba.

Egypt.

Equador.

Honduras.

Japan.

Mexico.

Russia.

Syria.

Turkey.

United States.

Venezuela.

Compounded with Compounded with Limestone (Contain- Sandstone (Containing Silicates, etc.). ing Carbonate of Lime, etc.).

Compounded with Earthy Matter (Large Per Cent, of Silicates, Alumina, etc.).

Argentina.

Australia.

Barbadoes.

China.

Colombia.

Cuba.

Egypt.

Equador.

France.

Germany.

Honduras.

Japan.

Mexico.

Peru. * Russia.

Syria.

Trinidad.

Turkey.

United States.

Venezuela.

♦From Paper on "ASPHALTUM" by J. W. Howard of New York, of the American Society of Municipal Engineers.

Austria.

Cuba.

France.

Germany.

Hungary.

Italy.

Russia.

Sicily.

Spain.

Switzerland.

Turkey.

United States.

France.

Germany.

Italy.

Russia.

Sicily.

Spain.

Turkey.

United States.

at convention

Chapter II. ROCK ASPHALT MASTIC OR ASPHALT COULE

ROCK asphalt mastic, or asphalt coule, as it should more properly be called, forms a most important branch of the asphalt industry, Dr. d'Eyrinis was its first exponent, and so far as I know Dr. Jeno Kovacs the last, the latter, in his report on asphalt read in 1901 before the Budapest congress of the "International Association for the Testing of Materials." The term mastic I must state is most misleading, and I fail to find how the term originated. The word is French, not English. The Anglican noun "mastic" distinctly applies to the resinous substance obtained from the mastic tree, or to a kind of mortar composed of finely-ground oolitic limestone mixed with sand and litharge and used with a considerable portion of linseed oil; hence frequent confusion when the word mastic is used in specifications. The French word "mastic" is used for cement, and is more applicable. Still, with the innumerable cements used in construction, it would seem better to refer to coule, or melted asphalt, when speaking of the use of asphalt in other than its powdered form. The preparation of asphalt coule is as follows :

The rock, after being reduced to a powder, is placed in cylindrical kettles, in which about 8 per cent, of Trinidad asphalt has previously been placed and melted. The mass is stirred by revolving arms and agitators at a temperature of about 350 degrees F. for about nine hours. It is thus thoroughly "cooked," and is then run out of the kettles into moulds, where it cools in the form of cakes or blocks, weighing from 56 to 60 pounds each. These are stamped with the brands of the mines. The mastic so prepared should show an analysis about as follows:

Bitmumen 14-50 per cent.

Carbonate of lime 85.00 " "

Silica, alumina and oxide of iron. .50 " "

100.00

16 ASPHALTS. [chap. ii.

To use it for walks or floors the blocks are broken up and again heated in suitable kettles and mixed with fine gravel or sand and Trinidad in the following proportions:

Mastic blocks (broken) 60 lbs.

Trinidad asphalt 4

Fine gravel and sand 36

This is ''cooked''' for about five hours at a temperature of about 360 degrees F., great care being taken constantly to stir the mixture. It is then taken out of the kettle by the bucketful and poured on the foundation prepared, its consistency being such that it will flow very slowly. It is then spread by means of wooden trowels and compressed and smoothed by rubbing, as in plastering. Soon after the introduction of asphalt coule in Paris it was introduced into the United States by a Philadelphia architect. The floors of the portico of the old Philadelphia Merchants' Exchange were laid with it about the year 1838, as stated by me in my paper on "Asphalt in Building Construction," read before the Brooklyn Architectural Students' League., May 14, 1890. Subsequently the War Department imported the material for covering the arches over casements and magazines in some of the forts, of which Fort William, on Governor's Island, was one. The great fire in Boston in 1872 first drew my attention to the desirable qualities of asphalt as a fireproof covering for roofs, and I introduced its use there in 1873. That this material is a most effective fireproof protection should be recognized.

In 1835 a number of the inhabitants of the city of Bordeaux certified that at the time of the conflagration of the Bazaar Bordelais, which happened on December 28th of that year, a number of burning beams, rafters and other bodies in flames fell on that part of the building covered with asphalt without causing it to melt, and further attested that the said roof so covered had not been injured to any material degree. Of the great fire in Hamburg in 1842, which destroyed, with other buildings, the Church of St. Nicholas, the London "Times"' of the 28th of May of that year, said :

"It was remarked as a singular circumstance during the conflagration that roofs covered with asphalt, of which there are some here, opposed rather than encouraged the progress of the flames.

h i, l,|J.

9 BrRNUVEmsOH.

CITY HALL, PHILADELPHIA.

Roofs and corridors laid with Asphalt Coule by The Vulcanite Paving Company.

ROCK ASPHALT MASTIC. 17

It was imagined on account of the substance of which these roofs were composed that they would easily catch fire and be the cause of great mischief. Such, however, was not the case, for it appears that the fire had little or no effect on them, and when the roofs of the houses fell in, the asphalte, in which a sort of rubble is mixed up, was found to have resisted the effects of the heat, and, like a mass of dirt, served rather to smother the flames than to give them increased vitality."

