Cathodic Protection of Structures (TR36 + TR37 = TR73)

Chris Atkins (Mott MacDonald)Chris Atkins (Mott MacDonald)

Thermodynamics

Thermodynamics

Electrochemistry

• When you make cement you force energy into it to drive off water

Thermodynamics

Carbonation

Chlorides

• When you make concrete you add water and it returns to thermodynamically more stable materialChlorides

TR36/37

stab e ate a

• It’s stability means nothing much can degrade

Progress

TR73

– Lempinski Vir, Serbia, ‘concrete’ from 5600 BC found.

P d t f i i t f th ldSummary

– Predates farming in many parts of the world

Thermodynamics

Thermodynamics

Electrochemistry

• When you make steel you drive off oxygen

• Thermodynamically unstable

Thermodynamics

Carbonation

Chlorides

– Concrete can help

– High pH = passive filmsChlorides

TR36/37• It Rusts

– Chlorides

Progress

TR73

– Carbonation

• Rust is bigger than steel

Summary• Bits fall off

Electrochemistry

Thermodynamics

Electrochemistry

• Anodes, Cathodes, Electricity, ElectrolyteElectrochemistry

Carbonation

ChloridesChlorides

TR36/37 ZI

CO

P

Progress

TR73

Salt Solution

NC

PPER

Summary

Carbonation

Thermodynamics

Electrochemistry

• General corrosion

• Anodes and cathodes evenly distributedCarbonation

Chlorides

y

• Where it can corrode it does

Fi th bit th t h f ll ff d i

Carbonation

Chlorides

TR36/37

• Fix the bits that have fallen off and in general it goes away

Progress

TR73

Summary

Chlorides

Thermodynamics

Electrochemistry

• Anode small, cathode large

• Chlorides extend beyond where the anode is

Carbonation

Chlorides

is

• If you fix the bit that is corroding, it starts corroding somewhere elseChloridesChlorides

TR36/37

co od g so e e e e se

• Either remove all the chlorides– Most of the structure

Chlorides

Progress

TR73

• Or play with thermodynamics– Use Cathodic Protection

Summary– Leave the chlorides in place

– Saves on access / propping / extent of repair / materials and carbon dioxidematerials and carbon dioxide

Chlorides

Thermodynamics

Electrochemistry

Carbonation

Chlorides

ANODES

RepairedChloridesChlorides

TR36/37CATHODES

CATHODEChlorides

Progress

TR73

SALTY and ANODIC

Summary

1988

Thermodynamics

Electrochemistry

• Midland Links Motorway Viaducts– 1500 crossbeams

Carbonation

Chlorides

– Large numbers chloride contaminated

– If we take out all the chlorides we need to Chlorides

TR36/37

prop each one

• £300,000 per crossbeamTR36/37

Progress

TR73

• Can we do something else?– CP trials

Summary

TR36 / TR 37

Thermodynamics

Electrochemistry

• No useful standards

• No useful guidance Carbonation

Chlorides

g– Academic papers do not a contract make

• Working group produced guidance andChlorides

TR36/37

• Working group produced guidance and a specification (ICE 5th)

• Published in 1989TR36/37

Progress

TR73

• Published in 1989

Summary

1989 • I was 17, Rene Brueckner had Coca Cola for the first time• Salvador Dali and Mel Blanc Died• Communism collapsed in Europe, Tianmen Square• George Bush President• Exxon Valdez dumped 11 million gallons of oil into Alaska

Thermodynamics

Electrochemistry

Exxon Valdez dumped 11 million gallons of oil into Alaska• Union Carbide agreed to pay Bhopal US $470 million • The U.S. government seizes the Irvine, CA Lincoln Savings and

Loan Association; Savings and Loan Crisis which costs U.S.

Carbonation

Chlorides

; gtaxpayers nearly $200 billion in bailouts.

• G7 calls for restrictions on gas emmissions, the commonwealth issues the Langkawi Declaration making environmental sustainability one of the main prioritiesChlorides

TR36/37

sustainability one of the main priorities• FW de Clerk elected president of South Africa, scraps the

separate amenities act• USSR pulled out of Afghanistan

TR36/37

Progress

TR73

p g• 1st computer virus creator prosecuted• First of 24 GPS satellites launched• Sky TV was formed

Summary

• Sky TV was formed• Last Golden Toad seen• Daniel Radcliffe / Theo Walcott born• MSDOS, LOTUS 123 and Wordperfect ruled, Windows were

something you looked out of.

Subsequent developments in CP

Thermodynamics

Electrochemistry

• Anode systems– Conductive coatings used less.

Carbonation

Chlorides

– Mesh and Overlay used more

– Discrete Anodes existChlorides

TR36/37– Galvanic Anodes exist

Progress

TR73

Progress

Summary

Subsequent developments in CP

Thermodynamics

Electrochemistry

• Control and monitoring systems have updated– Dos Windows 3 1 95 98 2000 XP Internet

Carbonation

Chlorides

Dos, Windows 3.1, 95, 98, 2000, XP, Internet Explorer

• Contracts have changedChlorides

TR36/37

– Partnering

– ECI

C i P ti A i tiProgress

TR73

• Corrosion Prevention Association– BS EN 12696, BA83/02, Training and Certification

via BS EN 15257, HA Spec

Progress

Summary • Procurement has changed

• Time to update 36 /37p

TR 73

Thermodynamics

Electrochemistry

• Produced by members of CPA, ICorr CED and Concrete Society, including HA

Carbonation

Chlorides

HA.

• Published by Concrete Society

R fl t t b t tiChlorides

TR36/37

• Reflects current best practice

• Includes Specification and Bill itemsProgress

TR73

– You need to delete bits to suit procurement route

• Available now in all good bookshopsTR73

Summary

• Available now in all good bookshops– Please stop specifying 36/37

Summary

Thermodynamics

Electrochemistry

• Steel rusts• For chloride induced corrosion CP saves

C b Di idCarbonation

Chlorides

– Carbon Dioxide– Repairs– Access

Chlorides

TR36/37

– Propping

• Codes are available

Progress

TR73

– Competence of personnel– Safe Operation of Systems

• TR73 is the most up to dateSummary

TR73 is the most up to date• Any Questions?Summary