Asphalt produced by asphalt mixing plants is mainly divided into three types, namely coal tar asphalt, petroleum asphalt and natural asphalt.

Coal tar asphalt is a by-product of coking, that is, the black substance left after the distillation of tar. The difference between this substance and refined tar is only in the physical properties, and there is no obvious boundary in other aspects. Coal tar asphalt contains substances such as phenanthrene and pyrene that are difficult to volatilize. These substances are toxic. Because the content of these ingredients is different, the properties of coal tar asphalt will also be different. In addition, asphalt mixing plant manufacturers tell users that temperature changes have a great impact on coal tar asphalt. This substance is more brittle in winter and easier to soften in summer.
Petroleum asphalt refers to the residue after crude oil distillation. Generally speaking, depending on the degree of refining, petroleum asphalt will be in liquid, semi-solid or solid state at room temperature. Natural asphalt is stored underground, and some may also form mineral layers or accumulate on the surface of the earth's crust. Natural asphalt is generally free of toxic substances because it is naturally evaporated and oxidized.