Purdue University
Purdue e-Pubs Joint Transportation Research Program
Civil Engineering
1-1999
Steel Bridge Protection Policy: Evaluation of Bridge Coating system for INDOT Steel Bridges Luh M. Chang Tarek Zayed Jon D. Fricker
Recommended Citation Chang, L. M., T. Zayed, and J. D. Fricker. Steel Bridge Protection Policy: Evaluation of Bridge Coating system for INDOT Steel Bridges. Publication FHWA/IN/JTRP-98/21-II. Joint Transportation Research Program, Indiana Department of Transportation and Purdue University, West Lafayette, Indiana, 1999. doi: 10.5703/1288284313319 This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact
[email protected] for additional information.
1
Joint
Transportation
Research
Program
JTRP FHW A/IN/JTRP-98/2 Final Report
Steel
Bridge Protection Policy
Volume II of V Evaluation of Bridge Coating System for INDOT Steel Bridges
Luh-Maan Chang Seunghyun Chung
May
1999
Indiana
Department of Transportation
Purdue University
FINAL REPORT
STEEL BRIDGE PROTECTION POLICY
VOLUME
II
EVALUATION OF BRIDGE COATING SYSTEMS FOR INDOT STEEL BRIDGES FHWA/IN/JTRP-98/21
by
Luh-Maan Chang Principal Investigator
and
Seunghyun Chung Research Assistant
Purdue University School of Civil Engineering Joint Transportation Research
Program
Project No.: C-36-26J File No.: 4-4-10
Prepared in Cooperation with the Indiana Department of Transportation and
The U.S. Department of Transportation Federal Highway Administration The contents of this
report reflect the views
of the authors who are responsible
for the facts
and the accuracy of the data presented herein. The contents do not necessarily official
reflect the
views of the Federal Highway Administration and the Indiana Department of
Transportation. This report does not constitute a standard, a specification, or a regulation.
Purdue University
West
Lafayette, Indiana
May
27, 1999
47907
TECHNICAL REPORT STANDARD TITLE PAGE Report No.
1.
2.
Government Accession No.
Catalog No.
3. Recipient's
FHWA/LN/JTRP-98/21 4. Title
and
Subtitle
Report Date
5.
May Steel
1999
Bridge Protection Policy
Volume II of"V: Evaluation ofBridge Coating System for INDOT Steel Bridges
7.
Authors)
6.
Performing Organization Code
8.
Performing Organization Report No.
Luh-Maan Chang, Seunghyun Chung
FHWATN/JTRP-98/21 9.
Performing Organization
Joint Transportation
Name and
Address
10.
Work Unit No.
Research Program
1284 Civil Engineering Building
Purdue University
West Lafayette, Indiana 47907-1284 11.
Contract or Grant No.
13.
Type ofReport and Period Covered
SPR-2038 12.
Sponsoring Agency
Name and Address
Indiana Department of Transportation Final Report
State Office Building
100 North Senate Avenue Indianapolis,
IN 46204 14.
15.
Sponsoring Agency Code
Supplementary Notes
Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. 16.
Abstract
The study
identifies various painting
systems that are successfully used in Indiana's surrounding states and other industries. The identified
systems are further screened and evaluated. After prudently comparing
INDOT' s
inorganic zinc
/
vinyl system with the
system, the moisture cure urethane coating svstem, and the 3-coat system of zinc-epoxv-urethane, the results fulfills
INDOT's
needs with the most benefits. Therefore, the 3-coat system
is
recommended
to replace
show
INDOT
waterbome
that the
new
acrylic
3-coat svstem
present inorganic zinc
/
vinyl
system.
To
deal with the problems facing the lead-based paint, a comparison
between full-removal and over-coating
might provide a good protection for
of full-removal; however
that over-coating
less than half the cost
it
alternatives is
made. Results show
delays the lead full-removal process and
does not completely solve the environmental problem.
The metalization of steel bridges is seemingly a potential protection policy. After reviewing standards and specifications on metalization, shown that metalization jobs require a higher degree of control. It suits on-shop practices, however, the initial cost is considerably high. This study also describes a
life
was done to determine an optimal painting system for INDOT. Herein, a deterministic method of Markov chains process are used. The analysis not only reconfirms that the 3-coat painting system, but also generates an optimal painting maintenance plan for INDOT.
cycle cost analysis that
method of economic analysis and a system
To
is
it is
the comparatively better
stochastic
assure the quality of paint material and workmanship after substantial completion of the painting contract, the development of legally is initiated in this study. The developed painting warranty clauses were primarily derived from the IDOT, MDOT, and INDOT's pavement warranty clauses. A comparative study was conducted on eleven Among them, it was found that the warranty period, the definition of "defect", and the amount of the warranty bond all
binding and dependable warranty clauses painting warranty clauses used by essential categories.
need further evaluation.
17.
KeyWords
coating, inspection, life cycle cost analysis,
18. Distribution
Markov Chains
Process,
metalization, painting, quality control, steel bridge, warranty
Statement
No restrictions.
This document
available to the public through the
is
National Technical Information Service, Springfield,
VA 22161
Clauses.
19. Security Classif. (of this report)
Unclassified
Form
DOT F
1700.7 (8-69)
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
98
22. Price
TABLE OF CONTENTS ABSTRACT LIST OF TABLES
i
iii
INTRODUCTION PROBLEM STATEMENT
CHAPTER I
/
1
1.1
Objectives
3
1.2
Scope of Study Method of Study
4
1.3
INDOT'S CURRENT COATING SYSTEM
6
Inorganic Zinc and Vinyl Coating System Problems Facing the Volatile Organic Compound Problems with the Lead-Based Paints
6
CHAPTER II 2.1
2.2 2.3
CHAPTER III
COATING SYSTEMS FOR STEEL BRIDGES
Inorganic
3.1
/
Organic zinc, Epoxy, and Urethane Coating System / Organic Zinc Primer
3.1.1
Inorganic
3.1.2
Epoxy Intermediate Coat
3.1.3
Urethane Topcoat
3.1.4
Comments
Waterbome Acrylic Coating Moisture Cure Urethane Coating System Inorganic Zinc and
3.2 3.3
3.3.1
Composition
3.3.2
Comments
Discussions
3.4
5
10 10
12
12 1
22 24 26 31
33 33
34 39
CHAPTER IV OVERCOATING VS. FULL-REMOVAL
42
CHAPTER V
54
REFERENCES Appendix Appendix Appendix Appendix
CONCLUSIONS
56
A: Sample Specification for Epoxy and Urethane 58 B: Qualified Product List C: Comparison of Specifications D: Factors Affecting Performance and Durability of Overcoating Systems
Digitized by the Internet Archive in
2011 with funding from
LYRASIS members and Sloan Foundation;
Indiana Department of Transportation
http://www.archive.org/details/steelbridgeprote9821chan
1
LIST OF TABLES
TABLE
3.1
Inorganic Zinc vs. Organic Zinc
21
TABLE
3.2
OZEU
29
TABLE
3.3
1
TABLE
3.4
Costs of Surface Preparation
35
TABLE
3.5
A Comparison of Various Paints Used for Coating Systems
38
TABLE
3.6
Comparison of Coating Systems
40
TABLE
4.1
A Comparison of Costs
45
TABLE
4.2
Cost Distribution
TABLE
4.3
Selected Coating System Lifetimes from
Bridge Painting Cost History
996 Bridge Paint Costs Lowbid
-
30
for Full-removal vs. Overcoating
Full-removal
vs.
Overcoating
SSPC PACE
47 5
CHAPTER I INTRODUCTION PROBLEM STATEMENT /
After
many
years of efforts to improve the paint quality of steel bridges, in 1996,
Indiana Department of Transportation
in search for
more
(INDOT) has decided
efficient coating systems.
INDOT's
to
conduct further research
current steel bridge coating system
of inorganic zinc and vinyl, a two coat system, has been accepted. But due
Compound (VOC)
environmental concerns, such as the high Volatile Organic the vinyl paint system and the relatively short useful
life
to
of the system
left
growing
present in
more
to
be
desired.
The revised environmental
regulations require the identification and removal of
lead-based paints, containment and disposal of lead paint debris, reduction of
in paints,
forced
and increased
INDOT to
efforts
identify
and
toward worker
safety.
utilize a different coating
VOC
level
These tougher regulations have system for
their steel bridges.
In choosing a bridge coating system, numerous environmental and economical
concerns must be addressed. The main goal for painting of bridges are for long-lasting corrosion protection and improvement of
its
aesthetics at a
minimum
cost.
The selection
of right coating system for the particular bridge involves careful consideration of
numerous aspects such
as the type of bridge, environmental surroundings, use
of the
bridge, location of the bridge, and economic concerns to mention but a few.
The of the
steel.
first
objective of the coating system
The primer
in a coating
is to
prevent or slow
down
the corrosion
system serves as the main protector from corrosion
attacks.
It
usually
contains
rust
inhibitive
pigments
reduce
that
corrosion.
The
intermediate coat and the topcoat are used to provide a barrier of protection from
moisture permeation,
UV
from the environment. The
protection, and constant attacks
second objective of the coating system
is
for aesthetics.
The
color of the topcoat
usually selected to harmonize with the adjacent topographic features.
quality for a topcoat in a coating system
is
An
is
important
the ability to retain the original color and
gloss.
