Hydration Characteristics of Tricalcium Aluminate in the Presence of Nano-Silica.

Tricalcium aluminate (CA) is the most reactive component of the Portland cement and its hydration has an important impact on the workability and early strength of concrete. Recently, nanomaterials such as nano-silica (nano-SiO) have attracted much attention in cement-based materials because of its pozzolanic reactivity and the pore-filling effect. However, its influence on the hydration of CA needs to be well understood. In this study, the hydration kinetics of CA mixed with different percentages of nano-SiO were studied and compared with pure CA. The hydration products were examined by different characterization techniques including XRD, XPS, and NMR spectroscopy and isothermal calorimetry analyses. The XRD results showed that the addition of nano-SiO promoted the conversion of the intermediate product CAH. The isothermal calorimetry results showed that the addition of nano-SiO significantly reduced the hydration exotherm rate of CA from 0.34 to less than 0.1 mW/g. With the presence of nano-SiO, the peaks for Q were observed in Si MAS-NMR measurements, and the content of Q increased from 6.74% to 30.6% when the nano-SiO content increased from 2 wt.% to 8 wt.%, whereas the proportion of Q gradually decreased from 89.1% to 63.6%. These results indicated a pozzolanic reaction provoked by the nano-SiO combined with aluminate structures generating C-A-S-H gel.