The freeze-thaw model of cementitious materials partially saturated with dissolved salts: From elastic deformation to non-uniform plastic deformation

This study establishes a fully coupled thermo-hydro-mechanical model to describe the damage evolution of cementitious materials with dissolved salts under freeze-thaw conditions, from unsaturated to saturated states of water. A pore pressure calculation equation, accounting for air, is proposed based on the thermodynamic equilibrium of substances in the pores and the initial material state, and integrated into the pore elastoplastic model.The model also considers the convective diffusion of the gas phase and the permeation adsorption process of dissolved salts. The freeze-thaw process is simulated using the equilibrium method, incorporating hysteresis effects, and combined with the saturation function to quantify the uneven ice distribution due to the saturation gradient from external moisture absorption.The effectiveness of the proposed model is validated through comparisons with experimental data and the results of classical models from the literature. The discussion section demonstrates that the model effectively describes the process of moisture replacing air in pores during freeze-thaw cycles and incorporates this into the subsequent cycle. It also shows that the surface moisture saturation is significantly higher than that of the interior, which is a key factor contributing to surface frost damage in the material.