Cost of Corrosion Corrosion Protection of Reinforcing Steel in Concrete

! !

Corrosion is the single most important cause of damage to concrete structures NACE estimates the cost of corrosion damage to concrete structures (in the USA) is approximately

$ 125 Billion per year!!!

Matt Miltenberger, P.E. Vector Corrosion Technologies, Inc.

Environmental Factors – Chloride Ion

Salt Dripping off Vehicles

Salting of Highways

Airborne Salt Deposition

!

Reduction of pH in cover concrete that causes loss of passive oxide layer

!

Increased rate with increased w/cm

!

Low pH caused by reaction of free lime (Ca(OH)2) in concrete with atmospheric Carbon Dioxide (CO2) Ca(OH)2 + CO2 CaCO3 + H2O lime (soluble) (insoluble) pH 12-13 pH < 9

Marine Exposure

Corrosion Service Life Damage

Environmental Factors - Carbonation

Requirements for Rebar Corrosion

End of Functional Service Life

!

1. Anode (location where metal is lost)

Anodic Ring Damage Repair Events

!

2. Cathode (steel surface)

!

3. Electrical connection (steel)

!

4. Electrolytic connection (moist concrete)

– pH < 11 and/or chloride ion initiate corrosion – Oxygen and water are consumed

Initial Damage

– Electron transfer from anode to cathode

Corrosion Initiation Transport

1-100 yr?

Time

5-10 yr

5-7 yr

– Ionic transfer from cathode to anode

1

Corrosion Macro-Cell in Concrete

Corrosion Macro-Cell

Chloride Contaminated Concrete

Fe + 2Cl-

FeCl2 + 2e -

2Cl-

FeCl2 Area ) Anode ( Corroding FeCl2 + 2OH-

Cathode

Fe(OH)2 + 2Cl-

Fe3O4 γFe2O3

Fe2O3 + 2H2O

2Fe(OH)2 + 1/2O2

2e -

2OH1/ O 2 2

+ H2O + 2e -

Anode

Fe3O4 γFe2O3

2OH-

Cathode ( Non-Corroding Area ) © Vector

Anodic Ring (Halo Effect)

Halo Effect

!

Anodic ring phenomena are associated with a repair area that is surrounded by “new” corrosion sites.

!

Anodic ring phenomena are one of the primary reasons for short-lived repairs.

Chloride Transport

Corrosion Initiation - Microcell Numerous anodic sites activate

O2 Cl -

Cl -

H2O

Cl-

O2

Cl Cl Cl Cl Cl Cl Cl Cl - Cl - Cl Cl Cl - Cl - Cl -

-

-

-

-

-

-

Cl -

Cl -

Cl Cl -

-

Cl -

Cl

Cl -

-

Cl -

H2O

Cl-

Cl Cl Cl Cl Cl Cl Cl Cl - Cl - Cl - Cl Cl -Cl - Cl Cl Cl Cl Cl Cl Cl Cl Cl -

-

-

Cl Cl -

Cl Cl -

Cl -

Cl -

Cl -

Cl Cl -

Cl -

-

Cl -

Cl -

Cl -

Cl -

Cl Cl -

-

2

Corrosion Damage - Macrocell

Structure after Repair

Primary anodic site cathodically protects smaller sites Cl-

O2

H2O

Cl Cl Cl Cl Cl Cl Cl Cl - Cl - Cl Cl -Cl - Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl

-

-

Secondary anodic sites activate O2

Cl Cl -

Cl Cl

Cl -

Cl -

Cl -

-

-

Cl Cl -

Cl

-

Cl -

Cl -

Cl

Cl -

Cl -

-

-

Cl -

Cl Cl Cl Cl - Cl Cl -Cl Cl Cl Cl - - Cl Cl

Cl -

Cl

Corrosion Cell at Repair Edge

-

Chloride Contaminated Concrete

2OH-

H2O Cl -

-

-

Secondary anodic sites grow Cl-

Cl Cl Cl Cl Cl Cl Cl Cl - Cl Cl Cl Cl -

Cl Cl Cl Cl - Cl Cl -Cl Cl Cl Cl Cl Cl

Anodic Ring Damage O2

H2O

Cl-

Cl

Cl

-

-

-

Cl -

Cl -

Cl -

Cl Cl -

Cl -

-

Cl -

Cl -

Cl -

Cl -

Cl Cl -

-

2e -

Anode Fe

1/ O + 2 2

H2O + 2e -

2OH-

Cathode

Fe2+ + 2e -

Fe2+ + 2ClFeCl2 +

Chloride-Free Patch

FeCl2

2OH-

2Fe(OH)2 + 1/2O2

Fe(OH)2 + 2ClFe2O3 + 2H2O

© Vector

Steel Corrosion “Battery” Anode (Corroding steel) Corrosion Current 0.2 to 0.4 V (µA) +

