Koryanova Yu.I.

Candidate of Engineering Sciences (Ph.D.), Assistant Professor of Department of Construction Production Technology, Don State Technical University

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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Specific heat dissipation of concrete and the risk of early cracking of massive reinforced concrete foundation slabs

https://doi.org/10.58224/2618-7183-2024-7-4-3
Аннотация
Introduction. The modeling of temperature fields and stresses used to prevent the risk of early cracking of massive monolithic reinforced concrete structures determines the relevance of improving the algorithm for calculating temperature stresses due to the «center-top» temperature difference depending on the magnitude and kinetics of heat dissipation of concrete, autogenous shrinkage, heat transfer conditions and ambient temperature. Purpose of the study: modeling of temperature fields and stresses of massive structures using the example of a flat foundation slab 1.5 m thick based on the proposed dependencies of the kinetics of strength, heat dissipation, autogenous shrinkage, and deformation properties of concrete of various classes. Methods. Modeling of temperature fields and stresses taking into account specific heat dissipation and properties of concrete. Results: A system of equations is proposed, identical in structure to the strength kinetics equation according to EN 1992-1-1, to describe the kinetics of autogenous shrinkage and heat dissipation of hardening concrete depending on the type of cement according to the hardening kinetics. Modeling of the formation of temperature fields and stresses of a massive flat foundation slab 1.5 m thick was carried out depending on the class of quick-hardening concrete and the specific heat dissipation of cement. It is substantiated that it is insufficient to prevent early cracking by limiting only the «center-top» temperature difference without taking into account the specific properties of concrete. It has been shown that autogenous shrinkage, when dependent on the strength of concrete according to the EN 1992-1-1 equation, can slightly reduce the level of tensile stresses in the early period of concrete hardening of a massive foundation slab. An approach to normalizing the heat dissipation of concrete and cement is proposed in order to limit the stress level under the conditions of the problem considered. The values of the permissible values of the «center-top» temperature difference taking into account the properties of concrete were obtained.
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