Propagation Fronts during Calcium Leaching and Chloride Penetration

Abstract

Calcium leaching and chloride penetration are modeled with regard to concrete chemical degradation and corrosion risk of steel reinforcement in RC structures. The presence of propagation fronts that move at finite velocity and that define the depth of material affected by dissolution or chloride penetration is particularly emphasized. This paper starts with a simple model of the coupled diffusion-dissolution process. This model makes it possible to construct an analytical solution. This solution is used to show that the finite volume method is well suited for modeling sharp dissolution fronts. Then, by considering a realistic chemical equilibrium relation, the variations of porosity, and the effective diffusion coefficient, the model is applied to calcium leaching of cement-based materials. The simulation of the propagation of portlandite dissolution fronts is in close agreement with experimental results of degradation of a cylinder sample with a notch. Finally, chloride penetration is modeled with a diffusion-sorption equation. It is shown that the use of Freundlich's isotherm of sorption leads to a finite penetration depth of chloride ions. These fronts have been observed in experiments of chloride penetration in concrete materials.