Nanotechnologies in Construction: A Scientific Internet-Journal @nanobuild-en
Статьи журнала - Nanotechnologies in Construction: A Scientific Internet-Journal
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Статья научная
Introduction. Phenols and petroleum products are common wastewater contaminants in many industries. Due to their persistence and toxicity in the natural environment, an efficient waste disposal technology is needed. Ozonation in the presence of heterogeneous catalysts is one of the advanced methods for treating wastewater from these toxicants. Since most catalysts are expensive, they are being sought on the basis of transition metals and their oxides, which have high activity and relatively low cost. In this regard, the Scientific and Educational Center for Innovative Technologies (SECIT) of USPTU carried out work on the search for an effective and affordable catalyst for the deep oxidation of phenol and petroleum products in wastewater under the influence of ozone. Methods and materials. To study catalytic ozonation, we used model waste water containing phenol and oil products at concentrations of 8 and 30 mg/dm3, respectively. Ozonation was carried out in the presence of fresh (1) and spent (2) NiO–MoO3 catalyst deposited in the form of a film on cylindrical Al2O3 granules weighing 0.5 – 2 g. Results. Optimal conditions of ozonation have been found (1), within 10 min of the decomposition process in its presence, COD decreased by 25% compared to the oxidation process with a catalyst (2), and by 40% compared to classical ozonolysis. It was found that the optimal loading of catalyst (1) is 1 g, duration is 35 min, pH = 8.5, temperature – 22 – 30оC, ozone dose – 5 g/dm3. Discussion. At catalyst dosages of less than 1 g/dm3, the low efficiency of removing phenol and hydrocarbons is probably due to a lack of the adsorption surface of the catalyst. Conclusion. The studied method of purification allows to reduce the content of phenol and oil products to the standard indicator of drinking water quality (0.001 and 0.05 mg/dm3, respectively), COD by 96% and solve the problem of the harmful effects of these toxicants on ecosystems.
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Research on the impact of nano carbon fillers on the morphology of epoxy binder
Статья научная
Introduction. When developing a composite material, it is important to understand how the components included in its composition affect its properties. Fillers, by interacting with the matrix, can alter its initial structure, resulting in the composite acquiring characteristics different from the matrix. The high modifying ability of nanofillers is determined by their significant specific surface area. This allows for the total interfacial area between the matrix and the dispersed phase to be covered even with a relatively low concentration of particles, thereby enabling the use of a small amount of filler. Methods and materials. Composite materials with nano carbon fillers were investigated, including fullerenes, nanotubes, and graphene. Fractographic analysis of the tensile fracture surfaces of the samples was chosen to evaluate the structure of the composites, which allows determining the nature of the failure and the ability of the composite to restrain crack propagation. The microstructure of the composite materials, as well as the morphology of the reinforcing nano carbon fillers, were examined with a Tescan MIRA3 scanning electron microscope. Results and discussion. In a graphene composite, crack energy is dissipated through branching and elongation of the crack path. Carbon nanotubes, being embedded in the crack walls, hinder the opening of the crack edges. Crack energy is also consumed in overcoming friction forces during the extraction of nanotubes from the epoxy matrix. Agglomerates of fullerenes act as effective crack front arresters, forcing the crack to circumvent them, thereby creating new areas of fracture surfaces. This leads to an increase in the crack front length and the energy required for material failure. Conclusion. Adding nano-carbon fillers (graphene, CNT and fullerenes) as reinforcing components in the epoxy binder alters the structure. The study defines possible mechanisms for hardening of the composite materials due to adding the nano-carbon fillers.
