SUSTAINABLE UTILIZATION OF COAL BOTTOM ASH AS AN ADDITIVE IN FIRED CLAY BRICK PRODUCTION

Abstract

The accumulation of coal bottom ash (CBA) poses environmental concerns, creating a need for sustainable recycling routes. This study investigates the feasibility of using CBA as a supplementary raw material in fired clay bricks. Specimens containing 0–40 wt.% CBA were fabricated and fired at 900, 1000, and 1100 °C. The effects of CBA incorporation on physical properties, compressive strength, and microstructural evolution were systematically evaluated. Increasing CBA content decreased bulk density and compressive strength while increasing apparent porosity and water absorption. SEM observations indicated that pore formation was mainly induced by sulfate decomposition and residual carbon combustion during firing. Raising the firing temperature promoted densification through flux-assisted liquid-phase sintering. XRD results highlighted the formation of albite from alkali-rich CBA and the presence of inherited mullite, which together influenced the sintering behavior and structural stability of the bricks. Bricks containing 10–30 wt.% CBA fired at ≥1000 °C achieved compressive strengths above 17.2 MPa, satisfying ASTM C62 requirements for moderate weathering (MW) conditions. The findings confirm that controlled CBA incorporation can produce durable, eco-friendly masonry bricks and support circular-economy-based resource utilization.