An aggregate base course is the layer of soil installed between the surface pavement layer and subgrade (foundation soils) of either flexible (asphalt) or rigid (concrete) pavement. Their purpose is to help transition surface loads from the pavement to the subgrade, evenly support the pavement surface profile, and protect the overall pavement system from water intrusion and deformation. While these objectives of base course layers are applicable to both types of pavements, load transfer is a more focused design consideration for flexible pavement, while moisture control is a priority for rigid pavement designs. Concrete base courses are further discussed in Article 32.11.36.

The main objective of concrete base courses is to regulate moisture, preventing the types of damage common to rigid pavement systems. Load transfer concerns, which can necessitate some base course applications, is less of an issue for rigid pavement.  Aggregate base courses for rigid (concrete) and flexible (asphalt) pavements are discussed in article 32.11.23.