Tracking the Acceleration of Hydration of β-C2S Due to Nanosilica Incorporation Using THz Spectroscopy

β-dicalcium silicate (β-C2S), the second most prevalent constituent of Ordinary Portland Cement (OPC), reacts slowly during the early stage of hydration but is responsible for long-term strength development of concrete. To accelerate the hydration during this stage, nanomaterials are incorporated in the β-C2S matrix which results in pozzolanic reactions. In this work, nanosilica has been added in different percentages, and the acceleration in hydration has been tracked by employing Terahertz spectroscopy for a period of 100 days. This study clearly demonstrates that nanosilica incorporation accelerates the early-stage hydration of β-C2S as seen by the reduction in intensity of the resonances between 500 and 520 cm−1. Density functional theory (DFT) simulations of β-C2S confirm these resonances to be due to SiO4 and CaO bending modes. The prominence of the resonance around 455 cm−1 for the nanosilica-incorporated β-C2S indicates early-stage formation of the key hydration product, calcium silicate hydrate (C–S–H). Furthermore, sharpening of the resonance around 283 cm−1 during hydration could possibly indicate the formation of more ordered structures of the hydration products. By tracking the shift of these resonances, it can be inferred that the degree of polymerization of silicates during C–S–H formation is different compared to cement and C3S. To track the structural changes during hydration, scanning electron microscopy (SEM) has been carried out which shows the formation of fiber-like morphologies, indicative of early-stage formation of C–S–H for the nanosilica-incorporated samples. This study could potentially help to engineer β-C2S-rich cement matrix with nanomaterials which could aid in reducing CO2 emission during cement manufacturing.