Key Engineering Materials Vol. 887

Abstract: The article presents the physical-chemical bases and as result – the technological bases of concrete resistance to ultra-low cryogenic (up to-196 °C) technical (engineering) temperatures, which is applied to the reinforced concrete structures of engineering constructions such as storage tanks for liquefied gases (in particular, liquid nitrogen and oxygen with cryogenic temperatures), as well as the enclosing structures of blocks (units) for air separation for various inert gases. The above-mentioned physical and chemical bases of concrete resistance to the ultralow cryogenic technical temperatures are developed, using the results of the analysis of modern ideas (hypotheses and theories) about the mechanism of low negative temperatures exposure on structural lightweight aggregate concrete and normal weight concrete due to the characteristics of their macro-and microstructure. The resistance of structural lightweight aggregate concrete in comparison with equal-strength normal weight concrete to the cyclic exposure of cryogenic temperatures was performed by the authors based on the results of the relevant analytical and experimental investigations. The results of these investigations are considered in the article as a modern scientific basis for the development of the main provisions for the manufacturing technology of structural lightweight aggregate concrete and normal weight concrete with high durability (frost resistance and water resistance) in conditions of cyclic exposure to cryogenic temperatures. The results of changes in strength and deformative characteristics of concrete in the process of cyclic freezing and thawing are accepted as evaluation criteria of the resistance of concrete, manufactured using the above-mentioned technologies, to such temperature exposure.

Abstract: The object of study is a cement composite material with powdered utilized optical discs. The objective is to establish the dependences of the main strength characteristics – com-pressive strength, bending strength, and density – on the amount of waste added into the mix-ture and the water-cement ratio.The compositions of the mixtures for the production of the cement composite material samples consisted of the following components: cement, sand, powdered waste in the form of utilized optical discs and water.Based on the results of testing the samples, mathematical models have been developed which describe the dependences of the physical and mechanical properties of the cement com-posite material samples on the fraction of waste and water-cement ratio. It was found that with an increase in the amount of powdered waste added into the mixture, it reduces the compressive strength, bending strength, and density of the samples under study, however, the optimization of the water-cement ratio makes it possible to obtain equal strength compositions with a differ-ent fraction of waste.Component compositions of cement composite material mixtures with the addition of powdered utilized optical discs in the amount of 10 to 25 % of the total filler mass, which can provide construction products with a compressive strength class B20, are presented.

Abstract: An effective highly dispersed additive based on the wollastonite Miwoll 05-97 with an average particle diameter of 6.5 microns is obtained. A stable effect of interacting the additive components with Portland slag cement CEM II/A–Ш 42.5H is revealed; it results in improving the strength of fine-grained concrete produced with the raw materials mentioned above. It is established that using water suspension of wollastonite solid particles, highly water-reducing/superplasticizing modifier based on the polycarboxylate ether Master Glenium 430, as a stabilizer of the surface-active substance allows producing an additive with an evener distribution of solid particles in the liquid, and with stable functional properties. A highly dispersed wollastonite-based additive, obtained by ultrasonic dispersion for 10 minutes in the bath-type activator at the frequency of 35 kHz in the aquatic environment with a suspension stabilizer, enables producing the wollastonite-modified fine concrete with a compressive strength of more than 50 MPa, with the 10% additive being 2 times higher than that of the control.

Abstract: A natural gypsum binder or its analogs, which are the products of local raw materials recycling or by-products of other industries, is used as a basic component in the composition of interior plastering mixtures. Plaster coatings based on a gypsum binder have two main features. The first is the ability to control room humidity and absorb harmful emissions. The second is the ability to implement the barrier protection function in case of fire.Improvement of plastering works quality and optimization of their cost is related to the development of modified gypsum-based compositions, the justified use of waste, and local building materials, which include a clay-gypsum binder. Clay gypsum as a natural material of sedimentary origin is widespread both in Russia and in post-Soviet countries. In terms of energy intensity and manufacturability, raw materials recycling into clay-gypsum binder does not differ from the conditions of traditional processing of natural gypsum. Compared with lime or cement mortars, mortars based on clay-gypsum binders have greater elasticity and plasticity. Such properties as convenient masonry and thixotropy as well as the interval for maintaining the viability of the mixture are related to application technology and regulated by the insertion of modifying additives, which formulation was the aim of the research. The research results are presented in this article. Studies have shown that varying the recipe parameters allows us to control both the strength and operating characteristics of clay-based mixtures, as well as their application technology.

Abstract: This report outlines the results of an experimental study conducted on the effects high temperatures have on changes in linear sizes, mass, and density of steel fiber concrete containing fiber with varying durability, types, diameter, and percentages by volume. After being exposed to heat, the steel fiber concrete reduces in linear size, as well as decreasing in mass and density. Changes are seen as a result of rising temperatures between 20-1100 °С The impact on the change in mass, size and density of the quantity and type of fiber is not unambiguous, it does not fully correspond to the theoretical concepts considered in the work and require additional research.

