Figure16-4.-Asphalt pavement cross sections, showing common and typical asphalt pavement structures.
Function of Base Course and Subgrade
The base course and subgrade are structural
elements of the pavement. In conjunction with the
overlying asphalt surface, their purpose is to distribute
traffic wheel loads over the whole foundation (fig.
16-4). To perform this function, you build the base
course and subgrade with the necessary internal strength
properties. In this respect, full-depth asphalt pavements
have a special advantage over pavements with granular
Asphalt pavement layers have both tensile and
compressive strength to resist internal stresses. For
example, figure 16-5 shows how wheel load (W)
slightly deflects the pavement structure, causing both
tensile and compressive stresses within the pavement.
Untreated granular bases have no tensile strength;
therefore, asphalt bases spread the wheel load over
broader areas than untreated granular bases. The result
of this is that less total pavement structure thickness is
required for an asphalt base.
Determining Required Pavement Thickness
A significant advance in highway engineering is the
realization and demonstration that structural design of