A Nonlinear Theoretical Study of Modelling Chloride Diffusion in Concrete Containing Fly Ash and Slag

Abstract

ABSTRACT The principal objective of this paper is to investigate the modelling of chloride diffusion in fly ash and slag concretes laden in chloride environments. The capacity of the concrete cementitious system to bind chloride ions has an important effect on the rate of chloride ionic transport in concrete. Four mathematical models concerning chloride binding in concrete are stated and used. The analytical solution of Fick’s second law of nonlinear (diffusivity ≠ constant) diffusion in conjunction with initial and boundary conditions is used as a predictive model. The experimental data obtained by Thomas and Bamforth [Modelling chloride diffusion in concrete: Effect of fly ash and slag. Cement and Concrete Research 1999;31:487-495] was cited as input parameters. The results at the present study show that after 30 years the predicted chloride profiles obtained by the nonlinear model may be one order of magnitude lower than that of linear (diffusivity = constant) model. The nonlinear model associated with four mathematical models related to chloride binding in concrete is not suitable to predict the transport mechanism of chloride diffusion in concrete containing fly ash and slag. However, the analytical solution of a nonlinear partial differential equation (PDE) in association with initial and boundary conditions for the concentration of Cl- in the aqueous phase [Cl-(aq)] (in kg/m3 pore solution) is proper to estimate the transport behavior of chloride diffusion in both fly ash and slag concretes. The Cl- bound in the solid phase [Cl-(s)] (kg/m3 concrete) can thus be computed algebraically. Further research in-depth is obviously needed and suggested.