DETECTION OF SUBSURFACE ANOMALIES IN CONCRETE BRIDGE DECKS USING GROUND-PENETRATING RADAR

This paper presents the findings of a study on the use of Ground Penet rating Radar (GPR) for nondestructive evaluation of concrete bridge de cks. A previously developed radar synthesis model and inversion proced ure was modified to account for the variation ill concrete properties along the depth of the deck. A geometric attenuation factor was also i ncorporated 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 a nd water-filled cracks, were cast in the laboratory. Radar waveforms o btained from these specimens were compared to study the effect of subs urface anomalies (e.g., cracks) on the waveforms. Waveforms correspond ing to all the specimens were synthesized using the theoretical model and compared with experimental waveforms. Also, waveforms inversion fo r all the specimens was conducted to determine the accuracy of the inv ersion procedure in predicting the internal conditions of the concrete specimens. The inversion procedure has been shown to be quite accurat e in estimating the concrete cover for the top longitudinal reinforcem ent. However, the usefulness of the inversion procedure for directly d etermining the location and thickness of cracks and delaminations has been found to be limited Therefore, a more prudent approach has been p roposed as one where spatial mapping of the computed porosity chloride content and top rebar cover is used to identify anomalies (deteriorat ed areas) bl the bridge deck.