Corrosion Behavior of Steel in Geopolymer Concrete Electrolyte Pore Solution and Microstructural Variation: Influence of GGBFS, Chloride, and Sulfate Ions

This study investigated the influence of variations in ground granulated blast furnace slag (GGBFS) content, NaOH solution molarity, and chloride and composite chloride–sulfate salts on the strength, ionic concentration of geopolymer concrete (GopC) electrolyte pore solution, corrosion behavior of steel, and microstructural properties of GopC and corrosion products. The research findings indicate that variations in concentrations of Ca2+, Na+, and K+ ions in GopC electrolyte pore solution were consistent with the extent of geopolymer gel formation between fly ash based GopC and fly ash–GGBFS-based GopC. Steel exhibited improved passivity at higher GGBFS content and NaOH solution molarity. The passivity range was lower in the presence of chloride ions than in the presence of composite chloride–sulfate ions. Variation of the [Cl–]/[OH–] ratio was in line with the passivity range of steel. X-ray photoelectron spectroscopy (XPS) results indicated that the Fe2+/Fe3+ ratio of corrosion products was higher in fly ash–GGBFS-based GopC and at higher NaOH solution molarity.