In-situ synchrotron powder diffraction study: activation of Portland and Belite cements

Abstract

Portland cement (PC), whose main phase is alite (Ca3SiO5, C3S), is one of the most manufactured products in the world. However, cement industry is one of the major contributors for greenhouse gases (GHG) emissions. In the fabrication of PC, 0.96 tons CO2 per ton PC are emitted into the atmosphere. Belite cements (BC), whose main component is the belite phase (Ca2SiO5, C2S), can decrease the CO2 footprint of cements. The main disadvantage of these BCs is its low mechanical strengths at early ages although they have very good mechanical values at late ages and also very good durability performances. Thus, it is necessary to study how to increase the mechanical properties at early ages, for instance, by activation. To do this, an in-situ synchrotron X-ray powder diffraction study has been performed up to 48 hours of hydration using a PC and two different BCs (one activated during the clinkering stage and one non-activated). These cements have been hydrated without and with three different admixtures, two of them C-S-H seeding based (XS100 and XS130) and the other one being a single alkanolamine (triisopropanolamine, TIPA). Data have been collected at the BL04-MSPD beamline at ALBA synchrotron (Barcelona, Spain). The results were analysed by the Rietveld methodology to determine the phase content evolutions with time and with the activators. Fig. 1 shows, as an example, the hydration evolution of the activated BC without and with the XS130 admixture. In this study, we have obtained two main conclusions. The first observation is that C-S-H seeding accelerates the hydration of the three cements at early ages, mainly by enhancing calcium sulphates and calcium aluminates dissolutions. It has also been observed that admixtures do not significantly accelerate the hydration of crystalline C3S and C2S. The second is a synergy between C-S-H seeding and alkanolamines when compare to single alkanolamine dosage.