Viscosity Grade

In the early 1960s, an improved asphalt grading system was developed that incorporated a rational scientific viscosity test.
The testing bath temperature must be 60° ± 0,3 °C,(average road surface temperature during sunshine) and 135 °C (average temperature of bitumen when mixing asphalt).
In hot climates, bitumen with low penetration and high viscosity is used (eg VG40), so it will not flow (deform) with the high ambient temperature., and bitumen with high penetration and low viscosity is used in cooler regions. so it will not “crack” under freezing temperatures (eg VG10) .