Статьи журнала - Nanotechnologies in Construction: A Scientific Internet-Journal
Все статьи: 496
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-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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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 study aims to carry out comprehensive comparative research of thermal degradation and inflammation parameters of timber covered with fire resistant biological flame retardants of different chemical composition. We also looked at the efficiency and the action mechanism of the latter. Materials and methods. As the objects of research, the means were selected – phosphorase-containing water-soluble compounds of the nanoscale series, complex biocides and special bioplasticizers (Agent 1) and water-soluble nanoscale diammonium hydrophosphate (Agent 2) applied to pine wood by surface treatment and deep impregnation methods. Results and discussion. Thermogravimetric studies of wood treated with flame retardants have shown that its decomposition occurs in the following temperature ranges: 30–150°C – the process of loss of moisture by wood; 150–400°C – the effect of protective mechanisms of the compositions, as well as the process of decomposition of the main components of wood (hemicellulose, cellulose, lignin) and the formation of a coke layer; 400–800°C – the process of gradual burnout of the coke layer taking into account its thermophysical characteristics up to the ash residue. It has been established that both flame retardants act by the mechanism of catalytic dehydration and reduce the rate of decomposition of wood from 29 to 10%/min. Conclusion. The features of the thermal decomposition of wood protected by two different chemical composition and method of its processing means are determined. The parameters of the flammability of pine wood treated with fire-protective compounds by surface and deep impregnation were obtained, which indicate their high efficiency, which is confirmed by the values of the coke residue at 400°C, the nature of DTG peaks and DSC curves. The possibility of using the obtained materials from wood for interior decoration and cladding of facades of buildings that meet regulatory requirements for their safe use is shown.
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Study of the effect of additives on biodegradation of PVC materials
Статья научная
Modern operating conditions of polyvinyl chloride (PVC) materials impose increased requirements for the additives used. Intensification of processing and expansion of PVC application areas, as well as providing a wide variety of its performance characteristics, are associated to a large extent with the successful solution of the problem of creating effective plasticizers. Therefore, when developing formulations of PVC plasticates, it is important to obtain and select plasticizers that meet modern high requirements for operation and environmental safety. One of the modern approaches to creating materials that can be destroyed in natural conditions is based on the use of additives that increase the ability of polymer materials to biodegrade. This paper presents the results of developing a PVC composition with increased biodegradation. For this purpose, a mixture of plasticizers was used: dibutoxyethyl phthalate (DBOEP) with a degree of ethoxylation of 1.5 and dibutoxyethyl adipate (DBOEA) with a degree of ethoxylation of 1.5. The results of testing samples of obtained PVC compositions for biodegradation are presented. It is shown that partial replacement of a phthalate plasticizer with a non-toxic biodegradable dibutoxyethyl adipate makes it possible to obtain PVC compositions with increased biodegradation, while maintaining excellent performance properties.
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Study of the kinetics structure formation of cement dispersed systems. Part I
Статья научная
Introduction. The study of the kinetics structure formation is rarely the subject of a careful study. Although it is important for materials used to create elements of building structures, energy elements, thermoelements and materials for other purposes. The article proposes refinements of the methodology for determining the parameters of the kinetics structure formation of cement composites, including modified compositions. Methods and materials. The structure formation of cement systems with plasticizers, microsized mineral additives (hydrosilicates of barium, copper and zinc) and nanosized particles of zinc hydrosilicates has been studied. Results and discussion. It is proposed to single out two stages of initial structure formation: the stage of setting the cement paste and the stage of hardening. The selection of the setting stage is connected with the natural laws of the development of natural systems, namely, the initial formation of a structural grid obeys an exponential law. Moment of time when a deviation from this law is observed is the time of occurrence of spatial and/or prescription difficulties that hinder the exponential development of the system. Conclusions. A strong negative relationship between the parameters φ and β of the equation H(t) = a exp(φt β) has been established. These parameters characterize the rate of structure formation at the setting stage (parameter φ) and the density of the structure (parameter β or the internal dimension Di, 0 associated with it). The presence of such a negative relationship indicates the inadvisability of accelerating the processes of structure formation at the stage of setting. This is supported by a strong positive relationship between the period of initial structure formation t0, s1 and the strength of the material R28.
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Study of the kinetics structure formation of cement dispersed systems. Part II
Статья научная
Introduction. The study of the kinetics structure formation is rarely the subject of a careful study. Although it is important for materials used to create elements of building structures, energy elements, thermoelements and materials for other purposes. The article proposes refinements of the methodology for determining the parameters of the kinetics structure formation of cement composites, including modified compositions. Methods and materials. The structure formation of cement systems with plasticizers, microsized mineral additives (hydrosilicates of barium, copper, iron and zinc) and nanosized particles of zinc hydrosilicates has been studied. Results and discussion. It is proposed to single out two stages of initial structure formation: the stage of setting the cement paste and the stage of hardening. It was found that the strength of the material at the stage of hardening should be influenced by an additional factor, depending on the type of the introduced substance. A strong negative relationship between the parameters α and n of the equation R(t) = Rmax(1–eatn) at the hardening stage was confirmed. The trends identified at the setting stage also demonstrated, namely: an increase in the rate of structure formation leading to the formation of a less dense structure. Conclusions. An analysis of the change in the value of the internal dimension of the system during the transition from the stage of setting to the stage of hardening made it possible to identify two trajectories of the system development. The first trajectory appears only by combining the elements of the structure (trajectory No. 1). Preservation of the characteristic dimensions of structural elements, but an increase in the proportion of elements with small dimensions (when the conditions that prevent the combination of elements of the structure are realized) describes the second trajectory (trajectory No. 2). The implementation of trajectory No. 2 is typical for compositions which the structure formation of cement stone is carried out in the presence of Melment F15G plasticizer or microsized particles of copper or zinc. For other studied compositions, structure formation is proceeding with the enlargement of structural elements.
