Revealing excellent passivation performance of a novel Cr-alloyed steel rebar in carbonized concrete environment

In this paper, the passivation behavior and corrosion resistance of a novel Cr-alloyed steel rebar in carbonized concrete environments were systematically studied, and its passivation mechanism was also revealed in view of the intrinsic relationship between the concrete alkalinity and the microstructure characteristic of the passive film. The electrochemical test results show that the alloyed rebar has excellent passivation performance under all carbonization conditions. Meanwhile, its passivation performance shows a trend of first strengthening and then slightly decreasing with the gradual intensification of carbonization, presenting better passivation performance in the mildly carbonized concrete (pH = 11) than in the non-carbonization (pH = 12.6) situation. X-ray photoelectron spectroscopy and Mott–Schottky tests indicate that the alloyed steel rebar has formed an n-p type semiconductor structure composite passive film, which was composed of Cr and Fe oxides/hydroxides under all conditions. The high passivation performance of the alloyed rebar is dominated by the excellent corrosion resistance of Cr oxide/hydroxide, which does not depend on the concrete alkalinity. On the contrary, the high alkalinity will inhibit the formation of Cr oxide to some extent and weaken the passivation performance of the rebar.