Influence of Supplymentary Cementitious Materials on Diffusion and Adsorptive Reaction of Chloride Ions in Concrete

Abstract

ABSTRACT The durability of Portland cement (PC) systems incorporating supplementary cementitious materials (SCM) such as silica fume, slag, low- and high-calcium fly ash (FA) is recently investigated by using a modified model which is extended from a previously mathematical model. This modified model is represented by a simultaneous system, one is a nonlinear partial differential equation (PDE) which can be solved only numerically, the other is a Langmuir isotherm equation. In this paper, to solve this nonlinear PDE, first, the Kirchhoff transformation is used to render the nonlinear problem into a linear one, then the Laplace transformation is used to seek an analytical solution. This analytical solution is represented as the chloride concentration in the aqueous phase. The Langmuir isotherm equation is represented as the chloride concentration in the solid phase which is derived from the Langmuiran isotherm linear ordinary differential equation at time infinite. Inserting the value of aqueous phase chloride concentration into the Langmuir isotherm equation, the solid phase chloride concentration can be estimated. The principle of superposition can be used to present the total chloride concentration which is the sum of solid phase chloride concentration and concrete porosity product aqueous phase chloride concentration. Thus, the existing modified model can be alternately expressed in terms of two analytical solutions. In order to verify the practical serviceability of the proposed model, the previously experimental data were cited as input parameters. It was found that the prediction results were usually in good agreement with the experimental results.