A Review of Agricultural by-Products in Unfired Mud Bricks for Sustainable Construction

Unfired mud bricks are a potential low-energy alternative to kiln-fired masonry, but their performance depends strongly on soil composition, moisture, compaction, curing and exposure conditions. Agricultural by-products—including rice husk ash (RHA), cereal straw, sugarcane bagasse ash and sawdust—have been investigated as partial constituents or modifiers in earth-based and other construction materials. This review synthesizes published research on how these residues may influence strength, density, water interaction, cracking, thermal behaviour and resource efficiency in unfired bricks. The literature indicates that mineral ashes can contribute reactive silica or act as fine fillers when their processing and compatibility with the soil/binder are suitable, while plant fibres may help control drying cracks and reduce density. These benefits are not automatic: excessive or poorly distributed additions can increase porosity, water uptake or variability, and fibre-rich mixes may lose compressive strength. Manufacturing variables— grading, water content, mixing sequence, moulding pressure and curing—are therefore as important as the waste type itself. Existing reviews also identify a gap between laboratory demonstrations and reliable industrial production, particularly in standardized mix design, durability testing and life-cycle assessment. The paper concludes that agricultural-waste mud bricks should be assessed using a balanced performance framework rather than strength alone, with local materials tested against applicable building requirements before practical use.