Materials Science Forum Vol. 1066

Abstract: We perform the density functional theory calculations (DFT) to study the effect of biaxial strain on the band structures of monolayer GaN. We apply compressive and tensile strains up to 10%. There is no change of bandgap for the applied tensile strains below 8%. The compressive strains have a constant bandgap which is slightly smaller than that of the zero strain. We find that the applied tensile strain above 8% affects its electronic structure and decreases its bandgap energy by about 0.05 eV while the compressive strain above 4% decreases its bandgap about 0.22 eV.

Abstract: Bi₂O₂X (X = S, Se, and Te) group materials are widely studied compounds by replacing X atoms with group VI transition metals (chalcogens). We have systematically studied the electronic properties of the ternary compounds using the first-principle calculation density functional theory (DFT). We found that the Bi-p orbital dominantly characterized the conduction band minimum (CBM) located around the Gamma point, while the valence band maximum (VBM) located around the X point is mainly originated from the contribution of the chalcogen X-p orbitals. Focusing on the CBM at the Gamma point, we observed a fourfold-degenerate state at each band. Turning the SOC split these bands become double degenerate, except the Gamma point due to time reversibility. Further investigation of the spin component confirms that the double degenerate bands of Bi₂O₂X at the CBM around the Gamma point indicates the existence of the hidden spin polarization, which is a promising candidate for spintronics applications.

Abstract: Concrete is characterized by its resistance to compressive forces; however, this material has a low resistance to tensile forces. Due to its resistance to tensile forces, we add steel reinforcements in order to increase the mechanical properties of concrete. In this work we simulated a direct traction test using the Abaqus software. The tensile test characterizes the elasticity of a material and measures its resistance to tensile forces, the tests were carried out on cylindrical specimens complying with the standards. We modeled this test because of the difficulty of carrying out the experiments due to the appearance of stress concentrations during tightening the specimen with the two fasteners of the traction machine. The aim of this simulation is to compare the resistance to the tensile strengths applied on a concrete test piece and a second reinforced concrete test piece. The study revealed that the reinforced concrete structure is more resistant than the concrete structure alone, and that concrete deformations are more significant than reinforced concrete deformations. Thus, the stresses generated in the concrete structure exceed those of the reinforced concrete.

Abstract: Studies have shown the effect of ultra-low doses of surfactants on the compressive strength of cement stone and fine-grained concrete, which harden under conditions of heat-wet treatment, due to lack of research and widespread use of such treatment in concrete technology. It is proved that in this case the effect of ultra-low doses of surfactants is to reduce the number of open pores in cement stone and concrete. Experimental studies have confirmed that the molecules of surfactants, such as sodium oleate, polyhydric alcohol or others, significantly changes the hydrogen content of water used for the manufacture of concrete. This increases the mechanical strength of cement stone and concrete. It is determined that the increase in temperature and humidity of the medium in which the concrete hardens leads to an increase in the effectiveness of ultra-low doses of surfactants on the formation of compressive strength

Abstract: Reducing the toxicity of plywood encourages the use of dry powder mixtures of polyester resin, as its dissolution in organic matter reduces environmental safety. The paper presents the results of studies of free surface energy and its components (polar and dispersed) for plywood, which is made on the basis of polyester resin. The sequences of polarity change and their ratio to the main component of wood after the formation of plywood board at high temperature, which are consistent with the structural and functional features of thermally modified wood. The resulting plywood is characterized by a reduced property of water absorption, because the free surface energy is reduced by 2.3 times and the polarity by 2 times, which is due to the thermal modification of the veneer. Thus, when applying a comprehensive approach to the study of wettability, polarity, interfacial tension, you can choose stable technologies for new wood products and expand its scope.

Abstract: Research on improving petroleum bitumen complex properties by modifying them with polymeric elastomers in the form of rubber waste are given in this article. The purpose of the research is to create a bituminous-rubber composition with an increased set of thermo-physical and physical-mechanical characteristics. The effect of bitumen modification with waste rubber crumb and powder in combination with the addition of taurite on the melting temperature, the degree of crosslinking, toughness and heat resistance of the compositions was studied. The optimal composition of bituminous-rubber compositions modified with taurite with high thermo-physical and physical-mechanical characteristics has been determined.

