CORROSION RESISTANCES OF PASSIVE FILMS ON LOW-CARBON REBAR AND FINE-GRAINED REBAR IN ALKALINE MEDIA

The passive ranges of low-carbon rebar and fine grained rebar in simulated concrete pore solution with pH13.0 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy and Mott-Schottky curves were employed to compare the passive films formed at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of passive films formed on the two rebars in alkaline media with or without Cl-. The results show that the passive ranges of the two rebars are all between -0.25 and +0.6 V, and the more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl-, the stability and corrosion resistance of the passive film formed on the fine-grained rebar are better than those of low-carbon rebar. However, the pitting corrosion resistance of the former is somehow lower than that of the latter in the presence of Cl-. The amounts of grain boundary and trace elements are responsible for the lower corrosion resistance of fine-grained rebar.