Abstract: Influence of exometabolites of Bacillus cereus strain microorganism on cement mortar properties was studied. According to the strength criterion, the optimal dosages of the bioadditives and the order of its introduction into the solution are established. The description of the mechanism of formation of the effect of bio-cementation is given.

Abstract: Systems of floor insulation on the ground, isolation of roads and shallow foundations suggest the use of heat-insulating products resistant to moisture, the minerals contained in it, having low heat conductivity and water absorption and relatively high strength for compressive loads.The aim of the research was to study the possibility of using mineral substances containing crystalline water as a dispersed component. Firstly, such compounds as a reinforcing component increase the strength characteristics of products. Secondly, being flame retardants, they contribute to increasing the fire safety of materials and building systems in which these materials are used. To achieve this goal, two particular tasks were set: determination of the optimal consumption of mineral modifying additives; assessment of exploitative stability of the received products. It was found that the introduction of a mineral modifying additive can significantly increase the compressive strength by 10% deformation of samples from extruded polystyrene foam. The exploitative stability of products with a mineral additive varies slightly and depends on its consumption and uniform distribution in the product matrix. The effect of additive consumption on the change in the thermal conductivity of products has not been established. A nomogram has been built which allows one to evaluate the properties of products and determine the optimal consumption of a modifying additive.Systems of using products from modified extruded polystyrene foam in monolithic foundations with insulation for buildings erected on problem soils are considered.

Abstract: The research objective is studying the effect of tailing slurry of chromite ore beneficiation on the phase composition and frost resistance of ceramic bricks obtained based on low-melting clay. For the study, two compositions were taken, % wt.: 1) the optimal composition ─ low-melting clay of the Ilek deposit - 70, tailing slurry of chromite ore beneficiation, 2) the reference composition ─ low-melting clay of the Ilek deposit - 100. Raw materials were crushed to pass through a sieve No. 1.0 mm; then, the components were thoroughly mixed. The bricks were prepared by melting at a batch moisture content of 22 %. The mold bricks were dried to a residual moisture content of 5 % max. The dried bricks were fired at temperatures, ^оС: 950 (the glass phase emergence), and 1,050 (the final brick firing temperature). The increased content of iron oxide (Fe₂O₃=12.3 %) and alkali oxides (R₂O=3.2 %) in the tailing slurry of chromite ore beneficiation contributed to the liquid phase emergence at 950 ^оС. Colorless, yellowish, and brown glasses with refractive indices N within 1.50-1.54, forming as a result of melting of spars and mixed-layer clayey formations, were observed under the microscope in the studied prototypes of composition No. 1 at a firing temperature of 950 °C. In the composition No. 2, a liquid phase also emerges, but in smaller quantities. Adding tailing slurry of chromite ore beneficiation to ceramic masses contributes to the formation of anorthite and glass phase in prototypes based on low-melting clay at a firing temperature of 950 °C. An increase in the firing temperature to 1,050 °C increases the content of the glass phase and anorthite, which significantly improves the frost resistance of ceramic bricks.

Abstract: Presented here are the results of assessing the effect of elevated temperature on the strength characteristics of reinforced concrete structures during operation. Described here are the features of the technical inspection of structures subjected to temperature effects (after a fire). The strength class of reinforced concrete structures was determined before temperature exposure (in places that were not exposed to fire) and after in the course of the study. Presented are the results of measuring the strength of concrete by the direct method of pulling off with spalling, as well as the results of verification calculations of reinforced concrete structures exposed to temperature effects. When performing verification calculations, the percentage of reduction in the bearing capacity of structures was established. Based on the results of the study, the percentage ratio of the decrease in the strength of prefabricated reinforced concrete structures after a fire during the operation of the facility was established.

Abstract: Wood composites are promising construction and finishing materials that offer the best properties of both wood and polymers. With the industry's need to use low-toxic adhesives in view, one of the ways to ensure the environmental friendliness of composites is the use of polyvinyl alcohol as a binder. In this respect, in order to streamline production, both in terms of reducing energy consumption and improving the quality of the final product, it is vital to choose the drying rate when pressing panels. The paper presents the results of a study of the process of vacuum-conductive drying of eco-friendly polyvinyl alcohol (PVA)-based wood-particle material. It was found that the composite samples with a PVA content of 40% in terms of physical and mechanical parameters (ultimate bending strength and ultimate tensile strength perpendicular to the panel face) fully comply with the established standards. The study provided the values of drying rate depending on 5 factors. The multi-factor regression analysis method was used to derive equations that determine the drying rate of polyvinyl alcohol-based wood-particle panels for two humidity intervals (above and below the cell walls humidification limit), taking into account the properties of different classes of bodies that make up the composite.