Sustainable\nDesign of Zinc Composite Coating Using\nAlkali-Activated Technology: Toward Long-Term Corrosion Protection\nfor Marine Steel

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