introduction to fhwa coatings studies (trb 2009)

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One-Coat Systems Applicable to Steel Bridge Structures

Coatings & Corrosion LaboratoryOffice of Infrastructure R & D

Turner-Fairbank Highway Research CenterFederal Highway Administration

McLean, VA 22101

TRB 2009

One-Coat Systems Applicable to Steel Bridge Structures

Coatings & Corrosion LaboratoryOffice of Infrastructure R & D

Turner-Fairbank Highway Research CenterFederal Highway Administration

McLean, VA 22101

TRB 2009

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Coating SystemsCoating Systems1. 3-coat control (Organic Zn + Epoxy + Polyurethane)2. 2-coat control (MCU-Zn + Polyaspartic)3. Polyaspartic (ASP)4. Epoxy Mastic (EM)5. Calcium Sulfonate Alkyd (CSA)6. Glass Flake Polyester (GFP)7. High Build Acrylic (HBAC)8. Waterborne Epoxy (WBEP)9. Polysiloxane (SLX)10. Urethane Mastic (UM)

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Test PanelsTest Panels

Unscribed Scribed Unscribed Scribed Unscribed Scribed

1 3-coat 3 3 3 3 6 6 24

2 2-coat 3 3 3 3 6 6 24

3 ASP 3 3 3 3 6 6 24

4 EM 3 3 3 3 6 6 24

5 CSA 3 3 3 3 6 6 24

6 GFP 3 3 6**

7 HBAC 3 3 3 3 6 6 24

8 WBEP 3 3 3 3 6 6 24

9 SLX 3 3 3 3 6 6 24

10 UM 3 3 3 3 6 6 24

30 30 27 27 54 54 222

Outdoor Weathering (6 x 12 in.)*Total

** Only laboratory test panels were prepared due to late arrival of test material.

Total

* The test panels will be exposed to natural weathering at Turner-Fairbank facility with periodic salt spray.

System No. System ID

Laboratory (4 x 6 in.) Sea Isle (4 x 6 in.)

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Accelerated Laboratory TestingAccelerated Laboratory Testing1. Freeze Cycle for 24 hours at -23 oC (-10 oF)

2. UV/Condensation Cycle for 168 hours:• 4-hour UV at 60 oC (140 oF)• 4-hour condensation at 40 oC (104 oF)

3. Alternating Salt-Fog Cycle for 168 hours:• 1-hour wet with 0.35% (NH4)2SO4 plus 0.05% NaCl solution at

ambient temperature• 1-hour dry at 35 oC (95 oF)

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Accelerated Laboratory Testing - ContinuedAccelerated Laboratory Testing - Continued

● Test Hours per Cycle: 360 Hours● Total Test Cycles: 19● Total Test Hours: 6,840 Hours● Performance Evaluation After Each Test Cycle

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Outdoor Exposure at TFHRCOutdoor Exposure at TFHRC

• Periodic performance evaluation every six months

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Outdoor Exposure at Sea Isle City, NJOutdoor Exposure at Sea Isle City, NJ

• Periodic performance evaluation every six months

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Periodic Performance EvaluationPeriodic Performance Evaluation1. Surface Defects and Failures ( By holiday detector and digital

microscope )2. Coating Impedance Properties3. Rust Creepage (ASTM D7087)4. Photographic Documentation5. Change of Gloss *

* For outdoor exposed panels only

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PhotomicrographsPhotomicrographs

(2-coat system, 20X) (3-coat system, 20X)

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Rust Creepage Growth (Lab Testing)Rust Creepage Growth (Lab Testing)

0

5

10

15

20

25

30

35

40

0 720 1440 2160 2880 3600 4320 5040 5760 6480 7200

Duration (hour)

Cre

epag

e (m

m)

3-coat2-coatASPEMCSAGFPHBACWBEPSLXUM

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Rust Creepage Growth (Sea Isle City)Rust Creepage Growth (Sea Isle City)

0

5

10

15

20

25

30

35

40

0 4320 8640 12960 17280

Duration (hour)

Cre

epag

e (m

m)

3-coat2-coatASPEMCSAHBACWBEPSLXUM

0.0

0.5

1.0

1.5

12240 129600.0

0.5

1.0

1.5

12240 129600.0

0.5

1.0

1.5

122400.0

0.5

1.0

1.5

12240 12960

0

5

10

15

20

25

30

35

40

0 4320 8640 12960 17280

Duration (hour)

Cre

epag

e (m

m)

3-coat2-coatASPEMCSAHBACWBEPSLXUM

0.0

0.5

1.0

1.5

12240 129600.0

0.5

1.0

1.5

12240 129600.0

0.5

1.0

1.5

122400.0

0.5

1.0

1.5

12240 12960

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3-Coat System (Control)3-Coat System (Control)

0 2,160 4,320 6,840

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CSACSA

0 2,160 4,320 6,840

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GFPGFP

0 2,160 4,320 6,840

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EMEM

0 2,160 4,320 6,840

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WBEPWBEP

0 2,160 4,320 6,840

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UMUM

0 2,160 4,320 6,840

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Findings Findings

1. Two control coating systems (3-coat and 2-coat) had a dry film thickness (DFT) of approximately 13 mils and a pencil scratch hardness of HB.

