The Coupled Deterioration Effect of Recycled Concrete Aggregate and Seawater Sea Sand on Steel Corrosion: An Electrochemical Study

To address the shortage of natural aggregates and freshwater, and promote the recycling of construction and demolition waste and localized construction materials for marine engineering, this study explores the electrochemical corrosion characteristics and deterioration mechanism of steel bars in recycled concrete aggregate (RCA)–seawater sea-sand concrete (SSC) concrete. Using RCA replacement rates (0%, 50%, 100%) as the core variable, specimens were prepared. Vacuum water saturation, open-circuit potential (OCP) monitoring, Tafel polarization scanning and electrochemical impedance spectroscopy (EIS) were adopted to study steel corrosion evolution within 180 days. The results show that RCA incorporation accelerates OCP negative drift and reduces passivation film stability, with more severe corrosion at higher replacement rates: the RCA100 group showed obvious corrosion after 60 days, while the RCA50 and RCA0 groups initiated corrosion at 90 days (RCA50 corroded faster). The surface mortar and internal microcracks of RCA enhance the water absorption and ion permeability of concrete, which, coupled with chloride ions, accelerates steel corrosion. This study clarifies the correlation between RCA replacement rate and corrosion parameters, providing data support for mix ratio optimization and marine engineering applications.