The effective near-surface defect identification by dynamic behavior associated with both impact-echo and flexural modes for concrete structures

The Impact Echo (IE) test is a robust Non-destructive Test (NDT) method where the dynamic response of a target area results from an impact event to make decisions about the damage identification of concrete structures. However, the IE data over the near-surface delamination typically developed by rebar corrosion at the cover depth is not easy in interpreting because of the difficulties in the dynamic analysis of flexural modes over the defects as well as in the identification of weak and unclear signal of the high IE frequency corresponding to the delamination depth. The shallow delamination in the concrete structures must be clearly identified and interpreted such that infrastructure engineers can effectively check the condition of the structure. To address this problem, we proposed the combined dynamic characterization with both impact-echo and flexural modes in order to identify the area and degree of damage and applied this technique to the designated concrete slab and the simulated bridge deck with various artificial defects at the depth of rebar. The test results proved that the imaging technique by the combined mode associated with the IE and flexural modes is more effective and accurate for the detection of shallow defects in the concrete slab than one by the individual mode.