This document provides an overview of corrosion protection for reinforcing steel through galvanizing. It discusses how corrosion occurs via electrochemical processes on steel and how zinc protects steel through barrier protection and cathodic protection. The hot dip galvanizing process coats steel in a protective zinc layer. Galvanized steel reinforcement provides corrosion resistance and maintains the mechanical properties of steel in concrete structures.

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 of Contents
CORROSION & PROTECTION OF STEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Corrosion of Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
How Zinc Protects Steel from Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Barrier Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Cathodic Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
THE HOT DIP GALVANIZING PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Surface Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Fluxing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Galvanizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
PHYSICAL PROPERTIES OF GALVANIZED COATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
The Metallurgical Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Impact and Abrasion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Corner and Edge Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Complete Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
MECHANICAL PROPERTIES OF GALVANIZED STEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Strength and Ductility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Fatigue Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Mechanical Properties of Galvanized Steel in Concrete . . . . . . . . . . . . . . . . . . . . . . . . .10
Zinc Reaction in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
DESIGN, SPECIFICATION, FABRICATION AND INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
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
FIELD PERFORMANCE OF GALVANIZED REINFORCED STEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Horizontal Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Vertical Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

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

4. ences in potential within the cell, negatively hydroxide. In such an alkaline environment, a pas-
charged electrons flow from anode to cathode and sivating iron oxide film forms on the steel, causing
iron atoms in the anode area are converted to pos- almost complete inhibition of corrosion. As the pH
itively charged iron ions. The positively charged of the concrete surrounding the reinforcement is
iron ions (Fe++) of the anode attract and react with reduced by intrusion of salts, leaching or carbona-
the negatively charged hydroxyl ions (OH-) in the tion, the passivity is reduced and corrosion may
Figure 1 electrolyte to form iron proceed.
oxide, or rust. The presence of chloride ions can affect the
Negatively charged elec- inhibitive properties of the concrete in two ways.
trons (e-) react at the The presence of chloride ions creates lattice vacan-
cathode surface with cies in the oxide film, thus providing defects in the
positively charged film through which metal ions may migrate more
hydrogen ions (H+) in rapidly and permit corrosion to proceed. This cre-
the electrolyte to form ates pitting corrosion. Also, if the hydroxyl ion
hydrogen gas. A simpli- concentration is reduced, for example by carbona-
Fe++ + 2OH- FeO + H2O fied picture of what tion (reaction of atmospheric carbon dioxide with
2H+ + 2e- H2 gas
occurs in this corrosion calcium hydroxide), the pH is lowered and the cor-
cell is shown in Figure 1. rosion proceeds further. In the presence of oxygen,
Impurities present in the electrolyte create an inhibition of corrosion occurs at a pH of 12.0. But
even better medium for the corrosion process. For as the pH is reduced, the corrosion rate increases.
example, these impurities can be the constituents With reduction of pH to 11.5, the corrosion rate
in which the steel is immersed, or present in increases by as much as five times the corrosion
atmospheric contaminants, including sulfur rate at a pH of 12.0.
oxides, chlorides or other pollutants present in At an active anodic site, particularly in pits,
damp atmosphere or dissolved in surface moisture. the formation of positively charged ferrous ions
Calcium hydroxide, present in hardened concrete, attracts negatively charged chloride ions, giving
will also act as an electrolyte in the presence of high concentrations of ferrous chloride. Ferrous
moisture. chloride partially hydrolyzes, yielding HCl and an
Under normal conditions, concrete is acid reaction. These reactions reduce protec-
alkaline with a pH of about 12.5, due tion at the steel-concrete interface.
to the presence of calcium At a corroding surface, the pH
Figure 2 may be 6.0 or less.
1. Corrosion of steel is an electrochemical As mentioned before, the
reaction. Minute differences in structure of
the steel’s chemistry create a mosaic pat- anode and cathode areas on
tern of anodes and cathodes containing a piece of steel are micro-
stored electrochemical energy. 2. scopic. Greatly magnified,
Moisture forms an electrolyte which com- 1 2
pletes the electrical path between the
the surface might appear as
anodes and cathodes, spontaneously releasing the mosaic of anodes and
the stored electrochemical energy. A small cathodes pictured in Figure 2,
electrical current begins to flow, carrying away all electrically connected by the
particles of the anode areas. The particles given up
combine with the environment to form rust. When salt or 3 underlying steel.
acid is added to the moisture, the flow of electric current, and Moisture in the concrete provides
corrosion, speeds up. 3. At this stage, the anodes are corroded and cathodes the electrolyte and completes the electrical path
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- between the anodes and cathodes on the metal sur-
rosion of the entire surface. 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
3

