Durability of desulfurized gypsum-gold tailings-fly ash-based concrete

To address the urgent demand for low-carbon durable concrete in saline-alkali environments, this study prepared alkali-activated concrete using desulfurization gypsum (DG), gold tailings (GT), and fly ash (FA) as primary cementitious materials, with recycled aggregates as aggregates. Microstructural analyses including isothermal conductive calorimetry (ICC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and simultaneous thermal analysis (TG-DSC-DTG), alongside macro-performance tests, were employed to investigate the hydration mechanism, mechanical properties, and salt corrosion durability of the system under triple action from endogenous and exogenous sulfates and alkali activation. Results indicate that a 10% DG dosage combined with NaOH-Na₂SiO₃ composite activation yields optimal performance. After 90 days of immersion in 5% Na₂SO₄ solution and 5% Na₂SO₄+NaCl mixed solution, the concrete exhibited strength decay rates of only 26.0% and 29.1%, respectively, with corrosion resistance coefficients maintained above 63.3%. Both endogenous and exogenous sulfates influence material performance through synergistic and competitive effects. Appropriate endogenous sulfates can pre-form ettringite and C-(A)-S-H gel, thereby inhibiting exogenous salt corrosion. This study provides scientific basis for the material design and application of low-carbon, durable, all-solid-waste concrete in saline-alkali land engineering.