Supplied air relative humidity effect on CO2 fixation ability of fly ash with different water retention characteristics

Although environmental moisture conditions strongly affect gas–solid carbonation, supplied air relative humidity (RH) effect on the CO 2 fixation ability of fly ashes with different water retention characteristics has not been investigated yet. To address this issue, constant-flow aeration type CO 2 fixation tests were conducted under different supplied air RH conditions using three fly ashes (FC, MF, and BBF) in this study. The CO 2 fixation ability was evaluated based on CO 2 fixation amount and the reaction rate per unit dry mass. The main findings are summarized as follows: 1) For all three fly ashes, CO 2 fixation was low under low RH conditions, suggesting the limitation from insufficient interfacial water; 2) for FC and BBF, higher RH conditions increased CO 2 fixation ability. However, MF, which had higher chloride content and higher water retention, exhibited reduced CO 2 fixation ability under high RH conditions, likely because excessive water accumulation reduced the pore space available for gas flow and impeded CO 2 transport; and 3) the suitable inlet RH depended on the material-specific water retention characteristics under the tested specimen and flow conditions.