The article deals with the solution of the problem of unilateral frictional contact on the example of an arched culvert in the embankment. Unilateral contact is modeled as a linear complementarity problem, which is solved using the Lemke method. The features of solving such problems are shown. A comparison with modern approaches is given, the advantages and disadvantages of the proposed method are indicated.
Keywords: constructive nonlinearity, frictional contact, unilateral constraints, linear complementarity problem, numerical models, finite element method, load increment
The application of the results of hardness measurements and its modeling in CAD as a 3D model is considered. Different welding modes were applied and electrodes CT-15, OZL-8 and CL-11 were used as consumables. The test material is a hot-rolled pipe with a diameter of 159 mm made of corrosion-resistant steel 12X18N10T with a thickness of 6 mm. The electrodes were fused to half its length and removed from the electrode holder, after cooling the remainder of the electrode, it was reused. For scanning measurement of microhardness of samples with a load of 100 g, the scanning step was applied 0.5 mm. The use of modern software was able to more accurately simulate the test results on a 3D model. The samples are welded with CT-15 electrodes at a maximum current of 100 A. the hardness is over 450-550 HV, regardless of what the passage was. Similarly, when welding with OZL-8 brand electrodes, but only at low currents, the hardness exceeds 450 HV. In both electrodes, the hardness is increased. When using OZL-8 electrodes, samples welded at high currents have less hardness than at low currents. When welding with these electrodes, it is possible to use them in certain passages, for example, when surfacing the root layer of the seam. In the case of full penetration in high-current modes with CT-15 electrodes, the result differs little as in low modes.
Keywords: steel 12X18N10T, multi-pass welding, welding of austenitic steels, pipe, coated electrodes, welding modes, mechanical properties, macrostructure. Excel, Autodesk Inventor, CT-15, OZL-8, CL-11, amperage
This article discusses the ways and methods of modifying bitumen with crumb rubber obtained from used recycled car tires. A method for modifying bitumen with crumb rubber in a two-stage technological process is proposed. The main modifiers are considered, the analysis of data from literature sources on the modification of bitumen with polymers to improve the physical and mechanical properties is given. Own research data on the modification of bitumen with crumb rubber are presented. The main conclusions are made, the analysis of the results obtained, and recommendations are made for the further use of bitumen modified with crumb rubber in a two-stage technological process.
Keywords: crumb rubber, bitumen, modification, polymer, improvement, quality, recycling, analysis, research
In recent decades, awareness of the environmental, social and economic crisis, both at the national and international levels, has prompted researchers to develop new, low-cost composites that are more environmentally friendly and safer for humans, using plant materials as reinforcing elements. Compared to conventional synthetic reinforcing materials, lignocellulosic fibers have many advantages. In addition to being renewable, inexpensive, widely available and harmless to health, plant fibers have relatively high specific mechanical properties combined with low density. However, there is a problem with the biostability of plant materials used in the production of composite materials, and to solve it, it was decided to pre-modify plant materials using the monoethanolamine (N-B) trihydroxyborate modifier. In order to find out the effect of the modifier on the plant material, the chemical composition of the plant material was determined before and after the modification. Determination of cellulose content was carried out by the nitrogen-alcohol method according to Kurshner and Hoffer; the amount of hemicelluloses was analyzed by treatment with 2% hydrochloric acid, followed by precipitation of furfural obtained by the bromide-bromate method; lignin content was determined by the Clason method using 72% sulfuric acid; and, finally, the content of extractive substances soluble in organic solvents was determined. It should be noted that, compared with the component composition of the raw plant material, there is a change, and this change is noticeable in the amount of lignin after the modification of the raw material and after extraction, which gives a decrease of almost 2.75 times. This is due to the formation of weak esters under the action of the modifier and, most strikingly, a strong increase in the amount of hemicellulose, which contributes to the depolymerization of cellulose macromolecules under the action of the alkaline modifier used. All this allows us to state that the modification of the crushed stems of Sosnowski's hogweed with monoethanolamine (N→B)-trihydroxyborate changes the composition of the components of the lignocarbohydrate complex of the substrate in the direction of reducing the degree of polymerization and the formation of esters.
