Corrosion Behavior of Fe-P Alloys, Low-Carbon and Low-Alloy Steels in Simulated Concrete Pore Solution and Cement Grout

The corrosion behaviour of three Fe-P alloys, i.e., P1 (Fe–0.11P–0.028C), P2 (Fe–0.32P–0.026C) and P3 (Fe–0.49P–0.022C) has been evaluated in saturated Ca(OH)₂ solution containing different chloride concentration simulating simulated concrete pore solution in chloride environments. The results have been compared with that of two commercial concrete reinforcement steels, a low carbon steel LCS (Fe–0.148C–0.542Mn–0.128Si) and a low alloyed corrosion resistant steel LAS (Fe–0.151C–0.088P–0.197Si–0.713Mn–0.149Cr–0.417Cu). The beneficial aspect of Fe-P alloys was revealed from potentiodynamic polarization experiments. The pitting resistances of Fe-P alloys and LAS were higher than that of LCS. Electrochemical impedance spectroscopy (EIS) studies revealed thickening and growth of passive film as a function of time in case of Fe-P alloys and LAS in saturated Ca(OH)₂ pore solutions without chloride and in the same solution with 0.05% Cl^- and 0.1% Cl^-. On the other hand, active corrosion, due to breakdown of passive film, occurred in the case of LCS in simulated pore solution containing 0.1% Cl^-. 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.

In the other part of the work, the corrosion behavior of cement grouted Fe-P alloys, LCS and LAS was studied using the potentiostatic polarization technique in 5 % NaCl solution. The breakdown of passivity by chloride ions occurred much below 500 mV vs. saturated calomel electrode (SCE) in the case of the low-carbon steeL The passive film was resistant to chloride in the case of Fe-P alloys and the low alloyed steel.

The better corrosion resistance performance of phosphoric irons in simulated concrete pore solution and cement grout has been attributed to the presence of phosphate species in passive film, which repelled chloride ions due to its cation selectivity nature. The formation of phosphate species in simulated pore solution was confirmed from the ultraviolet spectrophotometric analysis and also follow Pourbaix diagram of phosphorus–water system.