Portland/Sulfoaluminate Cement Blends for the Control of Early Age Hydration and Yield Stress

Early age hydration and the rheological behavior of cement pastes are related to their reactivity. The reactivity of Ordinary Portland Cement (OPC) and calcium sulfoaluminate cement (CSA) blends, with a CSA percentage of less than 10%, are investigated in this paper. Different percentages of CSA replacement are studied. First, an isothermal calorimetry study of the different cement pastes is performed to understand the effect of CSA on the evolution of the heat of hydration. Then, in order to understand the reactional mechanism of these cement pastes, X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) studies were conducted on one blended mix made out of 7% CSA and compared to the pure cement pastes of OPC and CSA. Later, the evolution of the yield stress as a function of the CSA percentage was studied. A synergy is shown between both OPC and CSA once mixed together, leading to a 57% and 45% higher ettringite formation for the blend compared to 100% OPC and 100% CSA cement pastes, respectively. This implies that the CSA amount affects the reactivity of OPC/CSA blends. This was confirmed by the variation in both the heat of hydration and yield stress evolution as a function of the percentage of CSA.