Prediction of total chloride content profile and concentration/time-dependent diffusion coefficients for concrete

This paper presents a new approach to the determination of the total chloride content profile and the concentration/time-dependent diffusion coefficients for water-saturated concrete (i.e. concrete where diffusion is the dominant permeation process) due to the ingress of chloride ions. The mathematical models developed are primarily based on the assumption that the total chloride content profile within a semi-infinite medium can be expressed as an exponential decay function of the Boltzmann variable. This assumption and the simulation results have been found in good agreement with published experimental data. A test period of less than several months for typical structural concrete is believed to be sufficient. The profiles of both the non-steady state and the steady state conditions can easily be predicted. Experimental works involve only a few measurements of the total chloride content of concrete samples at different times plus a conventional penetration test. The advantages of this approach over the conventional methods, using Fick's laws, are that the change in concrete characteristics with time can be accounted for and can produce reliable results in a shorter test period. In addition, the calculated concentration/time-dependent diffusion coefficients can also be used to study the non-linear chloride-binding capacity of concrete.