Microstructural and morphological development of eggshell powder and flyash-based geopolymers

Abstract

The microstructural and morphological development of eggshell powder (ESP) and flyash (FA)-based geopolymer, prepared using alkaline liquid activator which is a mixture of sodium silicate and sodium hydroxide solution, was investigated. Various synthesis parameters for geopolymer were adopted to study the microstructural changes viz. precursor combination (70% ESP and 30% FA, 50% ESP and 50% FA, 30% ESP and 70% FA), activator ratio (Na2SiO3/NaOH–0.5, 1, and 2) and curing temperature (25, 50, and 80 °C). Morphological features and structural characterization of raw precursor materials were analyzed using an X-ray diffractometer (XRD), X-ray fluorescent (XRF), and Scanning electron microscopy (SEM) techniques. The process of geopolymerization was explicated using SEM with an energy dispersive X-ray spectrometer (SEM-EDX) and mapping. Increase in curing temperature altered the morphology of ESP-FA geopolymer. Curing of samples at the lower temperature resulted in unreacted precursor particles, whereas curing at the higher temperature resulted in the porous structure. Formation of Nan–(–Si–O–Al–O–Si–O–Si–O–)n– was confirmed in the optimum geopolymer as Si/Al and Na/Al ratios were found greater than 1. The co-existence of calcium silicate hydrate (C-S-H) gel with the main geopolymeric gel and its bonding with the remaining unreacted precursor particles have also been confirmed.