Specifications for Waterproofing Floors of Steel and Concrete Bridges

In many places, if not in most places, where asphalt is used, its surface is subjected to the action of water. Street pavements are being continually washed by rains, and during the winter the surface of the asphalt may be for a long time in contact with snow and ice. The various forms of asphalt paints are intended primarily to protect metallic substances from weathering and from the cor rosive action of water. The use of asphalt as a lining for reservoirs brings this subject into still greater promi nence. Here the contact with water takes place under various conditions. Above the water line the asphalt sur face may be alternately wet and dry; near the water line it is subjected to the erosive action of the waves and to the force of the ice in winter ; while at the bottom of the reservoir there is the effect of pressure.

It is evident that one of the first requisites of an as phalt for reservoir lining is that it shall not be injuriously acted upon by water, either physically or chemically. If such an action does take place, the efficiency of the sub stance is impaired and the life of the structure reduced. Experience has shown that some asphalts are acted upon by water to a considerable extent, while others are ap parently unaffected.

The samples used in the experiments represented all the leading brands of asphalt on the market.

The experiments were conducted along the following three lines: First, that of placing samples of the asphalt in con tact with water in glass jars, and subsequently noting the change in the analysis of the water, thereby ascertaining the nature of the soluble constituents of the asphalts.

Second, that of immersing samples of the asphalts in water under various conditions, and noting their change in weight.

Third, that of observing the action of water upon the asphalts by noting changes in their physical condition.

In order to study the soluble constituents, the asphalts were melted and poured into glass jars so as to form a layer at the bottom about 1 cm. thick, and having an average area of about 60 sq. cm.; 800 cu. cm. of water were then added, and the jars closed to prevent evapora tion. Two jars were used for each sample, one being filled with distilled water, and the other with surface water from the eastern part of the Brooklyn watershed. In the case of the Trinidad and Bermudez (Venezuela) asphalts, a third jar was prepared and filled with water from some of the deep wells of the Brooklyn water sup ply. At the end of two months a portion of the water in each jar was removed and analyzed. After two years the remaining water was subjected to analysis. The sample of asphaltina was not received until December, 1898, and consequently the analysis represents but one year's action.

For the second series of experiments, the asphalts were melted at as low a heat as possible and poured into watch glasses, where they spread out into thin cakes with smooth surfaces. These cakes contained equal amounts of asphalt and presented surface areas that varied from 45 to 55 sq. cm. The watch-glasses, with their adhering cakes of as phalt, were dried in desiccators and weighed. They were then mounted on agate-ware plates, fastened with cop per wire, and suspended in water. In order to determine the effect of different waters and of different conditions, such as pressure, temperature, light, current, etc., the Trinidad, Bermudez, and Alcatraz D (California) asphalts were suspended in Mt. Prospect Reservoir near the sur face, where the pressure was small and the temperature changes considerable; in Mt. Prospect stand-pipe, at a depth of 50 ft., where they were in darkness, where the pressure was great and also variable, and where the changes of temperature were small; and in the conduit at Freeport, where they were subjected to the action of water different in quality from the two preceding, where the pressure was small, but the current strong. The re maining asphalts were exposed in but one place. From time to time, the samples were withdrawn from the water, and cleansed by washing with distilled water and rubbing with a fine camel's hair brush. They were then dried in desiccators, weighed, and replaced in the water.

The action of the water upon the various asphalts was observed in both sets of experiments by inspection and by microscopical examination of the surface, and, in the first set, by measurement of the depth to which the action of the water extended during two years' exposure. The figures obtained, of course, have only a relative value, as the conditions of the experiments were different from those to be met with in actual practice. The results of the observations were as follows: No. 1. Trinidad Lake Asphalt. The action of the water on this asphalt was strong. Two weeks' exposure caused a roughening of the surface and a change in color from black to brown. With longer exposure the brown color was more conspicuous, and the surface became granular. Finally, the upper portion of the asphalt changed to a soft, punky material, covered with cracks and pits. In the jars a thin layer of loose material had become more or less detached from the surface. The samples that stood in the drawers for two years were examined in cross-section under the microscope, and the depth of the action determined by careful measurement. In the distilled water, the soft, brown surface layer was 1.32 mm. thick; in the surface water, it was 1.12 mm.; and in the well water, it was 1.10 mm.