Passivation behavior of V microalloyed steel rebar in simulated carbonated concrete environment

Electrochemical tests (CV, PDP, M-S, EIS, I-T) and surface characterization techniques (SEM, AFM, TEM, XPS) were used to investigate the passivation behavior of V microalloyed steel rebar soaked for 10 d in simulated carbonated concrete environment. The results show that the experimental steel rebars can all form passive film with n-type semiconductor performance in SCP solutions with different carbonation degrees. With the progression of carbonation, the passivation reaction of carbon steel rebar slows down, and the passive film is compromised due to carbonation. This leads to a reduction in the thickness of the passivation film on carbon steel rebar to 1.6 nm and a decrease in E_corr to −0.257 V. Conversely, under the influence of carbonation, vanadium in microalloyed steel rebar participates in the formation of passive film and gradually accumulates in its inner layer in the form of oxides. The formation of these V oxides inhibits Fe dissolution and enhances the passivation reaction rate, leading to an increase in the corrosion potential of the passive film to −0.116 V and a film thickness of up to 3.1 nm. Furthermore, V oxides can bind to oxygen vacancies, thereby rendering the passive film of steel rebar more compact.