Field Application of Ground-Penetrating Radar for Measurement of Asphalt Mixture Density: Case Study of Illinois Route 72 Overlay

A study that validated the field performance of ground-penetrating radar (GPR) as a nondestructive tool to predict in situ asphalt mixture density is presented. New overlays using six types of asphalt mixtures were placed at Illinois Route 72 (IL-72) near the Chicago area. Both GPR and nuclear gauge data were collected from the construction site for density estimation. Six cores were extracted for each mixture, and their densities were measured in the laboratory. A density model named Al-Qadi, Lahouar, and Leng (ALL), developed in an earlier study by the authors, was used to predict the asphalt mixture density from GPR measurement. GPR performance was then verified by comparing the GPR-predicted densities with densities of 20 field cores measured with the nuclear gauge and in the laboratory. This study shows that GPR can provide reasonably accurate density prediction when an appropriate model is used. GPR's accuracy of density prediction is comparable with, or better than, that of the nuclear gauge when two calibration cores are used. GPR measurement of an asphalt mixture was not affected by temperature within the range of 90° to 190°F (32° to 88°C). The relationship between the GPR signal reflection amplitude and the number of roller passes could be used to monitor the asphalt mixture compaction process and determine the optimum number of roller passes.