The Effect of Addition Potassium Permanganate on Bond Strength of Hot-Dip Galvanized Plain Bars with Cement Paste

In this paper, the effect of gradually increasing amounts of KMnO₄ (10^-4, 10^-3, 10^-2 mol·L^-1) in cement paste on the bond strength of a plain hot-dip galvanized steel bar was evaluated. The open-circuit potential of HDG samples in cement paste with various additions of MnO₄^- was monitored in order to follow a transfer of zinc from activity to passivity. Furthermore, the influence of the addition of these anions on the physicochemical properties of normal-strength concrete or cement paste was evaluated by means of hydration heat measurements, X-ray diffraction analysis, and compressive strength. The effective concentration of MnO₄^- anions prevents the corrosion of the coating with hydrogen evolution and ensures that the bond strength is not reduced by their action, which was determined to be 10^-3 mol·L^-1. Lower additions of MnO₄^- anions (10^-4 mol·L^-1) are ineffective in this respect. On the other hand, higher additions of MnO₄^- anions (10^-2 mol·L^-1), although they ensure the corrosion of the coating in fresh concrete without hydrogen evolution, but affect the hydration process of the cement paste that was demonstrated by slight water separation.

The Influence of Graded Amount of Potassium Permanganate on Corrosion of Hot-Dip Galvanized Steel in Simulated Concrete Pore Solutions

This paper evaluates the amount of KMnO₄ in simulated concrete pore solution (pH 12.8) on the corrosion behaviour of hot-dip galvanized steel (HDG). In the range of used MnO₄^- (10^-4, 10^-3, 10^-2 mol·L^-1), corrosion behaviour is examined with regard to hydrogen evolution and composition (protective barrier properties) of forming corrosion products. The corrosion behaviour of HDG samples is evaluated using R_p/E_corr and EIS. The composition of corrosion products is evaluated using SEM, XRD, XPS and AAS. The effective MnO₄^- ion concentration to prevent the corrosion of coating with hydrogen evolution is 10^-3 mol·L^-1; lower concentrations only prolong the time to passivation (corrosion with hydrogen evolution). The highest used MnO₄^- concentration ensures corrosion behaviour without hydrogen evolution but also leads to the formation of less-protective amorphous corrosion products rich in Mn^II/Mn^III phases.

Kinetics of Zinc Corrosion in Concrete as a Function of Water and Oxygen Availability

This paper studies the effect of water as an oxidation agent and also of oxygen on zinc corrosion kinetics in active state in concrete, using high-sensitivity electrical resistance sensors. It was proven that zinc corrosion in active state is strongly affected by the presence of water at its surface. Zinc corrosion in real concrete in the absence of water can be misinterpreted as salt passivity. The presence of oxygen results in an increase of zinc corrosion rate, however at pH 12.6, passivity can occur. It was verified that corrosion products consisting primarily of Ca[Zn(OH)₃]₂·2H₂O cannot effectively passivate zinc surface in concrete, even after 1800 h of exposure and zinc, or hot-dip galvanized steel can corrode at an unacceptable corrosion rate (more than 4 µm·a⁻¹).