Operando 5D tomography uncovers carbonation-driven water transport and cracking in hydrated cement paste

Concrete production is responsible for roughly eight percent of global carbon dioxide emissions and generates more than a third of construction and demolition waste. Accelerated carbonation of recycled aggregates emerges as a promising solution, enabling simultaneous carbon dioxide sequestration and circular use of materials. Yet, the coupled physical processes governing carbonation under industrially realistic conditions remain poorly understood. Here we show, using time-resolved neutron and X-ray tomography, how heat, moisture, chemical reactions, and mechanical damage interact during cement paste carbonation. Conducted at eighty degrees Celsius and high carbon dioxide concentrations, our experiments reveal that carbonation drives rapid release of bound water, alters moisture distribution, and induces crack formation and sealing. These results demonstrate the inadequacy of purely diffusive models, and provide quantitative insight into carbonation kinetics and transport dynamics. Our approach establishes a robust foundation for designing optimized carbon dioxide capture strategies in recycled concrete, advancing both emissions reduction and resource circularity in construction. Carbonation of cement is a promising approach for carbon dioxide sequestration. This study explores the effect of heat, moisture, chemical reactions, and mechanical damage on carbonation via time-resolved neutron and X-ray tomography.