Ceramics-Silikáty 68, (3) 306 - 315 (2024)

Ultra-high performance concrete (UHPC) contains a significant number of unhydrated cementitious material particles due to its extremely low water-binder ratio. This makes UHPC highly susceptible to the external water supply. This paper examines the correlation between the moisture transfer and compressive strength development of UHPC under three conditions: sealed standard curing, sealed steam curing, and conventional standard curing. This study analysed the corresponding mechanisms using XRD, TG, SEM, MIP and other microscopic characterisation methods. The UHPC exhibited the best mechanical properties at the deepest moisture transfer positions, and the strength increase was most pronounced under sealed steaming. However, the UHPC experienced a reduction in strength under all three curing conditions. The XRD and SEM analyses indicated the presence of ettringite in the UHPC under various curing conditions. This was closely related to the strength reduction, and UHPC was more likely to produce ettringite in areas with higher water contents, which adversely affected its strength. When steamed, the reaction degree of the fly ash inside the UHPC intensified, resulting in a more favourable strength performance.