Very exhaustive tests were made for The Omnibus Co. of Paris in 1868 by MM. Flachat and Noissette, who submitted the results to the French Society of Civil Engineers. The insurance companies in the United States give special rates where asphalt is used for roofs.

The specifications usually read:

"For roofs on concrete , foundations properly leveled and graded, lay one inch of Seyssel or Neuchatel rock asphalt mastic, applied in two coats, on three thicknesses of roofing felt cemented with asphalt."

Copper flashing should always be specified in connection with this roofing. The roof of the Philadelphia City Hall was laid by the Vulcanite Paving Co. with asphalt mastic, and the same material was used in the corridors of the building. The use of asphalt coule is by no means confined to roofs ; it is a desirable material for construction, from the damp course in the foundation of a building to the roof on the top of the same. Used as a damp course in the foundation, it arrests absolutely the capillary attraction that is. so fatal to many buildings and renders them unhealthy through dampness. Cellars should be floored with asphalt so as to insure dryness and health.

As flooring for use in hospitals, lavatories, laboratories, laundries, refineries and mills it stands without a peer. It is impenetrable by moisture ,and will not crack from settlement of masonry, as will rigid and unyielding substance like artificial stone made from cement. Its characteristic of elasticity allows it to take up the varying strains and settlements that will occur in any masonry without cracking. Used as a foundation under heavy machinery, it absorbs all vibration and makes possible the mounting of the heaviest machinery in closely crowded quarters. As a flooring for railway stations, it will stand without cracking or splitting the impact of heavy blows from the dropping of baggage; it is not slipl8 ASPHALTS. [ch*ap. II.

pery, and can be laid in a monoltihic sheet without joints, which cannot be said of artifical stone. It is particularly recommended for breweries, paper mills, pulp mills, laundries and other floor surfaces, which from the nature of the business are frequently wet and covered with water. It will not rot; it has no joints; no water can leak through to damage ceilings or goods stored in lower floors.

Under usual circumstances one inch of asphalt mastic will stand any ordinary traffic. In exceptional cases, however, such as in wash houses and racking cellars of breweries, a thickness of one and a half to two inches is advisable.

For cellars and floors for light business purposes three-quarters of an inch will suffice.

Asphalt floors are preferably laid on concrete three inches thick, or in case of fireproof construction of hollow brick arches concrete leveled off about half an inch above the iron beams. Still, asphalt can be laid with advantage on wooden floors, in which case felt paper is laid on the boards to prevent any trouble from warping of the wood. One of the largest fields for the use of asphalt coule is for park walks. For nearly a quarter of a century the Park Department of New York has used this description of pavement, and with the exception of Madison Square, every park from the Battery to St. Mary's, in the Bronx, has had almost its entire walk areas finished with an asphalt surface.

In view of the satisfaction that this work has given, it may be well to give the specification prepared by the department engineer, who, after calling for a foundation of three inches of Portland cement concrete, says :

"After the base has been prepared as specified, and with its surface clean and dry, a layer of Seyssel or Mons, Neuchatel, Sicilian or Limmer asphalt mastic, in no place less than one inch in thickness, after having received its ultimate compression, is to be placed upon the base, carefully and evenly compressed with the proper tools for that purpose, and the finished surface to be free from depressions and truly and evenly surfaced to the finished grades and crown of the walk. The asphalt mastic to consist of natural bituminous limestone rock (i) from the French mines of Seyssel or Mons, equal in quality and composition to that mined by the Compagnie Generate des Asphalte de France; (2) from the Swiss mines at Val de Travers, equally in quality and composition to that mined by the Neuchatel Asphalt Co., Ltd.; or (3) from the Sicilian mines

ROCK ASPHALT MASTIC.

at Ragusa and the German mines at Limmer, equal in quality and composition to that mined by the United Limmer and Vorwohle Rock Asphalt Co., Ltd., mixed with fine, clean grit and refined bitumen, in such proportions and in such manner as to insure work that shall be sound and free from cracks and impervious to moisture under all climatic changes, and so as not to flow or spread in summer or crack or disintegrate in winter, and as shall be directed by and to the satisfaction of the engineer."

Rock asphalt coule has been used for many other purposes than in building and for sidewalks. The latest use I have seen was for medallion plaques. Among the larger calls for this material is that for reservoir linings. Municipal Engineering in one of its issues describes the construction of one in Astoria, Ore., where the bottom was covered with 6 inches of concrete containing 0.9 cu. yd. of crushed rock, 0.5 cu. yd. of gravel, 0.1 cu. yd. of sand and one barrel of Portland cement per cu. yd. cut in blocks of 20 ft. square, with y 2 -mch asphalt joints, and this was covered with a ^-inch cement mortar finish and two coats of asphalt, one soft and the other harder, and together a little more than one inch thick. The slope had 6 inches concrete, 2-3-inch asphalt, a layer of brick and a second layer of asphalt 0.5 inch thick. The most common practice is probably from 18 to 24 inches of clay puddle under concrete or paving.