Yazar "Mailyan, Levon R." 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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    Lightweight expanded-clay fiber concrete with improved characteristics reinforced with short natural fibers
    (Elsevier, 2023) Ozkilic, Yasin Onuralp; Beskopylny, Alexey N.; Stelmakh, Sergey A.; Shcherban, Evgenii M.; Mailyan, Levon R.; Meskhi, Besarion; Chernilnik, Andrei
    Weight reduction should be accompanied by maintaining the strength and quality of materials utilized in construction. One of the comprehensive solutions to this problem can be the utilization of dispersed fiber reinforcement of concrete with plant fibers of various origins, which led to the sustainable production of concrete. Knowledge regarding the behavior of lightweight concrete with plant fibers is currently rather limited. Therefore, the primary aim of this article was to study the possibility of creating lightweight expanded-clay fiber concrete (ECFC) with improved characteristics, considering the dispersed reinforcement of this concrete with coconut (CF) and sisal (SF) fibers. Test methods and scanning electron microscopy (SEM) analyses were used for the structural study. Dispersed reinforcement of lightweight expanded clay concrete with fibers of organic origin has a positive effect on its mechanical characteristics. The optimal content of expanded clay in lightweight concrete was obtained in terms of the ratio of strength and density. The content of CF and SF, which provides the highest increases in compressive and flexural strength, was 2% of the mass of cement. It was found that SF in lightweight ECFC performs better and provides greater strength gains than CF. The compressive strength of ECFC with CF increased by 8.9%, the bending strength by 16.1%, and with SF by 10.1% and 18.3%, respectively, compared to the fiber-free composite. The coefficient of the constructive quality values of lightweight ECFC is up to 16% higher with CF and up to 18% with SF than a concrete composite without fibers. Moreover, formulas were derived to predict the compressive of ECFC with and without CF and SF.
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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.