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The article considers the lack of production of products from hyperpressed concrete. At a high intensity of pressing in concrete, deformations of the elastic aftereffect are manifested. The magnitude of the deformations of the elastic aftereffect at the intensity of pressing 6, 12, 24 MPa is established. Methods have been established to reduce the effect of elastic aftereffect deformation on the strength and durability of hyperpressed concrete. An increase in the structural strength of hyperpressed concrete at the age of 4, 6 and 8 hours with reinforcement with basalt fibers by about 320 % was revealed. The structure of hyperpressed concrete reinforced with basalt fiber was studied. The issue of the complex use of reinforcing fibers and a plasticizing additive in order to prevent destructive processes occurring in hyper-pressed concrete at high pressing intensity is considered. An increase in tensile strength during splitting of hyperpressed concrete by 16 % was established with the combined use of basalt fibers and a plasticizing additive. The durability of hyper-pressed fiber-reinforced concrete was assessed by its frost resistance. A significant decrease in the water absorption of hyperpressed concrete has been established with the combined use of basalt fibers and a plasticizing additive. The absence of the influence of destructive processes during alternate freezing and thawing on the strength of hyper-pressed concrete with a high intensity of pressing with a change in recipe-technological factors was revealed. A material with a frost resistance grade of over FI 400 was obtained. [ABSTRACT FROM AUTHOR]

The urgency of the problem of using the raw material base of "green" composites on the basis of local stone materials does not cause doubts. For this purpose it is possible to use stocks of substandard and technogenic raw materials being in the Caucasian region which can serve as a starting material for the production of concrete aggregates. This article reflects the results of the study of technological parameters and construction and technical properties of construction materials using substandard natural and technogenic raw materials to produce "green" high-quality composites. It is established that the samples of "green" concrete due to the dense packing of the particles included in it and the completeness of the reactions occurring have a compressive strength above 60 MPa. The use of composite additive to the binder from technogenic products allowed not only to reduce the consumption of clinker, but also to improve the performance characteristics of concrete. The exact composition per 1 m3 of high-strength composition is a subject of know-how. The rate of strength gain of the proposed specimens is significantly higher than that of normal concrete under normal conditions. The fracture pattern of the concrete indicates that the strength of the cement matrix is about the same as the strength of granite rubble - cracks run along the contact zone and along the rubble grains. [ABSTRACT FROM AUTHOR]

The paper considers the issues of obtaining a composite material based on gypsum binder and sulfur with high performance. Technological factors influencing the hardening coefficient, water resistance and chemical resistance of gypsum products impregnated in sulfur melt have been studied. The regularities of impregnation of gypsum matrix with sulfur melt are established taking into account the capillary-porous structure of gypsum stone and physical and technical properties of sulfur. The regularities of impregnation of gypsum matrix with sulfur melt are established taking into account the capillary-porous structure of gypsum stone and physical and technical properties of sulfur. Research and consideration of mass transfer indicators during impregnation of gypsum concrete products with sulfur melt allowed to optimize the technology. Thus, the mass transfer coefficients for sulfur were measured using the method of capillary impregnation on the original laboratory installation. As a result of these studies, the dependences of the mass transfer coefficient on the temperature of the sulfur melt, the rate of heating of the melt, the concentration of the filler and the water-solid ratio were obtained. Products made of composite material based on gypsum and sulfur have the following construction and technical characteristics: compressive strength, not less than 30.0 MPa; flexural strength, not less than 6.0 MPa; water resistance coefficient, not less than 0.7; coefficient of corrosion resistance, not less than 0.7; wear resistance, no more than 0.3 g/cm2. Analysis of the main construction and technical characteristics of the composite material based on gypsum and sulfur shows that the resulting composite has high strength, water and corrosion resistance to various aggressive environments. Facing tiles made of this material have high performance characteristics and should be used in the lining of buildings of railway infrastructure, drainage systems, fertilizer storage, floors and walls of the chemical and food industries. [ABSTRACT FROM AUTHOR]

