Galvanic cathodic protection is currently an area of substantial growth. It is becoming increasingly attractive because of its simplicity and low monitoring and maintenance requirements. The anode which is normally made from metal such as zinc, is connected to the reinforcing steel and the potential difference between the zinc and the steel causes a small protection current to flow from the zinc to the steel.
Galvanic anodes may broadly be divided into surface-applied systems and embedded discrete systems. The surface applied systems achieve relatively good current distribution but poor adhesion in comparison with the embedded discrete systems.
Galvanic anodes in concrete are usually supplied with proprietary backfill which provides space for the products of anodic dissolution. Most of the recent innovation and research in galvanic anode technology has been associated with the backfill material.
The hybrid anode system is a relatively recent development and differs from the purely galvanic systems described above. The hybrid treatment consists of a temporary impressed current followed by permanent galvanic protection. The principle of this system is that during the initial impressed current phase, active pits are realkalised and this stops active corrosion and returns the steel to a passive state. Following the application of impressed current for a predetermined period, the passivity of the steel will then be maintained by the sacrificial anode system.
Key features of this technology are:
- Low monitoring and maintenance requirements.
- For buried/submerged applications, galvanic anode systems have an excellent performance track record.
- Under suitable conditions and generally when the corrosion activity is low, galvanic systems in concrete atmospheric applications can provide some level of protection against reinforcement corrosion.
- However, performance data from site applications suggests that it is unlikely for any of these systems to achieve the cathodic protection criteria (in accordance to current standards) for heavily chloride contaminated marine structures especially for areas of high corrosion activity and with direct exposure to tidal and splash zones.
Our recommended application:
- In structures where permanent power supply required for an impressed current system is unavailable or it is unlikely to maintain a monitoring program for an impressed current CP system.
- In conjunction with patch repairs to reduce the effect of incipient anode.
- In structures with only light chloride contamination and where low cathodic protection current density is sufficient to achieve an adequate level of protection.