IMPLEMENTATION OF GROUND PENETRATING RADAR TECHNOLOGY IN ASPHALT PAVEMENT TESTING

Over the past decade Ground Penetrating Radar (GPR) applications have been under development within both the Texas Department of Transportation (TxDOT) and the Finnish National Roads Administration (FNRA). In the mid 1990s GPR systems moved into mainstream usage, improved software was developed and training schools were conducted. TxDOT now has 4 complete air launched GPR systems for pavement evaluation. GPR technology is now used on a routine basis as the first step in planning the rehabilitation of flexible pavements. In Finland GPR has been implemented in the area of quality assurance testing of new asphalt overlays. Using a limited number of calibration cores the GPR data are used to compute the inplace air void content profile of new overlays. In the 2000 construction season a penalty system was implemented based on these GPR results, and the feedback from both FNRA and the contracting community has been positive. This paper will provide an overview of these development and implementation efforts. The basics of GPR will be presented together with a discussion of the methods used to convert GPR waveforms into information useful to pavement engineers. A number of successful case studies will be described. GPR was initially promoted as a rapid layer thickness measuring tool. It certainly provides useful thickness information for the upper layers of flexible pavements. However as will be described in the case studies GPR can provide substantially more information than simply layer thickness.