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Study of the properties of nanomaterials
Статья научная
To improve physical and mechanical properties of pavements new materials with nanomodified additives are being actively developed. The authors are investigating the properties of road petroleum bitumen with nanomaterial Taunit. At the initial stage, oil bitumen was heated to 100о C. Then carbon nanomaterial «Taunit» was added. After that, the mixture was stirred in an ultrasonic homogenizer until even distribution of the carbon nanomaterial in the total volume. The process of cooling of the final structure was carried out until the end of the crystallization process. Then, the specimens are exposed to tension and strength tests with a constant rate of deformation or loading until the moment of rupture on the testing machines. Mixing with other components of asphalt concrete in the standard mode follows the nanomodification of the bituminous mixture. Under increased temperatures the bitumen mixture keeps properties of an effective binder. It was revealed that the modified carbon bitumen has good thermal properties, namely, it has a higher softening temperature (Δt is in the range from 6 to 10ºС). The indicator, which indirectly characterizes the degree of hardness of bitumen solutions, is within the limits of GOST standards, decreases by 15–20%.
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Статья научная
Introduction. As part of the solution for the problem of creating a new class of materials for building additive technologies, cement composites reinforced with high-strength fiber, this work presents the results of experimental studies of the strength of the adhesive bonding between cement matrices and reinforcing fibers with different chemical compositions, diameters, and tensile strength. Materials and methods. Rheological properties of cement systems were studied using shear and squeeze rheometry, the method of micromechanical testing for determining the strength of the adhesive bonding “cement matrix – reinforcing fiber” based on the pull-out test, which involves pulling out the fiber from the cement matrix layer; after the pull-out test for all the studied systems, the microstructure of the contact surface “cement matrix – reinforcing fiber” was assessed using a Thermo Scientific™ Phenom ™ Desktop SEM scanning electron microscope; the compressive strength of hardened cement paste-samples was determined using an INSTRON Sates 1500HDS testing machine. Results and discussions. It was established that the combination of strength characteristics of matrices, fibers, and adhesive strength at their interface allowed securing the required strength characteristics of reinforced construction composites. In the “cement matrix – carbon fiber” systems, the value of adhesive strength was 9 – 11 MPa; in the “cement matrix – steel wire” systems, the value of adhesive strength was 3 – 4 MPa. Conclusions. Matrices with viscosity modifiers containing nano- and micro-sized particles of SiO2 (complex nano-sized additive and metakaolin) are reasonable options for combinations of the “cement matrix – reinforcing fiber” components. Carbon fiber and steel wire are recommended to be used as reinforcing fibers.
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Study of thermal effect based on liquid crystal nanoparticles
Статья научная
Introduction. Currently, the development of composite systems doped with nanoparticles and based on liquid crystal (LC) media is being actively pursued. The latter, having unique properties, can be used to improve various LC devices. For this purpose, it is very important to investigate the mechanism of change in the properties of liquid crystal systems from the size and concentration of nanoparticles. Recently, a sufficient number of methods have been applied to measure the flow of liquid or gas based on different physical principles. Information about the average mass flow rate of a liquid or gas can be obtained by a measurement method based on steady-state heat injection into the flow. The average flow velocity can be measured by electromagnetic and ultrasonic sensors, while the average volume flow rate can be measured by hydrodynamic (aerodynamic) as well as mechanical turbine methods. In heat transfer and mass transfer, convective motion in a fluid medium plays an important role in the vast majority of natural phenomena and technological processes. Many processes of convective mass transfer and heat transfer in chemical, petrochemical, construction, nuclear and other industries are carried out in heat pipes. Up to the present time the question about efficiency of heat pipes application with bodies from composite materials also remains open. In the presented work the following objectives were set: to assemble an experimental setup to study the thermal effect (flow), to conduct studies of temperature change on the surface of the conductor of the compound based on nanoparticles of liquid crystals and viscosity of liquid crystals from the concentration of nanoparticles. Methods and Materials. In this experimental work, a heat flux acts in the region of the outer boundary of the conductor. Note that the redistribution of the thermal field is influenced by such processes as heat conduction and heat transfer. To observe the thermal effect, compounds based on liquid crystal nanoparticles were used. Nanostructured liquid crystal systems have a unique property as fluidity inherent in ordinary liquids. For opaque conductor walls, a method for determining the direction of heat flow is proposed. Earlier experimental studies have shown that temperature measurement is possible only by pyrometric method. Therefore, the redistribution of temperature change on the conductor flow surface was recorded using an optical pyrometer that perceives thermal (infrared) radiation. In this work, a compound based on liquid crystal nanoparticles, namely with the addition of cholesteryloleate, was used as a base. Results and discussion. In the course of the study, temperature dependences in the heat flow zone of the conductor in the absence and in the presence of liquid motion were experimentally obtained. Dependences of temperature change on the surface of the conductor with compounds based on nanoparticles of liquid crystals have been measured. Inhomogeneous redistribution of the thermal field is shown. The results of the study of the dependence of the viscosity of nematic liquid crystals on the concentration of nanoparticles are presented. Conclusion. The above data show that the thermal effect on the surface is not uniformly distributed. For visualization of the thermal effect, compounds based on nanoparticles of liquid crystals turned out to be more effective. A technique has been developed to determine the direction and calculate mathematically the magnitude of the liquid heat flux in the opaque conductor flow. It should be noted that the viscosity of liquid crystals changes when nanoparticles are coupled.
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