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