Monitoring of Corrosion Resistance of Steel in Simulated Concreate Pore Solution By EIS

Abstract

The method to evaluate the reinforcing steel in concreate have been investigated because the degradation of reinforced concrete is a serious problem in the whole world. An electrochemical impedance spectroscopy (EIS) is the powerful tool to determine the condition of the reinforcing steel in concrete because it is possible to obtain the electrochemical parameters of the reinforcing steel in concrete without its destruction by EIS. Dawson et al. [1] applied EIS to the investigation of corrosion of rebar in concrete. In the present study, we proposed the method to determine the corrosion resistance of reinforcing steel in concrete using the cylindrical steel probes by EIS. Figure 1 shows the cylindrical steel probes developed in the present study. The diameter and thickness of the steel probe is 10 mm and 8 mm respectively. The distance between the steel probes are 50 mm. These probes are embedded in concreate with the reinforcing steel. We expect that the corrosion resistance of the reinforcing steel in concreate can be determined by monitoring of the electrochemical impedance of the cylindrical steel probes. In order to establish the proposed monitoring method, the electrochemical impedance of the cylindrical steel probes were measured in the simulated concreate pore solution. Figure 2 shows the experimental setup of the electrochemical impedance measurement of the cylindrical steel probes in Fig. 1. The electrolyte solution was the saturated Ca(OH)2. The cylindrical steel probes were immersed in the electrolyte solution for 2 days. The air was continuously provided by pump during the immersion of the cylindrical steel probes in the electrolyte solution. The electrochemical impedance was automatically monitored at 10 kHz and 10 mHz using a corrosion monitor (Corp. i-pec, CEM-100A) by two electrode system. The potential amplitude was 10 mV. In addition, the electrochemical impedance measurement was carried out using the Potentiostat (Toyo Corp., Solatron1287) and FRA (Toyo Corp., Solatron1255B) in the frequency range from 10 mHz to 10 kHz at five frequencies per decade with AC amplitude of 10 mV. The pH of the electrolyte solution was measured every 24 hours. The electrochemical impedance of the cylindrical steel probes determined using the corrosion monitor was compared to that measured using FRA. The changes of the charge transfer resistance R ct was discussed by the time variation of pH. Reference [1] J. Dawson, L. Callow, K. Hladky and J. Richardson, Corrosion/78, 125 (1978). Figure 1