**Viscosity Graded Bitumen:**

Viscosity graded bitumen is a classification of asphalt based on its viscosity at a specific temperature. It is a semi-solid form of petroleum primarily used in road construction for its adhesive and waterproofing properties. Viscosity is a measure of a fluid’s resistance to flow; in the context of bitumen, it determines the material’s performance in varying temperatures and loading conditions. Viscosity graded bitumen ensures that the asphalt has suitable viscoelastic properties to resist deformation at high pavement temperatures, while at the same time not becoming too brittle at low temperatures.

Typically, a viscometer is used to evaluate the bitumen’s viscosity at a standard temperature, most commonly at 60°C (140°F) for high-temperature grading and 135°C (275°F) for manufacturing temperature. These tests produce grades such as VG-10, VG-20, VG-30, and VG-40, indicating different classes with increasing viscosity levels. The appropriate grade is selected based on climate conditions and the expected loading on the road.

Two reliable sources for more information on viscosity graded bitumen are:

1. The Asphalt Institute: As a U.S.-based association of international petroleum asphalt producers, manufacturers, and affiliated businesses, The Asphalt Institute features detailed technical information on various types of asphalt and their applications, including viscosity graded bitumen.

Website: (https://www.asphaltinstitute.org/)

2. ASTM International: This international standards organization develops and publishes technical standards for a wide range of materials, including viscosity graded bitumen. Published standards provide detailed procedures for testing and classifying asphalt products.

Website: (https://www.astm.org/)

The URLs provided are active at the time of this writing, and the pages should contain information on viscosity graded bitumen relevant to both industry professionals and interested laypeople.