Construction materials science. Рубрика в журнале - Nanotechnologies in Construction: A Scientific Internet-Journal
Self-compacting concrete for monolithic constructions with highly dispersed silica-based additives
Scientific article
Introduction. Self-compacting concrete offers broad potential in construction due to its operational reliability and durability. However, the high cost of self-compacting concrete and the technological complexity of its production require the development of new concrete mix designs and improved placement technologies. When selecting concrete mix designs for self-compacting concrete, chemical additives can be used to reduce cement consumption and improve the concrete's properties. Materials and methods. To ensure the rheological and technological properties of the concrete mix, fly ash, a dry polycarboxylate-based superplasticizer, and ultrafine additives were used. The ultrafine additives were produced by hydrolysis, using pure Portland cement as a precursor, with the concentration in the solution varying from 1 to 5%. The cement hydrolysis reaction results in the formation of a multicomponent sol containing silicic acid, aluminum hydroxide, iron hydroxide and calcium hydroxide. Results and discussion. Experiments were conducted to modify self-compacting concrete with an ultrafine additive obtained using sol-gel technology. An optimal composition of modified cement containing an ultrafine additive with an average particle size of up to 100–150 nm was developed. The use of the ultrafine additive accelerated the cement hardening kinetics and improved the physical and mechanical properties of cement stone by 1.4–1.8 times compared to cement without the additive due to water accumulation, an increase in the volume of cement gel, and a decrease in capillary porosity. Based on an assessment of the technological and rheological properties of concrete mixtures containing fly ash as a microfiller and a modifying additive, compositions corresponding to strength classes B40–B60 were established, containing 7.5–44% fly ash and an additive in an amount of 0.1% of the cement weight on a dry matter basis. It has been established that the introduction of ultrafine fly ash and fly ash into the concrete mix reduces segregation by 17–19%, increases viscosity by 13% to 20%, and reduces flowability only slightly by 5–10%. It has been established that self-compacting concrete with the combined use of fly ash with medium pozzolanic activity, a chemically active ultrafine additive, and a polycarboxylate-based superplasticizer is characterized by intensive strength gain within 1–3 days of curing and an increase in strength by 15–17% within the design curing period. Conclusion. As a result of the research, a low-temperature method for producing a modifying additive using sol-gel technology was developed. This method is simple to synthesize, does not require complex process equipment, and can be added along with mixing water and uniformly distributed throughout the concrete mix. Concrete mix formulations for self-compacting concrete of strength classes B40–B60 were developed using an ultrafine additive, which improves the process properties, quality indicators, and physical and mechanical properties of the concrete.
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Strength and deformability of cement stone and powder-activated concrete. Part II
Scientific article
Introduction. Reinforced concrete structures in buildings and structures are subject to various loads during operation, which cause deformation and destruction. Materials and Methods. It has been shown that the strength and elastic-plastic properties of modern concretes can be broadly controlled using superplasticizers, nanoadditives, fillers, and fine aggregates. This article examines the deformation and fracture processes of cement paste and powder-activated concrete. The key characteristics of concrete deformation processes are determined using stress-strain diagrams, taking into account the downward strain curve. The concrete deformation diagram on the descending branch is fixed by the ultimate deformation, corresponding to the concrete reaching its maximum strength value, and the end point of the descending branch, corresponding to the residual strength of the concrete. Results. Complete concrete stress-strain diagrams with an extended descending section were obtained by loading specimens at a constant, decaying strain rate, resulting in a smooth decrease in stress in the specimen along the descending section. The influence of formulation factors on the key parametric points of the σ–ε diagram was studied. The influence of the W/C ratio, modifying additive, and polycarboxylate superplasticizer on the structure-forming factors for cement stone was examined. For concrete, the influence of the W/C ratio, modifying additive, polycarboxylate superplasticizer, fine filler, rheological filler, and reactive filler was examined. The resulting diagrams were analyzed for each material structure, both with an individual structure-forming factor and for powder-activated concrete as a whole. It was found that increasing the W/C ratio from 0.267 to 0.350 resulted in more elastic behavior of the material under load, a significant (4–5 times) elongation of the descending branch of the full equilibrium stressstrain diagram of hardened cement paste, and a change in the failure mechanism of the material. The specific parameters for static destruction of the sample are reduced by 12.1 times and the static J-integral Ji is reduced by 9.1 times.. It was shown that with the addition of the carboxylate superplasticizer "Melflux 1641F," the deformation pattern of the specimen under load was closer to that of cement paste obtained using normal-thickness cement paste, however, with a shorter (10 times) descending branch, indicating more brittle behavior of the specimen. The use of finely dispersed quartz also affected the nature of the deformation of the samples: their elasticity increased from 1.3 to 1.7 times, but at the same time the magnitude of ultimate deformations decreased by 20%, that is, the samples became more elastic and less deformable. Conclusion. It has been established that, with optimal component contents of cement stone and powder-activated concrete, crack resistance parameters significantly increase by 1.3 to 5.8 times, especially the static J-integral Ji, which characterizes the ductile fracture energy of the material at the crack tip, increasing due to the increased adhesion of the cement stone to the active surface of the microsilica. The curves of the complete equilibrium diagrams are approximated in sections by simple linear and quadratic functions or represented by a cubic polynomial.
