Corrosion of Strained Plain Rebar in Chloride-Contaminated Mortar and Novel Approach to Estimate the Corrosion Amount from Rust Characterization

Abstract

Some of the steel bars used in reinforced concrete construction experience plastic strain due to various operations at construction sites. The present work concentrates on the corrosion behavior of such prestrained reinforced bars (rebars) embedded in chloride-contaminated cement mortar and exposed to laboratory conditions (temperature of $27°\mathrm{C}\pm 2°\mathrm{C}$ and relative humidity of 60%) for 18 months. The corrosion behavior of these rebars was examined in terms of the electrochemical parameters [open circuit potential (OCP) and polarization resistance $(R_P)$ ], effective volumetric expansion ratio, and the thickness of the rust at the metal–mortar interface. Cyclic change in the OCP and $R_P$ of the bars with time has been observed due to the formation of corrosion products at the interface. The preinduced plastic strains affected both the polarization resistance and the corrosion-induced mass loss of the rebar. The strained rebars showed higher corrosion susceptibility and corrosion amount than the unstrained rebars due to the changes in the surface condition and microstructure on account of high plastic deformation. The mass of the iron lost to form rust at the interface has been estimated using a novel volumetric expansion ratio model by taking the individual contribution of corrosion products at the interface. Correlation between the degree of straining and the corrosion-induced cracks at the end of 18 months of exposure has also been established.