Custom formulation of red ceramics with clay, sewage sludge and forest waste

The large quantities of sewage sludge that are currently generated require new alternatives for its recycling and final destination, beyond already known methods in the agriculture and cement industry. The use of this sludge as raw material for the production of structural ceramics, such as clay bricks, may become an interesting alternative, both from an industrial and environmental point of view. Several investigations have addressed this issue by formulating binary mixtures of sludge with clay. However, the incorporation of forest waste into the binary mixture described in this paper allows a high amount of sewage sludge to be assimilated into an extrudable mix and represents a better choice for the valorization of this hazardous waste. In this study the physicochemical properties of several formulations of ternary mixtures were analyzed. A ternary pseudo diagram was obtained relating the physicochemical properties of the ceramic product to the fraction of the raw materials. The optimal ternary mixture of 10% sludge, 10% forest waste and 80% clay, yielded a ceramic material with compression strength of 96 kp/cm2. It also met the technological limit of 8 bar to give and extrudable material. The mixture would be suitable for building ceramics, with low thermal conductivity (0.31 W/m·K) and high porosity (59.4%). The environmental aspects of the production of these ceramics were investigated by leaching and outgassing tests.