Effect of relative air humidity on the creep coefficient of high-strength self-compacting concrete

Comparative long-term tests of high-strength self-compacting concretes of classes B70, B80, and B100 with the organomineral modifier MB10-50C were conducted to evaluate the effect of relative air humidity (20, 60, 90%) on their deformation and strength properties. The studies were carried out in accordance with GOST 24452–2023 and GOST 24544–2020. It was found that a decrease in relative air humidity from 90% to 20% slows down but does not stop the hardening processes of high-strength concretes from 28 to 268 days. This is explained by the specific structure of the cement paste, which can more effectively accommodate changes in relative air humidity. At the same time, the increase in compressive strength and elastic modulus of concretes of classes B70–B100 decreases from 7–12% to 4–5%. The experimentally obtained creep coefficients of high-strength self-compacting concretes of classes B70–B100, which determine the value of the concrete deformation modulus under prolonged load, fall within a narrow range at the same air humidity (0.32–0.38 at 90%, 0.41–0.50 at 60%, and 0.61–0.71 at 20%). These values are significantly lower-by a factor of 2 or more than the standardized values according to Eurocode EN 12390 (ranging from 0.71 to 1.41) and the set of rules SP 63.13330.2018 (ranging from 1.0 to 2.0).