asphalt

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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.

Asphalt

A mixture of bitumens obtained from native deposits or as a petroleum by-product used for paving, waterproofing, and roofing applications.

Asphalt

 

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.

REFERENCES

Osnovy geneticheskoi klassifikatsii bitumov. Leningrad, 1964.
Kostrin, K. V. Pochemu neft’ nazyvaetsia neft’iu. Moscow, 1967.

asphalt

[′a‚sfȯlt]
(materials)
A brown to black, hard, brittle, or plastic bituminous material composed principally of hydrocarbons; formed in oil-bearing rocks near the Dead Sea, and in Trinidad; prepared by pyrolysis from coal tar, certain petroleums, and lignite tar; melts on heating; insoluble in water but soluble in gasoline; used for paving and roofing and in paints and varnishes.

asphalt

1. A dark brown to black cementitious material, solid or semisolid, in which the predominating constituents are bitumens which occur in nature.
2. A similar material obtained artificially in refining petroleum; used in built-up roofing systems as a waterproofing agent.
3. A mixture of such substances with an aggregate for use in paving.

asphalt

1. any of several black semisolid substances composed of bitumen and inert mineral matter. They occur naturally in parts of America and as a residue from petroleum distillation: used as a waterproofing material and in paints, dielectrics, and fungicides
2. a mixture of this substance with gravel, used in road-surfacing and roofing materials