Effect of synthesis parameters on the alkali activation reaction degree and the relationship between reaction degree and microstructure of fly ash-based geopolymers

Abstract

This study systematically explored the impact of various parameters on the alkali activation reaction degree of fly ash-based geopolymers (FABGs) using the acid solubility test method. Key parameters such as the alkali activator modulus (AAM), alkali dosage (AD), and water-to-fly ash ratio (W/FA) were considered. The micromorphology, phase composition, and pore characteristics of FABGs were also examined, and the relationship between the alkali activation reaction degree and these microstructural characteristics was analyzed. The alkali activation reaction was relatively rapid during the early curing stage but slowed down in the later stage. The influence of synthesis parameters on the alkali activation reaction degree ranked from highest to lowest as AAM, W/FA, and AD. According to Spearman correlation analysis, the alkali activation reaction degree of FABGs is positively correlated with AAM and AD, and negatively correlated with W/FA. As the alkali activation reaction degree increases, the number of pores, cracks, and partially reacted FA particles decreases, and the bonding between FA particles and the matrix becomes denser. FABGs with higher alkali activation reaction degrees exhibit greater mass loss at 100–700 °C, indicating higher production of gel phases. Additionally, the pores in FABGs are predominantly gel pores and transition pores. Notably, there is a negative correlation between porosity and the alkali activation reaction degree of FABGs.