Electrochemical evaluation of hot-dip galvanized steel (HDGS) coated with organic-inorganic hybrid materials in simulated concrete pore solutions

Abstract

Organic-inorganic hybrid (OIH) sol-gel coatings based on ureasilicate gels present promising characteristics to be used as eco-friendly coatings for hot dip galvanized steel (HDGS), in contact with cementitious media, allowing to mitigate the harmful effects of an initial excessive reaction between cement pastes and the zinc. The long term performance of HDGS reinforcement coated with OIHs and embedded in concrete, in the presence of chloride ions is, however, unknown. In this paper, the behavior of HDGS, coated with five ureasilicate hybrid coatings, in chloride-contaminated simulated concrete pore solution, was assessed by electrochemical measurements. HDGS plates, with an average Zn layer thickness of 16 μm, were used. OIH sol-gel coatings were produced and deposited on the substrate by dip coating method. The ureasilicate matrices, U(X), were synthesized according to the literature. Concrete pore simulated solutions were prepared by the addition of 0.2 M KOH to a Ca(OH)2 saturated solution. Coatings performance was evaluated by polarization resistance, macrocell current density and polarization curves. SEM/EDS analyses of the coatings were also performed, before and after the tests. The results showed that the HDGS samples coated with the OIH coatings presented enhanced corrosion resistance to chloride ions, when compared to uncoated galvanized steel.