Abstract
The preparation of ultra-high-performance concrete (UHPC) with both high-early-strength and good workability contributes to further promotion of its development and application. This study investigated the effects of different accelerators (SM, alkaline powder accelerator; SF, alkaline powder accelerator containing fluorine; and AF, alkali-free liquid accelerator containing fluorine) on the workability and strength properties of UHPC. The microstructure of UHPC was also characterized by using XRD and SEM. Several dosage levels of accelerators (2%, 4%, 6%, and 8% by mass) were selected. The results indicate that the setting time and fluidity of UHPC are gradually decreased with an increase in accelerators dosage. Compared with fluorine-containing SF/AF, fluorine-free SM evidently facilitates UHPC early strength gain speed. However, the fluorine-containing accelerators have a higher 28 d strength ratio, especially AF. The maximum compressive and flexural strength ratios are obtained at a dosage of 6%, which are 95.5% and 98.3%, respectively. XRD and SEM tests further reveal the effect of different accelerators on the macroscopic properties of UHPC from the micro level.
Highlights
Ultra-high-performance concrete (UHPC) is a cement-based composite material mixed with different active powders and fiber materials [1]
It is urgent to prepare UHPC cured at room temperature with both high-early-strength and good workability to promote its innovative and engineering application
It could be seen that the incorporation of accelerators significantly reduces the setting time of these UHPC, and the acceleration effect of SF is the most obvious
Summary
Ultra-high-performance concrete (UHPC) is a cement-based composite material mixed with different active powders and fiber materials [1]. Due to the close packing of various material components and the bridging effect of fibers, UHPC has high compressive strength, good bending toughness, and excellent durability, and has excellent properties such as tensile strain hardening [2,3,4,5]. It is especially suitable for the construction of super long-span and super high-rise structures, as well as the reinforcement of existing concrete structures [5,6,7,8,9,10]. It is urgent to prepare UHPC cured at room temperature with both high-early-strength and good workability to promote its innovative and engineering application
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