This study focuses on the modification effect of incorporating polypropylene fibers to enhance the mechanical properties of self-compacting hydraulic concrete. It systematically investigates the influence patterns of fiber parameters (length and dosage) and curing time on its compressive strength, failure strain, and microstructural evolution. Experimental programs with varying polypropylene fiber parameters (length and dosage) and curing durations were designed. Multi-scale analysis was carried out through macroscopic mechanical testing and microstructural characterization techniques. At the macro level, standard compressive strength tests and failure strain measurements were conducted to analyze the mechanical response to different parameters. At the micro level, scanning electron microscopy (SEM) and computed tomography (CT) scanning techniques were employed to investigate the synergistic mechanisms between fibers and hydration products. Polypropylene fibers significantly improved the mechanical performance of the concrete through “crack bridging” and “energy dissipation” mechanisms. When the fiber dosage reached 0.8%, the compressive strength increased by up to 80.3% compared to the control group. Both compressive strength and failure strain initially increased and then decreased with increasing fiber content. Short-cut fibers exhibited the best performance due to their superior dispersion uniformity. Microstructural analysis revealed that the fibers and hydration products formed a dense three-dimensional network, effectively delaying the failure process. However, fiber agglomeration occurred when the dosage exceeded the optimal level, which weakened the overall mechanical performance. A self-compacting hydraulic concrete mix design incorporating 0.8% fiber dosage and short-cut fibers can significantly enhance the mechanical performance. The synergistic effect between fibers and hydration products is central to performance improvement, while balancing fiber dosage and dispersion is essential to prevent agglomeration. This research provides a theoretical foundation and practical guidance for improving the mechanical performance of self-compacting hydraulic concrete in hydraulic engineering applications.

hydraulic structures  /  self-compacting concrete  /  polypropylene fibers  /  material properties  /  mechanism