Archives

INCREASING IN IMPACT VISCOSITY OF FIBER-ASH-CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-6-5-16
Abstract
The trend in building materials science is to replace the different proportions of Portland cement in the binder. Therefore, the paper proposes the principles of controlling the static and dynamic strength of fiber-reinforced concrete, consisting in the complex effect of the hydro-removed ash and slag mix and basalt fiber on the processes of structure formation of the cement composite. A four-stage purification system for the hydro-removed ash and slag mixture has been developed, including disintegration, flotation and two-stage magnetic separation. It was found that the density of the fresh mix from the dose behaves naturally, and the density of solid samples at low doses slightly decreases. High early strength of the developed composites is noted, in particular, for specimens with ASM, one and a half increase in compressive strength is traced in comparison with non-additive specimens. Combinations of "fiber + ASM" with a quadrupling of strength have a significant effect on bending strength. Successful approximations of the compressive strength and bending strength on the ASM dose for different ages (1, 7, 28 days) are traced with the regular behavior of the coefficients in the power dependences. Revealed a multiple increase in the impact strength of the developed compositions. The use of the results will lead to the possibility of designing high-strength concretes, including for special structures.
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INCREASING THE BONDING STRENGTH OF THE PLASTERING COATING TO THE BASE

https://doi.org/10.34031/2618-7183-2020-3-6-17-26
Abstract
The strength of plaster coatings depends on the quality of adhesion of the applied plaster layer with the base. The bases for applying plaster coatings are necessarily prepared, the technology of preparing the bases may differ depending on the coating applied. It is established that the closer the initial structures are in structure, the higher the quality of the plaster coating as a whole. According to geonics, the relationship of structures in building composites is based on basic properties, general physical and mechanical indicators, which equally apply to both the building plaster solution and the base. At the same time, a contact binder is allowed between the base and the plaster layer with similar indicators, the presence of which guarantees reliable adhesion and strength of the resulting coating. The use of plaster solutions on enriched fine substandard sands with complex modified additives makes it possible to improve the technological qualities of the mortar mixture, the physical and mechanical characteristics of plaster solutions and optimize the technology of applying the plaster coating. Successive application of plaster layers on technogenic sands with different size modulus allows creating a base rough coating on the base, which closes the main defects and creates the base for the next layer of plaster solution. The Chechen Republic has extensive reserves of very fine and fine local sands, which in their basic properties are inferior to medium- and coarse-grained sands, but with a rational selection of composition, enrichment of grain composition can be used to produce high-quality construction composites. To enrich the grain composition of fine local sands, it is proposed to use dropouts of concrete scrap crushing, the volumes of which are significant on the territory of the Chechen Republic. Dropout of concrete scrap crushing by chemical composition is suitable for enriching local fine sands and when selecting the composition of the plaster solution increases the physical, mechanical and technological properties of the mortar mixture.
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INCREASING THE RESISTANCE OF MACADAM-MASTIC ASPHALT CONCRETE TO RUT FORMATION DUE TO THE USE OF POLYMER MODIFIERS

https://doi.org/10.34031/2618-7183-2020-3-6-27-34
Abstract
Rutting is an important problem in Russia today. One of the ways to improve the properties of asphalt concrete mixtures and reduce wear on road surfaces is to modify the binder with polymer additives. The aim of the work was to test the selected compositions of MMAC mixtures containing bitumen modified with the addition of sevilene and rubber for rutting resistance, which make it possible to predict the formation of plastic rut. It was revealed that when using sevilen in its composition, with an increase in the concentration of vinyl acetate, the depth of the track increases in comparison with the industrial polymer-bitumen binder. It is shown that with the introduction of a complex additive based on sevilen and rubber into the binder composition, its rutting decreases and the service life of the road surface increases, which indicates a high elasticity of the complex-modified binder. In this work, the calculation of the service life of the coating before the formation of a critical rut requiring repair of the coating is carried out. It was found that in terms of the slope of the rutting curve and the proportional depth of the rut, the compositions with sevilene and rubber are not inferior to traditional industrial PBB.
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RELIABILITY OF REINFORCED CONCRETE STRUCTURES TAKING INTO ACCOUNT THE CONCRETE CREEP FACTOR

