Exploring the role of calcium sulfate in supersulfated cement: A study of rheological, mechanical, and microstructural properties

In order to investigate the impact of different calcium sulfate (CS) sources and forms on the rheology, hydration, and mechanical properties of supersulfated cement (SSC), SSC pastes were produced with anhydrite from gypsum calcined at 650 degrees C and raw and calcined phosphogypsum (PG) at 150, 350, and 650 degrees C. Isothermal calorimetry, rheometry using parallel-plate geometry, compressive strength testing, and microstructural analysis through Xray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) were performed. Results showed that SSC containing gypsum and PG calcined at 650 degrees C exhibited similar rheological behavior. Pastes containing PG calcined at 150 degrees C and raw PG respectively, exhibited the highest and lowest shear stress at a given shear rate. The calcination temperature and CS source did not significantly impact SSC compressive strength. Rietveld XRD analysis revealed that pastes with PG calcined at 350 degrees C and gypsum calcined at 650 degrees C had the lowest and highest ettringite development, respectively, from 7 to 28 days of curing.