Hybrid reinforcement of steel-polyethylene fibers in cementless ultra-high performance alkali-activated concrete with various silica sand dosages

The effects of steel and polyethylene (PE) fiber hybrid reinforcement on the mechanical performance of cementless ultra-high performance alkali-activated concrete (UHP-AAC) containing an industrial by-product and various amounts of silica sand were investigated. Replacing steel fibers with PE fibers reduced the compressive and tensile strengths, with the best performance was observed in the hybrid specimens with a medium-grade fine aggregate-to-binder (FA/B) ratio. Increasing the PE fiber replacement ratio and decreasing the FA/B ratio increased the occurrence of multiple microcracks. The FA/B ratio had a greater effect on the variation in the pseudo-strain hardening indices than the fiber replacement ratio. The highest complementary energy, 1,762.5 J/ m2, was obtained for PE fiber-reinforced UHP-AAC at an FA/B ratio of 0.16, while the lowest value, 309.6 J/m2, was obtained for steel-fiber-reinforced UHP-AAC at the same FA/B ratio. In conclusion, the hybrid reinforcement of UHP-AAC can be optimized by considering the FA/B ratio and fiber replacement ratio.