Ureasilicate Hybrid Coatings for Corrosion Protection of Galvanized Steel in Cementitious Media

Abstract

This study is focused on the electrochemical behavior and surface analysis of an eco-friendly organic-inorganic hybrid (OIH) coating for hot dip galvanized steel (HDGS) in contact with cementitious media. This treatment is a proposed alternative to replace toxic Cr(VI)-based pre-treatments used to control reactions between the zinc and wet concrete. HDGS samples were coated with two different sets of OIH gels obtained by a sol-gel process using a dip-coating method. Five distinct OIH matrices were obtained by reaction of functionalized metal-alkoxide (3-isocyanatopropyltriethoxysilane) with five different molecular weight diaminealkylethers. One set of HDGS samples was coated with each of the five pure OIH matrices and another was coated with similar matrices doped with Cr(III). The morphology of OIH coatings over HDGS surface was characterized by SEM/EDS. Similar films were prepared separately and the respective resistivity was measured by electrochemical impedance spectroscopy. Polarization resistance and macrocell current density were used to evaluate the corrosion protection properties of the HDGS coated samples in contact with cementitious media for a period of 74 days. Results showed that the produced coatings provide barrier properties that withstand the high pH of the electrolyte, protecting the HDGS when it first contacts cementitious media.The corrosion of steel in concrete is one of the major causes of structures degradation, requiring expensive rehabilitation. The use of hot dip galvanized steel (HDGS) has been recognized as an effective measure to increase the service life of reinforced concrete structures exposed to carbonation or to chloride ions. 1-3 The galvanized coating is a physical barrier that hinders the contact of aggressive agents with the steel substrate and the zinc layer acts as a sacrificial anode, protecting the steel against corrosion. 4,5 Immediately after the HDGS is embedded in fresh concrete, a highly alkaline environment, the zinc coating corrodes for a limited period (from several hours to a few days) until passivating surface layers are formed and concrete hardens. This initial corrosion process may lead to zinc consumption between 5 to 10 μm. 2 At the same time hydrogen is produced which may lead to the loss of adhesion between steel and concrete.Several corrosion studies reported the behavior of HDGS in contact with concrete media and in alkaline solutions. 2-21 However, uncertainties concerning the initial corrosion behavior of the galvanized coating when embedded in concrete still remains. The main literature about corrosion and passivation mechanisms of zinc in concrete environments, suggest that the formation of the protective layer due to zinc oxidation takes place with water reduction and subsequent hydrogen evolution. 9-11 Other authors claim that the formation of protective layer is related to the presence of oxygen at the concrete/rebar interface. 12,14,18 Andrade and co-workers, 11,22,23 found that at pH ≥ 12.5 zinc dissolution and hydrogen evolution takes place p...

Alcohol-Aminosilicate Hybrid Coatings for Corrosion Protection of Galvanized Steel in Mortar

“…This might be explained by the lower reactivity between epoxy and amine groups comparatively with previously studied ureasilicate. 28 When the catalyst or the Cr(III) solution is added to the reactional media, without the reaction between GPTMS and Jeffamine having reached the end, existent epoxy side reactions could be catalyzed, turning the reaction between epoxy and amine group less favorable due to the decrease of available reactive epoxy groups. Simultaneously, the formation of products from the side reactions of the epoxy group could affect the formation of the silicate network by hydrolysis-condensation reaction involving the alkoxide groups.…”

“…The edges of both CE and WE plates, as well the non-active areas and connecting zones were protected with a dual-component epoxy resin (Araldite) using a previously established protocol. [27][28][29] For comparison purposes, cells prepared with non-coated HDGS WE electrodes were used as control. To assemble the electrochemical cells, 120 ± 10 g of fresh mortar was transferred to a 100 mL polyethylene flask, the electrodes were subsequently immersed and the flask closed.…”

Corrosion Protection of Hot Dip Galvanized Steel in Mortar

“…The OIH gel matrices were prepared following a well-established methodology described elsewhere [28][29][30]. Two sets of four different structural types of ureasilicate OIH gel matrices were prepared by a reaction between the isocyanate group of the derived siloxane (ICPTES) with four different di-amino functionalized polyether (Jeffamine® D-400, Jeffamine® ED-600, ED-900 and ED-2000, hereafter generically referred as Jeffamines) with different molecular weights, with and without incorporated Cr(III) ions, obtained by adding the correspondent salt aqueous solutions with a concentration of 0.01M.…”

New Sol-gel Formulations to Increase the Barrier Effect of a Protective Coating Against the Corrosion and Wear of Galvanized Steel

“…These materials combine the hardness, wear resistance and thermal stability of the ceramic component with the flexibility, transparency and tunable adhesion of the organic materials [5][6][7][8][9][10][11] . The sol-gel method allows to control the synthesis of multifunctional hybrid materials, where the organic, inorganic and, in some cases, biological constituents are mixed at a nanometer scale [12][13][14][15][16] .…”