developments in cathodic protection of steel in · pdf filedevelopments in cathodic protection...

CORROSION CONTROL

BRIAN WYATT BRIAN WYATT Eur Ing, BSc (Hons), C Eng, MIM, FICorr, FIHT, FCSEur Ing, BSc (Hons), C Eng, MIM, FICorr, FIHT, FCS

CORROSION CONTROLCORROSION CONTROL Affiliates Ltd3 Ivy Court, Acton Trussell, Staffordshire ST17 0SN3 Ivy Court, Acton Trussell, Staffordshire ST17 0SNwww.controlcorrosion.co.ukwww.controlcorrosion.co.uk

Developments in Cathodic Protection Developments in Cathodic Protection of Steel in Concreteof Steel in Concrete

CONCRETE BRIDGE CONCRETE BRIDGE DEVELOPMENT GROUPDEVELOPMENT GROUPEurocodes and InnovationEurocodes and Innovation

22ndnd July 2009: St HughJuly 2009: St Hugh’’s College s College OxfordOxford

CORROSION CONTROL

•• Concrete DurabilityConcrete Durability•• Corrosion of Steel in ConcreteCorrosion of Steel in Concrete•• Cathodic Protection of Steel in ConcreteCathodic Protection of Steel in Concrete•• Criteria of ProtectionCriteria of Protection•• System DevelopmentSystem Development•• StandardsStandards•• ApplicationsApplications

Developments in Cathodic Protection of Developments in Cathodic Protection of Steel in ConcreteSteel in Concrete

PAPER SUMMARYPAPER SUMMARY

CORROSION CONTROL

•• Cement paste pH 11Cement paste pH 11--13: steel is passive13: steel is passive•• Chlorides or acid gasses disrupt passivityChlorides or acid gasses disrupt passivity•• Concrete designed for durability: with low Concrete designed for durability: with low water cement ratio, with cement replacements water cement ratio, with cement replacements (silica fume, (silica fume, gbbsgbbs or or pfapfa) the pore structure is ) the pore structure is improved and concrete is more impermeable to improved and concrete is more impermeable to corrodantscorrodants


CONCRETE DURABILITYCONCRETE DURABILITYSteel in concrete is normally durableSteel in concrete is normally durable

CORROSION CONTROL

•• Chlorides disrupt passive film on steel surface Chlorides disrupt passive film on steel surface and allows pitting corrosionand allows pitting corrosion•• Present from sea dredged aggregates, marine Present from sea dredged aggregates, marine exposure, deexposure, de--icing salts or chemical icing salts or chemical contamination contamination •• Diffuse to level of steel: Critical Level:Diffuse to level of steel: Critical Level:•• 0.2% 0.2% ClCl -- by weight of cement postby weight of cement post--hydrationhydration•• ClCl -- ion/OH ion/OH -- ion ratio 0.6 better criterionion ratio 0.6 better criterion


CONCRETE DURABILITYCONCRETE DURABILITYWhy steel corrodes in concreteWhy steel corrodes in concrete

CORROSION CONTROL


Reinforcement Corrosion: Spalling of Reinforcement Corrosion: Spalling of Concrete: Chlorides from GroundwaterConcrete: Chlorides from Groundwater

CORROSION CONTROL


Marine contamination c. 10 year old Marine contamination c. 10 year old high quality prehigh quality pre--cast beamscast beams

CORROSION CONTROL

•• Acidification (neutralisation) of cement paste Acidification (neutralisation) of cement paste pore water by acid gases, COpore water by acid gases, CO22 NONOxx SOSO33 etcetc•• Carbonation front generally quite uniform Carbonation front generally quite uniform •• Corrosion more generally over steel surface Corrosion more generally over steel surface due to widespread loss of passivity as pH drops due to widespread loss of passivity as pH drops below c. pH 9below c. pH 9•• Seldom problem on civil structures due to Seldom problem on civil structures due to better quality concrete & better coverbetter quality concrete & better cover


