Galvanizing for Corrosion Protection (AGA)

1. Galvanizing for
Corrosion Protection:
A Specifier’s Guide to
Reinforcing Steel
Am e r i c a n Ga l v a n i z e r s As s o c i a t i o n

2. Table oof CContents
C CO OR RR RO OS SI IO ON N & & PPR RO OT TE EC CT TI IO ON NO OF F S ST TE EE EL L .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..2 2
Corrosion of Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
How Zinc Protects Steel from Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Barrier Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Cathodic Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
TT
H HE EH HO OT TD DI IP PG GA AL LV VA AN NI IZ ZI IN NG G P PR RO OC CE ES SS S .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..6 6
Surface Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Fluxing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Galvanizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
PP
H HY YS SI IC CA AL L P PR RO OP PE ER RT TI IE ES SO OF F G GA AL LV VA AN NI IZ ZE ED D C CO OA AT TI IN NG GS S .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..8 8
The Metallurgical Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Impact and Abrasion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Corner and Edge Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Complete Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
MM
E EC CH HA AN NI IC CA AL L P PR RO OP PE ER RT TI IE ES SO OF F G GA AL LV VA AN NI IZ ZE ED D S ST TE EE EL L .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..1 10 0
Strength and Ductility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Fatigue Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Mechanical Properties of Galvanized Steel in Concrete . . . . . . . . . . . . . . . . . . . . . . . . .10
Zinc Reaction in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
DD
E ES SI IG GN N, , SSP PE EC CI IF FI IC CA AT TI IO ON N , , FFA AB BR RI IC CA AT TI IO ON NA AN ND D I IN NS ST TA AL LL LA AT TI IO ON N .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..1 12 2
Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Steel Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Detailing of Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Dissimilar Metals in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Bending Bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Storage and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Local Repair of Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Removal of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
FF
I IE EL LD DP PE ER RF FO OR RM MA AN NC CE EO OF F G GA AL LV VA AN NI IZ ZE ED D R RE EI IN NF FO OR RC CE ED D S ST TE EE EL L .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..1 14 4
Horizontal Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Vertical Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

3. 2
INTRODUCTION
Corrosion and repair of corrosion damage are
multi-billion dollar
problems. Observations
on numerous structures
show that corrosion of
reinforcing steel is
either a prime factor, or
at least an important
factor, contributing to
the staining, cracking
and spalling of concrete
structures. These
effects of corrosion
often require costly
repairs and continued
maintenance during the
life of the structure.
Under normal ser-
vice conditions in a
non-aggressive envi-
ronment, Portland
cement concrete pro-
tects the reinforcing
steel against excessive
corrosion if the con-
crete permeability is
low and the steel-con-
crete interface is free of discontinuities such as
voids, cracks, etc. However, when a structure is
exposed to an aggressive environment, or if the
design details or workmanship are inadequate, the
concrete protection may break down and corrosion
of the reinforcement may become excessive.
Galvanized reinforcing steel is effectively
and economically used in concrete in those situa-
tions where black reinforcement will not have ade-
quate durability. Galvanized steel reinforcement is
especially useful where the reinforcement must be
exposed to the weather before construction com-
mences. Galvanizing can provide visible assur-
ance that the steel has not rusted, as well as an
additional safety factor after installation.
The intention of this
guide is to provide infor-
mation on the various fac-
tors involved so specifiers
can draw their own conclu-
sions as to when to specify
galvanized reinforcement.
The guide also provides
guidelines on the specifica-
tion and practices involved
for galvanized reinforce-
ment.
CORROSION OF
STEEL
Rust, the corrosion
product of iron, is the
result of an electrochemi-
cal process. Rust occurs
because of differences in
electrical potential
between small areas on the
steel surface involving
anodes, cathodes and an electrolyte. These differ-
ences in potential on the steel surface are caused
by:
·
variations in composition/structure
·
presence of impurities
·
uneven internal stress
·
presence of a non-uniform environment
These differences in the presence of an elec-
trolyte, a medium for conducting ions, create cor-
rosion cells. Corrosion cells consist of micro-
scopic anodes and cathodes. Because of differ-
Corrosion && PProtection
of SSteel
Corrosion oof rreinforced ssteel ccreates sseverely ddamaging sspalling
(above). GGalvanizing rrebar hhelps pprevent ccorrosion ((below).

