Utilization of cellulose nanocrystal as a bio‐based material and nanosilica in cement‐based systems: A comparative study

Abstract Cellulose nanocrystals (CNCs), increasingly utilized in cement‐bound materials, offer improved material properties and enhanced sustainability due to their bio‐based origin. Nanosilica (NS), known for its high reactivity and refinement of cement microstructure, also significantly impacts cement performance. Although CNC and NS differ markedly in composition, morphology, and interaction mechanisms with cement matrices, CNCs being organic rod‐shaped nanoparticles that modulate hydration kinetics, and NS being inorganic spherical nanoparticles promoting early hydration, their comparative investigation can yield deeper insights into optimizing cement‐based composites. This study comparatively investigates the effects of CNC and NS incorporation (0.25%, 0.50%, and 0.75% by cement weight) on the rheological, mechanical, and microstructural properties of cement pastes and mortars. Results revealed that both CNC and NS additions reduced flow diameters; however, CNC was acting as a setting retarder and NS as a setting accelerator. Rheological measurements showed increased yield stress and plastic viscosity with increasing concentrations of CNC and NS. Compressive strength was notably enhanced with CNC incorporation, achieving peak strength at 28 days with 0.50% CNC, whereas at 90 days, 0.75% CNC exhibited the greatest strength improvement. In comparison, NS significantly improved early‐age mechanical strength due to its high pozzolanic activity, achieving rapid hydration and a denser microstructure at earlier curing periods. Microstructural analyses validated these outcomes, linking CNC and NS incorporation to improved hydration products and densified pore structures. This comprehensive study addresses the current knowledge gap concerning the rheological impacts of CNC and NS in cementitious systems, presenting CNC integration compared to NS incorporation as a sustainable approach to enhance cement performance through environmentally advantageous bio‐based materials.