CONCRETE DURABILITYCONCRETE DURABILITYCarbonationCarbonation

CORROSION CONTROL

•• Reinforced concrete pipelines protected with Reinforced concrete pipelines protected with CP in 1950CP in 1950’’ss•• Trials of CP to atmospherically exposed Trials of CP to atmospherically exposed reinforced concrete bridge beams and then deck reinforced concrete bridge beams and then deck units in 1958units in 1958--19741974•• Criteria for CP of steel in alkaline concrete Criteria for CP of steel in alkaline concrete differ from those for steel in neutral soils or differ from those for steel in neutral soils or waterswaters


Cathodic Protection Cathodic Protection

CORROSION CONTROL

•• for steel in concrete: to refor steel in concrete: to re--establish or establish or maintain passivity by raising pH and shifting maintain passivity by raising pH and shifting potential into passive region of Pourbaix potential into passive region of Pourbaix diagram. 150mV decay or diagram. 150mV decay or --0.720V wrt 0.720V wrt Ag/AgCl/0.5M KCl: Current Density 2Ag/AgCl/0.5M KCl: Current Density 2--20mA/m20mA/m22

•• for steel in soils or waters: to render immune for steel in soils or waters: to render immune by depressing the potential into the immune by depressing the potential into the immune region. region. --0.800V wrt Ag/AgCl/0.5M KCl: Current 0.800V wrt Ag/AgCl/0.5M KCl: Current Density 20Density 20--250mA/m250mA/m22


Cathodic Protection CriteriaCathodic Protection Criteria

CORROSION CONTROL

•• for steel in new concrete, or before the [for steel in new concrete, or before the [ClCl--] is ] is sufficient to initiate corrosion: to maintain sufficient to initiate corrosion: to maintain passivity by maintaining/raising pH irrespective passivity by maintaining/raising pH irrespective of eventual [of eventual [ClCl--]. 150mV decay or ]. 150mV decay or --0.720V wrt 0.720V wrt Ag/AgCl/0.5M KCl: Current Density 0.2Ag/AgCl/0.5M KCl: Current Density 0.2--2mA/m2mA/m22

Also termed Also termed ““cathodic preventioncathodic prevention””



CORROSION CONTROL

These Criteria are applicable to steel in These Criteria are applicable to steel in concrete:concrete:•• Irrespective of chloride concentration or Irrespective of chloride concentration or carbonation levelcarbonation level•• To atmospherically exposed, buried and To atmospherically exposed, buried and immersed reinforced concreteimmersed reinforced concrete•• Oxygen flux will determine current density and Oxygen flux will determine current density and if potential decay or absolute potential criteria if potential decay or absolute potential criteria will be most applicablewill be most applicable



CORROSION CONTROL

SYSTEM DEVELOPMENT: Impressed Current

Cl-

+

-

PowerSupply

Anode

MonitoringSystem

ReferenceElectrodes

Reinforcing Steel

Concrete

Current Flow from Anode

Cl-

Cl- Cl-

Cl-CurrentFlow


CORROSION CONTROL

Developments in Cathodic Developments in Cathodic Protection of Steel in ConcreteProtection of Steel in ConcreteSYSTEM DEVELOPMENT: Galvanic

Galvanic Anode (usually Zn based)

-

+ + + + +

Concrete

Cur

rent

Flo

w

Current Flow

- - - - - - - -

CORROSION CONTROL

•• often applied as part of concrete repairoften applied as part of concrete repair•• element must be structurally sound: corroded element must be structurally sound: corroded bars may need replacement; cause of distress bars may need replacement; cause of distress must be assessedmust be assessed•• cracking, spalling and other concrete defects cracking, spalling and other concrete defects must be repairedmust be repaired•• chloride contaminated but not damaged chloride contaminated but not damaged concrete does not need to be removed: COST concrete does not need to be removed: COST SAVINGSAVING•• 22--20mA/m20mA/m22 of steel subject to [of steel subject to [ClCl--] and O] and O22 fluxflux•• 0.20.2--2mA/m2mA/m22 for for ““cathodic preventioncathodic prevention””


Cathodic Protection System DevelopmentCathodic Protection System Development

CORROSION CONTROL

•• MMO/Ti (MMO/Ti (““activatedactivated”” Ti) Mesh, Ribbon, Strip etcTi) Mesh, Ribbon, Strip etc•• anode embedded into or onto concreteanode embedded into or onto concrete

The most reliable anode material, flexible forms, The most reliable anode material, flexible forms, high current density products available.high current density products available.

