Galvanized Reinforcements in Concrete. Authors Authors and affiliations M. Andrade A. This process is experimental and the keywords may be updated as the learning algorithm improves. This is a preview of subscription content, log in to check access. C, Concrete , , 8 , Google Scholar. COOK, H. Civil Eng.
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Galvanized Steel Reinforcement in Concrete
N, July Note N, July Effect of Mix Design and Construction Parameters. Report no. Once the concentration of these corrosive elements surpasses steels corrosion threshold, the rebar starts to corrode. As the rebar corrodes, pressure builds around the bar leading to cracking, staining, and eventually spalling of the concrete. Because failure of the rebar leads to compromised or failing structural capacity, protecting against premature rebar failure is key.
Similar to in the atmosphere, galvanized rebar extends the life of the steel in concrete. The corrosion mechanisms in concrete are quite different than atmospheric exposure, and one of the biggest factors is chloride concentration.
Galvanized rebar can withstand chloride concentration at least four to five times higher than black steel, and remains passivated at lower pH levels, slowing the rate of corrosion. In addition to the higher chloride tolerance, once zinc corrosion products are formed from the galvanized rebar, they are less voluminous than iron oxide and actually migrate away from the bar. The less voluminous zinc particles migrate away from the bar galvanized coating and into the pores of the concrete matrix.
This migration prevents the pressure buildup and spalling caused by iron oxide particles. The total life of galvanized steel in concrete is made up of the time taken for the zinc to depassivate, plus the time taken for consumption of the zinc coating, as it sacrificially protects the underlying steel. Only after the coating has been fully consumed in a region of the bar will localized steel corrosion begin. Laboratory data support, and field test results confirm, that reinforced concrete structures exposed to aggressive environments have a substantially longer service life when galvanized rebar is used as opposed to bare steel rebar.
- Galvanized Steel Reinforcement in Concrete;
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Visit the Galvanized Rebar website for more information regarding market-specific information of hot-dip galvanized reinforcing steel. The Reinforcing Steel section in the AGA Publication area has many publications to learn more about using galvanized rebar. The corrosion mechanisms and performance of black and hot-dip galvanized steel in concrete are different than when exposed to atmospheric conditions. Steel embedded in concrete is exposed to a highly alkaline environment.
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Zinc, on the other hand, can withstand chloride concentration at least four to five times higher than black steel, and coupled with its impervious barrier protection, delays the onset of chloride corrosion on galvanized rebar. Chlorides penetrate the concrete through small pores and cracks that form on the surface through use and weathering. While black steel in concrete typically depassivates below a pH of In addition to the higher chloride tolerance, once the zinc coating does start to depassivate, the zinc corrosion products formed are less voluminous than iron oxides and actually migrate away from the galvanized bar into the matrix of the concrete.
Unlike the development of iron oxide, the migration of the zinc corrosion products from the rebar prevents the pressure buildup and eventual concrete spalling. Only after the coating has been fully consumed in a region of the bar will localized corrosion of the steel begin. Good bonding between reinforcing steel and concrete is essential for the reliable performance of reinforced concrete structures. When protective coatings on steel are used, it is essential to ensure they do not reduce bond strength.
Studies on the bonding of galvanized and black steel bars to Portland Cement concrete have been investigated. The results of these studies indicate:. The bond strength relies heavily on the deformation of the bar and not as much on the actual bond between the zinc and the concrete.
Galvanized Steel Bars
For plain bars with no deformation, the bond between the zinc and the concrete becomes very important. Pullout strength of hot-dip galvanized reinforcing steel has been tested many times, and the values of bond strength are equivalent to, or better than, black steel bond strength. During curing, the galvanized surface of steel reinforcement reacts with the alkaline cement paste to form stable, insoluble zinc salts accompanied by hydrogen evolution. This has raised the concern of the possibility of steel embrittlement due to hydrogen absorption.
Laboratory studies indicate liberated hydrogen does not permeate the galvanized coating to the underlying steel and the reaction ceases as soon as the concrete hardens. ASTM A requires hot-dip galvanized reinforcement be chromate passivated after galvanizing. Many cement mixtures contain small amounts of chromate that may serve the same purpose as chromate passivating the zinc coating. The reaction between the alkaline cement paste and the zinc coating is dependent on the amount of zinc-coated surface in the concrete with the potential for reaction increasing with more zinc metal in contact with the concrete.
Metal forms should be electrically isolated from the galvanized rebar to prevent dissimilar metal reactions during the concrete curing.
Galvanized Steel Reinforcement in Concrete: A Consultant's Perspective - ScienceDirect
Because types of cement with naturally low occurring levels of chromates may react with zinc, it is important to ensure that forms and supports are not removed before the concrete has developed the required strength to support itself. Normal form removal practices may be utilized if the cement contains at least ppm of chromates in the final concrete mix or if the hot-dip galvanized bars are chromate-passivated according to ASTM A Ductility and strength of reinforcing steel are important to prevent brittle failure of reinforced concrete.
Studies of the effect of galvanizing on the mechanical properties of steel reinforcing bars have demonstrated the tensile, yield and ultimate strength, ultimate elongation, and bend requirements of steel reinforcement are substantially unaffected by hot-dip galvanizing, provided proper attention is given to steel selection, fabrication practices, and galvanizing procedures.
The effect of the galvanizing process on the ductility of steel bar anchors and inserts after being subjected to different fabrication procedures also has been investigated. The results demonstrate conclusively with the correct choice of steel and galvanizing procedures, there is no reduction in steels ductility.