Use of volcanic ash and chamotte as substitute temper in the production of ceramic tiles

This paper explores the use of waste materials as substitutes in ceramic paste formulations. Building on previous research which has laid the groundwork for the use of volcanic ash as temper in ceramic tile manufacture, investigation is here extended to a broader spectrum of waste-based ceramic pastes. Specifically, five different mixtures have been manufactured through the hand-made technique by using Etna volcanic ash and/or tile processing residues (chamotte), mixed with clay in variable proportions. Physical-mechanical tests including flexural strength, water absorption, resistance to thermal shock, deep abrasion and impact, have been performed and results compared with those of reference tiles. Notably, ceramic pastes combining clay with chamotte or clay with chamotte and fine volcanic ash, show better performance. This is certainly due to the good physical-mechanical properties of chamotte which binds well with the clayey groundmass so reducing shrinkage / cracking and improving the overall quality of ceramic products. Conversely, volcanic ash does not show a high degree of union with the clayey matrix, particularly when occurring in larger grain size. However, when present in fine clasts and in combination with chamotte, the resulting products display good physical-mechanical characteristics. This study highlights once again the potential of waste materials in ceramic manufacturing, paving the way for a more sustainable and resource-efficient industry.