If applied to existing structure extra weight of If applied to existing structure extra weight of concrete overlay or complexity of slots/chasesconcrete overlay or complexity of slots/chases


Cathodic Protection: Anode TypesCathodic Protection: Anode Types

CORROSION CONTROL

MMO/Ti Ribbon anode applied MMO/Ti Ribbon anode applied to reinforcement in bridge deck to reinforcement in bridge deck reconstruction: Corrpro USAreconstruction: Corrpro USA

Developments in Cathodic Protection Developments in Cathodic Protection of Steel in Concreteof Steel in Concrete

CORROSION CONTROL


MMO/Ti Ribbon Anode installed on reinforcement of MMO/Ti Ribbon Anode installed on reinforcement of new construction bridge pier: CCSL Bahrain: 2002new construction bridge pier: CCSL Bahrain: 2002

CORROSION CONTROL


MMO/Ti Ribbon Anode installed on reinforcement of MMO/Ti Ribbon Anode installed on reinforcement of new construction Floating Jetty: new construction Floating Jetty: Corrosion Control Associates Detail Designer: 2007Corrosion Control Associates Detail Designer: 2007

CORROSION CONTROL

MMO/Ti mesh anode to repaired beam showing MMO/Ti mesh anode to repaired beam showing anode/cable connection, before 25mm concrete anode/cable connection, before 25mm concrete overlay: Abu Dhabi: Tarmac & Corrosion Control overlay: Abu Dhabi: Tarmac & Corrosion Control c. 1988c. 1988


CORROSION CONTROL

Permanent reference electrode being installed in Permanent reference electrode being installed in original concrete in repaired beam with MMO/Ti original concrete in repaired beam with MMO/Ti mesh anode, before 25mm concrete overlaymesh anode, before 25mm concrete overlay


CORROSION CONTROL

Manama Sitra Causeway Deck Repair: Concrete Manama Sitra Causeway Deck Repair: Concrete Removed exposing Corroding Reinforcement: Removed exposing Corroding Reinforcement: Bahrain: Tarmac & Corrosion Control c. 1990Bahrain: Tarmac & Corrosion Control c. 1990


CORROSION CONTROL

MMO/Ti Mesh cathodic protection system to MMO/Ti Mesh cathodic protection system to Manama Sitra Causeway: Laid on wet pavement Manama Sitra Causeway: Laid on wet pavement

concrete and overlaid within 30 minutesconcrete and overlaid within 30 minutes


CORROSION CONTROL

•• Coating containing conductive pigment Coating containing conductive pigment (normally graphite) applied to concrete surface(normally graphite) applied to concrete surface•• primary anode of Pt/primary anode of Pt/NbNb/Cu or MMO/Ti wire or /Cu or MMO/Ti wire or strip to facilitate cable connection and to strip to facilitate cable connection and to distribute currentdistribute currentAdvantages, light weight, low cost, if fails blows Advantages, light weight, low cost, if fails blows away.away.Not very durable, low current limitNot very durable, low current limit


Cathodic Protection: Anode TypesCathodic Protection: Anode TypesConductive CoatingsConductive Coatings

CORROSION CONTROL


Conductive Coating CP system on Midlands Links Conductive Coating CP system on Midlands Links Motorway support structures: Tarmac & Motorway support structures: Tarmac & Corrosion Control c. 1990Corrosion Control c. 1990

CORROSION CONTROL

•• MMO/Ti tubesMMO/Ti tubes•• Titania (Ebonex) tubesTitania (Ebonex) tubes•• MMO/Ti wire in carbon loaded gelMMO/Ti wire in carbon loaded gel

Advantages for current distribution into Advantages for current distribution into complex areas, if well designedcomplex areas, if well designedDisadvantages of holes and high current densityDisadvantages of holes and high current density


Cathodic Protection: Anode TypesCathodic Protection: Anode TypesDiscrete AnodesDiscrete Anodes

