What are the classifications of asphalt?

December 2, 2022

Asphalt can be mainly divided into three types: coal tar pitch, petroleum asphalt and natural asphalt.

1. Coal tar pitch: Coal tar pitch is a by-product of coking, that is, the black substance left in the still after tar distillation. It is different from refined tar only in physical properties, and there is no obvious boundary. The general division method is to stipulate that the softening point below 26.7°C (cube method) is tar, and the one above 26.7°C is pitch. Coal tar pitch mainly contains non-volatile 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. The change of temperature has a great influence on coal tar pitch, which is easy to be brittle in winter and easy to soften in summer. There is a special smell when heated; after heating to 260°C for 5 hours, the anthracene, phenanthrene, pyrene, and other components contained in it will volatilize.

2. Petroleum asphalt: Petroleum asphalt is the residue after crude oil distillation. 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. Because it has been distilled to above 400°C during the production process, it contains very little 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 ore layers or accumulate on the surface of the earth's crust. Most of this asphalt has been naturally evaporated and oxidized, and generally does not contain any toxins.

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