Investigation of Accelerated Hydration in Nanosilica Incorporated Tricalcium Silicate using THz Spectroscopy

The incorporation of nanosilica in cementitious systems helps in accelerating the cement hydration process and early-stage formation of the main hydration product, that is, calcium silicate hydrate. Nanosilica reacts with the other key hydration product, calcium hydroxide to form additional calcium silicate hydrate. In this work, Terahertz spectroscopy has been employed to study the variation in hydration kinetics of the main constituent of cement, Tricalcium Silicate, due to the addition of different percentages of nanosilica. The variation has been analyzed in terms of change in the absorbance as well as a shift in the wavenumber of the key resonances. The resonance around 520, 514 cm-1, due to symmetric-asymmetric bending of silicate tetrahedral units, decreases in intensity very rapidly as hydration progresses and more so for the nanosilica incorporated samples demonstrating accelerated hydration. Interestingly, the resonance around 451 cm-1, due to symmetric and asymmetric bending of silicate tetrahedral units along with some contribution of vibrational modes of calcium oxide polyhedral units, does not show a similar decrease in intensity. The prominence of the resonance around 451 cm-1 even after the onset of hydration is found to be mostly due to the contribution from the vibrational modes of the newly formed silicates tetrahedra chains of calcium silicate hydrate. Early-stage formation of calcium silicate hydrate due to nanosilica incorporation has been analyzed by tracking the shift in resonances as polymerized chains of silicates are formed. These results have been corroborated with Scanning Electron Microscopy results which clearly show the early changes in the morphology of the hydrated C3S due to nanosilica incorporation.