CORROSION CONTROL

European & Canadian Practice:European & Canadian Practice:•• Detailed design featuring LOCAL current Detailed design featuring LOCAL current demand determination and anode provisiondemand determination and anode provision•• Remote monitoring and controlRemote monitoring and control

USA PracticeUSA Practice•• Generalist design often current provision Generalist design often current provision based on mbased on m22 of concreteof concrete•• Low technology power supplies & minimal Low technology power supplies & minimal monitoringmonitoring

Cathodic Protection of Steel in Concrete: 20 Years Cathodic Protection of Steel in Concrete: 20 Years of Progressof Progress

System DevelopmentsSystem Developments

CORROSION CONTROL

Well Established Standards for Cathodic Protection of Well Established Standards for Cathodic Protection of Steel in ConcreteSteel in Concrete•• BS EN 12696: 2000 Cathodic Protection of Steel in BS EN 12696: 2000 Cathodic Protection of Steel in ConcreteConcrete•• HA BA 83/02 Cathodic Protection for use in Reinforced HA BA 83/02 Cathodic Protection for use in Reinforced Concrete Highway Structures: Main UK user Advice Concrete Highway Structures: Main UK user Advice NoteNote•• HA Specification for Cathodic Protection Drafted & HA Specification for Cathodic Protection Drafted & awaiting approvalawaiting approval•• 1989 Concrete Society TR 36 and TR 37 being Revised1989 Concrete Society TR 36 and TR 37 being Revised


StandardsStandards

CORROSION CONTROL

COSTS from HA BA (year 2002, broad brush):COSTS from HA BA (year 2002, broad brush):

Conductive coating: Conductive coating: ££20 20 -- ££40/m40/m22

Sprayed Zn: Sprayed Zn: ££60 60 -- ££100/m100/m22

MMO/Ti mesh & overlay: MMO/Ti mesh & overlay: ££60 60 -- ££100/m100/m22

Discrete anodes: Discrete anodes: ££40 40 -- ££100/m100/m22

Conductive cementitious overlay: Conductive cementitious overlay: ££30 30 -- ££60/m60/m22

BUTBUT……due to avoidance of removal of sound but due to avoidance of removal of sound but ClCl--

contaminated concretecontaminated concrete…… SAVINGS to as little as 1/8 SAVINGS to as little as 1/8 the costs of alternative long term repairsthe costs of alternative long term repairs


StandardsStandards

CORROSION CONTROL

RECENT APPLICATIONSRECENT APPLICATIONS


CORROSION CONTROL


Khalifa Bridge BahrainCCSL:c. 2002

MMO/Ti Ribbon castinto New

Constructionfor 50 Year

Durability in hot, saline marine

environment

CORROSION CONTROL


MMO/Ti Ribbon mounted on plastic spacer rails to

facilitate ease of installation

and no short circuits

Positive ring main cable to anodes

CORROSION CONTROL


Tanger New Port:SRPTM. Corrosion

Control Client Technical Advisor

2004-2007Slip-formed Caissons

CP for 50 year life

Atmospheric,Splash &

Tidal ZonesCP by cast in

MMO/Ti ribbonsImmersed structure CPby immersed MMO/Ti

tube anodes in seawater

CORROSION CONTROL


Floating Jetty Northern Europe: CP Design and Supervision by Corrosion Control 2006-2008

Conventionally cast 50 Year Life MMO/Ti Ribbon on

plastic spacer

rail

Ti Conductor

strip on plastic spacer

CORROSION CONTROL


Coastal Bridge Structure Performance Specification by Corrosion Control, Contractor Detail Design. Repair for 25+ Year Life. 2007-8

MMO/Ti mesh & gunite to deck

soffit and transverse

beams

MMO/Ti discrete anodes to front & rear beams

MMO/Ti mesh & micro concrete in GRP forms to

columns

CORROSION CONTROL


Coastal Bridge Structure Detail Design & Specification by Corrosion Control, Contractor

CRL. Repair for 50+ Year Life. 2008-9

RC CorbelsRC CorbelsMMO/Ti Discrete MMO/Ti Discrete

AnodesAnodes

Outer RC BeamsOuter RC BeamsMMO/Ti Discrete AnodesMMO/Ti Discrete Anodes

Inner Concrete Clad RSJInner Concrete Clad RSJBeams MMO/Ti Mesh and Beams MMO/Ti Mesh and

