In-situ Imaging of Crack Propagation in Sulfate-Attacked Cement Paste: X-CT Time-Lapse Microscopy

In-situ dynamic characterization of crack evolution is critical for elucidating fracture origination and propagation mechanisms, yet remains experimentally challenging across any material systems. Herein, we propose an X-ray computed tomography (X-CT) method enabling continuous time-lapse crack imaging. For sulfate attack-induced cracking progression in hardened cement paste, the temporal progression was converted into spatial coordinates along the sulfate-penetration direction via controlled sulfate diffusion kinetics, establishing a microscale "time-lapse microscope". Real-time visualization reveals ionic penetration and crack pathways through multiphase hydrates composites and complete cracks network development from nucleation to percolation. Greyscale analysis confirms the formation of sulfate-filling low-density (LD) hydrates, which generates interconnected networks serving as preferential fracture channels. The crack propagation rate is quantified for the first time, 36 ~ 77 μm/day. This platform pioneers continuous spatiotemporal analysis of fracture dynamics and has scalability for the study of crack propagation of structural materials.