On the corrosion behaviour of phosphoric irons in simulated concrete pore solution

The corrosion behaviour of three phosphoric irons P1 (Fe–0.11P–0.028C), P2 (Fe–0.32P–0.026C) and P3 (Fe–0.49P–0.022C) has been studied in simulated concrete pore solution (saturated Ca(OH)2 solution) containing different chloride concentration. This has been compared with that of two commercial concrete reinforcement steels, a low carbon steel TN (Fe–0.148C–0.542Mn–0.128Si) and a microalloyed corrosion resistant steel CS (Fe–0.151C–0.088P–0.197Si–0.149Cr–0.417Cu). The beneficial aspect of phosphoric irons was revealed from potentiodynamic polarization experiments. The pitting potentials and pitting nucleation resistances for phosphoric irons and CS were higher than that for TN. Electrochemical impedance spectroscopy (EIS) studies revealed thickening and growth of passive film as a function of time in case of phosphoric irons and CS in saturated Ca(OH)2 pore solutions without chloride and in the same solution with 0.05% Cl− and 0.1% Cl−. In case of TN, breakdown of passive film resulted in active corrosion in simulated pore solution containing 0.1% Cl−. Linear polarization resistance measurements complemented EIS results. Visual observations indicated that phosphoric iron P3 was immune to corrosion even after 125 days of immersion in saturated Ca(OH)2 solution containing 5% NaCl. The good corrosion resistance of phosphoric irons in simulated concrete pore solution containing chloride ions has been related to the formation of phosphate, based on ultraviolet spectrophotometric analysis and Pourbaix diagram of phosphorus–water system.