Numerous studies have established that the physicomechanical properties of concrete, in addition to cement activity, type of aggregates, etc., are determined by the V/C value of the concrete mixture [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. The dependence of the strength and water tightness of concrete on H/C follows from the physical nature of the formation of the concrete structure. Studying the process of cement hydration showed that cement, depending on the quality and duration of hardening, binds only 15 … 25% of the water of its mass [11, 12, 13]. During the first month, at least 20% of the water by weight of the cement is bound. At the same time, to give the concrete mixture plasticity, improve the conditions of binder hydration, a significantly larger amount of water is introduced, since at W/C = 0.20 the concrete mixture remains practically dry and it cannot be qualitatively laid, molded and compacted. Excess water, without entering into chemical reactions with cement, remains in concrete in the form of water pores and capillaries or evaporates, leaving air pores. Undoubtedly this is the main reason for the decrease in the strength and waterproofness of concrete.
It is possible to obtain highly efficient construction conglomerates by modifying the structure of cement stone and concrete. Consequently, modification of the concrete structure in this direction is intended to improve the technological properties of the material. By modifying, it is possible to change the kinetics of the growth of physical properties and the final values of the strength of concrete. Without considering the physical and analytical mechanism for modifying the structure formation of concrete, we note that it is primarily aimed at reducing the amount of water -a mixture in a unit volume of material. However, various studies have proved that in the initial period, the structure formation of the cement stone develops in the optimal direction only at a certain volumetric water content. The limiting reduction in water content makes it difficult to hydrate the binder, limiting the final strength properties of the material. At the same time, the final strength properties of the material are improved with an all-round decrease in the volumetric water content of the mixture. In all cases, the modification of concrete assumes its composition is unchanged from the mixing of the mixture to the final stage of the formation of the concrete structure. At present, only isolated attempts are known to physically modify concrete, for example, during its evacuation. In this case, the optimal amount of mixing water is introduced into the concrete mixture, which ensures the optimal flow of the binder hydration reaction. The subsequent suction of water, changing the initial composition of concrete, leads to a deep modification of its structure formation. In particular, the density of the material and its strength properties sharply increase. It should be noted that physical modification of concrete leads to a change in the nature of fixation of binder particles.
The conducted studies allowed us to establish that the shape of the filtration holes should be subject to the above patterns. The second - it was established on the basis of the analysis of real Reynolds numbers and visual observations that the water extraction mode in the zone of action of the peristaltic wave of compaction is divided into three stages: a) laminar spin mode; b) turbulent spin mode; c) intermittent spin mode. The first stage of water extraction is determined by the classical two-dimensional (coordinate X and time t) water movement in a porous medium. Usually, this task is complicated by the presence of a water and gas phase in the squeezed stream. The first phase ends with the turbulent motion of the liquid-air phase. Turbulence as the second stage of the extraction of the water-air phase is determined by the dependence of the critical Reynolds number on the action of complex technological factors of hyper-compaction. This includes vibro-shock of peristaltic pressure and shear deformations from the reciprocating movements of the moldable mixture. The second stage ends with the transition to intermittent extraction of residual water. The third stage of extraction is characterized by the ultimate level of compaction (P max ) by breaking continuous filter channels and the transition to a submicrocellular structure of the compacted mixture [1, 2, 3, 4].
The choice of the concrete composition following the set research tasks must satisfy the following requirements: 1-the maximum achievable strength on the given starting materials; 2-the required formability, corresponding to the accepted vibration-impact-peristaltic pressing; 3-a given level of dehydration of the concrete mixture, providing a residual W/C, close to the normal density of the cement paste. The accepted conditions are necessary and sufficient when using the physical-analytical method of designing concrete composition. Distinctive features of the method are the use of a large amount of information and the absence of arbitrary coefficients, technological constants, or parameters. The necessary data for the assignment of concrete compositions are determined according to the data of preliminary laboratory experiments, the given technological parameters of mechanisms and equipment, and the design characteristics of concrete and the structure to be formed. For the experimental study, a total of six independent information streams of initial data are used: 1-physical and mechanical properties of the constituents of concrete (Rc, ρc, ρc°, [V/C], рс, γ3, ρshch, γsh, γshch°); 2-laboratory data of tests of raw materials in concrete mix and concrete (a, b, c, Ku, A, B); 3-design characteristics of concrete mix and concrete (Rb, F, W, OK, Zh); 4-characteristics of the product to be concreted (V, h, l, μ); 5-technological characteristics of equipment, mechanisms, and devices (th, tb, TO, t0); 6-the cost per unit volume of raw materials (Sc, Cn, Ssh, Se, Sg). Obviously, the listed volume of initial information comprehensively characterizes the materials used and the conditions for forming the product. The previously developed technological conditions for forming concrete pipes, in addition to the above, require, when assigning the composition of concrete, to take into account the observance of the balance of masses in the concrete mixture and compacted, modified concrete. This should be manifested in checking the equation of absolute volumes for the original and compacted (dewatered) concrete.
The resistance of concrete to axial tension is much less than the resistance to compression and is largely determined by the adhesion of its components. The low tensile strength of ordinary concrete is explained by the heterogeneity of its structure and the discontinuity of concrete, which contributes to the development of stress concentration, especially under the action of tensile forces. To increase the tensile strength of concrete, it is necessary to eliminate, first of all, the heterogeneity of the structure of concrete - one of the main reasons for the large dispersion of the results of mechanical tests of this material, which affects the experimental determination of compressive strength. A significant difference between the compressive strength for ordinary concrete indicates a rather large spread of such values. This scatter is explained by the different influence of factors on tension and compression. For example, for ordinary concretes, it was found that with an increase in W/C , the tensile strength decreases, but to a lesser extent than the compressive strength. With an increase in the grade of concrete, the tensile strength increases. High-strength concretes, as a rule, prepared on concrete mixes with low W/C and on clean conditioned aggregates in the form of crushed stone and sand, have an increased density, therefore, they have less variation in strength readings both in compression and at stretching [1-4].
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