A non-equilibrium thermodynamic model for unfrozen liquid content of saline porous media exposed to freeze-thaw cycles

Abstract

Accurate prediction of unfrozen liquid content in saline porous media is essential for assessing the freeze–thaw durability of construction materials in cold and saline environments. This study proposes a non-equilibrium thermodynamic model that couples salinity, pore structure, and temperature to characterize the freezing–thawing characteristic curve (FTCC). This model incorporates a chemical potential imbalance formulation to capture rate-dependent phase transitions and recovers the classical equilibrium model as a limiting case under quasi-static conditions. Extensive validation against experimental data for various porous materials demonstrates the model’s ability to reproduce freezing-point depression, delayed ice formation, and freeze–thaw hysteresis. Parametric analyses further reveal the dominant influence of salt concentration, pore geometry, and contact angle on ice–liquid phase behavior. The non-equilibrium model captures delayed phase transitions and freeze–thaw hysteresis under rapid cooling, whereas the equilibrium model remains applicable for quasi-static conditions due to its simplicity. The proposed model provides a thermodynamic basis for investigating frost damage in construction materials exposed to cold regions.