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Cathodic prevention of steel rebars in concrete the international outlook


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The fundamental application of " cathodic prevention " of steel reinforcement in concrete was ideated and developed by Professor Pietro Pedeferri. It was successfully applied since 1989 in Italy on Viaduct St. Nicholas I of the highway Rome - Aquila - Teramo and in 1996 in the western underbroadwalk of the Sydney Opera House. Over the past 20 years it has spread throughout the world and particularly in Northern Europe, Middle East and Australia being recognized as the most reliable technique to combat corrosion for new buildings and infrastructure where reinforced concrete is exposed to possible contamination from chlorides. This memory is a review of some of the most significant industrial cases reported in the international literature.
Durrat Al Bahrain and the NAKILAT shipyard in Qatar are two recent projects developed in the Middle East. Cathodic Prevention of West Swanson Dock in Melbourne was the largest project completed in Australia in the last decade.
Other significant experiences in China and North Africa are a sign of the vitality of this technique in the developing countries.

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Cathodic prevention of steel rebars in concrete the international outlook

  2. 2. ELECTROCHEMISTRY AT YOUR SERVICETM 2 What have great projects in common?
  3. 3. ELECTROCHEMISTRY AT YOUR SERVICETM 3 Cathodic Prevention Pedeferri Diagram
  4. 4. ELECTROCHEMISTRY AT YOUR SERVICETM 4 Cathodic Prevention Limited embodied energy; small cathodic current. Extensive Reference in International Standard EN ISO 12696:2012 “Cathodic Protection of Steel in concrete” ANNEX A Concrete protection GJ/m2 Polymer Modified Cementitious Coating 0,015 Acrylic coating 0,025 Cathodic Protection (installed) 1,7 Cathodic Protection (per year) 0,004 PrevC (installed) 0,04 PrevC (operation per year) 0,002
  5. 5. ELECTROCHEMISTRY AT YOUR SERVICETM 5 St. Nicola I Viaduct – A24 (1989) De-icing salts
  6. 6. ELECTROCHEMISTRY AT YOUR SERVICETM 6 St. Nicola I Viaduct – A24 (1989) Continuous structure: 11 spans Total surface to be protected: 5600 m2 Prefabricated concrete segments post-tensioned with high strength steel cables. Hydrogen embrittlement: at pH > 12 potentials more negative than -950 mV (SCE)
  7. 7. ELECTROCHEMISTRY AT YOUR SERVICETM 7 St. Nicola I Viaduct – A24 (1989) Steel protection current density to a depth of 40cm: 10mA/m2 Anode layout: Titanium MMO Net single, double, triple Small anodic zones (100m2) with 4 current distributors Reference electrodes: Ag/AgCl and Titanium MMO close to post-tensioned cable and rebar Remote monitoring control unit
  8. 8. ELECTROCHEMISTRY AT YOUR SERVICETM 8 St. Nicola I Viaduct – A24 (1989) CP system performances Average current density: 6mA/m2 IR drops in the anode net each zone < 50 mV Average polarization 200 mV Tensioned cables potential >> -900mV
  9. 9. ELECTROCHEMISTRY AT YOUR SERVICETM 9 Sydney Opera House (1996)
  10. 10. ELECTROCHEMISTRY AT YOUR SERVICETM 10 Sydney Opera House (1996) Prevent corrosion of new precast elements of the substructure of western under broad-walk 68 Zones: geometry + environment (tidal, submerged and atmospheric) LIDA® GRID: flexibility of current density and Titanium MMO rods Total concrete area of CPrev application: 742 m2 Protection current density: 10 mA/m2 80 Reference electrodes: Ag/AgCl, Ti MMO, Zn
  11. 11. ELECTROCHEMISTRY AT YOUR SERVICETM 11 Sydney Opera House (1996)
