Damage detection in concrete using coda wave interferometry

Coda wave interferometry (CWI) is a nondestructive evaluation technique for monitoring wave velocity changes in a strongly heterogeneous medium as demonstrated in previous seismic and acoustic experiments. The multiple-scattering effect in such a medium promotes the rapid formation of a diffuse field, and waves can travel much longer than the direct path, and thus are more sensitive to small changes occurring in the medium. This research applies the CWI technique in conjunction with acoustoelastic measurements to characterize two different types of damage in concrete: damage due to thermal shock and dynamic cyclic loading. The diffuse ultrasonic signals are taken at different levels of compressive stress and then relative velocity changes are extracted using the CWI technique. The relative velocity change (or the material nonlinearity) increases considerably with increasing damage level in most samples for both types of damage. The feasibility and sensitivity of this CWI-based technique in characterizing damage in cement-based materials are demonstrated. (C) 2011 Elsevier Ltd. All rights reserved.