CT image-based experimental and numerical simulation methods for freeze–thaw concrete microstructure

Freeze–thaw cycling is a primary durability challenge for concrete structures in cold regions. This study presents an integrated experimental and numerical approach to visualize and quantify mesoscale freeze–thaw damage evolution in concrete. Indoor rapid freeze–thaw tests were conducted, combined with computed tomography (CT) scanning for three-dimensional (3D) microstructure reconstruction and finite element (FE) simulation for damage analysis. A CT-based 3D mesoscale model incorporating real aggregate, mortar, pore, and interfacial transition zone (ITZ) distributions was developed, with representative volume elements validated through statistical homogenization. Results indicate that macroscopic property degradation is accompanied by a significant increase in pores sized 20–50 μm and preferential crack propagation along the ITZ. The pore surface area growth rate substantially exceeds the volume growth rate beyond 75 cycles, confirming that microcrack widening rather than pore nucleation dominates damage progression. FE simulations reveal a maximum vertical strain of 9.95 × 10 − 4 and maximum principal stress of 23.5 MPa at − 15℃ after 125 cycles, with the ITZ identified as the critical damage zone—a finding consistently supported by both numerical predictions and experimental CT observations. This integrated framework provides a robust pathway for linking microscale structural evolution to macroscopic performance loss in freeze–thaw deterioration assessment.