Abstract

This paper investigates performance of different synergistic combinations of Rhizophora mangle L leaf-extract and sodium dichromate (Na₂Cr₂O₇) admixtures on the corrosion of steel-reinforcement in 0.5 M H₂SO₄-immersed concrete. Steel-reinforcement corrosion, in concrete slabs partially-immersed in the microbial/industrial simulating test-environment, were assessed using non-destructive electrochemical measurements of corrosion rate (CR) and open circuit potential (OCP) . Probability distribution function (pdf) analyses, as prescribed by ASTM G16-95 R04, of the scatter of corrosion test-data showed that while datasets of OCP distributed like the Normal, the Gumbel and Weibull pdf’s, the datasets of CR were best fitted by the Weibull pdf. Results identified 6 g Rhizophora mangle L leaf-extract + 2 g Na₂Cr₂O₇ synergistic admixture with both optimal inhibition efficiency, η = 90.12%, and synergistic parameter that indicated excellent synergistic interaction of the plant-extract with Na₂Cr₂O₇ chemical. That this synergistic admixture out-performed the also effective Na2Cr2O7 admixtures in the study suggests suitability of Rhizophora mangle L leaf-extract as eco-friendly replacement of toxic Na₂Cr₂O₇ inhibitor in H₂SO₄-immersed steel-reinforced concrete. This is potent with the advantage of reducing environmental effect from lower Na₂Cr₂O₄ usage for controlling corrosion in steel-reinforced concretes for the microbial/industrial environment.