A new approach in quantitative in-situ XRD of cement pastes: Correlation of heat flow curves with early hydration reactions

XRD measurements of the hydration of synthetical cement (SyCem) were used to calculate the resulting heat flow from changes in the phase content. Calculations were performed by application of thermodynamic data. The comparison with data recorded from heat flow calorimetry was in good agreement with the calculated heat flow.The initial maximum of heat flow mainly is caused by the aluminate reaction. During the entire main period the silicate reaction dominates hydration with a high and long first maximum of heat flow. The second but less intense heat flow maximum – only visible as a shoulder in most of the technical cements – can be attributed to an acceleration of the aluminate reaction with the enhanced dissolution of C₃A and the final formation of ettringite. Moreover, the investigation showed that the dissolution process of C₃A is directly controlled by the availability of the calcium sulfate phases.     

Quantitative determination of anhydrite III from dehydrated gypsum by XRD

Technical OPC contains mixed sulfate carriers in varying amounts. Gypsum and anhydrite are added to the clinker during the milling process where the gypsum dehydrates partially to bassanite and anhydrite. Due to different hydration kinetics of these phases, it is crucial to be able to characterize the composition of sulfate in a cement system to reach an optimal and reproducible cement hydration. In the current paper different calcium sulfate compositions are investigated by XRD methods in order to identify phase content. Special focus is put on the discrimination of the hemihydrate (bassanite) and anhydrite III as well as on transformation processes of anhydrite III through ambient humidity.