4. 3
ences in potential within the cell, negatively
charged electrons flow from anode to cathode and
iron atoms in the anode area are converted to pos-
itively charged iron ions. The positively charged
iron ions (Fe
++
) of the anode attract and react with
the negatively charged hydroxyl ions (OH
-
) in the
electrolyte to form iron
oxide, or rust.
Negatively charged elec-
trons (e
-
) react at the
cathode surface with
positively charged
hydrogen ions (H
+
) in
the electrolyte to form
hydrogen gas. A simpli-
fied picture of what
occurs in this corrosion
cell is shown in Figure 1.
Impurities present in the electrolyte create an
even better medium for the corrosion process. For
example, these impurities can be the constituents
in which the steel is immersed, or present in
atmospheric contaminants, including sulfur
oxides, chlorides or other pollutants present in
damp atmosphere or dissolved in surface moisture.
Calcium hydroxide, present in hardened concrete,
will also act as an electrolyte in the presence of
moisture.
Under normal conditions, concrete is
alkaline with a pH of about 12.5, due
to the presence of calcium
hydroxide. In such an alkaline environment, a pas-
sivating iron oxide film forms on the steel, causing
almost complete inhibition of corrosion. As the pH
of the concrete surrounding the reinforcement is
reduced by intrusion of salts, leaching or carbona-
tion, the passivity is reduced and corrosion may
proceed.
The presence of chloride ions can affect the
inhibitive properties of the concrete in two ways.
The presence of chloride ions creates lattice vacan-
cies in the oxide film, thus providing defects in the
film through which metal ions may migrate more
rapidly and permit corrosion to proceed. This cre-
ates pitting corrosion. Also, if the hydroxyl ion
concentration is reduced, for example by carbona-
tion (reaction of atmospheric carbon dioxide with
calcium hydroxide), the pH is lowered and the cor-
rosion proceeds further. In the presence of oxygen,
inhibition of corrosion occurs at a pH of 12.0. But
as the pH is reduced, the corrosion rate increases.
With reduction of pH to 11.5, the corrosion rate
increases by as much as five times the corrosion
rate at a pH of 12.0.
At an active anodic site, particularly in pits,
the formation of positively charged ferrous ions
attracts negatively charged chloride ions, giving
high concentrations of ferrous chloride. Ferrous
chloride partially hydrolyzes, yielding HCl and an
acid reaction. These reactions reduce protec-
tion at the steel-concrete interface.
At a corroding surface, the pH
may be 6.0 or less.
As mentioned before, the
anode and cathode areas on
a piece of steel are micro-
scopic. Greatly magnified,
the surface might appear as
the mosaic of anodes and
cathodes pictured in Figure 2,
all electrically connected by the
underlying steel.
Moisture in the concrete provides
the electrolyte and completes the electrical path
between the anodes and cathodes on the metal sur-
face. Due to potential differences, a small electric
current begins to flow as the metal is consumed in
the anodic area. The iron ions produced at the
11. . Corrosion of steel is an electrochemical
reaction. Minute differences in structure of
the steel’s chemistry create a mosaic pat-
tern of anodes and cathodes containing
stored electrochemical energy. 22. .
Moisture forms an electrolyte which com-
pletes the electrical path between the
anodes and cathodes, spontaneously releasing
the stored electrochemical energy. A small
electrical current begins to flow, carrying away
particles of the anode areas. The particles given up
combine with the environment to form rust. When salt or
acid is added to the moisture, the flow of electric current, and
corrosion, speeds up. 33. .At this stage, the anodes are corroded and cathodes
protected. However, the instability of the metal itself causes the anodes to
change to cathodes and the corrosion cycle begins again, resulting in uniform cor-
rosion of the entire surface.
Figure 22
Figure 11
1 2
3
Fe
++
+ 2OH
-
FeO + H
2
O
2H
+
+ 2e
-
H
2
gas

