Debonding Detection in the Grouted Joints of Precast Concrete Shear Walls Using Impact-Echo Method

A grout layer between precast concrete components in an assembly structure is required to bear high axial loads and withstand significant shear forces during earthquakes. Since the grout layer usually exists in a narrow space, examining the quality of the layer, particularly detecting debonding at the interface, is a difficult task. However, a debonding defect at the interface is likely to significantly reduce the safety performance of structures. To address this problem, this paper presents a combined experimental and numerical study to detect the interfacial debonding based on the impact-echo theory. Two precast concrete shear walls assembled in a structure were tested by the impact-echo method based on two different boundaries. It is shown that the thickness frequencies near a free boundary are considerably lower than those near a fixed boundary, and the boundary effect disappears when the impact position is far away from the free boundary or the fixed boundary. Such characteristics can be used to identify a debonded layer (i.e., approaching the free boundary) in the grouted joint. A blind in-situ test was also conducted to validate the effectiveness of the proposed impact echo method in detecting debonded layers.