Keywords: component composition, cellulose, hemicellulose, lignin, extractives, vegetable raw materials, ligno-carbohydrate complex
Experimental data are given on the change in temperature and end time of hardening of a gypsum binder in the presence of a fulleroid-type carbon nanomodifier, as well as the properties of nanomodified hardened high-strength gypsum: strength, density, water absorption, and softening coefficient. When performing the experimental part of the work, the gypsum binder was mixed with fullerenol solutions with different pH: neutral, acidic, alkaline. Conclusions are drawn about the effect of fulleroid nanoparticles on the rate of setting and hardening of gypsum and the characteristics of gypsum stone. The nanomodifier affects the rheological properties of the mixture and the temperature of the binder hydration process, which affects its physical and mechanical characteristics, density, and water absorption.
Keywords: gypsum binder, fulleroid nanomodifier, temperature, hardening time, gypsum dough, gypsum stone, properties
This article is devoted to the issue of the use of geosynthetic materials in drainage structures that can be used at oil and gas fields. In connection with the development of construction and building materials in the world, there is a need to apply technologies and solutions aimed at optimizing and reducing the cost of construction work, facility operation. The article presents block diagrams for the classification of geosynthetic materials according to various parameters. The issues of the use of geosynthetics and their functions in construction, in particular in drainage structures of oil and gas fields, are considered. The analysis of the regulatory and technical base within the framework of the study was made, the regulatory documents under consideration. The study of this topic makes it possible to determine the set of properties and functions required for geosynthetics, as well as to establish the most effective drainage structures using geosynthetics using the method of technical and economic comparison, which can be used in a real object.
Keywords: geosynthetic material, drainage structure, dewatering, groundwater, oil and gas field
One of the major disadvantages of the domestic industry is its high resource intensity, due, among other things, to the low level of use of secondary raw materials. There are a lot of problems associated with the disposal of polymer waste. They have their own specifics, but they cannot be considered insoluble. One of the methods of recycling is the use of plastic waste as aggregate in cement mortar and concrete preparation. The article contains and analyzes the methods, physical properties of concrete, with plastic aggregate and physical properties related to the operation, durability of concrete containing plastic aggregates. Based on the results of the review, it was concluded that the technique of using plastics in cement mortar and concrete preparation is effective and cost-effective. The results suggest that the use of recycled plastic fibers and pellets in concrete can lead to improved concrete properties. The article considers the physical properties associated with the operation and durability of concrete containing plastic aggregates and fibers, types of plastics and cement, the chemical composition of the cement used in the study, the main joints, shrinkage, compression strength, bending strength, modulus of elasticity, water adhesion and porosity, thermal conductivity, fire resistance. The use of recycled plastic aggregates and fibres as a building material is attracting increasing attention. The article considers the physical properties associated with the operation and durability of concrete containing plastic aggregates and fibers, types of plastics and cement, the chemical composition of the cement used in the study, the main joints, shrinkage, compression strength, bending strength, modulus of elasticity, water adhesion and porosity, thermal conductivity, fire resistance. The use of recycled plastic aggregates and fibres as a building material is attracting increasing attention.
Keywords: concrete, aggregate, plastic, strength, fibers, properties, waste, compression, mixture, material, quality
The researches results of the fuel ash waste’s and grain crops straw’s influence on the properties of the producing expanded clay gravel are presented in the paper. These wastes were used as auxiliary additives in the raw combination. The optimal composition of the raw combination has been established in the laboratory, for which physical and mechanical characteristics of the samples, including water absorption, compressive strength, bulk density, were analyzed. Characteristics of the expanded clay gravel samples are compared with the state standards requirements. It was found, that the addition 5% fuel ash and 1.5% crop waste (grain straw) ensures optimal swelling of the combination and high strength characteristics of the finished product.
Keywords: expanded clay, fuel ash, waste of crop production, swelling, construction materials, porosity.
