TECHBRIEF Performance Evaluation 

of One-Coat Systems on

New Steel Bridges 

FHWA Publication No.: FHWA-HRT-11-047

FHWA Contact: Paul Virmani, HRDI-60, (202) 493-3052, 

paul.virmani@dot.gov

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 leadbased predecessors. The purpose of this study is to evaluate the 

performance characteristics of various commercially available highperformance 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 evaluated 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 analysis 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

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 panels were blast cleaned to Scientific Society for Protective Coatings 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

http://www.fhwa.dot.gov/

research/
2

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 

(ASTM) D1654-08.(3) 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.

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 

freeze cycle for 24 h.(4,5)

Outdoor exposure conditions involved the following:

• Marine environment exposure (ME) occurred 

in Sea Isle City, NJ, for 24 months.(6)

• 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.

Performance Evaluation Techniques

Coatings were evaluated before and after exposure 

for the following parameters:

• Gloss (ASTM D523-08) and color (ASTM D2244-

09A).(7,8)

• Pencil scratch hardness (ASTM D3363-05).(9)

• Pull-off adhesion (ASTM D4541-09).(10)

• Number of coating defects/holidays (ASTM 

D5162-08).(11)

• Rust creepage (ASTM D7087-05A).(12)

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 System ID

Coating Type

Primer Intermediate Top

1 Three-coat Zinc-rich epoxy Epoxy Polyurethane

2 Two-coat Zinc-rich moisture 

curing urethane

Polyaspartic (ASP)

3

One-coat*

ASP

4 Epoxy mastic (EM)

5 Calcium sulfonate alkyd (CSA)

6 Glass flake reinforced polyester (GFP)

7 High-build waterborne acrylic (HBAC)

8 Waterborne epoxy (WBEP)

9 Polysiloxane (SLX)

10 Urethane mastic (UM)

* 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.
3

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.

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.

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 outdoor 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.

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.

2. Ault, J.P. and Farschon, C.L. (2009). “20-Year 

Performance of Bridge & Maintenance Systems,” 

Journal of Protective Coatings and Linings, 16–32.

3. 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.

Table 2. Comprehensive rank of one-coat and 

control systems.

Coating System Rank

Three-coat 1

CSA 2

HBAC 3

SLX 4

WBEP 5

ASP 6

Two-coat 7

UM 8

EM 9
4

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 distribution 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 products 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 understanding. 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. 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.

5. 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.

6. 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.

7. ASTM D523-08. (2010). “Standard Test 

Method for Specular Gloss,” Annual Book 

of ASTM Standards, Volume 06.01, ASTM

International, West Conshohocken, PA.

8. 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.

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.