Chemical Extraction and Mechanical Crushing Method for Fine Aggregate Recycling from Waste Concrete

A new fine aggregate recycling process from waste concrete using high-pressure carbon dioxide (CO2) solution is proposed. The basic mechanism of the recycling process is extraction of calcium from a hydrated cement component, which reacts readily with acid. Calcium extraction would be effective in promoting the separation of hydrated cement from aggregates. The aggregate component, mainly composed of SiO2, does not react with carbonic acid and would be recovered as the solid phase on filtration. Dissolved calcium can be recovered as calcium carbonate under low CO2 pressure conditions. The feasibility of the recycling process through laboratory experiments was examined using real concrete waste samples, which cannot be recycled effectively by current processes. A combination of CO2 solution treatment and ball-mill crushing was examined. High-quality recycled fine aggregate that can be used for the production of new concrete could be obtained using the proposed process.