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

6. Table 1
galvanized reinforcement compared to equivalent
CORRODED END black steel reinforcement. The total life of a gal-
Anodic or less noble Arrangement of Metals in
vanized coating in concrete is thus made up of the
(Electronegative) Galvanic Series:
time taken for the zinc to depassivate, which is
Magnesium Any one of these metals and known to be longer than that for black steel,
Zinc alloys will theoretically cor- because of both its higher tolerance to chloride
Aluminum rode while offering protection
Cadmium ions and carbonation resistance, plus the time
to any other which is lower in
Iron or Steel taken for the dissolution of the alloy layers in the
Stainless Steels (active) the series, so long as both are
electrically connected. coating. Only after the coating has fully dissolved
Soft Solders
Lead in a region of the bar will localized corrosion of
Tin In actual practice, however, the steel commence (Figure 5).
Nickel zinc is by far the most effec-
Figure 5
Brass tive in this respect
Bronzes
Copper Acceptable Limit of Damage
Nickel-Copper Alloys Zn+Fe
Stainless Steels (passive)
Silver Solder Fe
Corrosion
Silver
Gold
Platinum Zn
PROTECTED END A B
Time
Cathodic or most noble C D E
(Electropositive)
Adapted from Yeomans & Kinstler
area is consumed. Galvanizing protects the steel during in-
Both steel and pretreated zinc are normally plant and on-site storage, as well as after embed-
passive in the highly alkaline environment of con- ment in the concrete. In areas where the reinforce-
crete. However, penetration of chloride ions to the ment may be exposed accidentally, due to thin or
metal surface can break down this passivity and porous concrete, cracking, or damage to the con-
initiate rusting of steel or sacrificial corrosion of crete, the galvanized coating provides extended
the zinc. The susceptibility of concrete structures protection. Since the corrosion products of zinc
to the intrusion of chlorides is the primary incen- occupy a smaller volume than the corrosion prod-
tive for use of galvanized steel reinforcement. ucts of iron, the corrosion which may occur to the
Galvanized reinforcing steel can withstand galvanized coating causes little or no disruption to
exposure to chloride ion concentrations several the surrounding concrete. Recent tests also con-
times higher (at least 4-5 times) than what causes firm that the zinc corrosion products are powdery,
corrosion in black steel reinforcement. While nonadherent and capable of migrating from the
black steel in concrete typically depassivates surface of the galvanized reinforcement into the
below a pH of 11.5, galvanized reinforcement can concrete matrix reducing the likelihood of zinc
remain passivated at a lower pH, thereby offering corrosion induced spalling of the concrete. An
substantial protection against the effects of car- additional advantage is that zinc’s corrosion prod-
bonation of concrete. ucts are grayish white and do not produce unsight-
These two factors combined, namely chloride ly reddish-brown staining.
tolerance and carbonation resistance, are widely
accepted as the basis for superior performance of
5

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

8. by wiping, shaking or centrifuging; and control of developed procedures for galvanizing reinforcing
the cooling rate by water quenching or air cooling. steel, (i.e. “Process Manual for Hot Dip
The American Galvanizers Association has Galvanized Concrete Reinforcing Steel”) to assure
the galvanized coating will meet not only the min-
Table 2
imum coating weights for galvanized reinforce-
Coating Class Weight of Zinc Coating ment specified in ASTM A 767 “Standard
min, oz/ft2 of Surface Specification for Zinc-Coated (Galvanized) Steel
Class I
Bars for Concrete Reinforcement,” (Table 2) but
Bar Designation Size No. 3 3.00
Bar Designation Size No. 4 & larger 3.50 also the other requirements of the standard.
Class II
Bar Designation Size 3 & larger 2.00
A galvanizer removes reinforcing
steel from the bath of molten zinc.
Excess zinc running off the bars is
visible, but enough zinc has bond-
ed to the steel to protect the steel
from corrosion for decades.
7

