brian mcfarland - lnec

Carbonation, Chlorides & Electrochemical Repair

Brian McFarlandB.Eng (Hons) C.Eng M.ICE M.IEI M.ICorr MCS

McFarland Associates Limited

2nd Transnational WorkshopduratiNET

The Queen’s University of BelfastThe Queen s University of Belfast22nd June 2009

Overview

Carbonation, Chlorides& Electrochemical Repair& Electrochemical Repair

Carbonation

Chloride Attack

Inspection & Testing

Traditional RepairTraditional Repair

Electrochemical Repair

Case HistoriesCase Histories

The Problem

Millions of pounds are spent every year dealing with the symptoms of corrosion

Expense Disruption Danger

The Cause of the Problem

Poor design Chloride attackCarbonation Freeze thawCarbonation Freeze thawASR Low coverSulphate attack Poor site practiceImpact damage ErosionCh i l tt kChemical attack

Carbonation

Loss o f passivated

layer

C b

y

Carbon Dioxide

Rust

Carbon Dioxide

Chloride attack

P a s s iv e la y e r d e s t ro y e d , fo rm a t io n o f a n a n o d e a n d s u b s e q u e n t e le c t ro c h e m ic a l p ite le c t ro c h e m ic a l p it c o r ro s io n

C h lo r id e io n s p e n e t ra tep e n e t ra te c o n c re te

C h lo r id e c o n ta m in a te d c o n c re te

Chloride induced corrosion pits

Inspection & Testing

Chloride threshold values

Chloride content Risk of

(% cement) corrosion

< 0 4 Negligible< 0.4 Negligible

0.4 – 1.0 Possible

1.0 – 2.0 Probable

> 2.0 Certain

Ref: Browne (1982)( )

Half cell potential threshold values

CSE Corrosion Condition

> -200 mV Low – 10% risk of i

0 100 200 300 500400 600 200 mV corrosion

200 to 350 mV Intermediate corrosion

0 100 200 300 400 500 600

-200 to –350 mV risk

High <90% risk of

1

2< -350 mV High - <90% risk of

corrosion2

3

< -500 mV Severe corrosionA B C D E

Traditional repair methods

BUT traditional patch repair alone does not . . . . .

Stop ongoing corrosion

Prevent further spalling

Break the repair cycle

Chasing the corrosion

BRE Digest 444

The problem … “the newly established cathodic area within the repair will drive the new anode site in the contaminated region”

How does this mechanism work? …………….

Chloride contaminated concrete prior to patch repair

Steel

Chloride Chloride Chloride0.8% 4.0% 0.8%

Concrete

Chloride contaminated concrete prior to patch repair

Chloride Chloride Chloride0.8% 4.0% 0.8%

cathode anode cathode

Patch repair

i i i t d ff tincipient anode effect

Chloride Repair ChlorideChloride Repair Chloride0.8% 0.8%

anode cathode anodeanode cathode anode

Downsides of Traditional Repair

Break out all contaminated concrete

Expensive

Noisy

Dusty

DisruptiveDisruptive

Electrochemical Repair

Electrochemical Repair“Fighting Fire with Fire”

Cathodic Protection

Realkalisation

Chloride Extraction

Sacrificial Anodes

Next Generation Hybrid Systems

Cathodic Protection

Realkalisation

+ve

Anode Elec tro lyte

ve

- ve

ConcreteK 2 C O 3 .K H C O 3

ConcreteO H - N a +

N a +

Reinfo rcem ent

K +

Chloride Extraction

Current

+ve

Anode Elec tro lyteCurrentpaths

Cl-

Cl-

+ve

- veCl-

Cl- Cl-Cl-

Cl-

O H -

Cl-

Cl-

Cl

Cl-

Conc reteCl-Cl-

Re info rcem ent

Hydroxide Precipitation

Proc. 7th Int. Conf. Concrete in Hot and Aggressive Environments, Vol. 2, p.477, 2003

Sacrificial Systems

XP for patch repairs

CC for blanket protectionfor blanket protection

LJ for jetty piles

All the Galvashield systems work on the same principle …

Oil Rig Example

Photo Courtesy of Wilson Walton

Hybrid Systems

• Chloride extraction type process

• Cathodic prevention type process (low maintenance)( )

• Single electrode system

Hybrid Application

• Install discrete alloy electrodes

• Apply specialised electrochemical treatment for 1 week

• Connect activated sacrificial anode to steel

Hybrid Application

Duoguard AnodesIn Drilled Holes

Temporary DC p yPower Supply

(present for ~ 1 week)

Monitoring options

Measure …….

CurrentCurrent

Temperature

Steel potentialSteel potential

Residual life

Manual monitoring boxg

Automated monitoring box

Current output can be easily monitored

Eaton Park Pavillions, Norwich: CC anodes installed April 2001:Current Density results

6 30

5

6

25

30Current Density (mAm2) Temperature (degC)

July 01

June 02 June 03

3

4

sity

(mA

/m2)

15

20

ure

(deg

C)

June 03

2

3

Cur

rent

Den

5

10

Tem

pera

t

0

1

-5

0

Dec 01Feb 03

0 100 200 300 400 500 600 700 800

Time (days)

Residual life can be calculated

Predicted anode life (Galvashied CC65)

0.0010

mps

0.0006

0.0008

outp

ut /

Am

0 0000

0.0002

0.0004

Cur

rent

0.00000.00 5.00 10.00 15.00 20.00 25.00 30.00

Life / Years

Comber Bridge

Carrick Leisure Centre

Lakeland Forum

Eglinton Church

Red Arch Bridge

Ballylumford Jetty

Beatties Bridge

Conclusions

Carbonation & Chloride Attack are the main problems encountered

Traditional Repair alone rarely deals with the source of the problem

Electrochemical Repair treats “Fire with Fire” and deals with the source of the problem – reinforcement corrosion

Realkalisation & Chloride Extraction are time consuming and costly

Cathodic Protection requires a power source and monitoring and is prone to breaking down vandalism and failure of the anodesto breaking down, vandalism and failure of the anodes

Sacrificial Anodes are passive

H b id S l ti i i th b fit f CP CE d SA ith t thHybrid Solutions maximise the benefits of CP, CE and SAs without the downsides

brian mcfarland - lnec

Documents