Investigation of the Long-Term Corrosion Behavior of Steel in Nano-SiO2 Seawater Concrete

To address the corrosion issue of reinforcing steel in seawater–sea-sand concrete (SWSSC), specimens embedded with HRB400 carbon steel bars and 304 stainless steel bars were prepared with a fixed dosage of nano-silica (NS). A 150-day full-immersion test in artificial seawater was conducted, and the corrosion performance was systematically analyzed via multi-dimensional electrochemical measurements and microstructural characterization. The results indicate that the passive film on 304 stainless steel bars exhibited a superior stability, with a significantly higher charge transfer resistance (Rct) and a low-frequency impedance modulus (|Z|f=0.01Hz) compared to HRB400 carbon steel bars. Correspondingly, 304 stainless steel bars showed a lower corrosion current density (icorr) and calculated corrosion mass loss. SEM observations further showed that the NS-containing concrete had a locally denser matrix and interfacial transition zone (ITZ) than the NS-free concrete. This study provides a scientific basis for the selection of reinforcing steel in marine engineering and is of great significance for improving the durability of SWSSC structures.