Influence of steel fiber hybridization on the static mechanical performance of ultra-high performance geopolymer concrete (UHPGC)

This study investigated the influence of hybrid steel fiber reinforcement on the static mechanical properties of ultra-high performance geopolymer concrete (UHPGC). Three straight steel fibers of varying lengths (6, 8 and 13 mm) were examined. The flowability, compressive strength, and flexural and tensile characteristics of UHPGC with different steel fiber combinations were evaluated using the simplex centroid design method with axial design. The results showed that an inferior flowability was obtained with incorporations of longer steel fibers and the hybridization of three straight steel fibers exhibited a negative influence on the flowability. Hybrid steel fiber reinforcement had varying effects on the strength, deflection/elongation and energy absorption capacities of different mechanical properties of UHPGC. Compared to single steel fiber reinforcements, hybrid steel fiber reinforcements with two different fibers could improve the compressive strength and flexural behavior, while a negative synergy was observed when three fibers were used. Incorporating longer steel fibers enhanced the ultimate tensile strength, and the steel fiber hybridization had a considerable synergy on the tensile behavior of UHPGC. The highest ultimate tensile strain up to 0.27 % was achieved when 1 % long and 1 % medium-long fibers were added. Optimal hybrid steel fiber reinforcement meeting different mechanical performance for UHPGC can be determined using the simplex centroid design method with axial design.