Study on the drying shrinkage behavior and influencing factors of fly ash-based geopolymers under different humidity conditions

Abstract

Geopolymers have garnered significant research interest due to their low carbon emissions during production, low energy consumption, ability to utilize various industrial waste residues, and superior physicochemical properties. This study systematically investigated the drying shrinkage behavior of fly ash-based geopolymers (FABGs) in gradient and constant humidity conditions under different influencing factors (activator modulus, activator concentration, and liquid-solid ratio). The mechanisms by which these factors influence drying shrinkage were elucidated through a comprehensive suite of macroscopic and microscopic testing methods. The results indicate that FABGs subjected to various influencing factors exhibit distinct capillary pore characteristics and shrinkage resistance properties, thereby manifesting different drying shrinkage behaviors. Specifically, an increase in activator concentration and a decrease in modulus led to the refinement of capillary pores, which in turn increased capillary shrinkage stress under low-humidity conditions, resulting in greater drying shrinkage. Additionally, an increase in the liquid–solid ratio had minimal impact on the distribution of capillary pores but significantly deteriorated the shrinkage resistance properties of the paste, leading to increased drying shrinkage. Moreover, the persistence of geopolymer drying shrinkage is closely related to capillary pore characteristics. Smaller capillary pores hinder the escape of water from the geopolymer paste, thereby prolonging the drying shrinkage process and increasing subsequent shrinkage creep.