Numerous factors that determine the quality of monolithic reinforced concrete massive foundations predetermine the relevance of a thorough study of a set of issues related to the intensity of concreting, the technical capabilities of the contractor, temperature and humidity conditions, the characteristics of the technological properties of the concrete mixture and the kinetics of concrete hardening. To ensure the solidity of the structure, the expediency of determining the thickness of the layer to be laid is justified not only by the length of the working part of the vibrator, as prescribed by the standards, but also by the indicators of the intensity of concreting, determined by the design parameters, temperature and humidity conditions and the capabilities of the worker. The influence of the temperature and humidity conditions of the environment and the recipe features of the concrete mixture on the rational time of overlapping layers is shown. The results of modeling the level of tensile stresses on such recipe-technological factors as the class and kinetics of concrete hardening, temperature conditions and conditions of heat exchange with the environment are given on the example of a temperature-shrinkage block 20x20x2 m. the values of its parameters. An equation is given for relative moisture loss over the thickness of the structure in dry hot weather when self-compacting concrete mixtures are used.
Keywords: intensity of concreting, quality of massive monolithic foundations, overlapping time of layers, moisture loss, level of tensile stresses
Currently, one of the most promising and cost-effective methods of seismic isolation is the use of passive energy dissipation systems. The research carried out in this article focuses on the use of a new hybrid energy dissipation device that combines a parallel layer of an inexpensive viscoelastic material and a metal component. Typically, the viscoelastic material in such systems is attached to steel shock absorbers with an adhesive. In this article, the behavior of a viscoelastic material is studied when it is attached to a metal component without the use of glue, being held only by friction and pressure. The influence of the compression force on the elastic and damping properties of a viscoelastic material arranged in a seismic damper has been established, and the pressing force has been determined, which ensures the optimal functional properties of the viscoelastic material.
Keywords: earthquake, seismic safety, damper, thermal expansion, viscoelastic material, rubber compound, rubber, resin, polymer, vibration, seismic isolation
The relevance of modeling the temperature regime and the stress-strain state in the early period of the construction of massive monolithic reinforced concrete structures is shown. Some data are given on the temperature and time parameters of the formation of temperature fields in structures with a surface modulus from less than 1.1 to 2.4 from concrete classes from B25 to B70, both fast and slowly hardening. Based on the results of processing numerous data, the quantitative values of the parameters of the heat release kinetics for the proposed dependence are substantiated. A simplified method for calculating thermal stresses is proposed, based on the proposed and substantiated dependences of concrete properties on its degree of maturity, which are confirmed by numerous experimental data, incl. obtained by other researchers. The calculated values of stresses obtained during the construction of a temperature-shrinkage block 20x20x2 m from concrete of fast and slow hardening classes B25 and B45 were compared with some experimental results and modeling data. The conclusion is made about the inexpediency of using concrete of class B45 due to the high risk of cracking in the period of 1.5 - 3 days. When using concrete of class B25, preference should be given to fast-hardening.
Keywords: massive monolithic structures, thermal stresses, cracking, degree of concrete maturity, kinetics
As a result of processing the experimental data of the authors and other researchers, a relationship was obtained between the adhesion strength of the Acc with a concrete base and the axial tensile strength Rt of solutions without RPP Acc = 0.23ˑRt at R2 = 0.996. A tendency to increase the adhesion strength to 30% with an increase in the dosage of RPP to 2% and up to 130% with the dosage of RPP 3%, while a significant effect on the adhesion strength of the type of cement and RPP has been established. The data on the role of the age of the concrete base and its treatment before applying a repair (restoring) mortar or concrete mixture on the adhesion strength are given. The dependence of the elastic modulus of mortar or fine-grained concrete on the axial tensile strength, invariant to prescription factors, is obtained. The discrepancy of some standards in terms of the requirements for the base during tests for adhesion strength was noted.
Keywords: dry building mixes, adhesion strength, modulus of elasticity, redispersible polymer powders, repair mixes
An engineering technique for determining the bearing capacity of reinforced bending elements of building structures made of a binary composite material with a multi-modulus, nonlinearly elastic polypropylene matrix and powder filler is described. Information about various approaches to solving the problem proposed by other researchers is given. The author's method for obtaining the predicted physical and mechanical characteristics of binary composite materials is described, which gives more accurate results compared to known approaches. An algorithm for iterative refinement of the geometric characteristics of structural elements with an arbitrary cross section and a non-linearly elastic matrix has been developed. A computer program is described that automates the process of characterization, examples of specific cross sections are given. The possibility of refining the geometric characteristics of elements in the direction of their increase is proved.
