Properties and microstructure of fly ash geopolymer modified with beta-phosphogypsum

Phosphogypsum (PG), a by-product of the phosphate industry, poses environmental pollution due to long-term solid waste accumulation caused by natural processes. In this study, control and modified fly ash-based geopolymers were prepared with different contents of beta-phosphogypsum. The physical properties and durability of modified fly ash-based geopolymers as pavement materials were investigated for macroscopic tests. Microscopic analysis, including XRD, FT-IR, SEM, and BET, was characterized to reveal the mechanism. The results indicated that the modified fly ash-based geopolymer demonstrated a considerable mechanical strength when utilizing a 40% content PG substitution of fly ash, under the cured circumstance of 3d, 7d, and 28d. Moreover, suitable contents of beta-phosphogypsum effectively reduced the setting time and water absorption of fly ash-based geopolymer. Necessary durability tests of modified fly ash based geopolymer were also conducted. The XRD and FT-IR analyses confirmed that beta-phosphogypsum enhanced the geopolymer modification by the promotion of gels production. The SEM analysis indicated that appropriate beta-phosphogypsum substitution efficiently formed denser structures and decreased porosity, which was confirmed in BET test, thereby enhancing the physical properties and durability. The aforementioned material represents new, environmentally sustainable base-course materials which effectively enhances the utilization of beta-phosphogypsum waste.