Dual-path suppression of thermal and wetting-driven steel corrosion for marine structure

Steel corrosion in marine concrete structures is critically exacerbated by solar heating and seawater penetration, accelerating chloride ingress and electrochemical degradation. Existing strategies often fail to synergize efficient thermal regulation and anti-wetting functionality for costal structures protection. To address this limitation, we develop a double-effect protective bi-coating, consisting of a carbonated dicalcium silicate (C₂S)/BaSO₄ composite gel overlaid with a layer of hydrophobic SiO₂ nanoparticles, designed to passively suppress thermal and chemical corrosion drivers. The carbonation-activated C₂S forms a chemically bonded calcium-modified silicate gel matrix, ensuring robust concrete adhesion, while BaSO₄ nanoparticles enhance solar reflectance (94.6%) and mid-infrared emittance (92.8%), enabling efficient passive cooling. Integrated with the hydrophobic overlayer for waterproofing, this protective bi-coating achieves a sub-ambient cooling (4.13 °C) under direct sunlight and excellent anti-wetting property (water contact angle of 151.3°), effectively mitigating solar thermal loading and chloride penetration. Furthermore, after 30 days of cyclic solar illumination-salt spray exposure, the protective layer can significantly reduce corrosion initiation time and current density, demonstrating double-effect protection for reinforced concrete through ion-blocking and cooling-enabled corrosion buffering. This work pioneers a passive strategy that synergizes radiative cooling, chemical compatibility, and ion-blocking functionality to extend the service life of marine infrastructure under coupled thermo-chemo degradation.