Calcium aluminate cements are normally sulfate-free, but blending with calcium sulfate-rnhemihydrate (CSH0.5) or gypsum (CSH2) can lead to formation of the sulfatecontainingrnhydrate Ettringite (C6AS3H32).rnCA and Fe-doped CA1-xFx solid solutions were synthesized in laboratory furnaces atrn1250°C from reagent grade chemicals. All phases were checked for minor phases andrncharacterized by X-ray powder diffraction analysis. Structural parameter refinement byrnRietveld-analysis with fundamental parameter approach (Topas 2.1) was employed forrncrystallographic characterization of the anhydrous phases.rnDue to the wide technical importance of Ettringite-based binder systems model systemsrnof CA1-xFx with 0 ≤ x ≤ 0.1 with admixtures of CSH0.5 were hydrated at 23°C in arnheat flow calorimeter based on an quadruple arrangement as described before by [1]rnand fully revised by [2]. In accordance with calorimetric data the hydrating mixturesrnwere investigated by X-ray powder diffraction analysis in order to interpret the recordedrncaloric effects of the first 48 hours of in-situ hydration.rnReaction of pure CA with water is beginning after 17-18 hours of induction period [3].rnIn contrast mixtures of CA and CSH0.5 are reacting immediately with water during thernfirst minutes of hydration. This main phase of water absorption could be observedrnwithout induction period for all sulfate-containing mixtures. From XRD-investigationsrnwe could attribute this mainly to exothermic reaction of CSH0.5 (hemihydrate) transformingrninto CSH2 (gypsum). The following 2nd maximum of heat flow can be correlated
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