9. Physical Properties of Galvanized Coatings
Figure 7 THE METALLURGICAL BOND
Hot dip galvanizing is a factory applied coat-
ETA ing which provides a combination of properties
(100% Zn)
ZETA unmatched by other coating systems because of its
(94% ZN, 6% Fe)
DELTA unique bond to the steel.
(90%Zn, 10% Fe) The photomicrograph in Figure 7 shows a
GAMMA
(75%Zn, 25% Fe) section of a typical hot dip galvanized coating.
Steel
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.
Figure 8
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.
This is what happens This is what happens This is what hap-
IMPACT AND ABRASION RESISTANCE
at a scratch on galva- at a scratch on paint- pens at a scratch on The ductile outer zinc layer provides good
nized steel. The zinc ed steel. The exposed steel coated with a
coating sacrifices steel corrodes and less active metal, impact resistance to the bonded galvanized coat-
itself slowly to pro- forms a pocket of such as copper.
tect the base steel. rust, which lifts the The exposed steel ing. The photomicrograph in Figure 9 shows the
This sacrificial paint film from the corrodes faster
action continues as metal surface to form than normal to pro- typical hardness values of a hot dip galvanized
long as there is zinc a blister, which will tect the more noble
in the immediate area continue to grow. metal. 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.
Figure 9
CORNER AND EDGE PROTECTION
Eta Layer
Corrosion often begins at corners or edges of
70 Hardness Vickers
Zeta Layer products which have not been galvanized. Organic
179 Hardness Vickers coatings, regardless of application method, are
Delta Layer thinnest at such places.
244 Hardness Vickers
Base Steel However, the galvanized coating will be at
159 Hardness Vickers least as thick, possibly thicker, on corners and
8

10. edges as on the general surface. This provides required, so a fully protected item is delivered to
equal or extra protection in these critical areas (see the job site. This assures the customer will not
Figure 10). receive a coating which is not properly bonded to
the steel surface.
A GALVANIZED COATING IS A COMPLETE Figure 10
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
Because of galvanizing’s unique, tough coating, there’s no tip-toeing around the work site. A galvanized surface is actually
t
harder than the base steel, so galvanized rebar is extremely resistant to damage from abrasion and other installation elements.
9

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

12. 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
At a construction site, galvanized fabricated rebar has been
cement reaction. installed and is ready for concrete to be placed.
3. The fully developed bond strength of gal-
vanized and black deformed bars is the same. ZINC REACTION IN CONCRETE
For plain bars, the bond strength of gal- As stated previously, during curing the galva-
vanized bars is greater than for similar black
bars (Figure 11). 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
Because of the strong bond strength between galvanized steel
and concrete, galvanized rebar is used successfully in a vari- galvanized bars can be dipped in a chromate solu-
ety of applications to provide reliable corrosion protection. tion or chromates can be added to the water when
the concrete is mixed.
11

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

14. before bending, some cracking and flaking of the WELDING
galvanized coating at the bend may occur and is
Welding of galvanized reinforcement should
not a cause for rejection. The tendency for crack-
conform to the requirements of the current edition
ing of the galvanized coating increases with bar
of the American Welding Society (AWS) Standard
diameter and with severity and rate of bending.
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.
LOCAL REPAIR OF COATING
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
STORAGE AND HANDLING dust conforming to ASTM A780 “Standard
Practice for Repair of Damaged and Uncoated
Galvanized bars may be stored outdoors with
Areas of Hot-Dip Galvanized Coatings.”
complete assurance. Their general ease of storage
makes it feasible to store standard lengths so that
they are available on demand. Another important REMOVAL OF FORMS
characteristic of galvanized reinforcing steel is that Because cements with low natural occurring
it can be handled and placed in the same manner as levels of chromates may react with zinc and retard
black steel reinforcement, because of the great hardening and initial set, it is important to ensure
abrasion resistance of galvanized steel. 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 size reinforcing steel, both straight and fabricated can
be galvanized in advance and easily stored until needed (top
left). The abrasion resistant galvanized coating requires no spe-
cial handling procedures (bottom left).
13

15. Field Performance of Galvanized
Reinforcement
VERTICAL CONSTRUCTION
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.
The housing barracks Extensive use of galvanized reinforcement was speci-
at the U.S. Coast fied for a hospital in Australia, including this surrounding wall
Guard Academy were (above). Galvanizing will help keep corrosion from creating
built with galvanized severe spalling problems in this structure, located in coastal
reinforcing steel to city Katingal, which is home to a severely corrosive marine envi-
protect the building ronment.
from corrosion and spalling (left).
14

16. HORIZONTAL CONSTRUCTION
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
In order to combat the corrosive marine envi- are fully galvanized, and the Ministry of Works
ronment in Bermuda, the U. S. Army Corps of and Engineering continues to specify galvanized
Engineers built the Longbird Bridge, the first ever reinforcement because of its exceptional perfor-
bridge deck exclusively constructed with galva- mance.
For over 20 years galvanized rebar has provided the Boca
Chica Bridge near Key West, Florida (below) with maintenance
free corrosion protection. Galvanized rebar has helped avoid
traffic-snarling repairs of this 2,573 foot-long and 42 foot-wide
s l w
bridge. Despite heavy traffic and humid, salt water conditions,
core samples showed the galvanized rebar to have an average
thickness of 4 mils and no signs of corrosion are detectible.
The state of Pennsylvania’s DOT makes extensive use
of galvanized rebar. The bridge deck of the Schuylkill River
Expressway in Philadelphia (above), is protected by 400 tons of
galvanized rebar. After nearly a decade of service, the rebar is
in excellent condition, even in areas where the concrete covering
is thin.
15

