ASTM Proposes New Rebar Standard
This standard would cover steel reinforcing bars that are zinc-coated (galvanized) by the continuous hot-dip process in cut lengths or coils.
Infrastructure projects rely on reinforced concrete as a principal construction material. Each year, more than $1.3 trillion is spent constructing new infrastructure or repairing/replacing old infrastructure for energy, water, communications and transportation systems. A proposed ASTM International (West Conshohocken, PA) standard will cover the protection of zinc-coated steel bars used for concrete reinforcement in large infrastructure projects.
ASTM WK46112, Specification for Zinc-Coated (Continuous Hot-Dip Galvanized) Steel Bars for Concrete Reinforcement, will provide specifiers with a high-performance, low-cost option for protecting concrete structures. The unique fabrication properties in WK46112 will minimize installation costs, as well as long-term maintenance costs. This proposed new standard describes the product characteristics of steel reinforcing bars, zinc-coated (galvanized) by the continuous hot-dip process in cut lengths or coils.
“Galvanizing is a proven and effective way to protect reinforcing bars from corrosion as it provides both barrier and galvanic protection to the steel substrate,” says ASTM member Gary Dallin, the director of GalvInfo Center, a program of the International Zinc Association. “It also increases the chloride threshold of steel reinforcing bars. A process to continuously galvanize reinforcing bars (CGR) at a significant cost savings compared to other corrosion-resistant reinforcing bar systems is now operating in two locations.”
According to Dallin, using a small amount of aluminum in a zinc bath, the CGR coating process produces a 50 micron coating that is almost pure zinc. Such a coating, similar to those produced on continuously galvanized sheet products, adheres very well and is also highly resistant to corrosion in concrete.
“With no thick zinc-iron alloy layers, the coated bar can be bent, stretched, or twisted without cracking or flaking the coating, regardless of the total coating mass” says Dallin. “As a result, there is no zinc loss due to brittleness during forming in the field and repair requirements are minimal.”
Further, the CGR process coats the steel with minimum exposure time to the molten zinc before cooling. This allows all grades of steel (normal and high strength) to be galvanized with no change in mechanical properties and to have the same coating of essentially pure zinc.
ASTM WK46112 is being developed by Subcommittee A01.05 on Steel Reinforcement, part of ASTM International Committee A01 on Steel, Stainless Steel and Related Alloys. A01.05 welcomes all interested parties, particularly those with experience in galvanized reinforcing bar, to contribute to the ongoing development of the proposed standard.
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