Chloride ion solidification property in functional fly ash/slag based geopolymer (F-FASG) under dry-wet cycle condition

Fly ash-slag geopolymer (FASG) is recognized as a sustainable high-performance repair material for marine infrastructure, owing to its low-carbon footprint, high early-age strength, and excellent durability. In this study, a functional variant (F-FASG) was synthesized by incorporating a high-performance strong-base anion-exchange resin (HP-SBAER). The performance evolution of F-FASG under dry-wet cycle conditions was systematically investigated, with emphasis on mechanical degradation mechanisms, chloride ion transport behavior, and micro-structural reorganization using TEM, XPS, and MIP analyses. Results indicate that dry-wet cycle transforms the micro-structure of FASG from lamellar to flocculent, increasing interplanar spacing and reducing crystallinity. In contrast, HP-SBAER incorporation optimizes the pore structure of F-FASG toward a predominance of harmless or less-harmful pores. Resin hydrolysis promotes secondary polycondensation, which preserves crystallinity, mitigates structural degradation, and enhances molecular polymerization via increased long-chain formation. Macroscopically, F-FASG exhibits significantly less surface exfoliation than FASG. After 60 dry-wet cycles, F-FASG with moderate resin dosages (1.5 wt% and 3.0 wt%) have retained over 90 % of the baseline performance of FASG, demonstrating long-term protective efficacy. Furthermore, HP-SBAER substantially improves chloride ion solidification capacity, with distinct solidification behaviors observed between surface and interior regions.