Damage characterization in concrete using diffuse ultrasound

Abstract

Diffuse ultrasonic measurements were used to characterize the state of stress-induced damage (volumetric microcracking) in concrete specimens. The test specimens were subjected to cycles of stepwise uniaxial compression. At each step, the loading (stress- or strain-controlled) was held constant and a series of ultrasonic measurements parallel and perpendicular to the loading were obtained. Unusually long signals were recorded, so that the diffuse ultrasonic regime tailing the coherent field could be studied. In the diffuse regime, the measured ultrasonic response is a superposition of reflections from scatters within concrete and thus, very sensitive to the changes in concrete microstructure. Using Coda Wave Interferometry (CWI), the evolution of diffuse velocity with the increasing load was monitored. The rate of change in the diffusion velocities was shown to be a good indication of the state of (low to medium intensity) damage in concrete.