Development of New Functional Dense and Porous Materials from Opal Glass Cullet Through Mild Alkali Activation

Opal glass, known for its mechanical strength, hygiene, and aesthetic appeal, contains fluorides that hinder recycling and often lead to landfilling. This study investigates the use of discarded opal glass for the production of sustainable alkali-activated materials (AAMs), contributing to waste valorization and reduced raw material consumption. By optimizing the activation process, dense products with high compressive strength, comparable to conventional concretes, were obtained using low-molarity alkaline solutions and low-temperature curing (60 °C). In addition, lightweight porous structures with porosity exceeding 80% were successfully produced through direct foaming and salt templating. The developed materials exhibited good chemical stability under aggressive conditions. Preliminary biological tests indicated antimicrobial activity and low toxicity, supporting their potential use in applications where hygiene and durability are important. The results highlight the versatility of mild alkali activation for transforming waste opal glass into dense and porous materials with tunable properties.