Effect of alkalis on the mineral formation and properties of alite-sulfoaluminate cement

This work studied the effects of alkalis on the mineral formation of alite-sulfoaluminate cement clinker and the properties of its cement, using limestone, fly ash, clay and gypsum as raw materials. The results indicated that minor amount of alkalis can improve the burnability of raw mixtures and accelerate the absorption of free lime. Excess amounts of sodium oxide (Na₂O) or potassium oxide (K₂O) (about 1·2%) were found to be adverse to the formation of C₄A₃S¯. The alkali distributes mostly in the interstitial phase, much less in belite crystal and then only traces in alite crystal. When the amount of alkali is about 1·2%, Na₂O benefits the formation of C₃S and can increase the early strength of cement. K₂O, on the other hand, decreases the amount of formation of C₃S and lowers the various age strengths of the cement. Adding alkalis prolongs the cement setting time.