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Structural and heat-insulating cement-based concrete with complex glyoxal based additive
Scientific article
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
Scientific article
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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Scientific article
Introduction. The extension of the range of binders, aggregates, and fillers as well as functional additives and structural modifiers for concrete and composite materials currently allows for the production of innovative materials with enhanced mechanical, physical, and physico-chemical properties. Lightweight structural and functional materials derived from binders of different natures with fillers derived from vegetable raw materials, such as sawdust concrete, arbolite, fibrolite, or xylolite, are of particular interest. The aim of this research was to develop and investigate the properties of a wood-mineral cement-free composite material with a porous structure that has been stabilized using a finely dispersed aluminosilicate additive. Materials and methods of research. A cementfree slag-based silicate binder was utilized in the study, comprising ground blast furnace slag and a curing agent – a solution of sodium silicate (sodium liquid glass). A synthetic foam-forming agent with a finely dispersed additive (bentonite) was employed to create the porous structure of the material. Crushed softwood was used as an aggregate. A range of samples were produced, varying the composition within the following parameters: slag 330–440 kg/m3, crushed wood 120–160 kg/m3, and solution-to-slag ratio 0.5–0.7. Several samples were subjected to thermal treatment by heating in a temperature-controlled environment at 80–90 °C and at humidity of at least 90% for 6–12 hours. Samples were examined using mechanical testing methods, thermogravimetric analysis, X-ray diffractometry, porometry, and thermal conductivity measurements. Results and Discussion. A cement-free porous wood-mineral composite material (an analogue of arbolite) was obtained. It is shown that the introduction of ground blast furnace slag (330–440 kg/m3) and crushed softwood (125–160 kg/m3) into the mixture at optimal ratios of liquid glass/slag 0.7 and foaming mixture/slag 0.0035 (3.5% foaming agent + 4% bentonite) makes it possible to obtain a composite material with a density of 550–680 kg/m3, compressive strength of 1.35–3.65 MPa, an open porosity of 45–50%, and an average thermal conductivity of 0.08 W/(m·K). The heat and humidity treatment of the composite at 80–90 °C contributes to the achievement of ultimate strength within 10–12 h. The presence of a finely gel-forming additive (bentonite) with particle sizes of 1–5 m in the foaming mixture helps to stabilize the homogeneous porous structure of the composite material (spherical pore sizes less than 1 mm). Conclusion. The porous wood-mineral composite material obtained in the work can be used for the production of lightweight non-load-bearing structural elements, as a noise and thermal insulation material.