5. BARRIERPROTECTION
Zinc is characterized by its amphoteric nature
and its ability to passivate due to the formation of
protective, reaction product films. Reaction of
zinc with fresh cement paste leads to passivity by
formation of a diffusion barrier layer of calcium
hydroxy-zincate. Comparison of the two curves in
Figure 4, emphasizes the importance of the passi-
vating layer for corrosion protection against
chlorides.
CATHODICPROTECTION
Table 1 shows the galvanic series of metals
and alloys arranged in decreasing order of electri-
cal activity. Metals toward the top of the table,
often referred to as less noble metals, have a
greater tendency to lose electrons than the more
noble metals. Thus metals higher in the series pro-
vide cathodic or sacrificial protection to those met-
als below them.
Because zinc is anodic to steel, the galvanized
coating will provide cathodic protection to
exposed steel. When zinc and steel are connected
in the presence of an electrolyte, the zinc is slowly
consumed, while the steel is protected. Zinc’s sac-
rificial action offers protection where small areas
of steel are exposed, such as cut edges, drill holes,
scratches, or as the result of severe surface abra-
sion. Cathodic protection of the steel from corro-
sion continues until all the zinc in the immediate
Figure 44
4
anode combine with the environment to form the
loose, flaky iron oxide known as rust.
As anode areas corrode, new material of dif-
ferent composition and structure is exposed. This
results in a change of electrical potentials and also
changes the location of anodic and cathodic sites.
The shifting of anodic and cathodic sites does not
occur all at once. In time, previously uncorroded
areas are attacked and a uniform surface corrosion
is produced. This process continues until the steel
is entirely consumed.
The corrosion products which form on steel
have much greater volume than the metal from
which they form. This increase in volume exerts
great disruptive tensile stress on the surrounding
concrete. When the pressure is such that the ten-
sile stress in the concrete cover is greater than its
tensile strength, the concrete cracks (Figure 3),
leading to further corrosion. Corrosion cracks are
usually parallel to the reinforcement, and are thus
quite distinct from transverse cracks associated
with tension in the reinforcement caused by load-
ing. As the corrosion proceeds, the longitudinal
cracks widen and, together with structural trans-
verse cracks, may cause spalling of the concrete.
HOWZINCPROTECTSSTEELFROM
CORROSION
The reason for the extensive use of hot dip
galvanizing is the two-fold nature of the coating.
As a barrier coating, it provides a tough, metallur-
gically bonded zinc coating which completely cov-
ers the steel surface and seals the steel from the
corrosive action of the environment. Additionally,
the sacrificial action of zinc protects the steel even
where damage or minor discontinuity occurs in the
coating.
Figure 33
Effect of Chloride Concentration on the Critical
Pitting Potential (after Duval).
Before CorrosionBuild-up of
Corrosion Products
Further Corrosion
Surface Cracks,
Stains
Eventual Spalling
Corroded Bar
Exposed
Zinc
Zinc Passivated by
Ca(OH)
2
for 15 days
0
-200
-400
-600
-800
-1000
-1200
10
-2
10
-1 1
Concentration of Cl-(N)
mV
(SCE)

6. 5
area is consumed.
Both steel and pretreated zinc are normally
passive in the highly alkaline environment of con-
crete. However, penetration of chloride ions to the
metal surface can break down this passivity and
initiate rusting of steel or sacrificial corrosion of
the zinc. The susceptibility of concrete structures
to the intrusion of chlorides is the primary incen-
tive for use of galvanized steel reinforcement.
Galvanized reinforcing steel can withstand
exposure to chloride ion concentrations several
times higher (at least 4-5 times) than what causes
corrosion in black steel reinforcement. While
black steel in concrete typically depassivates
below a pH of 11.5, galvanized reinforcement can
remain passivated at a lower pH, thereby offering
substantial protection against the effects of car-
bonation of concrete.
These two factors combined, namely chloride
tolerance and carbonation resistance, are widely
accepted as the basis for superior performance of
galvanized reinforcement compared to equivalent
black steel reinforcement. The total life of a gal-
vanized coating in concrete is thus made up of the
time taken for the zinc to depassivate, which is
known to be longer than that for black steel,
because of both its higher tolerance to chloride
ions and carbonation resistance, plus the time
taken for the dissolution of the alloy layers in the
coating. Only after the coating has fully dissolved
in a region of the bar will localized corrosion of
the steel commence (Figure 5).
Galvanizing protects the steel during in-
plant and on-site storage, as well as after embed-
ment in the concrete. In areas where the reinforce-
ment may be exposed accidentally, due to thin or
porous concrete, cracking, or damage to the con-
crete, the galvanized coating provides extended
protection. Since the corrosion products of zinc
occupy a smaller volume than the corrosion prod-
ucts of iron, the corrosion which may occur to the
galvanized coating causes little or no disruption to
the surrounding concrete. Recent tests also con-
firm that the zinc corrosion products are powdery,
nonadherent and capable of migrating from the
surface of the galvanized reinforcement into the
concrete matrix reducing the likelihood of zinc
corrosion induced spalling of the concrete. An
additional advantage is that zinc’s corrosion prod-
ucts are grayish white and do not produce unsight-
ly reddish-brown staining.
CORRODED END
Anodic or less noble
(Electronegative)
Magnesium
Zinc
Aluminum
Cadmium
Iron or Steel
Stainless Steels (active)
Soft Solders
Lead
Tin
Nickel
Brass
Bronzes
Copper
Nickel-Copper Alloys
Stainless Steels (passive)
Silver Solder
Silver
Gold
Platinum
PROTECTED END
Cathodic or most noble
(Electropositive)
Table 11
Arrangement oof MMetals iin
Galvanic SSeries:
Any one of these metals and
alloys will theoretically cor-
rode while offering protection
to any other which is lower in
the series, so long as both are
electrically connected.
In actual practice, however,
zinc is by far the most effec-
tive in this respect
Figure 55
C
A B
D E
Time
Zn
Fe
Zn+Fe
Acceptable Limit of Damage
Corrosion
Adapted from Yeomans & Kinstler

