Micromechanical contributions to the behaviour of cement-based materials: Two-scale modelling of cement paste and concrete in tension at high temperatures

A numerical multiscale model is proposed to study the thermo-hydro-mechanical behaviour of cement-based materials. This model is based on a finite element approach coupled to a numerical generation of the material microstructure. A homogenization method is used to calculate the macroscopic thermo-hydro-mechanical properties and the macroscopic hydraulic properties of heterogeneous materials according to the components properties. At the microscopic scale, numerical simulations have been carried out on cement pastes and the hydraulic flows, strain and stress fields are localized. A recent study has been carried out on damage of concrete structures under fire conditions in compression. In this paper, the micromechanical approach is applied for the calculation of the thermo-mechanical properties of concrete under a tensile load at high temperatures and to localize damage within the microstructure. The equivalent permeability is computed in order to estimate the increase in the leakage rate, which is an important parameter for the risk analysis of nuclear power plants. We note a strong increase in permeability in the damaged cement paste of concrete.