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Resource-saving nanotechnologies in waste water treatment
Статья научная
This paper examines the prospective field of nanotechnology development in the area of wastewater treatment and water processing. The introduction showed (no need for comma) that the Russian problem is not the lack of water – but its quality. Water treatment is needed to prevent water facilities from pollution. Self-cleaning methods cannot withstand the massive impact of pollutants, some of which are unknown for their natural reproduction processes. The degree of purification depends on the concentration of the pollution and the content of different substances within it. The use of nanotechnologies in effluent neutralization (EN) processes will allow removing insoluble sludges, wastes of chemical industry, and harmful microorganisms. Methods and materials. This work presently uses analytical methods to study nanotechnologies. Nanofiltration and membrane methods are frequently used in wastewater treatment. Methods such as arc charge, ablation, and gas-phase deposition are applied to obtain carbon nanotubes. Results. The authors describe promising carbon nanomaterials for production of membranes used in purification/decontamination/ desalination of water. The new generation of membranes for filtering, disinfection, and desalination have been shown. These include graphene and carbon nanotubes which present absolutely new nanomaterial. Discussion. It was revealed that such membranes are characterized not only by a high water percolation rate, but also by extraordinary selectivity. Such membranes are particularly promising in the field of biomedicine, as large membranes are necessary for the nanofiltration and desalination processes. Conclusions. This paper examines new ecological and resource-saving technologies making possible improved research, industrial and commercial activities (which by means of practical implementation of inventions will lead to improved products), technologies and organizational decisions. One of the most promising areas for the development of nanotechnologies applied in waste water treatment is the advancement of membrane technology employing innovative materials, specifically graphene and carbon nanotubes.
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Статья научная
Introduction. For handling the problem of mixtures design for additive construction technologies, the paper presents the results of experimental studies of rheological behavior and production characteristics (plasticity and shape stability) of cement mixtures based on various types of fillers with different size, shape, and grade. Methods and materials. Rheological properties of 3Dprintable mixtures were investigated using squeezing rheometry methods. The constant strain rate mode of 5 mm/s was used to evaluate plasticity and the constant load rate of 5 N/s was used to evaluate form stability. Scanning electron microscopy method (Phenom XL) was used to evaluate the size-geometry characteristics of cement and filler particles. Image processing to determine particle length and width was performed using ParticleMetric software. The size and gradation of the cement and filler particles were evaluated using a laser particle size analyser “Analyzette 22”. Results and discussion. It was found that a necessary condition for the plasticity and stability of mixtures is the creation of dense spatial packing of disperse phase particles. The values of the plasticity limit rational for extrusion are ensured if the filler particles have a size comparable to cement particles and multi-size gradation. The characteristics of the fillers are not decisive for the shape stability of the mixtures. Conclusion. The numerical criteria of fillers for design of 3D-printable mixtures have been substantiated, including mean average particle diameter, particle shape factor, particle distribution constant as a characteristic of the particle size gradation.
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Статья научная
Utilizing the unique properties of CNTs and CNFs to enhance the mechanical and fracture properties of cement based materials and develop smart cementitious nanocomposites can be a challenge in terms of developing scalable manufacturing methods. Scaling up the manufacturing size of CNT and CNF reinforced cement based materials and produce multifunctional concrete that exhibits exceptional strength, stiffness and toughness and multifunctionality requires optimization of dispersion procedure. The effectiveness of successfully using CNTs and CNFs in concrete depends on the fiber count, the volume fraction of sand and coarse aggregates. In this work, we present the flexural strength and stiffness, fracture toughness and brittleness of nanomodified pastes and mortars reinforced at amount of 0.08 and 0.1 wt% and an investigation on the optimization of the fiber count proportioning of concrete. The addition of a very low amount, 0.1 wt%, of both CNTs and CNFs, increases approximately 1.5 times the flexural strength and the Young`s modulus of concrete nanocomposites. The nanomodified concrete also exhibits 60% higher energy absorption capability.
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Self-cleaning capacity of photocatalytic building plasters under frost attack
Статья научная
Introduction. The durability of the self-cleaning capacity of photocatalytic building materials under real operating conditions is a crucial issue, as their efficiency decreases over time due to surface degradation and carbonation. The purpose of the research is to evaluate the stability of the photocatalytic activity in two types of plasters – gypsum-cement-pozzolan plaster (based on red gypsum) and cement plaster (with anatase photocatalyst) – to cyclic freezing and thawing, as well as to investigate the effect of water-reducing and pozzolan additives on maintaining their self-cleaning ability. Materials and Methods. Series of plaster samples were prepared with and without different combinations of additives. Photocatalytic activity was assessed using the rhodamine test. Changes in the materials were analyzed using compressive strength, density, and water absorption test methods. Scanning electron microscopy with energy-dispersive spectrometry was used to measure the titanium (photocatalyst marker) and calcium (carbonation marker) content on the surface. Destructive frost effects were simulated by the cyclic freezing and thawing of samples in a water-saturated state. Results. It was found that the primary mechanism causing the loss of the self-cleaning capacity was photocatalyst washout due to surface degradation. Shielding of the photocatalyst by carbonation products is also crucial for cement plasters. Water-reducing additives increased the initial self-cleaning efficiency by 45% due to structure compaction, which slowed surface degradation. Pozzolan additives reduced surface calcium content by 6–8%, suppressing carbonation and almost doubled the initial efficiency. The combined use of these additives demonstrated the best results in maintaining photocatalytic activity after freezing and thawing. Discussion and Conclusion. The durability of the self-cleaning capacity directly depends on the resistance of the carrier material to climatic impacts. Combined modification with water-reducing and pozzolan additives is the most effective strategy for improving the durability of self-cleaning plasters, as it simultaneously counteracts two key degradation mechanisms: physical washout of the photocatalyst and its chemical shielding by carbonates. This study provides a practical approach to developing more sustainable photocatalytic building materials.