With today's technology many for various condition
paint materials and coating systems are available
and location of the bridge. Therefore,
it
can be said that the
efficiency and the effectiveness of the coating system are mainly dependent
on the
owner's needs, wants, and budget. Today's paint technology allows the owner to customize the bridge coating system to meet his/her needs.
An
economically attractive
coating system will only give a short amount of protection but the short protecting
duration might equal the bridge's useful
will last over
right coating
life.
There
is
no need
30 years when the bridge only has 15 years of system for a particular bridge
is difficult.
By
its
for a coating
useful
life.
system that
Choosing the
these reasons, nowadays,
many
endeavors are poured into the decision making process of selecting that "perfect" coating system.
1.1
OBJECTIVE With growing concern over environmental
with tougher regulations
set
by the government
issues, the bridge
owners are faced
for environmental protection.
include the identification and removal of lead-based paints and the reduction of
level in paints.
alternative
The new,
tougher, regulations have forced
advanced bridge coating systems
In selecting the right coating system,
considered.
The remaining main
owner must review
in the selection process.
The
use,
objective of this study
coating system for
many
is
to identify
INDOT. Various
bridge owners to seek
aspects of the bridge must be carefully
economic concerns,
its
VOC
in order to satisfy the requirements.
useful life of the bridge,
surrounding areas,
many
These
environmental impacts of the
etc. are
some of
the things that an
and recommend an advanced
steel bridge
bridge coating systems will be presented and
analyzed. This will be accomplished through extensive literary search, expert interviews,
evaluation of test result from government agencies and information collected from
various bridge owners.
system, a
recommended
By comparing
the advantages and disadvantages of each coating
coating system for
INDOT will be made.
SCOPE OF STUDY
1.2
This
study
evaluates
alternative coating system to
meet
The
performance requirement.
INDOT's
various
all
bridge-coating
and recommends
environmental regulations and satisfy
identified
current system of inorganic zinc
recommended system. The
systems
coating
systems
and vinyl
will
an
INDOT's
be compared with of the newly
to verify benefits
analysis procedure will be performed through extensive
literature search, expert interviews, test results
from government agencies, discussion
with paint manufacturers, and collection of experiences from bridge owners across the
country.
The problems
overcoating alternative
1.
The
is
facing the current system are observed and the evaluation of
presented.
The scope of this study
identification of advanced coating systems
is
as follows.
were accomplished through various
publications, interviews with paint manufacturers and bridge owners in
2.
The performance through the
verification of the presented coating systems
test results
Highway Research 3.
Although many
all
places.
was accomplished
from the Steel Structure Painting Council, the Turner-Fairbank
Center, and expert interviews.
steel bridge coating
considered for the comparison in
environment conditions
to Indiana
systems have been evaluated, some were not this
study.
were chosen
Areas with similar weather and for the comparison.
The coating
systems for the evaluation were selected from Ohio Department of Transportation
(ODOT),
Illinois
Transportation
Department of Transportation (IDOT), and Michigan Department of
(MDOT).
1.3
METHOD OF STUDY In this report, evaluations of various bridges coating systems are presented.
Indiana's need for a
new
bridge coating system will be stated and the current coating
system's performance will be analyzed. Indiana's bridge coating system will serve as a
base for comparison with other neighboring
Michigan and
Illinois will
states.
be evaluated. Through
Bridge coating systems from Ohio,
literary search, interviews
with the
bridge owners and paint manufacturers the coating systems will be studied and
its
merits
and demerits will be discussed. The costs associated with some of the painting systems will also
be presented. Also, other aspects of coating system, such as the need
for a
new
coating system and the issue of full-removal versus overcoating are discussed. This report
will be evaluated and consulted with
INDOT
system suitable for INDOT's applications.
committee members
to prescribe a coating
CHAPTER II INDOT'S CURRENT COATING SYSTEM
Currently the inorganic zinc and vinyl two-coat coating system
by
INDOT
for
many
years.
It
is
being utilized
has replace the antiquated lead-based system but
facing problems concerning the environment and
its
is
questionable performance.
now
Many
years ago, the vinyl coating system replaced the lead-based system due to problems
But now, with growing concerns over the high
relating to the lead-based paints.
level
of the
vinyl,
INDOT
has decided to search for a
new
VOC
coating system for their
bridges.
2.1
INORGANIC ZINC AND VINYL COATING SYSTEM As mentioned
above,
INDOT
is
currently using the inorganic zinc and vinyl two-
coat coating system for their bridges. With the high
relatively short useful
color retention,
life,
INDOT
and due
to
section, characteristics of vinyl will be discussed.
There
are,
level of the vinyl paint,
performance problems such as pinholes and poor
has decided to search for a
zinc will be presented in chapter
VOC
new
bridge coating system. In this
A detailed observation of the
inorganic
3.
generally, three types of vinyl binders available:
PVB, Polyvinyl
butyral resins, Polyvinyl Chloride and Polyvinyl Acetate, and Vinyl-Alkyd.
When PVB
or Polyvinyl butyral resins are combined with zinc chromate pigments and phosphoric
acid, the adhesion characteristic
of the paint
in
improved
greatly.
With some vinyl paint
may be
systems which
sensitive to surface conditions but offer excellent resistance and
durability the adhesion enhancing characteristic of PVB
is critical.
For extreme conditions such as marine or corrosive environments, the Polyvinyl Chloride and Polyvinyl Acetate resins offer great protection by producing lacquers that dry rapidly from solvent evaporation.
result
of
this
reaction
which
act
as
An
produced
as a
a barrier against any harsh environments.
The
extremely durable coatings
Polyvinyl Chloride and Polyvinyl Acetate resins are low
is
solids
is
which necessitates
for
multiple coats and are very sensitive to surface preparation. Vinyl are extremely resistant
(except to strong solvents), durable in most environments and can also be used for lining
tanks for water immersion service.
For most environments, a combination of hydroxyl modified vinyl and alkyd resin, the
is
Vinyl-Alkyd will be recommended.
easier to apply,
However, they
It is
has higher solid content and
it
are not
recommended
less sensitive to surface preparation,
it
it
offers excellent exterior durability.
for highly corrosive environments.
Numerous advantages and disadvantages of vinyl can be
realized.
The following
are the advantages:
1
Vinyls have excellent
stability during use.
2.
Vinyls have excellent
flexibility characteristics.
3.
Vinyls have very good resistance to abrasion, acid, water, and
4.
Vinyls have low moisture permeability.
5.
Vinyls offer excellent protection
to
normal, marine, and corrosive
exposure.
The following 1
.
are the disadvantages of using the vinyl:
Vinyl topcoat fade unevenly.
7
2
alkali.
2.
Vinyls have poor brushability.
3.
Vinyls have poor resistance to strong solvents.
4.
Vinyls only scored
6.
Vinyls do not have very good color and gloss retention.
7.
4 Vinyls do not have good performance record against chalk resistance.
8.
Vinyls have high
9.
When
states,
felt that
VOC. 4
full
include the fact that
industrial
it
was
is
Some
inadequate.
less costly
is
bond with
application to help the vinyls react and
applied the surface will bubble.
including Indiana, have utilized or are
it
4
applied to inorganic zinc, if no miss coat, a thin coat of vinyl
zinc/vinyl bridge coating system.
to a study
UV exposure.
test.
3
Vinyls will chalk upon
the inorganic zincs,
while others
adhesion
5.
applied before
Many
fair in the
states
Some
had good
still
results
4
utilizing the inorganic-
with
this coating
positive aspects of the vinyl coating system
when compared
According
to other coating systems.
performed by Tumer-Fairbank Highway Research Center, "in relation maintenance coatings, vinyls are generally the
least
expensive."
also noted for their easy handling characteristics. In Clive Hare's
steel bridges,
he
states,
system
"West Virginia expects
thirty years
3
The
to other
vinyls are
book about painting of
of service from the system.
Apart from some early delamination problems, West Virginia has so far not needed to repaint
any
structures.
topcoat systems
made of fifteen
is
...
In most cases, the service
most excellent; even
years and
in relatively
more of service."
Although the service
life
more recent coating systems
of these inorganic zinc
demanding zones.
...
/
vinyl
Claims are
3
of around 15 years seemed adequate during the
1970's to early 1980's, by today's standard
for
life
it fall
below par of 25
to
late
30 years predicted
available, such as the inorganic/organic zinc, epoxy,
and
urethane three coat system. The general consensus
zinc and vinyl
fall
short
when compared
is
that the coating
to other coating systems.
system of inorganic
From
the test results
performed by the Turner-Fairbank Highway Research Center, they have stated "vinyls exhibit reduced gloss-retention performance
yellow with age. Vinyls under
UV
tested over these surfaces."
J
to acrylics
and tend
exposure will chalk with time, absorbing
particles that will cause discoloration."
much
and SP-2 prepared surfaces was
compared
J
They
that,
to turn
and
soils
also added, "the performance over SP-3
poorer in comparison to other barrier coatings
Clive Hare
commented
in his
book
that,
has haunted the West Virginia as well as that of several other
"one problem
states,
that
such as Maine,
Tennessee, and Missouri (using similar vinyl topcoats), has been topcoat chalking and
fading.
The phenomenon
specific
pigments or pigmentation levels."
INDOT's own
is
reported to depend on color and
Todd
Tracy, a chemist for
for this coating system.
is
5
INDOT was INDOT,
The useful
also added, "with the vinyl
of vinyl paint
well be related to
experience with the inorganic zinc and vinyl coating system has
not been positive. For most part,
years.
may
it
is
life
only able to get a useful
stated,
"we were only
life
of around
able to get about
also
life
It
reacts with the inorganic zinc to
of the coating will be significantly effected."
