Application of Cellulose-Nano-Crystals in 3D Printed Alkali-Activated Cementitious Composites (2023-12)¶

With the rapid development of concrete 3D printing for construction projects, it is crucial to produce sustainable 3D-printed cementitious composites that meet the required fresh and hardened properties. This study develops sustainable 3D-printed cementitious composites of ordinary portland cement and alkali-activated materials using cellulose nanocrystals (i.e., green natural nanomaterials). The extrudability and buildability of the alkali-activated slag-fly ash mixtures were improved and the extrusion pressure was reduced by ~ 35 % by increasing the cellulose nanocrystals content (up to 1 %) suggesting their viscosity-modifying properties in alkali-activated materials. The inclusion of cellulose nanocrystals improves the overall mechanical performance (8–20 % increase) and reduces the porosity of ordinary portland cement and heat-cured alkali-activated samples. Further, the addition of cellulose nanocrystals (up to 0.30 %) in sealed-cured alkali-activated samples improves their flexural strength by 20 %. The ordinary portland cement sample with cellulose nanocrystals densifies the microstructure and has an approximately 25 % increase in the degree of hydration at inner depths indicating cellulose nanocrystals' internal curing potential. The developed 3D-printable alkali-activated composites with cellulose nanocrystals can provide an overall reduction in the environmental impacts by eliminating/reducing the need for chemical admixtures to improve material consistency and stability, and replacing 100 % of portland cement.