Deformation and Fracture Processes on Interface of High-Strength Mortar Sphere inside Mortar under Compressive Stress Using X-ray CT

The interfacial transition zone surrounding aggregates plays a crucial role in the strength and fracture behavior of concrete. Previous studies have primarily relied on surface observations of specimens to investigate cracking around coarse aggregates, leaving the three-dimensional internal mechanisms of compressive deformation and fracture unclear. To address this issue, the authors developed an X-ray CT system capable of imaging under loading conditions and applied digital image correlation to visualize internal strains in three dimensions. In this study, this system was used to examine the three-dimensional deformation of a specimen containing a high-strength mortar sphere embedded as a model aggregate. As the results, interfacial voids and transition zones ranging from 0.1 to 1.5 mm were identified. When the applied compressive stress exceeded the apparent critical stress, image measurement showed that expansion strain increased on the side surface after microfractures developed at the upper and lower interfaces of the sphere, ultimately leading to failure. And the local strain distribution around the interface extended approximately ±2 mm.