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  • On the dependence of "stress-strain" and "modulus of strain-loading level" for concretes with organomineral modifiers

    It is shown that the given ratio of the modulus of deformation and the initial modulus of elasticity of concrete depends not only on the type of the function ε = f(𝜎), and from the initial modulus of elasticity of the concrete, i.e. concrete with different values of initial modulus at equal strength, for example, with the introduction of the composition of concrete organo-mineral modifiers, the dependence of the ratio E𝜎/E0 from the loading level will vary. To describe the "stress-strain" or "modulus of deformation-level of loading" for concretes with organo-mineral modifiers, it is advisable to use The sargin diagram, taking into account the influence of modifiers on the main deformation constants: the initial modulus of elasticity, the coefficient of elasticity, the relative deformation corresponding to the short-term strength limit. The nature of deformation of concretes with organo-mineral modifiers at a loading level above 0.9 may differ from the known patterns for traditional concretes, in connection with which this issue requires special study.

    Keywords: modulus of deformation, stress-strain diagram, modified concretes, loading level, modulus of elasticity

  • On the question of assessing the frost resistance of concrete on the strength criterion

    Durability of concrete, including fine-grained, with alternating cyclic temperature effect of the external environment is normalized according to GOST 26633 mark on frost resistance, and frost resistance criterion for all concrete in accordance with GOST 10060-2012 is the ratio of ultimate strength on compression of the main and control samples not less than 0.9 with a coefficient of variation of strength in the series, while for concrete road and airfield pavements is another additional criterion is the loss of mass. In the previous edition of GOST 10060, the ratio of the compressive strength of the main and control samples not less than 0.95 was adopted as the criterion of frost resistance for all concretes. GOST 31357 normalizes the indicator "frost resistance of the contact zone" for a number of mortars or fine-grained concretes obtained from dry building mixtures. This indicator characterizes the ability of the solution or fine-grained concrete to maintain the strength of adhesion to the concrete base after a certain number of freeze-thaw cycles. For the brand for frost resistance of the contact zone from Fkz25 to Fkz100, the number of cycles is taken, after which the decrease in the adhesion strength to the base does not exceed 20% according to GOST 31356, and in this case the coefficient of variation of the clutch values measured in the series is not taken into account. Due to the limited information on the change in the in-series coefficient of variation of strength after cyclic freezing-thawing, as well as the ratio of frost resistance by the criterion of compressive strength and adhesion strength to the base, the purpose of this study was to identify patterns of change in the in-series coefficient of variation of strength and adhesion strength to the base of fine-grained concretes obtained from dry building mixtures based on various Portland cements with the content of various redispersible polymer powders from 0 to 3%. The studies were carried out on the basis of 75 freeze-thaw cycles. This paper presents the results on the change in the coefficient of variation of strength after cyclic freezing-thawing and the ratio of frost resistance coefficients

    Keywords: frost resistance of concrete, coefficient of variation of strength, coefficient of frost resistance, fine-grained concrete, dry mixes

  • The effect of redispersible powders and low modulus inclusions on the properties of fine-grained concrete after repeated freezing-thawing

    Low-modulus inclusions in the form of entrained air or ash microspheres in the composition of fine-grained concrete practically do not affect the ratio of the ultimate strength in bending and compression during hardening of concrete under normal conditions. After 75 freezing-thawing cycles, the ratio of the flexural and compressive strengths of fine-grained concrete with ash microspheres did not change, and in concretes with involved air, the influence of factors such as the type and dosage of redispersible powder and the type of cement increased sharply. Low-modulus inclusions have practically no effect on the ratio between the initial elastic modulus and the compressive strength of fine-grained concrete during hardening under normal conditions. After 75 cycles of freezing and thawing in concrete with entrained air, the influence of such factors as the type and dosage of redispersible powder and the type of cement on the ratio of the initial elastic modulus to compressive strength increases sharply. The cyclic freezing-thawing does not affect on the ratio of module and strength in concretes with an ash microsphere. Regardless of the presence of low-modulus inclusions, there is no clear relationship between adhesion to a concrete base and flexural strength of fine-grained concrete. In concretes with entrained air, the increase in adhesion to the concrete base after 75 freezing-thawing cycles, depending on the type of cement and dosage of redispersible powder, was up to 82%, and for compositions with an ash microsphere, up to 62%. Regardless of the presence of low-modulus inclusions, after 75 freeze-thaw cycles, adhesion to the base corresponds to class C-1. With an increase in the dosage of redispersible powder from 0 to 3% in compositions with low-modulus inclusions, an increase in adhesion to the base was noted up to 62%.

    Keywords: dry mortar mixes, redispersible polymer powders, low modulus inclusions, adhesion to the base, elastic modulus, tensile strength, freezing and thawing cycles

  • The effect of dosage of redispersible powders on the properties of fine-grained concrete after repeated freezing-thawing

    The introduction of RPP to 3% by weight of the dry concrete mixture is accompanied by a decrease in the compressive strength of fine-grained concrete aged from 28 days to 37%, and after 75 cycles of freezing and thawing - up to 46%. The decrease in tensile strength in bending at the age of 28 days was 25%, after 75 cycles - up to 23%. The dependence of the initial modulus of elasticity of concrete on the compressive strength remains virtually unchanged after 75 cycles of freezing and thawing. The dependence of the adhesion of MZB to the concrete base with increasing dosage of RPP is ambiguous. The maximum increase in adhesion to the concrete base after 28 days of curing in NU and after 75 cycles of freezing and thawing was 26%. An increase in RPP dosage to 3% leads to a decrease in the initial elastic modulus of MZB to 26% after 28 days of curing in NU and to 32% after 75 cycles of freezing and thawing.

