Due to the low reactivity of municipal solid waste incineration (MSWI) bottom ash, appropriate pre-treatment is required before its reuse as a construction material. Accelerated carbonation has emerged as a promising method owing to its sustainability advantages. A novel flow-through agitated carbonation method was developed to enhance the early-age reactivity of bottom ash. The results show that agitation during carbonation promotes CaCO3 crystal growth along the (104) primary crystal plane, increasing the proportion of thermodynamically more stable CaCO3 (Ⅰ) crystals among newly formed CaCO3 to over 30 %. In addition, the crystal size decreases and the morphology becomes more spherical, facilitating the formation of stable nucleation sites that accelerate cement hydration, particularly during the acceleration and deceleration stages. Carbonated BA also provides significantly higher lubrication compared with OPC particles, resulting in a 36 % improvement in paste flowability at a 50 % replacement ratio. Compared with conventional activation strategies, BA treated via agitated carbonation exhibits a pronounced strength enhancement in blended cement, driven by the synergistic effects of nucleation and particle-filling. For example, at a water-to-binder ratio of 0.4 and a 15 % replacement level, the 3-day compressive strength exceeds 30 MPa. Overall, carbonation transforms bottom ash from a low-reactivity residue into a value-added SCM, achieving 15–25 % lower GWP per MPa and 10–15 % lower cost per MPa than OPC while maintaining superior mechanical efficiency. The findings demonstrate a viable pathway for valorizing alkaline solid waste through CO2 utilization and provide mechanistic insights for developing sustainable cementitious materials.
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