Inhibition Effect of Vernonia amygdalina Extract on the Corrosion of Mild Steel Reinforcement in Concrete in 3.5M NaCl Environment

The inhibition effect of Vernonia amygdalina (bitter leaf) extract on the corrosion behaviour of embedded mild steel rebar in concrete has been investigated by electrochemical potential measurement, pH and gravimetric (weight loss) methods. The results were further analysed using the two-factor ANOVA test. The experiments were performed using bitter leaf extract as a green inhibitor in 3.5% sodium chloride solution. Inhibitor extracts concentrations of 25, 50 75, and 100% were prepared from the fresh leaves of Vernonia amygdalina with distilled water. The voltage (potential) measurements were recorded with a digital voltmeter and a copper-copper sulphate electrode as the reference electrode. The pH of the test medium was measured by a pH meter. Compressive strength of each of the block samples was determined after the experiments. Weight loss values were obtained from the weight loss method (gravimetric) and the inhibitor efficiency was computed from the corrosion rate of each of the tested samples. Results showed that varied concentration of Vernonia amygdalina and the test exposure time significantly affect both the corrosion potential of embedded steel rebar in concrete and the pH of the medium. The outcome of the ANOVA test confirmed the results at 95 % confidence, and further showed that concentration of Vernonia amygdalina had greater effect on potential measurements, whereas, exposure time had greater effect on pH measurements. Vernonia amygdalina extract gave good corrosion inhibition performance of the embedded steel rebar in concrete at 25%, 50% and 75% concentrations in NaCl test medium. The highest inhibition efficiency of 90.08 % was achieved at 25% concentration, the lowest inhibitor concentration used.