Fabrication and Testing of Low-Energy Calcium Sulfoaluminate-Belite Cements that Utilize Circulating Fluidized Bed Combustion By-Products

Abstract

The utilization of circulating fluidized bed combustion (CFBC) ash to make cement products that provide added value and offset CO2 production is the objective of this research. CFBC burns coal in the presence of a bed of slaked limestone, which effectively absorbs sulfur dioxide (SO2) to form anhydrite (CaSO4). CFBC produces two kinds of spent bed materials, coarse bottom ash and a much finer fly ash. Both of these products are very high in calcium. When properly conditioned, these materials are capable of acting as hydraulic cements, forming both calcium aluminosulfate minerals, most importantly ettringite, as well as calcium-alumina-silica gels, like that formed from Portland cement. The research to generate calcium sulfoaluminate-belite (CSAB) cement was centered on two components. The first was the production of a cement that maximizes the proportion of coal combustion by-products while achieving acceptable strength development. The second component focused on optimizing the laboratory-derived CSAB cement to have comparable strength characteristics with commercial CSAB cements.