Enhanced corrosion resistance of CPC coatings modified with rice husk ash for rebar applications in marine environment

Abstract

This work investigated the anti-corrosive properties of cement polymer composite coatings modified with fly ash and rice husk ash over steel rebars in a marine environment. So far there are no reports of supplementing rice husk ash in cement polymer coatings and hence, in this research work we attempt to develop a corrosion resistant cementitious composite coating over carbon steel reinforcements embedded in concrete structures in a marine environment. Four types of coatings were synthesized and designated as OC (100 wt% Ordinary Portland Cement), PC (100 wt% Portland Pozzolana Cement), OPF (OC replaced with 20 wt% fly ash), OPR (OC replaced with 20 wt% rice husk ash). The coatings were prepared with a commercially available polymer solution and applied on to the steel rebars in triplicate. Electrochemical studies like open circuit potential measurements, electrochemical impedance spectroscopy and potentiodynamic polarization measurements were carried out on all the coated rebars and compared with uncoated rebars under marine exposure conditions. Optical microscopy and Field Emission Scanning Electron Microscopy were used for understanding the morphology of coated surfaces. The results indicated that addition of rice husk ash improved the corrosion performance of CPC coatings as compared to others. The significantly lower Icorr value of 8.92e-08 μA (a order of magnitude less than reinforcements without coating) and the highest impedance value and polarization resistance, implied more corrosion resistance for OPR coated rebars than others. The characterization of the surfaces revealed the smooth morphology of the OPR coating. Our results highlight the significant benefits of using supplementary cementious materials in cement polymer composite coatings for improving the anti-corrosive properties of rebars and the findings will definitely throw light on a new direction of research towards development of eco-friendly coatings with improved corrosion resistance and durability to enhance the life of reinforced concrete structures.