Modeling of mass transfer in the micro-structure of concrete: Towards computational homogenization within a FE2-strategy

Other conference contribution, 2010

Chloride ion ingress in concrete is of great concern for concrete structures as the ions can initiate corrosion of embedded reinforcement bars. The micro-scale constituents of concrete are the cement paste and gravel, and the porosity of the cement paste allows for transport of chloride ions. Furthermore, the transport of chloride ions within the cement paste is nonlinearly coupled to the transport of moisture. Due to this nonlinearity, and the heterogenous micro-structure of concrete, it is of interest to find a suitable homogenization tool in order to simulate mass transfer on the macro-scale level. In this paper, simulations of coupled chloride ion and moisture transfer in concrete are presented. The problem is set up as an initial boundary value problem on a representative volume element (RVE) with impermeable gravel embedded in the porous cement paste. The mass transfer is modeled as being of diffusion type, which allows for implementation of Fick's law and adsorption isotherms as constitutive models. Boundary conditions are set up for varying conditions on the macro-scale and the problem is solved numerically using the cG(1)dG(0) finite element method in space-time. Finally, homogenization over the RVE is applied in order to establish the pertinent macro-scale quantities. A discussion of the mass transfer models and their assumptions is given in relation to the physical mechanisms governing mass transfer in concrete. Simulations are presented for different setups of micro-structures and boundary conditions, showing the relation between the macro-scale response and the micro-structure. Finally, an outlook towards a concurrent computational multiscale model is given, which means that a macro-scale problem is solved concurrently with multiple micro-scale problems in a nested, so-called FE^2, fashion.