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.

Steel-reinforced concrete is used throughout the world in the construction of bridges, marine structures, parking garages, and buildings. The alkaline environment of the concrete protects the steel from corrosion; however, this protective environment can be disrupted due to the migration of chloride ions to the steel and/or to carbonation of the concrete. In this paper several electrochemical techniques that can be used to determine and predict the corrosion of steel in concrete are described. Further, it is shown how these techniques can be used to show the effectiveness of corrosion inhibitors and other modifications to the concrete mixture on corrosion control. Solution testing in calcium hydroxide and in sodium/potassium hydroxide pore water solutions can be used to determine corrosion mechanisms and the effectiveness of inhibitors when chloride is present. The use of cyclic polarization in these solutions to determine the effects of chloride and calcium nitrite is discussed. Corrosion testing of steel in concrete provides more direct evidence of the effect of the concrete mix design on corrosion performance. Three techniques are quite common in this laboratory and in others. They are polarization resistance, electrochemical impedance, and the measurement of the macrocell corrosion between two layers of bars. The use of these techniques is discussed, and several examples of their use and comparison to visual attack of the steel are given. The techniques, as used, correlate very well with the observed corrosion damage on the embedded steel. Because polarization resistance and electrochemical impedance are nondestructive, they can be used to monitor the corrosion rates of steel in concrete, whereas mass loss or visual observation require destruction of the concrete to observe the bar. The use of these techniques to monitor the long-term behavior of steel in concrete is demonstrated.