Influence of calcination temperature on hydration behavior, strength, and weathering resistance of traditional gypsum plaster

The mineralogical composition, microstructure, and reactivity of traditional gypsum, a multiphase product, is closely connected to its calcination temperature, but systematic studies which relate those features to mechanical properties and weathering resistance of plasters are scarce. Here we examined the hydration behavior of gypsum calcined between 100 and 1000 degrees C, which contained varying amounts of uncalcined gypsum, bassanite, and/or anhydrite II. Detailed hydration and textural studies allowed the identification of the underlying mechanisms leading to differences in plaster performance related to (i) delayed hydration of anhydrite II along with modifications of the pore system; (ii) a filler effect exerted by anhydrite II and uncalcined gypsum; (iii) disruption of the plaster matrix by uncalcined gypsum; (iv) seeded crystallization in the presence of uncalcined gypsum and anhydrite II. Findings of this study further the understanding of traditional gypsum plaster performance and open opportu-nities for the development of sustainable building materials by designing optimized gypsum-based mixtures for specific application.