Influence of Geopolymerization Factors on Sustainable Production of Pelletized Fly Ash-Based Aggregates Admixed with Bentonite, Lime, and GGBS

This experimental research investigates the influence of geopolymerization factors such as Na2O dosages, water and mineral admixture [bentonite (BT), burnt lime (BL), and ground granulated blast furnace slag (GGBS)] on physiomechanical properties of the pelletized fly ash (FA)-based aggregates. Taguchi's L9 orthogonal array was adopted to design the mixing ratios for three kinds of fly ash-based aggregates (in the combinations of FA-BT, FA-BL, and FA-GGBS). The degree of geopolymerization of the produced aggregates was characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and a scanning electron microscope (SEM). Most influential response indices in the production of pelletized aggregates were identified using gray relational analysis. The physiomechanical characteristics of the fly-ash aggregates were significantly improved by admixing BL than that of GGBS and BT. However, pelletization efficiency was seen to be superior for GGBS-substituted fly-ash aggregates. The quantified amount of hydration products, i.e., sodium alumino-silicate hydrate (N-A-S-H)/calcium alumino-silicate hydrate (C-A-S-H) for fly ash-based aggregates intensified on increasing Na2O and mineral admixture dosages. The results strongly suggest the existence of a linear relationship between the quantified amount of N-A-S-H/C-A-S-H and individual pellet strength of produced aggregate. The FTIR spectrum showed strong and broadened bands of Si-O terminal for all types of aggregates, representing the conversion of unreacted minerals to chains of aluminosilicate gel (geopolymerized hydration product). Further, it can also be inferred from gray relational analysis that among all other factors, Na2O content significantly impacted the engineering properties of produced fly ash-based aggregates.