C ₃ S and C ₂ S hydration in the presence of Na ₂ CO ₃ and Na ₂ SO ₄

Abstract

Abstract This study analyses the behavior of calcium silicates C 3 S and C 2 S hydrated in two alkaline media, Na 2 CO 3 and Na 2 SO 4 . The silicates were synthesized with laboratory reagents and hydrated in water, to which solid‐state alkaline activators with 4 wt% Na 2 CO 3 or 4 wt% Na 2 SO 4 were added. Two‐ and 28‐day mechanical strength values were determined and the reaction products were characterized with XRD , SEM / EDX , and 29 Si and 23 Na MAS NMR . The findings showed that the presence of Na 2 CO 3 hastened hydration kinetics and stimulated early‐age mechanical strength development in both silicates. The most significant effect of sodium sulfate, however, was observed in the 28‐day material in both silicates, in which it raised strength by stimulating the precipitation of C–S–H gels with a high percentage of Q 2 units.