Threshold Chloride Concentrations and Passivity Breakdown of Rebar Steel in Real Concrete Solution at Different pH Conditions with the Addition of Glycerol

Abstract

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.

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

“…A three-electrode electrochemical cell as described in an earlier work [16] was used in all experiments. This cell consisted of the rebar working electrode described above (surface area of 0.636 cm 2 ), an Ag/AgCl leak-free reference electrode, and a platinum foil counter electrode.…”

“…The perturbations in linear current decay can be attributed to the instability of iron's passive film at pH 9 compared to pH 12.5. Blair et al [16] attributed this to the buildup of cation vacancies in the passive layer, resulting in an unstable film that frequently partially dissolved and then rapidly reformed resulting in current fluctuations. EIS data from Nyquist plots in Figure 9(b), and EEC modelling in Table 4 shows an order of magnitude increase for solution resistance corresponding to the pH reduction from 12.5 to 9.…”

Tribocorrosion Behavior of 304 Stainless Steel in 0.5 mol/L Sulfuric Acid

“…The electrochemical behavior of stainless steels was studied widely, which is strongly related to chemical compositions and microstructures of stainless steels and corrosive media [27,28]. [29,30]. Hu et al [31] studied the effect of solution pH on electrochemical behavior of an ultra-high-strength steel in acidic environments.…”

Pre-treatments in silicate solutions to mitigate reinforcing steel corrosion in chloride-contaminated environments

“…Reinforcement corrosion is known to affect concrete structures, particularly when they are located close to the sea [1][2][3]. Chloride ions in the air can reach these structures and migrate through the pores in concrete [4][5][6][7][8]. When they approach the metal, the stability of the passive layer that protects the steel rebars can be compromised and localised corrosion may initiate.…”