Utilization of Agricultural Waste in Concrete Production: A Review on Rice Husk Ash and Coconut Shell

Concrete remains the most widely used construction material globally, yet its reliance on Portland cement and natural aggregates contributes significantly to carbon emissions, resource depletion, and environmental degradation. To address these challenges, increasing attention has been directed toward the incorporation of agricultural wastes into concrete production, providing both ecological and economic benefits. Among various residues, rice husk ash (RHA) and coconut shell (CS) are particularly promising due to their abundance, chemical composition, and favorable physical properties. This review synthesizes existing research on the use of RHA as a supplementary cementitious material and CS as a lightweight aggregate in concrete. Studies consistently report that RHA, rich in amorphous silica, exhibits strong pozzolanic activity, enhancing compressive strength, durability, and resistance to chemical attack at optimal replacement levels. Coconut shell aggregate, characterized by its fibrous and lignocellulosic nature, produces lightweight concrete with adequate strength, improved toughness, and better thermal insulation compared to conventional concrete. However, challenges remain, including the variability in RHA quality due to uncontrolled burning, the high water absorption of coconut shells, and limited large-scale field applications. The review highlights the sustainability benefits of adopting these materials, including reduced cement consumption, conservation of natural aggregates, and diversion of agricultural residues from landfills or open burning. It also identifies research gaps related to durability, standardization of processing, synergistic use of multiple waste products, and life cycle assessment. Overall, the integration of RHA and CS into concrete production offers a viable pathway toward sustainable construction and circular economy practices.