    Keywords: dry building mixes, redispersible polymer powders, adhesion to the base, elastic modulus, tensile strength, freezing and thawing cycles

  • On the issue of high-strength concrete production in the Socialist Republic of Vietnam

    An assessment was made of the possibility of obtaining high-strength concrete based on certain materials of SRV. The analysis of the effect on the ultimate strength of concrete in compression for the duration of hardening, the magnitude of the water-cement ratio, and the properties of materials was performed. A technique for selecting efficient materials for the production of high-strength concrete based on an estimate of the specific consumption of cement is given. It is shown that on the basis of materials available in the northern regions of NRW, high-strength concrete with a specific cement consumption of about 6 (kg / m3) / MPa can be obtained. It was concluded that, in the production of high-strength concrete, it is advisable to increase the adhesion of cement stone to coarse aggregate, for example, by introducing active microsilica in the form of rice husk ash into the concrete mix. It has been suggested that it is necessary to study the effect of superplasticizing additives used in SRV on the kinetics of hardening of cements in order to determine the group of additives that have a minimal retarding effect on the growth of concrete strength in the early period

    Keywords: specific consumption of cement, high-strength concrete, tensile strength, cement, coarse aggregate, fine aggregate, adhesion of cement stone with aggregate, hardening kinetics

  • The study of the change in the composition of a concrete mixture and kinetics of concrete strength during centrifugation on the example of the production experience of power line supports at the enterprises of the Socialist Republic of Vietnam

    The experience of applying centrifugation as a molding and compacting method has opened new prospects for the production of highly efficient reinforced concrete products. The experience of production of centrifuged power line supports at one of the enterprises of the Socialist Republic of Vietnam is analyzed. The studies aimed at studying the change in the composition of the mixture during centrifugation and the kinetics of the strength of centrifuged concrete were carried out. The dependence of the ultimate strength of centrifuged concrete on compression on the value of B / W after HMT (heat and moisture treatment) and at the age of 3-7 days was studied. Conclusions are made on the correction of the known quantitative regularities of the change in the strength of vibrating concrete from the value of B / W and the porosity, taking into account the heterogeneity of the structure of the centrifuged concrete over the cross section.

    Keywords: centrifugation, heavy concrete, concrete mixture, power line supports, additives to concrete, enterprises for the production of reinforced concrete products

  • Deformation properties and parametrical points of concretes of frame structure

    The peculiarities of the deformation diagram under short-term central axial compression of concrete of the frame structure of class B60, obtained by immersing a large aggregate in a low-viscosity solution component, are revealed. The boundaries of microcrack formation of concrete are determined. A good correspondence of the main regularities of the change in the tensile strength and deformation properties of a concrete frame structure with some known data is shown. The possibility of an analytical description of the deformation diagram of a concrete frame structure known formula Sargine (Sargine) is confirmed. Data are presented on the change in the initial modulus of elasticity, the Poisson's ratio, the change in the volume of concrete and the propagation velocity of ultrasound in concrete, depending on the level of loading. The ratio of cubical and prismatic strength is given. The conclusion is made about the expediency of using concrete frame structure in reinforced concrete columns.

    Keywords: concrete frame structure, tensile strength, modulus of elasticity, deformation diagram, parametric points, microcrack formation, superplasticizing additive

  • Pulsed laser deposition of ZnO nanostructures

    The arrays of ZnO nanorods were obtained on the sapphire substrates by means of pulsed laser deposition under the high pressure of argon. The conditions of synthesis were optimized, and their influence on the morphology of  ZnO nanostructures were revealed. It is shown that the concentration of oxygen vacancies in ZnO nanorods can be changed by regulation of the synthesis temperature from 850 to 915 °. This process can be controlled by the ratio of intensities of the photoluminescence emission in the visible and ultraviolet regions. So, it allows to create nanostructures for UV photodetectors or chemosensors depending on the temperature choice.

    Keywords: ZnO nanorods, laser deposition, PLD, photoluminescence

  • The influence of some water-repellent additives on the change in the strength of cement stone

    The article briefly describes the history пояявления hydrophobic cements. Considered one of the прспективных directions for the use of water-repellent additives today - in the dry construction mixtures and confirmed the significance of this direction. The article describes the results of experiments on the impact on the indicators of a cement-sandy solution additives series GMI and the analysis of the received data  

    Keywords: hydrophobic cement, hydrophobic additives, dry construction mixtures, porosity of a cement stone, strength cement-sandy solution, involving air, antifoam, antifoam agent

  • the dependence of the column’s relatively carrying capacity on the relatively eccentricity

    "The results of the computational experiment, Show, that the dependence of the relatively carrying capacity on the relatively eccentricity is almost independent on the reinforcement Ratio or on and concrete type. "

    Keywords: High- Strong concrete, self-compacting concrete, modulus of elasticity, column.