Accelerated Rusting of Reinforcing Bars: The Role of Manganese Alloying in Concrete Reinforcement Steel Bars

Abstract

The role of alloying of manganese in mild carbon steel reinforcing bar on the rate of atmospheric rusting is investigated. Four types of steel reinforcing bar from different producers having variations in the rate of atmospheric rusting were collected and exposed to the atmosphere of Jamshedpur, India for 3 years. The corrosion rates of the exposed reinforcing bar samples were evaluated by determining the loss in weight of the samples. A direct relationship has been recorded between the rate of corrosion and the manganese content in the steel. The corrosion products formed on the surface of the exposed reinforcing bar samples were characterized by Raman spectroscopy and X-ray diffraction techniques. Electro-chemical impedance spectroscopy and DC polarization studies of the reinforcing bar samples were also performed to understand the causes for the difference in their rates of rusting. The mechanism for the accelerated rate of rusting recorded for the higher manganese-containing steel is discussed by proposing a schematic model incorporating different stages of reactions.