Using marble and granite rejects to enhance the processing of clay products

Abstract The heterogeneity of traditional clay-based materials accommodates a variety of waste products compositions with little sacrifice of the final product properties and a much welcome relief on waste disposal concerns. Hence, the incorporation of industrial wastes or sub-products in bricks and tiles is becoming common practice. However, the continued depletion of natural resources throws new light on the potential use of some industrial wastes and natural sub-products as full-fledged alternative ceramic raw materials. This work shows the changes in properties of an industrial red-clay-based mixture, already in use in the production of floor tiles, due to additions of an ornamental stone cutting reject (marble and granite). Samples containing up to 30 wt.% reject were uniaxially pressed and sintered in air in an electric furnace (1100–1150 °C, for 2 h). The results obtained (X-ray diffraction and fluorescence, thermal analysis, firing shrinkage, water absorption and mechanical strength), explain the effect that the marble and granite reject additions have on the clay mixture behaviour and show how the properties of the sintered red-clay products can be improved, with the possibility of using lower firing temperatures.