Karel Hurtig

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.