Optimizing Performance of Concrete Structures with Zinc Coated - - PowerPoint PPT Presentation

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Optimizing Performance of Concrete Structures with Zinc Coated - - PowerPoint PPT Presentation

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Optimizing Performance of Concrete Structures with Zinc Coated Reinforcing Steel Shannon Pole, EIT October 18, 2016 International Zinc Association Outline The Corrosion Problem Batch Galvanized Mitigation Solutions Zinc in

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International Zinc Association

Optimizing Performance of Concrete Structures with Zinc Coated Reinforcing Steel

Shannon Pole, EIT

October 18, 2016

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International Zinc Association

Outline

  • The Corrosion Problem
  • Batch Galvanized
  • Mitigation Solutions
  • Zinc in Concrete
  • Continuous Galvanized
  • Research and Current Projects
  • Next Steps
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International Zinc Association

International Zinc Association

  • Trade association that represents the

interests of the zinc industry

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International Zinc Association

Corrosion

  • Affects

– Roads, bridges, buildings, airplanes, machinery, automobiles

  • $2.2 trillion -> corrosion costs worldwide
  • $660 billion -> possible savings
  • 3.3% US GDP -> corrosion mitigation
  • Zinc provides the best corrosion protection
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International Zinc Association

The USA Bridge Problem

  • 604000 bridges across the USA

– 48% state owned

  • 2/3 built 26+ years ago
  • 50-80% maintenance funds for bridge decks
  • 25-30% of corrosion could be eliminated

– If proper materials are used and maintained

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International Zinc Association

Road Salt in North America

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International Zinc Association

Galvanized Reinforcing Steel

Built in 1995 Built in 1990

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International Zinc Association

Batch Galvanized Bridges

Tappen Zee Bridge, New York Boca Chica Bridge, Florida Curtis Road Bridge, Michigan Athens Road Bridge, Pennsylvania

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International Zinc Association

Corrosion of Black Bar

  • Initially – Cosmetic Staining
  • Later – Structural Weakening
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International Zinc Association

Corrosion of Black Bar

Fe FeO Fe3O4 Fe2O3 Fe(OH)2 Fe(OH)3 Fe(OH)3‧3 H2O

1 2 3 4 5 6 Volume (cm3）

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International Zinc Association

Corrosion of Black Bar

  • In concrete, steel corrosion can cause major

deterioration

  • Corrosive elements, diffuse through the

concrete matrix to reach rebar

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International Zinc Association

Corrosion Model

ß Protection à

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International Zinc Association

Zinc Protection

Zn++ 2(OH)- 2e- Zinc Steel Zn Zn++ + 2e- 2e- + H2O +1/2 O2 2(OH)-

Zi Zinc nc Pa Paint

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International Zinc Association

Zinc in Concrete

  • Passivated by formation of a layer of

adherent crystals

– Calcium Hydroxyzincate (CHZ)

  • Reaction begins upon contact with wet

cement solution

– Ceases once concrete hardens

  • Surface film stabilizes the zinc

– Second level of barrier protection

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International Zinc Association

Migration of Zinc

Partial dissolution of the galvanized coating and zinc corrosion product migrating into the cement matrix. Migration of zinc-rich corrosion products away from the bar/matrix interface and well into the cement matrix. 1000x 100x

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International Zinc Association

Bond Strength in Concrete

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International Zinc Association

Load-Slip Characteristics

50 100 150 200 250

Slip ( m)

10 20 30 40 50 60 70 80 90 100

Load (kN)

Black Steel Galvanized Steel Epoxy Coated Steel

Galvanized Reduced slip for galvanized bars Black Epoxy

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International Zinc Association

Zinc Protection

  • Passivation Reaction Product (CHZ)
  • Barrier Coating
  • Cathodic Protection
  • High Chloride Threshold (2-4x black steel)
  • Corrosion Product Migration

– Concrete Matrix Densification – No stress generated at rebar surface

  • Low pH Tolerance (Carbonation protection)
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International Zinc Association

Batch Galvanized Coating

ASTM A767 Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement

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International Zinc Association

Batch Galvanized Process

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International Zinc Association

Continuous Galvanized Coating

Pure Zinc Layer Thin Fe2Al5-xZnx Layer ASTM A1094 - Standard Specification for Continuous Hot-Dip Galvanized Steel Bars for Concrete Reinforcement

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International Zinc Association

Improved Corrosion Resistance

Coating Type Average Depth of Loss to Passivation (um) Annealed (Intermettalic) 1.18 Pure Zinc 0.45

  • Pure Zinc corrodes at a slower rate than Iron-

Zinc Intermettalic

  • Less zinc consumed to form CHZ passivation

layer

  • Less zinc required to provide corrosion

resistance

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International Zinc Association

Zn (eta) phase current density = 2.38 A/cm2 ( ______ line) Zeta (Zn-Fe) phase current density = 3.98 A/cm2 ( _ _ _ line) Therefore Zn 1.7 times more corrosion resistant than Zn-Fe in the concrete corrosion cell pH=13 NaOH

How does the 50 µm In-Line coating corrosion resistance compare to the 85μm General Galvanized coating? Results of potentiodynamic polarization tests

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International Zinc Association

Continuous Galvanized Rebar

  • Durable, Flexible Coating

– Fabricate after coating

  • Pure Zinc

– Improved corrosion resistence

  • Low cost

– Less material, shipping, weight, etc.

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International Zinc Association

Formability

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International Zinc Association

USA trademark application 85882085 made by IZA

ASTM A1055 - pending Standard Specification for Zinc and Epoxy Dual-Coated Steel Reinforcing Bars

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International Zinc Association

Duplex Bar Formability

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International Zinc Association

Continuous Galvanized Process

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International Zinc Association

Rollers into Induction Heater

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International Zinc Association

From Heater to Zinc Bath

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International Zinc Association

Zinc Bath

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International Zinc Association

Bath through Air Knife to Quench

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International Zinc Association

Continuously Galvanized

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International Zinc Association

Quality Assurance

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International Zinc Association

Installing Galvanized Rebar

Same as Black rebar:

  • Overlap links
  • Handling procedures
  • Field Bending Possible

Optional:

  • Touch-up field cut ends
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International Zinc Association

Route 66 Bridge

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International Zinc Association

University of Waterloo

  • Tomb stone samples

– Sound – Transverse & Longitudinal Cracks

  • Cyclical ponding

– 21% chloride brine

  • No visible corrosion
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International Zinc Association

Corrosion Current - Sound

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International Zinc Association

Corrosion Current - Transverse

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International Zinc Association

Corrosion Current - Longitudinal

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International Zinc Association

Shenzhen Metro Line No. 11, Shenzhen, China

  • Currently under construction
  • Opening later this year
  • Fastest Metro line in Shenzhen with speeds of 120 km/h
  • Galvanized rebar is being produced by Xiamen Newsteel
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International Zinc Association

G7 Beijing–Ürümqi Expressway

Connects the cities of Beijing, China, and Ürümqi, Xinjiang. When complete, it will be 2,540 km (1,580 mi) in length. Galvanized rebar is being produced by Xiamen New Steel

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International Zinc Association

Comparison versus Black Bar

1 2 3 4 5 6 7 Black Epoxy Galvanized MMFX Stainless CGR* Bluebar*

FHWA, 2012 *estimated

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International Zinc Association

USA Production

  • AZZ Galvanizing

– Fall 2016 – Oklahoma

  • South Atlantic Reinforcing

– Air Wipe Method

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International Zinc Association

Continuous Galvanized Rebar

Low Cost Tough Corrosion Resistant Formable For more Information and Samples contact: Shannon Pole spole@zinc.org