Download advances in the protection of concrete from reinforcement corrosion

CATHODIC PROTECTION
OF REINFORCED
CONCRETE STRUCTURES
Center for Engineering Research
Research Institute, KFUPM
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
Chloride-induced Reinforcement
Corrosion
• Due to external chlorides
• Due to chloride contamination from the mix
constituents
Chloride Limits
 ACI 318 (0.1 – 0.15%; water soluble)
 ACI 224 (0.2%; acid soluble)
 BS 8110 (0.4%; total)
CARBONATION
• Ca(OH)2 + CO2  CaCO3 + H2O
• Reduction in pH (up to 8.5)
FACTORS AFFECTING
CARBONATION
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Concrete quality
Concrete cover
Moisture condition
Temperature
Chloride-sulfate contamination
PREVENTION THROUGH
DESIGN
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Cover over reinforcing steel
Water-cement ratio
Cement content
Cement type
PROTECTION OF STEEL
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Metallic coatings
Non-Metallic coatings
Inhibitors
Electrochemical protection
• Cathodic protection
• Chloride removal
• Realkalization
CATHODIC PROTECTION
 Sacrificial anode
 Impressed current
Corrosion cell in concrete
Corrosion cell in a repaired concrete
Corrosion cell after CP
Comparison of CP systems (Merits)
Impressed current system
Sacrificial anode system
Longer anode life
Inherently simple
Current can be controlled
No monitoring and
maintenance
No requirement for electrical
isolation
Risk of hydrogen
embrittlement on high strength
steel is minimal
Saw cutting and concrete
encapsulation for anodes is not
required
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
Current cannot be adjusted or
controlled
Conduit and wiring required
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
Corroded pile in sea
Pier with SACP
Discrete anode for repaired structure
Discrete anode
Placement of discrete anodes
Mesh anode
Placement of anodes
Specimens with discrete anodes
Specimens with jacket anodes
Specimens with mesh anodes
Specimens and measurement boxes
Sacrificial Anode
Impressed Current CP
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
Current requirements
 Atmospheric zones
• 5 to 15 mA/m2
 Under water
• 0.2 to 2 mA/m2
 Decreases with time
ICCP – Power System
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Transformers/Rectifiers
Constant voltage/current system
Stable over long period of time
Solar- or wind-powered units are also used
ICCP - Connections
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Durable and corrosion resistant
Low-voltage wires
Diameter for minimum voltage drop
Color coded
Multiple connections and cables
recommended
ICCP Monitoring System
 Potential measurements
 Embeddable reference electrodes
• Ag/AgCl
• Mn/MnO2
Anode mesh fixed on concrete
Conductor bar welded to anode mesh
Negative connection to the steel bar
Connection of embedded items
Reference electrode
Installing overlay
Finishing operation
Anode and steel cage
Details of anode
Connection of anode ribbon to the
titanium conductor bar
Steel connection
Placement of electrodes and
connections to the steel bar
Pouring of concrete
Chloride Removal
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
Re-Alkalization
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
THANK YOU