Fly Ash–Based Self‐Compacting Concrete: A Critical Review of Mechanical Performance, Durability, Life Cycle Assessment, and Future Research Directions

Extensive research has investigated the use of fly ash (FA) in self‐compacting concrete (SCC); however, the available literature remains fragmented, with most studies focusing on individual performance aspects rather than providing an integrated assessment of fresh‐state behavior, mechanical performance, durability, microstructural evolution, and environmental sustainability. This review provides a comprehensive critical synthesis of the current knowledge on the role of FA in SCC, highlighting the governing mechanisms, identifying existing research gaps, and outlining future research priorities. The reviewed literature demonstrates that FA significantly influences the fresh properties, mechanical performance, durability, and sustainability of SCC. Moderate FA replacement levels (approximately 20%–30%) generally provide the optimum balance between workability, strength development, durability, and environmental performance. In contrast, higher replacement levels may delay early‐age strength development and increase carbonation susceptibility unless appropriate mixture optimization and curing strategies are adopted. The improvements in fresh and hardened properties are primarily attributed to the spherical morphology of FA particles, enhanced particle packing, and secondary pozzolanic reactions that promote calcium silicate hydrate (C–S–H) formation and pore refinement. Durability assessments, including rapid chloride penetration and chloride migration tests, further demonstrate improved resistance to chloride ingress, sulfate attack, and shrinkage. In addition, life cycle assessment (LCA) indicates that partial replacement of Portland cement with FA substantially reduces global warming potential (GWP) and CO ₂ emissions, supporting the development of low‐carbon SCC. Despite these advantages, important challenges remain regarding standardized mix design, variability in FA characteristics, early‐age strength development, carbonation resistance, and the integration of artificial intelligence (AI) with performance‐based mixture optimization. Overall, this review identifies key knowledge gaps and future research directions to facilitate the broader application of durable, low‐carbon, and sustainable FA‐based SCC in modern construction.