Compressive strength properties of hyper-compacted concrete

The most important property of a concrete mix is concrete workability, i.e., the ability of the mixture to spread and take a given form while maintaining solidity and uniformity. The main influence on the workability of the concrete mixture is exerted by water consumption and, in part, cement consumption. Workability is determined by the mobility of the concrete mixture at the time of filling the mold and plasticity, i.e., the ability to deform without breaking the continuity. In the process of vibrating and pressing the concrete mixture placed in the mold, the total volume of the mixture changes until the pressure is balanced by the resistance forces. Deformation of concrete mix or, more precisely, freshly laid concrete with any compaction methods, including vibration compaction, is divided into elastic (reversible) and residual (irreversible). Residual deformations during vibration compaction occur as a result of water squeezing out and redistribution of aggregate fractions. Permanent deformation is part of the total. Its value at the same composition of the concrete mixture depends on the shape and size of the pressed sample. At the same time, it is noteworthy that after reaching a certain pressure, only elastic deformations will be characteristic of the freshly laid concrete mixture. So, A.D. Nikitin, in the course of the experiments, found that at a pressure of 2.2 MPa, the elastic moduli of the components of the concrete mixture have the following values: for cement paste - 0.16 · 104 MPa, aggregate - 4.5 · 104 MPa and air - 3 MPa ... After reaching a static pressure of 2.2 MPa, the compressible mixture showed only elastic deformation. This indicates that by the time the specified pressure was reached, the relative movement of the aggregates had ended, i.e., they are located most compactly

Fundamentals of property and compositions management concrete mix and concrete

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

Production of extra-strong concrete axisymmetric products

The article presents the results of many years of comprehensive research on the new technology of forming extra-strong unreinforced pipes for hydro-engineering construction by vibro-peristaltic hyper-compacting with simultaneous modifying of the concrete mixtures and concrete itself. The regularities of occurrence of a compacted mixture in a column of high-intensity compression and tension zones varying in time, as well as the placement and configuration of the filtration fields of the formwork forms, taking into account the type and diameter of the holes preventing their blockage in the molding process, are given. As a result of experimental theoretical and industrial research, the scientific basis for the production of highly durable concrete has been developed. Technological bases of its production in axisymmetric products, as well as a new installation for molding concrete unreinforced pipes by vibro-peristaltic pressing, which is protected by copyright certificate and patent of the Republic of Uzbekistan. The installation is intended for forming low-pressure and free-flow pipes with a nominal diameter from 500 to 1500 mm and a length of up to 2000 mm. The purpose of this article is to share the results of research, experience to accelerate the widespread introduction of new technology

Compressive strength properties of hyper-compacted concrete

The most important property of a concrete mix is concrete workability, i.e., the ability of the mixture to spread and take a given form while maintaining solidity and uniformity. The main influence on the workability of the concrete mixture is exerted by water consumption and, in part, cement consumption. Workability is determined by the mobility of the concrete mixture at the time of filling the mold and plasticity, i.e., the ability to deform without breaking the continuity. In the process of vibrating and pressing the concrete mixture placed in the mold, the total volume of the mixture changes until the pressure is balanced by the resistance forces. Deformation of concrete mix or, more precisely, freshly laid concrete with any compaction methods, including vibration compaction, is divided into elastic (reversible) and residual (irreversible). Residual deformations during vibration compaction occur as a result of water squeezing out and redistribution of aggregate fractions. Permanent deformation is part of the total. Its value at the same composition of the concrete mixture depends on the shape and size of the pressed sample. At the same time, it is noteworthy that after reaching a certain pressure, only elastic deformations will be characteristic of the freshly laid concrete mixture. So, A.D. Nikitin, in the course of the experiments, found that at a pressure of 2.2 MPa, the elastic moduli of the components of the concrete mixture have the following values: for cement paste - 0.16 · 104 MPa, aggregate - 4.5 · 104 MPa and air - 3 MPa ... After reaching a static pressure of 2.2 MPa, the compressible mixture showed only elastic deformation. This indicates that by the time the specified pressure was reached, the relative movement of the aggregates had ended, i.e., they are located most compactly

Study of the strength properties of modified concrete in tension

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]

Change in the strength properties of modified concrete over time

To date, there is no data on the change in the strength of hyper - compacted concrete. The conducted field observations summarize the data of a long-term period and allow us to draw a number of conclusions. As shown by numerous studies, the nature of the development of the strength of concrete over time depends mainly on the type of cement, the composition of the concrete mixture, the temperature and humidity conditions of hardening, and also on many other factors. Obtaining highly efficient building materials is possible by modifying the structure of cement stone and concrete. Consequently, the 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 physico-analytical mechanism for changing the structure formation of concrete, we note that it is primarily aimed at reducing the amount of water - a mixing agent per unit volume of the material. However, various studies have shown that in the initial period, the structure formation of cement stone develops in the optimal direction only at certain volumetric water content. The limiting reduction in water content complicates the process of hydration of the binder, limiting the final strength properties of the material. At the same time, the final strength properties of the material are improved by reducing the volumetric water content of the mixture in every possible way. In all cases, the modification of concrete assumes its composition to be unchanged from the mixing of the mixture to the final stage of the formation of the concrete structure

Some aspects of the processes of obtaining and application of mineral powders as fillers for cement systems

The main theoretical prerequisites for the thermodynamic analysis of the process of grinding rocks are given. The structural-energetic relationships between the regularities of plastic deformation with energy characteristics that occur during the crushing of mineral substances are described. The evaluation of the grindability of rocks in a ball mill under different grinding modes was made. Rational operating modes of the mill have been determined to ensure the required degree of grinding, which makes it possible to significantly reduce the energy consumption of the grinding process. To assess the quantitative content of adsorption centers, a classification of the “indicator of reduced hydration activity” is proposed. (Ppga), allowing the most accurate assessment of the contribution of the surface activity of mineral fillers to the course of the processes of interactions and transformations occurring in a hydrated medium

Fundamentals of property and compositions management concrete mix and concrete

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