Non-equilibrium modeling hysteresis of water freezing: Ice thawing in partially saturated porous building materials

This article presents a novel mathematical model of hygro-thermal processes in a porous material, partially saturated with liquid water, exposed to temperatures below the freezing point of pore water. Water–ice phase transition is modeled by means of a kinetic approach considering water supercooling and thermodynamic non-equilibrium of the phases, what allows taking into account a hysteresis of ice content during freezing–thawing of moist porous materials. The model equations are solved for two numerical examples. The first one deals with laboratory differential scanning calorimetry test of a cement mortar saturated with water and exposed to temperatures below the freezing point of water (down to −40°C). The results are used for experimental validation of the proposed model, confirming its accuracy and practical usefulness. In the second example, the mesh refinement test is performed and the influence of the solid–liquid water phase change model parameters on the simulation results for a 1D model problem concerning water freezing–thawing are analyzed and discussed.