Exploring the Role of Cellulose Nanocrystal in the Hydration and Microstructure of Cement-Based Materials

Nanocellulose, as an excellent performance, widely sourced, and naturally renewable nano-reinforced material, shows great application potential in cement and concrete. This study explored the role of cellulose nanocrystal (CNC) in the hydration process, hydration products, pore structure, and morphology of cement paste through isothermal calorimetry, thermogravimetric analysis, nanoindentation analysis, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The hydration results indicate that CNC retards the early-age hydration process of cement, evidenced by a decrease in the cumulative hydration heat and hydration heat rate, as well as a delay in the induction period and the acceleration period. This phenomenon may be caused by the strong water absorption of CNC itself and its adsorption on the surface of cement particles. However, CNC gradually shows a promotion effect with the increase of hydration age, confirmed by the increasing hydration degree and C─ S─ H. Nanoindentation results further show that CNC promotes the formation of C─ S─ H and mainly increases high-density C─ S─ H. The results of pore structure show that CNC has a better effect on improving the pore structure than hydration, but the working mechanism of CNC is different in the early and late stages. In the early stage, CNC mainly exerts a filling effect to decrease more-harmful pores (>200 nm), while in the late stage, CNC decreases harmful and more-harmful pores (50–200 nm and >200 nm) through the filling effect and the acceleration of the formation of hydration products.