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Structure formation of lime composites with polysaccharide additives
Scientific article
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 the kinetics structure formation of cement dispersed systems. Part I
Scientific article
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
Scientific article
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 stability of zeolite suspensions for cement systems
Scientific article
Introduction. In Russia, the focus of scientific research in the construction industry is on the development of new materials with high functionality, durability, and strength. These materials also have various unique properties that make them suitable for a wide range of applications. Fine dispersed additives are used in the binder, for the construction of objects that require increased strength, or for repair work where early strength gain of the repair mixture is important. To improve the physical and mechanical properties of the hardened cement paste, which contains finely dispersed additives, it is necessary to consider the issue of uniform distribution of submicron particles in the volume of the cement composite. The study of this issue is one of the objectives of this study. Materials and methods. Fine dispersed zeolite, which has high ion-exchange, sorption, catalytic properties, was selected as the object of study, and the possibility of its introduction into the cement composition in the form of a stabilized suspension instead of mixing water was assessed/ Zeolite suspension with concentration of 10, 30, 50 g/l was prepared by mechanical stirring with a magnetic stirrer and ultrasonic dispersion under thermostatted conditions. The time of mechanical and ultrasonic treatment of suspensions was 20 min. Suspensions were prepared in two dispersion media – water and water-polymer (water + plasticizer). Physicomechanical tests of samples were carried out in accordance with current national and international standards and methods. Results. Studies of sedimentation stability of suspensions showed that the most stable suspension was stabilized by ultrasonic treatment and plasticizer. The sedimentation velocity of suspension particles in the first period was (3.43÷3.83)•10–6 m/s, in the second period – (0.98÷1.17)•10–6 m/s. The study of zeolite particle dispersion in suspensions showed that ultrasonic dispersion leads to a more significant shift in particle dispersion downwards from 25 μm to 3 μm, both in aqueous and aqueous-polymer suspensions with a concentration of 10–30 g/l. The conducted physical and mechanical tests of the samples showed that the introduction of an ultrasonic-stabilized aqueous-polymer zeolite suspension into the cement composition results in an increase in the initial and grade strength by 3.3 times and 51%, respectively. The analysis of the results for compressive strength showed the greatest efficiency when introducing a zeolite suspension into the cement composition instead of mixing water in an amount of 10–30 g/l. Conclusion. The studies conducted have shown the effectiveness of using ultrasonic treatment in combination with a plasticizer to stabilize the zeolite suspension. Stabilized zeolite particles, uniformly distributed in the volume of the cement matrix, act as a substrate for the nucleation and growth of crystal hydrate phases, thereby intensifying the process of hydration and formation of a crystal hydrate framework with a dense and strong structure of cement stone. Thus, the feasibility of considering zeolites as components of composite materials is a promising direction in solving multifaceted problems in the construction industry.
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Scientific article
Introduction. Nanomodification significantly enhances the performance characteristics of composite materials, particularly those based on polymers. A wide range of materials from natural to artificially created are being studied as nanoobjects. At the same time, carbon nanostructures, such as fullerenes, graphene and carbon nanotubes, are of great interest from the perspective of comprehensively improving material performance. The use of carbon nanotubes for the modification of building materials for various functional purposes, even at low (less than 1% by mass) and ultra-low (less than 0.1% by mass) concentrations, demonstrates a remarkable capability to enhance a multitude of parameters. At the same time, there are technological challenges associated with the need for compound homogenization, requiring the use of ultrasonic processing and other techniques. A new approach to applying nanomodifiers, including single-walled graphene nanotubes, emerged after the launch of a new synthesis facility by OCSiAl in 2020, as well as the introduction of these nanotubes into polymer compounds in the form of masterbatches, which are nanotube concentrates. Methods and materials. This research involved a masterbatch based on single-walled carbon nanotubes TUBALL MATRIX M201 manufactured by OCSiAl.ru LLC. The polymers were made on the basis of low-viscosity epoxy resin Etal–247 and two hardeners manufactured by ENPTs EPITAL JSC –Etal-45M and Etal-1472. Tensile testing was performed on briquet specimens according to GOST 11262-2017. The tests involved AGS-X series bursting machine with TRAPEZIUM X software at a temperature of 23±2 °C and a relative air humidity of 50±5%. The mechanical properties (tensile and deformation) of the polymers were measured in three different moisture conditions: equilibrium-moisture, dry, and moisture-saturated. Results and discussion. The research revealed variations in ultimate tensile strength, tensile elongation and elongation at break, tensile modulus as a function of SGNT concentration and the moisture content of the studied polymers (series “without conditioning”, “moisture-saturated”, and “dried”). Mathematical models were developed to assess the effect of the nanomodifier and moisture content on changes in the properties of the polymers under study. The research has identified the optimal concentrations of the nanomodifier injected for enhancing the elastic and strength characteristics of epoxy polymers. Conclusion. The research indicates that masterbatches based on TUBALL MATRIX M201 single-walled carbon nanotubes hold potential for enhancing the properties of epoxy polymers.
