Figure16-4.-Asphalt pavement cross sections, showing common and typical asphalt pavement structures.Function of Base Course and SubgradeThe base course and subgrade are structuralelements of the pavement. In conjunction with theoverlying asphalt surface, their purpose is to distributetraffic wheel loads over the whole foundation (fig.16-4). To perform this function, you build the basecourse and subgrade with the necessary internal strengthproperties. In this respect, full-depth asphalt pavementshave a special advantage over pavements with granularbases.Asphalt pavement layers have both tensile andcompressive strength to resist internal stresses. Forexample, figure 16-5 shows how wheel load (W)slightly deflects the pavement structure, causing bothtensile and compressive stresses within the pavement.Untreated granular bases have no tensile strength;therefore, asphalt bases spread the wheel load overbroader areas than untreated granular bases. The resultof this is that less total pavement structure thickness isrequired for an asphalt base.Determining Required Pavement ThicknessA significant advance in highway engineering is therealization and demonstration that structural design of16-4
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