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Concrete structures using rebar for structuralsupport often face corrosion problems.Staining, cracking and spalling can be attributedto the corrosion of reinforcing steel in the con-

crete. This problem causes expensive repair andmaintenance costs.

Ungalvanized reinforcing steel embedded inconcrete makes the concrete susceptible to stain-ing, spalling or even complete failure of the struc-ture. Reinforcing bar encased in concrete isexposed to moisture within the concrete mix ormoisture that seeps in and begins the corrosion ofrebar. The iron corrosion byproducts are morevoluminous than the metal and build up aroundthe reinforcing steel, distributing stress through-out the structure. The buildup of stress in con-

crete eventually causes the structure to crack,stain and ultimately spall.

Under normal service conditions in a non-aggressive environment, the corrosion reaction pro-ceeds very slowly, but only when concrete perme-ability is low and there are no cracks or voids in theconcrete surface. This is rarely the case.

Compared toungalvanized steelsexpansive corrosionbyproducts, galvanized

reinforcing steel pro-duces a white, pow-dery corrosion byprod-uct that migrates awayfrom the reinforcingsteel and into the con-crete matrix and doesnot cause destructivepressure on the con-crete.

Galvanized rein-forcing steel can be

effectively andeconomically usedin concrete in sit-uations where

black reinforcingsteel will not haveadequate durabili-ty. Galvanizedsteel reinforce-ment is especiallyuseful where thereinforcement isexposed to theweather beforeconstruction com-mences.

Mechanically,the strength andductilit y of rein-forcing steel hasbeen tested andfound to be unaf-fected by the gal-vanizing process.Additionally, in some tests, galvanized steel rebarwas found to have an even stronger bondstrength with concrete than black steel reinforc-ing bars.

Details regarding galvanizing reinforcingsteel, and specifics of bending galvanized rebar,are found in ASTM A767, Standard Specificationfor Zinc-coated (Galvanized) Steel Bars forConcrete Reinforcement.

The AGA has several publications that containinformation about galvanized rebar: Galvanizingfor Corrosion Protection: A Specifiers Guide toReinforcing Steel; Rebar: A Processing andInspection Guide for Quality Hot-Dip GalvanizedReinforcing Steeland Field Handling Guide: Hot-Dip Galvanizing vs. Fusion Bonded Epoxy.

GA LVA N I Z N GI N S I G H T SSp r i n g 2 0 0 1 Vo l . VI N o . I I

INTHISISSUE:Plainville Farms:An ApplicationReport

Pa

Dr.Galv comparesfusion-bonded epcoated rebar anddip galvanized reb

Pa

New PublicationsGalvanizeIt! Semin

Pa

GGI

An Application Report on the

Plainville Farms explains why

hot-dip galvanizing was cho-sen. See page 2

Concrete structures use gal-vanized reinforcing steel bars

to maintain stability.

T h e S p e c i f i e r N e w s l e t t e r o f t h e A m e r i c a n G a l v a n i z e r s A s s o c i a t i o n

Hot -dip galvanized rebar canbe walked on and does not

need to be treated as deli-

cately as epoxy-coated rebar.

Galvanized Rebar Protects

Concrete S tructures

I

8/4/2019 Acero Galvanizado en Concreto 2

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A GALVANIZED STEELAPPLICATIONREPORT

AGRICULTURE

American

Galvanizers

Association

6881 So. Holly Cir. #108Englewood, CO 80112(720) 554-0900(720) 554-0909aga@galvanizeit.org2001 AGA

SUBJECT:Plainville Farms in central upstate New York is a family-owned farm in business since 1835.The farm provides responsibly produced turkey and turkey products (no added filler,nitrites or phosphates) to regional grocery stores and its own Plainville Farms Restaurant.

LOCATION:

Plainville, upstate New York.

ENVIRONMENT:Plainville Farms is situated in a relatively non-aggressiveenvironment (average 3.2 inches of rainfall per month, sum-mer months average 79F [26C], winter months 32F [0C]).However, the complex design of the farms grain chutes andthe chutes supporting structures pose many maintenance dif-ficulties. Galvanizing is the chosen method of corrosion pro-tection because the minimum coating of 3.9 mils of zinc guar-antees maintenance-free performance for more than 60 years,allowing Plainville Farms to focus upon its core business.

DATE OF GALVANIZING:1994

DETAILS:Plainville Farms chose hot-dip galvanizing for the feedchutes that transport grain for storage and for the feed grain chutes supporting steel. Ona larger scale, the agricultural industry is one of the leading users of galvanized steel. Easeof installation, long service-life, material strength, fire-, rodent- and vermin-proofing, andsimplicity of keeping structures hygienic are just some of the reasons hot-dip galvanizingis specified for this mainstay industry.

PLAINVILLE FARMS

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A s kD r . G a l v :

Galvanized Rebar is Easier toH andle Than E poxy-coated

T h e S p e c i f i e r N e w s l e t t e r o f t h e A m e r i c a n G a l v a n i z e r s A s s o c i a t i o n

When galvanized rebar andepoxy-coated rebar are compared,one of the more notable advantages

of the galvanized rebar is that it isvery easy to handle and does notrequire any special care at the jobsite. Epoxy-coated rebar must behandled carefully to prevent damageto the coating. It must be inspectedto ensure that no damage has beendone to the coating and if so, mustbe repaired instantly.

Fusion-bonded epoxy (FBE) coat-ings are applied as dry powder andheated to form a coating on steel. If

the coating is damaged at cut endsor scratched during handling, corro-sion can start and progress unimped-ed along the steel under the FBEcoating as if no protection exists.The full extent of the corrosion willnot be visible since it proceedsunder the FBE coating.

Repair of corrosion beneath theFBE coated rebar is difficult andexpensive, and can run as high as 10percent of the entire structures orig-

inal cost. In some structures, replace-ment or repair of rebar may beimpossible.

Also, the process of bonding theepoxy to the steel does not ensurethat the base steel is clean. There isthe potential that corrosion alreadyexists or has started underneath thecoating.

A hot-dip galvanized coating, onthe other hand, provides both barri-

er and cathodic protec-tion to steel and can-not be chipped away

since it forms adurable metallurgicalbond with the steel.Zinc will also cathodi-cally protect steel fromcorrosion by sacrificingitself at a scratch orslight recess in thecoating.

The alloy layers ofthe zinc coating on gal-vanized rebar are actual-

ly harder than the basesteel, which furtherresists damage due to handling.

FBE rebar actually has a lowerbond strength to concrete than blacksteel. According to studies at theUniversity of California at Berkeley,hot-dip galvanized steel forms a

bond with concrete as strong as thatof black steel.

The AGA publication, FieldHandling Guide: Hot-Dip Galvanizingvs. Fusion Bonded Epoxy, comparesthese two types of rebar. It is avail-

able in pdf format on theWeb site: www.galva-nizeit.org. To receive a sin-gle complimentary copy,please contact the AGA at1-800-468-7732 orby e-mail at:marketing@galvan-izeit.org.

Dear Dr. Galv: What are the differences between hot-dip galvanized reinforcing steel and epoxy-coatedreinforcing steel?

Galvanized rebar can be stored safely on site without fear o

rusting or damage to the galvanized coating.

The coating on hot -d ip galvanized rebar will not becompromised during installation.