Mesoscale cracking mechanism of high-strength Engineered/Strain-Hardening Geopolymer Composites (EGC/SHGC) with recycled GFRP

In this study, High-strength Engineered Geopolymer Composites (HS-EGC) were developed by incorporating recycled glass fiber reinforced polymer (rGFRP) powder. A systematic experimental program was performed to evaluate how the rGFRP incorporation affects the mechanical performance, microstructure, cracking behavior, and flaw effects of HS-EGC. Results showed that although compressive strength dropped under higher rGFRP contents, it could remain above 100 MPa even at a 30 % rGFRP replacement. Higher rGFRP contents improved tensile and cracking strengths owing to stronger fiber–matrix bonding and greater matrix toughness. However, excessive fracture toughness reduced strain-hardening capacity and multiple-cracking potential. Microstructural observations revealed that increasing rGFRP replacement ratios reduced geopolymer reaction degree, lowered matrix microhardness, and caused a higher proportion of ruptured fibers. Flaw analysis indicated that, with increasing rGFRP replacement, the characteristic size of active flaws increased while the probability of flaws becoming active decreased, suggesting a more restrictive flaw-activation condition that hinders the development of distributed multiple cracking. Finally, considering both mechanical efficiency and environmental issues, a 10 % rGFRP incorporation offered the most favorable balance. The findings of this research offer valuable insights into the valorization of rGFRP from EoL-WTB recycling and contribute to the development of sustainable and high-performance fiber-reinforced concrete materials.