Sequential coupling of hydration and carbonation in alite: reaction dynamics and phase evolution

Wet carbonation emerges as a pivotal technology for CO 2 sequestration and performance enhancement, wherein hydration and carbonation occur simultaneously and interactively. However, the mutual influence between these processes remains insufficiently understood. In our work, to maximize wet carbonation efficiency, CO 2 flow rate is set at 150 mL/min, which demonstrates the lowest residual alite (12.38 wt%) and high TG weight loss (34.57 wt%). Under identical CO 2 injection conditions, various durations for pre-hydration and wet carbonation duration are set to study the reaction dynamics of pre-hydrated alite under wet carbonation. During the pre-hydration stage, calcium hydroxide (CH) formed initially is preferentially carbonated, while C-S-H coatings on alite particles mitigates CO 2 penetration, slowing down alite carbonation and extending the pH plateau. As a result, pre-hydration stabilizes the system pH and delays alite dissolution, among which the unhydrated sample (Pre-H0) yields the highest reaction degree between 10 and 40 min of carbonation. In the wet carbonation stage, amorphous calcium carbonate (ACC) forms consistently which is stable at high pH and with dissolved silicate oligomer and converses to vaterite and calcite as carbonation time extends due to the decreased pH and polymerized silicates. In the post-hydration stage, residual alite continuously hydrates to stabilize ions concentration and pH of liquid phase. Solid-phase transformations include C-S-H formation via alite hydration and secondary hydration of CH with silica gel, alongside phase transitions among ACC, vaterite, and calcite.