Nanotechnologies in Construction: A Scientific Internet-Journal @nanobuild-en
Journal articles - Nanotechnologies in Construction: A Scientific Internet-Journal
All articles: 652
Scientific article
Metal nanocrystals exhibit unique properties due to their high surface-to-volume ratio and have great potential for applications in the fields of electronics, magnetics, optics and catalysis. However, their high specific surface area leads to easy coarsening in operation, which may greatly degrade their performances, especially when they are exposed to various chemical environments or at high temperatures. Therefore, the direct visualization of nanocrystals' structural evolution when they are coarsening is crucial to gain insight into the mechanism and develop more effective means to improve the size stability of nanocrystals. In this work, we investigated the structural evolution of Pt nanocrystals with sizes of ~ 4 nm on SiNx film in both oxidizing and reducing atmospheres at a moderate temperature (300оС) in the aberration-corrected environmental transmission electron microscopy (ETEM). The sizes of nanocrystals remain almost unchanged when annealed in the oxygen atmosphere with volatile PtOx formation on the surface, hindering nanocrystals sintering and leading to Pt loss. On the other hand, obvious coarsening of nanocrystals resulting from Ostwald-ripening and nanocrystal migration and coalescence was observed in the reducing atmosphere. Our findings reveal the dynamic structural evolution of nanocrystals in different atmospheres and provide possible ways to improve the size stability of nanocrystals.
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Increasing the radioshielding properties of construction materials in the microwave range
Scientific article
Introduction. The intensive development of technology in the modern world is accompanied by the origin of new types of manmade hazards, one of which is microwave radiation. Despite the considerable range of protective materials, not all of them are suitable for construction purposes. The main obstacle to their use is their high cost, and integrating them into the main types of wall construction materials would require significant changes to their production processes. The most practical and reasonable way to solve the issue is to introduce special additives into concretes and mortars traditionally used for the production of building products. The paper examines the effect of additives of fine-dispersed black carbon and aluminum powder in the composition of cement and gypsum matrices on radio shielding properties in the frequency range 1800–2800 MHz. Materials and methods. Black carbon powder was added to cement and gypsum paste in dosages of 0, 2.5, 5%, aluminum powder was added to gypsum paste in dosages of 0, 2.5, 5%. Superabsorbent polymers pre-saturated with water have been studied. Radio shielding properties have been studied on a designed experimental laboratory installation using a vector circuit analyzer NanoVNA. Results and discussion. The influence of black carbon and aluminum powder additives on the strength and microwave protective properties of gypsum and cement stone is considered. It is found that the addition of black carbon in an amount of up to 3–3.5% of the cement weight shows a neutral effect on the strength of cement stone, providing a decrease in the signal level of about 50% (–6 dB) observed in the ranges 1800–2100 MHz and 2300–2650 MHz, which makes this additive promising for solving the highlighted task. When additives are introduced into the gypsum matrix, the addition of black carbon reduces the radiation level to 60% (–8 dB), and aluminum powder to 69% (–10 dB) in a dosage of no more than 5% of the mass fraction of the binder on samples with a thickness of 3 cm. However, the additives considered have a noticeable negative effect on the strength characteristics of gypsum stone, which allows recommending the use of only black carbon in an amount of no more than 2.5% to obtain products that do not require high strength. Conclusion. The problems of creating construction materials to reduce the level of microwave radiation in the studied frequency range are outlined. Data have been obtained on increasing the shielding ability of cement and gypsum binders with the use of additives.
