In this study, a small amount of cellulose nanocrystals (CNC) were added to fly ash (FA)/granulated ground blast furnace slag (GGBS)-based geopolymer mortars to investigate the performance influence and action mechanism of the modified FA/GGBS-based geopolymer mortar by CNC. The results showed that following a 28-day curing, the best mechanical performance was achieved when the FA/GGBS mass ratio was 3:7; compared to the 5:5 mass ratio of FA/GGBS, the compressive strength and flexural strength increased by 14.96% and 40.74%, respectively; and compared to the 7:3 mass ratio of FA/GGBS, the compressive strength and flexural strength increased by 112.12% and 80.95%, respectively. However, with higher GGBS proportions, the flowability decreased. Additionally, the effect of CNC was inconsistent in systems. At 3-day curing age, in the FA/GGBS=3:7 and 5:5 systems, the addition of CNC inhibited the strength development of geopolymer mortars, whereas in the FA/GGBS=7:3 system, it slightly accelerated the strength development. However, after 28 days of curing, the strength of the geopolymer mortars under all conditions increased to varying degrees after the addition of CNC. Microstructural tests via scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and isothermal calorimetry (IC) showed that increasing GGBS content and adding CNC enhanced the reaction activity and structural compactness of FA/GGBS-based geopolymer mortars.

geopolymer, fly ash, granulated ground blast furnace slag, cellulose nanocrystal