cathodic protection of concrete structures
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Cathodic Protection of
Concrete Structures
Systems By SRCP
Cathodic Protection Systems• Impressed Current
• Zebra• Cassette• CorroDisc Surface Embedded
• Sacrificial Anode• ZLA• Roll Anode• GSC Super Anode• Clip On Anode
• Monitoring and Control • Camur
Conductive coatingSurface mounted ribbon anodeMesh in precast stick-on shapes Ti wire in acid resistant cylinder for embedment
Zinc sheet with self adhesive activatorRolled ZLA grouted in drill holeZLA block for embedment in repairZLA block in precast container
Remote monitoring and control
Reinforcement Corrosion Process
Corrosion Reaction
CathodicReaction
2(OH)-
AnodicReaction
SecondReaction
H2O
Fe(OH)2
O2
Fe++ 2e-
WaterChloride Oxygen
Fe2O3H2O(Rust)
H2O ½O2
Rebar
OxygenAn area of reinforcement becomes anodic due to chloride or carbonation ingress.Corrosion is stopped if:• Oxygen at cathode
stopped• Full immersion• Small cathode
• Resistance of electrolyte high• Low due to chloride
& water• Electrons supplied from
alternative anode
Anodic and cathodic reaction are critical to how the cell works.
What is Cathodic Protection• Provides and alternate anode to prevent reinforcement corrosion
• Sufficient current to ensure protection over all rebar• Determined by code criteria
• 100mv decay at 24hrs• Eliminates need for breakout of sound but contaminated concrete• Eliminates structural problems
• Reduced noise and dust
Galvanic Anode
Curr
ent
C u r r e n t F l o w
Impressed Current Cathodic Protection• Powered system so no limit to the level of protection• Over protection
• Prestress particular concern
• Acidification around anode possible
• Under protection• System failure• Protection requirements change
• Reliable and total protection when maintained
• Detailed design • Expert commissioning• Regular monitoring
• High life cycle cost• Particularly for small projects
Zebra
Zebra Anode
Zebra PDR TapeZebra PDR
Concrete
Wearing Surface
Bond Coats
Layers of a Zebra System for the wearing surface of a car park deck
US Patent 6855199 B1 2005• Water soluble silicate carrier
• penetrates and forms micro-crystalline bond with concrete
• Filled graphite particles
ZebraProjects• 400+ projects • Light weight• Conventional painting skills
• Rapidly applied• Decorative• 20+ year lifeApplications
• Building facades, balconies and slabs.
Building facade Car park capillary rise zone
Balcony soffits Car park slab
Cassette• Ribbon anode in a surface mounted inert carrier.
• Ribbon anodes are a proven ICCP system except acidification of slotted systems can cause failure after 15-20 years.
• Cassette overcomes acidification issues.
10mm Stainless Steel Bolt
Inert Fibreglass Panel
Glasswool Contact Pad
Elgard 150 Ribbon Anode
80x80 mm HDG washer Isolating Washer
22mm long Glass Fibre Nut/washer
15mm diameter hole drilled in concrete
Polyester resin , e.g. Ramset Chemset 101 or similar
Fibre Glass Plate 80x80x9.5mm with 18mm diameter central hole
40m
m
½”ø 100mm long Glass FibreStud
25mm
Cassette• Proven Elgard 150 ribbon anode.• Surface mounted in own tray. No grinding or shotcrete.• Inert system. Acidification around anode not an issue.• Simple to install. Just bolt on (stainless steel or fibre glass).
