Review and Evaluation of Agricultural Biomass Ashes as Supplementary Cementitious Materials for Sustainable Concrete

Concrete is the second most consumed material after water, with cement as its primary binder. However, cement production accounts for nearly 7% of global CO2 emissions, posing a major sustainability challenge. This review critically evaluates 35 agricultural biomass ashes (ABAs) as potential supplementary cementitious materials (SCMs) for partial cement replacement, focusing on their effects on concrete strength and durability and highlighting performance gaps. Using a systematic methodology, rice husk ash (RHA), sugarcane bagasse ash (SCBA), and wheat straw ash (WSA) were identified as the most promising ABAs, enhancing strength and durability—including resistance to chloride ingress, sulfate attack, acid exposure, alkali–silica reaction, and drying shrinkage—while maintaining acceptable workability. Optimal replacement levels are recommended at 30% for RHA and 20% for SCBA and WSA, balancing performance and sustainability. These findings indicate that ABAs are viable, scalable SCMs for low-carbon concrete, promoting greener construction and contributing to global climate mitigation.