Microstructure and corrosion resistance of enamel coatings applied to smooth reinforcing steel

Corrosion behavior of enamel-coated reinforcing steel bars in 3.5 wt.% NaCl solution is evaluated by open-circuit potential, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization testing. Three types of enamel coating are investigated: a pure enamel coating, a mixed enamel coating that consists of 50% pure enamel and 50% calcium silicate by weight, and a double enamel coating that has an inner pure enamel layer and an outer 50/50 enamel layer. The coatings are characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) techniques. SEM images reveal that all three enamel coatings have a porous structure. The pores in the pure and double enamel are disconnected, while those in the mixed enamel are interconnected. Electrochemical tests demonstrate that both pure and double enamel coatings can significantly improve corrosion resistance, while the mixed enamel coating offers very little protection.

► Pure enamel coating has a few small disconnected and isolated cavities.
► 50/50 enamel coating has an amorphous structure with interconnected pores, a chloride pathway.
► Double enamel coating has the inner layer with relatively large pores and the outer scattered CS particles.
► All non-optimized enamel coatings can enhance the corrosion performance of reinforcing bars.
► The pure and double enamel coatings outperform the 50/50 enamel coating.