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Structure and Properties of Variatropic Concrete Combined Modified with Nano- and Micro-silica

https://doi.org/10.58224/2618-7183-2024-7-2-3
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Аннотация
The lack of systematic information on the influence of the combined modification of variatropic concrete on their characteristics was revealed. The purpose of this work was to study the influence of the type of modifying additive, namely micro-silica, nano silica and their combination on the properties of concrete made using three different technologies - vibration (VC), centrifugation (CC) and vibration centrifugation (VCC). Concrete elements made using centrifugal compaction technology were subjected to additional sawing. Three types of modifiers were studied: micro-silica (MS), nano silica (NS) and their combinations. To determine the degree of effectiveness of each recipe solution, the following main characteristics were monitored: workability of concrete mixtures; density of hardened composites; compressive strength (CS) and water absorption (WA). When modifying MS, the greatest effect for VC, CC and VCC was observed with its amount of 8% instead of part of the cement. CS gains were up to 17% for VCC, and WA decreased to 25% for VCC. The NS modification showed the greatest effectiveness at a dosage of 4%. CS gains were up to 19% and WA decreased to 28% for VCC. A combined modifier of 75% MS and 25% NS showed the greatest effectiveness. CS increased up to 17% compared to effective dosages of single-component modifiers. The effectiveness of VCC, characterized by the percentage increase in CS, was up to 55% higher in comparison with VC and up to 25% higher in comparison with CC. WA of concrete decreased to 14% in comparison with effective dosages of one-component modifiers. The effectiveness of VCC, characterized by the percentage reduction in WA, was up to 30% higher compared to VC and up to 12% higher compared to CC. The greatest efficiency of all types of modifiers was observed in combination with the synthesized vibration centrifugation technology.
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Artificial intelligence model for predicting the load-bearing capacity of eccentrically compressed short concrete filled steel tubular columns

https://doi.org/10.58224/2618-7183-2024-7-2-2
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Аннотация
The purpose of this work is to develop the artificial neural network (ANN) model to determine the load-bearing capacity of concrete filled steel tubular (CFST) columns of circular cross-section in a wide range of input parameters. Short columns are considered for which deflections do not lead to a significant increase in the eccentricity of the axial force. The input parameters of the artificial neural network are the outer diameter of the pipe, the wall thickness, the yield strength of steel, the compressive strength of concrete, and the relative eccentricity of the axial force. The artificial neural network is trained on the synthetic data. For training, the dataset of 179,025 numerical experiments with different values of input parameters was generated. Numerical experiments were carried out using the finite element method in a simplified formulation, which makes it possible to reduce the three-dimensional problem of determining the stress-strain state of a CFST column to a two-dimensional problem. The results of testing the developed model on the data from full-scale experiments are pre-sented.
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Thermovision study of a residential building under climatic conditions of South Kazakhstan in a cold period

https://doi.org/10.58224/2618-7183-2024-7-2-1
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Аннотация
In this study, a nine-storey residential building was examined for thermal protection, located in Shymkent, Republic of Kazakhstan. Two two-room flats were considered with the possibility to inspect the exterior envelopes in four orientations. The examination was carried out at different times of the day according to three criteria: exterior envelope in the form of corner joints, translucent enve-lope in the form of window openings and the exterior façade of the building. The study found that the temperature at the surface of the room joints at lunchtime increased from 0.8% to 12% depending on the orientation of the exterior envelope. At the same time, it was found that in the morning and evening hours the temperature inside the living rooms is maintained at 25.8 - 26.5ºC due to excessive con-sumption of heat energy by increasing the heating power up to 15.6% relative to lunchtime, which leads to an excessive increase in air temperature by 7 - 18%. The value of humidity of living rooms also showed non-compliance with the optimal value by 3 - 15% relative to the current norms. As a result of the analysis of thermograms of translucent openings it was found that the surface temperature of the envelope at lunchtime increased by 9.9 - 23.2% in all cases of orientations, and the surface tem-perature of translucent openings of southern orientation is on average 18.2% higher relative to other orientations, which also indicates the influence of solar radiation on the thermal values of translucent openings. The analysis of thermograms and temperature of characteristic points of the external façade with regard to orientations showed a temperature difference from 7.5ºC to 21ºC depending on the ori-entation of the building, where the most exposed to solar radiation façade of southern orientation, which showed an increase in surface temperature by 3 times. Thus, the obtained results of the study will further contribute to the development of energy-efficient designs of external enclosures, consider-ing the influence of all factors on the process of heat exchange, which is the main objective of the au-thors’ comprehensive study.
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Field thermovision study of externsl enclosure for multi-storey residential building under climatic conditions of Northern Kazakhstan

