Assessment of Strength and Deformation Characteristics of High-Strength Concrete in Structures and the Dynamics of Their Changes over Time

Abstract

Based on the data from numerous production and laboratory tests, an analysis of the actual values of the main standardized strength and deformation characteristics of high-strength concrete of classes B60-B100 was carried out: ultimate resistance to axial compression, initial modulus of elasticity and Poisson’s ratio. It has been established that the values of prismatic strength (Rb) are close to cubic (R), and the ratio between them (prismatic strength coefficient) is not lower than 0.85. A comparison of Rb values with those calculated for limit states of the 1st group according to SP 63.13330.2018 shows that for concrete classes above B70 in the regulatory document they are unreasonably underestimated. The value of the coefficient of variation of high-strength concretes does not exceed 6.5%, which is predetermined by the features of their compositions, which ensure stability of consistency, segregation stability and technological reliability of concrete mixtures. The values of the initial elastic modulus (Eb) exceed the normative ones provided for by SP 63.13330.2018.The dependence of the values of the initial modulus of elasticity of concrete of the same class on the nature of the coarse aggregate has been established. According to experimental data, the elastic modulus can vary in the range of up to 19% depending on the characteristics of the coarse aggregate used. This variability of Eb is consistent with the recommendations of EN 1992-1-1:2004 Eurocode 2, but is not taken into account in SP 63.13330.2018. The time factor affects the change in the values of strength (R and Rb) and elastic modulus (Eb). According to the data obtained, in the period from 28 days to 1.5 years the increase in strength was 15–17%, elastic modulus – 8.8–9.8%. It has been established that changes in these characteristics over time are described by mathematical models and, accordingly, can be predicted depending on the age of concrete. The results obtained indicate that the standardized parameters of SP 63.13330.2018 do not fully take into account the service life of modern high-strength concrete, which makes it necessary to make changes to the specified document.