Discrete AnodesDiscrete Anodes

RC Outer Deck Extensions MMO/Ti Mesh above and belowRC Outer Deck Extensions MMO/Ti Mesh above and below

CORROSION CONTROL

• Cathodic Protection is well established for both New Construction and Repair & Protection• There are well established Standards and an extensive Track Record• For New Construction first option should be competent design of a durable concrete and construction defect free concrete placement, compaction & curing, with correct cover• Cathodic Protection can be the optimum solution for added durability/reliability or for repair/protection when corrosion initiates


CONCLUSIONSCONCLUSIONS

CORROSION CONTROL

CP of Steel in Concrete is Cost Effective: CP of Steel in Concrete is Cost Effective: •• In repairs CP can reduce total project costs to In repairs CP can reduce total project costs to 1/8 of alternates: 1/8 of alternates:

-- No removal of undamaged but No removal of undamaged but contaminated concretecontaminated concrete-- Often avoids temporary supportOften avoids temporary support-- Reduced project programme: traffic Reduced project programme: traffic management and access costsmanagement and access costs

•• New construction CP costs c. 25% of those for New construction CP costs c. 25% of those for retrofitretrofit



CORROSION CONTROL

The Proper Design of CP to Steel in Concrete is:The Proper Design of CP to Steel in Concrete is:•• More complex than for steel in soils or watersMore complex than for steel in soils or waters

-- Close Anode/CathodeClose Anode/Cathode-- High IR errorsHigh IR errors-- Non uniform and non continuous Non uniform and non continuous CathodeCathode-- Extensive Anode network often Extensive Anode network often ““stuck stuck onon”” concreteconcrete



CORROSION CONTROL

The Proper Execution of CP to Steel in Concrete The Proper Execution of CP to Steel in Concrete is:is:•• More complex than for steel in soils or waters More complex than for steel in soils or waters due todue to

-- All the previous reasonsAll the previous reasons-- Necessity to integrate with civil Necessity to integrate with civil construction or repair worksconstruction or repair works-- Necessity to interface with those who Necessity to interface with those who know little, and may care little, for CPknow little, and may care little, for CP-- Often difficult accessOften difficult access



CORROSION CONTROL

As a result of the foregoing:As a result of the foregoing:•• Specifications are sometimes inadequate:Specifications are sometimes inadequate:

-- Written by the non Specialist or worseWritten by the non Specialist or worse•• Designs are sometimes inadequate:Designs are sometimes inadequate:

-- Negligible attention to balancing local Negligible attention to balancing local current demand and provision etc current demand and provision etc etcetc

•• Installations are sometimes inadequate:Installations are sometimes inadequate:-- Interfaces between different Engineering Interfaces between different Engineering or Trade skillsor Trade skills



CORROSION CONTROL

With the appropriate expertise in the selection With the appropriate expertise in the selection and specification of the CP systems, in their and specification of the CP systems, in their design, their installation, testing, design, their installation, testing, commissioning and operation there is clear commissioning and operation there is clear evidence that:evidence that:•• CP systems are reliableCP systems are reliable•• With appropriate anodes the theoretical life With appropriate anodes the theoretical life can exceed 100 yearscan exceed 100 years•• With replacement of electronics and external With replacement of electronics and external cabling practical life can exceed 25 yearscabling practical life can exceed 25 years



CORROSION CONTROL

If the CP industry, Designers, Manufacturers If the CP industry, Designers, Manufacturers and Specialist Contractors maintain a high and Specialist Contractors maintain a high quality of delivery to the Client base, Owners, quality of delivery to the Client base, Owners, Civil Consultants and Contractors there is every Civil Consultants and Contractors there is every reason to believe that this application of reason to believe that this application of corrosion control will grow significantly, in both corrosion control will grow significantly, in both new build and repair.new build and repair.This will benefit economies and provide This will benefit economies and provide sustainability & environmental benefits.sustainability & environmental benefits.IF we fail in quality, the sector will fail.IF we fail in quality, the sector will fail.



CORROSION CONTROL

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