A Novel Super Sulfated Cement Via Chemical Activation of Anhydrite and Calcium Sulfoaluminate Cement: Hydration Properties and Mechanism

Utilization of Portland cement to initiate slag dissolution in super sulfated cement is limited by low slag substitution level and poor early strength. In this work, a novel activator based on anhydrite and calcium sulfoaluminate cement was proposed to apply in super sulfated cement. The compressive strength and autogenous shrinkage of hydrated cement mortar and paste were tested respectively. The hydration of the super sulfated cement was characterized with respect to the nano and micro-structure, hydration heat, aqueous conductivity and pH evolution, while GEMS was adopted to explore the hydration thermodynamics. An optimum activator dosage (20%) was observed at which the properties of hydrated cement achieve an extremum level and that excessive activator leads to deterioration. Both experimental and modelling results indicate that ettringite and C-S-H comprise the major hydration products. When the reaction degree of slag increases, the Q1 silicate tetrahedrons also drops due to the re-polymerization of hydrates, the total porosity decreases as well, and thus compressive strength increases. The prepared super sulfated cement drastically reduces the emission of CO2, which provides an environmentally friendly and promising alternative to traditional binders.