7. 6
The hot dip galvanizing process consists
of three basic steps: surface preparation, flux-
ing and galvanizing. Each of these steps is
important in obtaining a quality galvanized
coating (Figure 6).
SURFACEPREPARATION
It is essential for the material surface to be
clean and uncontaminated in order to obtain a uni-
form, adherent coating. Surface preparation is
usually performed in sequence by caustic (alka-
line) cleaning, water rinsing, acid pickling, and
water rinsing.
The caustic cleaner removes organic contam-
inants, including dirt, paint markings, grease, and
oil. Next, scale and rust are removed by a pickling
bath in hot sulfuric acid (150 degrees F) or
hydrochloric acid at room temperature. Water
rinsing usually follows both caustic cleaning and
acid pickling.
Surface preparation can also be accomplished
using abrasive cleaning as an alternate to, or in
conjunction with, chemical cleaning. Abrasive
cleaning is a mechanical process where sand,
metallic shot or grit is propelled against the mate-
rial by air blasts or rapidly rotating wheels.
FLUXING
The final cleaning of the steel is performed by
a flux. The method of applying the flux to the steel
depends upon whether the “wet” or “dry” galva-
nizing process is used. Dry galvanizing requires
the steel to be dipped in an aqueous zinc ammoni-
um chloride solution and then thoroughly dried.
This “preflux” prevents oxides from forming on
the material surface prior to galvanizing. The wet
galvanizing process uses a molten flux layer float-
ed on top of the molten zinc. The final cleaning
occurs as the material passes through the flux layer
before entering the galvanizing bath.
GALVANIZING
The material to be coated is immersed in a
bath of molten zinc maintained at a temperature of
about 850 degrees F. A typical bath chemistry
used in hot dip galvanizing is 98.5 percent pure
zinc. The time of immersion in the galvanizing
bath varies, depending upon the dimensions and
chemistry of the materials being coated. Materials
with thick sections will take longer to galvanize
than those with thin sections.
Surface appearance and coating thickness are
controlled by the galvanizing conditions. These
include: steel chemistry; variations in immersion
time and/or bath temperature; rate of withdrawal
from the galvanizing bath; removal of excess zinc
The HHot DDip GGalvanizing PProcess
Figure 66

8. 7
developed procedures for galvanizing reinforcing
steel, (i.e. “Process Manual for Hot Dip
Galvanized Concrete Reinforcing Steel”) to assure
the galvanized coating will meet not only the min-
imum coating weights for galvanized reinforce-
ment specified in ASTM A 767 “Standard
Specification for Zinc-Coated (Galvanized) Steel
Bars for Concrete Reinforcement,” (Table 2) but
also the other requirements of the standard.
Coating Class Weight of Zinc Coating
min, oz/ft
2
of Surface
Class I
Bar Designation Size No. 3 3.00
Bar Designation Size No. 4 & larger 3.50
Class II
Bar Designation Size 3 & larger 2.00
Table 22
by wiping, shaking or centrifuging; and control of
the cooling rate by water quenching or air cooling.
The American Galvanizers Association has
A ggalvanizer rremoves rreinforcing
steel ffrom tthe bbath oof mmolten zzinc.
Excess zzinc rrunning ooff tthe bbars iis
visible, bbut eenough zzinc hhas bbond-
ed tto tthe ssteel tto pprotect tthe ssteel
from ccorrosion ffor ddecades.

