Performance Evaluationof One-Coat Systems on New Steel Bridges by FHWA Publication No. FHWA-HRT-11-047.pdf

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TECHBRIEF
Performance Evaluation
of One-Coat Systems on
New Steel Bridges
FHWA Publication No.: FHWA-HRT-11-047
FHWA Contact: Paul
paul.virmani@dot.gov
Virmani,
HRDI-60,
(202)
493-3052,
This document is a technical summary of the Federal Highway
Administration report,
Performance Evaluation of One-Coat Systems
on New Steel Bridges
(FHWA-HRT-11-046).
Introduction
The current state of practice in bridge coating usually involves
multilayer coating typically consisting of a zinc-rich primer over an
abrasive blast-cleaned surface and two additional coating layers on
top of the primer. Although this current coating technology provides
a comprehensive solution for better corrosion protection of steel
bridges, the overall cost involved is relatively higher than its lead-
based predecessors. The purpose of this study is to evaluate the
performance characteristics of various commercially available high-
performance coating materials that can be applied as one-coat
systems to steel bridges in shop application.
Eight one-coat systems and two controls, a three-coat system and
a two-coat system, were chosen, and their performance was evalu-
ated using accelerated laboratory testing (ALT) and outdoor exposure
conditions.
Performance of these coating materials was evaluated on the basis of
variations in color and gloss, changes in adhesion strength, changes
in pencil scratch hardness, and the development of surface defects
(holidays, blisters, and rusting) and rust creepage. Regression analy-
sis was used to identify correlations among the various performance
parameters, and a comprehensive system was developed to rank the
coating systems based on overall performance.
Approach
Coating Systems
Research, Development, and
Technology
Turner-Fairbank Highway
Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
http://www.fhwa.dot.gov/
research/
Eight one-coat systems and two controls that performed well in the
field and in earlier Federal Highway Administration (FHWA) studies,
were evaluated in this study.
(1,2)
Table 1 lists all of the 10 coatings
systems.
Test Panel Preparation
Steel test panels of two sizes were used in this study. The small
panels were 4 x 6 x 0.2 inches (10 x 15 x 0.48 cm), and the large
panels were 6 x 12 x 0.2 inches (15 x 30 x 0.48 cm). All test pan-
els were blast cleaned to Scientific Society for Protective Coatings
Surface Preparation 10 standard, and coatings were
applied on the cleaned test panels using airless
spray. Half of the total test panels (111 out of 222)
were scribed diagonally following the instructions
specified in American Society for Testing Materials
(3)
(ASTM) D1654-08. Panels were scribed to study
the potential performance of the coating systems at
local film damage. The other half of the panels were
left unscribed to characterize undamaged conditions
and physical properties such as gloss, color, pencil
scratch hardness, etc. Two additional panels of each
coating system were prepared exclusively for initial
adhesion strength and Fourier transform infrared
spectroscopy; they were not used in any of the tests.
Performance Evaluation Techniques
Coatings were evaluated before and after exposure
for the following parameters:
•
•
•
•
•
Gloss (ASTM D523-08) and color (ASTM D2244-
(7,8)
09A).
Pencil scratch hardness (ASTM D3363-05).
Pull-off adhesion (ASTM D4541-09).
(10)
(9)
Number of coating defects/holidays (ASTM
(11)
D5162-08).
Rust creepage (ASTM D7087-05A).
(12)
Test Conditions
ALT and outdoor exposure conditions were used
to test the coating systems. For ALT, 19 accelerated
test cycles (each test cycle = 360 h) were conducted
for a total test period of 6,840 h. This method is
similar to ASTM D5894-05, with the addition of a
(4,5)
freeze cycle for 24 h.
Outdoor exposure conditions involved the following:
•
•
Marine environment exposure (ME) occurred
(6)
in Sea Isle City, NJ, for 24 months.
Mild natural weathering exposure (NW)
occurred at the Turner-Fairbank Highway
Research Center (TFHRC) in Mclean, VA, for
18 months.
Mild natural weathering plus 15 percent salt
solution spray (NWS) sprayed manually every
24 h also occurred at TFHRC for 18 months.
