Measuring damage anisotropy in concrete from ultrasound velocity data

Abstract The uniaxial compression of an initially isotropic concrete specimen induces a damage pattern that is anisotropic: in the direction of loading the concrete undergoes compaction, while in the directions orthogonal to the loading direction concrete cracking can be observed. In order to quantify such damage patterns, one possibility is to observe the changes in the stiffness tensor of a compressed specimen with respect to the stiffness tensor of the corresponding virgin state specimen. The eigensolutions of the Kelvin-Christoffel matrix for anisotropic media provide the relation between ultrasound wave velocities in given wavefront and polarization directions and the stiffness matrix components. In this study, it is shown how using the pitch-catch method for the determination of first time arrival, one can evaluate the sound wave velocities in different directions and compute the stiffness tensor components for a damaged concrete specimen. Plots of stiffness tensor components as a function of non-recoverable strain gives a qualitative measure of the anisotropic strain degradation process.