Analysis of inhibition of concrete steel-rebar corrosion by Na₂Cr₂O₇ concentrations: Implications for conflicting reports on inhibitor effectiveness

J. O. Okeniyi¹, I. O. Oladele ¹, I. J. Ambrose¹, S.O. Okpala¹, O. M. Omoniyi¹, C. A. Loto^{1, 2}, A. P. I. Popoola²

(1. Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria;
2. Chemical, Metallurgical and Materials Engineering Department, Tshwane University of Technology,
Pretoria 0001, South Africa)

Abstract:Corrosion test data were measured using non-destructive electrochemical techniques and analysed for studying inhibition effectiveness by different concentrations of Na₂Cr₂O₇ on the corrosion of concrete steel-rebar in NaCl and in H₂SO₄ media. For these, specifications of ASTM G16-95 R04 were combined with the normal and the Gumbel probability density functions as model analytical methods for addressing issues of conflicting reports of inhibitor effectiveness that had generated concerns. Results show that reinforced concrete samples admixed with concentrations having 4 g (0.012 7 mol), 8 g (0.025 4 mol) and 6 g (0.019 1 mol) Na₂Cr₂O₇ exhibited, in that order, high inhibition effectiveness, with respective efficiency, η, of (90.46±1.30)%, (88.41±2.24)% and (84.87±4.74)%, in the NaCl medium. These exhibit good agreements within replicates and statistical methods for the samples. Also, optimal inhibition effectiveness model in the H₂SO₄ medium was exhibited by 8 g (0.025 4 mol) Na₂Cr₂O₇ concentration having η=(78.44±1.10)%. These bear implications for addressing conflicting test data in the study of effective inhibitors for mitigating steel-rebar corrosion in aggressive environments.

Key words:corrosion inhibitor effectiveness; saline/marine and industrial/microbial environments; concrete steel-rebar; normal and Gumbel probability distribution functions; Kolmogorov-Smirnov statistics; tests of significance