Addition of glycerol as a viscosity modifier in concrete is proposed to decrease the permeability of corrosioninducing ions such as chloride and sulfate. In addition to controlling the permeability of concrete, glycerol could perform as an inhibitor of corrosion of rebar steel. Cyclic polarization studies were carried out on metallographically polished rebar steel specimens in actual concrete solutions at two different pH conditions (pH 12.5 and 9.0) and different chloride concentrations. The threshold concentration of chloride for passivity breakdown at pH 12.5 was greater than 50 9 10 -3 mol/L in the absence of glycerol addition. The threshold increased to 81 9 10 -3 mol/L upon addition of 2 wt% glycerol. The threshold chloride concentration for passivity breakdown in pH 9.0 cement solution was 0.2 9 10 -3 mol/L without glycerol addition. No beneficial effect of glycerol was observed in the low pH condition. However, glycerol enhanced the passivation kinetics of the rebar steel in saturated cement solution, but did not affect the electronic properties of the passive layer. The passive layers exhibited n-type semiconductivity with a charge carrier density in the range of 2-7.5 9 10 20 cm -3 . Polarization of the specimens to potentials is higher than oxygen evolution potential, resulted in transition top-type semiconducting character due to an accumulation of holes. This phenomenon could be related to the passivity breakdown.

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 CO 2 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.