Improving corrosion resistance of reinforcement steel rebars exposed to sulphate attack by the use of electroless nickel coatings

Abstract

Fe-600 grade steels are recommended for high rises and other structures in India that require high-load carrying capacity (particularly in seismic zones) due to its excellent mechanical properties. But structures in food processing, agricultural waste handling, etc., industries and high rises are subjected to attack of sulphates as well as acid rain. The present work investigates the efficacy of electroless nickel coatings in corrosion prevention of Fe-600 grade rebars exposed to aggressive sulphate environment. Ni-P, Ni-P-W and Ni-P-Cu coatings were deposited on the rebars. Electrochemical tests such as potentiodynamic polarization and electrochemical impedance spectroscopy were employed to investigate the corrosion behaviour in 0.5 M sulphuric acid. It was seen that corrosion potential of rebars was nobler when they were coated with electroless nickel ternary variant coatings. Electrochemical impedance spectra also validated the same. Scanning electron microscope images of the surface of the bare rebars post electrochemical tests revealed a completely cracked morphology due to severe attack of sulphates. Whereas the surface of Ni-P-W coated rebar revealed the least damage and highest corrosion resistance.

Keywords:

• Rebar
• concrete
• corrosion
• electroless nickel
• potentiodynamic polarization
• electrochemical impedance spectroscopy

Acknowledgement

The authors acknowledge the support of Central Instrumentation Facility (CIF) of Birla Institute of Technology, Mesra, Ranchi 835215, Jharkhand, for providing FESEM and EDS analysis facilities.

Disclosure statement

No potential conflict of interest was reported by the authors.