Determining the Condition of Hot Mix Asphalt Specimens in Dry, Water-Saturated, and Frozen Conditions Using GPR

Abstract

A series of laboratory experiments were conducted to measure the dielectric constant of hot mix asphalt (HMA) pavement specimens in dry, water-saturated, and frozen conditions. We used a [Formula: see text] ground penetrating radar (GPR) system to measure the travel times for direct and reflected waves for computing the electromagnetic (EM) wave velocity. In conjunction with other information on geometry, void ratio, and composition, we computed the dielectric constants of 30 specimens. Our major conclusions are: (1) In general, EM wave velocity is highest in dry conditions, intermediate in frozen, and lowest in water-saturated conditions; (2) EM wave velocity increases slightly with the increase of void ratio for dry samples. In contrast, it decreases significantly with void ratio increase in water-saturated conditions. Correspondingly, the dielectric constant decreases noticeably with an increasing void ratio in dry conditions, and increases appreciably in saturated conditions, in the range of void ratio from zero to 6%; (3) The changes of EM velocity and dielectric constant for dry, saturated, and frozen conditions can be reasonably predicted by the complex refractive index model (CRIM) for porous media; (4) Variations in EM velocity and dielectric constant with respect to asphalt ratio implies that a low asphalt ratio corresponds with a high void ratio; and (5) The observed variations in EM velocity and dielectric constant can be attributed to the change of moisture content of an HMA specimen in different conditions.