Synergistic optimization of rheo-mechanical performance and sustainability in fiber-reinforced alkali-activated tailings backfill

• W/S and PPF volume interactively optimize FATB’s rheo-mechanical performance. • IT and FA solid wastes enable high-toughness FATB via fiber bridging and pull-out mechanisms. • FATB demonstrates superior sustainability with reduced cost and carbon footprint versus conventional backfills. This study focuses on fiber reinforced alkali-activated tailings backfill (FATB), systematically investigating its fresh properties, mechanical performance, rheological characteristics, toughening mechanism, and sustainability by regulating water-to-solid ratios (W/S) and polypropylene fiber (PPF) volume fractions. Results show that W/S and PPF volume fraction synergistically affect FATB performance. Higher W/S increases flow diameter but reduces compressive strength. Flexural strength first rises then falls with PPF volume fraction at low W/S (0.2, 0.3) due to fiber agglomeration, while increasing continuously at high W/S (0.4, 0.5) with uniform fiber networks. Rheologically, FATB exhibits pseudoplastic and Bingham plastic behaviors, with yield stress and plastic viscosity decreasing significantly with higher W/S, and PPF influence varying with W/S-dependent dispersion. DIC and SEM analyses reveal that PPF enhances toughness through bridging, crack resistance, and interfacial interactions (fiber tearing at low W/S, pull-out slip at medium-high W/S). Sustainability evaluation indicates FATB, utilizing iron tailings sand (AT) and fly ash (FA) as waste materials, achieves favorable economic and environmental benefits compared to conventional materials. This research provides theoretical support for the application of FATB in engineering.