FE² multiscale modelling of chloride ions transport in recycled aggregates concrete

In the context of climate change, reducing the production of CO2 emissions and preserving natural resources have proven to be necessary. One way to reach theses objectives is to recycle old concrete members: Recycle Concrete Aggregates (RCA) are aggregates obtained by crushing demolished concrete structures. Those aggregates can substitute the Natural Aggregates (NA) inside the so-called Recycled Aggregates Concrete (RAC). RCA are composed of natural aggregates and adherent mortar paste, the latter increasing the porosity and water absorption of RAC. Furthermore, water is necessary for, and even promotes, the penetration of aggressive ions such as chloride ions, possibly reducing the durability of said concrete.
This paper aims to model the influence of RCA on chloride ions ingress: several experiments have been performed to determine the transfer properties and the chloride ions diffusion coefficients of mortar pastes and concretes produced with NA or 100% RCA. The icrostructure of the RCA deeply influences the permeability, the water content distribution and the chloride diffusion. These properties have been included into a numerical model that integrates the microstructural information. A numerical homogenization technique, based on the Finite Element square (FE2) method, is implemented into a coupled multiscale model of water flows and advection/diffusion of chlorides in saturated concrete, in order to model the complex flow behaviour encountered.
The numerical model developed is compared to existing simple-scale models, using a simple RVE, in order to validate the implementation. The numerical convergence of the developed model is also studied, as far as the numerical cost of the FE square method is expensive.