Dielectric characterization of unstabilized aggregate base materials

Abstract

Because changes in moisture content can significantly alter the structural and strength properties of granular base materials, moisture susceptibility has a major impact on the field performance of these materials in highway applications. The extent to which moisture accelerates damage in granular materials depends upon the amount and distribution of free water within the pavement structure. The moisture susceptibility of aggregate base materials can be investigated in the laboratory by means of the Tube Suction Test (TST), and in-situ moisture conditions can be evaluated in the field using ground-penetrating radar (GPR). Both of these methods correlate moisture content and state of bonding with the dielectric values of base materials. High dielectric values can be attributed to a substantial presence of free water, a most detrimental factor in mechanisms of moisture damage in pavements. This project serves to further evaluate the TST methodology proposed for judging the moisture susceptibility of typical granular base materials. The influence of temperature on test performance is studied together with a correlation between moisture susceptibility as measured in the TST with strength as measured in the Texas triaxial test. Furthermore, this project investigates the correlation of dielectric values obtained using the dielectric probe in the laboratory with those calculated from GPR measurements of granular base materials beneath different pavement surfaces in field conditions. The influence of the type and thickness of the pavement surfacing on the ability of GPR to measure the dielectric propel-ties of in-situ base layers is explored.