Chloride ingress prediction: Part 1: Analytical model for time dependent diffusion coefficient and surface concentration

Prediction of chloride ingress into concrete is an important part of durability design of reinforced concrete structures exposed to chloride containing environment. This paper presents the state-of-the art: an analytical model which describes chloride profiles in concrete as function of depth and time, and where both the surface chloride concentration and the diffusion coefficient are allowed to vary in time; the Mejlbro-Poulsen model is the general solution to Fick’s 2nd law. The paper also presents conversion formulas for the four decisive but rather abstract parameters to parameters, which makes physical sense for the design engineer, i.e. the achieved chloride diffusion coefficients at 1 year and 100 years, D1 and D100 respectively, and the corresponding achieved chloride concentrations at the exposed concrete surface, C1 and C100. Data from field exposure supports the assumption of time dependent surface chloride concentrations and the diffusion coefficients. Model parameters for Portland cement concretes with and without silica fume and fly ash in marine atmospheric and submerged South Scandinavian environment are suggested in a companion paper based on 10 years field exposure data.