Yazar "Stel'makh, Sergey A." seçeneğine göre listele

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    Analytical Review of Geopolymer Concrete: Retrospective and Current Issues
    (Mdpi, 2023) Meskhi, Besarion; Beskopylny, Alexey N.; Stel'makh, Sergey A.; Shcherban, Evgenii M.; Mailyan, Levon R.; Shilov, Alexandr A.; El'shaeva, Diana
    The concept of sustainable development provides for the search for environmentally friendly alternatives to traditional materials and technologies that would reduce the amount of CO2 emissions into the atmosphere, do not pollute the environment, and reduce energy costs and the cost of production processes. These technologies include the production of geopolymer concretes. The purpose of the study was a detailed in-depth analytical review of studies of the processes of structure formation and properties of geopolymer concretes in retrospect and the current state of the issue. Geopolymer concrete is a suitable, environmentally friendly and sustainable alternative to concrete based on ordinary Portland cement (OPC) with higher strength and deformation properties due to its more stable and denser aluminosilicate spatial microstructure. The properties and durability of geopolymer concretes depend on the composition of the mixture and the proportions of its components. A review of the mechanisms of structure formation, the main directions for the selection of compositions and processes of polymerization of geopolymer concretes has been made. The technologies of combined selection of the composition of geopolymer concrete, production of nanomodified geopolymer concrete, 3D printing of building structures from geopolymer concrete, and monitoring the state of structures using self-sensitive geopolymer concrete are considered. Geopolymer concrete with the optimal ratio of activator and binder has the best properties. Geopolymer concretes with partial replacement of OPC with aluminosilicate binder have a denser and more compact microstructure due to the formation of a large amount of calcium silicate hydrate, which provides improved strength, durability, less shrinkage, porosity and water absorption. An assessment of the potential reduction in greenhouse gas emissions from the production of geopolymer concrete compared to the production of OPC has been made. The potential of using geopolymer concretes in construction practice is assessed in detail.
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    Composition Component Influence on Concrete Properties with the Additive of Rubber Tree Seed Shells
    (Mdpi, 2022) Beskopylny, Alexey N.; Shcherban, Evgenii M.; Stel'makh, Sergey A.; Meskhi, Besarion; Shilov, Alexandr A.; Varavka, Valery; Evtushenko, Alexandr
    The growth in the volume of modern construction and the manufacture of reinforced concrete structures (RCSs) presents the goal of reducing the cost of building materials without compromising structures and opens questions about the use of environmentally friendly natural raw materials as a local or full replacement of traditional mineral components. This can also solve the actual problem of disposal of unclaimed agricultural waste, the features of which may be of interest to the construction industry. This research aimed to analyze the influence of preparation factors on concrete features with partial substitution of coarse aggregate (CA) with rubber tree (RT) seed shells and to determine the optimal composition that can make it possible to attain concrete with improved strength features. CA was replaced by volume with RT seed shells in an amount from 2% to 16% in 2% increments. Scanning electronic microscopy was employed to investigate the structure of the obtained concrete examples. The maximum increase in strength features was observed when replacing coarse filler with 4% RT seed shell by volume and amounted to, for compressive and axial compressive strength (CS) and tensile and axial tensile strength (TS) in twisting, 6% and 8%, respectively. The decrease in strain features under axial compression and under axial tension was 6% and 5%, respectively. The modulus of elasticity increased to 7%. The microstructure of hardened concrete samples with partial replacement of CA with RT seed shells in the amount of 2%, 4% and 6% was the densest with the least amount of pores and microcracks in comparison with the structure of the sample of the control composition, as well as samples with the replacement of CA with RT seed shells in an amount of more than 6%. The expedient effective replacement of CA with RT shells led to a reduction in battered stone of up to 8%.
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    Flexural behavior of reinforced concrete beams using waste marble powder towards application of sustainable concrete
    (Frontiers Media Sa, 2022) Karalar, Memduh; Ozkilic, Yasin Onuralp; Aksoylu, Ceyhun; Sabri, Mohanad Muayad Sabri; Beskopylny, Alexey N.; Stel'makh, Sergey A.; Shcherban, Evgenii M.
