Coupled hygrothermal and mechanical simulations of highly anisotropic building material during freezing and thawing

Porous building materials, such as board materials, wood, stones, fired clay materials, and bio-based materials, often have anisotropic properties. This study investigates adequate numerical models for the coupled hygrothermal and mechanical behaviors of strongly anisotropic building materials during freezing and thawing. First, strain measurements are reported for two types of fired clay materials to confirm the anisotropy of deformation during freezing and thawing. In calculations, the anisotropy of the Biot coefficient of a material is considered based on anisotropic poroelasticity. The comparison between the measurements and calculations revealed that the anisotropic deformation during the measurement cannot be reproduced without considering the anisotropies of the Biot coefficient as well as those of the mechanical properties. In addition, analysis of the causes of the deformation reveals that the expansion in the direction normal to the material thickness due to the water pressure development during the freezing is suppressed by the small Biot coefficient. These results indicate that the anisotropy of the Biot coefficient significantly influence the deformation due to frost actions; consequently, the anisotropic Biot coefficient should be adequately considered in numerical simulations.