All coating systems were evaluated for color, gloss,
rust creepage, and holidays every 360 h in ALT and
every 6 months in outdoor exposure conditions.
Adhesion strength was evaluated once before
testing and once at the termination of testing.
Results
Correlation Among Performance Parameters
and Exposure Conditions
Correlation among test parameters, such as color
or gloss, for various coating systems can help
researchers better understand interactions among
test variables. This correlation would be specific
to the type of exposure condition such as ALT
or outdoor exposure testing. Linear regression
analysis was performed to identify relationships
between the various performance characterization
•
Table 1. Summary of coating systems.
System
Number
1
2
Coating Type
System ID
Three-coat
Two-coat
Primer
Zinc-rich epoxy
Zinc-rich moisture
curing urethane
ASP
Epoxy mastic (EM)
Calcium sulfonate alkyd (CSA)
One-coat*
Glass flake reinforced polyester (GFP)
High-build waterborne acrylic (HBAC)
Waterborne epoxy (WBEP)
Polysiloxane (SLX)
Urethane mastic (UM)
Intermediate
Epoxy
Top
Polyurethane
Polyaspartic (ASP)
3
4
5
6
7
8
9
10
* One-coat systems contain one coat of paint that acts as the primer/top coat and do not contain an intermediate coat.
Note: The blank cell indicates that the two-coat system does not contain an intermediate layer.
2
parameters. The objective of this analysis was to
observe whether any correlation(s) existed among
performance parameters. Regression analysis was
also performed to examine if any correlations
existed between the exposure conditions. Panels
with a GFP coating system were not available for
outdoor testing. As a result, the GFP system was
excluded from the regression analysis.
Conclusions
•
Although some of the one-coat systems
demonstrated promising performance, none
of the coating systems performed as well as
the three-coat control in ALT and outdoor
exposure conditions.
High-ratio calcium sulfonate alkyd performed
well in ALT and the outdoor exposures. While
this system is limited by its long curing time
after application, it presents an interesting
alternative for maintenance applications on
existing structures.
Several of the one-coat systems showed
promising performance in ALT and the outdoor
exposure conditions in terms of surface
failures and rust creepage. GFP and HBAC
were among the top performing candidates.
Comprehensive performance evaluation
showed that the three-coat system was the
best performing system, followed by CSA,
HBAC, and WBEP
.
The two-coat system developed many
coating defects in ALT and had significant
gloss reduction and rust creepage in out-
door exposure conditions, resulting in a low
overall ranking.
Regression analysis showed that color
correlated with gloss in all exposure conditions
as well as coating defects with adhesion
strength variation of unscribed panels in NW.
NW correlated with NWS for color, gloss,
and adhesion strength variations. Similarly,
adhesion strength variations of unscribed
panels in ME correlated well with unscribed
panels of NWS.
•
Performance Ranking
Based on final performance data in ALT and the
outdoor exposures, all one-coat systems and the
two controls were ranked. A comprehensive
numerical analysis was used to assign weighted
coefficients to the four exposure conditions. The
calculated coefficients for the four exposure
conditions are as follows:
•
•
•
•
ALT: 0.64.
ME: 0.11.
NW: 0.12.
NWS: 0.13.
•
•
•
Coefficients were also assigned to the performance
parameters based on the authors’ knowledge
and past experience with their overall impact and
significance in evaluating a coating system.
Weighted coefficients of the various performance
parameters are as follows:
•
•
•
•
•
Rust creepage: 0.35.
Holidays: 0.25.
Adhesion: 0.10.
Color reduction: 0.15.
Gloss reduction: 0.15.
•
•
Final performance ranking of all coating systems is
shown in table 2.
Table 2. Comprehensive rank of one-coat and
control systems.
Coating System
Three-coat
CSA
HBAC
SLX
WBEP
ASP
Two-coat
UM
EM
Rank
1
2
3
4
5
6
7
8
9
3.
2.
References
1.
Chong, S.L. and Yao, Y. (2003).
Laboratory
Evaluation of Water Borne Coatings on Steel,
Report No. FHWA-RD-03-032, Federal Highway
Administration, Washington, DC.
