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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 Adviesgroep Mijdrecht - Nederland
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Feasibility of externally bonded CFRP for cathodic protection PromotorenProf. dr. ir. S. Matthys, Prof. dr. ir. G. De Schutter BegeleidsterIr. D. Ertzibengoa Gaztelumendi Vakgroep Bouwkundige Constructies Voorzitter: prof. dr. ir. L. Taerwe Faculteit ingenieurswetenschappen en Architectuur Academiejaar 2010-2011 Hoofdstuk 1: Corrosie van wapeningsstaal in beton en kathodische bescherming Hoofdstuk 2: Uitwendig verlijmde carbonvezelwapening (CFRP) Hoofdstuk 3: Experiment en toetsing haalbaarheid 22/03/20122 VABOR bijeenkomst - Philippe de Schoesitter
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1. Corrosie en kathodische bescherming (ICCP) 22/03/20123 VABOR bijeenkomst - Philippe de Schoesitter 1.1 Corrosieproces en electrochemische achtergrond 1.2 Corrosiesnelheidsmeting 1.3 Kathodische bescherming: concrete toepassing
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1.2 Corrosieproces 22/03/20124 VABOR bijeenkomst - Philippe de Schoesitter Fe 2+
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 5 CriteriumCorrosion condition I corr <0,1 µA/cm²Passive condition I corr 0,1 to 0,5 µA/cm²Low to moderate I corr 0,5 to 0,1 µA/cm²Moderate to high I corr >1 µA/cm²High
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1.2 Corrosiesnelheidsmeting 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 6 Tafel-slope measurementLineaire polarisatie
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Mesh Draad Strip + coating (mortal, acryl…) Materials: Metaal (Pt, Ti, Ag, Ni …) Carbon (graphite …) 1.3 Kathodische bescherming concreet 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 7 Cathodic Protection surface Anode BUtgb, Technische goedkeuring sector Burgerlijke bouwkunde, Kathodische bescherming door opgelegde stroom van wapening Volume resistivity < 1 Ω.cm Current density ca. 20 mA/m²
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2. “CFRP EBR” 22/03/20128 VABOR bijeenkomst - Philippe de Schoesitter CFRP = Carbon Fibre Reinforced Polymer EBR = 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 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 9
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2.1 CFRP EBR 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 10
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2.1 CFRP EBR 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 11
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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 en kathodische 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 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 12
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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 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 13
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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! 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 14 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 program 3.2Results and discussion 3.3Conclusion 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 15
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3. Experiment en toetsing haalbaarheid 3.1 Experiment set-up and program 3.2Results and discussion 3.3Conclusion 22/03/2012VABOR bijeenkomst - Philippe de Schoesitter16
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3.1 Experiment set-up and program 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 17 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 directions CP-rad-…: CFRP wraps radial fibre direction CP-…: wraps consists of epoxy adhesive only
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 18 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 3.1 Experiment set-up and program
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 19 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/m² phase 2: 14 days 26,53mA/m² 3.1 Experiment set-up and program
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 20 Conductive epoxies: AdhesiveFiller Filler content (wt%) Bond strength [N/mm²] Resistivity [Ω.cm] Eccobond 50298Ni74-76>120,5 Eccobond 64CNi5,520,02 Eccobond 60L graphi te >1050 Eccobond 57 CAg>50<4,86x10 -4 ECC PC 5800 Carbo CB9,88(119,04) Epo-Tek 353NDCB12,97(78,72) 3.1 Experiment set-up and program
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 21 Serial circuit equal protection current! Separate baths no current loss through water! 3.1 Experiment set-up and program
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 22 Reference specimens: “Ref”: cyclic immersion but unprotected (CP) Ref-1,2,3: no CFRP wrap Ref-FRP: classic resistant CFRP wrap Tafel: not immersed, unprotected (CP) Tafel-ref: no wrap Tafel-50298: wrap 3.1 Experiment set-up and program
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3. Experiment en toetsing haalbaarheid 3.1 Experiment set-up and program 3.2Results and discussion 3.3Conclusion 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 23
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 24 CP and Ref specimens Linear Polarization (a) After 14 days CP/imm. (b) After 28 days CP/imm. CP switched off 48h in advance E corr ±20mV and 0,15mV/s Tafel specimens Potentiodynamic meas. Tafel extrapolation for I corr Slope measurements for B Cell set-up 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 25 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 26 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 27 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 28 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 29 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 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 30 I corr evolution: 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 31 Tafel slope measurements: B ≈ 26mV (depassivated steel) Good correlation with I corr from LP-measurements Mass loss measurements: Correlation with I corr from LP-measurements (within expected factor 2 error) 3.2 Results and discussion
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 32 - The steel potentials are not found in the safe passive zone -> influence added chloride - I prot 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 I corr evolution between both measurements. ->fibres play no role in combination with very conductive epoxies -The CB added epoxies show the worst results. 3.2 Results and discussion
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3. Experiment en toetsing haalbaarheid 3.1 Experiment set-up and program 3.2Results and discussion 3.3Conclusion 22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 33
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22/03/2012 VABOR bijeenkomst - Philippe de Schoesitter 34 - 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
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