Applications of galvanized reinforcing steel
12 Reasons to use hot dip galvanized reinforcing steel
Galvanized reinforcing steel is passivated in wet concrete by the formation of an adherent film of calcium hydroxyzincate. In forming this film, the bond strength between the galvanized reinforcing steel and concrete is increased.
Galvanized reinforcing steel is stable over a wide pH range and is completely unaffected by the carbonation of concrete.
Conservatively, galvanized reinforcing steel has a 2 to 2.5 times higher threshold to chloride attack when compared to uncoated reinforcing steel – this more than doubles the time to reinforcing steel depassivation and corrosion initiation. Typically, galvanized reinforcing steel increases the service life of the structure by 4 to 5 times when compared to uncoated reinforcing steel.
The time to corrosion initiation of galvanized reinforcing steel in concrete can be modelled using conventional industry chloride diffusion models based on Fick’s Second Law.
The passive behaviour of galvanized reinforcing steel in concrete makes it suitable for use in aggressive environments and is ideally suited for external facades, precast panel joints and surface elements, indeed any application where carbonation or chloride ingress is of concern.
There are no special requirements for the design of concrete using galvanized reinforcing steel and no extra steel or overlay is required. In fact, the higher chloride threshold of galvanized steel allows the option for a thinner cover to be used compared to uncoated reinforcing steel while achieving the same durability.
Should galvanized reinforcing steel become depassivated, zinc will corrode at a slower rate than iron, and the zinc coating provides a barrier to iron corrosion. And unlike iron, zinc corrosion products will migrate from the galvanized coating, and by reducing the porosity, will slow down the rate of chloride ingress. The relatively smaller volume of zinc corrosion products compared to iron, lessens the expansive pressure generated by the corrosion process, thereby reducing the size of any cracks which may form.
Galvanized reinforcing steel is an effective way to ensure the durability of a concrete structure at a much lower capital cost than using stainless steel reinforcing steel.
Galvanized reinforcing steel doesn’t have the ongoing testing and maintenance costs of associated with cathodic protection systems.
Unlike epoxy coatings, galvanized coatings on reinforcing steel provide barrier protection, improved bond strength, a superior passivating layer and act as a sacrificial anode should the reinforcing steel beneath the coating be exposed. It has excellent abrasion resistance, is unaffected by UV light and has no special requirements for storage, transport, handling and fixing.
The galvanizing process has no significant effect on the mechanical properties of reinforcing steel, and all available grades may be successfully galvanized.
Galvanizing is environmentally friendly and VOC free. An Environmental Product Declaration (EPD) is available for galvanized steel, and at the end of the life of the structure, any remaining zinc coating may be recycled along with the steel. The small amount of CO2 released during the galvanizing process is offset by the huge CO2 savings associated with the increased durability of the galvanized steel reinforced concrete structure.