9. 8
THEMETALLURGICALBOND
Hot dip galvanizing is a factory applied coat-
ing which provides a combination of properties
unmatched by other coating systems because of its
unique bond to the steel.
The photomicrograph in Figure 7 shows a
section of a typical hot dip galvanized coating.
The galvanized coating consists of a progression of
zinc-iron alloy layers metallurgically bonded to the
base steel. The metallurgical bond formed by the
galvanizing process ensures no underfilm corro-
sion can occur.
Organic coatings, on the other hand, merely
add a film to the steel which can be penetrated. As
illustrated in Figure 8, once the film is broken, cor-
rosion begins as if no protection existed.
IMPACT ANDABRASIONRESISTANCE
The ductile outer zinc layer provides good
impact resistance to the bonded galvanized coat-
ing. The photomicrograph in Figure 9 shows the
typical hardness values of a hot dip galvanized
coating. The hardness of the zeta and delta layers
is actually greater than the base steel and provides
exceptional resistance to coating damage from
abrasion.
CORNER ANDEDGEPROTECTION
Corrosion often begins at corners or edges of
products which have not been galvanized. Organic
coatings, regardless of application method, are
thinnest at such places.
However, the galvanized coating will be at
least as thick, possibly thicker, on corners and
Physical PProperties oof GGalvanized CCoatings
Figure 77
Figure 88
Figure 99
This is what happens
at a scratch on galva-
nized steel. The zinc
coating sacrifices
itself slowly to pro-
tect the base steel.
This sacrificial
action continues as
long as there is zinc
in the immediate area
ETA
(100% Zn)
ZETA
(94% ZN, 6% Fe)
DELTA
(90%Zn, 10% Fe)
GAMMA
(75%Zn, 25% Fe)
Steel
This is what happens at a scratch on paint- ed steel. The exposed steel corrodes and forms a pocket of rust, which lifts the paint film from the metal surface to form a blister, which will continue to grow. This is what hap- pens at a scratch on steel coated with a less active metal, such as copper. The exposed steel corrodes faster than normal to pro- tect the more noble metal.
Eta Layer
70 Hardness Vickers
Zeta Layer
179 Hardness Vickers
Delta Layer
244 Hardness Vickers
Base Steel
159 Hardness Vickers

10. 9
edges as on the general surface. This provides
equal or extra protection in these critical areas (see
Figure 10).
A GALVANIZEDCOATINGISACOMPLETE
COATING
Because galvanizing is accomplished through
total immersion, all surfaces of the article are fully
coated and protected, including areas inaccessible
and hard to reach with organic coatings.
Additionally, the integrity of any galvanized coat-
ing is ensured because zinc will not metallurgical-
ly bond to unclean steel.
Thus, any uncoated area is immediately
apparent as the work is withdrawn from the molten
zinc. Adjustments are made on the spot, when
Figure 110
required, so a fully protected item is delivered to
the job site. This assures the customer will not
receive a coating which is not properly bonded to
the steel surface.
Because oof ggalvanizing’s uunique, ttough ccoating, tthere’s nno ttip-ttoeing aaround tthe wwork ssite. AA ggalvanized ssurface iis aactually
harder tthan tthe bbase ssteel, sso ggalvanized rrebar iis eextremely rresistant tto ddamage ffrom aabrasion aand oother iinstallation eelements.