4
is
ignored
INDOT
has
experienced pinholes and poor color and gloss retention characteristics. Most
importantly, the most significant reason for the need for a
due
He
very important that a miscoat be applied. This thin layer
applied on top of the inorganic zinc.
done properly, the
5 years
depended heavily on the surface preparation." 4
allow good bonding between the vinyl and the inorganic zinc. If this procedure
or not
1
1
to the
high
VOC level of vinyl.
new
bridge coating system
is
PROBLEMS FACING THE VOLATILE ORGANIC
2.2
COMPOUND The
Volatile Organic
Compound (VOC)
in the paint has
been a hot debating issue
between the paint manufacturers and the environmental protection agencies. Todd Tracy
VOC
said that "in the past, the
level
of the paint had no specific or defined
1990, the Clean Air Act initially proposed to reduce the
an environmental hazard
"VOC
that
it
down."
about the acceptable
4
2.3
VOC
The
VOC
Although there has been numerous
VOC
level, there
approximate proposed limit for the lowered
level in the paint. ""
law will be
in
VOC is
needs to be controlled. Todd Tracy also commented that
evaporates and mixes in the air as the paint cures.
layer to break
this
VOC
But
limit.
reacts with the
talks
by the government
has been no set limit, as of now. Thus
VOC
is
around 2.0
-
3.5 lb/gal.
ozone
far,
the
In January of 1998,
in effect.
PROBLEMS WITH THE LEAD-BASESD PAINTS Traditionally steel bridges in the United States have been protected
by the
lead-
based coating systems but due to the recent regulations on the identification and removal
of lead-based paints, many old lead-based system.
bridge-paint systems
states are seeking alternative coating
systems to replace the
Clive Hare stated in this book that "the most recent revolution in
may
be summarized best as an abandonment of the inhibitive lead-
based systems for the zinc rich and barrier systems. This change was fostered not only by the
bridge
authorities'
desire
environmental pressures to (1)
for
better
initially
paint-system
curtail
10
performance,
but
also
by
the use of photochemically reactive
solvents (e.g., aromatics, olefinics, branch-chained ketones, etc.) and then to curtail the
general use of solvents once other solvent types were also found to be photochemically
reactive
is little
and
doubt
(particularly
more demanding environments),
more
year, the protection
5
and properly applied
that if carefully selected
substantially better and
Each
and hexavalent chromium."
(2) to eliminate lead
He in
also
added that "there
any given environment
new systems
the best of the
will produce
cost-effective protection than will the systems they replace.
of more and more bridges
is
consequently being converted from
the lead- and chromate-based inhibitive approach to zinc and barrier systems."
The old
'red lead' (four-coat red lead alkyd) system
was
unacceptable for five reasons:
1
It
contained lead. Whether in the form of red lead
(white lead being the unacceptable form) or not was not the issue;
nationwide
2)
It
is
it
contains lead and the use of lead
being discouraged or prohibited.
contained chromate. The problems with chromate
are very similar to those of lead.
3)
It
was
deceptively
such
violations
priming so
that,
effectiveness
was
in
of
tolerant
inadequate
as
some
specification
preparation
and
cases, long-term system
substantially reduced
below
that
of a properly applied system.
4)
The system so resembled simple household paint that the inspection process was perceived as being simple; if it looked good, it was good.
5)
The system,
maximum
at
best,
is
possible paint
not good
life is
enough.
The
about 20 years. The
current funding levels allow us to paint a bridge
approximately every 100 years.
11
5
CHAPTER III ATERNATIVE COATING SYSTEMS FOR STEEL BRIDGES A
system
bridge coating
intermediate coat, and topcoat.
It
is
a
combination of surface preparation, primer,
may have more
or less than three coats to achieve the
desired thickness. In choosing a coating system for a steel bridge numerous factors must
be considered and studied. The coating system must be suitable surrounding environment, corrosion,
it
must
Hare comments
its
must be easy
to apply,
it
aesthetically beautify the bridge,
in his
for surface preparation to
it
book
that
"each
new system
and application as well as
film-formation methodology and
its
of the
must provide great protection from
and
brings
its
for the climate
own
it
must be cost
its
own
effective.
Clive
particular requirements
peculiarities that relate not only
mechanism of
protection but also to
its
resistance to moisture, sunlight, corrodents, and physical abuse."
INORGANIC ORGANIC ZINC, EPOXY, AND URETHANE COATING SYSTEM
3.1
/
A
popular trend in implementing a
new
bridge coating system
is
the use of
inorganic/organic zinc primer, epoxy intermediate, and urethane topcoat. This three-coat
system has gained popularity of numerous department of transportations (DOT), such
Ohio DOT, Michigan DOT, Pennsylvania DOT, Spagnolli, a project
DOT)
stated that,
manager
"we did
for the Pennsylvania
steel, a
Dave
Department of Transportation (Perm
a lot of research on costs and materials, nationally and locally,
and determined the best system for bare
for the protection of their bridges.
as,
this bridge
would be inorganic
zinc-rich primer over
high-build epoxy intermediate coat and a polyurethane enamel topcoat."
12
5
INORGANIC ORGANIC ZINC PRIMER
3.1.1
/
Primers prevent corrosion of steel due to moisture penetrating to the
steel surfaces
through miscellaneous defects that might have formed either during the manufacturing process or during the application of the paint to the steel surface. In order for a primer to
be effective, primers must be
in direct contact
with
steel.
Generally, primers are not
formulated to be exposed to the environment therefore requiring a topcoat for protection.
The primer primers.
An
utilized
article
most frequently from the
Modem
utilized is the inorganic zinc
and the organic zinc
Metals publication simply states that "the zinc-rich
primer helps protect against corrosion because the metal will sacrificially react
exposed base
steel
from future damage."
to protect
6
INORGANIC ZINC PRIMER: The inorganic coating systems.
zinc primers
Most
may
be the most frequently used primer for
often they are applied to
new
steels.
They
is
that the inorganic zinc primers require
meticulous cleaning of the
steel in order to
bridge
are applied in the steel
fabricator's shop under a controlled environment for the painting process.
this
all
The reason
for
a careful application process and a
be highly effective as a protecting agent from
corrosion.
The inorganic
zinc coatings are reactive materials.
change which depends on the zinc is inactivated
They
are in state of constant
their exposure. This slow, continuing process is
by an accumulation of zinc
salts
continued until
on the coating
surface.
The
inorganic zinc coatings are composed of powdered metallic zinc mixed into a reactive
silicate solution.
The
first
reaction that takes place
13
is
the concentration of silicate zinc
mixture by evaporation of most of the solvent. The solvent can take on a form either as
water or as organic solvents. Once evaporated, environmental reactions take place and
chemical curing of the coating begins.
was organic but due
In the past, typically, the solvent
water-based solvents,
this trend is
sensitive to
fire
numerous advantages of
changing. Water-based solvents have lower
easier cleaning after application, provides greater
not contribute to any
to
On
hazard.
VOC
level,
worker safety when applying, and does
the other hand, the water-based solvents are
low temperature and humidity.
If applied at
low temperature, the water will
freeze and provide a poor protection. Also, if the water-based solvents are curing too
quickly, then bubbling and blistering
application and protection.
water-based solvents
is
4
may
According
because
it
is
to
occur.
Both types of solvents are comparable
Todd Tracy,
"the
more environmentally
main reason friendly.
spraying water, which contributes to cleaner environment and
workers.
Lower
based solvents."
Some
VOC
level
is
the
main contributor
Zn
(metal)
shown below.
!
+ H,0 -> ZrT + 2e
the normal corrosion reaction for zinc.
This
is
Zn +
H
2
+ -> Zn (OH), +
H
Zn +
H
2
+C0
C0
+
2
-» Zn
3
2
H
2
Zn + 2NaCl + 3H,0 -» ZnOZnCl, + 2NaOH + 2H,
14
change
to
Clean up are done by
is
less
hazardous for
change from organic to water-
4
typical zinc reactions are
2
to the
for the
in
protection of the steel if provided in the flowing way.
The corrosion
The
humidity, the condensation of moisture on inorganic surface and the carbon dioxide
work together
to create
an acid condition resulting
in continuous hydrolysis
of the vehicle
and ionization of zinc. The zinc ions are diffused into the gel structure until a zinc
cement or matrix
is
formed around each of the zinc
together and also bind to the steel surface.
insoluble, durable, and rock-like.
It is
The
particles.
all
silicate
These bind the coating
resulting zinc silicate
cement
is
the ionization of the surface of zinc particles
hard,
which
provides electrons to protect the steel from corrosion attacks. Inorganic zinc coatings have very high zinc loading,
between 75 and 95 percent
typically
zinc contents the
more
zinc.
The higher
the
electrically conductive the coating.
This feature allows the zinc metal within the inorganic zinc coating to sacrificially corrode and preserve the underlying steel substrate at the site
of any breach or defect in the
The lower
system.
coating
the
zinc
content,
the
less
conductive the coating and the less protection the coating will provide through "sacrificial" corrosion of the zinc
within the coating
A
itself.
very important characteristic of an inorganic zinc coating
is
the electrical
conductivity of the matrix. Electrons formed by the ionization of zinc can migrate to the
steel substrate to
provide cathodic protection to the exposed steel area.
