05 Corr Repair
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Transcript of 05 Corr Repair
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Repair & Maintenance ofRepair & Maintenance ofConcrete StructuresConcrete Structures
5. Repair of Corrosion5. Repair of Corrosion--Damaged StructuresDamaged Structures
Emmons, 1994
Innovative Repair?Innovative Repair?
Cause Effect
• Chlorides at steel
• Carbonation
• Insufficient cover
• Poor quality concrete
• Cracking
• Rust staining
• Spalling
• Delamination
Corrosion
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Repair the Symptom• Replace delaminated concrete• Fix cracks• Overlay
Address the Cause• Remove chloride-contaminated
concrete• Remove chlorides (ECE)
Alter the Process• Cathodic protection
Future Prevention• Impermeable repair material• Sealants/waterproofing• Improved drainage• Penetrating inhibitors
Do Nothing Else
Surface RepairsSurface Repairs
Delamination
Contaminated concretewith chlorides orcarbonation
Spall
Heavilycorrodedrebar
CrackDurable repair material
Bonding new to oldReinforcing steel protection
Concrete surface conditioning
Removal of contaminated concrete &undercutting of exposed steel
Edge conditioning
Reinforcing steel cleaning
Damage due to CorrosionDamage due to Corrosion
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Removal of Damaged ConcreteRemoval of Damaged Concrete
Patch with New ConcretePatch with New Concrete
Edited from ICRI Movie on Surface RepairEdited from ICRI Movie on Surface Repair
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Simple Patch Configuration
RightRight
WrongWrong
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Locate embedded electrical conduit or post-tensionning tendons using pachometer or other techniques (e.g. radiography).
Conduct structural review before removal of significant amounts of concrete to determine if support (e.g. shoring) is required.
Exposed corroded rebar should be undercut to ensure adequate coverage and bond with new concrete (minimum clearance of ¾ inch or ¼ inch more than max aggregate size in patching concrete)
The full circumference of the exposed bar should be cleaned
Care should be taken to avoid damaging the bond around any exposed uncorroded bar
Loose rebar should be tied to other secure bars
If more than 25% of the cross section of a bar has been lost (or more than 20% of the cross section of two bars in close proximity) a structural review should be conducted to determine if repair or replacement of the bars is necessary.
Unless shotcrete repairs are anticipated, the edges of the patch should be cut straight and square with the surface to ensure maximum integrity of the patch (i.e. avoid feathered edges)
Patch Repairs – Check List
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Repair/Substrate Repair/Substrate -- IncompatibilityIncompatibility
No chloridesHigh pH
Chloride & Lower pH
Creation of a New Galvanic CellCreation of a New Galvanic Cell
Anode:2Fe → 2Fe2+ + 4e-
Cathode:O2 + 2H2O + 4e- → 4OH-
Formation of ‘incipient’ anodeadjacent to the new patch
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SpallSpall in Slabin Slab
Patch RepairPatch Repair
““Anodic RingAnodic Ring”” EffectEffect
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Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
No chloridesHigh pH
Chloride & Lower pH
Treating the Surface
MembranesH2O
H2O vapour
Reduces moisture content in the slab & prevents further chloride ingress.
But does it reduce corrosion? But does it reduce corrosion?
Cl
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Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
No chloridesHigh pH
Chloride & Lower pH
Treating the Surface
H2O vapour
Reduces moisture content in the slab & prevents further chloride ingress.
But does it reduce corrosion? But does it reduce corrosion?
H2O Cl
Denseoverlay
Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
No chloridesHigh pH
Chloride & Lower pH
Treating the Surface
H2O vapour
Reduces moisture content in the slab & prevents further chloride ingress.
But does it reduce corrosion? But does it reduce corrosion?
H2O ClPenetratingSealer
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Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
Treating the Steel Rebar
Electrically isolates the steel in the patch and prevents it from becoming a cathode and reduces the risk of incipient anode formation.
But does it extend the time to the next repair? But does it extend the time to the next repair?
EpoxyEpoxy--coating the exposed steelcoating the exposed steel
Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
Treating the Steel Rebar
The zinc coating will become a “sacrificial” anode and may prevent the formation of an incipient anode formation adjacent to the patch.
But does it extend the time to the next repair? But does it extend the time to the next repair?
Coating the exposed steel with zinc paintCoating the exposed steel with zinc paint
−+ +→ eZnZn 22
Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
Installing a Discrete Sacrificial Anode
Courtesy of http://www.norcure.com
NorcureNorcure SystemSystem
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Sacrificial metal(zinc) core
Cementitiousmatrix
Tie wires
Norcure Embedded Galvanic Anode
Improving the Performance of Patch RepairsImproving the Performance of Patch Repairs
Installed Galvanic Anode
Courtesy of http://www.norcure.com
The zinc becomes a “sacrificial” anode and provides cathodic protection to the steel in the vicinity of the patch.
Recent testing has demonstrated that this system does extend theRecent testing has demonstrated that this system does extend the time to the time to the next repair? next repair?