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The strength and deformability of cement stone and powder-activated concrete. Part I
Scientific article
Introduction. During the operation of buildings and structures, reinforced concrete structures are subject to various loads that can cause deformation and destruction. The strength and elastic-plastic properties, as well as the durability of modern concrete, are controlled using superplasticizers, nanoadditives, fillers, and aggregates. The potential of using nanohydrosilicate technologies is demonstrated. This article examines the physical and mechanical properties of cement stone and powder-activated concrete – one type of next-generation concrete. Materials and methods. The influence of the water/cement ratio, the presence of a carboxylate superplasticizer, and a modifying additive were considered as structure-forming factors for cement stone, and the influence of the water/cement ratio, modifying additive, superplasticizer, finely dispersed filler, rheological fillers and reactive fillers were considered for concrete. Results. The article presents the results of a study establishing the relationship between the density of cement stone and powder-activated concrete with the porosity and strength indicators under static and dynamic loads. The rational compositions of the developed composites are characterized by a set of improved physical and mechanical properties. It was found that an increase in the W/C ratio from 0.267 to 0.35 causes a decrease in the compressive and tensile strength of cement stone when splitting by 22–30%. The addition of the superplasticizer ”Melflux 1641F“ led to a significant decrease in the water-cement ratio – from 1.56 times compared to the composition of normal consistency and by 2.04 times – compared to the composition with an increased W/C ratio, as well as a corresponding increase in compressive strength properties – by 1.20 times and 1.72 times – in flexural tensile strength. Conclusion. It was found that the introduction of finely dispersed fillers into the composition of sand concrete led to an increase in compressive, flexural, and tensile strength when splitting by 1.62 to 2.55 times, which is explained by a denser packing of quartz filler, causing an increase in the density of such samples by 9.5%, the plasticizing effect of microquartz, and the high activity of microsilica. The impact strength of the cement composite was studied. It was found that plasticized highly filled compositions of the new generation demonstrated high values of the maximum contact force, contact duration, and impulse magnitude. The composite containing microquartz, quartz filler, fine aggregate, and Melflux 1641F superplasticizer has a maximum contact force of 4.530 N, compared to a similar value of 2.073 N for a cement stone composition made from normal consistency paste. Moreover, the contact duration and impact impulse magnitude are approximately twice as high. The addition of microsilica to the highly filled compositions caused even better results. The maximum contact force at which the samples failed was 4.530 N. This is more than twice that of cement paste based on normal consistency.
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Use of pulp and paper industry waste in binding and cementitious materials technology
Scientific article
Introduction. Utilization of chemical cellulose fillers in construction industry is one of the ways of processing unused wastes from pulp and paper industry. Decorative, finishing, and heat insulation materials are widely used as construction materials. This paper proposes various compositions and insulation materials characterized by compressive strength of not less than 10 MPa, water tightness of 0.8, and density of not over 600 kg/m3. The likely curing mechanism is studied for cement systems. The possible mechanism of hardening structures formation in the systems is discussed. Methodology. Corrugated fibreboard МS-5B waste is used as a filler, high-early strength cement М-500 (CEM 47.5) – as inorganic binder, and elemental sulfur, polyethylene terephthalate, cementmodified polyurethane (PU) with the addition of nanosized silicon oxide are used as a polymeric matrix. Infrared spectroscopy, terahertz time-domain spectroscopy (THz-TDS), and scanning electron microscopy are used for investigations. Cement samples undergo compressive strength, water tightness and water absorption testing. Results and discussion. Physical and mechanical properties obtained for composites with the paper filler and polymeric matrix based on cement-modified PU, are described, and testing results are compared with the experimental data obtained for materials based on other binders. It is found that the paper filler–cement-modified PU composition is consistent with the purposes of this research. The understanding is improved for the curing mechanism of the polymeric matrix–paper filler system. The THz-TDS data demonstrate a correlation between the spectral transmission and thermal conductivity and density of synthesized heat insulation materials. Conclusion. Synthesized is the effective heat insulation material with relatively high compressive strength, low density, and high tightness to water. Scientific understanding of the curing mechanism is improved.
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