FEM simulation of chloride diffusion in modeled recycled aggregate concrete

This paper proposes a model to describe the effect of recycled aggregate (RA) on the chloride diffusion in recycled aggregate concrete (RAC). In this study, RAC is modeled in mesoscope as a five-phase composite material by considering the old and new interfacial transition zones (ITZs) as interphases, and the new mortar, old attached mortar and original aggregate as continuous phases. Based on the multiphase theory, new theoretical equations are derived to calculate the effective chloride diffusivity (Deff) in the modeled RAC. Using the finite element method (FEM) simulation, a parametric study has been undertaken to understand the effects of the RA volume fraction (Fra), the RA shapes, the boundary conditions, the adhesive rate of the old adhered mortar (Rrm) and the thickness of the ITZ (TITZ) on the chloride diffusivity in RAC. It is concluded that the discrepancy between the chloride diffusivities of different phases may remarkably complicate the chloride diffusion behavior in the modeled RAC. For the same volume of RAC, Deff decreases with the increase of Fra, but increases with Rrm and TITZ. The RA shape also influences the chloride concentration. Furthermore, the values of Deff calculated from theoretical equation and from the FEM are in reasonable agreement.