Synthesis of special cement with fluidised bed combustion ashes

Fluidised bed combustion (FBC) ashes containing a significant amount of free calcium oxide and calcium sulfate in addition to valuable inorganic acidic oxide ingredients such as silicon oxide, ferric oxide and aluminium oxide can be utilised as potential raw materials in the production of non-expansive belite-rich calcium sulfoaluminate cement, which is one of the special cement types having performance characteristics similar to those of ordinary Portland cement in addition to having lower energy requirements and carbon dioxide (CO₂) emissions during manufacture. Therefore, in the present study, the possibility of synthesising the above-mentioned energy-saving green cement was investigated by adding FBC ashes in various proportions to the raw meal. For this purpose, a raw meal composed of a mixture of limestone, bauxite and gypsum together with FBC bottom ash and baghouse filter ash was prepared. It was sintered in a laboratory-scale muffle furnace at temperatures of 1200, 1250 and 1300°C for various holding times. The results of chemical and mineralogical analysis as well as microscopic examination revealed that FBC ashes have the potential to be used in the raw meal due to the formation of characteristic mineral phases of this type of cement, namely yeelimite, belite, ferrite and anhydrite, in the sample sintered at optimum temperature of 1250°C for 60 min.