CO2 Sequestration by Carbonation Processes of Rubblized Concrete at Standard Conditions and the Related Mineral Stability Diagrams

A study is conducted to evaluate the carbonation processes from rubblized concrete (RC) as it relates to CO2 sequestration and carbon life cycle analyses for cement and concrete industries. In a one-year time frame, this study demonstrated that, during direct carbonation, RC absorbs up to 56 mg/g of CO2 when pretreated (suitable for mineral carbonation technology - MCT) and 19 mg/g of CO2 when unprocessed (suitable to create RC beds). RC is also found to be able to absorb CO2 during the indirect carbonation process of MCT (including high ionic strength (IS ≈ 0.1 to 0.5 M) and CO2 injection into solution). This condition results in r = Ca 2+ /SO4 2– ≈ 1, which favors the precipitation of calcite. However, when RC is treated as a bed of material, the indirect process does not appear to favor the CO2 absorption as the solution becomes low ionic strength (IS ≈ 0.06 M) and the r values stay close to unity for the entire carbonation process (resulting in gypsum precipitation). As part of the indirect carbonation evaluation from RC, a set of mineral stability diagrams and a Ca–CO3 2––SO4 2––H2O equilibrium system was developed that can provide an accurate prediction of the coexisting minerals from the RC solution.