One example of the unexplored possibilities of circularity is mineral wool. These are fibrous materials formed by the spinning or extracting of minerals or molten rocks, such as slag and ceramics. They work as excellent thermal and acoustic insulators, as they have an extremely low density. For this same reason, they can also become a problem during demolition, as they take up significant space in landfills; they are very light, but highly voluminous. As mentioned in this article, “In Europe, around 2.5 million tonnes of mineral wool waste are generated each year in construction and demolition. Currently, mineral wool waste is almost entirely deposited in landfills, resulting in an annual cost of around €250 million for the construction sector.”
The WOOL2LOOP project aims to use mineral wool waste, after processing, in products such as façade panels, acoustic sheets, paving tiles and even as aggregates for 3D printers. To this end, a process was developed that starts by separating mineral wool residues, grinding them and using them as products through alkaline activation (or geopolymerization), converting them into ceramic or concrete-like materials. Geopolymers are considered good alternatives for traditional Portland cement (OPC), mainly due to comparable mechanical properties, while releasing a fraction of the carbon dioxide. The great advantage is that several residues from existing industrial processes can be used for the manufacture of geopolymers, such as fly ash or kiln slag, which makes the process ideal both environmentally and economically. To get an idea of the impact, approximately 5-10% of all man-made CO2 emissions are generated in cement production. Geopolymerization is becoming a more widely accepted method for preparing low carbon dioxide binders, other products and materials from various industrial by-products, one of which is mineral wool waste.
Among the different areas of the project, 3D printing is one of the most promising. Different printing capabilities of different geopolymer blends containing insulation materials recovered from construction sites are currently being tested. With proper mixing ratios and the adaptation of printing technology, new geometries can be fabricated that otherwise could not be made with traditional techniques.