11. 10
STRENGTH ANDDUCTILITY
Strength and ductility of reinforcing steel are
important to ensure good performance of rein-
forced concrete and to prevent brittle failure.
Studies of the effect of galvanizing on the mechan-
ical properties of steel reinforcing bars have
demonstrated that the tensile yield and ultimate
strength, ultimate elongation, and bend require-
ments of steel reinforcement were substantially
unaffected by commercial hot-dip galvanizing,
provided that proper attention is given to steel
selection, fabrication practice and galvanizing pro-
cedures.
The effect of the galvanizing process on the
ductility of steel bar anchors and inserts after being
subjected to different fabrication
procedures has also been investi-
gated. The results demonstrated
conclusively that, with correct
choice of steel and galvanizing
procedures, there was no reduc-
tion in the ductility of the steel.
FATIGUESTRENGTH
An extensive experimental
program examining the fatigue
resistance of galvanized steel rein-
forcement showed that:
1. Concrete beams exposed
to cyclic loading in a corro-
sive environment performed
better when reinforced with
galvanized steel.
2. Galvanized steel exposed to calcium
hydroxide solution and subjected to full stress
reversal in a rotary bending tester performed
significantly better than black steel.
3. Deformed reinforcing steel, exposed to an
aggressive environment prior to testing under
cyclic tension loading, performed better when
galvanized.
MECHANICALPROPERTIES OFGALVANIZEDSTEEL
IN
CONCRETE
Good bonding between reinforcing steel and
concrete is essential for reliable performance of
reinforced concrete structures. When protective
coatings on steel are used, it is essential to ensure
Mechanical PProperties oof
Galvanized SSteel
Figure 111
Source: University of California, Berkeley
Concrete-Reinforcing Steel Bond
Study A Study B Study C
1000
800
600
400
200
1 3 12 1 3 121 3 12
Months of Curing
Stress in Pounds Per Square Inch
Galvanized
Black

12. 11
that these coatings do not reduce bond strength.
Studies of the bonding of galvanized and black
steel bars to Portland cement concrete have been
investigated. The results of these studies report the
following:
1. Development of the bond between steel
and concrete depends on age and environ-
ment.
2. In some cases, the time required for devel-
oping full bond strength between steel and
concrete may be greater for galvanized bars
than for black, depending on the zincate
cement reaction.
3. The fully developed bond strength of gal-
vanized and black deformed bars is the same.
For plain bars, the bond strength of gal-
vanized bars is greater than for similar black
bars (Figure 11).
ZINCREACTION INCONCRETE
As stated previously, during curing the galva-
nized 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 embrit-
tlement of the steel due to hydrogen absorption.
Laboratory studies indicate that this “liberated”
hydrogen does not permeate the galvanized coat-
ing to the underlying steel and the reaction ceases
as soon as the concrete has hardened.
Reaction of zincates with fresh Portland
cement mortar may retard set and early strength
development, but later, setting occurs completely
with no detrimental effects on the concrete. In
fact, a positive strength increase occurs.
Most types of cement and many aggregates
contain small quantities of chromates. These chro-
mates passivate the zinc surface, which is then
resistant to attack by fresh concrete. If the cement
and aggregate contain less chromate than will
yield at least 20 ppm in the final concrete mix, the
galvanized bars can be dipped in a chromate solu-
tion or chromates can be added to the water when
the concrete is mixed.
Because oof tthe sstrong bbond sstrength bbetween ggalvanized ssteel
and cconcrete, ggalvanized rrebar iis uused ssuccessfully iin aa vvari-
ety oof aapplications tto pprovide rreliable ccorrosion pprotection.
At aa cconstruction ssite, ggalvanized ffabricated rrebar hhas bbeen
installed aand iis rready ffor cconcrete tto bbe pplaced.

