Soy-protein and corn-derived polyol based coatings for corrosion mitigation in reinforced concrete

Different corrosion mitigation strategies (e.g. corrosion inhibitors, coatings) are employed in the construction industry to mitigate chloride-induced corrosion in bridge decks and reinforced concrete pavements. While epoxy coatings are effective in mitigating rebar corrosion, their local damage during transportation may lead to aggressive pitting corrosion. Besides, epoxy coatings cannot be repaired in-situ due to their toxic nature and requirement for special equipment. In this study, a new soy-based coating material is investigated which can be applied in-situ for protecting rebar from corrosion and repairing damaged epoxy coated rebars. Soy-based coatings are synthesized using denatured soy protein isolate (SPI) (5–15% wt. in deionized water) and corn-derived sorbitol plasticizer (10–30% wt. of SPI). The physical and chemical characteristics of the soy-based coatings and their corrosion protection performance are evaluated for cement mortar embedded SPI coated rebars. The results obtained from FTIR, viscosity, and abrasion tests demonstrated that soy-based coatings have an adequate abrasion resistance and include necessary functional groups for usage as a corrosion protection coating material. The potentiodynamic polarization tests results showed that soy protein coatings significantly reduce the corrosion current density (up to 96% when compared to bare rebar) in a simulated concrete pore solution that contained 3.5% wt. sodium chloride. The long-term corrosion data obtained from rapid macrocell corrosion tests showed that soy protein-coated rebars incur lower corrosion rates and exhibited a stable corrosion potential as compared to bare rebar specimens. Overall, the soy protein coating formulation with 15% wt. SPI and 30% wt. sorbitol exhibited the highest corrosion protection and abrasion resistance. The proposed soy protein coating materials can be used for in-situ repairs of damaged rebar coatings in aggressive chloride environments and as a standalone coating in moderately corrosive environments.