Micromechanics-based thermo-hydro-mechanical model for air-entrained porous materials subjected to freezing-thawing cycles

The freeze-thaw (FT) behavior of porous materials (PMs) involves the coupling of the thermo-hydro-mechanical (THM) processes and is significantly influenced by the microstructure. However, modeling FT in unsaturated PMs remains an open issue, and the influence of microstructure is not yet fully understood. To address these challenges, we propose a THM model for FT in PMs that considers microstructure and variable air content. In this work, a non-equilibrium thermodynamic approach is proposed to capture ice formation/melting, the microstructure is accounted for utilizing micromechanics, and the FT processes in air-entrained PMs are formulated within the proposed THM model. This model incorporates variable air void characteristics, e.g. air content, spacing factor, specific surface area, and supercooled water-filled regimes, and distinguishes the roles of air voids between freezing and thawing. The FT behaviors, including deformation, ice formation/melting, spacing factor, and pore water pressure evolutions, are focused. Comparisons with experimental results, confirm the capability of the present model. The results demonstrate the effects of variable air voids on the FT behavior of air-entrained PMs. The findings reveal that assuming fixed air void characteristics can lead to underestimation of pore pressure and deformation, particularly at low air content. Additionally, air voids act as cryo-pumps during freezing and when the cooling temperature stabilizes. During thawing, air voids supply gas to the melting sites (i.e. “gas escape”), preventing further significant deformation reduction. These results can provide novel insights for understanding the frost damage of PMs.