Cellulose nanofibrils with and without nanosilica for the performance enhancement of Portland cement systems

Abstract

This article presents a comprehensive investigation on the effects of pure cellulose nanofibrils (CNF) and nanosilica containing CNF on the performance of ordinary portland cement (OPC) paste. The effects of CNFs on cement paste rheology, hydration, microscopic phase formation, compressive strength, and fracture parameters were monitored. Sol-gel method was used to synthesis nanosilica particles within CNF slurry. The effects of CNF on cement hydration was found to be dependent on the water to cement ratio (w/c). Specifically, CNFs accelerated the early age cement hydration at 0.35 w/c, but this acceleration effect was not prominent for 0.45 w/c. Such w/c dependent effect was attributed to the negatively charged hydroxyl and carboxyl surface sites of CNFs which can bind alkali ions or cement particles. The concentration of alkali ions in cement pore solution depends on the w/c and hence, resulting the w/c dependent effects of CNF. The colloidal stability of CNF was found to improve due to the addition of nanosilica particles. Addition of CNF was found to increase the flexural strength of cement paste up to 75%. The effects of CNF addition on the compressive strength of cement paste matrix was negligible.