Estimating the Life Cycle of Reinforced Concrete Decks and Marine Piles Using Laboratory Diffusion and Corrosion Data

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Abstract
Chloride induced corrosion is a major cause of the deterioration of steel reinforced concrete structures in marine environments, and in Northern environments where deicing salts are used. The time-to-corrosion initiation and subsequent corrosion induced damage is related to the time that it takes chloride ions to reach a critical level at the steel. In this paper it is demonstrated that chloride ingress into concrete follows Fick's Diffusion equation for properly cured concretes. It is shown how the diffusion coefficients and chloride surface concentrations can be used to predict the chloride profile as a function of time. The effects of concrete mixture proportioning and concrete admixtures on the diffusivity of chloride and chloride corrosion threshold level are shown. The results of several experiments and models developed show that reducing the water-to-cement ratio and increasing concrete cover over the steel greatly reduce the chloride ingress as recommemded by the American Concrete Institute codes. Furthermore, even more dramatic decreases in chloride penetration can be obtained by the use of microsilica in the concrete mixture. It is also shown that calcium nitrite when admixed into the concrete significantly increases the chloride levels at which severe corrosion will occur. The above results are used to estimate the time to corrosion and failure for different types of reinforced concrete structures. These models can be used by a design engineer to estimate the life of reinforced concrete exposed to chloride ingress.

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