Threshold Chloride Concentrations and Passivity Breakdown of Rebar Steel in Real Concrete Solution at Different pH Conditions with the Addition of Glycerol
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Addition of glycerol as a viscosity modifier in concrete is proposed to decrease the permeability of corrosion-inducing 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 × 10−3 mol/L in the absence of glycerol addition. The threshold increased to 81 × 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 × 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 × 1020 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.
KeywordsCorrosion Passive film Electrochemical impedance spectroscopy (EIS)
This research was supported by the US Department of Energy under the NEUP PROGRAM, Contract No. DE-NE0000659-003.
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