CO2-bound waste ash could replace sand and gravel in roads, buildings

German researchers from Cologne University of Applied Sciences (TH Köln) and RWTH Aachen University, led by the Bergischer Waste Management Association (BAV), are developing a method to convert municipal solid waste incineration (MSWI) ash into a sustainable construction material by permanently binding CO2 through carbonation. MSWI ash, which contains hazardous substances like heavy metals and dioxins, is produced in large quantities in Germany and currently requires careful processing to remove contaminants. The project explores natural carbonation reactions where minerals in the ash chemically bind CO2, potentially transforming the ash into a substitute for sand, gravel, or concrete components. The team is testing two carbonation techniques—wet carbonation, which allows higher CO2 uptake but needs energy-intensive drying, and moist carbonation, which forms a dense carbonated surface layer but stores less CO2. A pilot plant at the Leppe Waste Management Center in Lindlar, Germany, will trial these methods under real-world conditions. The ultimate goal is to produce carbonated ash that