https://doi.org/10.58224/2618-7183-2024-7-1-1
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Аннотация
An in-place thermovision study was carried out in a multi-apartment apartment building of high comfort in a cold period of the year, located in the Northern part of the Republic of Kazakhstan in the work. The study result showed the presence of significant problems on thermal protection at the edge and inner corner fences where the temperature difference between the inner surface of an enclosure and the internal temperature was 6.4 - 19.4ºC. An analysis of thermograms of window joints in living rooms also showed a significant temperature drop from -9.3ºC to 18ºC, where total vulnerable area was up to 10%. Thermograms of window-sill joints of living rooms also showed a temperature drop to -21.1 ºC with an area of 15.7 %. The temperature on a reinforced concrete column’s inner surface showed a value of 6.5 ºC, which is typical for an area of 34.8 %. An analysis of outside and inside temperatures showed that as the temperature drops from -7 ºC to -23 ºC during the day, the inside temperature of the room remains relatively stable at 25.3 - 26.1 ºC, although there are problems with the thermal protection of the enclosures, which indicates overconsumption of heat energy. Moreover, the internal air temperature exceeds the permissible temperature for living rooms by 1.3 - 2.6 ºС. An analysis of air humidity also showed unsatisfactory values, which during the day varied from 17.4% to 21.2%. The deviations identified during the survey indicate the presence of problems on thermal pro-tection of external enclosures, which require additional surveys aimed at further development and op-timization of external enclosure designs to obtain optimal values in the issue of energy saving, consid-ering the climatic characteristics of the Kazakhstan regions.
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Processing of nonlinear concrete creep curves using nonlinear optimization methods

https://doi.org/10.58224/2618-7183-2024-7-1-2
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Аннотация
The article proposes a method for determining the rheological parameters of concrete based on creep curves at various stress levels using the theory of V.M. Bondarenko. Using the proposed methodology, the experimental data presented in the work of A.V. Yashin is processed. The problem of searching for rheological parameters is posed as a nonlinear optimization problem. The sum of squared deviations of the experimental values of creep strains from the theoretical ones is minimized. The interior point method is used as a nonlinear optimization method. Four different expressions for the creep measure are considered, including the creep measure by N.Kh. Harutyunyan, creep measure by A.G. Tamrazyan, a creep measure in the form of a sum of two exponentials, and McHenry’s creep measure. It has been shown that the best agreement with experimental data is provided by the McHenry’s creep measure. An expression has been selected for the nonlinearity function, which describes the nonlinear relationship between stresses and creep strains. It is shown that the instantaneous nonlinearity of deformation and the nonlinearity that manifests itself over time cannot be described by a single function.
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Stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements under the action of longitudinal and transverse forces

https://doi.org/10.58224/2618-7183-2024-7-1-3
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Аннотация
Most wall panels in operating multi-storey residential buildings are in a complex stress-strain state under the influence of vertical and horizontal loads, such as their own weight, wind, etc. These features must be taken into account in the calculation in order to ensure operational safety. The combination of vertical and horizontal forces acting simultaneously for three-layer bending elements leads to the fact that the boundary between the compressed and tensile zones not only moves from one layer to another, but also has a different geometric shape depending on the ratio between the vertical and horizontal load. The stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements is caused by the impact on layers of different concretes. The formation of normal cracks occurs due to the achievement of ultimate tensile strength by the most stretched concrete under the influence of external loads. Since three-layer reinforced concrete elements consist of two outer layers (reinforced concrete) and a middle layer (lightweight concrete), when such an element bends, the outer layers are subject to compression, and the middle layer is subject to tension. The boundary of the compressed zone can be located either in one of the outer layers or intersect the middle layer, which falls into both the compressed and stretched zones. To analyze the stress-strain state during the formation of normal cracks, it is necessary to take into account the fol-lowing parameters: geometric characteristics of the element (dimensions and shape of the section, layer thickness, etc.), physical and mechanical properties of concrete (compressive and tensile strength, elastic modulus, Poisson's ratio, crack resistance coefficient, etc.), characteristics of reinforcement (class, diameter, pitch of bars, etc.) and its location in the section.
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Calculation of monolithic buildings structures taking into account the nonlinear operation of reinforced concrete

https://doi.org/10.58224/2618-7183-2024-7-1-4
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Аннотация
Buildings and structures made of reinforced concrete are currently designed, as a rule, under the assumption of linear work of the material. However, in accordance with the requirements of modern standards, it is necessary to take into account the nonlinear operation of concrete and reinforcement in calculations. In the research presented in the article, using the example of a building with a wall structural system, the influence of taking into account the physical nonlinearity of reinforced concrete on the operation of its structures was considered. It was received that due to the nonlinear operation, there is a prospect of a possible reduction in the calculated forces affecting the strength and width of crack opening, and, consequently, the reinforcement consumption. In addition, when taking into account the work of reinforcement in the zone of yield stresses in ceilings and walls, local plastic areas may form that require reinforcement, which are not fixed in linear calculations.
The calculations were performed in the LIRA-CAD 2021 software package. The results of the calculations showed that taking into account the nonlinear operation of reinforced concrete when considering the floors of a building allows reducing the design efforts compared to calculations performed in a linear formulation by about (3 - 30)%, and when calculating walls, on the contrary, taking into account the physical nonlinearity of reinforced concrete, internal forces increase in some cases more more than twice. Taking into account the physical nonlinearity of reinforced concrete work also leads to a more correct assessment of floor deflections.
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Molding properties of clay mixtures in the soft mud brick manufacture

