The present study explores the behaviour of structural steel embedded in Portland cement (OPC) mortars and NaOH- and NaOH-waterglass-activated fly ash, in the presence and absence of 2 % Cl- (CaCl2). Variations were determined in the corrosion potential (Ecorr), linear polarization resistance (Rp) and corrosion current density (icorr) under different environmental conditions (90 days at 95 % relative humidity (RH), 30 days at ≈ 30 % RH, 760 days at ≈ 95 % RH). In the absence of Cl-, fly ash mortars were able to passivate steel reinforcement, although the stability of the passive state in changing environmental conditions was found to depend heavily on the activating solution used. Steel corrosion in the presence of 2 % Cl- was observed to be similar to the corrosion reported for the material in OPC mortars.