Electrochemical Performance of Phyllanthus Muellerianus on the Corrosion of Concrete Steel-reinforcement in Industrial/Microbial Simulating-environment

Abstract

Electrochemical monitoring techniques were employed in this study to assess anticorrosion performance of Phyllanthus muellerianus leaf-extract on concrete steelreinforcement in 0.5 M H 2 SO 4 , used for simulating industrial/microbial environment. For this, steel-reinforced concretes admixed with different concentrations of the natural plant leaf-extract were partially immersed in the acidic test-solution and subjected to electrochemical monitoring of corrosion potential, corrosion current and corrosion rate. Test responses analysed as per ASTM G16-95 R04, showed that the corrosion rate correlated, r = 84.93%, ANOVA p-value = 0.0403, with the leaf-extract concentration admixed in concrete and the ratio of the standard deviation of potential to the standard deviation of current. These identified the 0.3333% Phyllanthus muellerianus (per weight of cement) with optimum effectiveness at inhibiting steel-reinforcement corrosion both by the experimental model, η = 91.66±2.51%, and by the prediction from the correlation fitting model, η = 85.54±14.44%. Fittings of both the experimental and the predicted data followed the Flory-Huggins and the Frumkin adsorption isotherms which suggest prevalent mechanism of physical adsorption (physisorption) of the extract on steel-rebar surface. These support the use of Phyllanthus muellerianus as environmentally-friendly admixture for inhibiting concrete steel-reinforcement corrosion in the industrial/microbial service-environment.

Effects of Phyllanthus muellerianus Leaf-Extract on Steel-Reinforcement Corrosion in 3.5% NaCl-Immersed Concrete

“…It is also worth noting that the optimal inhibition efficiency in this study by the 0.3333% P. muellerianus The high range of idealized inhibition effects by the positive control samples laid credence to the fact that the corrosion effects from the normal controls followed from the immersion of the normal control samples in the saline/marine environment and not from any other effects. It is also worth noting that the optimal inhibition efficiency in this study by the 0.3333% P. muellerianus leaf-extract concentration finds similarity with the performance from previous work [36] by this same concentration on steel-reinforcement corrosion in H 2 SO 4 -immersed concrete. This performance was despite the longer experimental period of steel-reinforced concrete immersion in the chloride induced corrosive test-medium in this study.…”

“…In this study, however, P. muellerianus leaf-extract concentrations exhibited high effectiveness performance, which compares well to that obtained from positive (distilled water immersed) control samples, on the inhibition of steel-reinforcement corrosion in concrete for the saline/marine simulating environment. This performance was in similar manner with that by the P. muellerianus for the industrial/microbial environment in [36], and with that obtained by the also N-, S-, and O-containing Morinda lucida for the saline/marine environment in [72]. The corrosion inhibition effects by these natural plant-extracts find agreements with what obtained in reported works [73][74][75][76], where effective corrosion inhibition of steel material in acidic environments had been observed with uses of N-, S-, and O-containing and π-electron rich chemical derivatives.…”

“…This relationship of corrosion noise resistance with corrosion rate, and vice versa, had been employed for detailing correlation expressions between these corrosion variables in reported works [36,56,60]. In a similar manner, it could be shown that the corrosion rate, CR, obtained from this study, exhibited relationship with the corrosion noise resistance, R n , and the P. muellerianus leaf-extract admixture concentration, , which can be expressed in compact form as Equation (13):…”

“…As could be observed in Figure 3, studies have shown that the corrosion noise resistance is generally high-valued at low corrosion rate and low-valued at high corrosion rate due to the fact that the corrosion noise resistance tracks the linear polarization resistance [36,56,59,60]. This relationship of corrosion noise resistance with corrosion rate, and vice versa, had been employed for detailing correlation expressions between these corrosion variables in reported works [36,56,60].…”

“…Steel-reinforced concrete slabs for the study were cast in duplicates of size 100 mm × 100 mm × 200 mm that contained similar concentrations of P. muellerianus leaf-extract admixture, and which had been obtained following details from studies [33,36]. Six variations of the P. muellerianus leaf-extract were employed as admixtures in the duplicated design of steel-reinforced concrete specimens for the saline/marine test-environment.…”