Alkali-activated geopolymerization of a low illitic raw clay and waste brick mixture. An alternative to traditional ceramics

Geopolymerization was investigated as an alternative to traditional ceramic products by developing a more sustainable approach that avoids thermal treatment. The study presents the first known alkali-activation of the raw clay and waste clay brick mixture using the solid to liquid ratios of 2.33 and 2.78. Several experimental sets were prepared to harden under varying conditions (2–4 days drying in 60 °C–70 °C and 3 h steam-curing). Non-activated and activated samples were analyzed for their physical and chemical properties after 14, 21, and 28 days. The tile-shaped specimens exhibited better initial drying behavior than the cubes and produced stronger materials with fewer cracks. Pre-curing in steam conditions induced higher flexural strength (13.7 MPa) and water absorption (13.13%) for the geopolymer tiles. The highest Si/Al molar ratio in the amorphous portion of 5.78 induced the best flexural strength. The geopolymerization process showed microstructural changes associated with the appearance of fibrous Na-zeolite nanocrystals. The degree of geopolymerization and zeolite formation was enhanced by steam-curing, but the microstructural stress and heterogeneity induced by the reactions resulted in higher water absorption. Ongoing reactions of amorphization in the bulk material and further crystallization at the surface are documented after 6 months of curing. This first detailed study reveals that the production of geopolymer ceramics from brick waste is possible, but further optimization of the activating solution and curing parameters is required.