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CATHODIC PROTECTION OF REINFORCED CONCRETE STRUCTURES

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

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CATHODIC PROTECTION OF REINFORCED CONCRETE STRUCTURES

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  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)

  14. Comparison of CP systems (Demerits)

  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 • 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

  30. Current requirements • Atmospheric zones • 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 • 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

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