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Influence of a nanostructural modifier from automobile tires on consumer properties of bitumen
Scientific article
Introduction. Used tire rubber cracking with organic solvents leads to rubber devulcanization and dispersion of the material to nanosized particles. The process can be carried out in a flow reactor. The obtained nanomodifiers are compatible with bitumen and predictably change the bituminous binder technical characteristics. Various practical solutions have been proposed for the use of the resulting modified bituminous binders in the road construction and strengthening soil foundations. Methods and materials. It has been proposed to use a method of joint cracking of rubber with organic solvents to obtain a nanostructured modifier of bitumen. The obtained nanostructural modifier has been studied by the methods of analyzing the sizes of nanoparticles and solubility in toluene. For the bituminous binders obtained with the use of nanomodifiers, standard characteristics for bitumen, such as needle penetration depth, softening temperature, brittleness temperature and extensibility have been determined. Results and discussion. It is established that during the proposed process, a nanostructural modifier compatible with bitumen is formed. It is shown that the addition of a nanomodifier to bitumen makes it possible to purposefully change the properties of the resulting bitumen binder, improve the consumer properties of the bitumen binder and expand its application areas. It is proposed to use the obtained product as a component of waterproofing mastics for waterproofing the underground parts of buildings and structures. Conclusion. Joint cracking of rubber with organic solvents in a flow reactor allows obtaining a nanostructural modifier compatible with bitumen. The resulting product has improved properties compared to the original bitumen, which expands its scope of application. It is proposed to use the resulting product for the manufacture of waterproofing mastics. The proposed technical solutions make it possible to reduce the environmental load of automobile tires wastes.
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Scientific article
Introduction. We studied the effect of nanosized silicon dioxide (SiO2) on the structural and technological characteristics of nanomodified cement compositions introduced together with activated mixing water. Materials and research methods. Activation of mixing water was carried out by means of magnetic field and ultrasonic action. For investigation the capability to maintain their properties for a long time, the stability of silica suspensions in activated water was studied. For finding out the effect of activated silica suspensions on the structure and properties of composite materials based on cement, the physical and mechanical properties of the studied compositions were explored. X-ray and differential thermal analysis of the hardened activated nanomodified cement paste were also carried out. Results and discussion. The positive role of the suspension of silicon dioxide in activated water was associated with a decrease in the microheterogeneity of the hardened cement paste, ensuring the stability of its physical and mechanical characteristics. Based on the above mentioned observations, a mechanism was proposed for more efficient incorporation of nanosized silicon dioxide into cement hydration processes both due to chemisorption with Ca(OH)2 in the hardening cement paste and due to the topological effect of nanoparticle localization in defects and ultramicrovoids of a crystallizing disperse system. Conclusion. The results show that suspensions of silica in activated water can maintain their properties for a long time. Graphical dependencies are shown, indicating the effectiveness of the use of activated silica suspensions in the production of cement composites. This quality makes it possible to obtain repair compounds with the required properties during construction work for various purposes.
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Scientific article
Introduction. This study is part of a broader investigation into the phenomenon of delayed ettringite formation (DEF) in concrete and its consequences on the durability of concrete–mortar systems. The objective of the research is to analyze the influence of the initial thermal conditions of fresh concrete on the development of internal sulfate reaction (ISR), the mechanical properties of concrete, and the behavior of mortar applied to the surface after hardening. Materials and Methods. Three concrete mixtures, designated BP1, BP2, and BP3, were produced and subjected to DEF testing on cubic specimens, including continuous temperature monitoring. The temperature of fresh concrete was intentionally varied in order to evaluate its influence. The experimental program was carried out in Africa, specifically in Benin. Compressive and tensile strength tests were performed. After verifying that the concrete was suitable, mortar was applied to the concrete surface. The behavior of the mortar was then monitored over a period of 90 days through visual observation of the mortar surface. It was particularly interesting to observe the evolution of the mortar surface over time. Results and Discussion. The results has shown that for concretes BP1 and BP2, when the initial temperature was below 35 °C, the thermal behavior during the DEF test was stable, and the maximum temperature did not exceed 80 °C. Under such conditions, appropriate mechanical properties and a uniform coating of mortar were obtained without any visible cracking or surface damage. Nevertheless, for concrete BP3 with initial temperature higher than 35 °C, the thermal behavior became unstable, but the maximum temperature remained lower than the critical one. It was observed that this instability negatively affected the mechanical properties and reduced the durability performance of the material. Conclusion. The control of the initial thermal conditions of fresh concrete is a key parameter for limiting the development of DEF, preserving the mechanical properties of concrete, and ensuring the durability of applied mortars. In particular, the initial temperature of fresh concrete should not exceed 35 °C, since higher temperatures may promote the development of internal sulfate reaction (ISR) within the concrete itself.
