1. CATHODIC PROTECTION OF REINFORCED CONCRETE STRUCTURES
Center for Engineering Research
Research Institute, KFUPM

2. 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

3. Chloride-induced Reinforcement Corrosion
Due to external chlorides
Due to chloride contamination from the mix constituents

4. Chloride Limits ACI 318 (0.1 – 0.15%; water soluble)
ACI 224 (0.2%; acid soluble)
BS 8110 (0.4%; total)

5. CARBONATION
Ca(OH)2 + CO2  CaCO3 + H2O
Reduction in pH (up to 8.5)

6. FACTORS AFFECTING CARBONATION
Concrete quality
Concrete cover
Moisture condition
Temperature
Chloride-sulfate contamination

7. PREVENTION THROUGH DESIGN
Cover over reinforcing steel
Water-cement ratio
Cement content
Cement type

8. PROTECTION OF STEEL Metallic coatings Non-Metallic coatings Inhibitors
Electrochemical protection
Cathodic protection
Chloride removal
Realkalization

9. CATHODIC PROTECTION
Sacrificial anode
Impressed current

10. Corrosion cell in concrete

11. Corrosion cell in a repaired concrete

12. Corrosion cell after CP

13. 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

14. 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

15. 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

16. Corroded pile in sea

17. Pier with SACP

18. Discrete anode for repaired structure

19. Discrete anode

20. Placement of discrete anodes

21. Mesh anode

22. Placement of anodes

23. Specimens with discrete anodes

24. Specimens with jacket anodes

25. Specimens with mesh anodes

26. Specimens and measurement boxes

27. Sacrificial Anode

28. Impressed Current CP

29. ICCP Anodes Conductive coating Arc sprayed zinc Titanium anode mesh
Sparyed, rolled or brushed over a nibium wire (300 um thickness)
Arc sprayed zinc
Spraying metal on concrete with compressed air ( um)
Titanium anode mesh
Titanium anode mesh jackets
Titanium ribbon
Discrete anodes
Thermally sprayed titanium

30. Current requirements Atmospheric zones Under water Decreases with time
5 to 15 mA/m2
Under water
0.2 to 2 mA/m2
Decreases with time

31. ICCP – Power System Transformers/Rectifiers
Constant voltage/current system
Stable over long period of time
Solar- or wind-powered units are also used

32. ICCP - Connections Durable and corrosion resistant Low-voltage wires
Diameter for minimum voltage drop
Color coded
Multiple connections and cables recommended

33. ICCP Monitoring System
Potential measurements
Embeddable reference electrodes
Ag/AgCl
Mn/MnO2

34. Anode mesh fixed on concrete

35. Conductor bar welded to anode mesh

36. Negative connection to the steel bar

37. Connection of embedded items

38. Reference electrode

39. Installing overlay

40. Finishing operation

41. Anode and steel cage

42. Details of anode

43. Connection of anode ribbon to the titanium conductor bar

44. Steel connection

45. Placement of electrodes and connections to the steel bar

46. Pouring of concrete

47. Chloride Removal

48. CE - Details Anode Electrolyte Current Time
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

49. Re-Alkalization

50. 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

51. THANK YOU