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Self-compacting concrete for monolithic constructions with highly dispersed silica-based additives
Статья научная
Introduction. Self-compacting concrete offers broad potential in construction due to its operational reliability and durability. However, the high cost of self-compacting concrete and the technological complexity of its production require the development of new concrete mix designs and improved placement technologies. When selecting concrete mix designs for self-compacting concrete, chemical additives can be used to reduce cement consumption and improve the concrete's properties. Materials and methods. To ensure the rheological and technological properties of the concrete mix, fly ash, a dry polycarboxylate-based superplasticizer, and ultrafine additives were used. The ultrafine additives were produced by hydrolysis, using pure Portland cement as a precursor, with the concentration in the solution varying from 1 to 5%. The cement hydrolysis reaction results in the formation of a multicomponent sol containing silicic acid, aluminum hydroxide, iron hydroxide and calcium hydroxide. Results and discussion. Experiments were conducted to modify self-compacting concrete with an ultrafine additive obtained using sol-gel technology. An optimal composition of modified cement containing an ultrafine additive with an average particle size of up to 100–150 nm was developed. The use of the ultrafine additive accelerated the cement hardening kinetics and improved the physical and mechanical properties of cement stone by 1.4–1.8 times compared to cement without the additive due to water accumulation, an increase in the volume of cement gel, and a decrease in capillary porosity. Based on an assessment of the technological and rheological properties of concrete mixtures containing fly ash as a microfiller and a modifying additive, compositions corresponding to strength classes B40–B60 were established, containing 7.5–44% fly ash and an additive in an amount of 0.1% of the cement weight on a dry matter basis. It has been established that the introduction of ultrafine fly ash and fly ash into the concrete mix reduces segregation by 17–19%, increases viscosity by 13% to 20%, and reduces flowability only slightly by 5–10%. It has been established that self-compacting concrete with the combined use of fly ash with medium pozzolanic activity, a chemically active ultrafine additive, and a polycarboxylate-based superplasticizer is characterized by intensive strength gain within 1–3 days of curing and an increase in strength by 15–17% within the design curing period. Conclusion. As a result of the research, a low-temperature method for producing a modifying additive using sol-gel technology was developed. This method is simple to synthesize, does not require complex process equipment, and can be added along with mixing water and uniformly distributed throughout the concrete mix. Concrete mix formulations for self-compacting concrete of strength classes B40–B60 were developed using an ultrafine additive, which improves the process properties, quality indicators, and physical and mechanical properties of the concrete.
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Self-healing cements – the key to maintaining the integrity of cement sheath. Part 1
Статья научная
To control water production, it is necessary to seal the channels of 20–25 mm thickness in the cement sheath at a depth of hundreds and thousands of meters. The most promising solution is the use of self-healing cements. The concept of self-healing materials has been known since the 1980s due to the studies of Donald Jud. The most fundamental works are by Sybrand van der Zwaag, Sheba D. Bergman and Fred Wudl, Richard P. Wool, D.Y Wu, N.R. Sottos, Erin B. Murphy, Henk Jonkers, who substantiated the concept, suggested technologies and additives to restore the integrity of polymer and cement materials. Despite active research in this area, Schlumberger is the only service company which elaborated and successfully applied the «self-healing» well cement called Futur. The authors of the article set the task of well cement modification that enables autonomous «healing» of water-conducting channels through which formation water migrates. The following materials were used in the study: polyacrylamide (PAA), water-swellable polymer (VNP V-615), sodium polyacrylate (SP), cross-linked PAA copolymers, active waterproofing mineral additives and swelling elastomers. Most of the additives have a degree of swelling of more than 150%, they effectively reduce a permeability of the cement stone, however multi-layer coating is required to control the speed of their swelling. A significant drawback of the analyzed materials was the complexity of the coating. A cross-linked AA copolymer based on anionic polycrylamide was the most effective reagent, which was easy to cover with a water-soluble shell. The cement stone with integrated agent of AA copolymer demonstrated a permeability of 0.0018 μm2 with the strength of the samples for bending at the age of 2 days equal to 8.0 MPa.
