Carbonation of reclaimed concrete wash water for CO2 mineralization: Real-time monitoring using slurry density and pilot-scale validation

Reclaimed water generated during concrete production contains suspended cementitious solids that can serve as reactive phases for CO 2 mineralization. This study investigates the carbonation behavior of reclaimed water and evaluates its applicability for CO 2 sequestration and reuse in cementitious materials at both laboratory and pilot scales. Carbonation experiments were conducted under varying CO 2 injection rates and solid contents to examine their influence on carbonation kinetics and CO 2 uptake. The results showed that increasing the CO 2 injection rate significantly accelerated carbonation due to enhanced gas-liquid mass transfer, while excessive solid content introduced transport limitations that reduced effective carbonation efficiency. To enable real-time monitoring of the carbonation process, an in-line density measurement approach was developed and validated against thermogravimetric analysis (TG). The density-based method exhibited strong correlation with TG-derived CO 2 uptake at laboratory scale and remained reliable under pilot-scale conditions, although slight deviations were observed due to compositional heterogeneity in actual reclaimed water. Mineralogical and microstructural analyses confirmed that carbonation converted calcium-bearing phases into stable calcium carbonate, with calcite identified as the dominant carbonation product. Pilot-scale experiments using a 1000 L carbonation reactor demonstrated consistent carbonation behavior and confirmed the scalability of the process. Concrete mixtures prepared with carbonated reclaimed water exhibited mechanical performance comparable to those prepared with conventional mixing water. These results indicate that carbonation of reclaimed concrete wash water provides a feasible pathway for simultaneous CO 2 mineralization and recycling of wash water in concrete production systems.