13. DESIGNCRITERIA
When galvanized steel is specified, the design
requirements and installation procedures
employed should be no less stringent than for
structures where non-galvanized reinforcement is
used. There are, in addition, some special require-
ments to be observed when galvanized steel is
used. The following recommendations are intend-
ed as a guide to designers, engineers, contractors
and inspectors. They are intended as a supplement
to other codes and standards dealing with design,
fabrication and construction of reinforced concrete
structures, and deal only with those special consid-
erations which arise due to the use of galvanized
steel in place of black steel reinforcement.
STEELSELECTION
The concrete reinforcing steel to be galva-
nized shall conform to one of the following ASTM
specifications: A 615 (A 615M), A 616 (A 616M),
A 617 (A 617 M) or A 706 (A 706M).
DETAILING OFREINFORCEMENT
Detailing of galvanizing reinforcing steel
should conform to the design specifications for
non-galvanized steel bars and to normal standard
practice consistent with the recommendations of
the Concrete Reinforcing Steel Institute (CRSI).
DISSIMILARMETALS INCONCRETE
Another consideration when
using galvanized reinforcement in
concrete is the possibility of estab-
lishing a bimetallic couple between
zinc and bare steel (i.e. at a break in
the zinc coating or direct contact
between galvanized steel and black
steel bars) or other dissimilar met-
als. A bimetallic couple of this type
in concrete should not be expected
to exhibit corrosive reactions as long as the two metals remain passivated. To insure this is the case, the depth to the zinc/steel contact should not be less than the cover required to protect black steel alone under the same conditions. Therefore, when galvanized reinforcement is used in con- crete, it should not be coupled directly to large areas of black steel reinforcement, copper or other dissimilar metal. Bar supports and accessories should be galvanized. Tie wire should be annealed wire, 16 gauge or heavier, preferably galvanized. If desired, polyethylene and other similar tapes can be used to provide insulation between any dissim- ilar metals.
BENDINGBARS
Hooks or bends should be smooth and not
sharp. Cold bending should be in accordance with
the recommendations of CRSI. When bars are bent
cold prior to galvanizing, they need to be fabricat-
ed to a bend diameter equal to or greater than those
specified in Table 3. Material can be cold bent
tighter than shown in Table 3, if it is stress
relieved at a temperature from 900 to 1050 degrees
F for one hour per inch of bar diameter.
Galvanizers find it difficult, and therefore
costly, to handle bars of small diameter bent into
complicated configurations. It is therefore recom-
mended that the bars be bent after galvanizing
when possible. When galvanizing is performed
Design, SSpecification,
Fabrication, aand IInstallation
Minimum Finished Bend Diameters- Inch-Pound Units
Bar No. Grade 40 Grade 50 Grade 60 Grade 75
3,4,5,6 6 d
A
6d 6d ...
7,8 6 d 8d 8d ...
9,10 8 d 8d 8d ...
11 8 d 8d 8d 8d
14,18 ... ... 10 d 10d
Ad= nominal diameter of the bar
Table 33
12

14. 13
before bending, some cracking and flaking of the
galvanized coating at the bend may occur and is
not a cause for rejection. The tendency for crack-
ing of the galvanized coating increases with bar
diameter and with severity and rate of bending.
STORAGE ANDHANDLING
Galvanized bars may be stored outdoors with
complete assurance. Their general ease of storage
makes it feasible to store standard lengths so that
they are available on demand. Another important
characteristic of galvanized reinforcing steel is that
it can be handled and placed in the same manner as
black steel reinforcement, because of the great
abrasion resistance of galvanized steel.
WELDING
Welding of galvanized reinforcement should
conform to the requirements of the current edition
of the American Welding Society (AWS) Standard
Practice AWS D19.0 “Welding Zinc-Coated
Steel.” Welding of galvanized reinforcement
poses no problems, provided adequate precautions
are taken. These include a slower welding rate
and proper ventilation. The ventilation which is
normally required for welding operations is con-
sidered adequate. Also, heat damaged areas need
to be repaired.
LOCALREPAIR OFCOATING
Local removal of the galvanized coating in
the area of welds, bends, or sheared ends will not
significantly affect the protection offered by galva-
nizing, provided the exposed surface area is small
compared to the adjacent surface area of galva-
nized steel. When the exposed area is excessive,
and gaps are evident in the galvanized coating, the
area can be repaired with a paint containing zinc
dust conforming to ASTM A780 “Standard
Practice for Repair of Damaged and Uncoated
Areas of Hot-Dip Galvanized Coatings.”
REMOVAL OFFORMS
Because cements with low natural occurring
levels of chromates may react with zinc and retard
hardening and initial set, 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 20
ppm of chromates in the final concrete mix or if
the hot dip galvanized bars are chromate passivat-
ed per the requirements of ASTM A 767, Section
5.3.
Standard ssize rreinforcing ssteel, bboth sstraight aand ffabricated ccan
be ggalvanized iin aadvance aand eeasily sstored uuntil nneeded ((top
left). TThe aabrasion rresistant ggalvanized ccoating rrequires nno sspe-
cial hhandling pprocedures ((bottom lleft).

