Asphalt is a dark brown high-viscosity organic liquid composed of hydrocarbons of different molecular weights and non-metallic substances. It has a black surface and is soluble in carbon disulfide. Asphalt is a waterproof, moisture-proof and anti-corrosion organic gelling material. Pitch can be mainly divided into three types: coal tar pitch, petroleum pitch and natural pitch. Among them, coal tar pitch is a by-product of coking. Petroleum asphalt is the residue after distillation of crude oil. Natural bitumen is stored underground, and some form ore layers or accumulate on the surface of the earth's crust. Asphalt is mainly used in coatings, plastics, rubber and other industries as well as paving roads.