In this paper, work on air-coupled impact-echo is described. The method is applied to locate and to determine the depth of simulated delamination and void defects in a concrete slab. A small (6mm diameter) measurement microphone is used to sense impact-echo response without contacting the surface of the concrete. Ambient acoustic noise effects are significantly reduced by a specially-designed sound insulation device. Test results show that air-coupled sensors work as effectively as do contact impact-echo sensors when proper impactors are used. An air-coupled impact-echo scan was conducted over the entire slab area, and the defects are located in a generated 2-D contour image. Experiments show that the areal size of near-surface delamination defects can be accurately determined if the scan spacing is smaller than 1/2 of the expected defect size. The study presented in this paper shows air-coupled sensing offers an approach for rapid and effective evaluation of concrete deck structures through imaging.
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