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Self-healing cements – the key to maintaining the integrity of cement sheath. Part 2
Статья научная
To control water production, it is necessary to seal the channels of 20–25 mm thickness in the cement sheath at a depth of hundreds and thousands of meters. The most promising solution is the use of self-healing cements. The concept of self-healing materials has been known since the 1980s due to the studies of Donald Jud. The most fundamental works are by Sybrand van der Zwaag, Sheba D. Bergman and Fred Wudl, Richard P. Wool, D.Y Wu, N.R. Sottos, Erin B. Murphy, Henk Jonkers, who substantiated the concept, suggested technologies and additives to restore the integrity of polymer and cement materials. Despite active research in this area, Schlumberger is the only service company which elaborated and successfully applied the «self-healing» well cement called Futur. The authors of the article set the task of well cement modification that could enable autonomous «healing» of water-conducting channels through which formation water migrates. The following materials were used in the study: polyacrylamide (PAA), water-swellable polymer (VNP V-615), sodium polyacrylate (SP), cross-linked PAA copolymers, active waterproofing mineral additives and swelling elastomers. Most of the additives have a degree of swelling of more than 150%, they effectively reduce a permeability of the cement stone, however multi-layer coating is required to control the speed of their swelling. A significant drawback of the analyzed materials was the complexity of the coating. A cross-linked AA copolymer based on anionic polycrylamide was the most effective reagent that was easily covered with a water-soluble shell. The cement stone with integrated agent of AA copolymer demonstrated a permeability of 0.0018 μm2 with the strength of the samples for bending at the age of 2 days equal to 8.0 MPa.
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Статья научная
Introduction. Currently one of the focus areas for the development of construction material science is the creation of self-cleaning concretes characterized by polydisperse multicomponent composition with the presence of nanoscale photocatalytic additives, primarily based on TiO2. These photoactive modifiers give the material a number of positive properties, including the ability to decompose atmospheric pollutants, to self-clean the surface, etc. The promising method for improving the functional characteristics of titanium oxide photocatalysts is the creation of nanostructured systems with ‘core (substrate) – shell (photocatalyst)’ architecture. Previous research results show that the final efficiency of the synthesized composite photocatalytic modifiers largely depends on the level of substrate reactivity in the cement system. The purpose of this study is to investigate the impact of three types of siliceous rocks (diatomite, trepel, and opoka) on cement stone formation processes and to identify the most effective raw materials for use as photocatalytic carriers in self-cleaning concrete compositions. Methods and materials. The methods of Kozeny-Karman, laser diffraction and X-ray fluorescence spectrometry were used to determine the specific surface area and parameters of granulometric and chemical compositions of silicite samples. The phase composition of siliceous rocks and modified cement systems was studied by X-ray powder diffractometry. Results and discussion. The main parameters of granulometric composition of diatomite, trepel and opoka were determined. The predominance of reactive modifications of free silica (47.6–78.0 wt. %), represented by amorphous opal-A or cryptocrystalline OCT-phase (opal-CT), were revealed in the structure of silicites. It was found that increasing the dosages of silica-containing additives from 0 to 10% resulted in decreased by 10–27% in the quantity of portlandite in the phase composition of cement stone aged 28 days, while the content of high-strength low-basic calcium hydrosilicates (C–S–H (I)) increased by 11–27%. Conclusion. The chemical and mineralogical composition peculiarities of silicites, as well as the nature of the impact of silica-containing modifiers on the structure formation processes of cement systems, determine the prospects of using opal-cristobalite rocks as dispersed photocatalyst carriers for self-cleaning concrete.