Ault, J.P. and Farschon, C.L. (2009). “20-Year
Performance of Bridge & Maintenance Systems,
”
Journal of Protective Coatings and Linings,
16–32.
ASTM D1654-08. (2010). “Standard Test Method
for Evaluation of Painted or Coated Specimens
Subjected to Corrosive Environments,
Annual
”
Book of ASTM Standards,
Volume 06.01, ASTM
International, West Conshohocken, PA.
3
4.
ASTM D5894-05. (2010). “Standard Practice for
Cyclic Salt Fog/UV Exposure of Painted Metal,
(Alternating Exposures in a Fog/Dry Cabinet
and a UV/Condensation Cabinet),
Annual Book
”
of ASTM Standards,
Volume 06.01, ASTM
International, West Conshohocken, PA.
Chong, S.L., Jacoby, M., Boone, J., and Lum,
H. (1995).
Comparison of Laboratory Testing
Methods for Bridge Coatings,
Report
No. FHWA-RD-94-112, Federal Highway
Administration, Washington, DC.
Ault, P Ellor, J., Repp, J., and Shaw, B. (2000).
.,
Characterization of the Environment,
Report
No. FHWA-RD-00-030, Federal Highway
Administration, Washington, DC.
ASTM D523-08. (2010). “Standard Test
Method for Specular Gloss,
Annual Book
”
of ASTM Standards,
Volume 06.01, ASTM
International, West Conshohocken, PA.
ASTM D2244-09A. (2010). “Standard Practice
for Calculation of Color Tolerances and Color
Differences from Instrumentally Measured Color
Coordinates,
Annual Book of ASTM Standards,
”
Volume 06.01, ASTM International, West
Conshohocken, PA.
9.
ASTM D3363-05. (2010). “Standard Test Method
for Film Hardness by Pencil Test,
Annual
”
Book of ASTM Standards,
ASTM International,
Volume 06.01, West Conshohocken, PA.
5.
10. ASTM D4541-09. (2010). “Standard Test Method
for Pull-Off Strength of Coatings Using Portable
Adhesion Testers,
Annual Book of ASTM
”
Standards,
Volume 06.02, ASTM International,
West Conshohocken, PA.
11. ASTM D5162-08. (2010). “Standard Practice for
Discontinuity (Holiday) Testing of Nonconductive
Protective Coating on Metallic Substrates,
”
Annual Book of ASTM Standards,
Volume 06.02,
ASTM International, West Conshohocken, PA.
12. ASTM D7087.-05A. (2010). “Standard Test
Method for An Imaging Technique to Measure
Rust Creepage at Scribe on Coated Test Panels
Subjected to Corrosive Environments,
Annual
”
Book of ASTM Standards,
Volume 06.01, ASTM
International, West Conshohocken, PA.
6.
7.
8.
Researchers—This
study was performed by SES Group and Associates, Chesapeake City, MD, 21915,
Contract No. DTFH61-08-D-00001.
Distribution—ThisTechBrief
is being distributed according to a standard distribution. Direct distribu-
tion is being made to the Divisions and Resource Center.
Availability—This
TechBrief may be obtained from FHWA Product Distribution Center by e-mail to
report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at http://www.fhwa.dot.
gov/research/.
Key Words—One-coat,
Two-coat, Three-coat, Steel bridge coatings, Corrosion protection, Accelerated
testing, Outdoor exposure, and Coating performance evaluation.
Notice—This
document is disseminated under the sponsorship of the U.S. Department of
Transportation in the interest of information exchange. The U.S. Government assumes no liability for
the use of the information contained in this document. The U.S. Government does not endorse prod-
ucts or manufacturers. Trademarks or manufacturers’ names appear in this report only because they
are considered essential to the objective of the document.
Quality Assurance Statement—The
Federal Highway Administration (FHWA) provides high-quality
information to serve the Government, industry, and public in a manner that promotes public under-
standing. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and
integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and
processes to ensure continuous quality improvement.
MAY 2011
FHWA-HRT-11-047
HRDI-60/5-11(600)E
4

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