Heterostructured crystalline and non-crystalline carbon coatings -A sustainable solution for corrosion inhibition in reinforced concrete

Corrosion is the major form of deterioration in reinforced concrete structures which leads to reduction in strength followed by complete failure. The current work focuses on the development of a heterostructured composite coating on Fe500 steel consisting of hard carbon and soft carbon possessing anticorrosive properties. The interaction between amorphous and crystalline carbon significantly enhances corrosion resistance in Fe500 steel, with specific ratios improving inhibition efficiency, verified by physicochemical characterizations and tests. In this study, carbon coated Fe500 strips were exposed to a simulated concrete pore solution containing 3.5 % NaCl, replicating corrosive conditions. Different combinations such as 100 % hard carbon (HC), 100 % soft carbon (SC), 25 % soft carbon + 75 % hard carbon (25SC/75HC), 50% soft carbon + 50 % hard carbon (50SC/50HC), and 75 % soft carbon + 25 % hard carbon (75SC/25HC) were assessed and tested. Tafel plots were generated to assess the corrosion rate. Among the different coatings tested, the 50 % soft carbon + 50 % hard carbon (50SC/50HC) composite exhibited the highest corrosion inhibition efficiency, with a corrosion rate of 0.0103 mmpy. After 5000 cycles, the material showed no crystalline or morphological changes, maintaining stability and excellent corrosion resistance for concrete.