RHIZOPHORA MANGLE L. LEAF BIOCHEMICAL CHARACTERIZATION: NATURAL-GREEN TOTAL-CORROSION INHIBITION PROSPECT ON CONCRETE STEEL-REINFORCEMENT IN 3.5% NaCl

Effective corrosion-protection by plant-extract on metals, in aggressive service-environment, is dependent on the biochemical constituents of which the natural plant is made-up. This paper investigates biochemical characterization of inorganic and organic constituents of Rhizophora mangle L. leaf for gaining insight on its steel-reinforcement corrosion mitigating prospect in NaCl-immersed concretes. For the study, atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FT-IR) and phytochemical screening analyses were employed. Total-corrosion effect was also studied from steel-reinforced concrete samples, having different concentrations of the leaf-extract as admixture, and which were immersed in 3.5% NaCl (simulating saline/marine environment). Results, by AAS, showed that Rhizophora mangle L. leaf inorganic constituents were highest in iron, Fe = 10,316.17 μg/g and lowest in cadmium, Cd = 6.2019 μg/g but has neither lead (Pb) nor chromium (Cr). Also, organic constituents, by FT-IR, indicated extract from the leaf constitutes aromatic chained compounds rich in π-electrons as well as sulphur, nitrogen and oxygen-bearing ligands to which iron (steel-rebar) exhibits coordinate affinity. Phytochemical characterization showed that the leaf-extract contains alkaloids, tannins, phlobatannins, saponins, steroids and glycosides. Corrosion-inhibiting prospect testing, using the leaf-extract, indicated reduced steel-reinforcement total-corrosion effects that correlated with the extract admixture concentrations employed in the 3.5% NaCl-immersed steel-reinforced concretes.