Dependence of chloride ion diffusivity on evolution of pore-structures in freeze-thawed shotcrete: Multiscale characterization and modeling

The freezing-thawing (F-T) action-induced evolution of shotcrete pore-structure is the potential cause of resistance degradation of chloride ion diffusion in cold regions. To study the degradation mechanisms, a combined multiscale experimental characterization and numerical modeling study is conducted, considering the pore-structure evolution characterized with micro-computed tomography (micro-CT). The statistical micro-CT results show that the skeleton length and pore-structure connectivity are essential parameters to quantify the pore-structure evolution in microscale while the porosity in interfacial transition zones (ITZ) plays an important role in mesoscale. The multiscale model reveals that the F-T induced microcracks greatly affect the chloride ion diffusivity of cement paste and ITZ in shotcrete. The capability of identified parameters for describing cyclic F-T induced evolution in pore-structure is discussed by comparing the predicted results with the experimental data and two classical models. The combined multiscale characterization and modeling approach provides an effective tool to better understand the degradation mechanisms of chloride ion resistance of cement-based materials under F-T action.