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Статья научная
Introduction. Recently, the term “nature-like technologies” has appeared in the everyday life of scientists and politicians, which quite deservedly include the so-called alternative energy sources (sun, wind, heat). At the same time, despite the fact that installations using these sources are “seasonal” and low concentrated, their use is rapidly and haphazardly developing, and many economists and politicians mistakenly consider them as basics, misleading business. Based on the analysis of the epistemology of the origin of the term "nature-like technologies", this article shows the groundlessness, and even the harm of the rapid and unsystematic use of wind turbines. Evidence is given of the inconsistency of the "myths" that Nature cannot cope with the compensation of the economic activity of mankind, therefore, according to Academician Sergeyev S.M., President of the Russian Academy of Sciences, "reengineering of the technosphere" is required. At the same time, modern economic science is far from taking into account in his models of the assimilation potentials of the biosphere of regions and the functions of entropy production in them, preferring to model various “cycles and modes”, as well as calculate different “coefficients” in order to predict “crises and equilibria”, without taking into account the interaction nature and society. In this connection, a scientific and technical task about determinating the “place of reengineering of the technosphere” in the structure of the life support systems of society, and, consequently, to evaluate its effectiveness. Methods, models and tools. To solve the tasks set, it is proposed to use the “retro-forecast method” of socio-economic losses from the introduction of “natural nanotechnologies”, using as “tools” the method of “spatio-temporal analysis”, model of the Leontief-Ford and adaptive taxation systems of “harm production”, the use of which in solving the problems of fire and environmental safety in the "technospheres of the regions" of the South of Russia (in road transport infrastructures, in cities and towns, in buildings and structures), proved their adequacy to the processes under study and usefulness. Results and discussion. The results of modeling the costs of efficiency of "reengineering of the technosphere" in Russia, in particular individual residential buildings, and a retro-forecast of changes in socio-economic and environmental losses during the autonomy of their resource supply (electricity, water and heat) are presented. It is shown that the production of domestic innovations in this area (“Shukhov’s” wind turbines, atmospheric water condensation devices and electric heating) will allow stopping the “total gasification” of rural settlements, as well as more economically than abroad, to implement decentralized supply of resources in Russia more than 10 million individual houses and about 40 million country houses, thus determining the “true place of alternative energy” in the structure of the Russian systems of electricity, gas, water and heat supply. Conclusion. The proposed approach allows us to determine the place of the socalled renewable energy in the structure of resource supply systems for cities and rural settlements. At the same time, it is possible that the emergence of more productive design solutions of the proposed innovations in the field of wind energy and solar panels will expand the "autonomization" to low-rise and multi-apartment buildings in regional centers and workers' settlements, instead of a major restoration of centralized engineering systems with boiler houses and mini- CHP.
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Strength and deformability of cement stone and powder-activated concrete. Part II
Статья научная
Introduction. Reinforced concrete structures in buildings and structures are subject to various loads during operation, which cause deformation and destruction. Materials and Methods. It has been shown that the strength and elastic-plastic properties of modern concretes can be broadly controlled using superplasticizers, nanoadditives, fillers, and fine aggregates. This article examines the deformation and fracture processes of cement paste and powder-activated concrete. The key characteristics of concrete deformation processes are determined using stress-strain diagrams, taking into account the downward strain curve. The concrete deformation diagram on the descending branch is fixed by the ultimate deformation, corresponding to the concrete reaching its maximum strength value, and the end point of the descending branch, corresponding to the residual strength of the concrete. Results. Complete concrete stress-strain diagrams with an extended descending section were obtained by loading specimens at a constant, decaying strain rate, resulting in a smooth decrease in stress in the specimen along the descending section. The influence of formulation factors on the key parametric points of the σ–ε diagram was studied. The influence of the W/C ratio, modifying additive, and polycarboxylate superplasticizer on the structure-forming factors for cement stone was examined. For concrete, the influence of the W/C ratio, modifying additive, polycarboxylate superplasticizer, fine filler, rheological filler, and reactive filler was examined. The resulting diagrams were analyzed for each material structure, both with an individual structure-forming factor and for powder-activated concrete as a whole. It was found that increasing the W/C ratio from 0.267 to 0.350 resulted in more elastic behavior of the material under load, a significant (4–5 times) elongation of the descending branch of the full equilibrium stressstrain diagram of hardened cement paste, and a change in the failure mechanism of the material. The specific parameters for static destruction of the sample are reduced by 12.1 times and the static J-integral Ji is reduced by 9.1 times.. It was shown that with the addition of the carboxylate superplasticizer "Melflux 1641F," the deformation pattern of the specimen under load was closer to that of cement paste obtained using normal-thickness cement paste, however, with a shorter (10 times) descending branch, indicating more brittle behavior of the specimen. The use of finely dispersed quartz also affected the nature of the deformation of the samples: their elasticity increased from 1.3 to 1.7 times, but at the same time the magnitude of ultimate deformations decreased by 20%, that is, the samples became more elastic and less deformable. Conclusion. It has been established that, with optimal component contents of cement stone and powder-activated concrete, crack resistance parameters significantly increase by 1.3 to 5.8 times, especially the static J-integral Ji, which characterizes the ductile fracture energy of the material at the crack tip, increasing due to the increased adhesion of the cement stone to the active surface of the microsilica. The curves of the complete equilibrium diagrams are approximated in sections by simple linear and quadratic functions or represented by a cubic polynomial.
