Modelling the transport of chloride and other ions in cement-based materials

Abstract

Research on mechanisms of chloride ion transport in cement-based materials is relevant to improve the durability of reinforced concrete structures. Conventional chloride-transport models consider a linear diffusion equation, only valid for fully saturated and non-reactive concrete. This work proposes a model of chloride and other ions penetration in saturated concrete considering diffusion, chloride binding, chemical activity and migration. The model uses intrinsic diffusion coefficients. The influence of the ionic pore solution on chloride penetration into concrete is also studied. Chemical activity is introduced by coupling the transport equations to the Pitzer model. The migration is accounted for by imposing the electro-neutrality condition of the pore solution. It is shown that fitting the well known error function to experimentally obtained chloride profiles present results which are difficult to interpret. Moreover, it is shown that, by accounting for solely diffusion and chloride binding, good results are obtained. Contemplating chemical activity and migration slightly improves such results and allows concentration profiles of the present ionic species in the pore solution to be determined. Such profiles are involved in the degradation processes of cement-based materials exposed to aggressive environments.