Masonry Magazine June 1985 Page. 26
EMBEDDED STEEL IN MASONRY
continued
ent, the longer the protection afforded by the sacrifice of zinc will last.
It should be noted that once all of the available zinc has been consumed through sacrificial action, corrosion of the base metal will proceed as though no galvanizing exists, and the life of the material will be directly proportional to its thickness.
Since the protective value of the zinc coating is proportional to its thickness, the thickness of coating should be increased as corrosion problems intensify. Under average conditions, corrosion of steel is about 40 times the rate of corrosion of zinc, thus a relatively thin coating of zinc can provide a considerable amount of protection.
Several studies have been made to determine the amount of zinc coating that should be used in building products in the United States, Europe, and Canada. However, there is quite a disparity in the results, one indicating severe corrosion potential; the other a rather moderate one. As a result, there is no clear-cut corrosion rate available for use by designers. At the present time, the selection of the thickness of zinc coating still must be determined based on the experience and judgment of the designer and industry recommendations.
Zinc Coating Methods. There are two popular methods for applying zinc coatings to metal. One method is to apply the zinc before the base material is fabricated. This process called "mill galvanizing" takes place after wire is drawn
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Table 3
Highlights of ASTM Standards to Specify
Galvanizing"
ASTM A116-81-Zinc-Coated (Galvanized) Steel Woven
Wire Fence Fabric
* Covers mill galvanized wire for ties and joint
reinforcement
* Applies to wire from 9 ga to 14.5 ga
* Lists three classes of coating-Class 1. Class 2, and
Class 3
* For 9-ga wire minimum coating is 0.40, 0.60, and 8.80
oz/ft³ for Classes 1, 2, and 3, respectively
ASTM A641-82-Zinc-Coated (Galvanized) Carbon Steel
Wire
* Covers mill galvanized wire for ties and joint
reinforcement
* Governs full range of wire diameters from below 16 ga.
to ½ inch and larger
* Lists three class coatings and has values identical to
A116 for those wire sizes which are commonly used
* Three-sixteenth inch wire requires 0.50, 0.70, and 0.90
oz/ft. for Classes 1, 2, and 3
* One-quarter inch wire requires 0.65, 0.75, and 0.90 oz/
ft. for Classes 1, 2, and 3
ASTM A153-82-Zinc Coating (Hot Dip) on Iron and Steel
Hardware
* Governs four classes of product coatings of malleable
iron and steel; threaded fasteners and rolled, pressed, and
forged articles
* Class B addresses products used in masonry
* Zinc weight requirements for products generally used
for masonry are given in three categories as follows:
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26 MASONRY-MAY/JUNE, 1985