Durability Performance of Fly Ash Geopolymer Mortar under Long-Term Sulfate Exposure

The long-term durability of geopolymer mortar against sulfate attack is crucial for sustainable infrastructure, especially in aggressive environments. This study presents experimental findings on the performance of fly ash-based geopolymer mortars immersed in 5% sulfuric acid for 84 days. Two mix designs with different activator ratios (1:2 and 1:2.5) were evaluated through periodic testing of compressive strength, mass loss analysis, and sulfate content. The results showed that GMAk1 :2 mortar exhibited lower mass loss (maximum 6.53 g) and smaller reduction in compressive strength (from 44.80 Mpa to 39.63 Mpa) compared to GMAk1:2.5, which experienced a mass loss of up to 11.80 g and a strength decrease from 35.96 MPa to 26.08 MPa. The sulfate content in GMAk1:2 mortar remained relatively stable, indicating better resistance to sulfate ingress. These findings highlight that optimizing the activator ratio significantly enhances the sulfate resistance of geopolymer mortar, making it suitable for structural applications in chemically aggressive environments.