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TRB 92nd Annual Meeting January 13-17, 2013 Washington, DC
Session 748 – Steel Bridge Coating Systems, Part 2: Existing Structures – AHD30 January 16, 2013
Presented By: Eric Yermack, P.E. Vice President, Structures Co-Author Matthew Neary
Duplex Coating System
Bridge Survey Population
Industry Recommendations
Coating Specifications
Bridge Field Inspections
Paint System Performance
Performance Observations
Cost Comparisons
Recommendations
Yes
Topic
What & Why?
Discuss
Recommend
Finish
No Q&A
A hybrid method of corrosion protection, formed by painting over hot-dipped galvanized steel
ZINC PATINA • Zinc Oxide • Zinc Hydroxide • Zinc Carbonate
Extended corrosion resistance
Synergistic effect
– 1.5 to 2.3 times longer life
Economic benefit
– Lower life-cycle cost
Extend life of previously
hot-dipped galvanized structures
Ease of repainting
Owner preferences and requirements
Aesthetics
BRIDGES • 6 Truss Bridges – 7-Year Average Age • 3 Stringer Bridges – 3-Year Average Age • 1 Arch Bridge – 8-Year Average Age • 1 Replaced / Moved
11 Bridges Considered – 5-Year Average Age 10 of 11 Bridges over water
MATERIALS • Grade 50 (ASTM A707) Steel • Galvanizing – AASHTO M111 • Duplex Coating System (fascia girders only)
Galvanizing: AASHTO M 111M (ASTM A123)
Repair of Galvanizing: ASTM A780
Surface Preparation: ASTM D 6386-99
Paint Application Timing: After one to two years of
atmospheric exposure
Paint: AGA (American Galvanizers
Association) provides guidance, but
does not specify exact Base Primers
and Finish Coats
https://www.galvanizeit.org/
Special Provisions supplement NJDOT Standard Specs
Follow AGA Duplex Systems Recommendations
Typical coating specifications:
Galvanizing : AASHTO M 111M (ASTM A123)
Base Primer: Intercure 420 (Epoxy, 4-7 mils)
Finish Coat: Interthane 990 (Polyurethane, 2-3 mils)
(Both supplied by International Protective Coatings)
Coating Application: Within
24-Hrs of hot-dip galvanizing
Steel Stringer (2008) Exterior faces of fascia beams coated only Flood debris accumulation Coating Rating: 8
Successful in inhibiting iron oxide corrosion
No visible damage to underlying zinc coating
Localized chipping – possibly due to handling or debris collision
Paint adhesion issues present on all structures
Paint flaking in some large, localized areas
Paint failure in areas of debris buildup
Cracking of paint over welds
Gusset plates were a common failure location
Truss members performed well by comparison
Maintenance touch-up painting was effective
Inadequate surface preparation
Use of paint incompatible with zinc
Moisture or debris present on paint surface
Insufficient or excessive galvanizing thickness
Influence of irregularly shaped components (gusset plates) and weld metal
Timing of paint system application
CASE STUDY – Amwell Road Bridge: • 100 Tons of Steel (typical mix sizes/shapes); 25,000 SF • 80 Year Life-Cycle • C3 – Moderately Industrial Environment • 3% Inflation; 4% Interest • Initial Cost & Maintenance Touch-up Painting • 33 Tons for Duplex System (fascia girders only)
Source - American Galvanizers Association (AGA) “Galvanizing Cost” Online Life-Cycle Cost Estimator
AALLTTEERRNNAATTIIVVEESS IINNIITTIIAALL CCOOSSTT LLIIFFEE--CCYYCCLLEE CCOOSSTT
3-Coat Paint System (Entire Bridge) $3.17/ft2 $318,800 A
Hot-Dip Galvanizing* (Entire Bridge) $1.76/ft2 $56,000 B
Duplex System (Entire Bridge) $4.92/ft2 $199,500 C
Duplex System (Fascia Girders Only) $2.82/ft2 $106,600 B & C
A: Maintenance Cycle Years 21, 27, 38, 59, 66, 76 (6 Touch-ups Total) B: Maintenance Cycle Year 72 (1 Touch-up; *Reg. Maintenance Unnecessary) C: Maintenance Cycle Years 46 & 61 (2 Touch-ups Total)
Continue maintenance touch-up painting
Periodically monitor the subject bridge population
Promote the use of self-cleaning bridge details
Determine correlation between structure proximity to water and coating performance
Examine performance of irregular members (gusset plates)
Assess the effect of weld metal
Formulate detailed guidelines for specifying preferred Base Primer and Finish Coat paints
Develop best practices and prepare standard specifications for surface preparation and paint application
Modify Somerset County Special Provisions for paint application
Educate Bridge Owners, Engineers and Inspectors