INVESTIGATION OF CREEP DEFORMATIONS OF KERALITE CONCRETE ON CARBONATE SAND

Abstract

The aim of the work is to study the creep behavior of keralite concrete on carbonate sand including under the influence of composition factors and the initial relative stress level.Methodology. The study of creep of keralite concrete on carbonate sand was carried out according to the experiment planning technique. Experiments to determine the creep strain were carried out according to the Box-Benken plan of dimen- sion K=3. The factors taken as factors are: cement consumption (С), kg/m3 -X1; the aggregate structural factor r is X2; age of concrete by the time of loading (t0), days. – X3. Creep strains were determined in accordance with the requirements of [10]. The limiting relative and specific creep strains were determined according to the method described in [10]. In accordance with this methodology, to calculate the conditional-limit value of relative creep strains, a regression line should be drawn in coordinates [Δt/ εсс(t,t0,σ); Δt]. The values of the cotangent of the angle of slope of a line are given by their marginal value at the midpoints of the measurement.Results. To solve applied problems of the theory of reinforced concrete taking into account its creep, it is important to determine the main factors affecting creep and to establish appropriate dependencies that allow predicting these deformations. The determining influence on creep deformations is exerted by formulation and technological factors. The peculiarities of concrete on porous aggregates intensify their influence, which was confirmed by our research. Scientific novelty. Of all the variety of factors influencing creep deformations, on which the formation and establishment of keralite concrete as a material depends, the cement consumption, water consumption and concentration of keralite gravel should be referred to the most significant ones. The age of the keralite concrete at the time of stress application and the initial relative stress level also have a significant influence on these deformations.One of the objectives of the research was to clarify the influence of formulation factors, age of keralite concrete and initial stress level on the development in time and limiting values of creep deformations.Practical relevance. Mathematical and static analysis of the given experimental data of development in time of specific relative creep deformations С(t,t0,σ) keralite concrete of investigated compositions, loaded at ages t=7,28,115 days with initial relative stress levels η(t0)=σ(t0)/fcd(t0)=0,2;0,6;0,8, and specific linear creep strains C(t,t0) of keralite concrete of the same compositions and at the same loading ages, allowed to determine their limiting values. Studies [8,18] have confirmed a high degree of accuracy in predicting the ultimate creep characteristics using this methodology. In addition, in comparison with other methods, it is more universal and less labor-intensive.