Reliability of Electrochemical Techniques to Predict the Corrosion Rate of Steel in Concrete Structures

In corrosion affected concrete structures, periodic determination of the corrosion current, Icorr, is necessary to determine the magnitude of damage and hence the optimum time for repairs. Electrochemical techniques such as the linear polarization resistance technique (LPRT), Tafel extrapolation technique (TET), Electrochemical impedance spectroscopic technique (EIST), Galvanostatic pulse technique (GPT) and Harmonic analysis technique (HAT) are used to determine Icorr of rebar both under laboratory and field conditions. In this study, the reliability of the corrosion rates (CRs) determined by each of these techniques is established by comparing with the CR determined by the weight loss method for both passive and active states of the rebar. LPRT and TET were found to underestimate Icorr, because of the effects of diffusion polarization and the higher value of double layer capacitance of the steel in concrete. High time constant values and depressed semicircular plots with diffusion tails introduce errors in the estimation of Rp using EIST. Both GPT and HAT are able to overcome the above drawbacks and measure Icorr more precisely than EIST, LPRT or TET. A good agreement is obtained between the CR determined by GPT and HAT and those determined using the weight loss method. The errors introduced by assuming the Stern–Geary constant are eliminated in HAT as Icorr is measured directly from the harmonic currents.