Influence of cement- and gypsum-based construction waste on the processing and properties of ceramic tiles: A laboratory-scale study

Construction and demolition waste, CDW, represents one of the most abundant and often overlooked waste streams globally, posing both an environmental challenge and an opportunity for resource recovery. This study presents a systematic approach to valorise the mineral fraction of CDW as a secondary raw material, SRM, for ceramic tile manufacturing. Up to 20 wt% of non-ceramic CDW, including cement-based (mortar and concrete) and gypsum-based (plasterboard and plaster), was studied in compositions based on recycled ceramics (red brick and porcelain stoneware). Gypsum-based materials exhibited an unresolvable incompatibility with the process, particularly during thermal treatment, making them infeasible for use in ceramic tile compositions. In contrast, cement-based materials not only demonstrated compatibility with the process but also improved the final properties. Then, two different real CDW streams were tested at laboratory scale with plastic clay (0–20 wt%). The sintered samples were evaluated for modulus of rupture and water absorption, and the waste stream composed of discarded ceramic tiles was classified as BIII (monoporosa tiles) according to ISO13006:2018. This work offers a scientific perspective on ceramic strategies aligned with circular economy principles, thereby opening a tangible pathway toward more sustainable ceramic production.