Enthalpy-based framework for estimating CO2 storage in cementitious composites mixed by the air-tight carbonation method

Current approaches for evaluating CO 2 uptake in cementitious materials depend on post-carbonation characterization, which precludes the estimation of CO 2 uptake during fabrication. To address this limitation, this study developed an air-tight carbonation mixing (ACM) method for cementitious composites and established an enthalpy-based framework to estimate CO 2 storage through temperature variation during mixing. The framework is based on the assumption that the heat generation due to hydration is equivalent in the control and ACM groups; therefore, the CO 2 storage is estimated from the additional temperature rise across mixing cycles. The thermal responses of two specimen groups were compared: a control group undergoing pure hydration and an ACM group experiencing coupled hydration and carbonation. The additional temperature rise caused by carbonation was estimated by decoupling the hydration heat from the total heat generated. This additional temperature rise enabled the estimation of CaCO 3 formation through an enthalpy-based framework. The predicted CaCO 3 amounts from the proposed framework closely matched the quantitative X-ray diffraction (QXRD) and thermogravimetric analysis (TGA) results, with deviations within 8% across all measured mixing cycles. In terms of mechanical performance, the 28-day compressive strength of the ACM specimens remained comparable to that of the control, with differences of less than 5%. Based on cement mass normalization, the ACM method exhibited an estimated CO 2 storage of approximately 17 kg/m 3 of concrete. These results indicate that temperature variation provides an indicator of CO 2 storage during mixing.