2. The 3-coat demonstrated very good performance in almost all aspects and slightly better than the 2-coat.

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Findings - Continued Findings - Continued 3. With regard to initial DFT, pencil scratch hardness, and

adhesion properties, the eight one-coat systems varied significantly compared to those of the controls.

4. Four one-coat systems (ASP, WBEP, SLX, and UM) had either higher adhesion strength or thicker DFT compared to the controls, but their performance in terms of defect development, rust creepage, and rate of physical deterioration was far inferior to the rest.

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Findings - Continued Findings - Continued 5. The fifth one-coat system, HBAC, had a DFT of 10.4

mils with a very soft pencil scratch hardness (6B) and showed mixed results with a relatively low number of coating defects, moderate rust creepage resistance, and good physical appearance.

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Findings - Continued Findings - Continued 6. To date, CSA has been the best performer despite its

softness and very weak adhesion strength. 7. GFP is also an excellent coating system and is the 2nd

best in the overall performance rating. These two one-coat systems outperformed the controls.

8. Performance of EM was comparable to those of the control systems.

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100-Year Life Coating Systems

Coatings & Corrosion LaboratoryOffice of Infrastructure R & D

Turner-Fairbank Highway Research CenterFederal Highway Administration

McLean, VA 22101

TRB 2009

100-Year Life Coating Systems

Coatings & Corrosion LaboratoryOffice of Infrastructure R & D

Turner-Fairbank Highway Research CenterFederal Highway Administration

McLean, VA 22101

TRB 2009

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BackgroundBackground1. This is a Congress mandated study under the HPS

program.2. Main objective is to identify and evaluate coating

materials that can provide 100 years of maintenance-free service life for steel bridge structures.

3. This study started in November 2008 and will be carried out for 36 months.

4. Some types of weathering steel will be also tested.

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Coating Systems SelectedCoating Systems SelectedSystem

Number Category Generic Coating Name

1 Control - Conventional 3-coat Shop System IOZ / Epoxy / Aliphatic Polyurethane

2 Control -3-coat OZ Shop System Zn-rich Epoxy / Epoxy / Aliphatic Polyurethane

3 3-coat Fluoro-Topcoat System MCU Zn / Epoxy / Fluorourethane

4 2-coat Fast Dry Coating Zn-rich Epoxy / Aliphatic Polyurethane

5 2-coat Polysiloxane Inorganic Zinc / Polysiloxane

6 Metallizing (conventional) + Topcoat Thermal Sprayed Zinc / Linear Epoxy

7 Organic Zinc Rich Epoxy (Zinc Flake)/Linear Epoxy Experimental Primer / Topcoat

8 Calcium Sulfonate Alkyd HR Single Coat CSA

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Type 1 Test Panels (4 x 6 in.)Type 1 Test Panels (4 x 6 in.)

Accelerated Lab Test

Outdoor Weathering Test

Destructive Test (Ahesion)

Control 2 10 10 4 24

Others 6 30 30 12 72

Subtotal 8 40 40 16 96

Number of Test PanelsNumber of

Coating Systems

CategoryTotal Number

of Test Panels

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Type 2 Test Panels (18 x 18 in.)Type 2 Test Panels (18 x 18 in.)

Outdoor Weathering Test (without salt

spray)

Outdoor Weathering Test (with salt spray)

Outdoor Weathering Test

(Golden Gate Bridge)

Control 2 2 2 2 6

Others 6 6 6 6 18

Subtotal 8 8 8 8 24

Number of Test PanelsNumber of

Coating Systems

CategoryTotal Number

of Test Panels

[A-A] [B-B]

18 in.

18 in.

B

B

A

A

StripeCoat

Weld

Normal Test Area with Attachments

(No Cl-, target anchor profile,

target DFT)

Poorly Prepared Area (4 x 8 in.)(Cl-, less anchor profile, 20% less DFT)

20% Thicker DFTArea (4 x 8 in.)(No Cl-, target anchor profile)

Tee

AngleAngle

Bolt & nut Angle

FHWA Outdoor Large-Scale Weathering Test Panel for 100-Year Coating Study

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Test PanelsTest Panels

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TestsTests1. Coating Thickness2. Gloss3. Color4. Pencil Scratch Hardness5. Infrared Spectrometry6. Adhesion 7. EIS

8. Rust Creepage9. Surface Examination

(Defects & Other Types of Failures)

10. Digital Microscopy11. Digital Photography

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Future Research Ideas (Some Thoughts)Future Research Ideas (Some Thoughts)1. Chloride Tolerance on Various Steel Substrate Conditions

• Test Methods – Accuracy and New Methods• Threshold Values – 7 µg/cm2 (?)

2. Field Coating Performance Monitoring Devices • Thermography• Sensors, etc.

3. Protective Barrier Systems for Concrete Bridge Structures• Waterproofing Membranes for Bridge Decks• Traditional Coating Systems

4. Signage and Pavement Markings

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EIS Test Cells for Field MonitoringEIS Test Cells for Field Monitoring