Of
all
liquid applied coating systems tested over
blasted surface preparations, those incorporating a zinc-rich
primer
performed
better
than
coating
barrier
systems
without zinc -rich primers. In general, the use of inorganic zinc
pnmers (IOZ)
resulted in better overall
corrosion
protection performance than the use of organic zinc
(OZ)
primers such as zinc-rich epoxy and zinc-rich polyurethane.
While both types of zinc-rich systems showed good near- white blasted corrosion protection over SP-10 surfaces,
the
resistance
to
scribe
15
was IOZ primers than
undercutting
significantly better for those systems with
for systems with organic zinc primers.
These
results
were
consistent in both the 6.5-year Sea Isle City exposure testing and the 5-year field exposure testing.
3
There are numerous advantages of inorganic zinc primers. Some of these 1
Inorganic zinc rain,
is
unaffected by weather, sunlight, ultraviolet radiation,
dew, bacteria, fungus or temperature. The coating does not chalk or
change with time. The inorganic zinc film remains the
2.
are:
same
thickness, even after
The chemical bond formed by
many
intact
with essentially
years of exposure.
the reaction of inorganic binder and the
underlying steel surface prevents the undercutting of coating by corrosion.
3
The chemical bond formed between underlying
steel surface
the inorganic binder
and the
does not allow underfilm corrosion.
4.
Inorganic zinc does not shrink while drying or curing.
5.
Inorganic zinc coated steel
may be welded
without any reduction in
strength of the steel joint, because the zinc silicate matrix reacts with the
welding
6.
flux
and prevents zinc occlusions
in the weld.
The very
strong film and chemical adhesion of inorganic zinc coatings form a base with outstanding friction characteristics therefore providing
high coefficient of friction.
7.
Surface formed by inorganic zinc coatings
is
very hard, metallic and
abrasion resistant.
8.
Some 1
Chemical resistance of inorganic zinc coatings
is
excellent.
limitations of inorganic zinc primers are also realized:
Inorganic zinc primer requires high degree of surface cleanness and extensive surface preparation.
2.
Inorganic zinc primer will not tolerate application over organic material
and will immediately check, crack and chip off organic
surfaces.
3.
Inorganic zinc coatings should never be applied over old paint.
4.
Inorganic zinc
is
not effective in freezing conditions.
16
not effective in high humidity.
5.
Inorganic zinc
6.
Inorganic zinc requires reactions with the atmosphere. If overcoated too
is
quickly, a premature failure
may
occur due to the gases trapped
underneath.
7.
Inorganic zinc have a rapid drying time and time-to-water insolubility.
8.
Inorganic zinc needs direct metal-to-metal contact (zinc to steel) coating
/
substrate interface therefore a
good surface preparation
at the is
a must.
The high-pigment (zinc dust) loading of inorganic zinc coatings gives them poor binder-to-substrate adhesion when compared to organic resin-
9.
3
based systems.
10. Inorganic zinc dries fairly quickly, usually within 15 minutes. After this initial
drying stage, the coating
sufficient to control corrosion.
is
porous and will not provide a
Improper application over inorganic zinc will
1 1
blistering of the topcoat.
"barrier'"
3
result in pinholes
and
3
ORGANIC ZINC PRIMER When
the organic zinc primer to the inorganic zinc primer, a simple nature of the
organic zinc primer
discovered. Organic zinc primers involve very
is
little
chemistry in
formulation. These products are simple mixtures of zinc dust or metallic zinc pigment
into the organic vehicle.
with very
little
Zinc
is
the primary pigment in these organic zinc -rich coatings,
addition of other pigmentation.
There are two requirements essential for effective operation of organic zinc-rich coating:
1.
Zinc in the vehicle, in order to provide the cathodic protection required by zinc -rich coatings,
must be
in
particle-to-particle contact or contain conductive filler,
such
as
iron
phosphide,
to
make an
electrically
conductive path through the organic matrix. Without
17
this
particle-to-particle
contact,
zinc
in
the
coating
would be inert and surrounded by the organic vehicle, which would not allow the zinc to go essentially
into solution
and provide the cathodic protection.
The second important consideration
2.
primers
is that
in organic zinc
the vehicle or carrier of zinc
alkali resistant. This is
pigment be
important since zinc, particularly
under chloride environment, reacts to form a strong
would adversely effect any The primary organic
alkali that
resin or binder.
make
alkali-sensitive
resins used to
organic zinc-rich primers are chlorinated rubbers,
phenoxy resins, or catalyzed epoxy resins. While there are a number of other materials that can be used, these are the principal ones applied to steel structures.
Similar to the inorganic zinc primers, the organic zincs also use a high-film
loading of metallic zinc powder. This high-film loading allows the organic primers to be conductive. The goal
is to
create a conductive
polymer coating
that has the sacrificial
corrosion protecting properties of the inorganic zinc with the enhanced barrier properties
and applicability of the organic
zinc.
3
The most popular organic
zinc
coatings
are
polyurethane zinc-rich coatings. The epoxy zinc-rich resin to
which the curing agent
two-component system
the zinc dust and the vehicle
is
is
packaged
single
this is already
component system
is
zinc-rich
and the
based on the zinc-filled epoxy
The main
in the packaging.
For the two-component system
mixed
prior to application. For the single
mixed from the factory ready
packaged
difference between the
in separate container. In order for reaction to
take place, the zinc dust and the vehicle must be
component system,
epoxy
mixed. The polyurethane zinc-rich coatings are
is
available in both single and two-component systems.
single and the
is
the
in only
18
for use. Therefore, the
one container. According
to
Todd
Tracy,
"the
main disadvantage of
usually less than 6 months.
the single
Whereas
component system
is
that
it
has a short pot
two-component system can have a pot
the
around 18 months. Single component system also requires inhibitors
reacting.
These inhibitors may have an
component
system
more
requires
effect
idealistic
on the curing of the
application
condition,
keep
to
convenient to use since
component system
performance between the two
Many
is
to
requires no
greater
comparable."
of
from
Single
to
is that it
mix of components. The two-
stability
in
terms of storage.
The
4
of organic zinc primer are realized:
attributes
1
due
preferred
is
it
it
regards
temperature and humidity. The only advantage of a single component system
may be more
life
paint.
in
life,
Organic zinc-nch primer proved
to
be successful in arresting the
pit-
based corrosion characteristics of chloride-contaminated weathering steel.
This system added the extra benefit of a high gloss, low chalking
topcoat that
is
resistant to dirt
traveling public.
2.
pickup and aesthetically pleasing to the
8
Organic zinc primers are
less subject to critical surface preparation
than inorganic zinc materials.
3.
Organic zinc primers are more compatible with oleoresinous topcoats than inorganic zinc coatings. 9
4.
Organic zinc has an excellent adhesion and undercutting resistance.
5.
Organic zincs are easier
6.
"Organic zinc-rich epoxy primers are hard, tough, and solvent-resistant
to
apply than the inorganic zinc.
I0
as well as highly adherent. Tolerance for less-than-ideal surface
preparation
is
better than for inorganic zinc-rich primers.
provides a mechanism which sacrifices the base steel."
7.
The
itself,
8
recoatability of organic zinc primer
primers.
The zinc
delaying the corrosion of
8
19
is
better than inorganic zinc
organic coatings which
8.
Humidity conditions are less s depend on moisture to cure.
9.
Normally, no gassing or pinholes occur in the intermediate coat or in
critical for
the polyurethane topcoat due to less porous nature of the organic
primer coat, a
10.
common problem
Because curing time
is
1 1
warm
temperature.
Organic zinc primers
Some
new
it is
with inorganic coatings sprayed in
8
may be used
based coating directly over bare old and
8
predetermined by temperature, dry spray of the
primer will not be a problem as very
with inorganic primers.
for spot repair to provide a zinc-
steel
and yet provide a
tie
between the
organic coating.
disadvantages of organic zinc primers are as follows:
1
Organic zinc-rich primers are subject to the
difficulties
material applied directly over steel surfaces. This
of any organic
means they
are
subject to undercutting, blistering and similar adhesion problems not
normally encountered with the inorganic zinc-rich primers.
2.
A light rust coloration on the steel
surface
may be more
easily
by an inorganic zinc coating than by an organic based material due to the possibility of the inorganic thoroughly wetting tolerated
oxide and reacting with
3.
Organic zinc primer provides less overall protection when compared to inorganic applied with ideal surface preparation.
4.
10
Organic zinc primers shrink while drying or curing, therefore not good for overcoating rough, pitted, corroded surfaces or
5.
the
it.
rough welds.
A majority of organic coating failure under severe corrosion conditions is
by underfilm
corrosion, starting at small breaks in the coating.
20
Table
3.1
Inorganic Zinc
vs.
Organic Zinc Organic Zinc Primer
Inorganic Zinc Primer
Less subject to critical surface
Surface preparation
preparation than inorganic zinc materials
Easier to apply than inorganic
Application Overall Protection
Inorganic films
show
better protection
than most organics
Aging
The matrix of the inorganic primer film
is
not subject to age-related
deterioration as are organic primers.
Weathering may actually improve
its
physical properties.
Adhesion
Organic zinc primers are subject difficulties
to the
of any organic material
applied directly over steel surfaces.
This means they are subject to undercutting, blistering and similar
adhesion problems not normally
encountered with the inorganic zinc primers. Recoatability of organic
Recoatability
zmc
is
better
than morganic zinc.
