Layer of land situated under the surfacing on the sub-base and formation level that supports the surfacing, whose function is mainly resistant, absorbing the main part of the vertical stresses.
The materials that it is made of are:
- For medium and light weight traffic: macadam or artificial shingle is used.
- For heavy traffic: granular materials treated with a binder (emulsions, bitumen), or conglomerate (cement or lime) on semi-rigid pavements, are used.
- On rigid pavements: mixtures with cement are made in the form of cement stabilised soil, cement bound gravel or lean concrete, giving stability and resistance to erosion produced by water.