This scientific paper delves into 1the physical and chemical aspects of the interaction of the microfibers of mineral and polymer origins in cement solutions. The research done showed that the polyester microfiber with the silicon appret impart the properties to the fiber that allow it to be used as the substrate for cement hydration products just as the vitreous substrate and on the one hand it prevents the surface hydrolysis in the alkaline environment and on the other hand it facilitates an optimum binding of the fiber in the cement stone structure. It was established that during the hardening of the cement composition containing the polyester microfiber the cement hydration products, in particular hexagonal Portlantide crystalline hydrates, cubic hydrated calcium aluminate and gel-like hydrated calcium silicate can form the shell on the surface of its fibers that corresponds to the condensation and crystallization structure of the microfiber material. It was established that the addition of the polyester fiber to the cement waterproof composition in the amount of 4.0 to 4.2 % of the cement mass provides a maximum increase in the bending strength, however an increase in its content above 4.5 % results in an abrupt decrease of the strength. An increase in the cement stone strength requires the condensation and crystallization structure of its new hydrate formations consisting of the particles of a minimum size in order to increase the number of contacts and to decrease the probability of the formation of dangerous flaws inside the particles. [ABSTRACT FROM AUTHOR]

A two-dimensional finite element model of a cement stone with the addition of fly ash particles from thermal power plants has been developed. Fly ash was modeled by solid and hollow circular particles, regularly located on a plate of unit thickness, simulating cement stone. The model is verified by comparing the results obtained using the SCAD and Abaqus computing systems. Based on the results of a computational experiment on the model, graphical dependences of the change in the Young's modulus and Poisson's ratio of cement stone were established depending on the flow of fly ash and the content of solid and hollow particles in it. [ABSTRACT FROM AUTHOR]

The analysis of experimental studies presented in the scientific literature indicates that the strength and deformability of concrete during its dynamic reloading may depend on the initial level of stresses caused by a previously applied static load. In this regard, the purpose of this study was to build improved models of concrete deformation of operating reinforced concrete structures of load-bearing systems of buildings and structures during their dynamic loading, taking into account the nonlinear elastic law of material deformation at the stage of loading with a static load, as well as changes in the parameters of viscous resistance during loading. As a physical model of the power resistance of concrete of loaded reinforced concrete structures with their dynamic additional loading caused by an emergency, we accepted the Kelvin - Voigt model for an elastic-viscous body. On the basis of the adopted model, variants of solving the differential equation of uniaxial compression of concrete with its dynamic additional loading from an arbitrary level of initial stresses acting in it from a previously applied static load are obtained. A step-iterative approach to determining the parameters of concrete state diagrams under static-dynamic loading conditions is proposed. Analysis of the obtained relationships between stresses and deformations shows that an increase in the level of initial stresses acting in a compressed concrete element at the time of application of a dynamic load leads to a decrease in the dynamic strength of concrete with the same action parameters. [ABSTRACT FROM AUTHOR]

It is accepted that as a result of the complex impact of vibration-impact forces on the elementary volume of the concrete mixture with section F, the sum of the three main forces acts (Fig. 1). This includes the gravity force of the molded product and the outer shape m, inertial forces I, and the shock load P from the vibration core pressing band. The most difficult is determining the pressure from the impact of the shock load of the pressing band. Moreover, the use of a shock load resulting from the reciprocating movements of the outer shape and the concrete pipe being manufactured leads to a twisting shock. To determine the actual mechanical stress by the method of continuum mechanics, the following prerequisites were used: - there is a directly proportional relationship between stress and deformation upon impact; - the modulus of elasticity of the concrete mixture under static and shock loading is the same; - the height of the core section with the pressing band is equal to the initial displacement of the column of a concrete mixture. These prerequisites have been confirmed with a sufficient degree of accuracy by experiments. In this case, the system in which interactions are realized, representing the process of systematic collisions, is called a vibroimpact system. Naturally, these interactions have significant specificity in comparison with the act of a single impact. However, this is true if the frequency of forced collisions, as in the case under study, is comparable to the frequency of natural vibrations of the column of the compressed concrete mixture. In this situation, the collision of a pressing organ, for example, a bandage and a column of concrete mixture, occurs in an excited system with a certain reserve of energy, which can accumulate from impact to impact, causing the development of the process of hyperexposure of the mixture. [ABSTRACT FROM AUTHOR]

The article presents a new technique to determine the optimal parameters of the operating mode of a vibrating platform with modulated multi-parameter oscillations in the technology of compaction of heavy and light concrete mixtures, based on the intensity of vibration exposure. Here is also a design diagram and optimal operating parameters of the laboratory equipment, designed to generate modulated multi-parametric. Scientifically substantiated conclusions are given about the possibility of forming and compacting prefabricated reinforced concrete structures from lightweight concrete mixtures based on the new technology. [ABSTRACT FROM AUTHOR]

