Effect of Selected Process Parameters During Carbonation Hardening on the CO₂-Binding Potential of Cementitious Materials

The cement industry faces an urgent challenge to reduce CO₂-emissions. A promising technology to bind CO₂ permanently in cementitious systems is Carbon Capture and Utilization (CCU). Carbonation hardening represents one approach of CCU technologies, and consists of the following steps: pre-curing, carbonation curing and post-curing. The process parameters at each step affect the carbonation degree and rate. During carbonation curing, combined hydration and carbonation reactions take place. This includes the formation of hydrates as well as carbonates of anhydrous clinker minerals. These reactions proceed simultaneously and are difficult to separate. Therefore, to get a deeper insight into these reactions and to control them, the process parameters that affect the carbonation reaction need to be investigated. Particular interest is ascribed to the relative humidity (RH) in the system as this considerably affects the carbonation degree, since CO₂ needs to dissolve in water to react with the calcium from the cementitious phases. This study investigates the effect of selected process parameters during the pre- and carbonation curing on the CO₂-binding potential of cementitious systems. For this, cement pastes were prepared and pre-cured for 6 h or 12 h at 30–80% RH. The carbonation curing was performed in a CO₂ chamber at a CO₂ concentration of 50% for different durations at 50% RH. The carbonate and bound water content in the samples were quantified with thermogravimetric analysis (TGA). The results of this study will help elucidating the carbonation hardening mechanism and act as a basis for applying CCU on cementitious materials.