Zinc, as a sacrificial anode, has been used to cathodically protect ship’s hulls
for more than a century now. It has become a common practice to use cathodic protection either alone or in combination
with coatings for buried pipelines, storage tanks and offshore structures. It has been well established both in
theory and in practice that the process achieves an immediate reduction in corrosion rate by making the reinforcing
steel the cathode, inhibiting its tendency to oxidize. In addition, the cathodic reactions at the steel/concrete
interface increase the alkalinity (raise the pH) by hydroxyl ion (OH-) generation and drive chloride ions (Cl-) away from the steel as a result of the negative charge on the ions being repelled by
the negative polarity of the reinforcement and attracted to the positive polarity of an installed anode. Thus Cathodic
Protection of steel in concrete has always incorporated some degree of Realkalisation (increase in pH) and Chloride
Extraction (redistribution of chlorides). Both these processes reduce the risk of corrosion of steel in the concrete
and also achieve further protection. Recent innovations in materials and design have made CP, - the old remedy,
ever more attracting and promising today.
3.2 Pressure-sensitive Zinc-Hydrogel Anode
For conventional CP systems (SA or ICCP) to function properly, it requires the
presence of a continuous conductive electrolyte between the anode and the cathode. This is to form a closed circuit
such that the reinforcing steel is indeed made the cathode. In areas of electrical discontinuity, reinforcing steel
would not be cathodically protected. One of the recent innovations is the self-adhesive and conductive zinc-hydrogel
anode that provides a continuous electrolyte contact between the anode and the reinforcing steel embedded in the
concrete structure. The pressure-sensitive zinc-hydrogel anode is essentially a sheet of zinc foil coated with
an ionically conductive hydrogel pressure-sensitive adhesive (Figure 1), which serves as the electrolyte between
the anode (zinc foil) and the cathode (reinforcing steel in concrete). The hydrogel is covered with a liner to
help protect it from contamination. At time of installation, the protective liner is removed from the hydrogel
by hand, and the zinc-hydrogel anode is adhered to the clean, bare concrete surface.
