Parametric Rietveld refinement applied to in-situ monitoring of X-ray powder diffraction data of plaster hydration

The recycling of civil construction waste gypsum has been the subject of studies due to the nonexistence of economically viable technologies or applications that would allow it to be recycled. However, studies indicate that the material setting time reduces after recycling, generating more waste, but the cause of the phenomenon is not known. In-situ XRPD monitoring of plasters' hydration in their commercial form and after laboratory recycling process is carried out to verify both reactivity and hydration process. The samples are characterized by specific surface area, microporosity, and consistency tests. Sequential and parametric Rietveld refinements are employed to determine the weight fractions of calcium sulfate-based compounds present in the materials as a function of time. The increase in the consistency of the recycled plaster is not only associated with the increase of microporosity and specific surface area but also to the instant formation of gypsum as soon as the material comes into contact with water. These data also confirm the increase in the kinetic activity values calculated from the results of temperature kinetics tests, proving that the formation of hydrated compounds is much faster for the recycled plaster, which is associated with the increase of water contact area. (author)