    The performance of waste marble powder as a partial replacement for cement is examined with the aim to achieve more sustainable concrete. Pursuant to this goal, a total of 15 specimens were manufactured and then tested to examine the bending behavior. The effects of longitudinal reinforcement ratio and waste marble powder ratio were selected as variables. The experimental results showed that different proportions of tension reinforcement and waste marble powder had different crack and bending impacts on reinforced concrete beams. As the waste marble powder amount in the concrete mixture is increased from 0% to 40%, it was detected that the crack type changes from a shear crack from to a flexural crack as the amount of waste marble powder increases in the mixing ratio. The experimental findings revealed that the waste marble powder can be successfully used as 10% of the partial replacement of cement. Increasing the waste marble powder ratio by more than 10% can significantly decrease the capacity of the beams, especially when longitudinal reinforcement ratio is high. The influence of waste marble as partial replacement on the capacity decreases as the longitudinal reinforcement ratio decreases. Therefore, 10%-20% marble waste can be utilized as a replacement for cement when the longitudinal reinforcement ratio is close to the balanced ratio and more than 20% waste marble ratio should be avoided for any cases.
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    Modeling and Calculation of Improved Centrifuged Reinforced Concrete Columns with Variotropic Structure
    (Mdpi, 2023) Stel'makh, Sergey A.; Shcherban', Evgenii M.; Beskopylny, Alexey N.; Mailyan, Levon R.; Veremeenko, Andrey; Shilov, Aleksandr V.; Ananova, Oxana
    The use of vibro-centrifugation technology allows the manufacture of variotropic structures that are inhomogeneous in the annular section and have different characteristics along the section thickness. Hardening of the outer layers allows the structure to better resist bending conditions, however, the behavior of the variotropic column under central and eccentric compression remains unexplored. This article considers the problem of compression of hollow columns made of homogeneous concrete that is non-uniform in the annular section (variotropic), and is reinforced with steel reinforcing bars at different values of the load application eccentricity. Variotropic concrete obtained by vibro-centrifugation technology has a stronger outer part and a less durable inner part. The strength of a homogeneous column corresponds to the strength of the middle part of variotropic concrete. The problem was solved numerically in the ANSYS environment for a vertical column rigidly clamped at the bottom edge and loaded with eccentricity at the top edge. Three types of eccentricity are considered; e/r = 0, 0.16 and 0.32 (respectively 0 mm, 0.24 mm and 48 mm). The results of the solution in the form of stress fields, deformations and a pattern of crack development in a spatial setting are obtained. The results showed that for central compression, a homogeneous column has a better bearing capacity of 3.6% than a variotropic one. With the values of eccentricity e/r = 0.16 and 0.32, the variotropic column has a higher bearing capacity (by 5.5% and 6.2%) than the homogeneous one and better resists the development of cracks. The significance of the study lies in the practical application of the proposed approach, developed on a research basis, for non-trivial and complicated operating conditions of columns. This study influences the development of reinforced concrete structures and applies scientific findings to engineering practice.
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    Normal-Weight Concrete with Improved Stress-Strain Characteristics Reinforced with Dispersed Coconut Fibers
    (Mdpi, 2022) Shcherban', Evgenii M.; Stel'makh, Sergey A.; Beskopylny, Alexey N.; Mailyan, Levon R.; Meskhi, Besarion; Shilov, Alexandr A.; Chernil'nik, Andrei
    According to the sustainable development concept, it is necessary to solve the issue of replacing fiber from synthetic materials with natural, environmentally friendly, and cheap-to-manufacture renewable resources and agricultural waste. Concrete is the primary material for which fibers are intended. Therefore, the use of vegetable waste in concrete is an essential and urgent task. Coconut fiber has attracted attention in this matter, which is a by-product of the processing of coconuts and makes it relevant. This work aims to investigate the experimental base for the strength properties of dispersed fiber-reinforced concrete with coconut fibers, as well as the influence of the fiber percentage on the mechanical, physical, and deformation characteristics. The samples were made of concrete with a compressive strength at 28 days from 40 to 50 MPa. The main mechanical characteristics such as strength in compression (cubic and prismatic) and tension (axial and bending), as well as the material's compressive and tensile strains, were investigated. The percentage of reinforcement with coconut fibers was taken in the range of 0% to 2.5% with an increment of 0.25 wt.%. Tests were carried out 28 days after the manufacture. The microstructure of the resulting compositions was investigating using the electron microscopy method. The most rational percentage of coconut fibers was obtained at 1.75%. The increase in mechanical indicators was 24% and 26% for compression and axial compression, respectively, and 42% and 43% for tensile bending and axial tension, respectively. The ultimate strains in compression were raised by 46% and in tension by 51%. The elastic modulus was increased by 16%.
