A review on agricultural waste ashes as sustainable supplementary cementitious materials for concrete applications

The manufacturing of clinker is the main reason of cement and concrete sector contributes significantly to global carbon dioxide emissions. Agricultural waste ashes have drawn more attention as sustainable supplemental cementitious materials (SCMs) in response to the growing need for low-carbon and resource-efficient building materials. Rice husk ash, sugarcane bagasse ash, wheat straw ash, millet husk ash, wood waste ash, and corn cob ash are among the experimentally reported agricultural waste ashes that are thoroughly and critically reviewed in this study. Their physical, chemical, mechanical, durability, and microstructural performance in cementitious composites is also systematically evaluated. The review analyzes agro-ashes according to chemical composition (SiO₂–AlO₃–FeO₃ concentration), pozzolanic reactivity, particle properties, and compliance with ASTM-based SCM criteria by synthesizing data from a variety of peer-reviewed publications. Important results show that silica-rich agro-ashes have a high pozzolanic activity and may substitute cement to a certain extent (usually between 5 and 20%) without sacrificing and often improving durability, tensile strength, compressive strength, and pore structure refinement. Additionally, the analysis identifies important information gaps regarding long-term durability and standardization by highlighting the impact of fineness, ash processing, and combustion conditions on concrete performance. This review establishes agricultural waste ashes as competitive alternatives to traditional SCMs and provides clear directions for future research and large-scale implementation in sustainable concrete production by combining scattered experimental evidence and offering comparative performance insights.