Nanotechnologies in Construction: A Scientific Internet-Journal

200-210

Authors: Beregovoy V.A., Snadin E.V., Inozemtsev A.S., Pilipenko A.S.

ABSTRACT: Introduction. The unique combination of rheotechnological properties and mechanical performance opens up prospects for the application of self-compacting and high-strength concretes in the manufacturing of base elements for machines and industrial equipment. The processes of adsorption of modern plasticizers on various mineral and polymeric modifiers of concrete mixtures were investigated. The compatibility of nano- and micro-scale mineral additives in composite cementitious binders was determined using calorimetry with an improved semi-adiabatic setup. Materials and methods. The cementitious binders used were CEM 52.5N Portland cement (Asia Cement LLC, Russia) and Nanodur (Germany, Dyckerhoff GmbH); hyperplasticizers included Melflux 1641F, 2651F, 5581F (Germany), PCE TR-6088 (China), Sika ViscoCrete 240 HE Plus and 226-P (Russia); superabsorbent polymer; nano- and micro-scale mineral additives included microsilica MK-85, metacaolin VMK-45, microcalcite MM-315, marshalite Silverbond 15 EW, and ground silica-containing rocks. Selective dissolution, differential thermal analysis, laser granulometry, and semi-adiabatic calorimetry were employed. Results and discussion. The quality of ultrafine mineral additives determines their ability to chemically bind portlandite through pozzolanic activity. Among the investigated additives, microsilica and gaize demonstrated the highest pozzolanic activity. Thermal activation was effective for components consisting of crystalline silica (marshalite, ground quartz sand), resulting in a 25% increase in performance. There was no selective adsorption of hyper plasticizer molecules by superabsorbent modifiers based on sodium polyacrylate compositions. Metakaolin and tremolite exhibited high adsorption to hyper plasticizers among the mineral additives. The rapid evaluation of the influence of formulation factors on the setting of cementitious composites was tested on an improved version of the semi-adiabatic calorimeter. Conclusions. The presence of micro-scale mineral additives based on microsilica in composite cementitious binders enables the development of high-performance concretes adapted for machine building. The study of pozzolanic activity, adsorption capacity, and cumulative heat release curves has indicated the feasibility of replacing microsilica with metacaolin and the potential for its partial blending with finely ground natural gaize. Analysis of the thermal effects accompanying the hydration processes of the "cement-additive-water" system with calorimeters allows us to provide more efficient research on the compatibility of additives in high-performance concrete compositions.

220-227

Authors: Zhegera K.V., Ryzhov A.D.,Sokolova J.A., Shestakov N.I.

ABSTRACT: Introduction. One of the reasons for coating destruction enclosing structures is the formation of condensate at the boundary of the fence and the finishing layer. As a result of external impact and freezing of moisture in the pores of the plaster coating, a network of small cracks is formed, and it is also possible to peel off the finishing layer. To test this hypothesis, the facades of three different buildings were examined. It is established that all the studied plaster coatings are made on the basis of cement mortar. It is also known that lime mixture is used less often due to the lack of sufficient resistance to moisture. Therefore, there is a need to increase the resistance of coatings based on lime compositions. This can be achieved by introducing an alumosilicate-based modifying additive into it. Materials and methods. Liquid sodium glass, aluminum powder PAP-1 and distilled water were used for the synthesis of the additive. Slaked lime (pushonka) with an activity of 84% was used to prepare test samples. Fritsch particle sizer Analysette 22 was used to analyze the granulometric composition of the additive. Compressive strength was determined on the samples measuring 20×20×20 mm. A testing machine of the type “IR 5057-50” was used for the study of compressive strength of samples. The analysis of rheological properties was determined by the Shvedov-Bingham equation. To study the plastic strength (ultimate shear stress) of the finishing mixture, a conical plastometer KP-3 was used. The plastic viscosity of the composition was determined with a rotary viscometer BCH – 3. Results and discussions. The synthesized additive is a light powder of light gray color with a bulk density of 0.55 ± 0.05 g/cm3. The synthesized additive revealed a high content of oxides Al2O3, SiO2, Na2O respectively, amounting to 51.03%, 36.36%, 11.89%. The additive consists of particles of 100.0–200.0 microns, which make up more than 20% of the total composition. The influence of an aluminosilicate additive on a lime binder on rheological properties was investigated, a slight increase in static shear stress was revealed, respectively, an increase in the percentage of the additive. The value of the dynamic shear stress increases significantly with an additive content of more than 10%. Conclusions. The regularities of hardening of a lime binder with a nanostructured additive based on amorphous aluminosilicates are established, and the optimal content of an aluminosilicate additive in the amount of 10% by weight of lime is determined.