Keywords: composites, matrix, filler, non-linear elastic material, armature, iterative process, computer program, beam, I-beam, geometric characteristics
The importance of inert mineral additives for the development of modern concrete technology is considered. The results of a study of the influence of the dosage of limestone powder on the consistency and strength of fine-grained concrete with different ratios of its components are presented. It was established that in concretes with a high content of superplasticizer, the proportion of mineral additives in mixed cement is the main technological factor in controlling the strength characteristics of concrete.
Keywords: fine-grained concrete, mineral powder, inert mineral additive, superplasticizer, mix consistency, strength, strength control
An engineering technique for predicting the main physical characteristics of multicomponent composite materials with a polypropylene matrix is described. The technique is based on the calculated dependences obtained for a binary composite. Calculation formulas for determining the modulus of elasticity and Poisson's ratio of an artificial material are given. An algorithm for applying the proposed formulas is described, which consists in successively obtaining the desired characteristics, each time considering a two-component composite and taking as the initial material a composition of a polymer matrix and one of the fillers. A specific example shows that the order in which fillers are taken into account does not affect the final result. The proposed technique can significantly reduce the design time for new materials and will make it possible to reduce the number of real experiments. The difference between the theoretical results and the data of physical experiments does not exceed 10–15%.
Keywords: composites, matrix, filler, polypropylene, wood flour, chalk, modulus of elasticity, Poisson's ratio
This paper presents an analysis of the results of studies that relate to the rational use of waste products from the production of slab insulation based on polyisocyanurate foam (PIR). Its use as a filler for structural and heat-insulating materials based on cement and gypsum binders is considered, optimal compositions for obtaining products that meet the required performance characteristics are described.
Keywords: polyisocyanurate foam, PIR, thermal insulation, production waste, recycling, cement binder, gypsum binder, lightweight concrete
CLT panels (English: Cross Laminated Timber) were chosen as the object of the study. This is a multilayer material made of coniferous and hard-leaved wood, which has a system of cross—glued wood in its composition. As part of the work, the available literature on this topic was analyzed, the calculation and analysis of the results obtained were carried out. The article presents the results of the calculation of the CLT panel with consideration of the possibility of isotropic and orthotropic setting of the stiffness of the panel, using elastic modules along and across the fibers. The calculation results are presented in the form of maximum deflections of the panel. Applications in the calculation of the modulus of elasticity across the fibers and taking into account orthotropic stiffness clarifies the stress-strain state of the overlap panel. Based on the calculations performed and the analysis of the results obtained, conclusions are drawn.
Keywords: CLT-panel, transverse bending, modulus of elasticity, stiffness, stress, deflection, orthotropy
The expediency of using modeling using the finite element method to study the influence of certain prescription-technological factors on the resulting temperature fields and temperature stresses during the construction of massive foundation slabs is substantiated. A simplified method for determining thermal stresses based on the reduction of a three-dimensional problem to a one-dimensional one based on the hypothesis of flat sections is considered. The dependence is proposed and the quantitative values of the parameters for calculating the kinetics of heat release of concrete in the temperature-shrinkage block are substantiated. As a result of the implementation of a numerical experiment on the influence of the duration of breaks between overlapping layers, the temperature of the environment and the concrete mixture, the class and kinetics of concrete hardening, and heat transfer parameters, the dependences of the level of tensile stresses on these factors over time were obtained. It is shown that when developing technological regulations for concreting, the determination of technological parameters (the intensity of laying the mixture, the thermal resistance of the formwork, the arrangement of working joints, etc.) is impossible without taking into account the kinetics of concrete hardening, determined by the prescription features of concrete mixtures.
Keywords: massive monolithic structures, temperature fields and stresses, prescription-technological factors, heat release of concrete, stress-strain state
Dependences of strength and deformation properties of heavy concrete under early loading under conditions of negative temperatures are obtained on the basis of experimental data. Empirical coefficients are proposed to describe the measure of concrete creep through the temperature function. A significant increase in the strength of concrete hardening under load during freezing and thawing has been confirmed. The results can be used to assign the parameters of early loading and calculation of monolithic buildings at the stage of their construction.
