Tailored role of ternary precursor system and recycled sand in developing sustainable engineered geopolymer composites with low PE fiber content

This study successfully developed a high-ductility geopolymer composite with practical strength, requiring merely 0.7% volume fraction of PE fibers. The breakthrough was achieved by elaborately formulating a ternary precursor system (metakaolin, ground granulated blast-furnace slag, and silica fume) and leveraging the synergistic effects of porous aggregates (fly ash cenosphere, recycled sand). The uniaxial tensile tests were conducted to investigate the tensile properties and cracking characteristics of the EGC. The pore condition of the composites was evaluated through boiling water tests. Additionally, the mechanism of high ductility of EGC was systematically investigated through three-point bending tests and single crack tensile tests, supplemented by micromechanics- based theoretical models to verify the design principle underlying its strain-hardening behavior. Scanning electron microscopy (SEM) was employed to characterize the microstructure of EGC to reveal the microscopic mechanisms responsible for its high ductility. The results indicate that the intrinsic defects in RS contribute to a notable increase in the porosity of the EGC. The substitution of 50% RS exhibits optimal tensile and compressive properties, with a tensile strength of 4.98 MPa, a tensile strain of 7.15%, and a compressive strength of 38.24 MPa. Even when 100% of the FAC is completely substituted with RS, the tensile strain exceeds that of the control mix, reaching 6.75%, while the compressive strength remains satisfactorily high, above 20 MPa. The inclusion of RS facilitates the attainment of higher pseudo-strain-hardening (PSH) values, enabling the reduction fiber content necessary to achieve strain-hardening and multiple cracking behavior. Meanwhile, it also offers a new and promising pathway for the sustainable utilization of construction materials.