Nanotechnologies in Construction: A Scientific Internet-Journal @nanobuild-en
Journal articles - Nanotechnologies in Construction: A Scientific Internet-Journal
All articles: 636
Experimental study of heat-insulating aerogel-based nanomaterials
Scientific article
Research and synthesis of materials with fundamentally new properties play the key role in the development of modern science and technology. The most perspective materials are considered to be aerogels: nanostructured materials with many useful properties. The mesoporous structure of airgels determines their widespread use, both in industry and in science. Over the past few decades, nanostructured silica-based material has become an integral part of many industry segments: thermal and noise insulation, electronics, chemistry, medicine, environmental protection, industrial and fire safety, energy, aerospace industry, consumer goods and military technology. The article discusses an experimental study of the heat-shielding properties of a heat-insulating material based on silicon oxide airgel – Insuflex. This is a flexible rolled material used for thermal insulation of elements of technological installations, pipelines, valves and control valves. Using the method of ordinal statistics, the exponential dependence of the coefficient of thermal conductivity of the airgel on the average temperature of the sample is determined. The results obtained indicate the possibility of energy-efficient use of the material in heat supply and heat consumption systems.
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Scientific article
Introduction. The evolution of the construction industry in its current stage calls for the alteration of traditional building materials through the incorporation of nano- and fine-dispersed additives. These additions confer new, unique attributes to cement-based construction materials, enabling control over structure formation processes. Consequently, this allows for the creation of materials with specifically defined characteristics. Additives can be introduced into the cement composite during the joint grinding with clinker minerals, as a component of dry building mixture, or in the form of a suspension instead of mixing water. Therefore, it is essential to obtain fine particles suspensions resistant to aggregation and sedimentation. Thus, the purpose of this study is to obtain stabilized suspensions of bismuth titanate fine particles for cement systems and to study the properties of modified cement stone. Materials and methods. The purpose of this work was to establish the optimal concentration of polycarboxylate plasticizer in industrial water, necessary for the stabilization of fine bismuth titanate suspensions using surface tension and conductometric determination methods, the sedimentation stability of the obtained suspensions and the effect of ultrasonic exposure, as well as the physical and mechanical characteristics of cement stone modified with the obtained suspensions. Results and discussion. In order to establish the optimal concentration of the plasticizer necessary to obtain stable suspensions of bismuth titanate particles, the critical micelle concentration (CMC) for the plasticizer was determined with tap water as the dispersed medium. The CMC value was 1.3 g/l. If the concentration exceeds CMC, the process of micelle formation begins. In the micellar form, the plasticizer no longer provides stabilizing effect on the additive particles, therefore, the concentration of the plasticizer should be lower than the CMC. It was also found that ultrasound exposure increases the sedimentation stability of suspensions. The resulting stabilized suspensions were used instead of mixing water to obtain modified cement stone samples. There is an increase in the compressive strength of cement stone samples obtained after the introduction of fine bismuth titanate into the cement composite in the form of water suspensions stabilized by ultrasonic treatment with concentrations of 10, 30 and 50 g/l. The increase in compressive strength of modified samples compared to reference sample was from 24 to 33 MPa at first day age (by 13, 25 and 38% respectively), and from 80 to 93 MPa at 28 days age (by 4, 9 and 16%). Compressive strength of samples modified with bismuth titanate suspensions after ultrasonication compared to reference sample with plasticizer increased mostly at the first and third days age: from 29 to 42 MPa (by 31, 38 and 45%) and from 53 to 70 MPa (by 28, 30 and 32%) respectively. Conclusion. As a result of the research carried out in this study, the Critical Micelle Concentration (CMC) of a polycarboxylate plasticizer was determined, optimal for stabilizing fine-dispersed additive of bismuth titanate for cement systems, the effectiveness of ultrasonic treatment to achieve sedimentation stability of the obtained suspensions of the additive was confirmed, an increase in the strength characteristics of modified cement stone samples was established both in the initial hardening periods and at 28 days age. The results allow to consider a cement composite with fine bismuth titanate as a basis for obtaining building materials of new generation.
