Klyuev A.V.

Candidate of Engineering Sciences (Ph.D.), Associate Professor, Belgorod State Technological University named after V.G. Shukhov, Russia

Injection mortars based on composite cements for soil fixation

https://doi.org/10.58224/2618-7183-2023-6-4-15-29
Abstract
The fixation of subsidence soils is an important practical scientific and technical task, which makes it possible to carry out construction and repair work on weak (subsidence) base soils. Composite cements (CC) have been developed, including aluminosilicates (AS), obtained by enrichment of ash and slag mixture (up to 65 wt.%), Portland cement clinker and gypsum. Based on the developed CC, a wide range of injection solutions with water-binding ratios from 1.0 to 2.0, including screening of crushed granite from 0.7 fineness modules, has been created. The developed injection mortars are capable of effectively fixing the soils of the foundations of underground structures, providing the strength of the soil-concrete mass up to 25.6 MPa with a deformation modulus of 10.1 GPa. According to the sedimentation analysis of solutions, it can be seen that these materials have a percentage of water separation from 22.5% at W/B=1 to 36.5% at W/B=2. At the same time, the viscosity indicators of these materials indicate a high penetrating ability, since the time of the expiration of mortars through a Marsh viscometer for mortars IR5 and IR6 is 39 and 40 seconds at W / B = 1.5 and W/ B = 2, respec-tively. The effect of increasing the density of injection mortars on composite cement at the age of 28 days was maximum at an AS dosage of 45% by weight, then it decreased with an increase in the con-tent of the aluminosilicate component. There are high ratios of the values of strength properties on the second day to similar indicators in the 28-days age: for compressive strength 0.24 (0.20-0.22 for addi-tive-free clinker compositions), for flexural strength 0.16 (0.15 for additive-free clinker compositions; while increasing the AS content above 45%, this ratio decreases to 0.14). High early strength makes it possible to effectively use injection mortars for urgent fixing of soils during the repair of underground structures.
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Method for calculating the strength of massive structural elements in the general case of their stress-strain state (kinematic method)

https://doi.org/10.58224/2618-7183-2023-6-3-5-17
Abstract
A variant of the kinematic method of the theory of limit equilibrium is proposed; massive structural elements are considered, the material of which, in the general case, is anisotropic.
A rigid-plastic model of a deformable solid body is adopted. It is assumed that massive structural ele-ments are destroyed by dividing into parts that deform relatively little (“absolutely rigid finite ele-ments”, ARFE) and have 6 degrees of freedom in three-dimensional space. The process of destruction of the material goes along infinitely thin generalized destruction surfaces (GDS), on which the work of all acting internal force factors (IFF) is taken into account – 9 forces and 9 moments. Bodies made of homogeneous isotropic materials that resist tension and compression in different ways are considered. The strength surfaces in the IFF space are described by the corresponding parametric equations.
Using the equilibrium equation in the Lagrange form and the Mises maximum principle, as well as the proposed parametric equations of the limiting surface, the problem of determining the minimum value of the possible kinematic parameter of the load is reduced to a standard linear programming problem (LP), which is solved using the simplex method.
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Experimental studies of the processes of structure formation of composite mixtures with technogenic mechanoactivated silica component

https://doi.org/10.58224/2618-7183-2023-6-2-5-18
Abstract
The paper considers the issues of utilization of technogenic fibrous material – waste of basalt production. The chemical composition of the technogenic fibrous material was studied, it was found that it consists of 44% SiO2. The initial basalt rock, which undergoes changes during high-temperature processing in the process of obtaining basalt fiber, was studied using IR spectroscopy. The grinding of the crowns was carried out for 30 minutes, allowing to reach a specific surface area of 800 m2 / kg. Further grinding does not lead to an increase in the specific surface area, which is associated with the phenomenon of secondary aggregation of fine particles. Research on REM has shown that the “cold shots” before grinding are mostly rounded or oval in shape. The compositions were formed and the strength characteristics of the samples for the 3rd and 28th day were determined. The maximum strength gain of 59 MPa was established at the age of 28 days in samples with the addition of 5% ground “cold shots” . When introducing cold shots in an amount of 10% (composition 5) of the cement mass, an intensive strength gain is noted in the early stages of hardening (7 days) with a strength of 38 MPa, slightly higher than the strength of the control composition. The introduction of 15% ground “cold shots” gives a strength value slightly lower (32 MPa) than the values of the control composition (37 MPa) at all stages of hardening.
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Method for calculating the strength of massive structural elements in the general case of their stress-strain state (parametric equations of the strength surface)

