Research on the application of solid waste-derived reactive powder in engineered cementitious composites (ECC) and micro-mechanisms

Ultra-high-ductility engineered cementitious composites (ECC) face application limitations in infrastructure due to high costs and energy consumption. This study introduces recycled powder (RP) to reduce ECC production costs and environmental impact, developing a PVA fiber-reinforced economical ECC (Eco-ECC). The compressive, tensile, and flexural properties of Eco-ECC were investigated through nine different RP replacement levels, analyzing its load-bearing capacity and ductility variations. Through XRD, SEM, and BSE-EDS analyses, this study establishes the correlation between the macroscopic behavior and microscopic properties of Eco-ECC, revealing the interfacial mechanism between PVA fibers and the matrix. Special attention is given to the effects of RP content on PVA fiber bridging ability, fiber-matrix interfacial bond strength, and crack propagation. Results indicate that the compressive strength of Eco-ECC decreases with increasing RP content. However, when the cement content is 0.4 and the RP-to-FA ratio is 15 %:85 %, the compressive strength reaches 40.30 MPa. Tensile and flexural tests show that at a cement content of 0.2, the specimens exhibit multiple cracking in the tensile region, maintaining an ultimate tensile strain above 4.5 %, though tensile strength remains below 4 MPa. All Eco-ECC mixtures display distinct flexural hardening behavior, while increasing RP content negatively impacts cracking strength, peak deflection, and ultimate flexural strength. The optimal mix, R25-0.4, achieves a compressive strength of 33.3 MPa and a tensile strain of 3.72 %, balancing superior mechanical properties with enhanced ductility. Microstructural analysis reveals that higher RP content reduces matrix densification, leading to increased cracks, pores, and CaCO3 deposition. Additionally, fewer hydration products accumulate on the PVA fiber surface, making it smoother and weakening fiber bridging capacity. Compared to conventional ECC, EcoECC demonstrates the lowest energy consumption (14.63 %), a 28.00 % reduction in CO2 emissions, and a 32.11 % cost savings, showcasing significant sustainability advantages in energy efficiency, environmental impact, and economic feasibility. This study fills a research gap in understanding the role of RP in Eco-ECC, particularly its effects on mechanical performance and fiber-matrix interactions. However, further optimization is needed to enhance hydration activity and reinforcement mechanisms under high RP replacement levels.