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Fabrication of W nanodot and Nitrogen Co-decorated Carbon Skeleton for Hydrogen Evolution Reaction
Scientific article
Metal dots-nitrogen-carbon catalysts have become a hot topic in recent years because of special coordination environment. Herein, for the study the W nanodots and nitrogen co-decorated carbon skeleton (W@NC) was prepared for hydrogen evolution reaction (HER). In particular, NaCl templates not only restrict the growth of nanodots, but also improve the purity of phase. By optimizing the feeding ratio of ammonium metatungstate, W nanodots (the size is about 1.2 ± 0.6 nm) dispersed well on N-doped C skeleton, and this special structure could effectively promote electron transfer and ion diffusion during HER process. As a result, the optimized W@NC hybrids exhibited excellent HER performance in alkaline media with a rather low over-potential (228 mV at 10 mA cm–2) and outstanding durability over 10 h.
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Scientific article
Introduction. Cable-stayed structures occupy a special place in the modern construction industry due to their unique characteristics and wide application possibilities. They allow to convey architectural expression of large span buildings and to ensure high efficiency and minimal weight of structures. Systems with cross arranged cables and arch cable-stayed combined solutions, including "tensegrity" structures, are of particular interest nowadays. Materials and methods. The study is based on an analysis of regulatory documents, scientific and technical literature reflecting the installation of cable-stayed structures, including requirements for the quality of materials, installation processes and structural reliability control. A comparative analysis of various types of cable-stayed systems (parallel, radial and cross arranged) is carried out, and examples of their practical application are considered. Results and discussion. Based on the analysis of regulatory documents and scientific and technical literature review, cable-stayed structures were classified into various categories, reflecting their design features and applications. The advantages and disadvantages of each type of cable-stayed coverings were analyze as well as progressive methods of installations were revealed. Conclusion. The use of cable-stayed coverings, especially with cross-arranged cables and "tensegrity" structures are a promising direction in modern construction. These structures allow to create complex architectural solutions, creating lightweight, aesthetically attractive coverings. At the same time, the design and installation of cable-stayed structures require consideration of all their disadvantages and limitations to ensure the strength and durability of buildings and structures.
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Fillers for polymer composite materials
Scientific article
Introduction. For the production of building products made of PVC, compositions are used that, along with the polymer, include additives: plasticizers, stabilizers, modifiers. This leads to a decrease in the chlorine content in the composition and increases the flammability of the productitself. Therefore, nanoparticles of various fillers are added into the compositions. Fillers inPVC compositions (more often inorganic, less often organic substances) are solid additives that differ from the polymer matrix in chemical composition and structure.In most cases, the main function of fillers is to reduce flammability and cut costs of the products obtained, in some cases they serve to impart or improve the following properties: reducing plasticizer absorption, changing in dielectric properties, increasing rigidity and hardness, reducing noise transmission, reducing toxicity of combustion products. Main part. Fillers are classified according to various criteria. According to the state of aggregation, they are divided into gaseous, liquid and solid. By their nature, they are divided into organic and inorganic; according to the source of receipt – reinforcing, strengthening, reinforcing, neutral; bythe size, particle shape and structure – into 4 main types: dispersed (powder); fibrous (fibers, threads, bundles, etc.); sheet (film) with a given structure (fabrics, paper, tapes, sheets, films, nets); volumetric (framework) with a continuous three-dimensional structure (bulk fabrics, felt, skeletal and porous frameworks). The most commonly used solid fillers, which are also called dispersed. The introduction of dispersed fillers into polymer composite materials (PCM) is more appropriate for creating mass-produced materials, more technologically advanced, with a low level of strength characteristics. Dispersed fillers are introduced into thermoplastics with high fracture energy to reduce their cost, increase stiffness and compressive strength, and improve their technological characteristics during processing. At the same time, their tensile strength and impact strength decrease due to reduction in the proportion of polymer in the filled composition. The introduction of solid and hard particles leads to an increase in the elastic modulus (E); and soft, elastic or gaseous fillers – to its decrease. According to the mechanism of action, dispersed fillers can be divided into inert ones, which do not affect the properties of the matrix and are introduced into its composition to reduce the cost of the composition, and active ones. Dispersed fillers are divided into mineral, organic and metal. The commonest of those are minerals. Conclusion. Thus, at present, there are a large number of substances and materials used as fillers and making it possible to obtain PCM with low shrinkage and shape stability of products, high mechanical properties and the necessary set of special properties. Due to fillers, PCM can compete with other materials such as glass, ceramics and even metal in most areas of human activity.
