Chloride-binding isotherms in concrete submitted to non-steady-state migration experiments

Abstract

Chloride binding is an essential step in the determination of the chloride transport across concrete. The binding ability has been previously modelled in different ways, among which is that of assuming an adsorption process and fitting to the mathematical expression of an isotherm from data obtained from natural diffusion tests. In the present paper, chloride concentration profiles from non-steady-state migration tests have been fitted to a Brunauer, Emmett, Teller (BET) isotherm general equation to model chloride binding under these conditions and to compare it with natural diffusion results. The results indicate that chloride ions remains unbound until the concentration in the pore solution exceeds about 28 g/L and that interactions in the chloride/cement matrix could be similar to those of natural diffusion when the chloride external concentration is higher than 1 M in Cl −. In addition, it has been found that the “chloride isotherm” is of type V with a BET characteristic constant C < 2.