Bitumen-C450

Under AS 2008:1997, C450 is a Class 450 bitumen with a dynamic viscosity at 60°C of 370–470 Pa·s and a nominal kinematic viscosity of 450 mm²/s. This high-viscosity binder is significantly stiffer than C320 (280–380 Pa·s), reflecting the step-change in performance requirements between warm-climate and hot-climate Australian road environments. C450 broadly corresponds to 40/60 to 60/70 penetration grade bitumen and is approximately equivalent to AC-30 to AC-40 in the AASHTO system or VG-40 under IS 73:2013. Its softening point of 47–56°C means it remains structurally stable even at pavement surface temperatures of 60°C — well above the critical threshold where softer grades begin to deform. The C450 grade is also used as the standard base binder for producing high-performance PMB grades (Austroads A40E equivalent) for premium wearing courses on tropical Australian motorways and airport runways.