Organic zinc primers are more
Compatibility
compatible with oleoresinous topcoats than inorganic
zmc
coatings.
Recoatability of organic zinc
pnmer
is
better than inorganics.
Underfilm Corrosion
Chemical bond formed between the inorganic binder and the underlying steel surface
does not allow underfilm
corrosion whereas the majority of
organic coating failure occur by
underfilm corrosion, starting
at
small
breaks in the coating
Normally, no gassing or pinholes
Gassing or pinholes
occur in the intermediate coat or in the polyurethane topcoat due to less
porous nature of the organic primer coat, a
common problem with
inorganic primers. \
21
EPOXY INTERMEDIATE COAT
3.1.2
When with the
first
the bridge
a coat of paint
is
applied, mostly likely there will be missed spots or faults
layer therefore an intermediate or second coat
from harsh environments or application
topcoat perform different functions,
give
it
it is
faults.
is
applied to further protect
Also, since the primer and
usually best to apply the paints in three coats to
the thickness required for optimal protection.
Epoxy binders ester,
are available in three types:
epoxy
epoxy lacquer resin and two-component epoxy.
Epoxy
Ester
These
are
vegetable
oil-modified
epoxy
resins.
Consequently, they are similar to alkyds except they are
more expensive and produce films that are harder and somewhat more alkali resistant. Generally, they have less gloss retention when exposed. Epoxy esters are sometimes used where slightly more alkali resistance than provided by alkyds is desired, but at a lower cost than two-component epoxies.
Epoxy Lacquer Very
high
molecular
weight
epoxies
can
be
formulated as lacquer-type binders by solution in a mixture
of strong solvents. They are sometimes used zinc-rich
primers
because
they
dry
in organic
quickly
at
low
temperatures and can be recoated with topcoats, such as
two-component epoxy
paints.
The two-component epoxies
contain strong solvents that will soften the primer slightly
and improve intercoat adhesion.
Two-Component Epoxy Epoxy resins of this type cure by chemical reaction. The epoxy is generally combined with either of two types of hardners: polyamine or polyamide. Epoxy-polyamine blends are more resistant to chemicals and solvents and are often
used for lining tanks.
Epoxy-polyamides exhibit
superior flexibility and durability, and have
longer pot
life,
adequate
chemical
resistance
under
most
conditions.
Furthermore, they enable packaging of the epoxy and
hardener in separate equal size packages. Epoxy-polymide
22
paints are the
most popular of
structural steel.
quickly,
but
When
retain
all
epoxy binders
for use
on
exposed to weathering, they chalk
their
chemical
excellent
resistance
properties.
Generally,
high-build
epoxy
intermediate
coats
are
applied
over
the
organic/inorganic zinc primer. According to Clive Hare, "the high-build epoxy midcoats are subsequently recoated with urethane or another coat of epoxy, although once formed,
bubbling and
its
resultant catering tend to telegraph
solids normally range
between
55%
and
70% by
from coat
to coat.
volume. Resin systems
Epoxy midcoat at this
time are
most often based on medium molecular weight Bisphenol-A type epoxy resins with polyamide cures, although the use of lower molecular weight epoxies
Pigment Volume Concentration (PVC) is
is
increasing.
higher than the urethane finish coats and gloss
is
often reduced to semigloss or eggshell to improve intercoat adhesion and disguise gloss
reduction in application where urethane finish coats are not used."
The advantages and disadvantages of using epoxy
5
are discussed.
The advantages
are:
Epoxies has excellent adhesion and resistance
1
inorganic zinc coating.
to the alkalinity
of the
1
2.
Epoxies have good resistance against chemical fumes and splashes.
3.
PVCs
of epoxy are higher than the urethane finish coats and gloss
6
is
often reduced to semigloss or eggshell to improve intercoat adhesion
and disguise gloss reductions coats are not used.
Some
in applications
where urethane
finish
5
4.
Epoxies have very good resistance
5.
Epoxies offer excellent resistance against water and strong solvents.
to abrasion.
disadvantages of using epoxy as an intermediate coat are: 1
.
Epoxies have different expansion/shrinkage therefore causing splitting.
4
23
rate at freeze/thaw
2.
Epoxies are somewhat vinyls.
3.1.3
less sensitive to topcoat
bubbling than the
5
3.
Epoxies are not recommended for colder temperatures.
4.
Epoxies showed poor performance
5.
Epoxies has a poor rating for gloss retention.
6.
Epoxies offer poor resistance against chalking.
in color retention test.
URETHANE TOPCOAT The primer,
intermediate, and topcoat
different characteristics. Since a flaw in
process
is
maximum
always a big concern,
it
usually
all
perform different functions and have
workmanship is
in the application
of the paint
best to apply three coats of paint to ensure
protection from the environment. Also,
it is
generally accepted at a
minimum
of 5-6 mils of
total
exposed
Since most paints normally achieve a dry film thickness of about 2 mils,
steel.
dry film thickness
(dft) is
necessary to provide a good protection of
three coats usually are needed to achieve the desired total dry film thickness.
There are two types of urethanes, aliphatic and aromatic. These two types can be in a
form of following three types of binders. Urethane or polyurethane binders are available in three types:
Oil-Modified Urethane These are also called uralkyds, since they are similar to alkyds in processing,
method of
cure (oxidation), and use. However, they produce coatings that are harder
and more resistant to abrasion than alkyds.
Unfortunately, although uralkyds have excellent durability as
clear
finishes,
pigmented uralkyd coatings are not
durable enough to be used on exposed structural
steel.
Moisture-Cured Urethane The moisture-cured urethane react uniquely with air moisture to cure. They produce the
24
hardest,
toughest
Pigmentation
is
coatings
available
extremely
difficult
one
package.
because
of their
in
moisture sensitivity, so they are used primarily as clear finishes.
They can be pigmented, provided moisture-free
materials are used and proper precautions are taken during
manufacture and use.
Two-Component Urethane Urethane can
also
be reacted
with products such as polyols, polyethers, polyesters or acrylics to
produce extremely hard, resistant and durable
coatings. These are binders of major interest for use as
topcoats on structural steel exposed in marine or corrosive
environments.
Generally, for the three coat coating system of organic/inorganic zinc primer,
epoxy intermediate, and urethane
topcoat,
two
principal types of polyols are used in the
urethane systems: a hydroxylated acrylic or a hydroxylated polyester. According to Clive Hare, "the acrylic polyols, however, seem to have
market in
at this
at least as
large a share of the
young
time as do the polyesters. While the polyester-based products have the edge
chemical, solvent, and abrasion resistance, the acrylics have slightly better
resistance and faster initial drying profiles.
They
are also less costly.
volume-solids ranges for the urethane finish coats are between
Numerous
50%
UV
Conventional
and 60%.'"
merits of urethane can be realized.
1
Urethanes provide an extra protection from corrosion.
2.
Urethanes offer good chemical resistance qualities.
3.
Urethanes have good abrasion resistance.
4.
Urethanes provide excellent color and gloss retention.
5.
Urethanes provide excellent resistance against ultraviolet (UV) rays.
6.
Urethanes have very low moisture permeability qualities.
25
7
7
10
7.
Urethanes have excellent chalk resistance.
The disadvantages of urethane 1
Urethanes have higher material cost when compared to other paint materials.
2.
10
Urethanes are generally used only for
UV protection and appearance of
10
the bridge.
3.1.4
are also listed:
COMMENTS The
three-coat bridge coating system of inorganic/organic zinc primer,
epoxy
intermediate, and urethane topcoat have generally received positive feedbacks from
users.
Michigan Department of Transportation
of coating system
tested,
which
is
(MDOT) commented
that "the
its
second type
our current system, was an organic zinc -rich epoxy
primer with a polyamide epoxy intermediate coat and an aliphatic polyurethane topcoat.
The organic
zinc-rich primer proved to be successful in arresting the pit-based corrosion
characteristics of chloride-contaminated weathering steel. This
system added the extra
low chalking topcoat
pickup and aesthetically
benefit of high gloss,
pleasing to the traveling public."
three
DuPont maintenance
n
that is resistant to dirt
"After years of use, the coating, which consists of
finishes (Ganicin inorganic zinc primer, Corlar high-build
epoxy and Imron polyurethane enamel),
still
has a fresh, wet look."
6
After experimenting with various coating systems, the current system, an organic epoxy zinc-rich primer, an
epoxy intermediate This system
members
is
coat,
and a urethane topcoat, evolved.
used both for coating new bridge
in the shop, prior to shipping to the job site,
for repainting
and
existing structures after the old red lead
system has been removed. The advantages of the system
steel
are:
26
new
The new system has displayed
1)
substantially
improved
durability and corrosion protection in laboratory tests
and
applications
field
have
date
to
most
been
satisfactory.
Tests indicate that even
2)
coating
system
lasts
when poorly longer
and
applied, the
provides
new
better
protection than the corresponding lead-based system.
The new system employs a 'time-independent primer', which rapidly stabilizes and does not deteriorate with
3)
age, unlike the lead-based system
whose primer
resin
remains chemically active and eventually becomes so brittle that
The
4)
it
FHWA
peels off the structure.
will
now
fund only the
new
generation of
coatings developed to replace the red lead system.
The
5)
cost of the
new system
and significantly cheaper
is
lower on an
in the long run
square foot per year of service basis.