  12. 12. ELECTROCHEMISTRY AT YOUR SERVICETM 12 Sydney Opera House (1996 e 2005) Protection criteria: 100 mV potential decay in 24h (atmospheric and splash zones structures) Instant OFF potential: > -900 mV < – 1100 mV Ag/AgCl/0,5M KCl as per AS2832.5 (concrete elements submerged in SWT) System energized in 1996: Potential well above the limit for overprotection in A-frames (post-tensioned steel) After 10 years of operation: no visible deterioration, spalling or delamination Protection current density: 2-5 mA/m2 17% faulty reference electrodes (most Ag/AgCl)
  13. 13. ELECTROCHEMISTRY AT YOUR SERVICETM 13 Swanson Dock West (2008-2009) 1 Km Melbourne’s Main container Port 3 CP systems Construction in stages: 1974-1988 4 berths
  14. 14. ELECTROCHEMISTRY AT YOUR SERVICETM 14 Swanson Dock West (2008-2009) Cathodic Prevention applied to the new ship fender (500m) of berths 1 and 2 in the splash and tidal zones. Heavily chloride contaminated: cracking and spalling. 600 mm
  15. 15. ELECTROCHEMISTRY AT YOUR SERVICETM 15 Swanson Dock West (2008-2009) Fender beam sections reconstruction. CP rev applied in 30 locations: 3,5m in length up to 0,5m from the base Anodes: MMO titanium mesh ribbon anodes applied on insulating spacers Protection current density (conservative): 20 mA/m2
  16. 16. ELECTROCHEMISTRY AT YOUR SERVICETM 16 Swanson Dock West (2008-2009) Trial system: 2 anodes on each face and 3 on the base 3,5m long Reference electrodes: 2 embedded in concrete + external (250mm grid) 24h Depolarization 100 mV : only 40% of the grid points 72h Depolarization 100 mV: 90% of the grid but not at the extremities 0,5 m
  17. 17. ELECTROCHEMISTRY AT YOUR SERVICETM 17 Swanson Dock West (2008-2009) New design: additional anode on each side of the beam 500mm up from the base + additional transverse anode at the ends of the 3,5m beam section 30 reconstructed areas with new design: 6 zones 5 areas each Overall capacity (sized for future expansion): 30 A Since Jan 2009 energized and succesfully polarized achieving the 100 mV decay criterion
  18. 18. Durrat Al Bahrain (2007) 18
  19. 19. ELECTROCHEMISTRY AT YOUR SERVICETM 19 Durrat Al Bahrain (2007) 13 islands 13 bridges l: 3,5 km 2000 villas 3000 apartments
  20. 20. ELECTROCHEMISTRY AT YOUR SERVICETM 20 Durrat Al Bahrain (2007) T water: 35°C Salinity: 37-39 g/l Bridges height:2m Lifetime: 50 years Rebar corrosion chloride contamination Cost CPrev: 2.130.000 USD Cost stainless steel (304) 22 Millions USD
  21. 21. ELECTROCHEMISTRY AT YOUR SERVICETM 21 Durrat Al Bahrain (2007) Design Life 50 years Anode type MMO coated titanium ribbon mesh Cathode current density 5 mA/m2 Max Anode current density 110 mA/m2 Protection Criteria 100 mV decay or -720 mV vs. Ag/AgCl Max zone size 3A Power/Monitoring System Fully remotely controlled and monitored
  22. 22. ELECTROCHEMISTRY AT YOUR SERVICETM 22 Durrat Al Bahrain (2007) Name Length Total N° Atoll Bridges 162 m 6 Hotel Bridge 680 m 1 Ring bridges 518 m 2 Ring bridges 210 m 4
  23. 23. ELECTROCHEMISTRY AT YOUR SERVICETM 23 Durrat Al Bahrain (2007) Max Zone Size: 3 A 4 pre-cast decks + 4/6 pile heads Bridge end: 1 abutment, 2 pile heads + 2/4 pre-cast units Element Protection Current Pre-cast deck unit 662 mA Exposed section of abutments 287 mA Piles above casing (Pile Head) 31 mA
  24. 24. ELECTROCHEMISTRY AT YOUR SERVICETM 24 Durrat Al Bahrain (2007)
  25. 25. ELECTROCHEMISTRY AT YOUR SERVICETM 25 Durrat Al Bahrain (2007) Reference electrodes: embeddable Ag/AgCl Recorded native and instantaneous Eoff potentials after 1h up to 24h Good potential shift in 3-4 h Homogeneity of shifts and even protection