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Fine-grained concrete with recycled polyvinyl chloride fiber
Scientific article
Introduction. Polymer fiber is widely used in the production of structural concrete components, in shotcrete for tunnels, concrete slabs, blast-resistant concrete, and solid road pavements. Recently, numerous studies have been devoted to the use of fibers derived from recycled polymers in fiber-reinforced concrete. Most of these studies address the effect of fiber on the compressive, flexural and tensile strength properties of concrete. Fibers of various lengths based on nylon, aramid, polyester, polyethylene terephthalate, polypropylene, polyvinyl alcohol, and polyvinyl chloride are used in concrete. However, the insufficient amount of data, or its complete absence, regarding the effect on the properties of concrete with polymer fibers based on recycled PVC necessitates further research, which is particularly relevant given the generation of significant volumes of PVC waste during the production of plastic windows. Materials and methods. The electron microscopy and thermomechanical analyses (TMA) were used to investigate the properties of PVC-based polymer fibers. The effect of the polymer fiber on properties of fine-grained concrete mixtures and hardened concrete, the standard testing methods were used, including the determination of workability by flow table test diameter on a vibrating plate, the average density of concrete mixtures and concrete, and tensile strength under flexural and compressive loading. Results. It is shown the positive effect of the grinding process determined by electron microscopy, which produces a rough surface and fibers of 2.5–4 cm in length, 1.75–4 mm in width, and 0.2–0.3 mm in thickness. It is established that the PVC-based fiber belongs to amorphous polymers of linear structure with a crystallization temperature of 86.4 °C and a destruction temperature of 208.91 °C. It is determined that the optimal fiber content in concrete does not impair the workability of concrete mixtures or affect their cohesion. It is shown that the addition of PVC-based fiber to fine-grained concrete in amount up to 1.2% increases the concrete density of 1.6 times, increases flexural tensile strength by 22%, and has no effect on compressive strength. Conclusion. Conducted studies confirm the feasibility of using polyvinyl chloride-based fiber as a component of fine-grained concretes. However, there is the lack of sufficient data of fiber introduction method in concrete which requires additional scientific research to prevent fiber clumping, establish its compatibility with chemical additives added to the concrete mixture and the effect of curing conditions.
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Scientific article
Introduction. This article presents the results of the research works on formation of building gypsum plaster porous structure with the use of recovered anhydrite raw materials and chemical additives, and describes a method for production of wall materials. The relevance of this paper is stipulated by the need to expand the range and increase the manufacture of heat-insulating and structural-heat-insulating products based on gypsum binders and local mineral raw materials, as well as the development of technologies to ensure the production of gypsum materials with improved performance. The authors proposed certain methods for forming the porous structure of building gypsum plaster and improving its performance in terms of porosity and thermal conductivity through the use of modified recovered raw materials and chemical additives of calcium chloride and sodium carbonate. Materials and methods. The study of the effect of modifying additives on the properties of the mixture was carried out using gypsum paste of normal consistency (NC = 55%). The preparation of samples and testing were performed according to the methods specified in the national standards with the use of porous additives of calcium carbonate, fluoroanhydrite and chemical additives for the rheological properties of the mixture, average density and strength of the samples, the patterns and mechanism of the processes of gypsum stone structure formation were established. Results. The application of fluoroanhydrite modified in the disintegrator with an equimolar amount of calcium carbonate leads to a decrease in the average density of the samples to 40% with evenly distributed pores. The analysis of the microstructure of heat-insulating material samples with a density of 550 kg/m3 showed that the average diameter of micropores is 0.45 mm, while the thermal conductivity of samples with complex chemical additives has the thermal conductivity coefficient of 0.25 W/m°C, which is 30% lower than the thermal conductivity of samples without complex additives. Conclusions. The results obtained create the basis for using recovery raw materials and domestic modifying additives as a pore-forming agent, which allow regulating the structure of gypsum stone in order to produce effective wall materials.
