Analysis of physicochemical properties of clinker tiles with the addition of alternative waste raw materials

The feasibility of using sewage sludge ash (SSA) as an alternative raw material in ceramic clinker tiles was investigated at additions of 2–10 mass%. The effects of SSA on thermal behavior, sintering, phase composition and technological properties were evaluated using DSC–TG coupled with quadrupole mass spectrometry (QMS), hot-stage microscopy (HSM), dilatometry, X-ray diffraction (XRD), and measurements of bulk density, water absorption, apparent porosity and flexural strength. SSA exhibited a low-temperature mass-loss region associated with dehydration and decomposition of residual organics, followed at higher temperatures by sulfur-containing gas evolution. HSM and dilatometry showed that SSA shifted densification toward lower temperatures. The temperature of minimum specimen height decreased by 25–60 °C, while the temperature corresponding to 8% linear shrinkage decreased by 16–28 °C relative to the reference body. At excessive firing temperatures, especially for higher SSA additions, densification was followed by swelling and deterioration of physical properties. XRD showed quartz as the dominant crystalline phase in the fired bodies, with hematite and minor mullite also detected. Industrial firing at 1165 °C increased flexural strength from 41.4 MPa for the reference body to a maximum of 74.2 MPa for SSA08, followed by a decrease for SSA10. The results indicate that 2–8 mass% SSA can be incorporated into clinker-type ceramic bodies while promoting densification at lower temperatures, provided that the firing conditions are carefully controlled to avoid overfiring.