Electrochemical Evolution of Carbon Steel and Fe-9% Cr Steel Rebar in Simulated Concrete Pore Solution (SCPS) in the Presence of 3.5 wt% NaCl

Carbon steel rebar (ASTM A615) has been widely used in reinforced concrete (RC), but its susceptibility to chloride ions remains a critical issue. Low alloy chromium steel has been used to increase corrosion resistance and extend service life, such as in 9% Cr rebar (ASTM A1035-CS). In this work, we characterized two electrochemical systems over time: ASTM A615 and A1035-CS corrugated rebar immersed in SCPS in the presence of NaCl for 12 months. The interfacial processes evolution for the ASTM A1035-CS rebar for both general and local corrosion showed different active-passive responses from those of carbon steel. Because the 3.5% wt. NaCl exceeded the chloride threshold for passive breakdown of both materials, the ASTM A1035-CS showed a five-fold higher impedance and lower general corrosion rate. In localized conditions, the low alloy chrome content rebar showed less density localized attack than the ASTM A615 rebar. These results were attributed to the overall damage evolution involving the formation and stability of corrosion products over time. The local attack appeared to be a random spatial process due to changes in the local environment.