Diagenesis of FBC Ash in an Acidic Pit Lake

摘要

Mineralogical evolution of placed fluidized bed combustor ash for mineland reclamation can result in the development of cementitious monolithic solids. Hydration reactions based on the early formation of ettringite and gypsum can result in unconfined compressive strengths that vary, depending on the ash source, from a few hundreds of pounds per square inch to a few thousands of pounds per square inch. Extended hydration of these cementitious elements at elevated pH values further involves the reaction with dehydroxylated clays in the ash to form an amorphous hydrous calcium silicate phase similar to that found in ordinary Portland cement. This phase commonly identified in the cement literature as C-S-H, is the ‘glue’ that is responsible for the mechanical and chemical properties of Portland cement concrete. Hydration products formed from the reaction of FBC ash grouts with water have been identified in the laboratory, in field specimens, and most recently confirmed by thermodynamic modeling of the pore waters associated with placed ash. The confirmation at this level allows for further modeling of placed monolithic cementitious solids using Portland cement durability as an analog.