Exploratory Advanced Research . . . Next Generation Transportation Solutions

to steel and other coatings. This two-phase 

EAR project aims to deliver a nanotechnologybased coating that meets these requirements 

at a lower life-cycle cost. In phase 1, researchers 

incorporated nanomaterials in two novel coating systems: 

•	 A polyaniline (PANI) epoxy system with

added carbon black. A polymer with high 

electrical conductivity, PANI was used to reduce the need for added zinc and improve 

scratch resistance. 

•	 A nanomaterial-enhanced calcium sulfonate

alkyd (CSA) system. Nanoclay, which is less

costly than other nanomaterials, was used 

to improve corrosion resistance and scratch 

resistance.

Risks and Challenges

The researchers expect to learn much about

the behavior of nanomaterials within alkyd and 

epoxy coatings during this process. “The continuing challenge in using nanomaterials in this 

way,” says FHWA’s Paul Virmani, “is to disperse

the additives evenly throughout the mixture

and stabilize the uniform distribution. Nanoparticles tend to agglomerate into larger formations, disrupting availability of the advantageous properties they contribute.” Carbon

black also tends to clump when mixed in liquids, and rapid gelling of some PANI additives

could complicate large-scale, spray application of a coating.

Early Results and Next Steps

In phase I, the investigators compared the properties of the two experimental coatings, at

different concentrations of additives, with those 

of an organic zinc–rich epoxy-based primer.

(All coating systems in the project receive polysiloxane topcoats.) The PANI-epoxy system

performed well in short-term electrochemical 

impedance spectroscopy tests. The nanoclayenhanced CSA system was superior in adhesion

strength, drying time, and scratch resistance, 

The Exploratory Advanced Research Program Fact Sheet

The Search for Low-Cost, Safe Steel 

Coatings

Corrosion of steel bridges reduces bridge service life and compromises public safety. Caused

by exposure to moisture and atmospheric pollutants, particularly chlorides and sulfates, corrosion costs the Nation an estimated $500 million

annually based on year 2002 index of cost for

maintenance and rehabilitation. Consequently,

the development of more effective steel coatings has been a high-priority research area for 

many years.

The earliest protective steel coatings contained lead and chromate, and replacement of 

these deteriorating, toxic paints with safer coatings on older bridges continues at great expense

today. In the 1960s, zinc-rich epoxy primer coatings came into use. While zinc provides good 

protection from corrosion, it presents some environmental risks. Any new steel primer, besides 

providing better corrosion inhibition, greater 

scratch resistance, and reduced environmental 

risk, should be easy to apply, quick-drying, resistant to ultraviolet rays, and able to adhere tightly 

Slowing the deterioration of steel 

infrastructure with safer, corrosionresistant coatings is the goal of the 

Exploratory Advanced Research (EAR)

Program project “Green Advanced Coatings for Application on Steel Structures

and Bridges.” The project will also 

develop a model to assist bridge owners 

in setting optimal rehabilitation schedules 

for steel bridges. City College of New

York is conducting this research, which 

was funded by the Federal Highway 

Administration (FHWA) in 2009. 

Greener Protection for Steel Bridges

Testing Nano-Enhanced Corrosion-Resistant Coatings
but corrosion resistance seemed compromised 

by uneven dispersal of nanoparticles. 

In phase II, now underway, the project will 

explore two alternative additives for the CSAbased system and conduct accelerated testing 

and weathering studies of the CSA- and epoxybased coatings. Accelerated corrosion tests will 

be equivalent to 20 years of field exposure that

includes some elevated temperatures, salt exposure, humidity, and sulfur-dioxide exposure

cycles. In the outdoor weathering study, with 

and without salt, periodic testing at five intervals will be used to characterize performance 

over 18 months. For the CSA-nanoadditive

system, researchers will first concentrate on improving and quantifying the dispersal of nanoclay and re-testing the system’s properties. They 

will also conduct these activities using nanosilica and nanoalumina as alternative additives, 

and the most promising of the three CSA-nanoadditive coatings will be subjected to the accelerated environmental testing and outdoor 

weathering study. Finally, the epoxy-PANI coating and the best-performing CSA-nanoadditive

coating will be tested further in a 16-month, 

large-panel outdoor study. Throughout the project’s tests, performance will be compared to 

standard zinc-rich and zinc-free control coatings. The comprehensive testing program for 

this project will determine the realistic expected

life of the coating system for steel bridges 

located in adverse environments in the field.

Improving Steel Bridge Management

Detailed data on various performance parameters from the research during the investigation 

will be used to estimate lifetime deterioration of 

structural components. “Success in this project

will advance research and practice in steel coatings in several ways,” Virmani concludes, “first

by providing new insights into the process of 

incorporating nanomaterials in alkyd and epoxy

coatings; second, by presenting new formulations with potential for further development; 

and finally, by advancing life-cycle management

of steel bridges through improved understanding of steel corrosion processes.” Although 

this project is focused on protection of steel 

bridges, a new corrosion-inhibiting and environmentally friendly steel coating would have 

many other potential applications for other 

steel structures.

Learn More

For more information on this project, contact 

Paul Virmani, FHWA Office of Infrastructure

Research and Development, at 202-493-3052

(email: paul.virmani@dot.gov).

Publication No. FHWA-HRT-13-064

HRTM-30/05-13(1M)E 

Greener Protection for Steel Bridges 

Testing Nano-Enhanced Corrosion-Resistant Coatings

Photo credit, page 1:

© Thinkstock.com/

Keith Levit Photography

Photo credit, page 2:

© Shutterstock.com/PRILL

What Is the Exploratory 

Advanced Research Program?

FHWA’s Exploratory Advanced Research

(EAR) Program focuses on long-term,

high-risk research with a high payoff 

potential. The program addresses underlying gaps faced by applied highway 

research programs, anticipates emerging 

issues with national implications, and 

reflects broad transportation industry 

goals and objectives. 

To learn more about the EAR Program, visit the Exploratory Advanced

Research Web site at www.fhwa.dot.gov/

advancedresearch. The site features information on research solicitations, updates 

on ongoing research, links to published 

materials, summaries of past EAR Program events, and details on upcoming 

events. For additional information, contact 

David Kuehn at FHWA, 202-493-3414

(email: david.kuehn@dot.gov), or Terry

Halkyard at FHWA, 202-493-3467 (email:

terry.halkyard@dot.gov).