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• The passive film presented bilayer structure with FeO-rich inner layer and FeOOH-rich outer layer in AAFA pore solution. • The firmly adsorbed layer with zeolite-like structure (200 nm) formed on the steel surface in AAFA pore solution. • The corrosion resistance of the passive reinforcement was significant higher in AAFA pore solution. Due to different ion types and concentration in pore solution, the passive film on the steel surface possesses different characteristics in alkali-activated fly ash (AAFA). In this study, the passive film formed in simulated AAFA pore solution was investigated by surface analysis and electrochemical measurements. The passive film possessed bilayer structure with FeOOH-rich outer layer and FeO-rich inner layer in simulated AAFA pore solution. Further, a firmly adsorbed zeolite-like layer (200 nm) formed on the steel surface. The formation of more protective passive film and adsorbed layer resulted in higher corrosion resistance of the reinforcement in simulated AAFS pore solution. [ABSTRACT FROM AUTHOR]