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Framed composites based on liquid glass roller molding
Scientific article
Introduction. The work is devoted to the experimental and theoretical study of the technology and properties of composite materials based on soluble glass. The prospects for the manufacture of floor coverings and other products using frame technology and roller molding are shown. Materials and methods. The frame technology for the manufacture of building composites consists in the first stage of gluing grains of large filler to each other according to the shape of the future product, and in the second stage – filling the voids of the hardened porous frame with a solution component. Roller molding is used both when performing the operation of compacting the frame and when filling its voids with a matrix. The purpose of the work was to conduct an experimental and theoretical study of the manufacturing technology, physical and mechanical properties and chemical and biological stability of composites based on liquid glass. To analyze the mechanism of the stress-strain state of compacted mixtures, a rheological model is considered, in which the mechanical characteristics of the medium are determined by fundamental properties: viscosity, elasticity and plasticity. When conducting experimental studies, sodium liquid glass was used, sodium fluorosilicate was the hardener, and powders based on mineral and organic materials served as fillers. Furyl alcohol was used as a polymer additive. Results. The optimization of the compositions of frames and matrices for framed concretes was performed. The studies were carried out using mathematical methods of experiment planning. Three-factor matrices consisting of 10 experiments were considered. Discussion. The best strength characteristics are demonstrated by matrix compositions that include filler mixtures of quartz sand, pyrite cinders and diatomite, and the greatest strength of the framework is achieved by including granules of 5–10 mm in the composition – 7%, 2.5–5 mm – 23%, 1.25–2,5 – 70%. The chemical and biological resistance of composites on silicate and polymer silicate binders was studied. Chemical resistance was determined in water, aqueous solutions of caustic soda, technological environments of soft drink factories, and biological resistance – in a standard environment of mycelial fungi. It was found that composites containing modifying additives are characterized by higher resistance rates. Conclusion. Scientific and technological foundations for managing the structure and properties of liquid glass framed composites of vibration-free roller molding have been developed, as well as scientifically based solutions for improving the compositions of frame and matrix mixtures by regulating the processes of chemical interaction between components, the grain composition of fillers and aggregates, and the introduction of special additives to ensure increased strength, chemical and biological resistance of concrete.
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Scientific article
Introduction. The aim of the work is to determine the influence of the structure of the filter materials formed as a result of modification of the surface layer on their water permeability and the size of trapped solid particles. Materials and methods. The non-woven fabrics from a mixture of polyethylene-terephthalate (PET) (70 wt.%) and bicomponent fibers (BCF) of the coreshell structure were used as objects of the study. The non-woven fabrics were obtained by mechanically forming the canvas with its subsequent hardening by needle punching. The resulting materials were modified by heat treatment. The water transfer in the modified materials was determined by the permeability coefficient. The filtration efficiency was determined by the number of trapped particles of a certain size. Results and discussion. The needle-punched non-woven fabrics without additional heat treatment are not suitable for water filtration. The proposed method of thermal and deformation-thermal modification provides the production of gradient materials with a controlled thickness of the nanoscale surface layer. Although a decrease in water permeability is observed, the modified material traps solid particles with a smaller (compared to unmodified ~ 20 μm) equivalent diameter of 2–4 μm, which is sufficient to prepare water for use in steam generators and in the production of building materials. Conclusion. The optimal parameters of deformation-heat treatment for obtaining the high-effective filtration non-woven materials were established: the temperature – 180оC, the processing speed – 3.5 m/min.
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