https://doi.org/10.58224/2618-7183-2023-6-2-104-120
Abstract
In the mechanics of a deformable solid, there are rods (one overall dimension of which is significantly larger than the other two), plates and shells (one dimension of which is significantly smaller than the other two), arrays (all three dimensions of which are of the same order). The complexity of the corresponding calculation models grows in the same order: the calculation models for rods and rod systems are relatively simple, the most complex are the calculation models for massive structural elements.
In the work, parametric equations of the strength surface in the space of internal force factors (IFF) are obtained – 9 forces and 9 moments for homogeneous anisotropic bodies. As special cases, similar equations are given for isotropic bodies that resist tension and compression differently, for isotropic bodies that equally resist tension and compression. Algorithm A1 for constructing the desired sections of strength surfaces given by parametric equations is proposed. Algorithm A2 is proposed for deter-mining the safety factors for the bearing capacity, remaining in the space of the IFF. Some examples of calculations made using the proposed equations, algorithms and the corresponding computer programs compiled on their basis are given.
The proposed method for calculating massive bodies allows a more realistic assessment of the bearing capacity of massive structural elements.
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Development of Alkali-activated Binders based on Technogenic Fibrous Materials

https://doi.org/10.58224/2618-7183-2023-6-1-60-73
Abstract
The paper discusses the development of alkali-activated binders based on technogenic fibrous materials. An approach to the secondary use of technogenic fibrous materials as a filler of composite binders is offered. The properties of mineral wool waste have been established. The microstructure of finely ground fibrous particles has been studied. Compositions of alkali-activated binders were de-veloped, when grinding basalt insulation production waste to a specific surface of 300-330 m2 /kg, followed by the formation of a binder according to the first method with rod tamping sealing and, ac-cording to the second, by pressing a raw binder mixture at a pressure of 10 MPa. The developed com-positions of alkali–activated binder by pressing with a compressive strength of 22.8 MPa, and when compacted with subsequent rod tamping – 11.8 MPa.
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FLAT BENDING SHAPE STABILITY OF RECTANGULAR CROSS-SECTION WOODEN BEAMS WHEN FASTENING THE EDGE STRETCHED FROM THE BENDING MOMENT

https://doi.org/10.58224/2618-7183-2022-5-4-5-18
Abstract
The article presents the solution to the problem of calculating the lateral buckling of wooden beams with a narrow rectangular section, taking into account intermediate point fixing in the edge stretched from the bending moment. The structure is considered as an orthotropic plate, the calculation is performed by the finite element method (FEM). To obtain a result that is valid for any beam geometry, the system of FEM equations is reduced to a dimensionless form. The dimensionless parameter that determines the value of the critical load is calculated based on the solution of the generalized eigenvalue problem. The numerical calculation algorithm is implemented in the MATLAB environment. The developed technique is verified by comparison with calculations in the LIRA and ANSYS software systems using flat and volumetric finite elements. A comparison is also made with the calculation formula presented in the Russian design standards for wooden structures SP 64.13330.2017 for the coefficient, taking into account intermediate fixing, with pure bending. It has been established that this dependence rather roughly takes into account the fastening from the bending plane of the edge stretched from the bending moment. Using the package Curve Fitting Toolbox of the MATLAB environment, we have selected refined formula for the coefficient, which can be used in engineering calculations.
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RESULTS OF ENDURANCE TESTING OF PREFABRICATED CRANE STRUCTURES