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Stress-strain properties of polymer-based composite materials according to experimental evidence
Статья научная
Introduction. The use of polymer composites as structural materials for bridge superstructures represents a promising area for scientific research and development, particularly in challenging climatic and geological engineering conditions. The use of polymer composites as structural materials for bridge superstructures represents a promising area for scientific research and development, particularly in challenging climatic and geological engineering conditions. The aim of the work is to identify methods for increasing the efficiency of using polymer composite materials in bridge span structures based on the study of their physico-mechanical characteristics as part of experimental studies. Methods and materials. The relevance of this research stems from the need to develop a structurally similar model of a bridge superstructure made of polymer composite materials that meets modern stability and safety requirements, thereby facilitating infrastructure development in remote northern regions. The variety of fibers, matrix materials and reinforcement schemes used in the creation of polymer composite structures makes it possible to control characteristics such as strength, rigidity, operating temperature and other physical and mechanical properties of materials. Results and Discussion. The study included a brief overview of the components of polymer composite materials and the development of a testing program, which led to the production and testing of a batch of flat samples using domestically produced materials. Selecting the composition, adjusting the component ratios and improving the composite's macrostructure allows for optimal performance characteristics depending on the requirements. Conclusion. Tests of flat FRP samples aimed at determining the values of their physico-mechanical, strength and deformation characteristics have been carried out. The test results obtained for FRP are comparable to those of traditional structural materials. The expediency of using fiberglass in highly loaded structural elements is substantiated, which demonstrates the potential for developing a bridge superstructure design from FRP. The prospects for further research based on computational and experimental analysis of nodal connections of elements from FRP are outlined.
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Structural and heat-insulating cement-based concrete with complex glyoxal based additive
Статья научная
Introduction. The article presents the results of studies of the effect of complex additive based on glyoxal on the properties of cement-based foam concrete mix and foam concrete of natural hardening. The relevance of the study is determined by the necessity to provide the required process parameters of mixture for transportation and laying the formwork, as well as providing strength and thermal and physical characteristics of wall structures for the development of the northern regions of Russia, including the Arctic zone. It has been proposed to decrease the shrinkage deformations of the concrete mix and increase compressive strength of hardened foam concrete by affecting the cement matrix with complex modifier based on glyoxal. Materials and methods. The effect of modifying additives on the properties of the foam concrete mixture and foam concrete was studied at a W/S mixture ratio of 0.45. Research has been carried out using test methods set out in national standards. The results of the study of the effect of complex modifying additives (CMA) based on an aqueous solution of glyoxal and organic acids on the rheological and strength properties of foam concrete are presented, the regularities of the processes and the mechanism of structure formation of the modified foam concrete are determined. Results. The use of modifying additives leads to increase result in increasing the aggregative stability and reducing the plastic shrinkage of the foam concrete mix by 22–70%. In foam concrete with the complex additive LA 0.5% + Gl 0.55% the compressive strength rises from 1.96 to 2.43 MPa at the age of 28 days while maintaining the average density of D600. The thermal conductivity coefficient of foam concrete modified with various additives decreased by 5–30% compared to references. Conclusions. The obtained results of the study create in the construction industry the basis for the import substitution of modifying additives on the domestic mineral resource base and the production of effective structural and heatinsulating concretes for the development of the northern regions of Russia.
