聚丙烯纤维可显著提升堆石混凝土坝面层自密实混凝土(SCC)的抗裂性能,优良的工作性是其工程应用前提。采用数字视频方法,研究0%~0.4%不同体积掺量聚丙烯纤维对SCC坍落扩展动态流动行为的影响,分析流动圆度、扩展度时程、速率演化特征。结果表明:聚丙烯纤维显著降低了自密实混凝土的扩展度和流动速度;0.1%掺量下流动均匀性最优;0.2%为临界掺量,超过该掺量后混凝土流动性急剧劣化。SCC扩展度为713~490.5 mm;V型漏斗流动时间为10.6~13.3 s,两者变化趋势与全过程动态流动规律吻合。

[Objective] Polypropylene fibers can significantly enhance the crack resistance of self-compacting concrete (SCC) when it is applied in the surface layer of rock-filled concrete (RFC) dams, and excellent workability is a prerequisite for its successful engineering application. Digital video methods can capture the morphological evolution and spreading characteristics of concrete during the flow process, overcoming the information limitations of traditional single end-point measurements. However, existing studies based on digital video methods have mostly focused on the development of workability measurement techniques or flow analysis of paste systems, leaving a gap in systematic research on the morphological and velocity variation patterns throughout the entire slump flow process of polypropylene fiber-reinforced SCC. [Methods] Using a digital video method, we investigated the effects of polypropylene fibers at different volume fractions (ranging from 0% to 0.4%) on the dynamic slump flow behavior of SCC. Specifically, we analyzed the flow roundness, the time history of slump flow, and the evolution of flow rate during the slumping process. [Results] Polypropylene fibers markedly reduce both the slump flow distance and the flow velocity of SCC. The optimal flow uniformity is observed at a fiber content of 0.1%. The critical fiber content is determined to be 0.2%; beyond this content, the flowability of concrete deteriorates sharply. Under the five different fiber contents, the measured slump flow diameters of SCC range from 713 mm down to 490.5 mm, while the V-funnel flow times range from 10.6 seconds to 13.3 seconds. The trends of both conventional indicators are fully consistent with the full-process dynamic flow behavior observed in the experiments. [Conclusions] This study elucidates the influence mechanism of polypropylene fibers on the flow performance of SCC from a full-process dynamic perspective, thereby providing a valuable reference for engineering applications in dam construction.