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.针对盐碱环境下低碳耐久混凝土的迫切需求，本研究以脱硫石膏（desulfurization gypsum, DG）、金尾矿（gold tailings, GT）与粉煤灰（fly ash, FA）为主要胶凝材料，辅以再生骨料作为骨料，制备了碱激发混凝土。本研究采用等温传导量热法（isothermal conductive calorimetry, ICC）、X射线衍射（X-ray diffraction, XRD）、傅里叶变换红外光谱（Fourier transform infrared spectroscopy, FT-IR）及同步热分析（TG-DSC-DTG, simultaneous thermal analysis）等微观结构表征手段，结合宏观性能测试，探究了该体系在内、外源性硫酸盐与碱激发三重作用下的水化机理、力学性能与盐蚀耐久性。研究结果表明，当脱硫石膏掺量为10%且配合NaOH-Na₂SiO₃复合激发体系时，材料可获得最优综合性能。将该混凝土分别置于5%硫酸钠溶液与5%硫酸钠+氯化钠混合溶液中浸泡90天后，其强度衰减率仅为26.0%与29.1%，耐腐蚀系数均维持在63.3%以上。内、外源性硫酸盐通过协同与竞争双重效应共同影响材料性能：适量的内源性硫酸盐可预先生成钙矾石与C-(A)-S-H凝胶，从而有效抑制外源性盐蚀。本研究为盐碱地工程中低碳耐久全固废混凝土的材料设计与工程应用提供了科学依据。