Corrosion protection of reinforcement steel rebars by the application of electroless nickel coatings

Abstract

Pitting corrosion and susceptibility to chloride attacks are the shortfalls of reinforcement steel used in concrete structures. The present work proposes the deposition of electroless nickel coatings to provide barrier protection due to their proven corrosion resistance. The effect of deposition of Ni–P, Ni–P–W and Ni–P–Cu coatings on the corrosion behavior of Fe—600 grade rebars in 3.5% NaCl has been investigated with the aid of potentiodynamic polarization and electrochemical impedance spectroscopy. The corrosion potential of bare rebar was observed to be −653 mV while that of electroless Ni–P, Ni–P–W and Ni–P–Cu coatings was −436, −391 and −356 mV respectively. The corrosion current density of the rebars also decreased significantly by the application of electroless nickel coatings. Nyquist plots also revealed a bigger semicircular loop for the coated rebars. The chloride attack was severe on the bare uncoated rebar and scanning electron micrograph revealed severe cracking. On the other hand, the vulnerability of the electroless coated rebars to pitting corrosion decreased greatly.