Direct utilization of GFRP manufacturing waste for enhanced mechanical and sustainable cementitious composites

This study investigates the feasibility of incorporating as-received glass fiber-reinforced polymer (GFRP) manufacturing by-products as a partial cement replacement, providing a low-energy and scalable pathway for composite waste valorization. A comprehensive characterization program, including SEM/EDX, XRF, XRD, FTIR, and CT-scanning, was conducted to evaluate the effects of 20%, 40%, and 60% GFRP on the chemical, microstructural, and mechanical performance of cementitious composites. Increasing GFRP content shifted the binder chemistry toward a silica-rich system, reduced portlandite formation, and altered the C–S–H network, while microstructural analyses showed that 20–40% GFRP preserved matrix continuity with well-dispersed microfibers, in contrast to the significant porosity observed at 60%. These changes influenced the hardened properties: dry density decreased, and water absorption increased at moderate GFRP levels due to fiber-induced capillary pathways, and compressive strength declined with cement dilution. In contrast, tensile and flexural behaviors improved substantially; direct tensile strength increased by up to 136%, and flexural strength improved by approximately 39% at 20% GFRP and 47% at 40% GFRP, demonstrating the strong crack-bridging effect of GFRP. Embodied carbon analysis revealed substantial environmental benefits from replacing cement with GFRP manufacturing waste, achieving reductions of 20%, 36%, and 52% for mixtures incorporating 20%, 40%, and 60% GFRP, respectively, compared to the control mixture. Overall, the findings identify 20–40% GFRP as the optimal replacement range, providing significant mechanical enhancements while maintaining microstructural integrity, and establishing unprocessed GFRP waste as a promising, sustainable additive for improving the performance of cementitious materials.