advances in the protection of concrete from reinforcement corrosion

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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

Depassivation

Chloride ingress

Carbonation

Chloride-induced Reinforcement Corrosion

Due to external chlorides

Due to chloride contamination from the mix constituents

Chloride Limits

ACI 318 (0.1 0.15%; water soluble)ACI 224 (0.2%; acid soluble)BS 8110 (0.4%; total)

CARBONATION

Ca(OH)2 + CO2 CaCO3 + H2O

Reduction in pH (up to 8.5)

FACTORS AFFECTING CARBONATION

Concrete quality

Concrete cover

Moisture condition

Temperature

Chloride-sulfate contamination

PREVENTION THROUGH DESIGN

Cover over reinforcing steelWater-cement ratioCement contentCement type

PROTECTION OF STEEL

Metallic coatings

Non-Metallic coatings

Inhibitors

Electrochemical protection

Cathodic protection

Chloride removal

Realkalization

CATHODIC PROTECTION

Sacrificial anodeImpressed current

Corrosion cell in concrete

Corrosion cell in a repaired concrete

Corrosion cell after CP

Comparison of CP systems (Merits)

Impressed current systemSacrificial anode systemLonger anode lifeInherently simpleCurrent can be controlledNo monitoring and maintenanceNo requirement for electrical isolationRisk of hydrogen embrittlement on high strength steel is minimalSaw cutting and concrete encapsulation for anodes is not required

Comparison of CP systems (Demerits)

Impressed current systemSacrificial anode systemRequires monitoring and maintenanceShort anode lifeElectrical isolation required between anode and steelAnode current delivery is dependent on anode chemistry and surrounding environmentConduit and wiring requiredCurrent cannot be adjusted or controlled

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

Corroded pile in sea

Pier with SACP

Discrete anode for repaired structure

Discrete anode

Placement of discrete anodes

Mesh anode

Placement of anodes

Specimens with discrete anodes

Specimens with jacket anodes

Specimens with mesh anodes

Specimens and measurement boxes

Sacrificial Anode

Impressed Current CP

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 meshTitanium anode mesh jacketsTitanium ribbon Discrete anodesThermally sprayed titanium

Current requirements

Atmospheric zones

5 to 15 mA/m2

Under water

0.2 to 2 mA/m2

Decreases with time

ICCP Power System

Transformers/RectifiersConstant voltage/current systemStable over long period of timeSolar- or wind-powered units are also used

ICCP - Connections

Durable and corrosion resistantLow-voltage wiresDiameter for minimum voltage dropColor codedMultiple connections and cables recommended

ICCP Monitoring System

Potential measurementsEmbeddable reference electrodes

Ag/AgCl

Mn/MnO2

Anode mesh fixed on concrete

Conductor bar welded to anode mesh

Negative connection to the steel bar

Connection of embedded items

Reference electrode

Installing overlay

Finishing operation

Anode and steel cage

Details of anode

Connection of anode ribbon to the titanium conductor bar

Steel connection

Placement of electrodes and connections to the steel bar

Pouring of concrete

Chloride Removal

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 concreteImpressed/sacrificial anode cathodic protection systems may be usedSide effects Alkali-silica reaction

Re-Alkalization

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 concreteImpressed/sacrificial anode cathodic protection systems may be usedSide effects Alkali-silica reaction

THANK YOU

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