Introduction of corrosion -

bullCorrosion is the disintegration of an engineered material into its constituent atoms due

to chemical reactions with its surroundings

bullCorrosion is an electro-chemical process involving an anode a cathode and an

bullelectrolyte

bullIn the most common use of the word this means electrochemical oxidation

of metals in reaction with an oxidant such as oxygen

bullFormation of an oxide of iron due to oxidation of the iron atoms in solid solution is a

well-known example of electrochemical corrosion commonly known as rusting

bullThis type of damage typically produces oxide(s) or salt(s) of the original metal

bullCorrosion can also occur in materials other than metals such as ceramics or polymers

although in this context the term degradation is more common

bullIn other words corrosion is the wearing away of metals due to a chemical reaction

bullMany structural alloys corrode merely from exposure to moisture in the air but the

process can be strongly affected by exposure to certain substances (see below)

bullCorrosion can be concentrated locally to form a pit or crack or it can extend across a

wide area more or less uniformly corroding the surface Because corrosion is a

diffusion controlled process it occurs on exposed surfaces

bull The corrosion resistance of metals and alloys is

a basic property related to the easiness with

which these materials react with a given

environment

bull Corrosion is a natural process that seeks to

reduce the binding energy in metals

bull The end result of corrosion involves a metal

atom being oxidized whereby it loses one or

more electrons and leaves the bulk metal

bull Pure metals are used in many applications

Copper for example is used to make the wire

which goes inside electrical cables Copper was

chosen because it can be drawn into long thin

wires very easily (it is ductile) and because it is

a good conductor of electricity

bull Pure aluminium can also be used in wiring

bull It is also used as a cladding material for

aluminium alloy substrates

CORROSION OF METAL

CORROSION OF METAL

INTRODUCTION OF CORROSION -

TYPES OF CORROSION - 1 DRY CORROSION - It involves direct attack of dry gases (air+oxygen) on the metal

through chemical reaction As a result an oxide layer is formed over the surface This

type of corrosion is not common

2 WET CORROSION - It involves direct attacks of aqueous media strong or dilute acid or

alkaline on the metal through Electrochemical Reactions The moisture amp oxygen are

also responsible This type of corrosion is quite common

3 FLUID CORROSION GENERAL- When corrosion is generally confined to metal surface

it is known as general corrosion It occurs in inform fashion over the entire exposed

surface areas

4 FLUID CORROSION LOCALIZED- It is most commonly observed on following four

different locations Specific Site Corrosion ndash mechanically weak spots or dead spots in

reaction vessel Stress Induced Corrosion ndash residual internal stress in metal external

applied stress accelerate the corrosion Liquid Flow Related Corrosion ndash the driving

force is the tendency of the liquid to dissolve solid or penetrating the metal along the

grain boundries at place of wetting Chemical Reaction Related Corrosion ndash chemical

reactions such as oxidation amp reduction

5 FLUID CORROSION STRUCTURAL- Here the strength is reduced on account of

corrosion This may occur when one component of the alloy is removed or released into

solution The alloy is removed or released into solution

6 FLUID CORROSION BIOLOGICAL- The metabolic action of metal oxides can either

directly or indirectly cause deterioration of a metal

FACTORS INFLUENCING CORROSION - 1 TEMPERATURE - Rise in temperature rate reduces the solubility of oxygen or air The

released oxygen enhance the corrosion Increase in temperature induces phase change

which enhance the rate of corrosion At high temperature organic chemicals are

saturated with water as temperature decreases water gets condensed Oxygen is needed

for maintaining iron oxide film

2 VELOCITY - High velocity of corrosion medium increases corrosion Corrosion pots

are formed rapidly because chemicals are brought to surface high rate The corrosion

pots are easily stiffled amp carried away by expansion of the new surfaces for corrosion

3 OTHER FACTORS- The core of corrosive chemical in distillation column

evaporationthe concrete can change continuously so difficult to predict the corrosion

rate the presence of moisture that collects during cooling can turn innocious chemical

in to dangerous corroswes

techniques - The techniques presently available for examining RCC

structures for corrosion are as follows

1Visual investigation 2Weight loss

3Cover meter 4Chloride analysis

5Resistivity 6Water absorption

7Moisture content 8Cement content

9Pit depth 10Concrete strength

These tests are designed to check one or more of the factors

leading to corrosion such as-

-Poor quality of concrete

-Moisture content

-Reduced Electrical Resistance

-Poor cover to reinforcement

-Chlorides

-Less cement or widely varying cement content

-Carbonation

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

bull The corrosion resistance of metals and alloys is

a basic property related to the easiness with

which these materials react with a given

environment

bull Corrosion is a natural process that seeks to

reduce the binding energy in metals

bull The end result of corrosion involves a metal

atom being oxidized whereby it loses one or

more electrons and leaves the bulk metal

bull Pure metals are used in many applications

Copper for example is used to make the wire

which goes inside electrical cables Copper was

chosen because it can be drawn into long thin

wires very easily (it is ductile) and because it is

a good conductor of electricity

bull Pure aluminium can also be used in wiring

bull It is also used as a cladding material for

aluminium alloy substrates

CORROSION OF METAL

CORROSION OF METAL

INTRODUCTION OF CORROSION -

TYPES OF CORROSION - 1 DRY CORROSION - It involves direct attack of dry gases (air+oxygen) on the metal

