Modelling damaging processes of concrete at high temperature with thermodynamics of multiphase porous media

In this paper, the authors present a mathematical description of a multi- phase model of concrete based on the second law of thermodynamics. Explo- itation of this law allowed researchers to obtain definitions and constitutive relationships for several important physical quantities, like capillary pres- sure, disjoining pressure, effective stress, considering also the effect of thin films of water. A mathematical model of hygro-thermo-chemo-mechanical phenomena in heated concrete, treated as a multi-phase porous material, has been formulated. Shrinkage strains were determined using thermodyna- mic relationships via capillary pressure and area fraction coefficients, while thermo-chemical strains were related to thermo-chemical damage. In the mo- del, a classical thermal creep formulation has been modified and introduced into the model. Results of numerical simulations based on experimental te- sts carried out at NIST laboratories for two types of concrete confirmed the usefulness of the model in the prediction of the time range, during which the effect of concrete spalling may occur