Durability of reinforcing stainless steel ribbed bars in carbonated mortars

Abstract

Three different austenitic stainless steels were studied: UNS 30403, UNS 31600 and low-Ni UNS 20430. Moreover, the duplex stainless steel UNS 32205 was also included in the study. The four stainless steels were processed as ribbed bars through cold working. Mortar samples were prepared embedding the stainless steel bar in mortar and carbonating them after curing. Corrosion tests were carried out in 3 different exposure conditions: at high relative humidity (HRH9); partially immersed in 3.5% NaCl (PI9); and with CaCl2 added during mortar mixing and exposed to high relative humidity (HRH9Cl).

Corrosion potential (Ecorr) measurements and electrochemical impedance spectroscopy (EIS) were used to monitor the behavior during 8 years of exposure. Then, anodic polarization tests were carried out to obtain additional information about the pitting corrosion resistance of the bars in aged, carbonated mortars.

Stainless steels behave excellently in carbonated conditions without chlorides, but some grades can suffer localized corrosion if they are submitted to high anodic polarizations. The PI9 is the most aggressive testing condition and it causes low-intensity corrosion in S20430 austenitic stainless steel during the exposure. The S32205 duplex stainless steel shows excellent behavior in all the conditions considered in the study.