Corrosion Monitoring of Reinforcing Steel in Concrete By Electrochemical Impedance Spectroscopy

The corrosion of the reinforcing steel in concrete is strongly related to the loss of cover concrete and the steel bar diameter. These effects may cause sudden failure of a structure. Therefore, it is important to obtain the corrosion rate of the reinforcing steel in concrete precisely.

An electrochemical impedance spectroscopy (EIS) is the powerful method for evaluating the conditions of the reinforcing steel because the EIS enables us to discriminate the time constants of elementary steps in the dissolution process without causing damage to the electrodes. We applied the EIS to monitor the corrosion rate of the reinforcing steel in concrete. In order to establish the method of the corrosion monitoring by EIS, the effects of the covering depth and the concentration of chloride ions on the corrosion of the reinforcing steel in concrete were investigated. All reinforcing steels were cast using a concrete. The covering depth of the concrete is 10, 20 or 30 mm. The water-cement (W/C) ratio of the concrete is 40, 50 or 60. A NaCl was used as the source of the chloride ions. Impedance measurements were performed by a two-electrode system using potentiostat (Solartron, 1287) and a frequency response analyzer (FRA) (Solartron, 1255B) combined with oscilloscope (IWATSU, SS-7802). The working electrode and the counter electrode were the reinforcing steel. The impedance spectra were measured in the frequency range from 10 mHz to 1 MHz at 5 frequencies per decade with AC amplitude of 10 mV. The impedance spectra of the reinforcing steels in concrete with different covering depth and concentrations of chloride ions were discussed.