Monitoring of reinforcement corrosion by impedance technique

Monitoring of reinforcement corrosion by d.c. polarisation technique is found to be unreliable due to high resistance of concrete. In this aspect, a.c. impedance method is found to be useful since the resistance of concrete is eliminated in the measurements. The impedance of the steel embedded in concrete with and wlthout chloride has been measured for the frequency range of I mHz to 10 kHz at the corrosion potential using the frequency response analyser. It has been found that the impedance behaviour of steel in concrete without chloride is of pure capacitive nature due to passivation of steel by the concrete. But in the case of steel in concrete containing 496chloride the impedance diagram is found to be a distorted semicircle owing to the corrosion of steel. From the impedance values, it is possible to monitor the corrosion of reinforcemat by periodic measurements