The use of small electrochemical perturbations to assess the corrosion of steel in concrete

In this work an experimental and theoretical comparison has been made between the use of the potentiostatic and coulostatic methods to assess the corrosion rate of steel in concrete. Numerical Laplace transformation was used for preliminary impedance analysis of the coulostatic transients to aid the understanding of the experimental data. The corrosion tests were carried out on a range of reinforced concrete specimens made with various types of cements (plain, flyash and slag blended cements), different water to cement ratios (0.4 and 0.5) and various admixed chloride concentrations varying from 0 to 3% by weight of cement. Despite the inherent variability of concrete, which usually results in a large scatter of results, similar trends in the performance of the different concrete mixes were predicted by the two methods. Curve fitting analysis of the transients obtained from both methods was found to result in a lower estimate of the polarisation resistance parameter than other conventional methods. However, this analysis may represent an improvement over the other estimates of its value as it provides a consistent methodology of excluding the very fast or slow transient processes which may not result from the corroding interface. The differences in the results obtained from the various methods of analysis of the two methods, together with their advantages and disadvantages, are discussed.

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