https://doi.org/10.58224/2618-7183-2022-5-4-39-49
Abstract
The purpose of the work is to analyze the results of tests of prefabricated crane beams for endurance during cyclic tests on a specially designed stand. The method of carrying out such tests is given. It indicates the inadmissibility of the operation of steel crane structures with cracks and the importance of research aimed at increasing the endurance and durability of crane beams. It proves the need to develop new crane beams (various profiles) to increase the period of accident-free operation of industrial buildings (using bridge lifting mechanisms with heavy duty) up to 25 years. It is proved that the developed prefabricated crane beam has improved (in comparison with the standard) characteristics.
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TECHNOLOGICAL FEATURES OF THE CONSTRUCTION OF A DEMOUNTABLE FOUNDATION FOR TOWER STRUCTURES

https://doi.org/10.58224/2618-7183-2022-5-3-17-26
Abstract
The paper proposes a new type of modular demountable reinforced concrete foundation for the construction of tower-type structures. Numerical modeling and design features of the manufacture and installation of the foundation, implemented under patent 2633604 “Demountable foundation for support” for a real tower with a height of 30 meters and a power of a 150 kV wind power plant, are given. The reduction of material consumption is achieved due to the formation of a cavity in each typical module and filling it with soil or any inert material. The result of the proposed solution is to increase the bearing capacity of the foundation as a whole, increase the strength and rigidity of its main joints, as well as simplify installation in comparison with traditional approaches to design. Moreover, the foundation modules, where maximum stresses occur, can be made of fibre concrete.
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THE RELIABILITY COEFFICIENT FOR FIBRE CONCRETE MATERIAL

https://doi.org/10.58224/2618-7183-2022-5-2-51-58
Abstract
One of the main parameters of the method for calculating building structures made of concrete and fibre concrete by limiting states is the reliability coefficient for the material, which characterizes the heterogeneity of the physical and mechanical properties of the material. In national and foreign standards, it takes a constant value of 1.3 (obtained on the basis of direct tests), or 1.5 (obtained on the basis of indirect tests and the use of graduated dependencies). The concrete matrix for the formation of the structure of fibre concrete is most often fine-grained concrete with special additives, which has greater uniformity in comparison with heavy concrete, which cannot but affect the reliability of the composite material in question as a whole: the stock coefficients for fibre concrete should be lower than for normal concrete, which has not been reflected in modern standards for design yet. Starting from interval estimates of the average strength value, a new approach to determining the reliability coefficient for the material, differentiated by the 1st and 2nd groups of limit states, is proposed. The results of calculations according to the proposed formulas for previously conducted tests of steel- and glass-fiber concrete images allowed us to conclude: the introduction of fiber into the concrete matrix of the proposed effective composite composition increases the uniformity of the strength properties of the material, which leads to an increase in the reliability of its use in building structures, a decrease in the value of the reliability coefficient (margin) for the material to 1.164...1.235 for central axial compression and up to 1.172...1.272 – for central axial stretching. The obtained actual coefficients in strength calculations will allow to reveal the supplemented reserves of the bearing capacity of structures made of this material up to 22.4%.
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FIBER CONCRETE FOR 3-D ADDITIVE TECHNOLOGIES

https://doi.org/10.34031/2618-7183-2019-2-4-14-20
Abstract
Fine-grained fiber concrete used in 3D printing is significantly different from conventional heavy concrete, which is determined by the increased consumption of cement, low water-cement ratio and the absence of large aggregates. The largest grain size of fine aggregate is selected taking into account the thickness of the section, the frequency and type of reinforcement, as well as the method of concrete placement. Despite the fact that the tensile strength of concrete on fine sand is more than 1.5 times higher than the strength of concrete on coarse sand, while there is a decrease in compressive strength. Due to the peculiarities of the technology of concrete manufacturing for layering, the use of coarse sands is impractical, and therefore it was decided to use quartz sand with a particle size module of 1.12 as a filler.
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