Carbonation of recycled concrete aggregate in a fixed-bed reactor: effects of temperature, initial water saturation and particle size

Abstract

Accelerated carbonation of recycled concrete aggregates (RCA) in industrial CO2-rich environments is a promising technique to enhance CO2 sequestration while improving RCA properties. This study investigates the influence of temperature (50–110 °C), initial water saturation (0.34–0.93), and RCA particle size (0–4 mm) on carbonation efficiency in a fixed-bed reactor under controlled conditions, simulating cement plant flue gases. Results highlight that water saturation is a key parameter, as it influences both CO2 transport in the pore system and the dissolution of reactive phases. Temperature significantly impacts water saturation evolution, which in turn affects reaction kinetics. For each initial water saturation, an optimal temperature maximizes carbonation, reaching degrees above 40 % after only 2 hours carbonation. Particle size also influences carbonation efficiency: finer RCA exhibit higher carbonation rates. A novel Macro-TGA methodology was employed to quantify carbonate formation in 500 g samples, offering a more representative assessment compared to classical thermogravimetric analyses. Finally, water absorption tests before and after carbonation showed a slight reduction, with a maximum decrease of 2.7 % at 80 °C and 0.93 initial water saturation. However, no direct correlation between water absorption and carbonation degree was observed, suggesting complex porosity evolution that requires further investigation.

Keywords: Recycled concrete aggregates, carbonation, Carbon Capture and Utilization (CCU), Temperature, Water saturation