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Influence of high-dispersive powder mixture of WC and TiC on the composite materials properties
Scientific article
Introduction. The purpose of the research is to study the effect of a high-dispersive powder mixture of WC, TiC, obtained from recycling of hard-alloy manufactured articles from TK group (titanium-tungsten alloys), on the change in the structural and physical and mechanical properties of cement materials. Materials and research methods. WC, TiC Powder (particle size 20–150 nm, agglomerates 300 nm – 1.5 μm) was added to the cement mortar by partial replacement of cement in various concentrations of 0%, 1%, 2%, 3%, 4%, 5% by mass. The basic physical and mechanical properties of the cement paste and obtained cement materials were studied in accordance with standard methods, taking into account regulatory documents of Russian and foreign standards. Thermokinetic, X-ray phase analysis, scanning electron microscope investigation with an integrated system of energy-dispersive analysis were also applied. Results and discussion. It has been proved that highly dispersed WC, TiC powder additive to cement materials leads to increase in density, paste fluidity, reduction in setting time, decrease in water absorption, porosity, and increase in strength characteristics both in early and later periods of hardening. A highly dispersed additive promotes earlier hydration. The structure of the cement sample with powder additive is denser throughout the considered periods of hardening compared to the control sample. Conclusion. The obtained results are of great importance for understanding the action mechanism on cement materials of highly-dispersed particles of WC, TiC, which can later be used to improve the properties of composite cement-based materials in various fields of application.
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Influence of nanoadditives on PVC composition properties
Scientific article
Introduction. In this scientific article a scheme of the no synergistic effect is observedion process is considered. It has been shown that to slow down or suppress the main process occurring in the condensed phase and determining the formation of gaseous fuel several methods can be used: addition of polymers with increased thermal stability; addition of nanoadditives that reduce the amount of gaseous degradation products; introducing nanoadditives that affect the heat capacity or thermal conductivity of the system, thus changing the thermophysical characteristics of the polymer material. At the same time reduced reaction speeds, occurring in the gas phase and supporting the combustion process, can be achieved through reduction of the concentration of combustible gases and inhibition of the reactions responsible for the branching of the combustion chain process. Methods and materials. The composition and physical properties of kaolin are given. Kaolin monocrystal is a two-layer aluminosilicate containing water of hydration and consisting of chemically bonded layers of silicon dioxide and hydrated alumina. Results and discussion. We have studied the dependence of the attenuation time of a PVC composition on a composition containing from 3 to 10% kaolin. The introduction of kaolin into the PVC compound has led to decrease of decay time from 4.5 to 1 seconds. The effect of the amount of plasticizer on the oxygen index has been studied. We used dibutoxyethyl adipate (DBEA) as a plasticizer. It has good polymer compatibility and is environmentally friendly. The possibility of reducing the content of dibutoxyethyl adipate in the basic formulation of the original plasticate I40-13A by increasing the amount of calcium carbonate was studied, then the performance properties of the resulting compositions were studied. The content of PVC and other components in the basic recipe remained unchanged. Analysis of the data showed that for plasticization of 62% wt PVC contained in I40-13A, 20% wt DBEA is sufficient, while the filler content can be increased at least twice. The oxygen index (OI) value at a component ratio of 20% DBEA + 13.56% CaCO3 increases by 4 OI units and becomes equal to 29.1%. The dependence of the oxygen index of PVC compound on the composition containing from 5 to 20% kaolin has been studied. The results showed that the oxygen index of plastic compound increases significantly with increasing kaolin content. The OI drops with a decrease in the amount of the introduced, and it remains unchanged with its increase. Thus, the optimal content is 15%. Conclusion. Thus, kaolin is a promising, inexpensive and environmentally friendly filler for PVC materials, which effectively reduces their combustibility. The same effect is achieved by increasing the content of calcium carbonate in the original PVC compound formulation. However, no synergistic effect was observed while mixing kaolin and an excess of calcium carbonate.
