Ultrafine Fly Ash as a Single Pozzolanic Material in Self-Compacting Concrete: A Review of Fresh, Mechanical, Durability and Sustainability Performance

Self-Compacting Concrete (SCC) is an advanced cementitious material capable of flowing through congested reinforcement and completely filling formwork without mechanical vibration. Its production generally requires high powder content and chemical admixtures to achieve filling ability, passing ability and segregation resistance. The growing demand for sustainable concrete has encouraged the replacement of Portland cement with supplementary cementitious materials, particularly fly ash. Ultrafine Fly Ash (UFFA), produced by grinding or classifying conventional fly ash, possesses smaller particles, greater specific surface area and higher pozzolanic reactivity. This review examines the influence of UFFA on the fresh, mechanical, durability and microstructural properties of SCC. Published investigations indicate that moderate UFFA replacement improves flowability, particle packing and resistance to segregation through its spherical particle shape and micro-filler action. Pozzolanic reactions consume calcium hydroxide and form additional calcium-silicate-hydrate gel, resulting in improved compressive, tensile and flexural strength. UFFA also refines the pore structure, reduces water absorption and permeability and improves resistance to chloride penetration, sulphate attack and acidic exposure. However, excessive replacement may increase water demand and reduce early strength because of cement dilution. The reviewed literature suggests that properly proportioned UFFA can produce durable, high-performance and environmentally responsible SCC, although additional long-term, field-scale and life-cycle investigations remain necessary.