The Effect of Activator to Binder Ratio on the Compressive Strength of Fly Ash Based Geopolymer Mortar in Sulphate EnvironmentAndi Arham Adam, Suci Amalia Namira, Atur PN Siregar and MustofaMATEC Web Conf., 331 (2020) 05002DOI: https://doi.org/10.1051/matecconf/202033105002