Sustainable Design of Zinc Composite Coating Using Alkali-Activated Technology: Toward Long-Term Corrosion Protection for Marine Steel

This study reported an ecofriendly inorganic zinc composite coating for protecting marine steel based on alkali-activated technology, which coupled synergistically with the passivated effect of alkali-activated slag (AAS) and the cathodic protection of zinc dust. The coating was directly coated on carbon steel and exposed to simulated seawater to explore its protective properties. The effects of chemical compositions of AAS on the corrosion protection of steel and the chemical durability of the coating were investigated. Results showed that the zinc-based AAS coating had a passivated ability for steel with chemical bonding with steel by forming a C–A–S–H/C–S–H gel-like layer. Furthermore, the AAS coating guaranteed excellent barrier protection owing to its superior durability, and no obvious steel rust deposits were found after long-term exposure to the chloride solution. The concentration of NaOH influenced the protective properties of the passivated film due to the reducing effect of OH groups. The addition of nanosilica in the AAS formed a compacted coating structure, which was beneficial for the long-term passivation process of steel/zinc and improved the cathodic protection efficiency of zinc dust. The loss of alkaline species of the pore solution and degradation of the AAS structure were the main failure mechanisms of the coating during the chloride solution immersion. The optimal coating exhibited 3.8 MPa bonding strength, a cathodic protection period beyond 2800 h (2 times more than organic coating), and negligible degradation of the AAS coating binder. The AAS-based coating exhibited longer corrosion protection and advantages in durability and sustainability. This study provides new insight into designing sustainable anticorrosion coating for protecting steel in harsh marine environments.