Concrete Resistance (ohm)

Cathode (Passive steel) © Vector

Anodic Ring Corrosion Pier Cap Repair, Pennsylvania

© Vector

3

Spalled Ceiling Patches Concrete Building, Hawaii

Corroded Joint Pittsburgh, Pennsylvania

New Concrete Extension Old Parent Concrete

Old Retaining Wall Concrete Patch Failed Concrete Next to Joint Due to Corrosion © Vector

Corrosion Management Strategies

Corrosion Mitigation Options ! ! ! ! ! !

© Vector

Levels of Corrosion Protection

Address Cause for Corrosion Activity Remove Contaminated Concrete – Partial or full-depth repairs Dry the concrete Localized protection along interface Cathodic protection of entire element Electrochemical treatments

Corrosion Prevention

Preventing new corrosion activity from initiating

Corrosion Control

Significantly reducing on-going corrosion activity

Cathodic Protection

Highest level of protection intended to stop on-going corrosion activity

Corrosion Passivation

Stopping active corrosion by changing the environment around the steel

© Vector

Galvanic Corrosion Protection Diagram Zinc Anode

0.2 to 0.4 V

Corrosion Prevention in Concrete Repairs Using Discrete Galvanic Anodes !

GCP current (µA)

0.4 to 0.8 V Anodic steel

© Vector

-

Corrosion current (µA) +

Concrete Resistance (ohm)

Corrosion prevention – Use to prevent corrosion sites from initiating next to concrete repairs (ICRI Guideline 03730) – At joints between new and existing chloride-contaminated concrete

!

Alkali activated

!

Patented installation technique

!

Wide range of applications

– Contains no constituents corrosive to rebar – Quick and easy – Suitable for conventionally reinforced, prestressed and posttensioned concrete structures

Cathodic steel © Vector

© Vector

4

What is the purpose of the mortar shell around the anode? !

Mortar is specially formulated to keep the zinc active over time.

!

Mortar accepts corrosion by-products from the zinc core.

– pH ≈ 14

© Vector

Repair with Discrete Galvanic Anode Chloride-Free Patch

Chloride Contaminated Concrete

Zn + 2OH-

2e 1/ O + 2 2

2e-

Zn(OH)2 + 2e2e-

H2O + 2e 2OH-

2OH-

Galvanic Corrosion Prevention Parking Garage, North York, Ontario © Vector

© Vector

© Vector

© Vector

Galvanic Corrosion Prevention Port Mann Bridge: Deck Widening

5

Anode Installation with Rebar Coating

Post Tension Anchor Repairs Watergate Complex, Washington, D.C. © Vector

Corrosion Control in Sound Concrete with Discrete Galvanic Anodes

© Vector

Discrete Galvanic Anode Installed in Sound Concrete Corrosion Activity is Reduced In Rebar

Anode Galvanically Protects Surrounding Rebar

© Vector

© Vector

Steel connection next to pre-drilled 2” diameter hole Anode/Steel Connector Anode

Steel Connection

2” Diameter Hole © Vector

© Vector

6

Localized Protection with Discrete Galvanic Anodes in Critical Areas

Embedded Galvanic Anodes in Prestressed Box Girder Repair

Galvanic Anodes in Drilled Holes Prestressing Strands

© Vector

© Vector

Galvanic Anodes in Prestressed Box Girder

! !

Galvanic Corrosion Control NYSDOT: Prestressed Concrete Beam Repair

New York State Department of Transportation © Vector

Cathodic Protection Systems !

Work by applying sufficient current to reinforcing steel to overcome the corrosion process

!

Galvanic Systems: Sacrificial metal corrodes to provide protective current Impressed Current Systems: D.C. power supply provides current (rectifier or battery)

© Vector

Galvanic Cathodic Protection with Distributed Anodes

© Vector

7

! !

