The Use of Ground-penetrating Radar in the Surveying of Overlaid Bridge Decks: Summary Report

About the report:

It was shown in a previous study that the presence of delamination in concrete can be detected by the appearance of a distinctive signature in the analog radar reflection profiles recorded when a concrete deck is scanned with ground-penetrating radar. As a follow-up, radar was used on eleven overlaid bridge decks to assess the overall reliability of the technique when applied to the nondestructive inspection of such decks, using the identified radar signature as an indicator of the presence of concrete delamination. The radar results were verified by soundings conducted on the test decks after their overlays were removed. Among the decks tested, the average success rate of radar in detecting real concrete delamination was found to be 82 ± 20 percent (at 95 percentile). In addition, false indication of the presence of delamination had been observed. It was suspected, however, that the presence of debonding and damage in the overlay in some locations contributed extensively to this type of errors since such damages in the decks would likely manifest themselves as anomalies in the reflection profiles close to that associated with concrete delamination. On the other hand, although some concrete delaminations were missed by radar, these misses often involved relatively small delaminated areas. For future studies, it is recommended that additional radar parameters (including localized increased reflectivity at the bituminous/concrete interface, polarity change in the reflection at the interface, distortions in the reflection from the rebars, and attenuation of reflection from the concrete slab) be examined. These parameters can be related to other types of damages often found in overlaid decks in conjunction with the concrete delaminations.

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