Koryanova Yu.I. — Строительные материалы и изделия

Autogenous shrinkage of cement and concrete with superplasticizers of various chemical bases

https://doi.org/10.58224/2618-7183-2026-9-2-5

Chepurnenko A.S., Nesvetaev G.V., Koryanova Yu.I.

Аннотация

Introduction. The stress-strain state of massive monolithic reinforced concrete structures during the early stages can cause cracks due to temperature deformation and autogenous shrinkage of concrete. Ignoring the deformations caused by autogenous shrinkage in calculations of the stress-strain state is often an unjustified simplification. This emphasizes the importance of studying the influence of formulations and technological factors on the amount and rate of autogenous shrinkage in concretes. The kinetics of autogenous shrinkage, especially during the first two days of hardening, can vary significantly depending on the specific characteristics of the cement and superplasticizer used. The aim of the study. To investigate the influence of the type of cement and superplasticizers with different chemical basis on the magnitude and kinetics of autogenous shrinkage and to obtain the necessary equations for calculations of thermally stressed states in the early stages. Methods. Analysis of existing approaches to assessing autogenous shrinkage in cement paste and concrete. Experimental study of autogenous shrinkage of cement pastes. Comparison results with published data and EN and JSCE standards. Results. Based on the proposed equation a classification of autogenous shrinkage kinetic of cements is proposed. The kinetics of autogenous shrinkage was varied: at the age of one day, the amount of autogenous shrinkage relative to seven days can vary up to six times, at the age of three days up to two times. An equation of the dependence of autogenous shrinkage on concrete strength is proposed for calculating the thermally stressed state of massive monolithic structures in the early period.

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Experience of concreting a massive monolithic foundation slab

https://doi.org/10.58224/2618-7183-2025-8-5-2

Chepurnenko A.S., Nesvetaev G.V., Koryanova Yu.I., Shut V.V., Tyurina V.S.

Аннотация

The large number of recipe and technological factors affecting the stress-strain state of concrete in the initial period of massive monolithic structures erection predetermines the expediency of using modeling of temperature fields and stresses with software packages based on analytical and numerical solutions when developing technological regulations for concreting. Improving the algorithm for calculating temperature fields and stresses taking into account the kinetics of concrete heat release, heat exchange conditions, ambient temperature and the stages of construction of structures is a pressing task. A comparison was made of calculated, laboratory and natural values of some parameters when concreting a foundation slab with a volume of 1642 m3, a surface area of 821 m2, and a thickness of 2 m. Concreting was completed in 13.5 hours with an average intensity of concrete mix placement of 122 m3/h, and a peak intensity of up to 240 m3/h. A method for calculating temperature fields and stresses taking into account the staged nature of construction has been developed in the MATLAB environment. It does not require rebuilding the geometry of the finite element model, adding nodes and elements during the process of laying new layers, and allows for the correct consideration of the dependence of the strength and deformation properties of concrete on the degree of its maturity. The results of calculated and measured temperature values excluding heating from solar radiation showed a discrepancy of up to 10 °C on the upper surface at some points in time. Some discrepancy between the calculated and experimental values of stresses and deformations with a qualitative coincidence in the nature of the curves is due to the neglection of shrinkage and rapid creep of concrete and poor study of the deformation properties of concrete with additives based on polycarboxylate esters at an early age.

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

https://doi.org/10.58224/2618-7183-2025-8-1-3

Nesvetaev G.V., Koryanova Yu.I., Khezhev T.A.

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

Nesvetaev G.V., Koryanova Yu.I., Shut V.V.

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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