Enhancing CO₂ capture in cement-based materials with alkanolamines: A comprehensive study on efficiency, phase-specific impact, and carbonation mechanisms

The escalating issue of global warming, driven by the surge in CO₂ emissions, necessitates innovative strategies for reducing CO₂ emissions. A novel approach is explored in this study, where amines featuring a basic N atom with a lone pair are incorporated into cement paste to facilitate CO₂ capture from the environment. Unlike conventional applications, the focus is on the collaborative effect of various amines on CO₂ capture within diverse calcium-rich phases, encompassing portlandite and Calcium-Silicate-Hydrate (C-S-H). This investigation seeks to discern the most efficient amine and optimal concentration for CO₂ capture, particularly within distinct phases of cement paste. Notably, 2-(methylamino) ethanol (MAE) demonstrates superior performance in promoting CO₂ mineralisation and has been selected to further evaluate its ability in cement paste under natural carbonation conditions. Importantly, this research presents an exhaustive analysis of C-S-H carbonation with varying Ca/Si ratios, revealing carbonation mechanisms and consequential microstructural alterations in the presence of amine. Additionally, the presence of amine significantly influences crystal growth and the polymerisation of C-S-H. Furthermore, natural carbonation experiments underscore the efficacy of MAE, showcasing a 2.5-fold increase in calcite formation in the cement paste compared to scenarios without MAE.