Hydration and mechanical properties of FGD gypsum-cement-mineral powder composites

Abstract

Solving the problem of environmental pollution caused by flue gas desulfurization gypsum (FGD gypsum) accumulation is conducive to improving FGD gypsum green and sustainable development. In this study, the ternary system was prepared by using FGD gypsum, cement,and mineral powder. The simplex-centroid design method was used to determine the optimal proportions of FGD gypsum, cement, and mineral powder. The optimal proportions of FGD gypsum, cement, and mineral powder were designed by the simplex-centroid design method. The effects of cement and mineral powder contents on the mechanical and hydration properties of the ternary system were analyzed by contour map. Furthermore, the phase composition and microscopic morphology of the ternary system were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Hydration processes of all samples were observed by the hydration heat. It was observed that the optimal proportions of FGD gypsum, cement, and mineral powder were 75%, 5%,and 20%, respectively by comprehensive considerations of strength, softening coefficient, water absorption, hydration, and microstructure. Compared with pure gypsum, both binary and ternary systems consisting of gypsum, cement, and mineral powder showed good water resistance. The softening coefficient at 28 d improved, reached 0.71 at the optimal proportion.