Impact of marine environment on <scp>GGBFS</scp> / <scp>FA</scp> ‐based alkali‐activated concrete

Abstract Portland cement concrete is highly susceptible to deterioration in marine environments, leading to growing interest in geopolymer concrete for its enhanced durability. However, research on the long‐term performance of geopolymer concrete under such conditions remains limited. This study investigates the effects of marine exposure on alkali‐activated concrete (AAC) incorporating ground‐granulated blast furnace slag (GGBFS) and fly ash (FA). A total of 270 AAC specimens were exposed for 1 year in seawater, splash zones, and the middle of an island. The study varied the sodium silicate (SS) to sodium hydroxide (SH) ratios (1.5, 2, and 2.5) and the alkali‐activated material solution (AAMS) to binder ratios (0.35, 0.4, and 0.5). Results indicated that the optimal mix design for durability in all three exposure zones was an AAMS‐to‐binder ratio of 0.5 and an SS‐to‐SH ratio of 2.5. Extended exposure in splash zones significantly reduced mechanical properties compared to seawater and inland conditions, primarily due to sulfur ion penetration and inhibited C‐A‐S‐H gel formation. While the long‐term strength (365 days) remained stable relative to the 28‐day strength in seawater, the splash zone exhibited an 8%–29% reduction in strength, highlighting the adverse effects of intermittent wetting and drying cycles. Correlation analysis further elucidated the influence of exposure conditions and duration on mechanical performance.