| Ground penetrating radar (GPR) has been widely used in various geotechnical fields, but most GPR applications in terms of the non-destructive testing (NDT) of pavement and bridge structures are still experimental. Even when they appear to be successful, there are often discrepancies between GPR results and the result of the other traditional methods. The University of Missouri-Rolla (UMR) has been working with GPR successfully in many cases of geotechnical engineering problems in the state for many years and has been broadening its application into NDT fields in recent years.; The present study is comprised of two separate GPR case studies on a bridge deck and a concrete pavement respectively. These typical concrete structures were investigated using GPR with several objectives; (1) to find the reason of discrepancies between GPR results and the results of the other tests through bridge deck inspection, (2) to investigate the bridge deck under various weather conditions, (3) to determine the relative spatial locations of the imbedded dowel bars in the new concrete pavement, and finally (4) to evaluate the present capabilities of GPR technology including survey scheme and analysis through these two case studies.; The present GPR data analysis method of simply plotting and analyzing the rebar amplitude, or time-depth, has proved insufficient for precise evaluation of the bridge deck. The limitations of the analysis algorithm might be one of the reasons that cause discrepancies in the bridge deck inspection. Although a small section of the delaminated area was identified to be sensitive to weather conditions, the pre-existing or growing delamination might be detected and monitored by GPR. It was also observed that the overall rebar reflection amplitudes under wet conditions are higher than under dry conditions. The relative spatial locations of the embedded dowel bars in a new concrete pavement were precisely determined with GPR. Longitudinal displacement of the dowel bars was generally less than several centimeters, however at a few sites, longitudinal displacement was in excess of 11 cm. This study also showed that the GPR data quality is strongly dependent on data acquisition parameters as well as on weather conditions. The “unclear” characteristics of the GPR signals observed in these two investigations were discussed and recommendations for general NDT GPR survey procedures are presented. |
