Stainless steel reinforcements have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to highly chloride-contaminated atmospheres. In the present work, the corrosion behaviour of two traditional austenitic stainless steels (AISI 304 and 316L types), and one duplex type (2205) are compared with that of a low-nickel, much more economic, austenitic type (204Cu). Ribbed and ground bars of these four materials are studied in non-carbonated and carbonated, saturated Ca(OH)2 solutions with different chloride contents, using electrochemical techniques. The low-frequency time constant represents the charge transfer resistance (Rt) in parallel with the double layer capacitance. The Rt value of the passive reinforcements seems to be related with the quality of the passive layer. Rt values increase with the immersion time in the testing solutions and decrease with the chloride content. Moreover, Rt tends to increase when the ribs of the bars are removed.