5. PAVEMENTS COMPONENTS.
a. Rigid Pavements. Rigid pavements are usually composed of a concrete
surfacing and granular base on a prepared subgrade. For most types of road
construction, the surfacing is unreinforced. The base course is composed of
select granular material or granular material stabilized with cement, bitumen,
or lime. In some cases, when constructing rigid pavements on high quality
subgrades, the base may not be required.
b. Flexible Pavement. See Figure 1 for a description of flexible pavement
components. The three primary components are the surface, base, and subbase.
(1) Surface. For most roads and streets, the surface is composed of hot-
mixed asphalt concrete. A guide to the use of other types of bituminous
surfacings is given in Table 1.
(2) Base. Base is high quality granular or stabilized material able to
withstand high stresses. The base is a major load carrying component of a
(3) Subbase. Subbase is a lower quality granular material having certain
requirements. The subbase is placed on the subgrade and is intended to further
reduce the stresses transmitted to the subgrade. Where a good quality granular
subgrade exists, or where anticipated loading is light, the subbase may often