Morinda citrifolia (Noni) leaf extract as corrosion inhibitor for steel-reinforced concrete in saline environment

This study aimed to determine the effectiveness of Morinda citrifolia (Noni) leaf extract as corrosion inhibitor for steel-reinforced concrete exposed to saline environment. Chloride ingress in concrete structures exposed to saline environment that leads to corrosion of steel reinforcement is prevalent in many countries including the Philippines. The use of toxic organic and inorganic compounds as corrosion inhibitors is regulated in many countries due to detrimental effects on the environment. Thus, the development of green and eco-friendly corrosion inhibitor alternatives such as those derived from biodegradable plant materials is necessary. This study hypothesized that a sample concrete amended with Noni leaf extract (0.08, 0.17, 0.25, 0.33, and 0.42%) is better than ordinary Portland concrete cement as control (0%). Compression testing, colorimetric method, and steel reinforcement corrosion testing were used to measure the compressive strength, chloride penetration resistance, and corrosion rates, respectively. Results revealed that the application of > 0.33% Noni leaf extract improved the chloride penetration resistance of the concrete by 30–33% and reduced the corrosion rate on steel reinforcement by 57–59% without affecting the compressive strength of the concrete. Noni leaf extract concentration of 0.42% exhibited combined optimum compressive strength improvement, chloride penetration resistance, and corrosion inhibition. These results show that Noni leaf extract > 0.33% can protect the steel-reinforced concrete structure against corrosion in 3% sodium chloride test media under laboratory condition. This is the first report of using Noni leaf extract admixed in concrete for the protection of steel reinforcement against corrosion.