Degradation of fracture resistance, which is a phenomenon encountered in shotcrete as exposed to the cold environment, can lead to structural failure. Microstructural damage induced by freeze-thaw (F-T) cycles serves as the presage to macroscopic failure processes. To reveal the fundamental mechanisms of degradation, it is crucial to characterize and model the F-T damage in multiscales for the heterogeneous nature of shotcrete. In this paper, X-ray micro-computed tomography (micro-CT) is employed to describe the F-T damage in microscale and mesoscale shotcrete. Changes of the modulus of elasticity in cement paste and interfacial transition zone are analyzed using the cloud map obtained from the nanoindentation test. Micro-CT images capture the microstructural geometry, such as microcracks, aggregates, pores, and cement paste. Subsequently, microstructure-based finite-element modeling is developed to simulate the overall mechanical properties and fracture behavior of freeze-thawed shotcrete. The effect of F-T-induced damage is investigated on the three-phase fracture processes in terms of load versus deflection curves and cracking paths of shotcrete beams. The modeling results for damage and fracture are validated against the experimental data using the three-point bending tests of shotcrete beams.

抗裂性下降是喷射混凝土暴露于寒冷环境时遇到的一种现象，可导致结构失效。冻融 (FT) 循环引起的微观结构损伤是宏观失效过程的先兆。为了揭示退化的基本机制，对于喷射混凝土的异质性质，在多尺度上表征和模拟 FT 损伤是至关重要的。在本文中，X 射线显微计算机断层扫描 (micro-CT) 被用来描述微尺度和中尺度喷射混凝土中的 FT 损伤。使用从纳米压痕测试获得的云图分析水泥浆体和界面过渡区的弹性模量的变化。Micro-CT 图像捕获微观结构几何形状，例如微裂纹、骨料、孔隙和水泥浆。随后，开发了基于微观结构的有限元建模来模拟冻融喷射混凝土的整体力学性能和断裂行为。根据荷载-挠度曲线和喷射混凝土梁的开裂路径，研究了 FT 引起的损伤对三相断裂过程的影响。使用喷射混凝土梁的三点弯曲试验，对损伤和断裂的建模结果与实验数据进行了验证。