Corrosion behavior of reinforcing steel in concrete for nuclear facilities exposed in high chloride and low pH environment

The Cl ion concentration and pH were monitored by inserting micro-electrodes into artificial pores in the mortar which was exposed in 0.5 mol/l chloride solution (pH 4.0). At the same time, the electrochemical behavior of the reinforcing steel was investigated by EIS. The Cl ion concentration in the mortar was obtained using Ag/AgCl micro-electrodes, showing that this behavior is generally controlled by diffusion. When the diffusion equation was used in this work, the diffusion coefficient (Dc) showed a high value of Dc = 9.5 × 10−5 mm2/s. Similarly, the pH in the mortar was obtained using W/WOx micro-electrodes. With a 10 mm cover thickness, pH continued to decrease to pH 8.0, which was considered by penetration of H+ ions from the surface. Based on the results of monitoring with the micro-electrodes, solutions simulating those in the pores in mortar were prepared and used in EIS measurements. The charge transfer resistance Rct in the simulated solutions showed good correspondence with the impedance Z (Z1mHz – Zsol) in the actual mortar. This is attributed to the fact that the corrosion of reinforcing steel was controlled by the solution conditions (mainly Cl concentration and pH) in the pores in mortar.