The expected
life
initial
basis
on a cost per
12
expectancy of the inorganic/organic zinc primer,
epoxy
intermediate, and urethane topcoat coating system ranges anywhere from 20 to 40 years.
The Pennsylvania Department of Transportation (PennDOT) system to
last
20
coating systems.
to
.
.
.
25 years, which
is
more than twice
6
"we expect
this
the normal life of conventional
The alkyd-based paints generally begin
nine years, and after 12 years they need repainting."
stated that,
to deteriorate after eight or
MDOT also added that,
"although
the organic zinc-rich primer, epoxy intermediate coat, and the urethane topcoat have been
exposed
to a variety
their condition
With the
field
is
of environmental conditions
for a fairly limited time (about 7 years),
excellent and in line with the projected 30 to 40 year
evidence collected over the past several years,
we
life
of the system.
expect the coating
system to continue to perform satisfactorily with minor maintenance repairs, and
27
it
remains the system of choice
for
exsisting." "
new and
Transportation concluded that "the organic zinc system,
itself. It
used
to
be
that
As
it.
We
are expecting to get at least
far as the inorganic zinc
system on
good system."
With
it.
It
1
5 years out
on new bridges, we have been using
since 1978, around that neighborhood, and
that
are starting to see
it
pay
for
once you paint a bridge, you would have to come back eight or
nine years later and repaint
system.
we
The Ohio Department of
we
of
this
new
that probably
never had to repaint the bridge that had
has been almost 20 years. Therefore, the system seems to be a pretty
10
this
system, cost savings can also be realized.
"because of the expected 25-year service
life
bridge (with an expected 50-year service
life)
PennDOT
expects
that,
of the new three-tiered coating system, the will require only
instead of three, lowering maintenance costs considerably."
one maintenance painting
6
Reducing the number of necessary repaintings from three to
PennDOT millions of dollars. to 70% of the total painting "While we have no way of knowing
one could save
"Labor usually runs about 60 costs," said Spagnolli.
future labor costs, idea."
He
we can
look
at
some records and
cited the Fort Pitt Bridge,
paint about 10 years ago.
When
to
was repainted
in
the bridge
1979-80. the cost was $2.4 million."
get an
which cost 5240,000 6
A record of the painting cost history using this coating system is shown below.
2S
TABLE
3.2
CAL.YEAR
OZEU Bridge Painting Cost History PROJECTS
BRIDGES
13
"'SQ.'TTTr:-
LOWBID* "TOTAL COST 2
($/ft )
1990
7
40
499,742
$7.29
$3,646,100
1991
25
133
3,128,437
$6.96
$21,779,900
1992
27
134
3,350,000
$6.66
$22,311,000
1993 1994
26
141
2,870,900
$5.24
$15,043,600
16
85
1,696,200
$5.83
$12,667,100
1995
14
49
1,157,000
$4.43
$4,769,200
(THESE COST INCLUDE EVERYTHING EXCEPT TRAFFIC CONTROL) Note:$m 2 = 10.76 $/m 2 *
$/ft
2
are estimated by dividing the total cost of the project
steel to
be painted. The
total surface area
whether the owner decides
of steel
to
by the
be painted
total surface area
may
to paint the inner side of the steel girder.
29
of
vary depending on 5
:
TABLE 3.3
1
1996 Bridge Paint Costs Lowbid
1
PROJECTNO.
SQ. FT
SURFACE
PRIME
INTER
FINISH
X(1000)
PREP.
COAT
COAT
COAT
20
129
$1.55
$0.50
$0.60
21
59
$2.72
$0.30
70
114
$2.00
90
77
105
7
TOTAL
NO. OF BRIDGES
$0.50
$3.15
8
$0.30
$0.30
$3.62
6
$0.50
$0.50
$0.50
$3.50
8
$2.00
$1.00
$0.50
$0.50
$4.00
3
28
$1.50
$0.60
$0.60
$0.60
$3.60
1
469
32
$3.00
$0.55
$0.55
$0.55
$4.65
1
147
218
$2.20
$1.10
$0.50
$0.50
$4.30
5
291
86
$1.94
$0.70
$0.70
$0.70
$4.04
1
340
229
$2.25
$0.50
$0.50
$0.50
$3.75
16
390
94
$2.76
$0.55
$0.55
S0.55
$4.41
4
408
34
$2.50
$0.50
$0.50
$0.50
$4.00
1
412
9
$4.00
$0.75
$0.75
$0.75
$6.25
1
419
17
$2.10
$1.10
$0.53
$0.53
$4.26
1
425
5
$4.75
$1.00
$1.00
$1.00
$7.75
1
434
243
$2.75
$0.50
$0.50
$0.50
$4.25
9
445
46
$1.65
$0.50
$0.50
$0.50
$3.15
3
494
123
$2.50
$0.50
$0.50
$0.50
$4.00
6
PROTECTS
2 A/ote:$/ft = 10.76
Appendix
1
,543,000 sq.
$4.28
/
sq.
75
ft.
BRIDGES
$/m 2
A contains the sample specification for the inorganic
urethane coating system. Appendix
C
ft.
B
/
organic zinc, epoxy, and
contains the prequalified product
compares the specification from INDOT,
MDOT and ODOT.
30
list
and appendix
3.2
INORGANIC ZINC AND WATERBORNE ACRYLIC COATING SYSTEM Another frequently used bridge coating system
waterborne acrylic three-coat system. The
is
good
currently using this system with
with our coating system.
It is
more
inorganic
zinc,
and
Department of Transportation (IDOT)
Illinois
results.
the
is
According
to
IDOT, "we
cost effective than the urethane system 4
IDOT
are satisfied
and
we
expect
"we
also
use the inorganic zinc, epoxy, and urethane system for cold weather applications.
We
when
the
it
to last
around 15
would not object temperature
falls
to
to
20 years without major service."
below 50° F."
14
IDOT was
IDOT
"we
that
VOC
level,
we made
waterbome
that,
we've only used the
acrylics for about
only getting about 10 to 15 years for the vinyl system."
The
acrylics,
But
we
two
years.
14
resins in the waterborne acrylic system give
gloss,
development
very
fast
of film
drying
properties.
systems
These
with
rapid
properties
similar to those obtained from conventional acrylics
No
are
made
from solvent-based thermoplastics. Paint formulation also different.
is
external thickeners are usually required.
For the resin formulations, the polymers generally bear carboxylic acid groups copolymerized into their backbone.
These groups are neutralized amines. The resultant
salt
at the
formulation stage with
can be solvated, which increases
the viscosity of the resin. This eliminates the need for
thickener in the formulation and enables the resin to be
used for pigment dispersion. For good film formulation, both coalescents and sometimes plasticizers are used. The fast evaporating
systems give short tack-free drying times,
31
VOC
the switch to acrylics."
are anticipating 25 years for our coating system.
the chance to prove that since
high
added
also concerned with the high
stated that, "before the
using the vinyls. But do to the high
added
also
a contractor using the epoxy and urethane system
the vinyl coating systems.
also
'
level of
we were 14
IDOT
haven't had
We were
and the slower solvents give the best coalescence. Flash rusting inhibitors are used to diminish flash rusting of steel.
Flow agents
are often used in balanced
amounts with a
defoamer. This use gives optimum resistance to cratering
and bubbling and eliminates flow problems such as orange peel.
The advantages of acrylics
are as follows:
1
Acrylics are less expensive than urethane.
2.
Acrylics have good
3.
Acrylics exhibit
UV resistance.
little
periods of exposure.
4.
14
3
yellowing and maintain their clarity for long
J
Acrylic coatings are potentially less hazardous to personnel than
polyurethanes and are not as prone to moisture-related difficulties.
5.
Acrylics exhibit excellent flexibility characteristics.
6.
Acrylics have good color and gloss retention.
The disadvantages of acrylics 1
3
4
are as follows:
Acrylic coatings will soften and sometimes disbond if exposed to
aromatic naphtha. For these reasons, most acrylic coatings should not be overcoated with coatings containing aromatic naphtha. 3
2.
The
solvents in epoxies and polyurethanes will dissolve acrylic
coatings, and overcoating acrylics with solvent-borne epoxies or
polyurethanes can result in swelling, blistering, and disbondment of the acrylic.
3.
Due
J
to the thinner coats,
it
more
requires
application of paints
contributing to the increase in labor and material costs.
4.
Acrylics only performed
fair for the
I4
resistance to abrasion, water,
strong solvents, and acids.
5.
Acrylics only showed
fair rating in
32
the corrosive exposure
test.
3.3
MOISTURE CURE URETHANE COATING SYSTEM As an
alternative to the three-coat bridge coating system
of inorganic/organic zinc
primer, epoxy intermediate, and urethane topcoat, a moisture cure coating technology
also available. Moisture cure coatings offer years
sensitivity
of
steel protection
is
while requiring less
toward surface preparation and application process. Although the moisture
cure coatings
seem superior
to other coating systems, the
process of the paint leads limits
its
need for moisture
in the curing
use to environments with high moisture content for
ideal performance.
3.3.1
COMPOSITION Moisture cure coatings are single package compositions that cure by the reaction
of residual isocyanate groups with atmospheric moisture
They
biuret-linked polymers.
are prepared
by
to
form disubstituted urea and
reacting excess diisocyanates with a
hydrogen donor having a functionality of two or more
to give
an isocyanate-terminated
product that can be subsequently used for crosslinking with water. The reaction of these products with atmospheric water in the filed involves a two-stage process with the water
and the isocyanate groups dissociates to form an
first
producing the unstable carbamic acid, which immediately
amine and carbon dioxide. The carbon dioxide leaves the film by
evaporation, and the amine reacts with a second group giving a urea.
reaction
is
given below.
