Hydrating Behaviour of Activated Belite Sulfoaluminate Cements

摘要

Belite calcium sulfoaluminate (BCSA) cements are an alternative to deplete up to 35% CO2 emissions, comparing to the Ordinary Portland Cements (OPCs) production process. However, hydration reactivity of belite phase is slow which leads to low mechanical strengths at medium ages. In this work, we will present some details about the hydrating behaviour of BCSA cements. We have prepared BCSA clinkers with nominal mineralogical composition of C2S (50 wt%), C4A3S (30 wt%) and C4AF (20 wt%). In order to enhance their hydraulic reactivity, these clinkers have been doped with borax (0.0, 1.0 and 2.0 wt% expressed as B2O3) to promote stabilization of -forms of C2S which were expected to be more reactive. The Rietveld quantitative phase analyses indicate that BCSA clinker without borax has all belite as -polymorph; the clinker with 1 wt% borax has 47% as and 53% as , and finally, the clinker with 2 wt% borax has all belite as -polymorph. These clinkers have been mixed with gypsum to prepare cement pastes for the hydration study. We report calorimetric data for all the cements with a w/c ratio of 0.5 and up to 6 days. The total heat evolved during early age hydration is useful information to have insights about the performances of the cements and to decide the optimum amount of gypsum to be added. These data are supported by an optical and environmental scanning electron microscopy (OM and E-SEM) study. We will correlate the morphology and amount of hydrated phases with specific signals in the calorimetric curves. Moreover, we will present Rietveld quantitative phase analyses of pastes hydrated during 1, 3 and 6 months to better characterize the hydraulic behaviour of these cements at later ages.