https://doi.org/10.34031/2618-7183-2020-3-6-35-43
Abstract
In the process of inspection of reinforced concrete structures being in long-term service, deflections of beams and slabs beyond the standard values are often detected, which is attributable to concrete creep occurring in the case of the early dismantling of shuttering. At the same time, any visual signs of their reduced load-bearing capacity are absent. Taking into account the high degree of uncertainty of the factors influencing the long-term strains of the concrete, the safe service life of such structures can vary within a rather wide range, and its actual value can be assessed only through probabilistic methods of the reliability theory. The paper presents the results of the investigation of the influence of concrete creep caused by the early dismantling of the shuttering on the reliability of prefabricated reinforced concrete floor beams of a three-storey building. The data obtained through the instrumental verification of the mechanical characteristics of the beam materials and their deformed state were used for design modelling. The authors carried out the probabilistic creep analysis of the beam through the method of statistical modelling taking into account the variability of concrete strength for various values of the relative humidity of the ambient air and the age of concrete at the moment of the load application. The statistical characteristics of the stress-strain modulus and the beam deflection values with various levels of probability were obtained. Due to con-crete creep, the safety analysis showed a 2,4 times reduction in the beam reliability index at the service life of a structure of 70 years.
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PERFORMANCES OF HIGH POROUS CELLULAR CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-5-5-14
Abstract
The widespread use of cellular concrete for enclosing structures forces researchers to develop ways to improve their performance and durability. Compositions of aerated and foam concrete with the use of waste heat power engineering have been developed. The optimal formulation ratios have been identified that contribute to the creation of a rigid interpore matrix and water-repellent pore protection. The regularities of the synthesis of aerated concrete and foam concrete were established, which consist in optimizing the processes of structure formation through the use of a polymineral cement-ash binder and a pore-forming agent. The mix composition intensifies the process of hydration of the system, which leads to the synthesis of a polymineral highly porous heterodispersed matrix. The increased activity and granulometry of aluminosilicates predetermine an increase in the number of contacts and mechanical adhesion between particles during compaction, strengthening the framework of the interpore partitions. The mechanism of the influence of the composition of the concrete mix on the microstructure of the composite is established. The calculated sound insulation of airborne noise shows sufficient characteristics for using aerated concrete blocks as enclosing structures. One of the main advantages of aerated concrete is its low thermal conductivity, which is especially important from the point of view of ensuring the energy efficiency of buildings and structures. Even in spite of the high values of open porosity of the developed aerated concrete, the rigid frame makes it possible to achieve almost 2 times higher frost resistance characteristics than that of the reference specimen.
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DETERMINATION OF RHEOLOGICAL PARAMETERS OF POLYMERIC MATERIALS USING NONLINEAR OPTIMIZATION METHODS

https://doi.org/10.34031/2618-7183-2020-3-5-15-23
Abstract
The article is devoted to the problem of processing the experimental creep curves of polymers. The task is to determine their rheological characteristics from tests for any of the simplest types of deformation. The basis for the approximation of the experimental curves is the nonlinear Maxwell-Gurevich equation.
The task of finding the rheological parameters of the material is posed as a nonlinear optimization problem. The objective function is the sum of the squared deviations of the experimental values on the creep curve from the theoretical ones. Variable input parameters of the objective function are the initial relaxation viscosity and velocity modulus m*. A theoretical creep curve is constructed numerically using the fourth-order Runge-Kutta method. The nonlinear optimization problem is solved in the Matlab environment using the internal point method. The values m* and are found for which the objective function takes the minimum value.
To test the technique, the inverse problem was solved. For given values of the rheological parameters of the material, a theoretical curve of creep under bending was constructed, and the values m* and were found from it. The technique was also tested on experimental stress relaxation curves of secondary polyvinyl chloride and creep curves of polyurethane foam with a pure shear.
A higher quality approximation of experimental curves is shown in comparison with existing methods. The developed technique allows us to determine the rheological characteristics of materials from tests for bending, central tension (compression), torsion, shear, and it is enough to test only one type of deformation, and not a series, as was suggested earlier by some researchers.
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DEVELOPMENT OF RADIATION-PROOF CONCRETE COMPOSITIONS

