A novel geopolymer application: Coatings to protect reinforced concrete against corrosion

This study evaluates the performance of two hybrid type geopolymer mortars composed of alkaline-activated fly ash (FA) and metakaolin (MK) as protective coatings against chloride-induced corrosion in reinforced concrete. In both cases, the coated, Portland cement (OPC)-based concretes (substrates) were subjected to accelerated techniques such as impressed voltage and wetting/drying (w/d) cycles in the presence of a 3.5% NaCl solution. The corrosion was also monitored by applying techniques involving linear polarization resistance and open circuit potential. The results allowed for the conclusion that the MK-based geopolymer coating exhibited the best performance, reducing the corrosion rate compared to concrete without coating (reference) by 4 cycles of w/d. After cycle 5, the corrosion rate was similar for the specimens with or without coating. The application of geopolymer type coatings (mortars) is suggested as a method of protecting structures exposed to marine environments.