Detecting Stripping in Asphalt Concrete Layers Using Ground-Penetrating Radar (7-2964-S)

This study was undertaken by the Texas DOT to nondestructively detect stripping in the asphalt surfacing on IH45 in the Bryan District. This highway was constructed in the 1960s and 1970s, with an initial concrete slab thickness of 200 mm (8 in). Since then several asphalt overlays have been applied. Maintenance of this highway is a recurring headache, and it is known that in several locations, moderate to severe areas of subsurface stripping are present.In order to plan the future rehabilitation of this important highway, the Bryan District investigated the ability of ground-penetrating radar (GPR) to provide subsurface condition information. A GPR survey was conducted at close to highway speeds, and the data was interpreted prior to taking validation cores. The GPR was used to provide information on the following: 1) the section breaks along the highway based on asphalt layer thickness and condition, 2) the average thickness of the asphalt layer within each section, and 3) the extent and severity of any defect in the asphalt layer.Over 60 cores were taken to validate the GPR interpretation. The comparison of GPR results and ground truth cores are given in this report. In general, the comparisons were good. The GPR equipment and interpretation schemes used were found to provide information of sufficient quality and accuracy to permit the district to make programming decisions.GPR is now being used on several additional projects in the Bryan District. The best use appears to be for both defect detection and thickness estimation prior to deflection testing and coring. GPR will not eliminate coring or deflection testing, but by using all three in a coordinated approach the pavement designer will have more confidence in his or her design decisions.