238-245

Authors: Morozova М.V.

ABSTRACT: Introduction. The simplest and most common method of obtaining fine mineral powder is mechanical dispersion. In the process of grinding the material went through some work (energy), which is spent on the formation of a new surface. Therefore, it is not always clear whether the destruction of the crystal lattice of a solid lead to the activation of the resulting crushed material. Thus, the key characteristics of finely dispersed mineral powders, by which activation processes can be judged, are the value of the specific surface area (Ssp) and the specific free surface energy, numerically equal to the surface tension (σ) of the solid. Therefore, a number of models based on the determination of these characteristics have been proposed to estimate the mechanical activation process of the raw material. So, one of the most correct methods, in our opinion, is the method based on an energy approach to the evaluation of mechanical activation processes. This model determines the relative change in the free surface energy (ΔES/ES0) of the material when obtaining a dispersed system. At the same time, the choice of the most effective raw materials for obtaining composite binders can be carried out on the basis of the surface activity criterion (ks), which is used as a criterion characterizing the reactivity of fine mineral powders after their mechanical disintegration. Therefore, the aim of this study was to calculate the relative change in the surface energy of fine mineral powders of various raw materials and to identify possible functional relationship between the parameter ΔES/ES0 and the amount of surface activity for the studied rock systems. Methods and Materials. Sedimentary rocks formations the Arkhangelsk region were selected as materials for the research: polymineral sand and saponite-containing material (a representative of bentonite clays). Before conducting experiments, rock samples were brought to a constant mass at a temperature of 105о С. The chemical composition of the samples was determined on an X-ray fluorescence analyzer “Metexpert”. Highly dispersed rock fractions were obtained by dry grinding on a planetary ball mill Retsch PM100. The dimensional characteristics were determined using the DelsaNano submicron particle size analyzer by photon correlation spectroscopy. The specific surface area was determined by the gas permeability method on the PSX-10 device. To calculate the surface tension, the edge angle was measured on the “Easy Drop” installation. The surface tension for highly dispersed samples was calculated by the OWRK method. Results and Discussion. The calculated macro-energy characteristics of the studied samples have showed that the atomization energy for polymineral sand was 1910.72 kJ/mol, and for saponite–containing material was 1826.94 kJ/mol. At the same time, the mass specific atomization energy for sand and SCM are 30.41●103 kJ/kg and 26.94●103 kJ/kg, respectively. In the process of dispersion, several fractions of highly dispersed rock powders were obtained, which are characterized by an average particle size and specific surface area. The surface tension (and its components) calculated by the OWRK method showed that for all the samples studied, the polarization effect (σSP) prevails over the dispersion interaction (σSD). At the same time, as Ssp increases, the numerical value of the ratio σSP/σSD increases. This indicates an increase in the number of active surface centers associated with the redistribution of the energy potential of the system. The calculated values of free surface energy (ЕS), surface activity (ks) and the relative change in free surface energy showed, that ks and ΔES/ES0 increase as the duration of powder dispersion increases.The obtained functional dependences ks = f(ΔES/ES0) for the studied samples of polymineral sand and saponitecontaining material are linear in nature and obey the general equation у = a●x + b. In this case, the coefficient “a” characterizes the dynamics of changes in the reactivity of the material with an increase in the duration of mechanical grinding, and the parameter “b” – reactivity in the microstate. Comparison of the coefficients “a” of the studied dispersed systems showed that, unlike polymineral sand, the reactivity of saponitecontaining material increases 1.5 times faster as the grinding duration increases. The obtained functional relationship between the criteria used for evaluating the process of mechanical activation of mineral raw materials of various natures shows the correctness of the models used. Conclusion. The calculated macro-energy characteristics of rock samples showed that the atomization energy for polymineral sand and saponitecontaining material has similar values. To assess the effectiveness of the process of mechanical activation for mineral raw materials, it is proposed to use the relative change in free surface energy or surface activity. A functional relationship between above mentioned criteria has been established, which is characterized by a linear dependence

258-266

Authors: Poluektova V.A., Shapovalov N.A., Cherkashina N.I., Kozhanova E.P., Starchenko S.A.

