Durability properties of ambient-cured fly ash-phosphogypsum blended geopolymer mortar in terms of water absorption, porosity, and sulfate resistance

Abstract This paper aimed to investigate the durability of ambient-cured fly ash-phosphogypsum blended geopolymer mortar (GPM) when exposed to a water and sulfate environment at different durations. Water absorption, porosity, and sulfate resistance tests were conducted to determine the durability. The GPM was prepared at 0 wt%, 30 wt%, and 40 wt% PG replacement of fly ash content in the mixture. The mix proportions were determined experimentally at 10 M sodium hydroxide, alkaline liquid/precursor of 0.4, sodium silicate/sodium hydroxide of 1.5, and binder/aggregate of 1.0. The samples were immersed in potable water and magnesium sulfate solution. The changes in weight, length, and compressive strength were monitored. Scanning electron microscopy-energy dispersive X-ray spectroscopy was used to analyze the structure and composition. The findings showed that GPM with 30 wt% phosphogypsum added had lower water absorption, porosity, and sulfate attack than GPM with 0 wt% phosphogypsum attributed to the formation of hydrated gels leading to a dense microstructure and improved strength. The changes in weight, length, and strength variations trend for GPM were within optimal performance standards. This has implications for the practical application of GPM in construction where it can be used as an alternative to Portland cement mortar in sulfate-rich environments.