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Abstract
One new flue gas desulfurization (FGD) gypsum-based binder is attempted in this article, which is made up of FGD gypsum, ground granulated blast furnace slag (GGBS) and ordinary Portland cement (OPC). Influences of raw materials, chemical activators, and curing conditions on the compressive strength of this new binder-based mortar, as well as its durability performances and microscopic characteristics, are investigated in consideration of utilizing FGD gypsum as much as possible. Results show that the compressive strength of this new binder-based mortar under normal curing conditions could increase along with GGBS dosages from three days to 90 days. The compressive strength of one selected mix proportion (FG-4550), which contains the highest dosage of FGD gypsum (45 wt.%), is much the same as those containing the highest dosage of GGBS. A better compressive strength of FG-4550 under normal curing conditions could be gained if the fineness of GGBS is improved. The activated effect of CaCl2 on the compressive strength of FG-4550 is superior to that of Ca(OH)2 under steam curing conditions. FG-4550 shows a good capacity for resistance to water, a low shrinkage ratio, but poor compressive strength after 30 freeze-thaw cycles. Based on the mineralogy of X-ray diffraction, the morphology of scanning electron microscopy and the pore diameter distributions of 1H nuclear magnetic resonance, the compressive strength of this FGD gypsum-based mortar mainly depends on clusters of ettringite.
Highlights
The main chemical composition of gypsum is sodium sulphate (CaSO4 ) which can be dehydrated to bassanite and anhydrite
flue gas desulfurization (FGD) gypsum has been made into prefabricated building elements such as bricks, blocks, and wallboards [7], but some mercury is likely to be embedded in FGD gypsum due to the wet FGD scrubber [8]
We present the pioneering experiments of applications of 1 H nuclear magnetic resonance (NMR) on the porosity of gypsum-based binders to motivate further NMR investigations on the porosity of cementitious materials
Summary
The main chemical composition of gypsum (dehydrate) is sodium sulphate (CaSO4 ) which can be dehydrated to bassanite (hemihydrate) and anhydrite (anhydrous). FGD gypsum is a manmade gypsum from the flue gas desulfurization (FGD) process of air pollution controls at coal-fired power factories. This by-product has almost the same composition as natural gypsum [3,4,5]. Resource recovery of the FGD process has been emphasized for many years, especially for FGD gypsum [6]. FGD gypsum has been used in Portland cement [9], calcium aluminate cement [10], calcium-sulfate-bearing material [11], and various binders of blended cement [12,13]
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