Reuse of Industrial Sludge as Pelletized Aggregate for Concrete

Industrial sludge is generated at a rate of 100 metric tons/day, from a copper slag recycling plant. The industrial sludge is currently being landfilled. However, limited availbility of landfill sites has raised the need of an alternative disposal. A renewed interest in converting the industrial sludge into construction materials has been prompted to achieve a viable disposal option in saving the depleting natural resources of raw materials as well as the environment. This study describes the use of sintered sludge pellets as a complete replacement for regular granite aggregates in concrete. The pelletized sludge was fired to a temperature of 1,135°C at which the sintering process occurs, producing a hard fused basalt-like mass. In comparison with normal granite aggregates, the sintered sludge pellets display a higher aggregate strength, a higher porosity, and a lower aggregate density that manifests attributes better than that required of construction aggregates. The concrete cast with the pelletized aggregtes achieved a compressive strength of 38.5 N/mm2 after 28 days and was comparable to the control specimen. Leaching tests conducted on the sludge pellets and concrete showed that all leachate contamination levels determined using the column leaching test are within acceptable ranges after 130 days of stabilization. The experimental results indicated that a complete replacement of conventional aggregates with sintered sludge pellets for structural concrete is both technically and environmentally feasible.