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Thermodynamic stability of ettringite formed by hydration of illite clinker

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Document pages: 7 pages

Abstract: In order to use industrial by-products to save limited natural resources, this paper focuses on the new application of fluidized bed combustion fly ash (fbcfa) in Portland composite cement. Because unqualified ettringite 3CaO · Al2O3 · 3caso4 · 32h2o is formed during the hydration of fbcfa, the ettringite is not used at present. Although the stability of ettringite has been the subject of many studies, the solution is not completely clear. Ettringite is generally considered to be stable below 110 ° C; However, some researchers claim that ettringite may have decomposed even at ambient temperature. In order to prove these claims, ettringite is prepared by hydration of yersinite 3CaO · 3Al2O3 · CaSO4. The system is stored in two environments at laboratory temperature: inboratory settings and in an environment of saturated water vapour. The mineralogical composition of ettringite was long term (up to 160 days of hydration) and was analysed by X-ray diffraction (XRD) and differential thermal analysis (DTA). The hydration of ye’elimite is a relatively complex process. Only approximately 30 of ettringite was formed under laboratory conditions that appeared to gradually convert into metaettringite. Within an environment of saturated water vapour, we observed the conversion of ettringite into monosulfate. Original ye’elimite was indicated as the dominant phase of both storages.

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