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Influence of nanoadditives on the physical and mechanical performance of cement concrete
Scientific article
Introduction. The influence of nanoadditives on the physical and me-chanical performance of cement concrete remains a relevant issue driven by the need for finding the most promising and cost-effective solutions to enhance performance during in situ concreting. This issue has been thoroughly examined by the authors in earlier publications. Methods and Materials. Two experimental formulations of a composite concrete nanoadditives were developed, based on ammonium hexafluorosilicate ((NH4)2SiF6) and silicon carbide (SiC). Results. In the first part of the study, concrete samples were tested after 28 days of hardening to assess mechanical strength properties. The kinetics of hardening and the influence of each of the specified additives on the concrete were studied. Discussion. The conducted studies allowed for the establishment of the optimal combination of nanoparticles included in the special additive, as well as a detailed investigation of the mechanism of strength gain in cement stone. It was found that the use of the best additive formulation (combination No. 2) significantly improved the strength characteristics of the concrete mix, providing an average strength increase of 38%, as confirmed through both destructive and non-destructive testing. Conclusion. The optimal dosage of nanocomponents for the production of the recommended additive per cubic meter of concrete is approximately 0.0141 of the mass of the main raw material, which confirms the economic feasibility of its application. In addition, low concentration of nanoparticles in the additive ensures environmental compatibility of the finished product, minimizing the impact on the environment. The optimal dosage of nanocomponents ensures the uniform distribution of particles in the concrete structure, contributing to an increase in its durability and resistance to environmental influences.
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Scientific article
Introduction. Detonation spraying is an effective method for applying high-quality coatings to various materials, widely used in industry to improve wear resistance and corrosion resistance of surfaces. This article examines the influence of key process parameters, such as gun-to-substrate distance and nozzle velocity, on the structure and properties of the resulting coatings. Materials and methods of research. The Ti–TiO2 coatings on hot-rolled carbon steel are studied. The spray distance and the speed of nozzle passage are varied while the rest spraying parameters are fixed. The obtained coatings were studied using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Results and discussion. It is found that the phase composition of the coating changes depending on the detonation spray conditions. The fraction of rutile exceeds the fraction of anatase in the obtained samples except for the samples obtained with the fastest nozzle passage. The rutile fraction monotonically decreases with an increase in the spray distance with fixed values of the rest parameters of spraying process. It is found a nonmonotonic changing the rutile fraction with an increase in the speed of nozzle passage and found its optimal values. Two new theoretical models for the spray process based on differential equations are proposed, the solutions of which sufficiently describe the dependencies of the rutile fraction on the distance and speed of the nozzle, respectively. Conclusion. It has been demonstrated that the theoretical values of the parameters, calculated using the formulated equations, are in good agreement with the experimentally measured values.
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Scientific article
Introduction. An urgent problem today is determining the rational composition of an injection solution to improve the quality of soil stabilization and strengthening of foundations of buildings and structures subject to renovation, without impact, vibration, and mechanical effects. The aim of the study is to substantiate the possibility of using a composite solution modified with an ANT additive to increase the stability of foundations. Methods and materials. To strengthen soils to increase the stability of building foundations, injection is carried out with composite solutions based on various materials. In composite injection solutions, in addition to the main component – cement – various additives capable of accelerating structure formation and reducing its consumption in the recipe are used. Such additives include aluminosilicate nanotubes. Results. The value of the optimal concentration of the nano-aluminum-containing additive, which maximizes the strength of the composite system, was revealed. An approximating plane was constructed, representing a two-factor regression model of experimental data, depending on time and concentration, representing a polynomial with a degree of 5 in x and a degree of 3 in t. The data were implemented in the MathWorks MATLAB program. Discussion. It was found that the maximum structuring rate of the composite system occurs at an additive content of 0.125% ANT. The appearance of this effect can be explained by the formation of a new phase of cement stone with increased adhesion. Conclusion. The introduction of the optimal concentration of aluminosilicate nanotube additive into the composite solution allows it to be used as a composite solution to increase the stability of foundations.
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