SHEET ASPHALT PAVEMENTs A sheet or monolithic asphalt pavement consists primarily of (1) a wearing coat 1 1/2 to 2 inches thick composed of asphaltic paving cement mixed with sand; (2) a binder course composed of broken stone and asphalt cement; and (3) a foundation of hydraulic cement concrete or an old pavement of cobble stones, granite blocks, bricks, or the like. In this country when the term asphalt pavement is used the above form is usually intended. The term sheet or mono lithic pavement is not distinctive, since rock asphalt also is laid as a continuous sheet; but no confusion is likely to result, since in this country the term sheet is commonly used to distinguish the mono lithic form from the asphalt block pavement, and since in Europe only one form of asphalt pavement is used, monolithic natural rock. In contra-distinction to a pavement made of natural as phaltic limestone or sandstone, the above pavement could with some propriety be called an artificial asphalt pavement, or the wear ing coat could with still more propriety be called an artificial asphal tic paving compound; but the distinction is not important since the sheet asphalt pavement is laid almost exclusively in this country and the rock asphalt almost exclusively in Europe.
HISTORICAL.The first artificial sheet asphalt pavement in this country was laid in Newark, N. J., in front of the city hall in 1870. In 1873 a small piece was laid on Fifth Avenue, New York City, opposite the Worth Monument. A few other experimental sections were laid; but the first test on a large scale was in 1876 on Pennsylvania Avenue in Washington, D. C. Preceding 1882, out side of Washington, D. C., there were not more than half a dozen streets in this country paved with any form of asphalt; but since that date, asphalt pavements have increased rapidly, and now hun dreds of miles of it are in use on the streets of American cities. The following statistics show the rapid growth of this industry: In this country in 1880 there were 300,000 square yards of sheet asphalt pavements; in 1885, 1,800,000; in 1890, 8,100,000; in 1895, 21,500,000; in 1900, 38,000,000.* In Europe in 1900 there were only about 3,000,000 square yards of asphalt pavements of all kinds.