Sulfate Corrosion Resistance of Fly Ash-Based Geopolymer Concrete for Corroded Tunnel Linings
This study aims to evaluate the sulfate corrosion resistance of fly ash-based geopolymer concrete for tunnel linings and to identify an appropriate alkaline activator proportion. Ordinary Portland cement concrete was used as the control, and four geopolymer mixtures with different sodium silicate-to-sodium hydroxide proportions were prepared. Using a self-developed accelerated corrosion apparatus, specimens were subjected to 150 days of wet–dry cycles in 5% Na₂SO₄ solution. Mass variation, compressive strength, acoustic emission responses, and digital image correlation strain fields were analyzed. The control concrete showed an initial increase followed by marked deterioration: its compressive strength rose from 46.2 MPa to 49.7 MPa at 60 days and then decreased to 36.45 MPa at 150 days. In contrast, the geopolymer mixtures exhibited better mass stability, strength retention, and crack resistance. The G3 mixture performed best, retaining 50.6 MPa after 150 days, corresponding to a strength retention ratio of 1.07, while showing limited strain concentration, crack penetration, and surface spalling. The improvement is attributed to the denser N-A-S-H gel network and reduced formation of expansive sulfate corrosion products. The main novelty lies in combining an accelerated tunnel-lining corrosion simulation with multiple damage-characterization methods to optimize the activator proportion for sulfate-rich tunnel environments.