Upcycling di vetri di scarto per nuovi materiali da costruzione sostenibili

Alkali activation is an efficient method for the reuse of waste materials. This process proves to be economically advantageous and environmentally sustainable, provided that the starting materials are truly considered waste and alkaline solutions used have a relatively low concentration. The goal of the research activities is the upcycling of glass waste materials, which are characterized by heterogenous chemical compositions. Not all type of glass can be recycled through remelting, leading to an accumulation of waste glass in landfills. Boro-alumino-silicate glass, predominantly derived from pharmaceutical vials, has seen a significant increase in production due to the COVID-19 health emergency. For this type of glass, close-loop recycling remains currently limited, as it is necessary to meet stringent chemical and optical quality requirements for the final product. The alkaline activation process involves the production of suspensions of fine glass powder in weak alkali solutions. The hardening of the material occurs through low temperature treatment [40- 75 °C] in a process known as ‘cold consolidation’. The process has highlighted the uniqueness of mild alkali activation applied to waste glass, whose molecular hardening mechanism is not comparable to that of geopolymers, or alkali activated materials. During the hardening phase, condensation reactions occur on the surface of the hydrated layers of the glass particles. These reactions promote the formation of strong bonds, such as Si-O-Si and Al-O-Si, which are essential for the integrity of the material. At the same time, the glass components released into solution undergo a rearrangement process to from a ‘secondary phase’. This phase can consist of a newly formed gel, crystalline phases, and alkaline carbonates. The approach has also been extended to various type of alkaline activators, such as cesium hydroxide, used to simulate the storage of radioactive materials. Additionally, other activators, such as ammonium hydroxide and tetraethylammonium hydroxide, have been examined to assess their potential in hardening process. Alkali activated glass can also be used as a matrix for the encapsulation of the other industrial waste, such as foundry sands. Besides boro-alumino-silicate glass, sodalime glass waste has also been used, combined with volcanic ash, for the production of dense alkali activated foams, at room temperature, ideal for thermal insulation. Furthermore, other pozzolanic material like tuff can be activated alone or with sodalime glass waste. Recent investigations have finally confirmed the potential of alkaline activation, not only for the recovery and valorisation of glass materials in building materials, but also in the development of glass intended for the storage of nuclear waste.