C3S and C2S hydration in the presence of Na2CO3 and Na2SO4
This study analyses the behavior of calcium silicates C3S and C2S hydrated in two alkaline media, Na2CO3 and Na2SO4. The silicates were synthesized with laboratory reagents and hydrated in water, to which solid‐state alkaline activators with 4 wt% Na2CO3 or 4 wt% Na2SO4 were added. Two‐ and 28‐day mechanical strength values were determined and the reaction products were characterized with XRD, SEM/EDX, and 29Si and 23Na MAS NMR. The findings showed that the presence of Na2CO3 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 Q2 units.
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