Özet:

The paper reports results of examining the influence of modifier admixtures on the corrosion resistance of concrete for reinforced concrete sleepers based on the criteria of electric resistance, resistance to alkaline corrosion and corrosion due to the crystallization of delayed and secondary ettringite. This study was conducted within the framework of resolving the issue on premature destruction of reinforced-concrete sleepers caused by the progressing crack formation at the stage of heat treatment and subsequent operation. It has been established that the introduction of pozzolanic admixtures containing active Al2O3 in their formulation to the composition of concrete for sleepers makes it possible to minimize the risk of corrosion predetermined by the reaction between aggregates’ silica and alkali and corrosion as a result of crystallization of delayed and secondary ettringite. The high efficiency of pozzolanic admixtures containing active Al2O3 regarding the specified types of corrosion is due to binding alkali into the insoluble alkaline hydroalumosilicates, contributing to the compaction of the system with a decrease in the content of Na+/K+ ions in the solution. A decrease in the content of alkali in the porous solution predetermines blocking the «alkali-silica reaction» and increasing the temperature of ettringite stability to higher values. This reduces the potential number of secondary ettringite forming cycles and the probability of delayed ettringite formation. The alternative mechanism of action of active Al2O3 on pozzolan implies binding the SO42– and Ca2+ ions from a porous solution into low-sulfate forms of calcium hydro-sulfoaluminates, which excludes the crystallization of delayed and secondary ettringite.Reducing the consumption of cement and water through the use of admixtures-plasticizers makes it possible to increase the electrical resistivity of the modified concrete for sleepers above the level of a control composition without admixtures. The obtained results provide an opportunity to ensure the design durability of concrete in reinforced-concrete sleepers through their comprehensive modification by plasticizers and active mineral admixtures that contain active Al2O3 Author Biographies Vyacheslav Troyan, Kyiv National University of Construction and Architecture Povitroflotsky ave., 31, Kyiv, Ukraine, 03037 Doctor of Technical Sciences Department of Technology of Building Structures and Products

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