Using ornamental stone cutting rejects as raw materials for red clay ceramic products: Properties and microstructure development

The incorporation of various wastes in red clay-based ceramic products has been widely investigated, frequently with the aim of reducing the waste environmental impact. This work explores the not so obvious waste potentialities and describes the properties and microstructure development in a natural clay showing large processing limitations, upon the addition of two different ornamental stone cutting rejects, granite and marble + granite. All materials were collected at industrial sites and the behavior of mixtures containing 70 wt.% clay + 30 wt.% reject is detailed. Powder samples were uniaxially pressed under 20 MPa, sintered in air in an electric furnace for 2 h at a temperature in the range 950–1150 °C, and characterized. The experimental results obtained (firing shrinkage, porosity, flexural strength, microstructure) show that the rejects can be used to replace traditional fluxing agents, helping the sintering process, and simultaneously control the plasticity and shrinkage of an otherwise unusable clay, with obvious economical and environmental benefits.