Assessment of Damage in Heterogeneous Concrete Composites

Ultrasonic testing provides non-destructive measurements, which are widely used to evaluate stiffness degradation in materials and structures. In a recent study, a computational simulation method was developed for modeling ultrasonic pulse propagation in heterogeneous concrete materials. This method is based on a two-phase finite element model of the particle composite consisting of linearly elastic aggregate inclusions and a cement matrix, the damage of which is assessed via dynamic wave transmission analogous to ultrasonic testing. The advantage of this approach is its ability to examine the heterogeneous meso-structure and the progressive degradation of the elastic stiffness properties of the cement matrix. Although it proved very informative to simulate the ultrasonic response in coarse concrete mixes, it is unfortunately computationally very demanding because of the high mesh resolution necessary in space and time. The question arises, whether a simpler, less expensive method based on homogenized effective stiffness properties can provide comparable results. It is the objective of this paper to show, that, in fact, the resolution of the heterogeneities is necessary, and that the use of homogenized concrete properties cannot provide the information when progressive degradation is considered in the cement matrix which magnifies the contrast of the heterogeneous meso-structure.