Mechanical and shrinkage properties of cellulose nanocrystal modified alkali-activated fly ash/slag pastes

Alkali-activated materials based on fly ash (FA) and ground granulated blast furnace slag (GGBFS) offer lower carbon footprints but face challenges like low tensile strength and shrinkage susceptibility. This research explores the potential of cellulose nanocrystals (CNC) as additives to enhance the mechanical and shrinkage properties of alkali-activated fly ash/slag (AAFS) pastes to advance sustainable construction materials. A comprehensive examination is conducted on the impact of different contents of CNC (0.05 %, 0.1 %, 0.2 %, and 0.3 % by mass of FA + GGBFS) on the properties of AAFS pastes with two different alkaline activator contents (4 % and 8 % by mass of FA + GGBFS). It is found that incorporating 0.3 % CNC into AAFS pastes respectively improves the 28-day compressive and flexural strengths by 18.54 % and 60.87 % (8 % alkaline activator) and by 16.99 % and 50.12 % (4 % alkaline activator), and reduces the autogenous shrinkage and drying shrinkage by 26.42 % and 50.32 % (8 % alkaline activator) and by 11.74 % and 22.05 % (4 % alkaline activator). Also, the flexural/compressive strength ratio of AAFS pastes is increased with increasing CNC content. The microstructural analysis shows increased hydration product formation and a smoother, more compact morphology in CNC-modified samples, which together with water retention and distribution effect and nano-reinforcing effect of CNC explains the improvements in mechanical properties and volume stability. The research findings highlight the great potential of CNC as a reinforcing agent for sustainable construction materials, aligning with the demand from industries for eco-friendly alternatives to traditional cementitious materials.