Preparation of waterproof block by silicate clinker modified FGD gypsum

•When silicate clinker was added, the strengths of FGD gypsum were increased.•Reducing the particle size of clinker can improve mechanical properties and water resistance.•Adding silicate clinker to FGD gypsum can reduce the hydration reaction rate With silicate clinker being added to FGD gypsum, calcium silicate and ettringite were formed. Silicate clinker was used to modify flue gas desulfurization (FGD) gypsum. Then the effects of the amount and particle size of silicate clinker on the mechanical properties, softening coefficient and water absorption of modified FGD gypsum materials were studied. The results show that adding a proper amount of silicate clinker could improve the water resistance and mechanical properties of FGD gypsum. When 6% of silicate clinker with average particle size of 26.83 μm was added, the dry flexural strength and dry compressive strength of FGD gypsum were 5.4 MPa and 10.7 MPa, respectively, 80% and 15% higher than those of pure FGD gypsum, respectively, and flexural softening coefficient and compressive softening coefficient reached 0.61 and 0.54, 52.5% and 58.8% higher than those of pure FGD gypsum, the water absorption rate was 28.5%, 17% lower than that of pure FGD gypsum. According to the microscopic characterization results, the improvement of the mechanical strength and water resistance of FGD gypsum after the addition of silicate clinker was due to the formation of a high-strength and insoluble C-S-H gel and ettringite on the surface of FGD gypsum crystals.