One Coat Systems for New Steel Bridge Structures

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One Coat Systems for New Steel Bridge Structures
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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

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Introduction

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

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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

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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

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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

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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

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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)

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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

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Coating Systems
System ID Volatiles Pigment Binder Initial Scratch Hardness Final Scratch Hardness
3- Coat NA NA NA HB HB
2- Coat NA NA NA HB HB
Polyaspartic 22.7 38.1 39.2 6B 4B
Epoxy Mastic 11.1 39.2 49.7 HB HB
Calcium Sulfonate Alkyd 23.1 26.6 50.3 Softer than 6B Softer than 6B
Glass Flake Polyester 35.0 18.7 46.3 2H 2H
High Build Acrylic 33.2 27.1 39.7 6B 6B
Waterborne Epoxy 43.5 31.0 25.5 HB HB
Polysiloxane 7.7 30.2 62.1 HB 2H
Urethane Mastic 23.6 29.4 47.0 2B HB
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Pencil Scratch Hardness

• Tested per ASTM D3363-05, Standard Test Method
  for Film Hardness by Pencil Test

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Pencil Scratch Hardness
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Pencil Scratch Hardness
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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

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DFT
Coating System 5-10 mils 10-15 mils Greater than 20 mils
Epoxy Mastic X
Polysiloxane X
Urethane Mastic X
Calcium Sulfonate Alkyd X
High Build Acrylic X
Waterborne Epoxy X
3- coat control X
2- coat control X
Polyaspartic X
Glass Flake Polyester X
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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

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Outdoor Exposure at Turner Fairbank Research
Center

• Periodic performance evaluation every six months

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Outdoor Exposure at Sea Isle, NJ

• Periodic performance evaluation every six months

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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

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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)

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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

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Electrochemical Impedance Spectroscopy (EIS)

• EIS is used to forecast the remaining life of a
  coating system

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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

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Rust Creepage Growth
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Rust Creepage Growth

• Poor Performance
• ASP, SLX, UM and WBEP
• Intermediate Performance
• HBAC and EM
• Good Performance
• GFP and CSA

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Surface Coating Defects

• Holidays were measured per ASTM D5162-01,
  Standard Practice for Discontinuity (Holiday)
  Testing of Nonconductive Protective Coating on
  Metallic Substrates

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Surface Coating Defects
Coating System of Coating Defects (Holidays, Rust and Blisters)
Urethane Mastic Uncountable
Polyaspartic Uncountable
Polysiloxane 32 at 4320 hours
High Build Acrylic 7
Waterborne Epoxy 5
Calcium Sulfonate Alkyd 2
2- Coat Uncountable Holidays at 5760 hours
Epoxy Mastic Uncountable Holidays at 6120 hours
Glass Flake Polyester 0
3- Coat 1
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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

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Adhesion Strength
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Adhesion Strength
Coating System Initial Adhesion Strength Final Adhesion Strength
3- Coat Greater than 1500psi Lost Adhesion
Waterborne Epoxy Greater than 1500psi Lost Adhesion
Epoxy Mastic Greater than 1500psi Lost Adhesion
Polysiloxane Greater than 1500psi Lost Adhesion
Urethane Mastic Greater than 1500psi Lost Adhesion
Glass Flake Poylester Near 1000psi Gained Adhesion
2-Coat Near 1000psi Gained Adhesion
Polyaspartic Less than 650psi Gained Adhesion
High Build Acrylic Less than 650psi Gained Adhesion
Calcium Sulfonate Alkyd 280psi Gained Adhesion
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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

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• Second Study

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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

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2005 FHWA Connecticut DOT Study

• The 3 coating systems were tested for
• Accelerated testing
• Rust Creepage
• Gloss Retention
• Color Retention
• Adhesive Strength
• Abrasion Resistance

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Accelerated Testing

• Polyaspartic and Waterborne Epoxy coating systems
  did not blister after 15,336 hour cyclic
  weathering exposures

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Rust Creepage

• All three coating systems exhibited severe
  blistering along and away from the scribe area,
  as well as undercutting beneath the scribe

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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

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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

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Abrasion Resistance

• The coating system that exhibited the best
  abrasion resistance was polyaspartic with
  waterborne epoxy performing the worst

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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

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Summary

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

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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