CATHODIC PROTECTION OF
Concrete is a porous (microstructure)
material, which readily absorbs contaminants
from the surrounding environment.
The water and oxygen in presence of the
chlorides reacts with iron to create corrosion
product on surface of the reinforcing steel.
The growth in volume of these corrosion
products exerts tensile stress that eventually
causes the concrete to crack.
Corrosion of the Reinforcement steel is main
cause for the deterioration of steel which is usually
initiated through chloride attack, or carbonation.
Carbonation: it refers to the penetration of
atmospheric carbon dioxide into concrete matrix.
To prevent the corrosion in steel Cathodic
protection method is most widely used
worldwide in the developed countries.
Fig:Chloride attack And Spalling
Ref: Report on Cathodic Protection of reinforced concrete structure at
Metal that has been extracted from its primary
ore (metal oxide or other free radicals like
sulphides, chlorides) has a natural tendency to
revert to a native form under the action of
oxygen and water.
The process by which this transformation occurs
is known as corrosion. It is an electrochemical
process. The change from the metallic to the
combined forms occurs by an “anodic reaction”.
The Anode Reaction
Metal Metal ions (dissolved in solution) + electrons
Fe Fe++ + 2e-
This reaction produces free electrons , which pass within
the metal to another site on the metal surface
(Cathode), where it consumed by cathodic reaction.
The Cathodic Reaction
O2 + 2H2O + 4e- 4OH-
Recombination of these ions at active surface produce
2Fe + O2 + 2H2O = 2Fe (OH)2
Methods to Prevent Corrosion
Cladding and Chemical Additives
Electrochemical Method (Cathodic Protection)
What is Cathodic Protection (CP) ?
Cathodic protection is a technique used to
control the corrosion of a metal surface by
making it the cathode of an electrochemical cell.
Principle- The Principle of cathodic protection is
in connecting an external anode to metal to be
protected and the passing of an electric DC
current so that all areas of metal surface
become cathodic and do not corrode.
Accessed on 19-09-2013.
• In usual application a Galvanic anode, a piece of
more electrochemically active metal is attached
to vulnerable metal surface where it is exposed
to the corrosive liquid. The anode metals
gradually dissipate over a period when
connected to and in a common electrolyte, and
are termed as “Sacrificial Anodes”
In the case of aluminum anodes, the reaction at the
aluminum surface is: (four aluminum ions plus twelve
4Al = 4AL+++ + 12 e-
And at the steel surface: (oxygen gas converted to
oxygen ions which combine with water to form hydroxyl
3O2 + 12e- + 6H20 = 12OH-
As long as the current (free electrons) arrives at the
cathode (steel) faster than oxygen is arriving, no
corrosion will occur.
Galvanic anodes are selected because they
have a more "active" voltage (more negative
electrochemical potential) than the metal of the
target structure (typically steel)
The galvanic anode continues to
corrode, consuming the anode material until
eventually it must be replaced.
Anode Material: Alloys of Zinc, Magnesium and
Sacrificial Anode Facts
Magnesium 8 5 50% RC Pipelines
Aluminum 4 10 90% Sea Water
Zinc 12 20 95% Coating
Partially corroded sacrificial anode on the hull of a ship.
Cathodic Protection-Galvanic System
Impressed Current Method
In this method a potential difference is artificially
created by applying an external positive voltage
to an anode with the negative current return path
through the reinforcement cage and cabling.
ICCP system use a nodes connected to DC
power source. Usually this will be a cathodic
protection rectifier, which converts an AC power
supply to DC output.
Anode Material can be inert or at least capable
of offering up to a nominal a 20 years life
This current given to insoluble anode like
graphite stainless steel or scrap iron buried in
The negative terminal of D.C is connected to a
pipeline to b protected. The anode is kept in
Impressed Current System
Comparison of CP System
Longer Anode Life,
Simple, No Monitoring &
Current can be controlled No requirement for electrical
Can be used in any
Usually Used in lower
Can Be Used for any type
Used for very small or well
Higher Cost Lower Cost
Pipelines are routinely protected by a coating
supplemented with cathodic Protection.
Placement of Anode on reinforcement Bar
• The White Patches visible on the ship’s hull are Zinc
Block sacrificial anodes.
K G C Berkeley, S Pathmanaban, “Cathodic
Protection of Reinforcement Steel in Concrete”,
Butterworth & Co. (Publishers) Ltd, 1990,
Alan R Bird, “Cathodic Protection of reinforced
concrete Structures-A Practical Methods of
Arresting Rebar Corrosion” Report published at
WWW.marineandcivil.com.au, pp 1-5
Baeckman, Schwenck & Prinz, Handbook of
cathodic corrosion protection” 3rd edition 1997
• Dr. S.R Karade & Team, Corrosion Mitigation in RC
structures Through Cathodic Protection, CSIR-CBRI
News Letter,Vol-32 No-1 Jan-March 2012,pp. 1-2
Denny A.Jones, “Principles and Prevention of
Corrosion” 2nd Edition, Prentice Hall, ISBN 0-13-
V Ashworth, “Principle of Cathodic Protection”
Elsevier B.V, 3rd Edition, Volume-2, pp 10:3-10:28
Ref: Cathodic Protection of Reinforced Concrete
Structures’, in NACE Technical Report No. 36, 1989,
The Concrete Society, London.