Synthesis and characterization of ceramics from coal fly ash and incinerated paper mill sludge

Powders obtained from coal fly ash and paper mill sludge were milled alone or in mixture, pressed into specimens and sintered. Fired materials were characterized by density, water absorption, shrinkage on firing, crystal structure, microstructure, strength, hardness and toughness. Samples made with paper mill sludge alone had a high sintering temperature, contained extended fractures after sintering and were not further studied. All the other compositions, sintered between 1130 and 1190 °C, showed low water absorption, density below 2.6 g/cm3, fair mechanical properties and contained several phases. More in particular, the material containing 25 wt% of coal ash and 75 wt% of powder from paper sludge displayed the best overall behaviour.