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Structural and heat-insulating foam concrete for individual monolithic housing construction
Статья научная
Introduction. The article presents the results of studies of structural and heat-insulating cement-based foam concrete for monolithic individual housing construction using porous aggregates sand and superplasticizers. The relevance of the study is to improve the technological properties of foam concrete mixtures to enhance their transportation and laying in formwork, as well as to increase the strength and thermal insulation parameters of wall materials used in individual housing construction. A synergistic effect is ensured and increased stability of the foam concrete mixture is achieved, resulting in an increase in the grade of compressive strength of foam concrete and a decrease in thermal conductivity by partially replacing quartz sand with expanded clay or slag sand in the amount of 25% by volume and introducing the superplasticizer “Steinberg MP-4”. Materials and methods. The study of foam concrete mixture and foam concrete was carried out in the accredited laboratory of TSUAB in accordance with the requirements of national standards. Results. The use of combined additives, including a superplasticizer and a mineral porous aggregate, leads to increase the grade of compressive strength of foam concrete from B1 to B2 while maintaining the average density grade D600, and also allows reducing the thermal conductivity coefficient of foam concrete to 17% compared to the basic composition. Conclusion. The developed compositions for the production of monolithic structural and heat-insulating foam concrete of natural hardening with a combined additive, including mineral porous aggregate and current plasticizers, are recommended for individual housing construction of low-rise buildings.
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Structure formation in the «clay soil – carbide sludge» dispersed system
Статья научная
Introduction. Clay soil is a multiphase, multicomponent aluminosilicate dispersed system with specific properties determined not only by its composition but also by the formation of coagulative and transition contacts (binds) between the soil particles. One of the methods of changing soil properties is the introduction of active mineral additives that promote the formation of phase contacts (binds) between soil particles as a result of the pozzolanic reaction. The effectiveness of using carbide sludge, which is a multi-tonnage lime-containing waste (the content of active calcium oxide reaches 56%) as an additive, has been proved. However, to date, the proposed mechanism of interaction in the «clay soil – carbide sludge» system is based only on the literature data and has not been experimentally verified. The purpose of this research is to study the mechanism of structure formation in the «clay soil – carbide sludge» dispersed system. Methods and materials. A soil model has been created by mixing saponite-containing material with sand, which corresponds to the composition and properties of sandy loam. The carbide sludge in the form of a suspension was selected from the sludge collector, dried to a constant mass and sieved. Microstructural analysis, differential thermal analysis (DTA), and X-ray phase analysis were used to study the mechanism of structure formation. Results and discussions. Based the results of the differential thermal analysis, there is a decrease in the intensity of the endothermic effect in the range of 460 to 470°C associated with the decomposition of calcium hydroxide in the treated sample. Additionally, an endothermic effect is observed at 750°C, which indicating the decomposition of calcium silicate hydrate. The results of differential thermal analysis are confirmed by X-ray phase analysis, which shows the presence of tobermorite group hydrosilicates in the reaction medium. The study of the microstructure of the analyzed mixtures revealed a decrease in the specific volume of pores with a diameter of 4–5 nm in the modified clay soil. This is associated with gelling from particles of new hydrate formations. Besides that, the volume of pores with a diameter of more than 6 nm increased, which indicates the process of contraction. Conclusion. The mechanism of structure formation in the «clay soil – carbide sludge» system has been established.