https://doi.org/10.34031/2618-7183-2020-3-5-24-33
Abstract
The article considers the possibility of using composite binders and magnetite as components of concrete with radiation-proof properties. The use of the developed concrete is possible not only when it is necessary to build nuclear power plants, but also to create bunkers or anti-radiation shelters. A special feature of con-cretes used for the protection and design of nuclear reactor cranes is their properties, which they must have. These properties include: low thermal conductivity, increased density, high temperature resistance, reduced values of the coefficient of thermal expansion, shrinkage and creep. Technogenic raw materials for the production of very heavy concrete are studied, the main physical and mechanical characteristics, the requirements that need to be considered in the selection of raw mix composition for protective concrete are analyzed. The paper presents a comparison of physical and mechanical characteristics, the advantages and disadvantages of introducing a binder of various types: cement, cement with a superlasticizer and a binder of low water consumption. It was found that the use of a low-water-consumption binder increases the physical and mechanical characteristics while reducing the consumption of cement in the raw material mix compared to traditional heavy concrete with cement.
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EFFECT OF WOLLASTONITE ON THE MECHANICAL CHARACTERISTICS OF CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-5-34-42
Abstract
Improvement of the physical and mechanical properties of cement composites should be accompanied by the disposal of industrial waste of various generation. Therefore, the paper proposes the principles of con-trolling the strength properties of concrete, which consist in the complex effect of wollastonite obtained from boron production waste on the processes of structure formation of the cement matrix. When this introduced in an amount of 2-8 wt. % wollastonite has a dual function as a mineral filler and a reinforcing fiber. It has been proven that in the presence of wollastonite, the concrete mix becomes lighter without reducing its physical and mechanical properties. It was revealed that the early strength for all the developed compositions with the addition of wollastonite increases due to the acceleration of hydration processes. Calcium silicate, which is wollastonite CaSiO3, has a close chemical composition with cement clinker, especially with Ca2SiO4 belite and Ca3SiO5 alite. This leads to the formation of a chemically homogeneous and, as a result, hardened microstructure. Elongated wollastonite fibers with good adhesion to the cement stone provide effective micro-reinforcement of the concrete composite. Using the results will lead to the possibility of designing high-strength concretes, including for special structures.
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DEVELOPMENT OF SPECIAL RECIPES OF BINDING COMPOSITIONS WITH IMPROVED PROPERTIES

https://doi.org/10.34031/2618-7183-2020-3-4-5-12
Abstract
Abstract: the ecological safety of earthly civilization suffers from the accumulation of huge volumes of industrial waste, the natural resource potential is decreasing, therefore, special attention is paid to the development of less costly and low energy-intensive technologies for obtaining new building materials, the implementation of which does not require high-temperature and expensive technological processing, and will allow the use of secondary and substandard raw materials.
The work presents the results of the development of special formulations of binder compositions of alkaline activation based on cement production wastes in the form of aspiration and clinker dust from electrostatic precipitators of rotary kilns and waste from the metallurgical industry - ferrosilicon additives in the form of active silica, which will allow obtaining new building materials with improved properties.
The paper investigates the properties of an alkaline cement paste and cement stone, reveals issues related to the theoretical foundations of the formation of the structure and strength of an artificial stone based on an alkaline activator. The research results, in our opinion, are certainly of practical importance for the construction industry, as the proposed formulations of clinker-free cements can partially replace expensive and energy-intensive Portland cement, making it possible to create strong and durable concrete and reinforced concrete structures.
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RESEARCH ON THE STRUCTURE OF CLAY RAW MATERIALS FOR CERAMIC PRODUCTS

https://doi.org/10.34031/2618-7183-2020-3-4-13-23
Abstract
Abstract: the research uses some methods for determining materials, strictly applying the current standards and requirements of the Russian Federation. The degree of scientific development of this research is that specialists of the Department of Engineering Physics and Materials Physics of Engineering Faculty of Bashkir State University and the laboratory of JSC "Ceramics" of the Republic of Bashkortostan conducted research in the field of ceramic materials science for construction purposes. The methodological basis of the research is based on well-known methods of studying the structure of clay raw materials suitable for the production of construction products, with the choice of a stable light range of products and eliminates cracking in the technological process of brick production. The correct composition leads to a reduction in energy consumption without compromising the physical and mechanical characteristics of products.
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