Prediction of free chloride concentration in concrete using routine inspection data

This Paper presents a wide range of experimental data on chloride concentrations in the pore fluid (free chloride contents) of various mixes of concrete. The results show that Fick's second law for unidirectional diffusion into a semi-infinite medium is valid for free chloride penetration into concrete. The values of diffusion coefficient D-c decrease with time and it is shown, on the basis of substantial experimental data, that diffusion coefficients of free chloride penetration D-c(f) and acid-soluble chloride penetration D-c(a) can be correlated over a wide experimental range. The Paper derives expressions based on Fick's second law of diffusion which can be used to predict long-term concentrations of free chloride in concrete using data obtained in a routine inspection of a concrete structure. These data include acid-soluble chloride concentrations in concrete cores and the chloride concentration of the solution to which concrete is exposed. The free chloride concentration profiles across the depth of concrete derived using these procedures show fairly good agreement with long-term experimental data. Since the pore fluid in concrete provides the electrolyte for reinforcement corrosion, the procedures derived in the Paper will be valuable in the setting up of accurate practical procedures for assessment of corrosion in concrete.