Bitumen-C320

Under AS 2008:1997, C320 is a Class 320 bitumen with a dynamic viscosity at 60°C of 280–380 Pa·s and a nominal kinematic viscosity of 320 mm²/s. This stiffness profile is significantly higher than C240 (200–300 Pa·s) but lower than C450 (370–470 Pa·s), making C320 the right choice when temperate-grade C240 is insufficient but full hot-climate C450 is unnecessary. In global equivalents, C320 broadly corresponds to 60/70 to 80/100 penetration grade bitumen and is approximately equivalent to AC-20 in the AASHTO system or VG-30 under IS 73:2013. Its higher softening point (42–51°C vs 39–47°C for C240) ensures the binder film in the pavement maintains viscous stability at elevated temperatures, directly reducing permanent deformation risk. C320 is also used as a base binder for producing stiff polymer-modified bitumens (C320+SBS = A35E or equivalent) for premium wearing courses on Queensland motorways and Northern Territory highways.