When forming in the process of centrifugation an annular section by the method of ""separate"" concreting with the formation of a section of the product at the first stage from the original, including fine-grained concrete mixture, and with the introduction of a coarse aggregate at the second stage into the formed circular section, followed by the final formation of the section and compaction of the concrete mixture by centrifugation, the speed, calculated for the compaction stage, increases, depending on the section zone, the concrete compressive strength from 20% up to 47%, the initial modulus of elasticity from 6 to 19% relative to single-stage centrifugation. The ratio vint / vext of ultrasonic pulse velocities for surface sounding along the inner (vint) and outer (vext) faces of a centrifuged annular section can be considered as a conditional indicator of the uniformity of the concrete structure over the cross section of a centrifuged product. Key words: centrifugation, separate concreting, structure homogeneity, strength and deformation properties, porosity.

Keywords: centrifugation, separate concreting, uniformity of structure, strength and deformation properties, porosity

Today, the development and research of new designs requires a systematic approach, including design, manufacture of products and construction. Further development of construction follows the path of improving the designs and forms of buildings, which is facilitated by the improvement of the physical and mechanical properties of building materials. The use of high-strength concrete and steel leads to the creation of lighter thin-walled reinforced concrete structures and is fundamentally possible only with perfect technology for the manufacture of elements. Since in the manufacture of reinforced concrete products by a centrifugal method, radially directed filtration channels are formed, it is in them that the manifestation of destruction is most likely. It is aggravated by the fact that the inner layer of such products is more porous than other layers of concrete. The presence of such a structure is determined even if all the requirements for the quality of the raw materials, the preparation of the concrete mix and the use of optimal centrifugation modes are met. The authors in the process of confirming the working hypothesis in this study developed a method of introducing aggregate during centrifugation, on the basis of which prototypes were obtained, which are characterized, compared with the control, improved physicomechanical and structural properties; an increase in the carrying capacity of centrifuged reinforced concrete columns of annular cross section was achieved at the stage of their manufacture by changing the nature of the manufacturing process from one stage to two stages. Testing the hypothesis was carried out by the determined increments of the structural and physical characteristics of the concrete samples. The density of concrete prototypes of centrifuged reinforced concrete columns of annular section of two-stage molding with all three ratios of fractions was higher than that of single-stage concrete. Water absorption at concrete capillary suction of prototypes of centrifuged reinforced concrete columns of annular section of two-stage molding with all three fractions ratios was lower than that of single-stage concrete.

Keywords: centrifuged concrete, reinforced concrete columns, aggregate fractions, two-stage technology, annular section, density, water absorption, structural and physical properties

The article presents and studies the theoretical foundations of vibration and centrifugal compaction of heavy concrete in the production technology of building products and structures. Attention is paid to such a technique as vibropressing. The physical entity is described, the phenomena of the processes occurring during the molding of such products and structures are disclosed. The influence of dispersed reinforcement of vibrated and centrifuged concretes by various types of fiber fibers on their coefficient of structural quality is considered and evaluated.

Keywords: vibrated concrete, centrifuged concrete, dispersed reinforcement, coefficient of structural quality, vibropressing

The current state of the issue of the nomenclature of centrifuged thin-walled prefabricated reinforced concrete products of the ring configuration is analyzed. The scientific interest, which is represented by the technology of fiber reinforcement for such concretes, is grounded. The actual problems for concretes produced by the centrifugation method are indicated. A series of large-scale experimental studies has been carried out to establish the nature of the change in the properties of heavy concrete manufactured by various methods, depending on the reinforcement by different types of dispersed fibers. To systematize the accumulated experimental data, at the first stage of the investigation, products of low-strength concrete, class B20, manufactured by vibration and centrifugation, were molded and investigated, followed by a reduction to uniformity. The compressive strength and tensile strength, as well as their increments, depending on the type of reinforcing fiber-polypropylene, basalt or steel fiber, were studied. The effect on the properties of the investigated concrete of the B20 class is determined by the combination of various prescription and technological factors.

Keywords: centrifuged concrete, vibrated concrete, thin-walled reinforced concrete products, fiber reinforcement, polypropylene fiber, basalt fiber, steel fiber, compressive strength, tensile strength

The scientific interest, which is represented by research for concretes differing in strength characteristics, is substantiated. A series of large-scale experimental studies has been carried out to establish the nature of the change in the properties of heavy concrete manufactured by various methods, depending on the reinforcement by different types of dispersed fibers. At this stage of the study, in order to systematize the accumulated experimental data, the authors molded and examined products made of concrete of class B35, manufactured by vibration and centrifugation, with subsequent reduction to uniformity for the convenience of an analytical comparison of the results obtained. The compressive strength and tensile strength, as well as their increments, depending on the type of reinforcing fiber-polypropylene, basalt or steel fiber, were studied. The influence on the properties of the investigated concrete of class B35 on the combination of various prescription and technological factors has been established.

