Discrete Hygro-Thermo-mechanical Coupled Modeling of Concrete under Freeze-Thaw Cycles: Cracking Pattern, Mechanical Degradation and External Load Effect

This study proposes a novel discrete hygro-thermo-mechanical model for concrete under freeze-thaw cycles (FTCs) within the framework of the Multi-physics Lattice Discrete Particle Model. The evolution of ice content and its hysteretic behavior are simulated using a modified liquid-solid interfacial energy function. The non-uniform local eigenstrains induced by temperature variation and ice formation govern the FTC-induced cracking behavior; accordingly, these eigenstrains are incorporated into the mechanical constitutive model via a one-way coupling scheme. Notably, the model successfully captures cracking patterns, which initiate at the surface and propagate inwards over hundreds of FTCs. It also accurately predicts the associated degradation in both tensile and compressive strength. Therefore, this study finds that an external compressive load exerts a complex influence on FTC-induced degradation. Specifically, a moderate compressive load equal to 50% of the material’s compressive strength increases the residual strength by approximately 1.5 MPa after 50 FTCs. This beneficial effect arises because the applied external load restrains frost-heaving deformation and thereby suppresses the initiation of FTC-induced micro-cracks. In contrast, when the external load exceeds 70% of the compressive strength, degradation is significantly accelerated.