15. 14
Field PPerformance oof GGalvanized
Reinforcement
VERTICALCONSTRUCTION
The Empire Center at The Egg, a performing
arts center in Albany New York, was a massive
undertaking of architecture, combining aesthetics
and function, and concrete and steel designed to
service the citizens of New York state for
decades.
Despite it’s name and elegantly simple
design, The Egg is a pillar of strength— literally.
The Egg balances on a concrete and steel stem
extending six stories into the ground.
The “shell” of The Egg is shaped by a heavi-
ly reinforce concrete “girdle” which helps keep the
egg’s shape and directs the weight of the structure
onto the supporting pedestal and stem.
Adding even more durability to this decep-
tively fragile structure are thousands of miles of
galvanized rebar, weaving in and out of the shell
and stem.
The Egg, underwent construction in 1966,
(left) and took 12 years to build. Today, The Egg
remains a beautiful piece of rust-free architecture.
Extensive uuse oof ggalvanized rreinforcement wwas sspeci-
fied ffor aa hhospital iin AAustralia, iincluding tthis ssurrounding wwall
(above). GGalvanizing wwill hhelp kkeep ccorrosion ffrom ccreating
severe sspalling pproblems iin tthis sstructure, llocated iin ccoastal
city KKatingal, wwhich iis hhome tto aa sseverely ccorrosive mmarine eenvi-
ronment.
The hhousing bbarracks
at tthe UU.S. CCoast
Guard AAcademy wwere
built wwith ggalvanized
reinforcing ssteel tto
protect tthe bbuilding
from ccorrosion aand sspalling ((left).

16. 15
HORIZONTALCONSTRUCTION
In order to combat the corrosive marine envi-
ronment in Bermuda, the U. S. Army Corps of
Engineers built the Longbird Bridge, the first ever
bridge deck exclusively constructed with galva-
nized rebar. The year was 1948, and since then the bridge has per- formed beautifully in this highly corrosive atmosphere.
Inspection 20 years after con-
struction showed no evidence of
deterioration of the concrete, and
core samples found the galvanized
rebar retained about 98 percent of
its zinc coating.
This lead officials to predict
another 80 years of maintenance
free service for the Longbird
Bridge.
Currently, 12 bridges in Bermuda
are fully galvanized, and the Ministry of Works
and Engineering continues to specify galvanized
reinforcement because of its exceptional perfor-
mance.
The sstate oof PPennsylvania’s DDOT mmakes eextensive uuse
of ggalvanized rrebar. TThe bbridge ddeck oof tthe SSchuylkill RRiver
Expressway iin PPhiladelphia ((above), iis pprotected bby 4400 ttons oof
galvanized rrebar. AAfter nnearly aa ddecade oof sservice, tthe rrebar iis
in eexcellent ccondition, eeven iin aareas wwhere tthe cconcrete ccovering
is tthin.
For oover 220 yyears ggalvanized rrebar hhas pprovided tthe BBoca
Chica BBridge nnear KKey WWest, FFlorida ((below) wwith mmaintenance
free ccorrosion pprotection. GGalvanized rrebar hhas hhelped aavoid
traffic-ssnarling rrepairs oof tthis 22,573 ffoot-llong aand 442 ffoot-wwide
bridge. DDespite hheavy ttraffic aand hhumid, ssalt wwater cconditions,
core ssamples sshowed tthe ggalvanized rrebar tto hhave aan aaverage
thickness oof 44 mmils aand nno ssigns oof ccorrosion aare ddetectible.

17. Additional RResources
16
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Adnrade, C. et al. “Corrosion Behavior of Galvanized Steel in Concrete”; 2nd International Conference
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410, 1987.
Arup, H. “The Mechanisms of the Protection of Steel by Concrete”; Society of Chemical Industry
Conference of Reinforcement in Concrete Construction; London, June 1983.
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18. 17
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Yeomans, S.R. and Hadley, M.B. “Galvanized Reinforcement - Current Practice and Developing
Trends”; Australian Corrosion Association Conference, Adelaide, 17pp., November, 1986.
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Coated Reinforcement in Concrete”; ILZRO Project ZE-341, June, 1990.
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Concrete”, Research Report N0. R103, University College, Australian Defense Force Academy, The
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ADDITIONALRESOURCESCONTINUED