ABSTRACT: Introduction. In the binary dispersed systems of different origins (mineral and polymer) with particles differing in size by an order of magnitude, heterocoagulation is observed. Regulation of the aggregate stability is crucial in controlling the properties of functional dispersed materials based on such mixed dispersions. This study focuses on the investigation of waterborne mono and binary dispersions of polyvinyl acetate, Portland cement, and chalk by means of static laser light scattering and optical microscopy. Materials and research methods. In order to investigate the action mechanism of the FF modifier based on phloroglucinol furfural oligomers as disperse phase we used chalk (CaCO3 – chalk dispersed technical MTD-2, LLC “Technostroy”, Kopanishchenskoe deposit), Portland cement CEM I 42.5N (JSC “Belgorod Cement”), and polyvinyl acetate (LLC “Kuban-Polymer”). Particle distribution and the aggregate stability of dispersions were studied with an Analysette 22 NanoTecplus device. The particle sizes were determined by optical microscopy with “Axio.Scope.A.1” microscope, and the adsorption of oligomers on the particles of dispersions was analyzed using a UV spectrometer (SPECORD UV). Results and discussion. It has been established that the phloroglucinol furfural modifier contributes to the stabilization of binary polymer-mineral dispersions. Integral and differential distribution curves of polymeric particles have been obtained in a wide range of 0.01–2100 µm. Research has shown the regularity of the modal diameter reduction of adsorption-modified particles with a transition from a narrow to a wider distribution with the absence of large coagulums. Conclusion. The hypothesis has been proposed that the adsorption-solvation factor of aggregate stability makes a significant contribution to the aggregate stability of binary polymer-mineral dispersions. The impact of this factor is different for mono-mineral and binary polymer-mineral dispersions and depends on the hydrophilicity of the surface, increases with the transition from mineral surface to the polymer surface as the Hamaker constant increases.

274-284

Authors: Denisova О.А.

ABSTRACT: Introduction. The use of liquid crystals is attractive for solving technical problems when creating a new generation of monitors, pressure sensors, seismic activity, determining the level of dry or liquid media, indicators of the concentration of harmful substances due to the small size of devices, low power consumption, simple design, low cost, and easy controllability of liquid crystals by various external fields. Under the action of mechanical shear, the liquid crystal layer is deformed, as a result of which surface polarization occurs. The purpose of the research is to conduct an experimental study of the effect of an electric field on flexopolarization occurring in a thin layer of a liquid crystal to create an acousto-optic shutter. Materials and methods. Nematic liquid crystals 10 – 100 µm thick with homeotropic orientation of molecules were used as materials: n – methoxybenzylidene n – butylaniline; 4 – octyl – 4 – cyanobiphenyl; nitrophenyloctyloxybenzoate; cyanophenyl ester of heptylbenzoic acid. Methods. The experimental setup consisted of a charge-sensitive amplifier with a high input resistance of 10 GΩ and a selective amplifier (2 MΩ). The design of the amplifier made it possible to apply a constant voltage of up to 100 V to its input, as well as linear and synchronous signal detections, which were then fed to the ADC that recorded them. Results and discussion. The behavior of charges induced on the surface of a liquid crystal due to internal mechanisms of molecular-orientation polarization was considered as a function of the magnitude and direction of the external electric field. For this, a liquid-crystal layer (MBBA) was placed in an electric field. The dependences of the first U1ω and second U2ω harmonics, when a positive potential is applied to a deformable plate, reach lower values than with a negative one. The electric field at a positive potential stabilizes the molecules of the polarized layer, and at a negative potential it makes it less stable, which leads in one case to a decrease in the slope angle on the surface, and in the other to an increase, which leads to an increase in the second harmonic. Under weak boundary conditions, a polar deformation occurs in the bulk of the NLC. When the field is applied to the homeotropic layer of NLC (CPEHBA), the value of the second harmonic U2ω increases linearly from the voltage Uc up to the achievement of “saturation”, which is due to an increase in the stabilizing dielectric moment over the viscoelastic one. At low fields (Е ≤ 104 V/cm), the value of U2ω first increases and then decreases due to an increase in the tilt angle of the director relative to the normal to the surface. At low polarizing voltages Uc ≤ 15 V (CPEHBA) dependence U1ω is approximated by a power function of the Uc3 type, at Uc >> 15 V the second harmonic U2ω depends as Uc–1. At low bias voltages, the position of the minima of the values of the first U1ω and second U2ω harmonics (for MBBA and CPEHBA) does not coincide with the zero point along the abscissa at Uc = 0. The harmonics U1ω and U2ω have a maximum when a positive potential is applied to the moving electrode. In the region of positive displacement voltages, the molecules stabilize, while at negative voltages, the molecules are less resistant to orientational perturbations. The value of the second harmonic U2ω sharply decreases with the perturbation frequency. Conclusion. The obtained research results can be used in the development of pressure sensors, seismic sensors for buildings and structures, light modulators, as well as an acoustooptic switch for glass units