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    Physical, Mechanical and Structural Characteristics of Sulfur Concrete with Bitumen Modified Sulfur and Fly Ash
    (Mdpi, 2023) Stel'makh, Sergey A.; Shcherban', Evgenii M.; Beskopylny, Alexey N.; Mailyan, Levon R.; Meskhi, Besarion; Shilov, Alexandr A.; Evtushenko, Alexandr
    Industrial waste usage in the technology of construction materials is currently in a relevant and promising direction. Materials made of industrial waste have a lower cost and are highly environmentally friendly. The objective of this study is to develop effective compositions of sulfur concrete based on the maximum possible number of various wastes of the local industry for this and to investigate the characteristics of this composite. Test samples of sulfur concrete were made from sulfur, fly ash, mineral aggregates and bitumen additive. The dosages of fly ash, sand and bitumen varied, while the content of sulfur and crushed stone remained constant. The following main characteristics of sulfur concrete were determined: density; compressive strength; and water absorption. Tests of sulfur concrete were carried out after 1 day and 28 days of hardening. The best values of compressive strength (24.8 MPa) and water absorption (0.9%) were recorded for the composition of sulfur concrete at the age of 28 days with the following content of components: sulfur-25%, modified with 4% bitumen of its mass; fly ash-10%; crushed stone-40%; and sand-25%. The optimal composition of modified sulfur concrete showed compressive strength up to 78% more and water absorption up to 53% less than the control composition. The characteristics of the sulfur concrete samples after 28 days of hardening differ slightly from the values after 1 day of hardening (up to 1.8%). An analysis of the structure confirmed the effectiveness of the developed composition of sulfur concrete in comparison with the control.
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    Shear and Bending Performances of Reinforced Concrete Beams with Different Sizes of Circular Openings
    (Mdpi, 2023) Ozkilic, Yasin Onuralp; Aksoylu, Ceyhun; Hakeem, Ibrahim Y.; Ozdoner, Nebi; Kalkan, Ilker; Karalar, Memduh; Stel'makh, Sergey A.
    The present study pertains to the effects of transverse opening diameters and shear reinforcement ratios on the shear and flexural behavior of RC beams with two web openings across different spans, i.e., a single opening in each half-span. Within the scope of the study, a total of 12 RC beams with five different opening diameter-to-beam depth ratios (0, 0.20, 0.27, 0.33, 0.40, and 0.47) and two shear reinforcement ratios were tested to failure under four-point bending. The load capacities, ductilities, rigidities and energy dissipation capacities in the elastic and plastic ranges of beam behavior were compared. Furthermore, the load capacities of the beams were compared to the existing analytical shear strength formulations in the literature. The test results indicated that whether an RC beam with openings has adequate or inadequate amounts of shear reinforcement, the frame-type shear failure becomes much more pronounced with increasing opening diameter. The reductions in the load capacity and modulus of toughness with increasing opening diameter are more considerable in the presence of inadequate amounts of shear reinforcement, while the beam ductility is less affected in shear-deficient RC beams with openings as compared to the ones with adequate shear reinforcement.
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    Shear performance of reinforced expansive concrete beams utilizing aluminium waste
    (Elsevier, 2023) Ozkilic, Yasin Onuralp; Karalar, Memduh; Aksoylu, Ceyhun; Beskopylny, Alexey N.; Stel'makh, Sergey A.; Shcherban, Evgenii M.; Qaidi, Shaker
    Shear damage is a catastrophic failure in the design of reinforced concrete structural ele-ments. To prevent it, the effect of aluminum wastes on reinforced concrete shear beams was investigated in this study. There is a gap in the scientific field on the expanding concrete with aluminium waste, and no research has been done on the utilizing of aluminum waste to produce expandable concrete. Moreover, there is a gap in expandable concrete usage with aluminum waste reinforcing, which is crucial for engineering applications especially beams, slabs and columns. For this purpose, experimental investigations were performed on a total of 12 Reinforced Concrete Beams (RCB) with different aluminum waste ratio (0, 1, 2 and 3 vol.%) and different shear reinforcement spacing (270, 200 and 160 mm). The depth span ratio was chosen as 1.6, 2.0 and 2.7. RCB was simply supported on the loading frame and subjected to four-points bending. As a result of experimental tests for each sample, the maximum load, stiffness, ductility and energy dissipation capacity were calculated. It was observed that the load capacity of the Al refuse combined RCBs raises as the vacancy of the stirrup rein -forcement reductions compared with reference RCBs. Furthermore, it was found that the load capacity of the RCBs reduced as the Al refuse quantity in the concrete mixture was increased from 0% to 3%. However, it was found that the decrease in load capacity for 1 vol.% aluminum waste could be tolerated. For this reason, it can be stated that aluminum waste (AW) in reinforced concrete shear beams will contribute to the beam up to 1%.& COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).