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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 Rp/Ecorr 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 MnII/MnIII phases.

Presented paper studies corrosion kinetics of zinc dust in cement paste using acoustic emission and impedance spectroscopy (measurement of electric resistance of compact samples) method. The focus is on determination of hydrogen evolution period and its effect on porous structure of cement paste. Results more or less confirm results of other authors that the corrosion products of zinc are unable to efficiently fill the pores forming due to hydrogen. Time period of hydrogen evolution - cathodic corrosion reaction of zinc in alkaline environment of cement paste can be up to several days long. Keywords: hot-dip galvanized reinforcement, corrosion of zinc dust, acoustic emission method, hydrogen evolution, porosity of cement paste, electrochemical impedance spectroscopy

The paper verifies anti-corrosion barrier protective properties of PE/PAK (polyethylene/polyacrylate), PE/PPE (polyethylene/polyproplylene) and PAD (polyamide) coatings of specific thickness on the surface of conventional ribbed bar B500B. Using pull-out test, the bond strength of such system was compared with bond strength of normal strength concrete (C30/37). Results of these tests show that key properties of coated systems are comparable to the previously tested epoxy coatings in case of their use in technical practice (protection of conventional rebar). In conclusion, their effective protective effect corresponds to minimal thickness higher than 300 μm but simultaneously lower the bond strength between the ribbed rebar and concrete. Keywords: corrosion of steel in concrete, organic coatings, bond strength, pull-out test, porosity

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.