Zhernovskaya I.V.

Senior Lecturer, Belgorod State Technological University named after V.G. Shukhov, Russia

EFFECT OF THE CURING CONDITIONS ON THE CHARACTERISTICS OF CITROGYPSUM-CONTAINING ALKALI-ACTIVATED BINDERS

https://doi.org/10.34031/2618-7183-2021-4-5-24-34
Abstract
When hardening the binder system and it transforms into a consolidated conglomerate, the efficiency of the formation of the structural framework and the main operational characteristics of the final product dramati-cally depend on the thermal and humidity conditions of the environment medium, where the binder or raw material is consolidated. In this study, various conditions of hardening of binders with alkaline activation of various compositions were studied. Based on the literature analysis, the following were chosen as the hardening conditions for the experimental alkali-activated systems: 1) - thermal drying, which was carried out in an oven at a temperature of 60°C for 24 hours; 2) hardening in ambient laboratory conditions, at a temperature of 23 ± 2°С, relative humidity - 33 ± 2%. An aqueous solution of alkali NaOH and salt Na2SiO3 were used as alkaline activators. The resulted data of the change in the average density showed that when using an alkaline activator, heat drying promotes the compaction of the hardened composite (typical for both types of the alkaline component) by 5 and 7 % for NaOH and Na2SiO3, respectively. The absence of alkaline activators in the experimental samples leads to decompaction of the structure after exposure to thermal drying and a decrease in the average density to 18%. The experimental results showed that thermal drying contributes to an increase in the strength parameters of experimental samples of an alkali-activated binder using Na2SiO3 to 110% (from 1.9 to 4 MPa). For the rest of the samples, a significant decrease in strength is observed (more than 2 times). A visual analysis of experimental samples of alkali-activated binders showed that the binders containing the addition of citrogypsum showed clear signs of efflorescence in the case of their hardening in ambient laboratory conditions. At the same time, for similar compositions from a series of samples hardened under thermal drying conditions, there is a complete absence of this phenomenon.
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THEORETICAL ASPECTS OF DEVELOPMENT OF COMPOSITE NANOSTRUCTURED GYPSUM BINDER CHARACTERIZED BY INCREASED HEAT RESISTANCE

https://doi.org/10.34031/2618-7183-2019-2-4-5-13
Abstract
There are a lot of different types of binders for construction purpose, a strong interest is focused on free-of-cement binders of new generation, which are characterized by unique and/or improved performance proper-ties. Among them there is composite nanostructured gypsum binder (CNGB) as a quite new binding system. In the framework of this study the hypothesis of synergetic effect in hardened binding system was proposed and approved. The hypothesis is realized when interaction of two binding systems with different structure formation mechanism such as followings: polymerization-polycondensation and hydration. A number of experiments were carried out and the results were obtained, which demonstrate a resistance of CNGB under high-temperature effect (up to 1000ºC) vs. ordinary gypsum binder. It was determined that a heat-resistance of CNGB is associated with joint crystallization of sulphate-based component (gypsum binder) and highly-reactive silica-based component (in nanostructured binder). Normally, nanostructuted binder is stable under high-temperature exposure. The indicator of synergetic effect is formation of new crystalline phase – hydroxyellestadite Ca5(SiO4)3(SO4)3(OH)2. This phase has unit cell size which is stable under temperature gradient. This characteristic allows saving structure framework in CNGB under high temperature.
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