FE² Multiscale Modelling of Chloride Ions Transport in Recycled Aggregates Concrete

Reinforced concrete structures are subjected to various degradation processes throughout their service life. Chloride-induced corrosion is one of the most common; it usually occurs by the roads where de-icing salts are used, as well as in coastal regions. This corrosion leads to a continuous increase in maintenance costs for bridges and other infrastructure.
The use of Recycled Concrete Aggregates (RCA) instead of Natural Aggregates (NA) in concrete can worsen durability concerns due to the adherent mortar paste that reduces the mechanical and durability properties of concrete. Nevertheless, Recycled Aggregates Concrete (RAC) is a sustainable approach for reducing waste and preserving natural resources. Therefore, understanding chloride ingress in recycled aggregate concrete is crucial for its development and use.
An extensive experimental campaign was conducted on concretes produced with 100% natural aggregate or recycled concrete aggregate, as well as equivalent mortar and cement pastes, in order to evaluate their intrinsic properties in terms of water transport and chloride ion ingress. It enabled a better understanding of the effect of replacing NA with RCA in concrete. The findings revealed that recycled aggregate concrete is more porous and permeable, and promotes the diffusion of chloride ions in comparison to Natural Aggregates Concrete (NAC).
The Finite Element Square (FE²) method was subsequently used to develop a multiscale chemo-hydraulic model, which was implemented in Lagamine software (from the University of Liège). The model was verified numerically, analytically, and then calibrated experimentally. The model’s constitutive equations are based on intrinsic properties obtained from experimental results. The model demonstrated its accuracy in replicating experiments and providing additional insight into chloride ingress in both saturated and unsaturated concrete.
The implementation of Water Retention Curves (WRC) and their hysteresis takes into account unsaturated conditions, following an empirical model by Van Genuchten (1980). The water retention curves are calibrated experimentally and then used to assess the degree of water saturation in concrete, which is a crucial factor for the ingress of chloride ions.
The results suggest that the durability of recycled aggregate concrete may be comparable to that of natural aggregate concrete under specific mixture quality and environmental conditions. A modelling application was carried out to evaluate this, replicating actual conditions on a maritime lock wall.