Chloride diffusion in concrete/prediction of the onset of corrosion in reinforced concrete structures

Abstract

Deterioration of concrete structures deu to the corrosion of reinforcement is the major problem of durability in the Gulf countries. It is ncessary to study the diffusion of chloride ions in concrete, to determine the time for the onset of corrosion in concrete structures. This research was aimed at determining the diffusion coefficients for chloride ions in Type V Sulphate Resisting Cement concrete made from local materials, using tow approaches: (a) Sustained chloride exposure test, assuming the applicability of Fick's laws of diffusion for the transport of chloride ions, and (b) Gas diffusion tests which have never been applied to concrete before.

The results indicate that the effective diffusion coefficients (De) for chloride ions in concrete is dependent on the water-cement ratio, cement content and exposure conditions, but are independent of the exposure chloride concentrations. From a non-linear regression analysis of the test results, De is expressed in terms of w/c ratio and cement content. The gas diffusion test appears to be a promising rapid technique for evaluating De for chloride ion in concrete. It is also observed that under idealized conditions, the solution to Fick's second law for the appropriate boundary conditions can be used to reasonably predict the time to initiation of corrosion.