5
33
3
An example
of this
H I
R-N=C=0
R-N-C-OH
+ H,0
decomposes
R-NH 2
The R-NH,
reacts again with
+
R-N=C=0
C02
to
form
O II
R'-
NH2
+
R
-
N = C =
O
R
-
NH - C - NH
-
R'
UREA
COMMENT
3.3.2
Moisture cure urethane coatings have been utilized
Although the history of the use of moisture cure coatings short,
many
in
Europe
in the
for over
30 years.
United States
is
rather
important and famous bridges across the country have already applied
moisture cure technology for their protection. These bridges include the
Tacoma Narrows
Bridge, the George Washington Bridge, the Golden Gate Bridge, and
Currently numerous department of transportation
(DOT) of
many more.
various states are using the
moisture cure technology for the protection of their bridges. The moisture cure coating
system
is
currently used
by
the Wisconsin
DOT, Alaska DOT, Maine DOT, Vermont
DOT, New Hampshire DOT, New York DOT, Kentucky DOT, and Minnesota
34
DOT
to
name just years.
a few. Moisture cure urethane coating has a life expectancy
of around 20 to 30
I5
The moisture cure coatings
offer
numerous advantages when compared
to the
conventional system mentioned above. Moisture cure coatings require less surface
which leads
preparation,
to considerable, cost savings.
by Juergen Schwindt, "abrasive the best
method of surface
I5
According
blasting of the steel to white metal
preparation. But,
it
also
is
the
to a
is,
study performed
without question,
most expensive method.
By
comparison, power-tool cleaning requires less effort and saves money. Power-tool
cleaning
is
achieved with a high-pressure needle-gun, or grinding and abrasive tools.
A
newly developing hand-tool-cleaning technique uses an inductive delamination apparatus.
With any of these methods, waste and blasting, the
amount of generated waste
costs can be reduced.
is
Compared
dramatically decreased. Expenses related to
shrouding, blasting media, and waste disposal are reduced as well."
involved in the surface preparation
TABLE 3.4
is
shown below.
Costs of Surface Preparation
1
White Metal
Handtool Cleaning
Housing
V
Dust collection
V
Blasting media
V
X X X
Waste disposal
V
1/10-1/100
Climatization
V
X
Wages
V
V
Paint
V
V
Associated Costs
to abrasive
V = Costs
X = No costs
35
16
A
table of costs
One example of
the use of
MC-PUR
coatings to
reduce costs associated with the refurbishment of a bridge,
was overcoating Pittsburgh
in
the
1978.
Homestead High Level Bridge in The bridge had an estimated 20%
surface rust. After a spot commercial blast, a spot primer
MC-PUR were
and intermediate coat based on
The topcoat was
based formulation. After 14 years with system, an inspection revealed less than cost,
including containment,
overcoat system would be as
75%,
A
bridge
in
30%, and maybe
full paint
Tarentum,
$450,000 saved was due in part
MC-PUR
was only SSPC 6
-
At today's
rust.
removal.
as
much
16
Pennsylvania
another example of savings achievable with
preparation
polyurethane
this
5%
has been estimated this
it
at least
expensive than
less
applied.
a two-component polyurethnae-
provides
MC-PUR. The
to the fact that the surface
commercial blast
-
and the
could be applied inside the containment structure
even when the temperature varied between -15 and -29.4°C (5 and -22°F) or when it was snowing and raining outside the structure.
maintained
at
The
air
in the containment
structure
was
4.4°C (40°F) during cold weather. Rapid dry
times meant recoat times were shortened and blasting on adjacent areas could be started sooner.
Clive
Hare
polyurethane are
its
stated
single
that
"the
principal
package and
its
16
advantages
ability to
of the
be applied by brush,
squeegee, or spray without great demands on the applicator.
typified
by the same general property
moisture
...
The
curing
roller, trowel,
final
films are
profiles that characterize all polyurethanes, great
harness without brittleness, toughness combined with excellent elongation, and excellent
resistance to acids, alkalis, halogens, sulphates and other salts, solvents, and other strong
chemicals."
5
Other significant advantages of moisture cure urethane require for each coat.
l3
Usually only 3 mils for each layer
36
is
is
that less thickness
required.
I5
is
Therefore the
total thickness required for
a three coat coating system
is
only 9 mils.
When compared
to
conventional system, such as the inorganic/organic, epoxy and urethane three-coat system, which require a total thickness of around 15 mils, this relates to considerable
n
savings in the paint usage.
due
to its faster curing.
16
Also, with moisture cure urethane, recoating time
Reduced recoating time
leads to decrease in
is
reduced
down time such
as
holding of traffic or other inconveniences experienced by the public due to the painting of the bridge. Lastly, moisture cure urethane coatings remain elastic and resistant to
radiation, ensuring the long-term durability of the coating.
disadvantage
is that it
cure urethane
splitting
16
disadvantages of moisture cure urethane are reviewed. The most significant
Some
and
UV-
is
used
of the
requires moisture for the curing of the paint. Therefore, if moisture
dry sunny environment,
in a
paint.
Moisture cure urethane
high humidity of moisture, that "the curing
it
is
is
it
will result in devastating cracking
only suitable for environments with
not effective on dry environment.
and quality of the
product
final
is
4
Clive Hare also added
greatly dependent
upon atmospheric
humidity during application. Below 30 percent humidity, cure will occur too slowly.
Above 75
percent relative humidity, cure
the carbon dioxide generated
by
may be
the reaction
cost for the moisture cure urethane
is
10%
trapped in the set-up film."
5
The material
higher than conventional paints normally used.
Wasser High-Tech Coating company quoted around
is
too fast and result in films bubbling as
higher than regular paints."
that "the material cost
15
can be expected to be
Clive Hare concluded in his book that
"bubbling becomes a more severe problem as film thicknesses increase. High film thicknesses
may
also entrap solvent. This
phenomenon
although temperature will have somewhat less effect."
37
s
is
aggravated by high humidities,
Table 3.5
A Comparison of Various Paints Used in Epoxy
Chemical resistance
Coating Systems
Polyurethane
Vinyl
Water-borne Acrylics
Epoxies have
Urethanes offer
Vinyls have poor
Acrylics only performed fair for
good
good chemical
resistance against
the resistance to strong solvents
resistance
strong solvents
and
Vinyls have
Acrylics exhibit excellent
excellent
flexibility characteristics.
resistance
against chemical
acids.
fumes, splashes.
and strong solvents.
Flexibility
flexibility
characteristics
Color and gloss retention
Epoxies showed
Urethanes provide
Vinyls do not
Acrylics have good color and
poor
excellent color
have very good
gloss retention.
in
and gloss
color and gloss
color and gloss
retention.
retention
performance retention
Chalk resistance
tests.
Epoxies offer
Urethanes have
Vinyls do not
poor resistance
excellent chalk
have good
against chalking.
resistance.
performance record against
chalk resistance.
Abrasion
Epoxies have
Urethanes have
Vinyls have very
good
good abrasion
good
resistance.
to abrasion.
Urethanes provide
Vmyls
excellent
upon
resistance against
exposure.
resistance
to abrasion.
UV protection
resistance
will chalk
UV
Acrylics have good
UV
resistance.
UV rays. Moisture permeability
Urethanes have
Vinyls have low-
Acrylic coatings are not as prone
very low moisture
moisture
to moisture related difficulties.
permeability
permeability.
qualities.
38
DISCUSSIONS
3.4
Due
abolish lead-based paints and decrease
new
from the environmental protection agencies to
to the increased pressure
VOC
level,
INDOT
has decided to search for a
bridge coating system. This paper has already reviewed various coating systems
utilized
by neighboring
states
such
as, Illinois,
Ohio, and Michigan. This paper has also
presented other coating technology such as the moisture cure urethane coating system. In review of
all
coating systems presented above,
it
is
recommended
use the inorganic zinc, epoxy, and urethane coating system for
zinc,
is
new
that
INDOT
bridges and organic
epoxy, and urethane for existing bridges. The justification for the recommendation
as follows.
The inorganic
zinc should be used for
preparation for the inorganic zinc
is critical
for long
new
life.
bridges because the surface
The inorganic zinc requires high
degree of cleanness and extensive surface preparation therefore
shop where a controlled painting environment used for existing bridges since
it
is
is
possible.
it
should be applied
at the
The organic zinc should be
less sensitive to the surface preparation than the
inorganic zinc. Although the inorganic zinc
may
offer slightly better protection,
due
to
the uncontrollable painting environment at the field the organic zinc will offer better
protection for application environment that
The
table
shown below compares
is less
than ideal.
the bridge coating systems mentioned above.
39
o
of Spot Ease
o o
a.
Old
S— Coatings
1—
o o
'3
-
-
"ab
*ob
Cu
with
Times
s-.
*S '3 fe
l-l
o O
Compatibility
Recoat
*J
o o
Repair
-
(Days)
in from
Early
Application
Probability Deviations
of
Failure
X
X
Poor Adaptability
Poor
Surfaces
(Inorganic)
Fair
(Organic)
Oh
to
Surface
Preparation
—
o o
(Minimum
-
V©
\o
o
o
CO
CN
SSPC-SP)
Mils) Typical
Film
at
Thickness
(Dry
o
U o m
Life
Expected
(Years)
o m
o
o
7
Estimated
ir> Useful
85
Q.
