Study on the Use of Coal Bottom Ash as a Raw Material Replacement for the Production of Clay Bricks

Context: Masonry bricks are one of the most widely used building materials in the world, which leads to the overexploitation of its raw materials. Its production consumes a large amount of energy and has a large environmental footprint. The clay brick industry can add residues to its raw materials; among those reported are tea processing waste, brick waste, paper industry residues, waste from coffee mills, and coal ashes. Method: Bottom coal ashes were characterized by X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, electronic microscopy, and particle size analysis. In addition, their density and loss on ignition were determined. The incorporation of ashes in the elaboration of clay bricks was evaluated, with sand replacement percentages of 0, 3, 5, and 7%. Finally, the physical and mechanical properties of the bricks were evaluated. Results: The water absorption and apparent porosity increased, while the compressive strength and bulk density decreased with the incorporation of ash in the brick samples, except for those with a 3% replacement, which showed a better performance in the evaluated properties. Conclusions: Coal bottom ashes have great potential in the manufacturing of clay bricks. The findings of this study indicate that, by incorporating up to 3% ashes, bricks can be obtained which comply with the Colombian regulations.