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Corrosion Mechanism and Bond-Strength Study on Galvanized Steel in Concrete Environment
( M. Kouril ),( P. Pokorny ),( J. Stoulil ) 한국부식방식학회 2017 Corrosion Science and Technology Vol.16 No.2
Zinc coating on carbon steels give the higher corrosion resistance in chloride containing environments and in carbonated concrete. However, hydrogen evolution accompanies the corrosion of zinc in the initial activity in fresh concrete, which can lead to the formation of a porous structure at the reinforcement -concrete interface, which can potentially reduce the bond-strength of the reinforcement with concrete. The present study examines the mechanism of the corrosion of hot-dip galvanized steel in detail, as in the model pore solutions and real concrete. Calcium ion plays an important role in the corrosion mechanism, as it prevents the formation of passive layers on zinc at an elevated alkalinity. The corrosion rate of galvanized steel decreases in accordance with the exposure time; however, the reason for this is not the zinc transition into passivity, but the consumption of the less corrosion-resistant phases of hot-dip galvanizing in the concrete environment. The results on the electrochemical tests have been confirmed by the bond-strength test for the reinforcement of concrete and by evaluating the porosity of the cement adjacent to the reinforcement.
Cold-cap reactions in vitrification of nuclear waste glass: Experiments and modeling
Chun, J.,Pierce, D.A.,Pokorny, R.,Hrma, P. Elsevier 2013 Thermochimica acta Vol.559 No.-
Cold-cap reactions are multiple overlapping reactions that occur in the waste-glass melter during the vitrification process when the melter feed is being converted to molten glass. In this study, we used simultaneous differential scanning calorimetry-thermogravimetry (DSC-TGA) to investigate cold-cap reactions in a high-alumina high-level waste melter feed. To separate the reaction heat from both the heat associated with the heat capacity of the feed and experimental artifacts, we employed the run/rerun method, which enabled us to define the degree of conversion based on the reaction heat and to estimate the heat capacity of the reacting feed. Assuming that the reactions are nearly independent and can be approximated by an nth order kinetic model, we obtained the kinetic parameters using the Kissinger method combined with least squares analysis. The resulting mathematical simulation of the cold-cap reactions provides a key element for the development of an advanced cold-cap model.