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Nanosilica incorporation in cement has been of great interest for its accelerating effect on the hydration process as well as providing higher compressive strength and durability. During hydration, cement constituents, such as tricalcium silicate (C3S) and dicalcium silicate (β-C2S) react with water to form key hydration products, such as calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)2, CH). In this work, Mid-infrared and Terahertz spectroscopy has been employed to study the effect of nanosilica incorporation in cement hydration. The acceleration due to the presence of nanosilica has been demonstrated by the reduction in peak intensity of the resonances related to Si-O stretching (925 cm-1) and Si-O bending modes (520 cm-1) which confirms faster consumption of the cement constituents. Furthermore, the formation of the hydration products C-S-H and CH is vital since C-S-H contributes to the early stage strength development in concrete and CH is an undesirable hydration product. CH content in the cement matrix can be minimized by nanosilica incorporation resulting in pozzolanic reactions as CH reacts with nanosilica to produce more C-S-H. Formation of C-S-H has been demonstrated by the prominence of the resonances related to deformations of SiO4 chains around 455 cm-1 and 1100 cm-1. The type of C-S-H can also be predicted by tracking the shift of resonances to higher/lower wavenumbers, denoting polymerization which is more prominent for the nanosilica incorporated sample. Formation of the other key hydration product is observed as the resonance related to CH around 314 cm-1 is seen to get sharper with hydration. This study has also been able to show a reduced carbonation effect in the nanosilica incorporated sample as evident from the less prominent carbonate peaks around 1425 cm-1 after 28 days of hydration.
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