  26. 26. ELECTROCHEMISTRY AT YOUR SERVICETM 26 Durrat Al Bahrain (2007)
  27. 27. ELECTROCHEMISTRY AT YOUR SERVICETM 27 Nakilat – Qatar (2006 -2009) 54 ships 610 Mil US$
  28. 28. ELECTROCHEMISTRY AT YOUR SERVICETM 28 Nakilat – Qatar (2006 -2009) 2 Km quays and piers
  29. 29. ELECTROCHEMISTRY AT YOUR SERVICETM 29 Nakilat – Qatar (2006 -2009) 54 cellular caissons in reinforced concrete Overall dimensions: 36 m x 36 m x 11 m; weight 4000 ton CPrev to grant 50 years design life in the Persian Gulf MMO mesh ribbon anodes for splash and atmospheric zone
  30. 30. ELECTROCHEMISTRY AT YOUR SERVICETM 30 Tangiers-Med Port (2005 -2012)
  31. 31. ELECTROCHEMISTRY AT YOUR SERVICETM 31 Tangiers-Med Port (2005 -2012) Tangier Med: 2007 first multi-purpose wharf 2008 second terminal 3,5 Millions container py Tangier Med II: 2012-2015 2 new terminals 2800m long 5 Milions container Larger port in the Mediterranean Sea
  32. 32. ELECTROCHEMISTRY AT YOUR SERVICETM 32 Tangiers-Med Port (2005 -2012) Primary and secondary breakwaters builded by consortium Bouygues-Bymaro-Saipem to protect the port Water depth > 20m zone: 40 precast reinforced concrete caisson built on land then placed in the seawater and completed with the second phase of concreting
  33. 33. ELECTROCHEMISTRY AT YOUR SERVICETM 33 Tangiers-Med Port (2005 -2012) 1 caisson = 4 cells 28mx28mx35m h, weight 7900 ton 550 ton of steel and 3000 m3 of concrete CPrev in tidal and splash zone to stop corrosion induced by chlorides Grid system with MMO Titanium mesh ribbon
  34. 34. ELECTROCHEMISTRY AT YOUR SERVICETM 34 Hangzhou Bay Bridge (2004-2005) 36 km Opening: 14/06/2007 Among the ten longest trans-oceanic bridges
  35. 35. ELECTROCHEMISTRY AT YOUR SERVICETM 35 Hangzhou Bay Bridge (2004-2005)
  36. 36. ELECTROCHEMISTRY AT YOUR SERVICETM 36 Xia-Zhang Bridges (2011-2013) Total length North Branch: 6392 m L cable-stayed: 1290m 720m main span 6° world-wide long cable-stayed combined with steel and concrete
  37. 37. ELECTROCHEMISTRY AT YOUR SERVICETM 37 Xia-Zhang Bridge (2011-2013) Cprev 4 main pylons and 4 piers Tidal and splash zone: 13100m2 Anode: MMO Ti activated mesh ribbon applied on the rebar with concrete spacer
  38. 38. ELECTROCHEMISTRY AT YOUR SERVICETM 38 Louvre Abu Dhabi, UAE (2013-2015) On Saadiyat Island due to open end of 2015 Cprev installed on all exposed surfaces of the reinforced concrete sub-structure up to a height of +3.45m
  39. 39. ELECTROCHEMISTRY AT YOUR SERVICETM 39 Louvre Abu Dhabi, UAE (2013-2015) Cprev system for a design life of 100 years Anode: MMO Ti activated mesh ribbon installed in the screed to protect rebar in the lower reinforcement of the strip footings, ground beams and slabs Fixed to the rebar cage using plastic clips for all other surfaces
  40. 40. ELECTROCHEMISTRY AT YOUR SERVICETM 40 Conclusions Cathodic Prevention, conceived by Prof. Pietro Pedeferri, has proven to be a viable technique to stop corrosion of steel reinforcement in concrete. From the first trials in the mid-’80s this idea has evolved over the course of thirty years becoming a well established technique to preserve structures subject to corrosion induced by chlorides contamination. Several aspects of cathodic prevention have been incorporated in international standards such as ISO 12696:2012 and AS2832.5- 2008. The diffusion of the technology from the US and Europe to Australia, Middle East, China and North Africa is a sign of the relevance of this idea in the corrosion prevention global market.
  41. 41. ELECTROCHEMISTRY AT YOUR SERVICETM 41 Thank you for your time Q&A