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.