ABSTRACT

Electrochemical measurements were obtained from steel-reinforced concrete samples immersed in 0.5 M H2SO4 medium, for simulating industrial/microbial environment, to assess the corrosion-inhibition effects of two admixtures. Cymbopogon citratus (C. citratus) leaf-extract was used in comparison with the well-known but toxic inhibitor, Na2Cr2O7 (sodium dichromate) as a reference. Equal mass fractions, as percentage by mass/weight of cement (wt%) for concrete mixing, of the plant-extract and Na2Cr2O7 were admixed separately in steel-reinforced concrete samples immersed in the industrial/microbial simulating-environment. From these, corrosion-rate by linear polarization-resistance (LPR) and corrosion-potential as per ASTM(1) C876-15 were measured and statistically analyzed as per ASTM G16-13. Corrosion-potential results showed that both admixtures reduced corrosion risk as per ASTM C876-15 criteria. However, high concentrations of C. citratus leaf-extract surpassed the highly effective performance of Na2Cr2O7 at inhibiting reinforcing-steel-corrosion in the test-medium. The 0.417 wt% C. citratus leaf-extract exhibited optimal inhibition efficiency, ? = 92.36% in the study. In comparison, the 0.250 wt% Na2Cr2O7 exhibited the highest inhibition effectiveness performance of ? = 83.96% among the concentrations of Na2Cr2O7 chemical inhibitor. These indicate prospects on the suitability of C. Citratus leaf-extract as an environmentally friendly corrosion inhibitor in the industrial/microbial service environment that are discussed in the study.

INTRODUCTION

Corrosion of reinforcing steel in concrete is a major deterioration mechanism militating against the use of steel-reinforced concrete material, whose structural integrity and durability otherwise makes it the most widely used construction material. Usually, steel-reinforcement corrosion in concrete is caused by aggressive agents in the environments, especially those that are present in the service environment for which the steel-reinforced concrete is designed.1-4 Such service environments include those where the reaction of industrial SO2 effluents with atmospheric water vapor culminates in the production of sulfuric acid.4-7 Also included in these service environments are microbial environments where biological activities of sulfate reducing and sulfur oxidizing microorganisms (e.g. thiobacillus spp.) result in the production of sulfuric acid.8-10 The acidic sulfate in these environments attacks both the concrete, by forming gypsum and ettringite with hydrated products of the concrete matrix,11-14 and the reinforcing steel embedment, which corrodes by acidic dissolution and/or embrittlement.4-6,15-18

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