Role of CO2 in enhancing geopolymer properties formulated with fluidized bed combustion ash

Abstract

Fluidized bed combustion coal ash was used together with conventional coal ash and alkaline materials to synthesize geopolymer cement. The production process was performed in a carbon dioxide-rich environment to integrate carbon dioxide into the cement. The presence of carbon dioxide was found to enhance the formation of crystalline carbonates during the hydration reaction yielding an enhanced geopolymer matrix with improved binding characteristics. The non-crystalline (metastable) carbonates formed undergo crystallization processes that complement the hydration reactions, and yield carbonate with beneficial binding effects. Experimental optimization was designed and implemented to select the desired formulation of raw materials for achieving high levels of carbon capture and engineering properties. The optimized formulation produced a geopolymer cement with 7.4 wt% CO2 content, which produced concrete materials with a flow table of 68 cm, an initial set time of 34 min, and 28-day compressive strength reaching 28.2 MPa with acceptable residual compressive strength.