Incorporation of sludge waste from water treatment plant into red ceramic

The influence of the firing temperature on the technological properties of red ceramics made of a kaolinitic clay incorporated with a sludge from water treatment plant was evaluated. The sludge was initially submitted to characterization tests to determine its particle size distribution, chemical composition, mineralogical composition, thermal behavior and morphological aspects. Mixtures were prepared with amounts of 0, 3, 5 and 10 wt% of sludge incorporated into the clayey body. Rectangular specimens were obtained by 20 MPa pressure molding and then fired at 700, 900 and 1100 °C in a laboratory furnace. Ceramic properties related to the bulk density, linear shrinkage, water absorption and flexural rupture strength were determined. The results indicated that the incorporation of the sludge increase the water absorption and reduce the mechanical strength of the clayey fired ceramic. This is a consequence of the changes caused in the porosity by the relatively elevated weight loss during the firing stage.