Supersulfated binders based on volcanic raw material: Optimization, microstructure and reaction products

The characterization and optimization of supersulfated binders based on a volcanic material was carried out by Taguchi orthogonal array experimental design, investigating the effects of four factors: type of calcium sulfate, % calcium sulfate, %Portland cement and initial curing temperature. The binders increased strength over time. The statistically defined optimum formulation was: 70%volcanic material-10%Anhydrite-20%Portland cement and curing 22 h at 60 °C then at 20 °C; the predicted and confirmed 28-day strength was 20.2-20.6 MPa; optimum conditions are discussed for other ages. The microstructures and chemical composition of hydration products (EDS) and XRD indicated the formation of C-S-H and ettringite as the main hydration products.