The influence of cellulose nanocrystals on the microstructure of cement paste

This paper reports the influence of raw and sonicated cellulose nanocrystals (CNCs) on the microstructure of cement paste. A novel centrifugation method is designed to measure the concentrations of the adsorbed CNCs (aCNCs) on the cement surface, and the free CNCs (fCNCs) which are mobile in water. It is found that, the majority of the CNCs (>94%) are aCNCs. More importantly, sonication does not significantly reduce the amount of aCNCs (reduction of less than 2%). We surmise that, after sonication, the aCNCs are primarily dispersed over the cement surface, instead of becoming fCNCs via sonication. Isothermal calorimetry and energy-dispersive X-ray spectroscopy (EDX) results support this theory. The water desorption tests show that the total porosities of cement pastes with raw and sonicated CNCs are 14.8% and 14.4%, which showed a reduction from 16% for the plain cement paste. The porosity reduction is a result of an increase in the degree of hydration. The advantage of sonicated CNCs is they are dispersed, avoiding therefore agglomerates that can lead to pores, voids, and air entrapment. The nanoindentation results show that the reduced indentation modulus on the interfacial regions between cement particles and the low density CSH is increased when CNCs are used.