A layer of material of specified thickness constructed on the subgrade of a pavement to serve one or more functions, such as distributing loads, providing drainage, or minimizing frost action.

Generic term for material installed prior to asphalt paving. May be a crushed stone product or asphalt product (see full-depth asphalt pavements). The base material provides the load bearing characteristics of the finished pavement and may vary from 3-4" for a residential driveway to 18" or more for parking areas or roadways. The correct type and amount of base material must be determined and specified prior to paving. Lack of adequate base material is a primary cause of pavement failures.

The course or layer of materials in a roadway section on which the actual pavement is placed. It may be of different types of materials ranging from selected soils to crushed stone or gravel.

Placed over subgrade, consists of various sized rock and finely ground stone.

A material of a designed thickness placed under the surface wearing course of paving units and bedding course. It is placed over a sub-base or a subgrade to support the surface course and bedding. A base course can be compacted aggregate, cement or asphalt stabilized aggregate, asphalt or concrete.