17. Additional Resources
ACI Committee 222. “Corrosion of Metals in Concrete”; American Concrete Institute, 222R-85, 1985.
Adnrade, C. et al. “Corrosion Behavior of Galvanized Steel in Concrete”; 2nd International Conference
on Deterioration and Repair of Reinforced Concrete in the Arabian Gulf; Proceedings Vol. 1, pp. 395-
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.
Structures - A Scientific Assessment”; CSIRO Paper, Sydney, 1979.
Bird, C.E. “Bond of Galvanized Steel Reinforcement in Concrete”; Nature, Vol. 94, No. 4380, 1962.
Breseler B. and Cornet I. “Galvanized Steel Reinforcement in Concrete”; 7th Congress of the
International Association of Bridge and Structural Engineers, Rio de Janeiro, 1964.
Chandler, K.A. and Bayliss, D.A. “Corrosion Protection of Steel Structures”; Elsevier Applied Science
Publishers, pp. 338-339, 1985.
Cornet, I. and Breseler, B. “Corrosion of Steel and Galvanized Steel in Concrete’; Materials Protection,
Vol. 5, No. 4, pp.69-72, 1966.
Concrete Institute of Australia. “The use of Galvanized Reinforcement in Concrete”; Current Practice
Note 17, September 1984. ISBN 0 909375 21 6.
Duval, R. and Arliguie, G.; Memoirs Scientifiques Rev. Metallurg.; LXXI, No. 11, 1974.
Galvanizers Association of Australia. “Hot Dip Galvanizing Manual”; 1985.
Hime, W. and Erlin, B. “Some Chemical and Physical Aspects of Phenomena Associated with Chloride-
Induced Corrosion”; Corrosion, Concrete and Chlorides; Steel Corrosion in Concrete: Causes and
Restraints; ACI SP-102, 1987.
Hosfoy, A.E. and Gukild, I. “Bond Studies of Hot Dipped Galvanized Reinforcement in Concrete”; ACI
Journal, March, pp. 174-184, 1969.
India Lead Zinc Information Centre. “Protection of Reinforcement in Concrete, An Update,
Galvanizing and Other Methods”; New Delhi, 1995.
International Lead Zinc Research Organization. “Galvanized Reinforcement for Concrete - II”; USA,
1981.
16

18. ADDITIONAL RESOURCES CONTINUED
Kinstler, J.K. “Galvanized Reinforcing Steel - Research, Survey and Synthesis”; International Bridge
Conference Special Interest Program, Pittsburgh, PA, 1995.
MacGregor, B.R. “Galvanized Solution to Rebar Corrosion”; Civil Engineering, UK, 1987.
Page, C.L. and Treadway, K.W.J. “Aspects of the Electrochemistry of Steel in Concrete”; Nature,V297,
May 1982, pp. 109-115.
Portland Cement Association. “An Analysis of Selected Trace Metals in Cement and Kiln Dust”; PCA
publication SP109, 1992.
Roberts, A.W. “Bond Characteristics of Concrete Reinforcing Tendons Coated with Zinc”; ILZRO
Project ZE-222, 1977.
Tonini, D.E. and Dean, S.W. “Chloride Corrosion of Steel in Concrete”; ASTM-STP 629, 1976.
Warner, R.F., Rangan, B.V., and Hall, A.S. “Reinforced Concrete”; Longman Cheshire, 3rd edition, pp.
163-169, 1989.
Worthington, J.C., Bonner, D.G. and Nowell, D.V. “Influence of Cement Chemistry on Chloride Attack
of Concrete”; Material Science and Technology; Vol., pp. 305-313, 1988.
Yeomans, S.R. and Hadley, M.B. “Galvanized Reinforcement - Current Practice and Developing
Trends”; Australian Corrosion Association Conference, Adelaide, 17pp., November, 1986.
Yeomans, S.R. “Corrosion Behavior and Bond Strength of Galvanized Reinforcement and Epoxy
Coated Reinforcement in Concrete”; ILZRO Project ZE-341, June, 1990.
Yeomans, S.R. “Comparative Studies of Galvanized and Epoxy Coated Steel Reinforcement in
Concrete”, Research Report N0. R103, University College, Australian Defense Force Academy, The
University of New South Wales, 1991.
Yeomans, S.R. “Considerations of the Characteristics and Use of Coated Steel Reinforcement in
Concrete”; Building and Fire Research Laboratory, National Institute of Standards and Technology,
U.S. Department of Commerce, 1993.
17