Detection of sub-surface anomalies in concrete bridge decks using ground penetrating radar

This paper presents the findings of a study on the use of Ground Penetrating Radar (GPR) for nondestructive evaluation of concrete bridge decks. A previously developed radar synthesis model and inversion procedure was modified to account for the variation ill concrete properties along the depth of the deck. A geometric attenuation factor was also incorporated in this improved model. This model was used for analyzing the radar waveforms from various simulated bridge deck specimens cast in the laboratory. Several simulated bridge deck specimens of varying internal conditions, such as with/without reinforcement and with air and water-filled cracks, were cast in the laboratory. Radar waveforms obtained from these specimens were compared to study the effect of subsurface anomalies (e.g., cracks) on the waveforms. Waveforms corresponding to all the specimens were synthesized using the theoretical model and compared with experimental waveforms. Also, waveforms inversion for all the specimens was conducted to determine the accuracy of the inversion procedure in predicting the internal conditions of the concrete specimens. The inversion procedure has been shown to be quite accurate in estimating the concrete cover for the top longitudinal reinforcement. However, the usefulness of the inversion procedure for directly determining the location and thickness of cracks and delaminations has been found to be limited Therefore, a more prudent approach has been proposed as one where spatial mapping of the computed porosity chloride content and top rebar cover is used to identify anomalies (deteriorated areas) bl the bridge deck.