SUSTAINABLE MORTAR DEVELOPMENT USING MINERALIZED SPENT LIME

In contemporary times, the concepts of sustainability and recycling have become increasingly important in economic strategies, reinforcing the importance of the circular economy as a central way to reduce the environmental impacts of industrial processes, through the valorization of waste. For the Italian economy, hard-to-abate sectors such as ceramic tile manufacturing play a crucial role, and in the context of ecological transition, they require innovative solutions both to reduce carbon dioxide emissions and to valorize the by-products generated during emission abatement processes. Within this framework, the CCS4CER project (Carbon Capture, Storage and CO2 Mineralization for the Ceramic Industry), funded by the European Regional Program PR-FESR 2021–2027 of Emilia-Romagna was launched. The project aims to develop an effective approach to capturing CO2 from ceramic tile plants while, simultaneously, valorizing spent lime, an industrial waste currently disposed to landfill for hazardous waste. Spent lime is generated by the reaction of lime normally employed for the removal of acidic flue gases released during the firing stage. However, spent lime still contains a significant fraction of calcium hydroxide that can be exploited for CO2 capture through mineralization. The present work addresses the formulation of low-carbon cement by reusing spent lime, once mineralized with CO2 under laboratory-scale pilot conditions. Reducing the environmental impact of Portland cement-based materials is of particular interest, given the substantial greenhouse gas emissions associated with their production. The proposed approach follows this rationale by developing cements with a reduced clinker content (the primary constituent of Portland cement) and calcium carbonate produced via mineralization. Hydrated lime, spent lime, and mineralized spent lime from the production cycle of a selected ceramic manufacturer were characterized by laser granulometry, ICP-OES analysis for evaluation of the major compositional oxides and calcimetric analysis. In a second time, following this characterization, low-carbon cement formulation was developed and standardized mortar specimens were prepared in accordance with EN 196-1. After 28 days of curing, the mortars were evaluated through compression tests and water absorption measurements. All tests were benchmarked against a commercial limestone cement (CEM II-B/LL) containing an identical clinker content to the investigated low-carbon formulations. As second reference, a mortar containing the same amount of clinker content and calcium carbonate instead of mineralized spent lime was prepared, characterized and compared with the others formulations.