Organic-inorganic hybrid (OIH) sol-gel coatings based on ureasilicates (U(X)) have promising properties for use as eco-friendly coatings on hot dip galvanized steel (HDGS) and may be considered potential substitutes for pre-treatment systems containing Cr(VI). These OIH coatings reduce corrosion activity during the initial stages of contact of the HDGS samples with highly alkaline environments (cementitious media) and allow the mitigation of harmful effects of an initial excessive reaction between cement pastes and the zinc layer. However, the behavior of HDGS coated with U(X) in the presence of chloride ions has never been reported. In this paper, the performance of HDGS coated with five different U(X) coatings was assessed by electrochemical measurements in chloride-contaminated simulated concrete pore solution (SCPS). U(X) sol-gel coatings were produced and deposited on HDGS by a dip coating method. The coatings performance was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curves measurements, macrocell current density and polarization resistance in contact with chloride-contaminated SCPS. The SEM/EDS analyses of the coatings before and after the tests were also performed. The results showed that the HDGS samples coated with the OIH coatings exhibited enhanced corrosion resistance to chloride ions when compared to uncoated galvanized steel. Corrosion of the reinforcing steel is one of the most important causes of degradation in reinforced concrete structures (RCS).1 The presence of chloride, carbonation of the concrete or the low quality of the concrete cover causes serious damage to RCS. The entrance of chloride ions through the concrete from marine environments or deicing salts can cause rupture of the passive layer, allowing the steel surface to act as a coupled anodic and cathodic reaction cell in which corrosion processes take place.1-3 Therefore, the presence of chlorides in concrete can seriously shorten the service life of RCS.
3,4The expanded volume of corrosion products deposited in the interface between the concrete and the steel imposes expansive stresses, leading to delamination, cracking or spalling and eventually to the collapse of the RCS. 1 Several methods to improve the corrosion resistance of RCS have been proposed. 1,[5][6][7] In the last few years, the use of hot-dip galvanized steel (HDGS) has been recognized as an effective measure to increase the service life of RCS. [8][9][10][11] The galvanized coating (zinc layer) acts as a physical barrier, hindering the contact of aggressive agents with the steel substrate and the zinc acts as a sacrificial anode protecting the steel against corrosion. In addition, the formed zinc corrosion products have a smaller volume than those produced from iron, thus reducing the corrosion-induced delamination, cracking or spalling of the concrete.8 Additionally, the galvanized steel reinforcement can withstand exposure to chloride ion concentrations several times higher than the chloride level that causes corrosion in ste...