What road base actually is
Road base is not one stone size. It is a deliberately blended mix of crushed rock that runs continuously from the largest stone (the "nominal size", usually 20mm or 40mm) all the way down through smaller stones to a fine, sand-like dust. That spread of sizes is the whole point.
When the mix is spread, watered and rolled, the small particles fill the gaps between the big ones. Everything locks together with very little air left, and the layer becomes hard enough to drive a truck on. A single-sized aggregate cannot do this, because with no fines to fill the gaps it just shifts around underfoot.
What it is used for
Anywhere you need a firm, stable foundation that spreads load onto the ground below, road base is the material.
The classes and sizes in Victoria
In Victoria, road base quality is set by the VicRoads classification system. The class describes the quality and intended layer, not the stone size.
| Class | What it is | Typical use |
|---|---|---|
| Class 2 | Premium fully crushed base | Base course directly under the surface, heavier pavements |
| Class 3 | Standard sub-base | The everyday road base order: sub-base, driveways, trench fill |
| Class 4 | Economical lower layer | Lower sub-base, pads and select fill on a budget |
The number after the class (20mm or 40mm) is the largest stone in the mix. 40mm builds up deep layers faster; 20mm gives a finer, tighter finish.
There is also crushed concrete (recycled road base), which is the same idea made from reclaimed concrete and brick, accepted by most specs and cheaper. Our Class 2 vs 3 vs 4 guide goes deeper on choosing the right class.
Road base versus the other crushed products
Road base is often confused with crusher dust and aggregate, but they do different jobs. Road base is the graded blend that compacts. Crusher dust is only the fine end, used for bedding. Aggregate is only the clean single-sized stone, used in concrete and drainage. We compare all three in crushed rock vs dust vs aggregate.