Hydration mechanisms of two polymorphs of synthetic ye'elimite

Abstract

1Ye'elimite is the main phase in calcium sulfoaluminate cements and also a key phase in sulfobelite 2 cements. However, its hydration mechanism is not well understood. Here we reported new data on 3 the hydration behaviour of ye'elimite using synchrotron and laboratory powder diffraction coupled 4 to the Rietveld methodology. Both internal and external standard methodologies have been used to 5 determine the overall amorphous contents. We have addressed the standard variables: water-to-6 ye'elimite ratio and additional sulfate sources of different solubility. Moreover, we report a deep 7 study of the role of the polymorphism of pure ye'elimites. The hydration behaviour of orthorhombic 8 stoichiometric and pseudo-cubic solid-solution ye'elimites is discussed. In the absence of additional 9 sulfate sources, stoichiometric-ye'elimite reacts slower than solid-solution-ye'elimite, and AFm-10 type phases are the main hydrated crystalline phases, as expected. Moreover, solid-solution-11 ye'elimite produces higher amounts of ettringite than stoichiometric-ye'elimite. However, in the 12 presence of additional sulfates, stoichiometric-ye'elimite reacts faster than solid-solution-ye'elimite. 13 14 15

Characterisation and hydration process of synthetic Sr-bearing ye'elimite

“…However, it should also be noted that there is a limitation for the reaction shown in Equation I, as certain amounts of AFt can be identified at the early stage of C 4 A 3 $ hydrating without a sulfate source (Berger et al, 2011a;Cuesta et al, 2014a). The phenomenon has been attributed to critically supersaturated domains with respect to AFt (Damidot, 2007).…”

“…With regard to the characterisation of C 4 A 3 $, the Rietveld method is well suited for investigating the crystal structural characteristics (Cuesta et al, 2013(Cuesta et al, , 2014a(Cuesta et al, , 2014bHargis et al, 2014;Kurokawa et al, 2014); moreover, Rietveld quantitative phases analysis (RQPA) can also be used to quantify the phases in cements containing ye'elimite (Li et al, 2014;Álvarez-Pinazo et al, 2012). In recent years, RQPA has also been expanded to hydrated systems to identify both the crystalline phases and total amorphous contents (Álvarez-Pinazo et al, 2014(Álvarez-Pinazo et al, , 2016Cuesta et al, 2014a).…”

“…The phenomenon has been attributed to critically supersaturated domains with respect to AFt (Damidot, 2007). However, considering CSA cement is interground with 16-25% gypsum/anhydrite (C$H 2 /C$) to improve the performance, so the hydration of C 4 A 3 $ with C$H 2 /C$ is another type of important reaction (shown in the reactions in Equations II and III); in this condition ettringite (AFt) is formed along with AH 3 (Chang et al, 2016a(Chang et al, , 2016bCuesta et al, 2014a;Han et al, 2015;Hargis et al, 2013).…”

“…In recent years, RQPA has also been expanded to hydrated systems to identify both the crystalline phases and total amorphous contents (Álvarez-Pinazo et al, 2014(Álvarez-Pinazo et al, , 2016Cuesta et al, 2014a).…”

“…As for the hydration of C 4 A 3 $ without an additional sulfate source, the reaction of C 4 A 3 $ with water is always described by the reaction shown in Equation I, the hydration products include monosulfate (AFm) and aluminum hydroxide (AH 3 ) (Chang et al, 2016a(Chang et al, , 2016bCuesta et al, 2014a). However, it should also be noted that there is a limitation for the reaction shown in Equation I, as certain amounts of AFt can be identified at the early stage of C 4 A 3 $ hydrating without a sulfate source (Berger et al, 2011a;Cuesta et al, 2014a).…”