This article presents the results of theoretical and experimental studies on the development of a classification of mineral fillers for concretes, taking into account the number and nature of the distribution of active centers on their surface. Studies are presented to assess the influence of the presence and number of adsorption centers on the surface of mineral fillers to reveal the mechanism of formation of physical and mechanical parameters of cement concretes, as well as the possibility of using indicators of the surface activity of dispersed mineral substances as a criterion for determining the most effective method of their use in the composition of cement concretes. Despite the presence of many publications and performed studies, it seems advisable to study this area in more depth in modern concrete science, given the presence of various methods of introducing mineral powders into cement compositions, peculiarities of origin, and physical and mechanical parameters. [ABSTRACT FROM AUTHOR]

Probabilistic-statistical models are widely and effectively used for qualitative and quantitative assessment and prediction of physical and mechanical properties of various types of concrete. The obtained models of the properties of expanded clay concrete have a high degree of reliability, which allows us to speak about their sufficient adequacy to the main parameters of real ones; deformation curves. Variations of factors are determined by the area of workable concrete and the range of strength properties of cement and expanded clay used to obtain structural expanded clay concrete of a dense structure. [ABSTRACT FROM AUTHOR]

The use of gypsum-cement-puzolan binder (GCPB) as binders for the production of heavy fine-grained concrete instead of cement binder is a way to reduce the consumption of cement binders, as a result of which CO2 emissions into the atmosphere will decrease. In the building materials industry, products based on gypsum and gypsum- containing binders, with their high manufacturability, are produced without fillers, which leads to a significant increase in the cost of finished products. The purpose of this study was to establish the influence of the fractional composition of fine aggregate on the technological and physical-mechanical properties of GCPB-concrete. The paper presents the results of a study of the effect of the composition of fractionated sands on the physical and mechanical properties of GCPB-concrete. According to the research results, structural concrete was obtained on cast mixes with a strength of 50 MPa on the 7th day of normal moisture hardening. To determine the optimal fractional composition of sand by the method of regression analysis, adequate mathematical models were constructed that describe the physical and mechanical properties of GCPB- concrete. With the help of the constructed mathematical models, optimization problems were formulated and solved to determine the fractional compositions of sands that provide the best values of physical and mechanical parameters of concrete such as density and compressive strength. Solving the problems of optimizing the physical and mechanical properties of concrete depending on the fractional composition of the aggregate, which was used sand of six different fractions, made it possible to predict the composition of GCPB-concrete with a strength of 66 MPa and an average density of 2295 kg/m3. [ABSTRACT FROM AUTHOR]

The paper presents a comparative analysis of the fatigue effects in conventional and fibre-reinforced cement- matrix composites under few repeated loads with zero asymmetry coefficient and 0.6÷0.9 amplitude. This study applies the method of automated multi-factor deformation control indicating structurally relevant characteristics. The indicators of residual deformations and the cyclic kinetics of deformation increments are the key parameters of the internal resistance. This shows an increase in shock-absorbing ability of fibre composite resulting in a greater potential of fatigue resistance in the stress state fluctuation. [ABSTRACT FROM AUTHOR]

The paper states main provisions of the method for assessing the accumulation of damage in the structure of polymer materials under tensile stresses. The proposed method involves fractal analyses of deformation curves recorded with a high frequency. The minimum coverage method was used to determine the coordinates of critical points identified by the minimum levels of the fractality index. To determine the change in the fractality index depending on the relative elongation, we used a sequence of nested partitions. The amplitude variation was calculated for each of them as a sum of the differences between the maximum and minimum increase in tensile stresses in each analyzed time interval. The fractality index values were determined in the previous time interval of 0.16 sec. with a step of 0.01 sec. The paper provides the results of implementing the proposed method, which makes it possible to determine critical levels of stresses and relative deformations of polymer samples under tensile loads. We used ten samples of epoxy polymer based on modified Etal-247 resin cured by Etal-1472 hardener, including one sample with initial structural defects, as objects of study. We have identified the "critical" levels of tensile stresses and relative elongations, at which the failure rate grows, assessed by the minimum levels of fractality indices of the deformation curves. [ABSTRACT FROM AUTHOR]