Thebase course orbasecourse in pavements is a layer of material in anasphaltroadway, race track, riding arena, or sporting field. It is located under the surface layer consisting of thewearing course and sometimes an extrabinder course.
If there is a sub-base course, the base course is constructed directly above this layer. Otherwise, it is built directly on top of the subgrade. Typical base course thickness ranges from 100 to 150millimetres (4 to 6 in) and is governed by underlying layer properties. Generally made of aconstruction aggregate, it is spread and compacted to at least 95% relative compaction, thus providing a stable foundation for additional layers of material.[1][2]
Aggregate base (AB) is typically a mix of different sizes of crushed rock20 mm or3⁄4 in Aggregate Base, Class 2, is used in roadways and consists of rock particles of size20 mm (3⁄4 in) and less. An aggregate is normally made from newly quarried rock, or it is sometimes allowed to be made from recycled asphalt concrete and/or Portland cement concrete.