Sonic Methods to Detect Delamination in Concrete Bridge Decks

Accurate assessment of the condition of concrete bridge decks leads to a bridge management system that is mechanistic and reliable, qualities of great importance to transportation agencies. In this study, two sonic–seismic methods—impact echo (IE) and ultrasonic surface waves (USW)—were used to characterize material properties and to identify fabricated delaminated areas inside a concrete bridge deck. The reliability of IE and USW is affected not only by the strengths and weaknesses of these methods but also by the ways in which data are collected, interpreted, and presented. The data obtained from the two methods were visualized in both traditional and checkerboard formats. The checkerboard format located the delaminated areas more precisely because the smoothing algorithm was avoided in this contouring method. This observation is more critical as the density of data collection is reduced. The evaluative power of each method and the power in combination, were also compared and discussed in terms of detectability and accuracy. The combined results from USW and IE were preferred to the individual results of each method because the combined results provided redundant and complementary data that reduced uncertainty in the identification of defects with no added overhead for field data collection. A relationship between the size of the defect and measurement density was recommended through evaluation of the bridge deck at three measurement densities. The measurement spacing should be equal to or less than the smallest defect deemed critical by the owner agency.