One Coat Systems for New Steel Bridge Structures

1. One Coat Systems for New Steel Bridge Structures

2. Learning Outcomes • At the end of this webinar you will be able to: • Define a one-coat system for bridge structures • Report the results of a two year study conducted by the Federal Highway Administration • Report the results of a Federal Highway Administration funded study conducted by Connecticut DOT • State the advantageous and disadvantageous of using a one-coat system on a bridge structure

3. Introduction Federal Highway Administration (FHWA) funded two studies that evaluate the use of a one-coat system to protect bridges from corrosion

4. Why a One-Coat System? • The typical coating system consists of 3 coats: • Zinc-Rich Primer • Epoxy Intermediate Coat • Polyurethane Topcoat • Going to a one-coat system will lower: • Overall Cost • Amount of time and space needed for application

5. One-Coat System Development of a one-coat system would involve formulation of a coating system that will provide a lifetime of corrosion protection and be applied in one, quick-dry coat at the time of initial fabrication of the bridge in the fabrication shop

6. One-Coat Coatings • The current standard for evaluating coatings applied to structural steel is “AASHTO R31, Project Work Plan for the Laboratory Evaluation of Structural Steel Coatings” • Performance of a one-coat coating system should equal or exceed the performance of the current “gold” standard system: IOZ/EP/URE

7. FHWA Study • Test panels prepared to SSPC SP 10 level of cleanliness with an anchor profile between 2-3 mils • 2 control systems • 3 coat system • 2 coat system • 8 one-coat test systems

8. Coating Systems • Control Systems: • 3-coat control (Organic Zinc + Epoxy + Polyurethane) • 2-coat control (Zinc-Rich Moisture Cured Urethane + Polyaspartic) • One-Coat Systems: • Polyaspartic (ASP) • Epoxy Mastic (EM) • Calcium Sulfonate Alkyd (CSA) • Glass Flake Polyester (GFP) • High Build Acrylic (HBAC) • Waterborne Epoxy (WBEP) • Polysiloxane (SLX) • Urethane Mastic (UM)

9. FHWA Study • Performance of coating systems were evaluated by: • Volatile content • Binder content • Pigment content • Pencil scratch hardness • DFT • Accelerated Laboratory Testing • Surface Defects • Adhesion Strength

10. Coating Systems

11. Pencil Scratch Hardness Tested per ASTM D3363-05, “Standard Test Method for Film Hardness by Pencil Test

12. Pencil Scratch Hardness

13. Initial Final 6H 5H 4H 3H 2H H F Scratch Hardness HB B 2B 3B 4B 5B 6B <6B 3-coat 2-coat ASP EM CSA GFP HBAC WBEP SLX UM Coating System Pencil Scratch Hardness

14. DFT • Measured per SSPC PA 2, “ Measurement of Dry Film Thickness with Magnetic Gage” • Appendix 6 - Method for Measuring Dry Film Thickness of Thin Coatings on Coated Steel Test Panels that Had Been Abrasive Blast Cleaned

15. DFT

16. Accelerated Laboratory Testing • Total hours per cycle = 360 hours • Freeze Cycle for 24 hours at -23 oC (-10 oF) • UV/Condensation Cycle for 168 hours: • 4-hour UV at 60 oC (140 oF) • 4-hour condensation at 40 oC (104 oF) • 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) • Total test cycles = 19 • Total hours = 19 X 360 = 6840 hours • Performance evaluation after each test cycle

17. Outdoor Exposure at Turner Fairbank Research Center • Periodic performance evaluation every six months

18. Outdoor Exposure at Sea Isle, NJ • Periodic performance evaluation every six months

19. Outdoor Exposure Test Sites Due to insufficient data, test results obtained from the outdoor exposure test sites will not be included in this presentation and will be reported at a future time

20. Outdoor Exposure Test Sites • Data being gathered on panels at these sites are: • Gloss per ASTM D523, Standard Test Method for Specular Gloss • Color per ASTM D2244, Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates • Coating Impedance per Electrochemical Impedance Spectroscopy (EIS)

