The freeze-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 experimental data and two classical models. The combined multiscale characterization and modeling approach provide an effective tool to better understand the degradation mechanisms of chloride ion resistance of cement-based materials under F-T action.

冻融（FT）作用引起的喷射混凝土孔隙结构演化是寒冷地区氯离子扩散阻力下降的潜在原因。为了研究降解机制，考虑到微计算机断层扫描 (micro-CT) 表征的孔隙结构演变，进行了多尺度实验表征和数值建模研究的结合。统计显微 CT 结果表明，骨架长度和孔隙结构连通性是量化微观尺度孔隙结构演化的重要参数，而界面过渡区 (ITZ) 中的孔隙率在中尺度中起着重要作用。多尺度模型表明，FT 诱导的微裂纹极大地影响了喷射混凝土中水泥浆和 ITZ 的氯离子扩散率。通过将预测结果与实验数据和两个经典模型进行比较，讨论了用于描述循环 FT 诱导的孔隙结构演化的已识别参数的能力。结合多尺度表征和建模方法为更好地理解水泥基材料在 FT 作用下耐氯离子降解机制提供了有效工具。