advances in the protection of concrete from reinforcement corrosion
Transcript of advances in the protection of concrete from reinforcement corrosion
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CATHODIC PROTECTION CATHODIC PROTECTION OF REINFORCED OF REINFORCED
CONCRETE STRUCTURESCONCRETE STRUCTURES
Center for Engineering ResearchResearch Institute, KFUPM
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REINFORCEMENT CORROSION
Passivity• High pH leading to formation of passive layer• Chemical binding of chlorides• Dense and relatively impermeable structure of
concrete Depassivation
• Chloride ingress• Carbonation
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Chloride-induced Reinforcement Corrosion
• Due to external chlorides
• Due to chloride contamination from the mix constituents
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Chloride Limits
ACI 318 (0.1 – 0.15%; water soluble) ACI 224 (0.2%; acid soluble) BS 8110 (0.4%; total)
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CARBONATION
• Ca(OH)2 + CO2 CaCO3 + H2O
• Reduction in pH (up to 8.5)
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FACTORS AFFECTING CARBONATION
• Concrete quality• Concrete cover• Moisture condition• Temperature• Chloride-sulfate contamination
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PREVENTION THROUGH DESIGN
Cover over reinforcing steel Water-cement ratio Cement content Cement type
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PROTECTION OF STEEL
• Metallic coatings• Non-Metallic coatings• Inhibitors• Electrochemical protection
• Cathodic protection• Chloride removal• Realkalization
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CATHODIC PROTECTION
Sacrificial anode Impressed current
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Corrosion cell in concrete
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Corrosion cell in a repaired concrete
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Corrosion cell after CP
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Comparison of CP systems (Merits)Impressed current system Sacrificial anode system
Longer anode life Inherently simple
Current can be controlled No monitoring and maintenanceNo requirement for electrical isolationRisk of hydrogen embrittlement on high strength steel is minimalSaw cutting and concrete encapsulation for anodes is not required
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Comparison of CP systems (Demerits)
Impressed current system Sacrificial anode system
Requires monitoring and maintenance
Short anode life
Electrical isolation required between anode and steel
Anode current delivery is dependent on anode chemistry and surrounding environment
Conduit and wiring required Current cannot be adjusted or controlled
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Sacrifical Anode System
Anode material• Alloys of Mg, Al, Zn
Anode shapes• Zinc foil (Zinc hydrogel)• Metallized zinc (thermal spray)• Jackets• Zinc capsules or discs encased in mortar
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Corroded pile in sea
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Pier with SACP
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Discrete anode for repaired structure
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Discrete anode
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Placement of discrete anodes
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Mesh anode
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Placement of anodes
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Specimens with discrete anodes
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Specimens with jacket anodes
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Specimens with mesh anodes
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Specimens and measurement boxes
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Sacrificial Anode
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Impressed Current CP
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ICCP Anodes Conductive coating
• Sparyed, rolled or brushed over a nibium wire (300 um thickness) Arc sprayed zinc
• Spraying metal on concrete with compressed air (300 -400 um) Titanium anode mesh Titanium anode mesh jackets Titanium ribbon Discrete anodes Thermally sprayed titanium
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Current requirements
Atmospheric zones• 5 to 15 mA/m2
Under water• 0.2 to 2 mA/m2
Decreases with time
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ICCP – Power System
Transformers/Rectifiers Constant voltage/current system Stable over long period of time Solar- or wind-powered units are also used
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ICCP - Connections
Durable and corrosion resistant Low-voltage wires Diameter for minimum voltage drop Color coded Multiple connections and cables
recommended
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ICCP Monitoring System
Potential measurements Embeddable reference electrodes
• Ag/AgCl• Mn/MnO2
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Anode mesh fixed on concrete
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Conductor bar welded to anode mesh
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Negative connection to the steel bar
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Connection of embedded items
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Reference electrode
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Installing overlay
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Finishing operation
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Anode and steel cage
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Details of anode
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Connection of anode ribbon to the titanium conductor bar
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Steel connection
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Placement of electrodes and connections to the steel bar
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Pouring of concrete
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Chloride Removal
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CE - Details Anode
• Titanium or steel mesh Electrolyte
• Water or saturated calcium hydroxide solution Current
• 1 to 2 A/m2
Time • 6 to 10 weeks
Not advisable for prestressed concrete Impressed/sacrificial anode cathodic protection systems
may be used Side effects – Alkali-silica reaction
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Re-Alkalization
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Realkalization - details Anode
• Steel or titanium mesh Electrolyte
• Sodium carbonate solution (1 mole/L) Current
• 1 to 2 A/m2
Time• Days to weeks
Not advisable for prestressed concrete Impressed/sacrificial anode cathodic protection systems
may be used Side effects – Alkali-silica reaction
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THANK YOU