The hybrid effect of twisted steel (T) fibers with an aspect ratio of 100 and polyethylene (PE) fibers with four different aspect ratios of 400, 600, 900, and 1200 on the mechanical performance of ultra-high-performance cementitious composite (UHPCC) was investigated. This involved a total of 17 different sample types at an identical fiber volume fraction of 2% being made and subjected to compressive and tensile loads. Samples were made by replacing 0.5%, 1.0%, 1.5%, and 2.0% of T fibers with four different types of PE fibers. In addition, the pullout behaviors of fibers at cracked sections and the cracking behaviors of specimens were evaluated in order to determine the effect of the pullout mechanism of each fiber on the overall tensile performance. Test results indicate that the compressive strength decreased in proportion to the amount of PE fibers, regardless of their aspect ratio. The fiber hybridization had a great synergetic effect, successfully improving the tensile strength and strain capacity of UHPCCs; this effect was dependent on the aspect ratio of the PE fibers. Finally, the cracking behaviors were determined to be more related to the fiber type and pullout mechanisms than the tensile strength or strain capacity of UHPCCs.
Keywords: fiber aspect ratio; hybrid reinforcement; mechanical property; polyethylene fiber; twisted steel fiber; ultra-high-performance cementitious composite.