The physical characterization of wastewater dry sludges for concrete use

The use of dry sludge in concrete manufacturing may contribute to reducing the impact of sludge pollution on the environment. Dry sludge is used in agriculture as a soil fertilizer. However, not all sludge is suitable for this purpose, as sludge collected from different treatment works may display different characteristics. Three test samples were collected from three different wastewater treatment plants owned by Johannesburg Water: namely, Bushkoppies, Driefontein, and Goudkoppies. The three dry sludge samples were then analyzed to determine their physical characteristics. The tests used to determine the physical characteristics of the dry sludge were grading analysis (including the fineness modulus), bulk density, and relative density. Using the crusher sand as a reference sample, the results of the three tests were compared to those of the crusher sand. The fineness modulus of the crusher sand obtained was 2.71, and that of the sludge samples ranged from 1.67 to 2.93. The relative density of the crusher sand was 2.620 and the sludge samples ranged from 1.506 to 1.706. The compacted bulk density of the crusher sand was 1906 kg/m³ and the sludge samples ranged from 621.7 kg/m³ to 711.3 kg/m³.