A Mechanistic Investigation on Cation-Modified Cellulose Nanofibrils-Reinforced Cement Composite

Cellulose nanofibril (CNF), as a renewable biomass material, has the characteristics of low density, high strength, and high hydrophilicity. It can also overcome shortcomings of traditional inorganic nano materials, such as difficult dispersion, high cost, and high health risks. In this work, CNF was modified with a cationic surfactant to further enhance the compatibility with hydrating cement. The effects on cement paste were assessed via compressive and flexural strength, heat of hydration, and restrained ring cracking. The reinforcing mechanisms were analyzed by microhardness test, XRD, and BSE-SEM/EDS. Results showed that cation-modified CNF improved mechanical performance, with an optimal dosage of 0.15 wt.% (by binder). Restrained ring test showed that cation-modified CNF-cement composite delayed crack initiation. An isothermal calorimetry test revealed that cation-modified CNF can increase hydration rate in early age. Microstructural analysis confirmed promotion of denser hydration products. A comprehensive consideration of experimental results indicates internal curing and "short-circuit diffusion" are likely the enhancing mechanism.