O.B. Berdiyev, B.F. Botirov

Annotation:

This article experimentally investigates the changes in the compressive strength of conventional B30 concrete depending on the curing age, as well as the processes involved in the formation of the mineralogical composition of the cement stone. The compressive strength of the concrete specimens was determined at 3, 7, and 28 days, while the mineralogical changes occurring in the cement stone were evaluated using X-ray diffraction (XRD) analysis. The test results showed that the compressive strength of concrete was 25.11 MPa at 3 days, 28.07 MPa at 7 days, and 40.02 MPa at 28 days. These values corresponded to 62.7%, 70.1%, and 100%, respectively, of the 28-day compressive strength. The XRD analysis showed that significant changes occurred in the mineralogical composition of the cement stone with increasing curing age. In the 3-day specimen, a high-intensity diffraction peak was recorded at 2θ ≈ 29.4°, along with diffraction peaks associated with the C₃S, C₂S, C₄AF, and C₃A phases. At 7 days, an increase in the prominence and intensity of the diffraction peaks was observed, and the portlandite Ca(OH)₂ phase was also detected. In the 28-day specimen, the formation of a stable crystalline structure and densification of the cement stone microstructure were observed. The obtained results indicate a close relationship between the kinetics of concrete strength development, cement hydration processes, and changes in the mineralogical composition of the cement stone over time.

Keywords: concrete, B30 class, compressive strength, strength development kinetics, cement hydration, X-ray diffraction analysis, XRD, mineralogical composition, alite, belite, portlandite.