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Steel bar embedded in an alkali-activated slag (AAS) concrete was tested under complete immersion, in 3.5% NaCl solution by weight of the slag. Ordinary Portland cement (OPC) was also tested for comparative purposes and exposed to the same solution. Monitoring of open-circuit potential, polarization resistance measurement and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of steel bar. The corrosion resistances of AAS and OPC concretes were performed at 0, 3, 6, 9 and 12 months. Electrochemical measurements shows that AAS concrete presents passive corrosion behavior the first 3 months, after this period of time, it presents corrosion resistance decreased due to the chlorides presence at the steel/AAS interface. For 0 months immersion (28 days of curing) the AAS and OPC concretes presented a 10% of corrosion probability. After 3 months of immersion the tested AAS and OPC concretes showed similar behavior, the active potentials in the range from −0.2 to −0.6 V vs. Cu/CuSO 4, indicate a 90% probability of corrosion.