https://doi.org/10.58224/2618-7183-2024-7-1-5
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Аннотация
The article reveals physical and mechanical characteristics of clay mixtures in the soft mud brick manifacture. Considering that currently Russia has no advisory or regulatory documents on the selection of raw materials for soft mud bricks and requirements for their physical and mechanical properties, this issue is quite relevant. The authors, based on their extensive practical experience, present data on acceptable ranges of clay mixtures deformation and critical compressive stress in the soft mud brick manufacture, as well as the results of studies on the influence of electrolyte additives on these indicators. The findings of how the mineral composition of clay raw materials and moisture con-tent influence the critical compressive stress and stickiness of clay mixtures are also presented. Thus, it has been experimentally established that the critical compressive stress of clay mixtures for soft mud bricks should be in the range of 0.2 – 0.8 kg/cm2, and the deformation degree of raw bricks should be in the range of 3 – 5 units. Moreover, even within such narrow limits, depending on their variation as well as on the method of molding and the composition of clay mixtures, it is possible to obtain differ-ent structures of the brick front surface: granular, tuberculate, grooved, wavy, corrugated, spotted, scaly, and their combinations. The moisture content of clay mixtures, depending on the type of clay raw material, can vary within very wide limits: from 20 to 38 per cent. The data obtained will make it possible to develop methods for selecting raw materials for soft mud bricks, which in turn will con-tribute to the organization of its wide production in various regions.
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Stereotypical ideas in the perception of spatial marginality of urban outskirts

https://doi.org/10.58224/2618-7183-2024-7-1-6
Аннотация
According to the territorial-regional development policy of Russia, a rigid structuring of the country's space is applied through the prism of a hierarchical management system. As a result, the structure of the space of the entire country was fixed through a system of boundaries, the markers of which highlight management objects at the national level, subject of the Russian Federation, territory, region, district. This article will present the main stereotypes that influence the creation of the perception of new territories in the nature of marginality. As is known, the formation of marginal communities can be traced throughout the history of civilizations. It is important to separate geographical marginality from spatial marginality. In geography, there is the concept of “marginal territories”, which can be considered those located on the remote periphery of the region or in isolated places. Such a phenomenon as spatial marginality is characterized precisely by the prevailing stereotypes in society about a specific area. Urban spatial perception critically influences human behavior and emotional responses, emphasizing the need to align urban spaces with human needs to improve the quality of urban life. However, the classification of urban architecture based on functionality is subject to biases stemming from discrepancies between objective representation and subjective perception. These biases can lead to city planning and designs that fail to adequately meet the needs and preferences of city residents, negatively impacting their quality of life and the overall functionality of the city. In this study, we apply machine learning to uncover these biases in urban spatial perception research using a three-step methodology: objective mapping, subjective perception analysis, and perceptual bias assessment. Our results show that machine learning can reveal hidden patterns in this area of research with significant implications for urban planning and design. Of particular note, the study found significant discrepancies in the distribution centroids between commercial buildings and residential or public buildings. This result sheds light on the spatial organization characteristics of urban architectural functions, serving as a valuable guide for urban planning and development. Moreover, it reveals the advantages and disadvantages of different data sources and methods for interpreting urban spatial perception, paving the way to a more complete understanding of the subject. These results highlight the importance of integrating both objective mapping and subjective perspectives when classifying the functionality of urban architecture.
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Structure and properties of modified shungite concrete during electrode heating

https://doi.org/10.58224/2618-7183-2023-6-6-1
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Аннотация
Concrete composition modifying by different electrically conductive components is one of less laborious but relatively effective methods between wide variety of electrode concrete heating effectiveness improvement methods. The purpose of this study is investigation of special aspects of cement systems modified by powdered shungite (Ssp 400 m2/kg) in combination with active mineral and plasticizing admixtures that harden under electrode heating at below zero temperatures. By the method of differential thermal analysis anomaly of exothermic reaction of cement stone specimens was discovered, that is due to formation of hydrated calcium silicate С2SH (A) discovered by the method of quantitative XRDA, and is verified by results received from scanning electron microscopy method, which among other factors provides higher strength and low permeability to these composites. Stabil-ity of cement systems modified by shungite and curing under electrode heating has been proved.
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