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

Accelerated carbonation of recycled concrete aggregates (RCA) in industrial CO 2 -rich environments is a promising technique to enhance CO 2 sequestration while improving RCA properties. This study investigates the influence of temperature (50–110 °C), initial water saturation degree (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 degree is a key parameter, as it influences both CO 2 transport in the pore system and the dissolution of reactive phases. Temperature significantly impacts water saturation degree evolution, which in turn affects reaction kinetics. For each initial water saturation degree, an optimal temperature maximizes carbonation, reaching degrees above 40 % after only 2 h 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 degree. However, no direct correlation between water absorption and carbonation degree was observed, suggesting complex porosity evolution that requires further investigation. • A recycled concrete aggregates (RCA) bed through which a CO 2 -rich gas stream flows was developed to study CO 2 sequestration. • Temperature and initial water saturation degree are interdependent parameters strongly influencing carbonation of RCA. • Optimizing temperature with initial water saturation degree is crucial to balance CO 2 diffusion and reactant dissolution. • Finer fractions mineralize more CO 2 and faster. • An innovative Macro-TGA method was used to quantify CO 2 uptake on RCA.