Exploration of the Factors Affecting Ground Penetrating Radar Response in Bridge Inspection Applications

Ground Penetrating Radar (GPR) is a nondestructive evaluation technique that is recently employed in various civil engineering applications such as concrete quality evaluations, locating reinforcing rebar, and bridge deck integrity assessments. Previous research has shown that the chloride and moisture content of concrete, corrosion state, and depth of reflecting objects (e.g., steel reinforcing bars) have some impact on the strength of GPR signals. What is not yet clear, however, is to what extent these factors can affect GPR response. This research has sought to quantitatively determine the effects of these factors on the attenuation and the resulting response of GPR signals reflected from reinforcing bars in concrete. The effects of these factors were experimentally demonstrated by analyzing data from four reinforced concrete slabs. Analysis of the processed data showed that attenuation was highly attributed to the depth of the reinforcing bars as compared to the concrete chloride and moisture content, where the amplitude of the reflected signals decreased by 4.5dB for every 25 mm increase in depth as compared to about 1.0 dB reduction in signal amplitude due to the presence of chloride and moisture. Corrosion of reinforcement bars, on the other hand, slightly increased the amplitude of the reflected signals by 1.0 dB.