Stone Sludge as a Resource: Developing High-Performance Alkali-Activated Materials for Local Circular Economy Models

Waste from the processing of stone materials remains an unresolved issue: this represents a significant volume of material – 347,000 tonnes in Italy in 2023 – which is classified as inert waste (EWC code 01 04 13 in Italy). This generally constitutes an environmental problem, particularly in terms of its impact on the landscape, compounded by specific issues such as landfill safety management. On this regard, to this day, there is not a solution that can constitute a true circular economy model, in which waste, once recovered, can effectively re-enter as a resource into the local production cycles. The present research want to suit this particular issue. In this context, some specific research focuses on using stone sludges in alkali-activated materials (AAM) and geopolymers. AAM consist of inorganic aluminosilicate polymeric materials which have numerous applications in various fields, but which primarily offer an alternative to conventional Portland cement, producing 80% less CO2. Depending on the formulation, they can be designed to withstand high temperatures, chemical or saline environments, and their mechanical properties can have average values ranging from 40 MPa to 70 MPa. The ongoing research is part of a broader programme, with two main objectives: the first is to obtain a stable geopolymer mixture, increasing stone sludges ratio as precursors. The second consists in the study and design of a recycle system for the stone process wastes that could lead to a local process innovation in the construction field. With this in mind, the research is exploring two potential applications: a modular elements produced using additive manufacturing for the building sector, and a composite material designed for cycle paths. To this end, specific on going studies are carried out to improve the initial formulations, with known mechanical properties, in order to optimize their suitability for the application of 3D printing technologies.