Abstract: Consideration was given to the issues relating to safety conditions and security arrangements during the thermal decomposition of wood at the time of the fire in the premises of domestic buildings. The data of experimental investigations obtained for the thermal decomposition of wood were given with the measurement data of the concentration of toxic gases (СО, СО₂), oxygen (О₂), and temperature depending on time and fire spreading conditions in the premises. The studies were carried out by comparing the changes in the temperature of the solid flammable materials with time and the emission intensity of toxic gas (СО, СО₂) under the limited oxygen access at the time of the fire. The research data confirm those obtained for the gaseous atmosphere composition in the premises during the thermal decomposition of the solid flammable materials.

Abstract: This article presents the results of determining the fire-retardant efficiency of heat-insulating granular plate based on geocement to protect metal structures from fire. According to the results of fire tests, it they found that with a plate thickness of 40 mm, the metal surface of an I-beam they heated to a critical temperature of 500 °C after 100 minutes of fire tests. This indicator provides the fire resistance class of metal structures P90 and the III group of fire retardant efficiency of metal structures. Based on the calculated data according to Eurocode 3, it they found that the critical heating temperature of an I-beam up to 538 °C with a plate thickness of 40 mm they achieved after 105 minutes of fire tests. This provides the fire resistance class of the steel column P90 and the III group of fire retardant efficiency. In order to ensure the fire resistance class P120, in the future, it is necessary to increase the thickness of the heat-insulating granular plate to 50 mm, which will allow transferring metal structures to the II group of fire retardant efficiency.

Abstract: Methods for determining the actual limit of fire resistance of reinforced concrete building structures in case of fire are analyzed. On the basis of the offered methods the technique which gives the chance to receive data of temperature distributions on a surface of a fragment of a wall and in its section is created. The method of conducting a fire test to calculate the limit of fire resistance of a small fragment of the load-bearing wall and verify the reproducibility of experimental data is described. The distribution of temperatures over the entire area of the fire furnace, the studied fragment was checked and the obtained results were analyzed. According to the results of this work, the following was established: the aim of the work was to obtain the results of temperature distributions on the surface, in the points of integration in the cross sections of fragments of reinforced concrete walls for further calculation of their fire resistance limit and check reproducibility of experimental data. It is established that the temperature obtained as a result of the fire test corresponds to the standard temperature of the fire and this method of fire test to determine the temperature distributions of a small fragment of the load-bearing wall in fire conditions is acceptable for use. The error between the experimentally determined and theoretically calculated limit of fire resistance is not more than 3%.

Abstract: The existing means for calculating the fire resistance of steel reinforced concrete horizontal structures beyond the fire resistance limit for more than two hours have been studied. There were conducted the computational experiments on the analysis of thermal load in case of fire for up to 3 hours, without taking into account the mechanical load on steel reinforced concrete slabs, modeled using steel sheets. The indicators obtained as a result of thermal computational experiments provide an opportunity to analyze the temperature distribution in the thickness of steel reinforced concrete horizontal structures made with a steel sheet. The relevant results can be used to determine the indicators of fire resistance of these structures for at least 3 hours. Thus, the thermal dependences, studied in this work, are a scientific basis for improving the capabilities of existing methods for determining the fire resistance of steel reinforced concrete horizontal structures with a steel sheet. The process of determining the temperature distribution indicators in these structures was performed using the standard method for solving the equations of thermal conductivity using the finite element method. Based on the results of solving the thermal problem, the graphs of thermal dependences were constructed, providing an opportunity to further analyze the indicators of fire resistance on the basis of the onset of signs of loss of load-bearing and insulating capacity. In order to perform computational experiments, the necessary calculation models were built that take into account the thermal effect on the studied structures under the standard temperature mode of fire.