Tajunnisa, Y. et al. 2025. Performance Changes in Mass and Compressive Strength of High-Calcium Fly Ash Based Geopolymer Concrete Due to Sodium Sulphate Exposure. IPTEK The Journal of Engineering. 10, 1 (Sep. 2025), 1–10. DOI:https://doi.org/10.12962/j23378557.v10i1.a16232.