Hydration kinetics and mechanism of C3S with cellulose nanocrystals

Tricalcium silicate (C3S) is the primary ingredient in ordinary Portland cement (OPC). Understanding the hydration kinetics of C3S with cellulose nanocrystals (CNC) is the key to unveiling the intrinsic mechanism of CNC affecting OPC hydration. This study investigates the hydration interactions between C3S and CNC through extensive testing. Findings indicate that CNC incorporation can initially slow the hydration reaction and postpone the early-stage hydration of C3S. However, past the initial period (3 days in this study), CNC presence enhances the hydration pace and aids the hydration process, leading to an increase in the formation of calcium silicate hydrate (C–S–H) and calcium hydroxide (CH) without creating new phases. Further, the presence of CNC promotes the homogenous hydration of C3S, ensuring a homogenous distribution of hydration products. It also reduces the Ca/Si ratio in the C–S–H, without altering the C–S–H morphology. A correlation is made between heat flow and the thickness of hydration products enveloping C3S particles, confirming that CNC can intensify the inward water diffusion rate through C3S particles for the same hydration product thickness. Critically, it is found that the effect of CNC on C3S hydration is dependent on the water/C3S ratio. A low or moderate water/C3S ratio can promote C3S hydration but a very high water/C3S ratio diminishes the beneficial effects of CNC on C3S hydration. Finally, the study proposes a mechanism of CNC's influence over the hydration of C3S with varying water/C3S ratios.