Effect of Reinforcing Bar Microstructure on Passive Film Exposed to Simulated Concrete Pore Solution

Abstract

Use of thermomechanically treated (TMT) reinforcing bars has become popular in the concrete construction industry after their introduction in the 1980s. This can be attributed to the fact that thermomechanical treatment enhances the strength and ductility of reinforcing bars remarkably. However; limited research is available on the corrosion behavior of TMT reinforcing bars after they are embedded in concrete. To enhance knowledge and insights into this area, the authors investigated the protective properties of two types of steel reinforcement bars (reinforcing bars)-namely tempered martensite (TM) and pearlite-ferrite (PF)-after exposing them to concrete pore solution. The microstructures of both types of reinforcing bars were investigated, and their kinetics of growth and mechanism of nucleation were recorded by employing electrochemical impedance spectroscopy and polarization. Studies reveal that protective film on the surface of steel with TM microstructure develops at a significantly higher rate and is more stable compared to that on steel with PF microstructure. This superior protective nature is attributed to the development of a compact and adherent oxide film on TM steel. A model is proposed to explain the results obtained during the study. Raman spectroscopy of passive films formed on the surface of reinforcing bars exposed to concrete pore solution supports the proposed model.