Rice husk ash and silica fume in low carbon concrete: A comprehensive review of physicochemical properties, mechanical performance, embodied carbon, and waste valorization

Utilization of supplementary cementitious materials (SCMs) presents an opportunity for achieving lower carbon intensity in cement while upholding concrete performance; particularly, silica-rich rice husk ash (RHA) and silica fume (SF) provide benefits both in terms of performance and resource efficiency. This review, therefore, provides a comprehensive summary of experimental studies conducted on RHA- and SF-based concrete, covering their material properties, mechanical performance aspects, strength-enhancement mechanisms as well as their contribution toward environmental sustainability. Normalized performance trends are presented in tabular and graphical forms, enabling a comparative assessment of the results for compressive, split-tensile, and flexural strength across replacement levels and curing ages. The review also assesses life cycle assessment (LCA)-based CO 2 reduction, embodied carbon behaviour, waste valorization and circular-economy effects. Across the studies reviewed, it was observed that 5–10% SF replacement resulted in a higher compressive strength of 25–35% after 7–28 days, but RHA at 10–15% registered 15–25% increased compressive strength between 28 and 90 days which suggests its potential for later-age activity. Both RHA and SF were associated with global warming potential reductions of about 20–50% at favourable replacement levels. The integrated comparison of materials-performance-environment trade-offs is designed to provide practical guidance on SCM selection, performance optimization and low-carbon concrete development.