Types of Bitumen
Australian Standard Bitumen
Class 170, 320, 600 and multigrade binders produced to AS 2008 — written for high ambient heat and heavy axle loads.
AS 2008 grades residual bitumen by viscosity at 60 °C expressed in pascal-seconds, and the class number is that viscosity. Class 320 bitumen has a viscosity of approximately 320 Pa·s at 60 °C.
The standard was developed for Australian conditions — sustained high pavement temperatures, long haul routes and heavy vehicle combinations — which makes it directly relevant to Gulf, North African and other hot-climate markets facing the same loading.
The classes
- Class 170 — softer binder for cooler regions, sprayed sealing and lighter traffic
- Class 320 — the general-purpose asphalt binder across most of the country
- Class 600 — hard binder for heavy-duty pavements and very hot locations
- Multigrade 500/170 — wider temperature susceptibility range in a single product
- Multigrade 1000/320 — high-performance multigrade for demanding pavements
What multigrade binders do
A multigrade binder is formulated to behave like a harder grade at high service temperature and a softer grade at low service temperature. In practice that means better rutting resistance in summer without sacrificing fatigue and thermal crack resistance in winter, and it removes the compromise that a single-class binder forces on projects with a wide temperature range.
Where it is specified
- Dense graded asphalt for highways and arterial roads
- Sprayed seals and primer seals on rural networks
- Stone mastic asphalt wearing courses
- Heavy-duty industrial and port pavements
- Projects written to Australian or New Zealand road authority specifications
Typical specification
| Viscosity @ 60 °C | AS 2341.2 — to class, in Pa·s |
|---|---|
| Viscosity @ 135 °C | AS 2341.4 — 0.5 Pa·s maximum for Class 320 |
| Penetration @ 25 °C | AS 2341.12 — 40 to 70 for Class 320 |
| Flash point | AS 2341.14 — 250 °C minimum |
| Viscosity of RTFO residue | AS 2341.10 — 2.0 maximum ratio |
| Density @ 15 °C | AS 2341.7 — approximately 1.03 t/m³ |
Values are indicative and given for guidance. Contract specification is agreed in writing and certified per batch on the certificate of analysis issued with each shipment.