Keywords: monolithic buildings, building structures, heavy concrete, strength, deformation, creep, creep measure, early loading, loading intensity
The article discusses various mechanisms of self-healing of concrete used in the construction of buildings and structures designed for certain operating conditions and the environment, which saves resources and time during maintenance and repair of objects for various purposes. Types of self-healing of concrete: With hollow fibers; Microcapsulation; Expanding additives; Bacteria. Conclusions. Today, progress has been made in understanding the relationship between the structure of materials and their properties. Thanks to the knowledge gained about the structure of materials, the possibility of designing materials of directional quality was considered, which guarantees their compliance with certain operating conditions and the environment.
Keywords: concrete, destruction, self-healing, hollow fibers, microcapsulation, expanding agent, bacteria
The article considers possible ways to increase energy efficiency of ventilation systems in residential buildings via replacing natural ventilation by means of mechanical systems with heat recovery of exhaust air. A feasibility study has been completed covering the application of the central zone and single apartment mechanical air-handling ventilation units with respect to social and planning solutions approved in the course of renovation of residential buildings under Volgograd specifics, which showed that the single apartment systems are not economically viable for use with smaller apartments in terms of number of rooms and overall area (economy housing).
Keywords: energy saving, natural ventilation, the mechanical central zone ventilation system, the single apartment ventilation system, recovery, a planning solution for a building, economic feasibility
The problems of modern methods of building construction, namely the obsolescence of construction technologies and the production control system at most facilities under construction do not provide the required level of quality. Due to low-quality materials, formwork, reinforcement, laying and ramming, defects and deviations from the most important requirements for the finished product appear and resource costs increase significantly. Therefore, in order to develop and introduce effective measures to improve the existing methods of building construction, this paper lists the main disadvantages of the technologies used. The practice of applied innovative technologies that can increase the quality and speed of the structures being built is given. The technologies of erecting buildings using various fixed formwork designs are considered.
Keywords: sound insulation, shock noise, residential buildings, noise insulation, air noise, monolithic house, comfortable environment, noise, construction, materials
The study is devoted to the generalization of the existing world experience on the impact of recycled polyethylene terephthalate (PET) products when they are added to concrete on its characteristics. Analysis of the available data shows the effectiveness of the use of PET fiber in a concrete matrix in order to recycle plastic waste, facilitate concrete structures, save cement consumption and improve the strength characteristics of concrete. But the researchers did not come to a consensus on the effective consumption of fiber during reinforcement, the influence of the shape of the fibers used on the properties of fiber concrete, as well as the areas of application of this material.
Keywords: concrete, concrete matrix, fiber, dispersed reinforcement, polyethylene terephthalate, tensile strength, compressive strength
This article contains the results of a study of the strength characteristics of building mortars of various compositions based on magnesia binder (magnesia oxychloride cement). The results obtained: the final compressive strength (28-day) within the studied compositions is from 12 to 45 MPa, the kinetics (rate) of strength growth on the first day of hardening is from 22 to 38%, on the third day of hardening – 33-68%, on the seventh day – from 50-88%, and about 120% from the design (28-day) with further hardening.
Keywords: magnesia oxychloride cement, magnesia binder, magnesia mortar, magnesia concrete, caustic magnesite, magnesium chloride, compressive strength, strength set kinetics
The paper presents a model for the distribution of sulfur by types of states and a model for the coalescence of sulfur droplets in a sulfur-bitumen binder, as well as a model for the coalescence of sulfur droplets in a bitumen melt. The developed models well explain the mechanisms of structure formation of sulfur bitumen materials, leading to the formation of their mechanical properties, determined experimentally both for the sulfur bitumen binder and for sulfur asphalt concrete.The model of sulfur distribution by types of states demonstrates that with an increase in the sulfur content in the bituminous binder, the proportion of sulfur in a physically free state increases, which forms a dispersed phase that increases the viscosity of the binder. This leads to a natural increase in the properties of the bituminous binder with the introduction of sulfur. The sulfur droplet coalescence model demonstrates that this process is energetically favorable. The driving force of coalescence is the Laplace pressure, which increases with an increase in the size ratio of contacting sulfur droplets. Also, with an increase in the sulfur content, the probability of overcoming the interfacial film of bitumen between sulfur drops increases, which naturally increases the likelihood of the formation of spatial sulfur structures that adversely affect the crack resistance of sulfur asphalt concrete.
Keywords: sulfur, sulfur states, strength, crack resistance, sulfur-bitumen binders, sulfur-asphalt concrete, asphalt concrete, coalescence of sulfur droplets