Abstract
In order to explore the influence of the types of waste gypsum on the properties of alkali slag cement, fluorogypsum (FG) and flue-gas desulfurization (FGD) gypsum were comparatively investigated. Moreover, the action mechanisms of FG and FGD gypsum on the properties of alkali slag cement were analyzed. The results show that both the FG and FGD gypsum prolonged the setting time of the alkali slag cement paste. However, the prolongation effect of FG was more pronounced than the FGD gypsum. When the compressive strength was maximum, the contents of FG and FGD gypsum were 5 and 6 wt.%, respectively. At 3 and 28 days, compared to the control sample, the compressive strengths increased by 59.3% and 24.3%, and 66.9% and 33.9%, respectively. Furthermore, the XRD, TG-DTA and SEM-EDS results showed that, with the increase in the contents of FG and FGD gypsum, ettringite was more easily produced and the hydration products were more abundant in the system. The greater the gypsum content of the paste, the less accumulated was the heat of hydration. The change of micro-structure caused by the formation of ettringite was the main reason for the difference in the properties of cement.
Highlights
During the production of Portland cement, a large amount of carbon dioxide is produced, which leads to the greenhouse effect [1,2]
In order to reduce the environmental concerns arising from the preparation of clinkers for Portland cement, the search for new cementitious materials requiring low or no clinker has become a research focus
The application prospects of alkali slag cement, which uses the reactivity of slag with alkaline activators to prepare hydraulic cementitious materials, are becoming increasingly promising [3,4]
Summary
During the production of Portland cement, a large amount of carbon dioxide is produced, which leads to the greenhouse effect [1,2]. In order to reduce the environmental concerns arising from the preparation of clinkers for Portland cement, the search for new cementitious materials requiring low or no clinker has become a research focus. The application prospects of alkali slag cement, which uses the reactivity of slag with alkaline activators to prepare hydraulic cementitious materials, are becoming increasingly promising [3,4]. Flue-gas desulfurization (FGD) gypsum is the waste produced during the flue-gas desulfurization process in thermal power plants. Both of them have the characteristics of large output, high purity, and difficulty in being reused. Both the byproducts are a waste of resources and result in environmental pollution
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