In this study, quantitative microstructure-property relationships are mainly used to characterize the damage due to high-strain-rate impact loading and the mechanical behavior of concretes prepared by substituting natural aggregate (gravel) with recycled aggregates having different rigidities (blue brick and rubber). Based on the results obtained, a possible mechanism for microstructural damage in concrete is proposed. It is concluded that the aggregate causes a change in the initial interfacial transition zone (ITZ) condition, and it is this altered ITZ condition that has a major effect on overall mix behavior. The analysis also indicates that there is almost a linear correlation between the roughness values (Ra) of the region near the paste-aggregate interface and the dissipated surface fracture energy values of the specimens. Moreover, three-dimensional topographic images of the specimens constructed using a vertical nanotech scanning interferometer show that the paste region of the gravel specimen has the smoothest profile due to the relatively strong hydrated paste. DOI: 10.1061/(ASCE)MT.1943-5533.0000616. (C) 2013 American Society of Civil Engineers.