Engineering and Contracting, Vol. 52

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Excerpt from Engineering and Contracting, Vol. 52: Devoted to the Economics of Civil Engineering Design and to Methods and Costs of Construction, July December, 1919The Top or Bituminous Course - This brings us to the bituminous macadam itself, the materials of which are the stone and the bitumen.The broken stone should not be so soft as to crush under the roller so as to fill the voids before the bitumen is ap plied. When this occurs the bitumen does not fill the voids, and from such spots slack of bitumen there may arise two bad results. There may be a wave, due to the surplus of bitumen on top because it could not penetrate down into the stones, or there may be a breaking up of the surface because the stones have nothing to bind them together. The best results are obtained when hard rocks are used, such as trap rocks. There are many localities where it is impossible to get trap rock or stone with a coefficient of wear sufficiently high to obtain. Results required. In such cases bituminous macadam should not be laid. For ordinary traffic such as exists on most of the main through state roads bituminous macadam can be laid economically, provided broken stone has a coefficient of not less than about 15, and provided the bitumen is of suitable quality. The size of the broken stone should be 114 to or 3 in., according to the thick ness of the course. A top course 2 in. Thick may be obtained with the -in. Stone, while a Sin. Course may' be obtained with the larger size. If the traffic is very heavy it is better to lay the thicker course with the larger stones.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.