Characterization of Fly Ash Sources in the Synthesis of Geopolymer

Abstract

Fly ash (FA) based geopolymers are affected by the reactive nature of FA, concentration and quantity of alkali activators and the curing conditions. However, for the geopolymer production, researchers are still focusing on the concentration and quantity of alkali activators and the curing conditions. In the present study, FAs from two distinct thermal power plants and their activated geopolymer paste were investigated under physical, chemical, spectroscopic, mineralogical and microstructural characterizations. Based on the characterizations, the suitability of FAs for the geopolymer production was determined and validated by the compressive strength of geopolymer concrete. Additionally, the effect of critical parameters such as sodium hydroxide (NaOH) molarity, alkaline to FA ratio, curing time and curing temperature were studied. From the results, it is inferred that the FA’s potential reactivity is to be identified through its characterization techniques before the synthesis of geopolymers. The quantity of vitreous silica (Si) and alumina (Al) contents in the FA significantly affects the geopolymerisation process. In order to choose the right source of FA, it is required to characterize the FA and its activated geopolymer paste. Thereby, the wide variation of the geopolymer synthesis parameters that leads to undesirable production cost and hazardous work environment can be avoided.