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This research focuses on an evaluation of mineral phase and structure transformations in Class F fly ash-based geopolymer systems. The research also studies the strength response of geopolymers when exposed to temperatures between 25 and 800 °C. The purpose of this research is to understand the processes that occur in alkali-activated systems within a wide range of high-working temperatures. The XRD, SEM, and DTA/TG analyses performed for the alkali-activated compositions after exposure to different temperatures confirmed a direct correlation of structural transformations with strength performance. The detrimental effect of sodium hydrocarbonate Na3(HCO3)(CO3) 2H2O or trona contained in one of the fly ash products was observed for the corresponding alkali-activated composite under high-temperature exposure between 600 and 800 °C. It was also detected that a high-temperature interval of 400–800 °C created favorable conditions that helped to form nanosized nepheline crystals and an additional vitreous substance that also contributed to a denser alkali-activated matrix.

Normally, the component composition of building materials makes a significant contribution when formation of final performance properties of them. Moreover, new types of binding systems, in spite of their poor knowledge, this effect on the structural characteristics of final composites also takes place. In this work, perlite-based geopolymer binder as an example, was studied. In framework of the study, it was found that the application of grinding mill with a metal lining leads to the formation of Fe- milling yield, which is included into crushed raw materials (perlite) com-position. It was established that the particles of the resulting Fe- component are nanoscaled. The X-ray phase and chemical analyzes were used to determine the mechanism of the effect of the Fe- component on the properties of perlite-based geopolymer. Microstructure of the hardened geopolymer paste were studied using SEM microscopy. Phase and mineral composition of geopolymer paste obtained by XRD-analysis showed, when the hardening process, nanosized iron hydroxide or bernalite Fe(OH)3(H2O)0.25 is formed in the geopolymer system, that is 5 times more than metallic iron. This is initiates the structure destruction and confirmed by the low values compressive strength of the geopolymer stone. Keywords: Fe-bearing component, metallic milling yield, geopolymer binder, friable structure, the Scherrer formula

Among the main promising research areas in materials science and construction industry, where a significant amount of studies is concentrated in the world, it is, primarily, the materials those contain a secondary or low-demand raw materials, industrial wastes. As well as it can be composites synthesized using low-temperature and environmentally friendly technologies. In this study, the influence of high-temperature effects on the structural phase transformations in matrix of granite-based nanostructured binder (NB) was considered. As an analytical tool, confirming this assumption, X-ray phase (XRD) analysis and derivatographic (DTA) analysis, as well as a calculated estimate of the volume of the cells of the crystal lattices of the mineral phases were applied. It was established that thermal exposure in the temperature range from 20 to 900 ºС leads to mineral transformations (α–β transition of quartz) in granite-based NB, but the cell volumes changing of the crystal lattices was not found. Thermal exposure of granite-based NB at 1000 ºС initiates a new crystal phase formation – Leucite K[AlSi2O6], that is structurally identical to zeolite-type mineral such as Analcime Na[AlSi2O6]∙H2O. This phenomenon confirms a structural affinity of between granite-based NB and geopolymer.

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 properties. 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.

Current trends in the field of construction material is focused on enhancement of sustainability of building materials and constructions urging on development of new types of inorganic binders and composites in order to meet the modern requirements of service performance and special properties. This research studied and demonstrated the opportunity to develop zero-cement heat-resisting granite-based nanostructured binder (GNB) using «green» technology production. XRD and DTA analyses demonstrated that the thermal exposure of GNB to wide range of temperatures of 20–1000 °C leads to such phase transformations in the binder as α-quartz to β-quartz transformation; amorphous alkali-aluminosilicate (gel) to crystal phase of Са-albite. The calculation of cell volumes characteristics for low-temperature (before thermal exposure) and high-temperature (after thermal exposure) phases was performed using following equation: where is concentration (by wt. %) of mineral phases;Viis unit cell volume of mineral phases, Å. The calculated ratios of unit cell volumes were close to 1 which ensures a structural stability of the GNB under thermal exposure and confirms its heat-resistant performance.

Жерновский Игорь Владимирович, кандидат геолого-минералогических наук, профессор кафедры материаловедения и технологии материалов.

Fly ash based hybrid geopolymers (HGP) containing different type of mineral admixtures such as portland cement (PC), kaolin and metakaolin (MK) were developed in this study. The improved values of compressive strength, water absorption and water resistance for PC-modified hybrid geopolymers versus MK-modified HGP and reference mix was observed. High-temperature treatment (600 °C) enables to boost compressive strength by 177 % and 55 % as well as water resistance by 34 % and 40 % for MK-modified and kaolin modified HGP, respectively. At the same time, the PC-modified HGP demonstrated a very low thermal resistance, which was confirmed by a rapid drop of compressive strength and distracted structure of the specimen subjected to high temperature.