• Doesn’t add significant weight. • MMO coated titanium, life typically 50 years.Applications
• Where aesthetics not critical, e.g. tanks, car parks• Confined spaces, e.g. basements, tunnels• Projects where wet exposure, wharf and bridges splash zones
Cassette ProjectsPipe tunnel, poor access
Prestressed bridge T-Roffs
Car park capillary rise area
Cast insitu bridge beam
Roof of Tunnel Soffit Brdige deck soffit
CorroDisc• MMO coated titanium mesh in a silicate based mortar• Mesh
• long term proven performance• 50 year life
• Mortar • resistant to strong acids• Permeable to water vapour &
oxygen• Real CP
• Satisfies the 100mV criteria• Convenient testing
• Use individual Corrodisc anodes
CorroDisc 125 – 125mm diameter circular surface applied anode typically applied on a rectangular grid to give 4-8 anodes/m2
CorroDisc R – 60x400mm wide surface applied anode typically applied in line to give 3-4 anodes/m2
MMO coated
titanium mesh
CorroDisc• Easy & economic installation
• Surface applied• Avoids grinding, drilling or embedding the anodes in the structure
• Local surface preparation only
• Flexible anode placement
• Reasonable appearance once coated
• Not suited to wet areas
Pressing CorroDisc R onto surface
Pressing CorroDisc 125 onto surface
Camur Monitoring and Control• Remote control & monitoring essential for ICCP
• Power supply units 3 or 8amp
• Single bus cable• Power control • Power monitoring• Half cell monitoring
• Integral computer logs data
• Data accessed remotely• Data collection software• Web viewing software
Bus interface
Computer
1 zone system (Available for control and monitoring of trial areas).
Transformer
Rectifier
Camur• Camur System• IP box• Computer• Transformer• Fix Volts• Transformer• Bus Interface• Light/fan/heater
• Fuses/sockets• Connectors• Software• Web Site
Concrete Structure
220/240V Power
Supply
Control Cabinet
Gen. Skt 1 (e.g. Insp. Comp.)1
Cabinet Fuse1
9m max1.7m max
Anode Wire Grid
Bus
P-Node
120ohm
120ohm
P-Node
P-Node
P-Node
P-Node
P-Node
Anode Zone 3
Anode Zone 2Anode Zone 1
Transformer for each Fix Volta)so Fix Volt is all
low voltb)to eliminate
ground loops
Fix Volt Fix VoltFix Volt
Bus (plug together)
4 or 8 Amp
24V AC
Anode Zone 1
Power Term.4
Sensor wires5
Anode Zone 2
Anode Zone 3
Comp. Skt
Gen. Skt 2 (e.g. GSM)Fuse All
other than Gen. Skt. 11
Heater2
Light/ /Heat/ Fan Fuse
FanThermostate2
Thermo-stat2
GSM (USB)
Screen (HDMI)
Keyboard (USB)
Client Supplied
Network (LAN port)Bus (USB)
24V
DCBu
s Tra
nsfo
rmer
Bus Interface3
Controller
3 zone system with all anode beds in same location.
Concrete Structure
220/240V Power
Supply
Concrete Structure
Transformer for each Fix Volta)so Fix Volt is all
low voltb)to eliminate
ground loops
Fix Volt Fix Volt
Bus (plug together)
4 or 8 Amp
24V AC
Anode Zone 1
Power Term.
Sensor Term.
Anode Zone 2
Transformer Fuse
Bus
9m max1.7m max
Anode Wire Grid
P-Node
120ohm
P-Node
P-Node
P-Node
Anode Zone 2Anode Zone 1
W-Node
Area 7*3*1.7m*1.9m =
Approx.320m2
Typically max around 500m2 but
could be much lower with high density steel
Strips 500-600
wide with 50mm
gaps
GSM (USB)
Control Cabinet 1
Controller
Bus (USB)
Cabinet Fuse1
Gen. Skt 1 (e.g. Insp. Comp.)1
Screen (HDMI)
Keyboard (USB)
Gen. Skt 2 (e.g. GSM)
Comp. Skt
24V
DCBu
s Tr
ansf
orm
er
Client Supplied
Light/ /Heat/ Fan Fuse
Fuse All other than
Gen. Skt. 11
Fan
Heater2
Thermostate2
Thermo-stat2
Network (LAN port)
Fix Volt
P-Node
P-Node
Anode Zone 3
Fuse All
120ohm
Bus
Tran
sfor
mer
24V DC
Cabinet Fuse
W-Node
120ohm
120ohm
Gen. Skt (e.g. Insp. Comp.)1
Aux Cab.
Anode Zone 3
2 Zones 3 Zones
Right: 3 zone system where anode beds separated. Note wireless link of bus cable.
Camur
Working systems.
Concrete Structure
• Components sold individually
• Computer• Transformer
• Fix Volts• Transformer
• Bus Interface
ZLA Range of Sacrificial Anodes• High output for true cathodic protection• Simple to install; limited wiring, no power source• Doesn’t add significant weight. Decorative after coating.