Keywords: centrifuged concrete, vibrated concrete, thin-walled reinforced concrete products, fiber reinforcement, polypropylene fiber, basalt fiber, steel fiber, compressive strength, tensile strength

The article is devoted to the study of the problem of determining the mechanical properties of vibrating centrifuged concrete with a combined aggregate and fibrous additive, which was basalt fiber. Experimentally obtained data on the optimal consumption of disperse fiber. The dependence of the strength properties of concrete with a combined aggregate on the amount of fiber additive added is graphically presented. Also graphically shows the increase in the speed of the passage of an ultrasonic wave in the body of concrete when determining the prismatic strength. It was found that the presence of porous particles in a concrete mixture facilitates the directed distribution of mineral fibers along the section of the concrete ring. This, in turn, leads to an increase in the fracture toughness of the material. The conclusion is made that the joint introduction of porous and fibrous additives into the concrete mix determines the production (at the same cement costs) of high-strength concretes with an increased crack resistance, as evidenced by the data on the displacement of the boundaries of microcracks formation in the direction of their increase.

Keywords: structures and products of annular section, centrifuged concrete, vibrocentrifuging, mechanical properties of vibrating centrifuged concrete, combined aggregate, fiber additive, basalt fiber, prismatic strength

The analysis of the experimental data is carried out and the works devoted to the account of the influence of the compressive pressure factor with the purpose of optimizing the parameters of the centrifuged products of the annular section at the compaction stage are studied. The number of rotations of the mold at the compaction stage is calculated for different values of the compressive pressure. A statistical analysis of the regression equations obtained is performed using three criteria: homogeneity of variances, significance of coefficients and adequacy, which was tested with the help of Fisher's criterion. The data were statistically processed using the Mathcad program, which allowed obtaining regression equations in the form of polynomials of the second degree with specific values of their coefficients. Graphic interpretation of mathematical dependencies is constructed. The calculated dependencies are obtained that allow to determine the required number of revolutions for any required diameter and wall thickness of annular centrifuged products for a given fixed value of the compressive pressure in concrete.

Keywords: compressive pressure, centrifuged products of annular section, response function, factor of variation, least squares method, regression equation

A review of the literature concerning the molding of centrifuged concrete products was carried out. The peculiarities of centrifugation of concrete, in particular, the manufacture of centrifuged pipes, have been studied. The main parameters and indices of the quality of concrete and the centrifuged tubes themselves are considered. The traditional mode of forming non-pressure pipes is described. The calculation formulas for the parameters of the centrifugation process and their graphical dependences are given. Based on the calculated data, it is concluded that the traditional modes of shaping of non-pressure pipes are characterized by the rotation speed of the mold from 82 to 300 rpm in the stages of loading and distribution of the concrete mixture. At the sealing stage, the control of the rotation speed of the mold varies over a very wide range and depends largely on the viscosity of the concrete mix and the pressing pressure: from 825 to 4400 rpm for concrete pipes with a diameter of 100 to 300 mm. Modeling the parameters of the molding regime during the centrifugation of ring-shaped products in a laboratory installation at a maximum compaction pressure of p = 2.16 kg/cm2 will allow us to refine the obtained data and study their effect on the variability of the concrete structure

Keywords: centrifugal force, centrifugation parameters, charging speed of the mold, speed distribution of the shape, sealing speed of the mold, pressing pressure, centrifugation time, ring-shaped products

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

"n this article, the influence of the physical state of chemical additives at the moment of their introduction into a gas-concrete mixture on the kinetics of gas evolution and the gas diffusion coefficient is considered. To test the working hypothesis, two compounds were designed and manufactured. As a part of С№1 chemical additives were entered in the form of a colloidal solution. A comparative analysis of the results of physical and mechanical tests of the aerated concrete samples of the tested compositions showed that the introduction of chemical additives in the form of a colloidal solution lowers the average density in the dry state due to a more intensive course of the gas evolution reaction without significantly reducing the compressive strength. At the same time, the average density increases in the composition of CN2.

Keywords: kinetics of gas evolution, gas diffusion coefficient, aerated concrete mixture, reactivity, expansion of aerated concrete mixture, colloidal solution

This article considers the effect of the introduction of a partially hydrated aerated concrete mixture on the intensity of gas evolution, the reactivity of a disperse gas generator, and the physical and mechanical properties of aerated concrete. To test the working hypothesis, two compounds were designed and manufactured. The pure dispersed gas generator was introduced into composition C№1, and a mixture of a gas generator with a partially hydrated gas-concrete mixture was introduced into the composition C№2. A comparative analysis of the results of physical and mechanical tests of the aerated concrete samples of the tested compositions showed that its introduction increases the compressive strength, while reducing the density of aerated concrete. At the same time in the composition of С№1 there is a higher density and a drop in strength

Keywords: Partially hydrated mixture, gas generator, aluminum powder PAP-1, reactivity, device PGV-2, kinetics of gas evolution, average density in the dry state, compressive strength

The methods of directed formation of the variational structure of concrete products and structures are considered in the article. The experience of Russian scientists in the issues of obtaining articles of different density over the section has been studied. The problems of the technology of obtaining articles of different density along the section are considered, the main principles of shaping the variational pore structure of aerated concrete for monolithic enclosing structures, the optimal schemes for forming two-layer wall products from concrete of various densities, forming a structure with a double skeleton - mineral and polymeric - by sintering the polystyrene grains, the formation of variational structure of magnesian foam concrete, which involves sequential laying of foam masses with various average, perspectivity of the use of reinforced concrete constructions of a variational structure.

Keywords: Variational structure, concrete products and structures, reinforced concrete, aerated concrete, foam concrete, expanded clay concrete, density, fire resistance