Khezhev T.A.

Doctor of Technical Sciences, Professor, Kabardino-Balkarian State University named after H.M. Berbekov

Heat dissipation of cement and design the composition of concrete for massive structures

https://doi.org/10.58224/2618-7183-2025-8-1-3
Аннотация
Introduction. When designing a concrete composition depending on the type of structure, cement content is determined taking into account regulatory requirements for the minimum cement content depending on the operating environment. The maximum cement content is limited by economic indicators and technical conditions depending on the methods and conditions of work; the limitation on the amount of heat dissipation is not considered. Research objective: to develop a methodology for accounting for the heat dissipation of cement when assigning its consumption in concrete compositions for massive structures depending on their parameters and construction conditions. Methods. Experimental studies and analysis of regulatory documents and literary data on heat dissipation of cements and concretes. Modeling the parameters of temperature fields and stress fields depending on the class of concrete and its specific heat dissipation using the example of a foundation slab with specified dimensions and parameters of heat exchange with the environment. Results: An approach is proposed to standardizing the value of the maximum heat dissipation of concrete when designing a concrete composition for massive reinforced concrete structures. The article substantiates the position that the value of the level of tensile temperature stresses is less significantly affected by the concrete class than by its specific heat dissipation, since it is the heat dissipation of concrete that forms the temperature field and the temperature difference "center – top". Prevention of the risk of early cracking is associated not with slowing down heat dissipation, but with the value of specific heat dissipation, which determines the parameters of temperature fields, temperature gradients and stresses. The example shows that for a massive flat foundation slab with an accepted permissible level of tensile stresses of 0.67, the value of specific heat dissipation of concrete should not exceed 140 mJ / m3. A principle is proposed for determining the maximum class of concrete for compressive strength depending on the properties of cement. A dependence between the level of tensile temperature-shrinkage stresses and the criterion of thermal crack resistance of Zaporozhets I.D., independent of the concrete class, is revealed.
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Application of ash and slag waste from coal combustion in the construction of the earth bed of roads

https://doi.org/10.58224/2618-7183-2024-7-6-3
Аннотация
More than 1.5 billion tonnes of ash and slag waste from thermal power plants have been accumulated in the RF. The most promising direction of reuse is construction and repair of roads. The most material-intensive direction is the construction of earth bed. The aim of the study is to expand the practice of using ash and slag mixtures from thermal power plants for the construction of roadbeds in continental and polar climate. In order to achieve the goal set in the work the ash and slag mixture from different ash dumps of Irkutsk region was sampled. Ash and slag wastes can be considered as technogenic soils and classified according to GOST 25100 as gravelly sands and dusty sands. Ash and slag mixtures do not possess cohesion, have low values of internal friction angle, high porosity of particles and low specific weight, and small frost heave deformation. To evaluate the efficiency of ash and slag mixtures application in the structures of the roadbed of roads the design and construction of the roadway and the roadbed on the section of the road in the Irkutsk region was carried out. The technology of works on construction of earth bed layers from ash and slag mixtures is similar to the technology of erection of layers from soils. The constructed construction of road with earth bed from ash and slag mixtures has operational characteristics not lower than the construction of the adjacent road section with earth bed from local soils. Ash and slag mixtures can be used for construction of earth bed layers practically without restrictions.
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Design of steel fiber-reinforced concrete for slip forming

https://doi.org/10.58224/2618-7183-2024-7-5-2
Аннотация
Introduction. Slip forming is one of the effective and promising methods of concrete mix casting. Development of slip forming technologies largely depends on accumulated experience and tools, one of which is the composition design methodology. The use of special types of concrete, such as fiber-reinforced concrete, requires additional knowledge and the creation of special technological tools. The purpose of the study: to develop a methodology for designing steel fiber-reinforced concrete composition for slip forming. Methods and materials. Known methods for designing concrete and steel fiber-reinforced concrete compositions are used. A methodology for designing steel fiber-reinforced concrete composition for slip forming has been developed, consisting of two stages: designing the matrix composition to ensure a given ultimate extensibility of the mixture; designing steel fiber-reinforced concrete based on a pre-obtained matrix composition. Cement CEM I 42.5N, medium-sized sand, crushed stone with particles size 5-10 mm and 36 mm length steel milling fiber are used. Results and discussion. According to the proposed methodology, the composition of steel fiber-reinforced concrete with specified properties was designed (ultimate extensibility not less than 100 mm/m; cone slump 1...4 cm; compressive strength not less than 40 MPa; flexural strength not less than 6.5 MPa). The results of laboratory tests of the obtained composition are presented. In terms of strength, workability and ultimate extensibility, the composition meets the technical specifications. Conclusions. The proposed methodology of designing the composition of steel fiber-reinforced concrete for slip forming has been successfully tested in laboratory and can be recommended for use in production.
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