Understanding the effect of nanosilica incorporation on dicalcium silicate hydration using terahertz spectroscopy

Ordinary Portland Cement (OPC) primarily constitutes Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) making up 60–70 % and 20–30 % of the cement matrix respectively. During cement hydration, C3S starts to react faster contributing to early stage strength in comparison to C2S, which reacts slowly and is responsible for long term strength development of concrete. C2S is manufactured at lower temperatures compared to C3S, resulting in lesser emission of carbon dioxide as compared to C3S. Moreover, C2S produces less Ca(OH)2 than C3S, which is an undesirable hydration product. Thus, incorporation of greater percentages of C2S in cement matrix will be highly beneficial, provided it’s early stage reactivity can be increased. One of the key methods to increase reactivity of C2S is incorporating nanosilica which accelerates the hydration along with the formation of greater amount of calcium silicate hydrate (C-S-H) which is responsible for the strength development of concrete. Hence, understanding the acceleration in hydration dynamics of the nanosilica incorporated β-C2S can help in optimizing the percentages of C3S and C2S in cement. In this study, Terahertz spectroscopy has been employed to track the acceleration of hydration of C2S due to the addition of nanosilica. Results show early stage reduction in peak height of the resonance around 520 cm-1 in nanosilica incorporated sample which indicates faster hydration of C2S during hydration. Furthermore, early stage formation of a prominent resonance around 453 cm-1 for the nanosilica incorporated C2S sample implies formation of C-S-H like structures confirming the accelerated hydration rate.