Mechanical properties of hybrid fiber reinforced ternary-blended alkali-activated materials

•Using PVA and steel fiber enhanced mechanical performance of ternary geopolymer.•Higher PVA fiber ratio reduced setting time and fluidity of HFRG.•The best performance was achieved at a PVA: steel fiber volume ratio of 1:1. This study employed fly ash, blast furnace slag and steel slag to synthesize ternary-blended alkali-activated materials (AAMs) in order to make full use of the industrial solid wastes and improve the mechanical performance by synergistic effects of the precursors. However, peudo-brittle nature is still the main problem of ternary-blended AAMs. To solve this problem, the effect of hybrid fibers consisting of high-modulus steel (ST) fiber and low-modulus Polyvinyl Alcohol (PVA) fiber on the mechanical properties of the ternary-blended AAMs was evaluated by testing their setting time, flowability, uniaxial compressive strength (UCS), indirect tensile strength (IDT), uniaxial tensile strength (UTS), and three-point bending strength (3PBS). Also, the microstructure of the matrix and fibers were analyzed using a scanning electron microscope. The results show that the flowability and setting time increased with the increasing replacement of PVA fiber by ST fiber. At the PVA/ST fiber volume ratio of 1:1, the AAMs cured for 28 days achieved the highest UCS, IDT, UTS, and 3PBS, which were 32 %, 91 %, 80 % and 114.7 % higher than the AAMs without fiber reinforcement, respectively. The fracture pattern and microstructure illustrated that the best synergistic effect of hybrid fibers was achieved at the PVA:ST fiber ratio of 1:1, at which the small-sized PVA fibers and large-sized ST fibers can inhibit the propagation of micro- and macro-cracks at early and late deformation processes. Furthermore, the ultimate elongation of the composite was improved from 2.62 % to 4.21 % and 5.3 % by modifying the PVA fiber with acrylic polyurethane copolymer and replacing the PVA fiber with polyethylene fiber, respectively, implying the significance of surface hydrophilicity of low-modulus fiber on the ductility of AAMs. This study provided a guide for synthesizing and tailoring the mix design of hybrid-fiber-reinforced ternary AAMs with better strength and ductility.