Base course

File:Class 3 Road Base.jpg

Image:MortarlessPavement.jpg
B. Subbase
C. Base course
D. Paver base as binder course
E. Pavers as wearing course
F. Fine-grained sand]]

The base course or basecourse in pavements is a layer of material in an asphalt roadway, race track, riding arena, or sporting field. It is located under the surface layer consisting of the wearing course and sometimes an extra binder 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 {{convert|4|to|6|in|mm|lk=on|order=flip}} and is governed by underlying layer properties. Generally made of a construction aggregate, it is spread and compacted to at least 95% relative compaction, thus providing a stable foundation for additional layers of material.{{cite book|title=Handbook of Road Technology|first=M. G.|last= Lay|edition=4|publisher=Taylor & Francis|year=2009|isbn=978-0203892534}}{{cite book|first1=D. R.|last1=Phatak|first2=H. K.|last2=Gite|title=Highway Engineering|publisher=Nirali Prakashan|isbn=978-8185790923}}

Aggregate base (AB) is typically a mix of different sizes of crushed rock {{Convert|20|mm|in|frac=8|abbr=on|disp=or}} Aggregate Base, Class 2, is used in roadways and consists of rock particles of size {{convert|3/4|in|mm|-1|abbr=on|order=flip}} 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.