Corrosion analysis and monitoring of the environmental factors for the deterioration of chromium-bearing reinforcing steel in mortar

To understand environmental factors, Cl ion concentration and pH were monitored by inserting microelectrodes into artificial pores in the mortar. The corrosion behavior of reinforcing steels containing chromium were investigated with carbon steel (SM) by electrochemical impedance spectroscopy (EIS). From the EIS, the corrosion resistance of the Cr-bearing reinforcing steel was visibly higher than the SM reinforcing steel. Simultaneously, the Cl ion concentration in the mortar was obtained using Ag/AgCl microelectrodes, showing that this behavior is generally controlled by diffusion. Similarly, the pH in the mortar was obtained using W/WOx microelectrodes. With a 20-mm cover thickness, pH was limited to approximately pH 11, but with a 10-mm cover thickness, pH continued to decrease to around pH 9.5. Solutions were prepared simulating the condition in the pores in mortar and were used in EIS measurements. The charge transfer resistance, R (ct), in the simulated solutions showed good correspondence with that 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 mortar. Moreover, it was found that, as compared with SM, Cr-bearing steel could keep the passive film in severe condition, and have long incubation time until the passive film was destroyed.