Nanotechnologies in Construction: A Scientific Internet-Journal @nanobuild-en
Статьи журнала - Nanotechnologies in Construction: A Scientific Internet-Journal
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Hydrophobization of concrete and aerated concrete by impregnation with calcium polysulfide
Статья научная
Introduction. A method for protecting concrete and aerated concrete by treatment with a calcium polysulfide-based solution is considered. The solution penetrates into the pores of the materials and, after drying, forms a water-repellent nanoscale layer, protecting the material from water penetration. This ultra-thin layer is formed as a result of the destruction of calcium polysulfide molecules while drying the impregnating solution and gives the material hydrophobic properties. The paper presents research results of the properties and composition of the forming protective layer and its effect on water penetration into the materials. Materials and methods. In the article authors present data on water penetration into the studied concrete and aerated concrete samples, the size and composition of the hydrophobic agent using laser and X-ray diffraction, ultraviolet spectroscopy, as well as using visual research methods, including electron microscopy. Results. It has been revealed that the hydrophobic surface is formed from a mixture of sulfur and calcium carbonate. It is shown that concrete and aerated concrete impregnated with a calcium polysulfide-based solution acquires pronounced water-repellent properties, expressed in contact angles corresponding to superhydrophobic surfaces. The presence of sulfur was established by ultraviolet spectroscopy, and force microscopy showed the formation of nanocomposite particles from sulfur and calcium compounds. X-ray phase analysis showed that the protective layer deposited on the surface of the materials consists of sulfur nanoparticles (65%), as well as nanoparticles of calcium compounds – vaterite (21%) and calcite (13%). Surface treatment of concrete with a sprayer leads to a decrease in water absorption from 5.4% to 3.1%, and in the case of treatment by immersion to a value of 1.5%, while the use of preliminary vacuuming before immersion of the samples allows achieving a water absorption parameter of 0.9%. It is shown that impregnation with preliminary vacuuming leads to water absorption values of less than 1%, which indicates the practical water impermeability of samples of full-scale products (concrete curbs and pipes). Discussion. It is noted that during surface treatment of aerated concrete with a sprayer, a chemically resistant superhydrophobic layer in the form of a nanocomposite is being formed, which penetrates to a depth of 3–3.5 cm, reliably protecting the material from water and chemical penetration. Surface treatment is effective in cases where objects (facades, above-ground structural elements, etc.) are exposed to water in the form of rain. Treatment of concrete products by immersion and immersion treatment with vacuuming can be carried out in harsh cases of constant water exposure (underground utilities, tunnels, manholes). Conclusions. The limitation of water penetration, and in some cases the absence of water in the pores of building materials impregnated with calcium polysulfide, indicate the preservation of substance, since water is a carrier of substances that destroy concrete and aerated concrete. Accordingly, there is no destructive effect from freezing of water in the pores of such materials as a result of the formation of a nano-sized coating of sulfur particles. Comparison of the results for aerated concrete shows that it acquires superhydrophobic properties, which indicates its excellent modification and expands the possibilities of its use. The data observed for concrete products indicate that after treatment with a calcium polysulfide-based solution, they can be used under conditions of long-term and constant exposure to water.
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Статья научная
Introduction. Approximately 20% of accidents in buildings and structures are associated with the destruction of metal structures. Nanocoatings applied to metal structures significantly improve their operational properties, but at the same time make it difficult to use traditional non-destructive testing methods that require access to the surface of the base metal. The quality of the nanocoating is controlled during its formation. To prevent the destruction of metal structures, it is necessary to identify structural heterogeneities of the base metal in micro- and sub-micron sizes, which arise in areas of increased mechanical stress concentration and transform into macrodefects leading to structural failure. Methods and tools are required to non-destructively identify the stress-strain state and damage of the base metal structure through the layer of nanocoating. Electromagnetic-acoustical (EMA) transformation, is considered promising for solving this problem. Existing EMA tools do not fully utilize the potential of EMA conversion, have insufficient sensitivity and the lack of informativity. Methods and materials. For experimental research, we selected widely used in construction structures steels. Research was conducted on the interrelationship of structural alterations in standard samples of metals and the parameters of the electro-magnetic (EMA) transducer under static and cyclic loads. Results. Load diagrams of metal samples were obtained, with accompanying photographs of microstructure in control points, along with their frequency models derived through spectral analysis of the signal from EMA transducer. Discussion. Changes in the stress-strain state of the metal and accumulation of damage in its structure result in a complex interrelated set of changes in mechanical, acoustic, and electro-physical properties, all of which are reflected in the changes in the parameters of the frequency model. Conclusion. Based on the results of the conducted research, the use of a frequency model has been proposed as an integral parameter for identifying the stress-strain state and damage of metal in the equipment. The use of an artificial neural network for analyzing frequency model parameters simplifies the process of identifying the stress-strain state and damage of metal structures and increases its reliability.
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Improving the performance characteristics of gas concrete impregnated with calcium polysulfide
Статья научная
Introduction. Impregnation with a solution based on calcium polysulfide showed excellent results in the hydrophobization of concrete, brick and shell rock due to the formation of a water-repellent coating of sulfur nanoparticles on the surface of their pores. This paper presents the data of studying the properties of aerated concrete, widespread in construction practice, which has a widely developed pore system. Materials and methods. The data on the penetration of water into the studied samples of aerated concrete using the methods of visual examination, including electron microscopy, as well as methods for measuring the water absorption and strength of the samples impregnated with a solution based on calcium polysulfide are presented. Results. It is shown that aerated concrete impregnated with calcium polysulfide, despite the developed pore system, acquires pronounced water-repellent properties. It was found that the optimal processing time is 20 minutes, and the increase in the water-repellent properties of aerated concrete depends on the density of the impregnating solution. As a result of impregnation of aerated concrete by immersion in a solution with a density of 1.16 g/cm3, a decrease in 3.7 times occurs, and when treated with a solution with a density of 1.25 g/cm3, it decreases 6.8 times and becomes equal to 6%. For samples processed with the use of vacuum, in the case of processing a solution with a density of 1.16 g/cm3, water absorption decreases by 7.9 times, and when processing with a solution using vacuum, it decreases 19.8 times, while the compressive strength increases by 1.7 once. Samples of aerated concrete, treated with a polysulfide-based solution with a brush, showed that in this case, water absorption in the sprinkling mode decreases to values of 1.5–2.0%. Discussion. It is noted that during the surface treatment of aerated concrete, a chemically resistant, water-repellent layer 3–3.5 cm thick is formed, which reliably protects the material from the penetration of water and chemicals. The results of the performed experiments give reason to believe that on the surface of the pores of aerated concrete treated with a solution based on calcium polysulfide, as well as on the surface of the pores of previously investigated materials, a nanosized coating is formed of sulfur particles that hydrophobic aerated concrete. Conclusions. Comparison of the results for aerated concrete with excellent data for concrete, brick, shell rock shows that the efficiency for aerated concrete is no less and allows us to recommend the specified solution for long-term protection of the surface of aerated concrete walls
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