Manufacturing and mechanical performance of interlocking bricks using coal ash: a sustainable environmental solution and structural integrity

The over-reliance on traditional burnt clay bricks has raised serious environmental concerns due to the excessive use of fertile soil and the emission of harmful gases during manufacturing. This study aims to develop and evaluate interlocking bricks (IBs) using coal bottom ash (CBA), a waste by-product of thermal power plants, as a partial replacement for cement, to offer a sustainable alternative in masonry construction. Six different mix designs were formulated with varying CBA (30–55%) and cement (5–30%) contents while maintaining a total binder proportion of 60%. The physical, mechanical, and durability properties of the IBs were assessed, and wall panels constructed from the optimized IBs were tested under both in-plane and out-of-plane loading conditions. Results indicated that the optimal mix comprising 30% CBA, 30% ordinary portland cement (OPC), and 40% sand achieved a compressive strength of 18 MPa, meeting international building code standards. Compared to conventional and fly ash bricks, the developed IBs showed enhanced durability, lower porosity, reduced water absorption, and minimal efflorescence. Structurally, the IB panels exhibited superior shear resistance and deflection control under lateral loads, with in-plane and out-of-plane strengths of 53.18 MPa and 45.92 kN, respectively. The interlocking design minimized lateral displacement and delayed crack propagation, resulting in improved structural integrity. These findings demonstrate that CBA-based IBs are not only structurally reliable but also offer an environmentally sustainable solution to coal waste disposal and conventional masonry challenges.