Asphalt, also known as bitumen , is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used.
The Asphalt Institute specifies four penetration grades: 60-70, 85-100, 120-150, and 200-300. The 60-70 grade is usually used only in pavements where traffic is very heavy such as principle city streets and very heavily trafficked rural highways.
