Electrochemical Methods of Determining the Corrosivity of Steel in Concrete

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Abstract
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.

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