Enhancing nano-CaCO₃ dispersion with cellulose nanocrystals for high-strength low-carbon concrete

To produce low-carbon concrete, nano calcium carbonate (nano-CaCO₃) has been used as a partial cement replacement to enhance concrete properties through nucleation and filler effects. The nano-CaCO₃ is being synthesized by reacting CO₂ with calcium-rich natural and/or waste materials. However, a critical challenge in this approach is the poor dispersion of nano-CaCO₃ which tends to agglomerate due to van der Waals forces. This agglomeration severely affects the mechanical performance and durability of concrete, particularly at higher dosages. This study introduces a novel solution to enhance nano-CaCO₃ dispersion by leveraging cellulose nanocrystals (CNC) and their abundant hydroxyl functional groups. Nano-CaCO₃ was synthesized via the carbonation of calcium hydroxide (Ca(OH)₂) suspension in the presence of CNC and incorporated into cement paste at up to 0.9 % replacement. The results demonstrate significant advancements: (1) CNC markedly improves nano-CaCO₃ dispersion in both water and cement paste; (2) CNC-incorporated synthesis reduces nano-CaCO₃ crystallinity which may provide more nucleation sites due to higher surface area; (3) while pure calcite forms in the absence of CNC, its presence promotes additional polymorphs, including aragonite and vaterite, and (4) well-dispersed nano-CaCO₃ achieved with CNC leads to a substantial 52 % increase in compressive strength and a 30 % increase in flexural strength. This research introduces an innovative strategy to overcome nano-CaCO₃ dispersion challenges for scaling production, enabling its effective use in cementitious materials and significantly enhancing concrete performance.