Influence of Mixing Time of Concrete Mixtures on the Strength Characteristics of Structural Concrete
Year: 2025
Type: article
Abstract: Problem statement. Currently, in Ukraine, the vast majority of buildings and structures are built using structural concrete. The growing demand for monolithic concrete poses the task of ensuring the quality characteristics of concrete mixtures, which significantly affect the strength and deformation characteristics of structural concrete. One of the directions for achieving high quality concrete mixtures is the technological direction, which includes the use of modern concrete mixers and optimal technology for mixing the mixture components. Analysis of the current state of development and research of concretes has shown that one of the technological factors for mixing a concrete mixture is the choice of the optimal mixing time of the mixture, which significantly affects the strength characteristics of the resulting concrete. Analysis of publications has shown that its duration has a significant impact on the quality of mixing, which in cyclic mixers is determined from the moment of loading all materials to the beginning of unloading [1]. With insufficient mixing duration, the homogeneity of concrete deteriorates and its strength decreases. Increasing the mixing time leads to obtaining a homogeneous concrete mixture, but has little effect on the strength of concrete, which increases insignificantly. Practical studies by Chalon [2] show that the homogeneity of the concrete mixture is determined by the compressive strength of concrete samples after a certain mixing time, and the most noticeable effect of increasing the strength of samples is observed when mixing the mixture in the interval of 1–2 minutes. However, increasing the mixing time to 10 minutes leads to only a slight increase in the strength of concrete samples. The authors [3], based on research, present the achievement of mixture uniformity in the form of a graph depending on the conditional mixing time. In this case, the conditional mixing time corresponds to the time interval from the start of mixing to achieving mixture uniformity and is within 30−600 seconds, and the optimal achievement of strength is achieved within 30−240 seconds of mixing the concrete mixture. The regulatory document [4] regulates the duration of mixing the mixture in a stationary cyclic mixer, which is in the range from 50 to 120 seconds and depends on the density of the aggregate and the mobility of the mixture. The regulation for the production of high-mobility mixtures [5, p. 3.16] provides that the mixing time of the concrete mixture should be at least 4–5 minutes, and when using fiber additives – at least 7 minutes, of which 5 minutes is the time of dry mixing of the components. The authors [6], as a result of tests, concluded that the mixing time of 45 seconds for concrete mixtures intended for the construction of road and airfield surfaces is insufficient, since the spread of values is quite large and goes beyond the lower and upper limits, both for the air entrainment parameter and for the mobility of the mixtures. When mixing the concrete mixture for 90 seconds, the air entrainment and mobility indicators stabilize. The mixing time of 120 seconds according to the scatter of the results coincides with the mixing time of 90 seconds, therefore longer mixing is not advisable. The regulatory document [7, p. 5.2.2] determines that the order of loading the components, the duration of mixing the concrete mixture should be established for specific materials and conditions of the concrete mixing equipment used by assessing the mobility of the concrete mixture, the homogeneity and strength of concrete in a specific batch. The purpose of the article is to study the technological factor of obtaining high-quality concrete mixtures depending on the time of their mixing. In this case, it is necessary to determine the pattern of changes in the strength and deformation characteristics of structural concretes depending on the time of mixing the mixtures. Conclusions. It was established that one of the main technological factors that significantly affect the quality of concrete mixtures is the duration of mixing the concrete mixture. Studies of the cubic and prismatic strength of structural concretes obtained with a mixing time of the mixture from 90 to 480 s were conducted. The concrete classes determined by the results of cubic strength, obtained on the basis of the calculated coefficients of variation of strength at different times of mixing the mixture, turned out to be the same and amounted to C16/20 (B20). The concrete classes determined by the results of prismatic strength turned out to be different, with the highest indicators of the concrete class C30/35 (B35) and C25/30 (B30) being found in concretes of compositions no. 1 and 3 at a time of mixing the mixture of 480 and 180 s, respectively. In this case, the obtained result of exceeding the prismatic strength over the cubic strength is not typical, and confirmation or refutation of the determined concrete classes by strength can be obtained as a result of studying the deformation characteristics of concretes by determining their modulus of elasticity.
Authors: O.Yu. Konoplianyk, D.V. Zhuk
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W4411383492