Effect of nano-silica on hydration and conversion of calcium aluminate cement

This study investigated the effect of nano-silica on the hydration and conversion of calcium aluminate cement (CAC). The specimens were exposed to 60 °C to accelerate the transformation of hydrates in CAC after initial curing at 20 °C. At an early stage of curing, adding nano-silica in CAC mitigated the formation of C3AH6 and AH3. At 1 day after exposure to 60 °C, the compressive strength reduction was observed in all specimens, and it was closely related to the conversion of CAH10. That is, the conversion of all specimens occurred at 28 days after exposure, which resulted in a reduction in compressive strength. However, adding nano-silica mitigated the conversion from metastable phases (CAH10 and C2AH8) to stable phases (C3AH6 and AH3). As a result, the extent of compressive strength loss could be reduced by the formation of strätlingite (C2ASH8) in the case of 4% addition of nano-silica. In conclusion, adding nano-silica in CAC was effective regarding structural integrity by delaying the conversion of metastable hydrates, as well as maintaining the long-term strength of CAC by forming strätlingite.