Utilization of circulating fluidized bed coal ash in autoclaved aerated concrete manufacture by mineral carbonation

Using circulating fluidized bed combustion (CFBC) ash discharged from thermal power plants, we identified factors affecting mineral carbonation to sequester CO₂ and produced autoclaved aerated concrete (AAC). To use CFBC ash as a raw material for AAC, free-CaO, which causes volume expansion, was replaced through hydration and carbonation. During the raw material replacement process, carbonation behavior was confirmed through pH and temperature. A Ca(OH)₂ to liquid ratio similar to a fly ash to liquid ratio of 0.25 is considered to provide sufficient diffusion distance, and the reaction rate may increase due to the rise in water temperature caused by Ca²⁺ leaching. Additionally, the results of XRD, XRF, TG-DTA, and SEM analyses indicate that hydration and carbonation reactions were stably achieved in the materials, suggesting that CO₂ sequestration allows the materials to be used as alternative raw materials. After identifying the characteristics of the CFBC ash and the substituted material, AAC was manufactured through pressurized carbonation. The weight change rate, carbonation depth, ventilation rate, pore structure, and compressive strength of the manufactured AAC were measured. As a result, the alternative raw material exhibited higher permeability and a larger pore size range in the specimens compared to the original material, indicating easier CO₂ penetration into the specimens. Consequently, this experiment suggests the potential of using the material in AAC production by providing a theoretical basis for solving volume expansion issues associated with concrete admixtures and CO₂ sequestration in waste materials.