Asphalt is a dark-brown complex mixture composed of hydrocarbons of different molecular weights and their non-metallic derivatives. It is a type of high-viscosity organic liquid. It is liquid, has a black surface, and is soluble in carbon disulfide. Uses of asphalt: The main uses are as infrastructure materials, raw materials and fuels. Its application areas include transportation (roads, railways, aviation, etc.), construction, agriculture, water conservancy projects, industry (extracting industry, manufacturing), civil use, etc. department.

Types of asphalt:
1. Coal tar pitch, coal tar pitch is a by-product of coking, that is, the black substance remaining in the distillation kettle after tar distillation. It is only different from refined tar in physical properties, and there is no obvious boundary. The general classification method is to stipulate that those with a softening point below 26.7°C (cubic method) are tar, and those above 26.7°C are asphalt. Coal tar pitch mainly contains refractory anthracene, phenanthrene, pyrene, etc. These substances are toxic, and due to the different contents of these components, the properties of coal tar pitch are also different. Changes in temperature have a great impact on coal tar pitch. It is prone to brittleness in winter and softening in summer. It has a special smell when heated; after 5 hours of heating to 260°C, the anthracene, phenanthrene, pyrene and other components contained in it will volatilize.

2. Petroleum asphalt. Petroleum asphalt is the residue after distillation of crude oil. Depending on the degree of refining, it becomes liquid, semi-solid or solid at room temperature. Petroleum asphalt is black and shiny and has high temperature sensitivity. Since it has been distilled to temperatures above 400°C during the production process, it contains very few volatile components, but there may still be high molecular hydrocarbons that have not been volatilized, and these substances are more or less harmful to human health.

3. Natural asphalt. Natural asphalt is stored underground, and some form mineral deposits or accumulate on the surface of the earth's crust. Most of this asphalt has undergone natural evaporation and oxidation, and generally does not contain any toxins. Asphalt materials are divided into two categories: ground asphalt and tar asphalt. Ground asphalt is divided into natural asphalt and petroleum asphalt. Natural asphalt is the residue after long-term exposure and evaporation of oil seeping out of the ground; petroleum asphalt is the product obtained by treating the residual oil remaining from refined and processed petroleum through appropriate processes. . Tar pitch is a reprocessed product of tar obtained from the carbonization of coal, wood and other organic matter.

The vast majority of asphalt used in engineering is petroleum asphalt, which is a mixture of complex hydrocarbons and their non-metallic derivatives. Usually the flash point of asphalt is between 240℃~330℃, and the ignition point is about 3℃~6℃ higher than the flash point, so the construction temperature should be controlled below the flash point.