Ground-penetrating radar calibration at the Virginia Smart Road and signal analysis to improve prediction of flexible pavement layer thicknesses

A ground-penetrating radar (GPR) system was used to collect data over the different pavement sections of the Virginia Smart Road from June 1999 until December 2002. Three antennae at different frequencies were used for this research. The collected data were successfully used to evaluate the physical GPR detection limitations, to evaluate the GPR accuracy for pavement layer thickness determination, to control the installation of three different types of reinforcing meshes installed within the pavement, and to estimate the in-situ complex dielectric constant of several types of hot-mix asphalt (HMA). The data analysis results were verified by the well-documented structure and composition of each section of the road, in addition to the embedment of 35 copper plates (perfect electromagnetic reflectors) at the different layer interfaces during construction of the pavement. It was found that GPR is a feasible nondestructive tool to estimate the layer thicknesses of bound and unbound aggregate layers, HMA layers, and concrete slabs. However, interface detection can be altered if the layers have comparable dielectric constants. A technique was developed to estimate the frequency-dependent in-situ complex dielectric constant of HMA materials. Results have shown that the effect of the variations of the dielectric properties within the GPR bandwidth is insignificant vis-à-vis the accuracy of thickness estimation. The use of GPR as a quality control tool to verify the success of steel reinforcing mesh installation was also found to be feasible. Given the success of using GPR for the aforementioned applications in the Virginia Smart Road, it is recommended that the Virginia Department of Transportation use GPR more frequently as a quality control tool during new pavement construction projects and as an assessment tool prior to project rehabilitation and as part of Virginia's pavement management system.