English English

Klyuev S.V.

Doctor of Engineering Sciences (Advanced Doctor), Associate Professor, Belgorod State Technological University named after V.G. Shukhov, Russia

THE RELIABILITY COEFFICIENT FOR FIBRE CONCRETE MATERIAL

https://doi.org/10.58224/2618-7183-2022-5-2-51-58
, , , , ,
 51-58 p.
Abstract
One of the main parameters of the method for calculating building structures made of concrete and fibre concrete by limiting states is the reliability coefficient for the material, which characterizes the heterogeneity of the physical and mechanical properties of the material. In national and foreign standards, it takes a constant value of 1.3 (obtained on the basis of direct tests), or 1.5 (obtained on the basis of indirect tests and the use of graduated dependencies). The concrete matrix for the formation of the structure of fibre concrete is most often fine-grained concrete with special additives, which has greater uniformity in comparison with heavy concrete, which cannot but affect the reliability of the composite material in question as a whole: the stock coefficients for fibre concrete should be lower than for normal concrete, which has not been reflected in modern standards for design yet. Starting from interval estimates of the average strength value, a new approach to determining the reliability coefficient for the material, differentiated by the 1st and 2nd groups of limit states, is proposed. The results of calculations according to the proposed formulas for previously conducted tests of steel- and glass-fiber concrete images allowed us to conclude: the introduction of fiber into the concrete matrix of the proposed effective composite composition increases the uniformity of the strength properties of the material, which leads to an increase in the reliability of its use in building structures, a decrease in the value of the reliability coefficient (margin) for the material to 1.164...1.235 for central axial compression and up to 1.172...1.272 – for central axial stretching. The obtained actual coefficients in strength calculations will allow to reveal the supplemented reserves of the bearing capacity of structures made of this material up to 22.4%.
PDF

INCREASING IN IMPACT VISCOSITY OF FIBER-ASH-CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-6-5-16
, , , , ,
 5-16 p.
Abstract
The trend in building materials science is to replace the different proportions of Portland cement in the binder. Therefore, the paper proposes the principles of controlling the static and dynamic strength of fiber-reinforced concrete, consisting in the complex effect of the hydro-removed ash and slag mix and basalt fiber on the processes of structure formation of the cement composite. A four-stage purification system for the hydro-removed ash and slag mixture has been developed, including disintegration, flotation and two-stage magnetic separation. It was found that the density of the fresh mix from the dose behaves naturally, and the density of solid samples at low doses slightly decreases. High early strength of the developed composites is noted, in particular, for specimens with ASM, one and a half increase in compressive strength is traced in comparison with non-additive specimens. Combinations of "fiber + ASM" with a quadrupling of strength have a significant effect on bending strength. Successful approximations of the compressive strength and bending strength on the ASM dose for different ages (1, 7, 28 days) are traced with the regular behavior of the coefficients in the power dependences. Revealed a multiple increase in the impact strength of the developed compositions. The use of the results will lead to the possibility of designing high-strength concretes, including for special structures.
PDF

DEVELOPMENT OF RADIATION-PROOF CONCRETE COMPOSITIONS

https://doi.org/10.34031/2618-7183-2020-3-5-24-33
, , , ,
 24-33 p.
Abstract
The article considers the possibility of using composite binders and magnetite as components of concrete with radiation-proof properties. The use of the developed concrete is possible not only when it is necessary to build nuclear power plants, but also to create bunkers or anti-radiation shelters. A special feature of con-cretes used for the protection and design of nuclear reactor cranes is their properties, which they must have. These properties include: low thermal conductivity, increased density, high temperature resistance, reduced values of the coefficient of thermal expansion, shrinkage and creep. Technogenic raw materials for the production of very heavy concrete are studied, the main physical and mechanical characteristics, the requirements that need to be considered in the selection of raw mix composition for protective concrete are analyzed. The paper presents a comparison of physical and mechanical characteristics, the advantages and disadvantages of introducing a binder of various types: cement, cement with a superlasticizer and a binder of low water consumption. It was found that the use of a low-water-consumption binder increases the physical and mechanical characteristics while reducing the consumption of cement in the raw material mix compared to traditional heavy concrete with cement.
PDF

FIBER CONCRETE FOR 3-D ADDITIVE TECHNOLOGIES

https://doi.org/10.34031/2618-7183-2019-2-4-14-20
, ,
 14-20 p.
Abstract
Fine-grained fiber concrete used in 3D printing is significantly different from conventional heavy concrete, which is determined by the increased consumption of cement, low water-cement ratio and the absence of large aggregates. The largest grain size of fine aggregate is selected taking into account the thickness of the section, the frequency and type of reinforcement, as well as the method of concrete placement. Despite the fact that the tensile strength of concrete on fine sand is more than 1.5 times higher than the strength of concrete on coarse sand, while there is a decrease in compressive strength. Due to the peculiarities of the technology of concrete manufacturing for layering, the use of coarse sands is impractical, and therefore it was decided to use quartz sand with a particle size module of 1.12 as a filler.
PDF