Ternary geopolymers synthesized with fly ash, granulated blast furnace slag, and steel slag offer a combination of improved mechanical properties, environmental sustainability, cost-effectiveness and flexibility in composition. However, the brittleness of the ternary geopolymer limits its wide employment. This problem can be addressed by integration of low-modulus polyethylene (PE) fibers and high-modulus steel (ST) fibers in ternary geopolymers. This study systematically investigates the mechanical properties and multi-scale strain hardening mechanisms of hybrid fiber-reinforced engineering geopolymer composites (HFEGC). The results reveal that the hybrid fiber with 1 vol% PE fiber and 1 vol% of ST fiber results in the highest compressive, tensile, and four-point bending strength of the ternary geopolymer, which were 32% (62 MPa), 123% (7.1 MPa), and 214% (16 MPa) higher than that of the geopolymer without fibers, respectively. Furthermore, the ultimate tensile strain of HFEGC is 7.4%, which is 155% higher than the geopolymer composite with single PE fiber. This study provides a viable solution for enhancing the ductility of ternary geopolymers, paving the way for their broader utilization in construction.
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