Piles are structures used to transfer loads from superstructure to the sub surface strata.
When the subsurface stratum is water based or if we deal with a hydraulic structure, the
piles are to be driven into water and under water strata. Piles used in underwater structures
are often subjected to corrosion. There is no absolute way to eliminate all corrosion; but
corrosion protection measures are employed to control the effect of corrosion. Corrosion
protection can be in different ways according to the environment and other factors. Forms
of corrosion protection include the use of inhibitors, surface treatments, coatings and
sealants, cathodic protection and anodic protection. The control measures explained in this
are Protective coatings, cathodic treatment and application of Fibre Re-inforced Polymer
(FRP) Composites.
1
,1. INTRODUCTION
Corrosion is the destruction of metals and alloys by the chemical reaction with the
environment. During corrosion the metals are converted to metallic compounds at the
surface and these compounds wears away as corrosion product. Hence corrosion may be
regarded as the reverse process of extraction of metals from ore.
Reinforced concrete structures in a marine environment are under constant attack from
various elements,which result in the corrosion of the reinforcing steel, thereby weakening
the structure and shortening theirlifespans. The longer corrosion is left to progress, the more
damage it causes; therefore, early detection isessential. Corrosion of reinforcement causes
a volume increase of the corroded part of the rebar material,and splitting stresses are
induced in the concrete. This often determines the durability of concretestructures. Existing
specifications for concrete do not appear to be effective in ensuring longtermperformance
in the marine environment, and many structures require repairs during their design lives.
The main cause of corrosion of steel in the marine environment is the presence of chloride
in theenvironment. When the percentage of chloride ions at the steel interface exceeds the
threshold value,assuming oxygen is present, corrosion initiates. Depending on the
effectiveness of the corrosionprotectionmeasures, the penetration of chloride ions into the
concrete from seawater, or deicing salts, canresult in the corrosion of the reinforcement.The
main form of attack is the penetration and diffusion of chloride ions into the outer layer of
theconcrete, causing the destruction of the gamma-ferric oxide layer on the reinforcement,
and exposing it tocorrosion. The selection of materials for concrete repairs is more difficult
than for new construction. Therange of materials used is broader than just cementitious
materials, because many polymeric compositionscan be used effectively for concrete
repair. Frequently, the period in which the structure can be broughtback into service, the
accessibility, and the position of the repair in relation to the level of the tide are
alsoimportant considerations in the selection of materials and methods for repair.
2
, Fig 1: One of the Bryant Patton Bridges Displaying Reinforced Concrete Piles with
Significant Corrosion Induced Damage - Florida
1.1 Corrosion Mechanism of Steel in Sea Water
On steel piling in seawater, the more chemically active surface areas (anodes) are
metallically coupled through the piling itself to the less chemically active surface areas
(cathodes) resulting in a flow of electricity and corrosion of the anodic areas. General
surface roughening occurs when these local anodic and cathodic areas continually shift
about randomly during the corrosion process. Sometimes these active local areas do not
shift position end, therefore, the metal suffers localized attack and pitting occurs. In
general, the depth of pitting is related to the ratio of the anodic sites to the area of cathodic
site in contact with the electrolyte (seawater). The smaller the anode area relative to the
cathode area, the deeper the pitting.
Corrosion of steel reinforcement limits the service life of concrete exposed to sea water.
Because of theexpansion of the steel due to corrosion, concrete piles are extremely
susceptible to cracking and spalling.Although steel reinforcing bars are initially protected
3
When the subsurface stratum is water based or if we deal with a hydraulic structure, the
piles are to be driven into water and under water strata. Piles used in underwater structures
are often subjected to corrosion. There is no absolute way to eliminate all corrosion; but
corrosion protection measures are employed to control the effect of corrosion. Corrosion
protection can be in different ways according to the environment and other factors. Forms
of corrosion protection include the use of inhibitors, surface treatments, coatings and
sealants, cathodic protection and anodic protection. The control measures explained in this
are Protective coatings, cathodic treatment and application of Fibre Re-inforced Polymer
(FRP) Composites.
1
,1. INTRODUCTION
Corrosion is the destruction of metals and alloys by the chemical reaction with the
environment. During corrosion the metals are converted to metallic compounds at the
surface and these compounds wears away as corrosion product. Hence corrosion may be
regarded as the reverse process of extraction of metals from ore.
Reinforced concrete structures in a marine environment are under constant attack from
various elements,which result in the corrosion of the reinforcing steel, thereby weakening
the structure and shortening theirlifespans. The longer corrosion is left to progress, the more
damage it causes; therefore, early detection isessential. Corrosion of reinforcement causes
a volume increase of the corroded part of the rebar material,and splitting stresses are
induced in the concrete. This often determines the durability of concretestructures. Existing
specifications for concrete do not appear to be effective in ensuring longtermperformance
in the marine environment, and many structures require repairs during their design lives.
The main cause of corrosion of steel in the marine environment is the presence of chloride
in theenvironment. When the percentage of chloride ions at the steel interface exceeds the
threshold value,assuming oxygen is present, corrosion initiates. Depending on the
effectiveness of the corrosionprotectionmeasures, the penetration of chloride ions into the
concrete from seawater, or deicing salts, canresult in the corrosion of the reinforcement.The
main form of attack is the penetration and diffusion of chloride ions into the outer layer of
theconcrete, causing the destruction of the gamma-ferric oxide layer on the reinforcement,
and exposing it tocorrosion. The selection of materials for concrete repairs is more difficult
than for new construction. Therange of materials used is broader than just cementitious
materials, because many polymeric compositionscan be used effectively for concrete
repair. Frequently, the period in which the structure can be broughtback into service, the
accessibility, and the position of the repair in relation to the level of the tide are
alsoimportant considerations in the selection of materials and methods for repair.
2
, Fig 1: One of the Bryant Patton Bridges Displaying Reinforced Concrete Piles with
Significant Corrosion Induced Damage - Florida
1.1 Corrosion Mechanism of Steel in Sea Water
On steel piling in seawater, the more chemically active surface areas (anodes) are
metallically coupled through the piling itself to the less chemically active surface areas
(cathodes) resulting in a flow of electricity and corrosion of the anodic areas. General
surface roughening occurs when these local anodic and cathodic areas continually shift
about randomly during the corrosion process. Sometimes these active local areas do not
shift position end, therefore, the metal suffers localized attack and pitting occurs. In
general, the depth of pitting is related to the ratio of the anodic sites to the area of cathodic
site in contact with the electrolyte (seawater). The smaller the anode area relative to the
cathode area, the deeper the pitting.
Corrosion of steel reinforcement limits the service life of concrete exposed to sea water.
Because of theexpansion of the steel due to corrosion, concrete piles are extremely
susceptible to cracking and spalling.Although steel reinforcing bars are initially protected
3