21. Electrochemical Impedance Spectroscopy (EIS) EIS studies the system response to the application of a periodic small amplitude ac signal. These measurements are carried out at different ac frequencies and, thus, the name impedance spectroscopy was adopted Analysis of the system response contains information about the interface, its structure and reactions taking place

22. Electrochemical Impedance Spectroscopy (EIS) EIS is used to forecast the remaining life of a coating system

23. Rust Creepage Measured per ASTM D7087-05a, “Standard Test Method for an Imaging Technique to Measure Rust Creepage at Scribe on Coated Test Panels Subjected to Corrosive Environment”

24. Rust Creepage Growth

25. Rust Creepage Growth • Poor Performance: • ASP, SLX, UM and WBEP • Intermediate Performance: • HBAC and EM • Good Performance: • GFP and CSA

26. Surface Coating Defects Holidays were measured per ASTM D5162-01, “Standard Practice for Discontinuity (Holiday) Testing of Nonconductive Protective Coating on Metallic Substrates”

27. Surface Coating Defects

28. Adhesion Adhesion was measured per ASTM D4541-01, “Standard Test Method for Pull-Off Strength for Coatings Using portable Adhesion Testers” Initial adhesion tests were conducted using a pneumatic adhesion tester, which was replaced with a new hydraulic adhesion tester in the middle of the study

29. 3000 Initial Initial Final - Unscribed Final - Unscribed Final - Scribed Final - Scribed 2500 2000 Adhesion Strength (psi) 1500 1000 500 0 3-coat 2-coat ASP EM CSA GFP HBAC WBEP SLX UM Coating System Adhesion Strength

30. Adhesion Strength

31. FHWA Study Findings • Based on the initial coating characteristics of eight one-coat materials and two controls, and their 20-month performance data, the following findings were made: • Calcium sulfonate alkyd has been the best performer • Glass flake polyester is an excellent coating system and is the 2nd best in overall performance • Both of these coating systems out performed the control systems • Organic Zinc + Epoxy + Polyurethane • Zinc-rich Moisture Cured Urethane + Polyaspartic

32. Second Study

33. 2005 FHWA Connecticut DOT Study • 3 one- coat systems were tested per “AASHTO R31, Project Work Plan for the Laboratory Evaluation of Structural Steel Coatings” • Polyaspartic • Polysiloxane • Waterborne Epoxy

34. 2005 FHWA Connecticut DOT Study • The 3 coating systems were tested for: • Accelerated testing • Rust Creepage • Gloss Retention • Color Retention • Adhesive Strength • Abrasion Resistance

35. Accelerated Testing Polyaspartic and Waterborne Epoxy coating systems did not blister after 15,336 hour cyclic weathering exposures

36. Rust Creepage All three coating systems exhibited severe blistering along and away from the scribe area, as well as undercutting beneath the scribe

37. Aesthetics Color retention for the three systems was excellent. The gloss retention was approximately 40-50% for polyaspartic and waterborne epoxy coating systems Polysiloxane did not complete test- was pulled early due to poor performance

38. Adhesion Adhesion strength of the materials was high and well in excess of the suggested minimum (600 psi) adhesion values prescribed by AASHTO Specification R31

39. Abrasion Resistance The coating system that exhibited the best abrasion resistance was polyaspartic with waterborne epoxy performing the worst

40. 2005 FHWA Connecticut DOT Study Findings • The two systems that performed the best were: • Polyaspartic • Waterborne Epoxy • Neither materials tested as well IOZ/Epoxy/Polyurethane and are recommended only for mild environments

41. Summary In summary, while not yet equal to the standard three-coat systems, one-coat materials tested show significant promise

42. What is the Next Step? To determine the ultimate field performance of one-coat systems.. Field exposure will be targeted to different demanding environments, e.g., freshwater marine, saltwater marine, inland dry, and control test sites