Sounding of subsurface concrete defects using frequency response of flexural vibration

Abstract

Standard sounding procedures such as hammer percussion and chain drag can be used to locate subsurface concrete defects, but are often subject to the individual judgement and ear of trained inspectors. However, defect depth information can be difficult to gauge by ear alone. By recording audio and analyzing the frequency content of sounding via hammer percussion, a single- and triple-link chain drag, and a novel speaker-based excitation procedure, simulated defects in concrete test slabs were detected. The speaker-based method shows the capacity to detect a similar number of defects as chain drag methods, though it is slightly less effective than the hammer method. The duration and type of the acoustic signal used by the speaker to induce vibration are important factors in performance of the speaker-based method. The detectability of a defect via all methods tested depended largely on the ratio of defect depth to defect lateral dimensions; defect detectability was shown to drop after this ratio exceeded about 0.35.