Green Engineering of Surfactant-assisted Nano Silica Dispersion in Alkaline Cementitious Systems Using Chitosan

Achieving uniform dispersion of nanosilica (NS) is critical for enhancing the performance of cementitious composites, yet conventional dispersants such as polycarboxylate ether (PCE) pose environmental and economic drawbacks. This study investigates a combined ultrasonication and chitosan stabilization approach as a sustainable strategy to disperse NS. Multi-scale analyses were performed to evaluate its influence on hydration kinetics, phase composition, pore structure, microstructural morphology, and macro-scale properties, including compressive strength, ultrasonic pulse velocity (UPV), and electrical resistivity, relative to PCE-treated NS and plain OPC. The synergistic action of ultrasonication and chitosan enhanced NS dispersion, accelerated cement hydration, and promoted pozzolanic reactions, fostering denser C-S-H gel formation and reducing calcium hydroxide content. The resulting microstructure exhibited reduced critical, average, and median pore diameters by 23.2%, 32.3%, and 41.7%, respectively, and total porosity decreased by 21.3% compared with OPC. These structural refinements translated into improved performance: at 90 days, compressive strength, UPV, and resistivity increased by 5.0%, 7.1%, and 12.1%, respectively, over PCE-NS. Furthermore, chitosan's water-retention and crack-mitigation abilities enhanced internal curing and long-term durability. Overall, the combined ultrasonication-chitosan strategy provides a green, biodegradable, and highly effective dispersant approach, enabling the fabrication of durable, high-performance cementitious composites.