Comparative study on the impact-induced microstructural damage in concrete using X-ray computed micro-tomography

To better understand the failure behavior of cementitious materials during dynamic loading, the microstructural damage initiation and development in an ultra-high-performance concrete (UHPC) and a special type of conventional concrete (CC) with an average aggregate size of only 2–3 mm are comparatively studied using the X-ray computed micro-tomography (micro-CT) technique. Quantitative measurements of reconstructed 3D crack morphology are performed on specimens recovered from controlled intermittent dynamic loading experiments, with different extents of damage introduced through a modified Kolsky bar apparatus. By correlating the loading history of the recovered specimen with the crack development within the bulk, a quantitative relationship between several crack parameters (e.g., crack volume, crack surface area, and void-crack interaction) and the increasing plastic strain are obtained. The results demonstrate the formation of cracks prior to the peak stress and reveal a fundamental difference in crack development between the two different concretes being investigated. Further evaluation between the measured crack parameters and the calculated constitutive damage variables indicates that compared to UHPC, CC is capable of sustaining considerable post-peak strain softening and its residual mechanical properties (strength and stiffness) are more susceptible to crack development in the bulk material. Comparative analyses on the size distribution of different void subsets also reveal the inherent connection between the pre-existing large-size voids in the bulk material and the loading-induced crack network. These experimental results provide a comprehensive view on the microstructural damage evolution mechanisms for these two concrete materials under dynamic loading conditions and may shed light on the development of future multi-scale concrete damage models. •The analysis of microstructural damage characterized by crack and voids by dynamic intermittent loading were performed.•Our data confirm the pre-peak damage development and demonstrate a fundamental difference of the crack development between UHPC and CC.•A clear preference of interaction between the crack network and the pre-existing large size voids in the bulk material is validated.