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In this study, corrosion test-data of steel-rebar in concrete were subjected to the fittings of the Normal, Gumbel and the Weibull probability distribution functions. This was done to investigate the suitability of the results of the fitted test-data, by these distributions, for modelling the effectiveness of C 6 H 15 NO 3 , triethanolamine (TEA), admixtures on the corrosion of steel-rebar in concrete in NaCl and in H 2 SO 4 test-media. For this, six different concentrations of TEA were admixed in replicates of steel-reinforced concrete samples which were immersed in the saline/marine and the microbial/industrial simulating test-environments for seventy-five days. From these, distribution fittings of the non-destructive electrochemical measurements were subjected to the Kolmogorov-Smirnov goodness-of-fit statistics and to the analyses of variance modelling for studying test-data compatibility to the fittings and testing significance. Although all fittings of test-data followed similar trends of significant testing, the fittings of the corrosion rate test data followed the Weibull more than the Normal and the Gumbel distribution fittings, thus supporting use of the Weibull fittings for modelling effectiveness. The effectiveness models on rebar corrosion, based on these, identified 0.083% TEA with optimal inhibition efficiency, η = 72.17± 10.68%, in NaCl medium while 0.667% TEA was the only admixture with positive * For correspondence Joshua Olusegun Okeniyi et al effectiveness, η = 56.45±15.85%, in H 2 SO 4 medium. These results bear implications on the concentrations of TEA for effective corrosion protection of concrete steel-rebar in saline/marine and in industrial/microbial environments.

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This paper investigates Phyllanthus muellerianus leaf-extract effects on steel-reinforcement corrosion in concrete immersed in 3.5% NaCl, simulating saline/marine environment. Different concentrations of the leaf-extract were admixed in steel-reinforced concrete samples, which were immersed, with normal control, in the test-environment, while positive control samples were immersed in distilled water. Electrochemical measurements of corrosion-rate (by linear-polarizationresistance instrument), corrosion-current (by zero-resistance-ammeter) and corrosion-potential (by high impedance multimeter) were obtained for assessing the reinforcing-steel corrosion. Analyzed results showed that the corrosion-rate exhibited excellent correlation (R = 98.82%, Nash-Sutcliffe Efficiency = 97.66%, ANOVA p-value = 0.0006) with function of the admixture concentration and of the corrosion noise-resistance (ratio of corrosion-potential and corrosion-current standard deviations). The 0.3333% Phyllanthus muellerianus (per weight of cement) exhibited optimal efficiency, η = 97.58% ± 1.28% (experimental) or 95.33% ± 4.25% (predicted), at inhibiting concrete steel-reinforcement corrosion in the test-environment, which compares well with the positive control performance model, η = 97.96% ± 0.03%. The experimental and predicted models followed the Langmuir adsorption isotherm, which indicated physisorption as the Phyllanthus muellerianus leaf-extract adsorption mechanism on the reinforcing-steel. These support suitability of the N-, S-, and O-containing and π-electron rich Phyllanthus muellerianus leaf-extract as an environmentally-friendly inhibitor for effective corrosion-protection of steel-reinforcement in concrete designed for the saline/marine environment.

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