Corrosion inhibition of green tea extract on steel reinforcing bar embedded in mortar

Polar atoms and π-electron bonds in molecular structures of natural antioxidants make the antioxidants potential mixed-type corrosion inhibitors and 'green' alternatives to commercial inorganic corrosion inhibitors. In this paper, the corrosion inhibition efficiency (IE) of green tea extract (GT), being one of the richest sources of natural antioxidants, was compared against commercial calcium nitrite corrosion inhibitor (CI) on steel reinforcing bars (rebars) embedded in mortar. Rebar corrosion was accelerated with impressed current and cyclic wetting-drying, and corrosion development was measured with linear polarization resistance. The IE of CI and GT were compared at same inhibitor volume. Results show that GT had a significantly higher IE than CI (75-80% vs. 14-24%), due to a reduction in iron oxidation rate (βa) and an increase in rebar resistance to polarization potential/current (Rp). Meanwhile, oxygen reduction rate (βc) and rebar open circuit potential (OCP) did not change significantly. The changes in βa and βc with an insignificant change in OCP suggest that GT was a mixed-type corrosion inhibitor, which formed a protective layer on rebar surface and increased Rp of the rebars.