Journal of Engineering Research and Reports

Hydraulic concrete structures—including gravity dams, arch dams, sluice gates, navigation locks, hydropower tunnels, and coastal sea walls—operate under sustained hydrostatic pressure, hydraulic abrasion, and chemically aggressive environments that impose demanding requirements for impermeability, mechanical performance, and long-term durability. Nano-silica (NS), an amorphous silicon dioxide (SiO₂) material with primary particle sizes typically between 5 and 100 nanometres, has attracted substantial research interest as a supplementary cementitious material capable of simultaneously improving concrete strength, densifying microstructure, and substantially reducing water permeability. This article critically reviews the current state of knowledge on NS application in hydraulic concrete, encompassing NS synthesis routes and physicochemical characterisation, effects on fresh concrete workability and setting, cement hydration mechanisms and microstructural development, mechanical performance, impermeability, and durability under hydraulic service conditions. Evidence drawn from the literature consistently shows that NS additions of 1–3% by mass of cementitious binder yield the most favourable outcomes, owing to the dual action of pozzolanic reactivity and nano-filler densification. The review also examines NS in combination with other supplementary cementitious materials and assesses current and emerging field applications. Barriers to wider adoption—principally agglomeration, elevated water demand, cost premium, and absence of hydraulic-specific test protocols—are examined critically. A literature search spanning 2004 to 31 March 2026 was conducted across multiple academic databases. Key research gaps are identified, and priorities for future investigation are proposed with particular focus on mass concrete applications, long-term hydraulic performance monitoring, and life-cycle assessment.