2
I
s o
u
8J
/
3 U
"n zinc,
so "S
o
3 H
85
_
-2
«
11
-
=
85 OX)
Inorganic urethane
organic
epoxy,
As
it
can be seen from the
table, the inorganic
/
organic zinc, epoxy, and urethane
system and the moisture cure urethane system offers the longest useful urethanes require moisture to cure. Unless there
is
life.
Moisture cure
a lot of humidity or moisture in the
air,
the moisture cure urethanes will not cure properly. Therefore, the moisture cure urethanes
are not suitable for Indiana's hot, dry, blistering sun.
The inorganic
/
organic zinc, epoxy, and urethane system
by both Ohio and Michigan.
It
is
also being used
application temperature less than 50° F.
Ohio and Michigan
may
occurred during the
system
is
some have noted
be higher, the projected
initial
life
painting of the bridge.
currently being used
Illinois for their projects
expert interviews,
are very satisfied with their results.
years from this system. Although
urethane system
From
be
is
They
it
is
concluded that both
are expecting about 25 to
that the initial material cost
will cover
The long-term
41
30
of the
any additional expense benefit of the urethane
superior to any other coating systems presented in this report that
Indiana's climate conditions.
with
is
suitable for
CHAPTER IV
OVERCOATING VS. FULL-REMOVAL
With
the high cost of bridge painting, increased pressure from the environment
protection agencies to get rid of the old lead paint, and limited funding from the
government
for bridge
maintenance and protection, many bridge owners are searching for
alternative strategies involved with the maintaining and protecting of the bridge against
corrosion.
Bernard Appleman stated in his
article that "repainting structures
coated with
lead-based paint challenges highway agencies and other public and private owners to
balance
corrosion
protection,
environmental
protection, and aesthetics and public perception."
worker
protection,
protection,
legal
18
Overcoating can simply be defined as spot cleaning and priming degraded areas, cleaning intact paint, and applying the
system. Bernard
Appleman
states that
new
lead-free coating system over the existing
"Overcoating typically includes preparing rusted or
degraded areas by mechanical, chemical or water cleaning methods; feathering the edges
of the existing paint
to
sound paint and cleaned
provide a smooth transition
areas; spot cleaning
at
the interface
and priming of rusty areas; low-pressure
water washing of the entire structure to remove loose chalk,
dirt, dust,
debris; applying full intermediate coat over existing and repaired areas;
topcoat over the entire structure (optional, but
In deciding
must be
whether
to overcoat or
recommended
perform
carefully evaluated before a decision
42
between existing
is
full
in
grime, and other
and applying
most instances)."
full
IS
removal of the paint, many factors
made.
A common
decision
making
checklist
is
given below. These areas must be reviewed extensively before an effective
judgment
is
made.
Check 1
List for
3.
4.
5.
Extent of metal corrosion and pitting
•
Percent of surface requiring mechanical preparation
•
Age and
Structure
average thickness of existing coating
Usage of structure
•
Additional service
•
Rehabilitation or related
life
work planned
Exposure Environment •
Presence of chlorides or other chemicals
•
Proximity to industrial fallout
•
Areas prone
to splash, spillage, or
high humidity
Coating Factors •
Evidence of early
•
Evidence of compatibility problems
•
Presence of soluble
failure
salts,
of previous coating system grease, or oil
Sensitivity of Location •
Proximity to residence, schools, day care centers
•
Height of structure (prevalent wind patterns)
•
Proximity to navigate waterway, reservoir, or other sensitive
6.
18
Condition of Structure •
2.
Decision-Making
body of water
Constraints •
Limited access
•
Limited time
to
(e.g.,
requiring traffic control)
perform work
(e.g.,
during turnaround
or due to weather) •
Specific environmental regulations
•
Application restrictions
•
Surface preparation restrictions
(e.g.,
on spraying) (e.g., to
eliminate dust
contamination of machinery or products)
43
Numerous bridge. Bernard
aspects play as a factor in determining the cost of full removal on a
Appleman
depends on each
states that "the cost
fully contained lead
structure, differences in access, the
enforcement of regulations, and inconsistency contractors
of a
may have
different
means
removal project
impact of shutdown, variability of
in quality
and
detail
for achieving these
of specification. Also,
requirements and varying
degrees of willing to accept risks such as low productivity, a lesser degree of cleaning,
environmental
spills,
elevated blood lead levels, and fines or penalties."
study done by the Steel Structures Painting Council (SSPC), the cost of
on a bridge ranges from S3 per square
$150.64/m
2 ).
A
feet to
$14 per square
comparison between costs for the
represented in the table below.
44
full
feet
removal
1S
According
full paint
removal
(from S32.28/m
vs.
to a
:
overcoating
to
is
COMPARISON OF COSTS FOR FULL-REMOVAL VS. OVERCOATING
TABLE 4.1
18
Full
Removal
Overcoating
Structure ID
sq.
1
Bridge over river
40,000
4.95
2.00
2
Highway overpass
10,000
8.50
3.00
3
Highway overpass
18,000
5.50
2.75
4
Bridge over wharf
20,000
3.00
2.00
5
Riveted girder span
8,000
13.13
3.00
6
Rail bridge trusses
300,000
7.00
2.00
7
Deck truss
1,000,000
10.00
5.00
8
3 span
N/A
11.25
N/A
9
Plate girder
14,000
2.72
N/A
10
Plate girder
1,336,000
3.17
N/A
11
Plate girder
520,000
2.95
N/A
12
Rolled
2,953,000
3.55
N/A
13
Girder over river
500,000
4.00
N/A
14
Girder overpass
180,000
6.75
N/A
15
Tied arch over river
220,900
11.21
N/A
16
General, recyclable
N/A
12.00
N/A
17
General disposable
N/A
10.00
N/A
18
7 spans over water
100,000
18.00
N/A
19
Overpass
10,000
3.30
1.05
20
Overpass
20,000
8.50
N/A
21
Girder, double deck
350,000
8.00
4.00
22
Suspended cable/river
300,000
12.00
N/A
Average
7.47
2.76
Median
7.50
2.75
I
beam
beam
2 A/ote:$/ft = 10.76
$
ft
$/m 2
45
/
sq. ft
S
/
sq.
ft
The following overcoating.
As
it
table
compares the cost distribution of
can be seen from the
table, the cost
full
of overcoating
is
removal versus
more than half of
the full removal process. Eric Kline and William Corbett stated in their article that
"although the cost comparisons are based on the same methods form different sources,
it
has been discovered that total lead removal/containment projects undertaken in the early
1990's
may
cost as
much
as $5 and $10 per sq
2
ft
($53.8/m and $107.60/m
2 ).
It
becomes
apparent that minimal surface preparation, followed by upgrading with one or more of the
materials discussed,
sq
ft
($21.52/m
many
2
)
would provide
achievable."
19
substantial savings
Due
by making coating costs of S2 per
to this significant cost savings
states are pursuing the overcoating approach.
46
and a limited budget,
ox
a
o a"
o
1—
a.
O
d
o t> d
ri
ri
o q
o q fa
fee
fee
fee
fee
fee
&e
&e
in
in
o d
O d
c in
d
o m d
in JZ,
s r^
o
p
'a
CO
13
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Appendix
D
Factors Affecting Performance and Durability of Overcoating Systems
In the following section
The
overcoating job.
we
will discuss the factors that affect the success or failure
relative
understood. Furthermore, in
22
of the
importance
many
discussed
factors
is
not
of an
clearly
cases the current test methods available do not clearly
characterize various factors.
1
.Adhesion/cohesion
The use of adhesion and
tests to rate the ability
to estimate the durability/compatibility
of an existing paint system
to
be overcoated
of the repair merit review. Current and the meaning of the
tests are
time consuming to perform,
difficult to repeat,
to individual interpretation.
For example large differences have been observed between
the test results
when
different
methods
are used. Existing paints
cohesion and intercoat adhesive strength
(i.e.,
may
typically occurring
results are subject
be
brittle
and lack
between an alkyd
primer and existing intermediate or top coats of alkyd paints containing aluminum pigments). Knifing adhesion tests such as
ASTM
D3359-90 ("Measuring Adhesion by
Tape Test")
typically fracture old alkyd paints causing intracoat (cohesive) failure.
pull-off test
ASTM
D-4541 ("Standard
test
Method
for Pull-Off Strength
The
of Coatings
Using Portable Adhesion Testers) measures adhesion between existing coats or between the primer and the substrate, or the cohesive strength of a specific coat depending
which component knifing adhesion
fails first. Brittle
test.
If used
alkyds
may
on existing paint
provide only a IB or
OB
upon
rating using the
that contains several overcoated layers, the
knifing adhesion test
may provide
similar values.
same system may provide readings
2.
in
However, a pull-off adhesion
test
on the
excess of 300 psi.
Surface Contamination
The presence of soluble
salts
on
existing paint surfaces and in corrosion products pose a
distinct threat to repair coating's durability. Soluble salts
must be removed
in order to
provide extended paint durability even though their affects are difficult to assess. They
are difficult to detect in the field
and
their concentration
may vary depending on
level
of
de-icing salt application, bridge design, and structural location. Currently, the primary
tests for
chloride surface contamination are wet chemical tests that are slow to perform
and are questionable as
to
accuracy and precision.
