What the class actually means
In Victoria, crushed rock is graded to the VicRoads classification in Section 812. The class is a quality grade tied to where the material sits in the pavement. It is not the stone size; that is the separate 20mm or 40mm figure. A higher class (lower number) has tighter limits on grading, strength and plasticity, because it is doing more work closer to the traffic.
The three classes side by side
| Class | Role in the pavement | Typical use | Relative cost |
|---|---|---|---|
| Class 2 | Base course, directly under the wearing surface | Trafficked roads, heavy pavements, the strength layer | Highest |
| Class 3 | Standard sub-base | Driveways, car parks, trench reinstatement, subdivision roads | Mid |
| Class 4 | Lower sub-base and select fill | Pads, working platforms, bulk filling, budget bases | Lowest |
There is also Class 1, a premium fully crushed base for the heaviest pavements. Class 2 covers most base-course work.
When you would spec each
Class 2
Reach for Class 2 when it is the base course directly beneath asphalt or a seal on a road that carries real traffic. It compacts to a high strength and meets the tight VicRoads limits, which is why engineers call it up for the layer that takes the load.
Class 3
Class 3 is the workhorse and the most common order. It is the right choice for domestic driveways, car park sub-base, slab bases, shed pads and reinstating service trenches. For most non-engineered jobs, Class 3 is what you want.
Class 4
Class 4 is the economical option for lower sub-base, bulk filling, capping over soft ground and select fill where a premium grade is not needed. It still compacts well, it just sits deeper in the structure where the demands are lower.