Mixtures of calcium sulfoaluminate and Portland clinkers with gypsum were hydrated with deionized water. The pastes were introduced in 0.7 mm borosilicate capillary tubes and kept at 40 ??C while diffraction patterns were collected every 35 s for approximately 3 hours with a monochromatic radiation of 12 keV at the XRD1 beamline of the Laborat??rio Nacional de Luz S??ncrotron (LNLS) in Campinas, SP - Brazil. The main crystalline phases (C2S, C3S, ettringite, ye???elemite and gypsum) involved in the hydration were quantified by Rietveld analysis. The most noticeable fact was the absence of portlandite as a crystalline precipitate, most likely due to the capture of calcium ions to form ettringite.