Road Base Materials Explained
A graded blend built to compact into a stable structural layer
A blend, not a single size
Unlike a clean, single-size drainage stone, road base (sometimes called crusher run or graded aggregate base) is a mix of particle sizes, from larger crushed stone down to fine particles. That range of sizes lets smaller particles fill the voids between larger ones, producing a dense, well-compacted layer once rolled or plate-compacted.
Its job in the pavement structure
Road base sits beneath the surface course (asphalt, concrete, or a wearing layer of pavers) and spreads the load from traffic above across a wider area of the underlying subgrade soil, reducing the stress the weaker native soil has to carry directly. A well-compacted, properly-graded base is a major factor in how well a driveway or pavement performs over time.
Thickness depends on the load and the subgrade
How thick a road base layer needs to be depends on the subgrade's strength (often characterized by a CBR test) and the loads the surface will carry — a light-use garden path needs far less base than a driveway carrying vehicles, and a driveway needs less than a road designed for heavy trucks. Pavement design methods and local specifications set the specific thickness for a given application.