Lezing: Feasibility of externally bonded reinforcement for cathodic protection Philippe De Schoesitter Op uitnodiging van de Vereniging Adviseurs Beton

Lezing: Feasibility of externally bonded reinforcement for cathodic protection

Philippe De Schoesitter

Op uitnodiging van de Vereniging Adviseurs Beton Onderhoud en Reparatie (VABOR)

VABOR bijeenkomst 22 maart 2012

Nebest AdviesgroepMijdrecht - Nederland

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Feasibility of externally bonded CFRP for cathodic protection

Promotoren Prof. dr. ir. S. Matthys, Prof. dr. ir. G. De SchutterBegeleidster Ir. D. Ertzibengoa Gaztelumendi

Vakgroep Bouwkundige ConstructiesVoorzitter: prof. dr. ir. L. TaerweFaculteit ingenieurswetenschappen en ArchitectuurAcademiejaar 2010-2011Hoofdstuk 1:

Corrosie van wapeningsstaal in beton en kathodische bescherming

Hoofdstuk 2:Uitwendig verlijmde carbonvezelwapening (CFRP)

Hoofdstuk 3:Experiment en toetsing haalbaarheid

22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter

VABOR bijeenkomst - Philippe de Schoesitter

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1. Corrosie en kathodische bescherming (ICCP)

22/03/2012

1.1 Corrosieproces en electrochemische achtergrond

1.2 Corrosiesnelheidsmeting

1.3 Kathodische bescherming: concrete toepassing


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1.2 Corrosieproces

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Fe2+


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Criterium Corrosion condition

Icorr < 0,1 µA/cm² Passive condition

Icorr 0,1 to 0,5 µA/cm² Low to moderate

Icorr 0,5 to 0,1 µA/cm² Moderate to high

Icorr > 1 µA/cm² High


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1.2 Corrosiesnelheidsmeting

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Tafel-slope measurement Lineaire polarisatie


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Mesh Draad Strip + coating (mortal, acryl…)

Materials: Metaal (Pt, Ti, Ag, Ni …) Carbon (graphite …)

1.3 Kathodische bescherming concreet

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Cathodic Protection surface AnodeBUtgb, Technische goedkeuring sector Burgerlijke bouwkunde, Kathodische bescherming door opgelegde stroom van wapening

Volume resistivity < 1 Ω.cmCurrent density ca. 20 mA/m²


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2. “CFRP EBR”

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CFRP = Carbon Fibre Reinforced PolymerEBR = Externally bonded Reinforcement

2.1 Wat, hoe en waarom?

2.2 Mogelijkheid tot combinatie met K.B.-> geleidbaarheid van carbon -> overlap toepassingsgebied

2.3 Probleem: geleidbaarheid lijmmiddel


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2.1 CFRP EBR

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2.1 CFRP EBR

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2.1 CFRP EBR

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Interesse in combinatie vanuit verschillende perspectieven:

CFRP EBR heeft positieve invloed op corrosie (zgn. “passieve bescherming”)

Sterke geleidbaarheid van carbonvezels: eis van 1Ω.cm ruimschoots voldaan

De toepassingsgebieden van aanbreng externe wapening enkathodische bescherming (of preventie) vertonen enige overlap.

I.h.b. wanneer grote betonoppervlakken onder trekspanning extra wapening vergen

2.2 Toepassing van CFRP als anode-materiaal

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2.3 Geleidbaarheid epoxy-lijm

Epoxy is insulative conductive adhesive additives in epoxy:

- Metal- Carbon particles:

>‘Carbon black’ (powder)>graphite (fibres)>nanotubes

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2.3 Geleidbaarheid epoxy-lijm: Carbon Black

- small conductive particles- form a 3D-network as ‘electron path’

+ tunnel effect- chemically rather inert, temperature

resistant- “threshold concentration”- very high surface area (6 to 1500 m²/g)

= problem!

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Coville NJ, Mhlanga SD, Nxumalo EN, Shaikjee A. A review of shaped carbon nanomaterials. S Afr J Sci. 2011;107(3/4), Art. #418, 15 pages. DOI: 10.4102/ sajs.v107i3/4.418


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3. Experiment en toetsing haalbaarheid

3.1 Experiment set-up and program3.2 Results and discussion3.3 Conclusion

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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter


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3.1 Experiment set-up and program

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Lollypop specimens: h=100mm, D≈50mm, reinforcement bar d=10mm

Mortar composition: C:SAND = 1:3 W/C = 0,65 Cl-/C = 4,25 wt%

WET LAY-UP CFRP wraps:

CP-ax-… : CFRP wraps axial fibre directionsCP-rad-…: CFRP wraps radial fibre directionCP-…: wraps consists of epoxy adhesive only


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Primary anode: for connec-tion to DC power supply and current spread over anode surface

Axial fibre direction: optimal current spread through fibres (expected), “Ax-…” specimens

Radial fibre direction: worse current spread expected (bad conductivity of fibres in transversal direction), “Rad-…” specimens



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CP/immersion program

Accelerated corrosion initiation and process: initial chloride content (4,25wt%) cyclic immersion in saline water (1wt%)

CP program:phase 1: 14 days 58,35mA/m²phase 2: 14 days 26,53mA/m²



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Conductive epoxies:

Adhesive Filler Filler content (wt%)

Bond strength [N/mm²]

Resistivity [Ω.cm]

Eccobond 50298 Ni 74-76 >12 0,5

Eccobond 64C Ni 5,52 0,02

Eccobond 60L graphite >10 50

Eccobond 57 C Ag >50 <4,8 6x10-4

ECC PC 5800 Carbo CB 9,88 (119,04)

Epo-Tek 353ND CB 12,97 (78,72)



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Serial circuit equal protection current!

Separate baths no current loss through water!



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Reference specimens:

“Ref”: cyclic immersion but unprotected (CP)Ref-1,2,3: no CFRP wrapRef-FRP: classic resistant CFRP wrap

Tafel: not immersed, unprotected (CP)Tafel-ref: no wrapTafel-50298: wrap



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CP and Ref specimens Linear Polarization

(a) After 14 days CP/imm.(b) After 28 days CP/imm.

CP switched off 48h in advanceEcorr±20mV and 0,15mV/s

Tafel specimens Potentiodynamic meas.Tafel extrapolation for Icorr

Slope measurements for B

Cell set-up

3.2 Results and discussion


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Ref-1 Ref-2 Ref-3 Ref-FRP Tafel-ref Tafel-502980

1

2

3

4

5

6

7

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Ref aRef b

Icorr

(µA/

cm²)



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60L 57C 64C 50298 ECC Epo0

0.5

1

1.5

2

2.5

3

3.5

Axial aAxial b

Icorr

(µA/

cm²)



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60L 57C 64C 50298 ECC Epo0

0.5

1

1.5

2

2.5

3

3.5

Rad aRad b

Icorr

(µA/

cm²)



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60L 57C 64C 50298 ECC Epo0

0.5

1

1.5

2

2.5

3

3.5

CP aCP b

Icorr

(µA/

cm²)



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On average and compared to Ref specimens:

AX-specimens: 56%Rad-specimens: 53%CP-specimens: 64%

60L specimens: 53%57C specimens: 71%64C specimens: 51%50298 specimens: 68%ECC specimens: 61%Epo specimens: 44%

lower corrosion rates



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ax rad fibreless

-1.25

-0.75

-0.25

0.25

0.75

1.25

1.75

60L57C64C50298ECCEpoΔI

corr

(µA/

cm²)

Icorr evolution:



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Tafel slope measurements:B ≈ 26mV (depassivated steel)Good correlation with Icorr from LP-measurements

Mass loss measurements: Correlation with Icorr from LP-measurements (within expected factor 2 error)

0.1 1 10 1000.1

1

10

100

Actual measured mass loss (mg/cm²)

Calcu

late

d m

ass l

oss (

mg/

cm²)

CP-64C

CP-ax-ECC



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- The steel potentials are not found in the safe passive zone -> influence added chloride

- Iprot decrease (from 0,11 to 0,05mA) results in potential increase -> except: fibreless specimens

- Active chloride corrosion initiation was not prevented, but ICCP was effective.- > influence added chloride

-The radial fibre orientation gives the most consistent results. - >This overall improvement may be due to better concrete confinement

-Anode resistivity: the most conductive epoxies show low change in Icorr evolution between both measurements.

->fibres play no role in combination with very conductive epoxies-The CB added epoxies show the worst results.



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- CP was effective, CPrev was not obtained

-Some improvements for further research:- Integration of reference electrodes

- >Suspicion of fibre influence on polarization- >Depolarization measurements

- No addition of Chlorides to the mortar and prolonged experiment to investigate Cprev

- More specimens (for Tafel experiments and statistical certitude)

-Further research on effects of conductive fillers on mechanical behaviour-Further research on integrating this addition in fabrication of prefab laminates

3.3 Conclusion

Documents

Lezing: Feasibility of externally bonded reinforcement for cathodic protection Philippe De Schoesitter Op uitnodiging van de Vereniging Adviseurs Beton