Passivation behavior of steel bar connectors in simulated pore solution with different pH values

The passivation behavior of steel bar connectors directly affects their corrosion resistance, thereby influencing the durability of engineering structures. This study investigates the passivation behavior and corrosion resistance of HRB400 rebars, ribbed rolling straight thread sleeves, sleeve connectors, and welded connectors in simulated pore solutions with pH values of 12.5, 13.0, and 13.5. The investigations employ electrochemical measurement methods including open-circuit potential, corrosion current density, and electrochemical impedance spectroscopy. The results show that the open circuit potential E_ocp of each specimen shifts positively with the increase of pH value of the solution. After 10 d of passivation, it increases from −130 mV, −220 mV, −135 mV and −27 mV to −90 mV, −180 mV, −100 mV and −11 mV, respectively. The corrosion current density I_corr decreased and the passivation ability increased. The time required to reach the passivation state is significantly shortened with the increase of pH value. The passivation time of steel bars, sleeve connectors and welded connectors is shortened from 7 d, 9 d and 10 d with pH value of 12.5 to 2 d, 4 d and 6 d with pH value of 13.5, respectively. The sleeve can be passivated in only 1 d in the three pH solutions. The four specimens form a stable passivation film under different pH values, and the passivation effect is positively correlated with the pH value. Combined with electrochemical impedance spectroscopy and equivalent circuit analysis, it was found that the charge transfer resistance R_ct of the four specimens reached 592000 Ω·cm², 931580 Ω·cm², 398130 Ω·cm², 205685 Ω·cm² after passivation in a solution with a pH of 13.5 for 10 d. The passivation effect of the sleeve was the best, and the integrity of the passivation film was the highest, showing the best corrosion resistance, followed by the steel bar, the sleeve connector, and the welded connector. The passivation film has the lowest integrity and the worst corrosion resistance.