(90b) CO2 Mineralization Kinetics of Portlandite-Enriched Cementing Systems Exposed to Flue Gases

When in contact with flue gases, cementitious binders featuring portlandite (Ca(OH)₂) can take up CO₂ by forming stable carbonate minerals (i.e., CO₂ mineralization/carbonation reactions). As these reactions induce cohesive strength between particles, they may be exploited to capture/utilize CO₂ from dilute streams for the fabrication of concrete products with reduced carbon intensities compared to their conventional counterparts. To inform process design, the influences of relative humidity, temperature, and CO₂ concentration on the carbonation kinetics of portlandite within these components must be clearly understood. However, such understanding has been limited by the lack of portlandite kinetics data within conditions relevant to direct flue gas exposure, and due to the complex linkages between the carbonation kinetics of portlandite-enriched components and of the reactants from which they are formed. For instance, CO₂ transport limitations increasingly influence carbonation kinetics as component size increases and are highly dependent on properties such as the porosity and degree of pore saturation with liquid water. Here, we discuss the influences of processing conditions on carbonation kinetics of portlandite-enriched binders at both the particulate scale and the component scale. We assess the sensitivity of the carbonation kinetics of portlandite particulates and portlandite-enriched monoliths to relative humidity, temperature, and CO₂ concentration. The relationships between the CO₂ uptake of portlandite particulates and portlandite-enriched monoliths in relation to their thickness and geometric surface area/volume ratio (SA/V) are elucidated. The temperature rise due to the exothermic carbonation reactions as a function of the component size is also investigated. The findings of this study inform the design of CO₂ mineralization processes in relation to component geometry, aiming towards the scalable production of low-carbon concrete components by direct flue gas utilization.