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Structure formation of lime composites with polysaccharide additives
Статья научная
Introduction. The research is aimed at obtaining a lime composition and coating based on it for the restoration of cultural heritage sites. Materials and methods. We used for study slaked lime (fluff) with an activity of 83%. Sunbo PC 1021 (a superplasticizer based on polycarboxylate ether), MasterGlenium 115 and Sika ViscoCrete-226 P were used as plasticizing additives. The cohesive strength of the coatings was determined by the axial tensile strength. Rheological properties were assessed by plastic strength, which was determined using a KP-3 conical plastometer. Results and discussions. It was revealed that the introduction of polysaccharide additives contributes to a sharp increase in plastic strength compared to the control composition. The additive Sika ViscoCrete-226 P has the greatest plasticizing effect. It was revealed that the qualitative mineralogical composition of lime composites is the same. However, analysis of X-ray diffraction patterns indicates an increase in the intensity of CaCO3 reflections, which indicates an increase in the carbonization front. Control samples contain higher amounts of portlandite. A slight increase in the width of the CaCO3 peaks is observed, which indicates the possible introduction of organic molecules into the calcite composition. A change in the parameters of the crystal lattice was established in samples prepared with slaked lime in the presence of polysaccharides. Conclusion. The absence of chemical interaction between lime and polysaccharides has been established. It has been shown that coatings based on lime compositions with the addition of polysaccharides are characterized by higher cohesive strength. A change in the parameters of the crystal lattice was established in samples prepared with slaked lime in the presence of polysaccharides.
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Study of flocculating effects of ozone on wastewater of woodworking enterprises
Статья научная
The sewer of woodworking enterprises in the construction industry are characterized by a high content of suspended and dissolved toxic substances, including phenol, and a high value of chemical oxygen consumption (COD). At the same time, some enterprises do not have their own local treatment facilities and need to develop their own integrated treatment systems. One of the effective methods for removing pollution is wastewater ozonation, used in three versions: flocculation with small doses of ozone (pre-ozonation) at the initial stage to remove suspended substances, oxidative ozonation and decontamination. However, methods for treating wastewater from wood processing plants using ozone have not been sufficiently studied. Therefore, we investigated the flocculating effect of ozone in the process of cleaning the effluents of the plywood-plate mill, tested the effect of the dose of ozone during flocculation in the presence of a small number of coagulants VPK-402 and Kaustamine-15 on the concentration of suspended substances, phenol and COD value. VPK-402 and Kaustamine-15 – reagents of regional production, are low-toxic and are allowed for use in the treatment of even drinking water. The results of the experiments on the pre-ozonation of wastewater showed a high efficiency of this method, which allows reducing COD by 3.8 (VPK-402) and 2.3 times (Kaustamine-15), phenol content by 2.9 (VPK-402) and 1.9 times (Kaustamine-15), suspended content by 4.0 (ВПК-402) and 3.5 times (Kaustamine-15). The use of pre-ozonation makes it possible to completely abandon flocculants in the physicochemical stage of wastewater treatment. Coagulation-flocculation can be successfully carried out with ozone and coagulant in small doses of 2–5 and 40 mg/dm3 (VPK-402) or 50 mg/dm3 (Kaustamine-15), respectively, for 5 minutes. Physicochemical indicators of water quality improved compared to treatment with coagulant alone: COD decreased by 23%, phenol content by 55%, suspended substances by 22%. The use of ozone as a flocculant in the clarification of wastewater reduces the cost of reagents, prevents secondary contamination of water, and increases the efficiency of further oxidative treatment.
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Статья научная
Introduction. This paper examines the original design of a high-temperature tubular electric heater cartridge designed for heating industrial tooling used in the production of VT6 alloy parts. The process requires maintaining stable high temperatures exceeding 1000 °C. Without proper heat treatment after welding, cracks form in the components, which can lead to subsequent failure. This becomes especially critical when the structure of the weld and base metal is highly heterogeneous, ranging from nanoscale to coarse-grained. Furthermore, undesirable thermal effects on tooling components require additional costs for cooling and monitoring. The aim of the research is to evaluate the heat transfer of the original design of electric heaters used in the production of parts from VT6 alloy. Methods and Materials. The heat transfer study of the proposed heater design was performed using the finite element method in the Ansys software package, using the Transient Thermal calculation module. To validate the calculated values, a test rig was developed that reproduced the simulation results. A qualitative analysis of the temperature fields confirmed the hypothesis of uniform operation of the proposed heater design. Results and discussion. A quantitative analysis reflected the heating conditions of the VT6 alloy. The temperature modeling results at tooling control points were experimentally confirmed, ensuring that the target temperature of 1000 °C was achieved in a localized zone. The error was ± ≈ 70 °C. The microstructure of VT6 titanium alloy samples was examined in various zones after heat treatment. Conclusion. Based on the conducted research, recommendations are proposed for selecting optimal operating conditions for high-temperature tubular electric cartridge heaters of this design, and their potential applications are described.
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