Corrosion studies of rebar in contact with saturated solution produced by leaching of Portland Type-II cement: examining the effects of chloride, carbonation and an amorphous silica additive

摘要

This study examined the effects of silica addition on electrochemical behavior of rebar in native pH 12.5 saturated solutions prepared by leaching of Portland Type-II cement, and in solutions reduced by CO2 to pH 9. Cyclic polarizations showed that at pH 12.5 the silica additive increased the threshold concentration required for pitting from 100 to 105mM, and from 0.3 mM to 0.5 mM at pH 9. Passivation kinetic exponents were consistently larger for solutions with either pH when silica was present. The silica additive provided the passive film with generally increased resistance and lower capacitance, as confirmed by electrochemical impedance spectroscopy. Charge carrier densities calculated from Mott-Schottky plots were on the order of 1020 (cm(-3)), increasing significantly after the passive film breakdown. Raman spectroscopy of rebar samples immersed in saturated cement solutions showed films predominantly composed of iron oxyhydroxides with a new shoulder attributed to amorphous silica.