• Low design; installation and monitoring costs• Zinc consumed, life typically 20 yearsApplications
•Low cost or limited life projects•Applicators not expert in cathodic protection•Holding repairs•Prestressed items
Cathodic Protection vs Prevention+400
0
-400
-800
-12000 0.5 1.0 1.5 2.0
Pote
ntia
l (m
V vs
SC
E)
Chloride Content (wt % cement)
PittingCondition conducive to stable propagation of pits
Perfect Passivity
Allows pre-existing pits may propagate but new pits unlikely
Imperfect Passivity
Hydrogen DischargeOxide unstable, hydrogen formed cathodically
A
B C
D
E
F
Cathodic Prevention
Cathodic Protection
Initiation and propagation of pits inhibited
A small potential shift gives cathodic prevention, i.e. a high chloride corrosion threshold for cathodic steel. Use low output anodes for incipient anode protections.A large potential shift gives cathodic protection, i.e. immunity from corrosion for active steel. Use high out put anodes (ZLA range) for true CP and no breakout.
SACP systems must provide 100mv 24hr potential decay criteria
Cyclic Voltametric Testing• Standard electrode test procedure• Cycle voltage and measure current
• Zinc Activator Paste (ZAP) optimised by CVT trials
Cat
hode
Cur
rent
Den
sity
[mA/
100c
m2 ]
Polarisation [mV Ag/AgCl]
0.01
0.1
10
100
1
-800 -600 -400 -200
Zinc in LiOH based mortar
Expected Polarisation
Steel
Current for 0.167mv/s sweep rate
ZAP outputLiOH output
Intersection of steel and anode tests gives polarisation expected from anode
Test system set up
Zinc Layer Anode (ZLA)• Zinc in contact with concrete passivates• Activator applied to zinc keeps it active and ensures continuous cathodic protection
• Reactions at the anode / activator interface critical• Zinc chloride formed with ZLA anodes gives high output and long term performance
• Anodes lead to true CP with meeting 100mv 24hr decay criteria
Roll Anode and GSC Super Anode derived for ZLA and both give CP meeting 100mv criteria.
Roll of ZLA as applied to the
surface of concrete to
provide full CP meeting 100mv
criteria
ZLA Projects
Balconies Walkways Facades Bridges
After ZLA Application
After Coating
Roll Anode• Drill hole
• Depth to move away from extreme fibre stress as required
• Insert anode and grout• ZAP for best CP performance
• Cement grout for strength
Anode string connected to rebar
27mm diameter Roll Anode
Typical Roll Anode Installation
GSC Super Anode• Bolt to rebar• Cast into repair• Cathodic Protection
• No breakout behind bars
• Incipient anode protection Anode
string connected to rebar
30/20 GSC Super Anode
SACP Performance Data• Seineflat Apartments• 100mv criteria met at installation and after 2 years
SACP Performance Data• Cape Perpetua Viaduct• 100mv criteria met at installation and after 5 years
0 1 2 3 4 5Time (Hours)
300
200
100
0
Pote
ntia
l Dec
ay (m
v C
SE)
Installed 1998
April 2002
Jan 2003
SACP• Stockton Bridge Trial
• ZLA provides three times the polarisation of the other SA anodes
1
2
3
1.5m
1.7m
Ref Cell
123
Potential (mV vsAg/AgCl) Before
Connecting Anode-87mV -25mV-22mV
Potential mV vsAg/AgCl 2-3min After Connecting
Anode-393-609-602
Current (mA) 3-4min After Connecting
Anode
22
Voltage (mV) 2-3min After Connecting
Anode
0.987
Anode
ZLA
Inst. Off
-476-416-469
24hr off-58-50-18
24hr decay418366451
Monitoring results 23/1/13 (mv)
CM2 Rebar Continuity
• ICCP and SACP wont work if there is not rebar continuity
• CM2 Continuity Tester measures :
• resistance at high current (1 Amp) to test connection under load. This is a common failure of connections tested with standard voltmeters. Criteria ≤1ohm)
• residual voltage 0.1 sec after the resistance test. Criteria =0V
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