cathodic prevention of steel rebars in concrete the international outlook

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Cathodic prevention of steel rebars in concrete: the international outlook.


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What have great projects in common?


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Cathodic PreventionPedeferri Diagram


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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/m2Polymer Modified Cementitious Coating 0,015Acrylic coating 0,025Cathodic Protection (installed) 1,7Cathodic Protection (per year) 0,004PrevC (installed) 0,04PrevC (operation per year) 0,002


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St. Nicola I Viaduct – A24 (1989)

De-icing salts


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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)


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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


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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


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Sydney Opera House (1996)


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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


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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)


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Swanson Dock West (2008-2009)

1 Km

Melbourne’s Main container

Port

3 CP systems

Construction in stages: 1974-1988

4 berths


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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


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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


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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 points72h Depolarization 100 mV: 90% of the grid but not at the extremities

0,5 m


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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 eachOverall capacity (sized for future expansion): 30 ASince Jan 2009 energized and succesfully polarized achieving the 100 mV decay

criterion

Durrat Al Bahrain (2007)

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13 islands

13 bridges l: 3,5 km

2000 villas

3000 apartments


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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


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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


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Name Length Total N°Atoll Bridges 162 m 6Hotel Bridge 680 m 1Ring bridges 518 m 2Ring bridges 210 m 4


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Max Zone Size: 3 A

4 pre-cast decks + 4/6 pile headsBridge 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


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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


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Nakilat – Qatar (2006 -2009)

54 ships610 Mil US$


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Nakilat – Qatar (2006 -2009)

2 Km quays and piers


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Nakilat – Qatar (2006 -2009)54 cellular caissons in reinforced concreteOverall dimensions: 36 m x 36 m x 11 m; weight 4000 ton

CPrev to grant 50 years design life in the Persian GulfMMO mesh ribbon anodes for splash and atmospheric zone


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Tangiers-Med Port (2005 -2012)


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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 long5 Milions containerLarger port in the Mediterranean Sea


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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


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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


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Hangzhou Bay Bridge (2004-2005)

36 km

Opening: 14/06/2007

Among the ten longest trans-oceanic bridges


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Hangzhou Bay Bridge (2004-2005)


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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


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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


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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


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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


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ConclusionsCathodic 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.


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cathodic prevention of steel rebars in concrete the international outlook

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