Mechanical characteristics of clay structural ceramics containing coal fly ash

In this work, the mechanical characterization of ceramic products processed from red clay with different amounts of added coal fly ash was investigated. Coal fly ash produced by power plants is a waste material that constitutes an alternative source of minerals for the production of traditional building ceramics, as it is a complex mixture of several oxides such as SiO₂, Al₂O₃, CaO, Fe₂O₃, Na₂O, TiO₂, which are usually present in the composition of such ceramics. A powder technology and firing route was followed for the processing of the clay and coal fly ash based ceramics. Different proportions of waste (10, 25 and 50%, by weight) were added to red clay, and then the mixed powders were pressed to form compacts that were fired at a selected temperature in the range 850-1,150°C. The effects of waste content and of heating conditions on the microstructure and mechanical characteristics of the obtained materials were investigated. The density, porosity, water absorption, flexural strength, hardness and fracture toughness of the produced materials were evaluated. A comparison was made between the properties of the produced ceramics with those of traditional ceramic materials used in construction, e.g. floor or wall tiles, and it was observed that the clay based products with coal fly ash additions may be used in similar applications.