Keywords: autogenous shrinkage

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

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