Types of Bitumen
Performance Grade
PG binders certified against the actual climate of the project — rutting resistance at the high temperature, crack resistance at the low.
Performance grading came out of the American Strategic Highway Research Program and is now written into AASHTO M320. Instead of describing consistency at an arbitrary laboratory temperature, it certifies the binder against the temperature extremes the pavement will actually see.
The designation carries both numbers. A PG 70-10 binder must resist permanent deformation at a seven-day average maximum pavement temperature of 70 °C, and resist thermal cracking at a minimum pavement temperature of −10 °C.
How the grade is verified
Three instruments do the work. The dynamic shear rheometer measures the complex modulus and phase angle that govern rutting and fatigue. The bending beam rheometer measures low-temperature stiffness and how fast the binder relaxes stress. The pressure ageing vessel conditions the binder to represent five to ten years of service before those tests are run.
Because the binder is tested in the aged state as well as the fresh state, the grade reflects long-term behaviour rather than the condition it left the refinery in.
Common grades in hot-climate markets
- PG 64-10 — moderate high-temperature requirement, mild winters
- PG 64-22 — the general-purpose grade across much of the temperate world
- PG 70-10 — hot climate, normal to heavy traffic
- PG 76-10 — very hot climate, heavy and slow-moving traffic, usually polymer modified
- PG 82-10 — extreme service: ports, bus lanes, aircraft hardstandings
- PG 58-28 — cold climate grade where thermal cracking dominates
When to specify PG over penetration
- Projects with a wide annual temperature swing
- Slow-moving or channelised heavy traffic where rutting risk is high
- Airfield and port pavements with concentrated static loads
- Where a polymer modified binder needs its elastic recovery certified
- Where the client specification is written to AASHTO or a Superpave mix design
Typical specification
| Original binder, G*/sin δ | AASHTO T315 — 1.00 kPa minimum |
|---|---|
| RTFO residue, G*/sin δ | AASHTO T315 — 2.20 kPa minimum |
| PAV residue, G*·sin δ | AASHTO T315 — 5000 kPa maximum |
| Creep stiffness, S | AASHTO T313 — 300 MPa maximum |
| m-value | AASHTO T313 — 0.300 minimum |
| Rotational viscosity @ 135 °C | AASHTO T316 — 3 Pa·s maximum |
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.
