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asphalt(ăs`fôlt, –fălt), brownish-black substance used commonly in road making, roofing, and waterproofing. Chemically, it is a natural mixture of hydrocarbons. It varies in consistency from a solid to a semisolid, has great tenacity, melts when heated, and when ignited will burn with a smoky flame leaving very little or no ash. It is found in nature in deposits called asphalt lakes. Natural asphalt was probably formed by the evaporation of petroleum. Asphalt is obtained as a residue in the distillation or refining of petroleum. This is its important commercial source. It occurs also in asphalt rock, a natural mixture of asphalt with sand and limestone, which when crushed is used as road-building material. Asphalt is also used in the manufacture of paints and varnishes, giving an intensely black color.
a resin; a distinction is made between natural and artificial asphalts.
Natural asphalt is formed from petroleum as a result of the evaporation of light fractions and of oxidation under the influence of hypergenesis. The petroleum first changes into thick and highly viscous maltha, then into hard and easily fusible asphalt. Further change in natural asphalt usually leads to the formation of asphaltite. Sometimes natural asphalt forms a fairly thick crust on the surface of large petroleum lakes (such as the asphalt lake on the island of Trinidad). Natural asphalt is widespread in regions where oil-bearing rocks occur on or not far below the earth’s surface.
Natural asphalt usually fills crevices and caverns in limestone, dolomite, and other rocks. Its content in rocks varies from 2–3 to 20 percent by mass. Large natural-asphalt deposits in the USSR are located in Kuibyshev and Orenburg oblasts and in the Komi ASSR. Elsewhere, they are found in the oil-bearing regions of Venezuela, France, Jordan, Canada, and Israel.
Artificial asphalt is a mixture of bitumens (13–60 percent) with finely pulverized mineral fillers (chiefly limestone). It differs from natural asphalt by the presence of paraffin (up to a few percent) and by a significantly greater content of petroleum oils.
The most important areas of application for asphalt are in road-building and in construction. When applied, asphalt is usually mixed with sand, gravel, or crushed rock (forming asphalt mastic) for building floors, sidewalks, and road surfaces; for waterproofing; and for other uses. Asphalt mastic is a component of asphalt concrete.
Artificial asphalt is also used in electrical engineering as an insulating material and in the production of roofing paper, plastering materials, glue, asphalt lacquers, and other products.
REFERENCESOsnovy geneticheskoi klassifikatsii bitumov. Leningrad, 1964.
Kostrin, K. V. Pochemu neft’ nazyvaetsia neft’iu. Moscow, 1967.