Courtesy of http://www.norcure.com
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Courtesy of http://www.norcure.com
Courtesy of http://www.norcure.com
Courtesy of http://www.norcure.com
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Courtesy of http://www.norcure.com
Courtesy of http://www.norcure.com
Courtesy of http://www.norcure.com
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Courtesy of http://www.norcure.com
Courtesy of http://www.norcure.com
Removing all the Chloride Contaminated ConcreteRemoving all the Chloride Contaminated Concrete
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Hydromilling
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Complete Slab ReplacementComplete Slab Replacement
Cathodic ProtectionCathodic Protection
−+ +→ eZnZn 22
O2
+ H
2O +
4e-→
4OH
-
Less noble metal (e.g. Zinc) connected to steel reinforcement and confers protection to the steel through “sacrificial” corrosion.
Note: the anode is consumed by the process.
Only suitable when the resistivity of the system is low and good electrolytic contact is maintained – e.g. submerged or buried structures, particularly marine structures
Sacrificial AnodeSacrificial Anode
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“Inert Anode”
2e-
−− →++ OHeOHO 2221
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2e-
−+ ++→ eOHOH 222 22−+ ++→ eClNaNaCl 222 2
Impressed CurrentImpressed Current
−− +→+ OHHeOH 2
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Requirements for Impressed Current CPRequirements for Impressed Current CP
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Summary of CP RequirementsSummary of CP Requirements
• Direct current supply• Impressed current anode• Electrolyte (concrete)• Cathode (rebar)• Electrical and electrolytic conductivity
Control & MonitoringControl & MonitoringCurrent Density
Typically current densities are in the range of 10 to 20 mA per m2 steel although higher values (up to 50 mA/m2) may be required in the most severe environments (e.g. poor quality concrete, low cover, high chlorides, high O2 environment, fluctuating moisture, high temperatures, extensive active corrosion on the steel)
Power Supply
It is usual to provide a number of small power supply units to protect individual (isolated) zones - typically 50 to 100 m2 area.
This usually translates to total current requirements of < 10 A and relatively low voltages of < 10 V (DC) to drive an individual zone (circuit). The actual voltage needed to deliver the required current will depend on the electrical resistivity of the concrete.
Supplies are usually transformer rectifier units that run on standard AC mains voltage and provide full control of the DC output currents and voltage.
Chess, 1998
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Cl-rich patch
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−+ +→ eFeFe 22
2e-2e-
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Cl-rich patch
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−+ +→ eFeFe 22
2e-2e-
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Apply Cathodic Apply Cathodic ProtectionProtection
Ie-e-
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Apply Cathodic Apply Cathodic ProtectionProtection
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Macrocell Probes – based on creating a local aggressive condition around an isolated piece of steel. An area of concrete is cut out and the steel bar isolated.
Cl-rich patch
The isolated bar – “probe” – is then connected to the main reinforcement via a “zero-resistance” current meter.
The hole is filled with chloride-rich concrete (Cl in patch > Cl in parent concrete)
Cl-rich patch
The current flow between the probe and main reinforcement is measured. Current should flow from the main reinforcement to theprobe (electron flow in reverse direction)
−+ +→ eFeFe 22
2e-2e-
I
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The CP system is then connected.
−+ +→ eFeFe 22
2e-2e-
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As the system current is increased the current flow to the probe will be reduced as the system becomes more negative.
−+ +→ eFeFe 22
e-e-
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e-−− →++ OHeOHO 222
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As the system current is increased the current flow to the probe will be reduced as the system becomes more negative. When the current flow between the probe and main reinforcement passes through zero, this is considered to be a satisfactory level of protection.
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2e-−− →++ OHeOHO 222
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e-e-
−− →++ OHeOHO 2221
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Measuring potential versus an embedded reference half-cell (e.g. Ag/AgCl, Mn/MnO2)
Criteria:• Absolute potential• “Instant-off” potential• Polarization decay
CP RepairCP RepairStrategyStrategy
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Electrochemical Chloride Extraction
www.norcure.com
www.norcure.com
www.norcure.com
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www.norcure.com
Cellulose fibres soaked in ‘anolyte’ (e.g. sodium borate) sprayed on concrete surface
www.norcure.com
www.norcure.com
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www.norcure.com
www.norcure.com
www.norcure.com
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www.norcure.com
www.norcure.com
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www.norcure.com
www.norcure.com
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www.norcure.com
www.norcure.com
www.norcure.com
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www.norcure.com
CP RepairCP RepairStrategyStrategy
ApplyECE
Protect from further Cl
ingress
Yes
ECE RepairECE RepairStrategyStrategy
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Repair of Carbonation-Induced Corrosion
Reinstate damaged concrete
Apply Coating(e.g.CO2 Barrier)
ElectrochemicalRealkalization
NaNa++
KK++
CO2
NaNa++
KK++
CO2
CO2-resistantCoating
Realkalization
www.norcure.com
www.norcure.com
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www.norcure.com
www.norcure.com
www.norcure.com
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BeforeBefore AfterAfter
Protecting the Repaired Structure
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REPAIR?REPAIR?Yes EXECUTEEXECUTE
REPAIRREPAIRDESIGNREPAIR
No
Adapted from Emmons, 1994
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We will look at the issues that affect these steps in the process later on in the course!
Broomfield, 1997
Broomfield, 1997
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Broomfield, 1997
Broomfield, 1997
REPAIR?REPAIR?Yes EXECUTEEXECUTE
REPAIRREPAIR
DESIGN/SELECTREPAIR
Adapted from Emmons, 1994
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