GalFan ZGF 255 expected design life 50yrs to 150yrs
The estimated time to first maintenance for a hot-dip galvanized coating that experiences common atmospheric exposure can be seen below. Time to first maintenance is defined as the time to 5% rusting of the substrate steel. The time to first maintenance of hot-dip galvanized steel is directly proportional to the zinc coating thickness. Source American Galvanisers Association www.galvanizeit.org
1.5mil = 255grams/m2 = ZGF255 spec
GalFan (95% zinc, 5% aluminium) has proven to be 2 to 3 times more corrosive resistant than the same thickness of Hot Dip 100% zinc Galvanising. Depending on the environment, it may take 50yrs to 150yrs for 5% rust to show on the surface of GalFan ZGF 255 spec, when above ground.
AS / NZS 4534 Zinc and zinc/aluminium-alloy coatings on steel wire. Class W10 (heavy coating)
When constructing gabion retaining walls in strongly acidic soils (PH over 5.5), the soil and the corrosive groundwater must be separated from the gabion structure by using geotextile fabrics and a properly designed drainage system.
Good drainage behind and below your gabion retaining wall will not only improve the retaining walls stability, it will also increase the expected design life of the gabion wall
In New Zealand there are areas where local conditions create an increased likelihood of corrosion. Special consideration should be given to material selection and design in these areas. They include:
1. Geothermal Areas
Hydrogen sulphide associated with geothermal activity creates a corrosive environment. Variations in natural activity or draw-off from steam bores plus the effects of weather conditions make the high risk areas hard to define.
2. West Coast, South Island
In this area, smoke from the coal burning fires may cause high concentrations of sulphur dioxide in the air. The combination of this and the high rainfall for the region creates an aggressive situation which must be considered . The effects of a severe coastal environment aggravate the situation. This area combines the most severe features of both industrial and coastal environments.
3. Coastal Environment
Within 1000m of the coast, characterised by:
Light salt deposits
A frequent smell of salt in the air
In the immediate vicinity of large expanses of calm salt water such as harbour foreshores
This environment may be extended inland by prevailing winds and local conditions.
4. Industrial Environments
Within 500m of corrosive industrial emissions and subject to heavy fallout from them.
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