Galvanic Cathodic Protection Deck Overlay Ontario Ministry of Transportation

Galvanic Cathodic Protection in Pile Jackets © Vector © Vecto

Galvanic Cathodic Protection with Activated Arc-Sprayed Zinc

© Vector

Impressed Current Cathodic Protection Discrete Anode System Discrete Anodes

+

Permanent DC Power Supply

Rebar

Slot Cut for Wiring Anodes © Vector

Installation of Discrete Anode ICCP System Winnipeg, Manitoba

Installation of Discrete Anode System Winnipeg, Manitoba © Vector

© Vector

8

Impressed Current Cathodic Protection Using Distributed Anode System +

Permanent DC Power Supply Concrete Overlay Concrete Rebar Embedded Anode

Electrochemical Treatments

Corrosion Passivation !

!

Extensive ECE Testing Undertaken (SHRP) Confirmed ECE’s Ability to: – Halt Corrosion – Restore Passive Oxide Film on Rebar

! ! !

!

No Adverse Chemical or Mechanical Effects ECE Deemed one of the Most Valuable Technologies Evaluated Long Term Data Shows Rebar Still Passive

Proven long term performance Measurable criteria: – ECE: Chloride content before and after 700 to 1500 A*hr/m2 (SHRP) – Realk: pH before and after (phenolphthalein) 100 to 250 A*hr/m2

Modify the chemistry of the concrete to create a passive environment around the reinforcing steel.

Electrochemical Chloride Extraction SHRP Research !

!

Electrochemical Chloride Extraction (ECE) From Salt Contaminated Concrete Temporary Anode

Conductive Media

DC Power Source Cl-

ClCl-

ClCl-

Cl-

-

Cl Cl-

Cl-

Concrete ClCl-

Cl-

Reinforcement © Vector

9

Electrochemical Chloride Extraction (ECE) From Salt Contaminated Concrete Temporary Anode

Current paths

Electrochemical Chloride Extraction (ECE) From Salt Contaminated Concrete

Conductive Media

Current paths

DC Power Source

DC Power Source Cl-

Cl-

-

Cl

Cl-

Cl

Cl-

-

Cl

Cl

Cl-

-

Cl

Chloride migrates toward surface

OH-

Cl-

ClCl-

Cl Cl-

-

-

Cl-

Cl-

Cl-

Conductive Media

Temporary Anode

Cl-

Cl-

Cl-

-

Cl

Cl-

Cl-

Chloride migrates toward surface

OH-

Increased pH at Reinforcement © Vector

Increased pH at Reinforcement

© Vector

Electrochemical Chloride Extraction (ECE) From Salt Contaminated Concrete Current paths DC Power Source

Cl-

Cl

Cl-

Cl

Cl-

Temporary Anode

Conductive Media

Cl-

Cl-

Cl-

Cl--

Cl-

ClCl-

Chloride migrates toward surface OH-

Step 1 : Concrete Repair

Increased pH at Reinforcement © Vector

Step 2 : Install Battens

© Vector

© Vector

Step 3 : Install Temporary Anode

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Step 4: Spray Cellulose Fiber

© Vector

© Vector

St. Adolphe Bridge over Red River St. Adolphe, Manitoba Manitoba Highways and Transportation

Piers after ECE Treatment Cleaned and Sealed

© Vector

Realkalization !

Several Piers Wrapped and Undergoing ECE Treatment Omaha, Nebraska

© Vector

Realkalization

Draws highly alkaline electrolyte to the reinforcing steel to restore lost alkalinity to carbonated concrete

Anode

Electrolyte

+ve

!

Alkalinity around reinforcing steel is maintained over time, will not re-carbonate

-ve

Concrete

!

Lower cost, less disruptive than mechanical removal and replacement of carbonated concrete

Section 3

Reinforcement © Vector

11

Realkalization

Realkalization Electrolyte

Anode

Anode

+ve

+ve

-ve

-ve

Electrolyte

Na2CO3 & NaHCO3 Concrete

Concrete

OH-

Reinforcement

Reinforcement © Vector

© Vector

Realkalisation Project Xerox Document University Leesburg, Virginia

Phenolphthalein Testing !

Testing on Cores Before After

!

The affects of realkalization: increased pH around steel

Section 2 © Vector

© Vector

Summary

Reagan National Airport Facade Washington, DC

Level of Protection Corrosion Prevention Corrosion Control

Description

Typical Solution

Preventing new corrosion activity from initiating

Discrete Galvanic Anodes

Significantly reducing active corrosion

Discrete Galvanic Anodes

Cathodic Protection

Stopping active corrosion by applying on-going electrical current

Distributed Galvanic Anodes or Impressed Current Cathodic Protection (ICCP)

Corrosion Passivation

Stopping active corrosion by changing the concrete environment around the steel

Electrochemical Treatments (ECE or Realkalization)

12