Constitutive Modeling of Unsaturated Drying Deformable Materials

Thermodynamics of open continua, when applied directly at the macroscopic engineering scale, allows one to extend unambiguously the principal concepts of continuum thermomechanics of solids to polyphasic porous materials, whose fluid constituents are subject to liquid-vapor phase change. This approach provides a consistent and relevant framework for the formulation of the constitutive equations of partially saturated deformable porous materials such as concrete. After recalling the general theory, the modeling is specified for porous materials that are partially saturated by a liquid water phase changing into its vapor phase, the latter forming with the dry air an ideal mixture. The nonlinear poroelasticity, as reference modeling, is then detailed. The theory is applied to the modeling of the drying shrinkage of concrete samples with isothermal sorption curves as only experimental data. The predicted shrinkage is found to be in close agreement with the observed one for a range of humidity greater than 50%. The drying shrinkage of a wall is finally examined. The analysis includes the study of the temperature variations due to latent heat effects. These variations are shown to be negligible.