USING HIGH-SPEED GROUND PENETRATING RADAR FOR EVALUATION OF ASPHALT DENSITY MEASUREMENTS

The objective of the study was to determine the practicality of using ground penetrating radar (GPR) based devices for post-construction HMA density measurements. Non-nuclear density measurement techniques such as GPR are of interest to state highway agencies as substitutes to nuclear gauges primarily for safety concerns and to eliminate costs associated with radioactive material licensing. In addition, GPR has the ability to obtain 100% coverage of the section being tested. The work on this project was carried out using the Florida Department of Transportation (FDOT) 2.0 GHz Horn Antenna GPR system, and included an assessment of its capabilities and limitations, and determination of optimal operational parameters for asphalt density measurement. Key elements of this work were the implementation of automated software for processing the GPR data and a laser trigger system to automatically mark the start and end of the GPR survey sections. A GPR survey protocol, established from test track surveys at FDOT's state materials office test facility, was applied to the field validation trials. Validation and companion testing of the FDOT GPR system was completed on an active construction project. The new construction project was located in District 2, on State Road 20 (SR20). Along various lengths of this project, multiple areas were surveyed, cored, and tested to determine if GPR is suitable for determining asphalt densities. The data collection methodology involves collecting data over a series of longitudinal lines on the pavement surface. Analysis of the collected GPR information is completed using the customized GPRQA software application. The results were mapped using a contour plotting program. The surface dielectric map is used to locate high, low, and mid-range areas for density calibration cores. Selected locations were then cored and tested in accordance with FM-1-T 166, “Florida Method of Test for Bulk Specific Gravity of Compacted Bituminous Mixtures.” Using the obtained, or determined, maximum theoretical specific gravity for the asphalt mixture, the individual density measurements can be converted to determine the compaction effort (in percent) of the contractor.