The applications of using fly ash-based geopolymer as a structural member and a repair materials in reinforced concrete structure was conducted. The optimum mix proportion of fly ash-based geopolymer concrete using for structural beam and fly ash-based geopolymer mortar using for repair material were developed. The flexural behavior of fly ash-based geopolymer reinforced concrete and the durability aspect namely the corrosion of steel reinforcement were investigated using the electrical acceleration. For the repair purpose, the fundamental properties; that is, compressive strength, flexural strength, bonding strength between fly ash-based geopolymer mortar and mortar substrate, setting time and chloride penetration were investigated. Also, the durability of conventional reinforced concrete beam repaired by the fly ash-based geopolymer mortar comparing with the comercial repair mortar was investigated. The behavior of the fly ash-based geopolymer reinforced concrete beam was similar to that of the conventional reinforced concrete beam; however, the corrosion of the steel reinforcement of the fly ash-based geopolymer reinforced concrete beam was higher than that of the conventional reinforced concrete beam. The fundamental properties of the fly ash-based geopolymer mortar were not different from that of the commercial repair materials; however, the durability of the reinforced concrete beam repaired by the fly ash-based geopolymer mortars performed a little lower than that of repaired with the commercial repair motar and also the control reinforced concrete with no repair. As a result, even there will be still a need of improvement there was a good tendency for using the fly ash-based geopolymer as the structural member and the repair materials.