through chemical reaction As a result an oxide layer is formed over the surface This

type of corrosion is not common

2 WET CORROSION - It involves direct attacks of aqueous media strong or dilute acid or

alkaline on the metal through Electrochemical Reactions The moisture amp oxygen are

also responsible This type of corrosion is quite common

3 FLUID CORROSION GENERAL- When corrosion is generally confined to metal surface

it is known as general corrosion It occurs in inform fashion over the entire exposed

surface areas

4 FLUID CORROSION LOCALIZED- It is most commonly observed on following four

different locations Specific Site Corrosion ndash mechanically weak spots or dead spots in

reaction vessel Stress Induced Corrosion ndash residual internal stress in metal external

applied stress accelerate the corrosion Liquid Flow Related Corrosion ndash the driving

force is the tendency of the liquid to dissolve solid or penetrating the metal along the

grain boundries at place of wetting Chemical Reaction Related Corrosion ndash chemical

reactions such as oxidation amp reduction

5 FLUID CORROSION STRUCTURAL- Here the strength is reduced on account of

corrosion This may occur when one component of the alloy is removed or released into

solution The alloy is removed or released into solution

6 FLUID CORROSION BIOLOGICAL- The metabolic action of metal oxides can either

directly or indirectly cause deterioration of a metal

FACTORS INFLUENCING CORROSION - 1 TEMPERATURE - Rise in temperature rate reduces the solubility of oxygen or air The

released oxygen enhance the corrosion Increase in temperature induces phase change

which enhance the rate of corrosion At high temperature organic chemicals are

saturated with water as temperature decreases water gets condensed Oxygen is needed

for maintaining iron oxide film

2 VELOCITY - High velocity of corrosion medium increases corrosion Corrosion pots

are formed rapidly because chemicals are brought to surface high rate The corrosion

pots are easily stiffled amp carried away by expansion of the new surfaces for corrosion

3 OTHER FACTORS- The core of corrosive chemical in distillation column

evaporationthe concrete can change continuously so difficult to predict the corrosion

rate the presence of moisture that collects during cooling can turn innocious chemical

in to dangerous corroswes

techniques - The techniques presently available for examining RCC

structures for corrosion are as follows

1Visual investigation 2Weight loss

3Cover meter 4Chloride analysis

5Resistivity 6Water absorption

7Moisture content 8Cement content

9Pit depth 10Concrete strength

These tests are designed to check one or more of the factors

leading to corrosion such as-

-Poor quality of concrete

-Moisture content

-Reduced Electrical Resistance

-Poor cover to reinforcement

-Chlorides

-Less cement or widely varying cement content

-Carbonation

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

TYPES OF CORROSION - 1 DRY CORROSION - It involves direct attack of dry gases (air+oxygen) on the metal

through chemical reaction As a result an oxide layer is formed over the surface This

type of corrosion is not common

2 WET CORROSION - It involves direct attacks of aqueous media strong or dilute acid or

alkaline on the metal through Electrochemical Reactions The moisture amp oxygen are

also responsible This type of corrosion is quite common

3 FLUID CORROSION GENERAL- When corrosion is generally confined to metal surface

it is known as general corrosion It occurs in inform fashion over the entire exposed

surface areas

4 FLUID CORROSION LOCALIZED- It is most commonly observed on following four

different locations Specific Site Corrosion ndash mechanically weak spots or dead spots in

reaction vessel Stress Induced Corrosion ndash residual internal stress in metal external

applied stress accelerate the corrosion Liquid Flow Related Corrosion ndash the driving

force is the tendency of the liquid to dissolve solid or penetrating the metal along the

grain boundries at place of wetting Chemical Reaction Related Corrosion ndash chemical

reactions such as oxidation amp reduction

5 FLUID CORROSION STRUCTURAL- Here the strength is reduced on account of

corrosion This may occur when one component of the alloy is removed or released into

solution The alloy is removed or released into solution

6 FLUID CORROSION BIOLOGICAL- The metabolic action of metal oxides can either

directly or indirectly cause deterioration of a metal

FACTORS INFLUENCING CORROSION - 1 TEMPERATURE - Rise in temperature rate reduces the solubility of oxygen or air The

released oxygen enhance the corrosion Increase in temperature induces phase change

which enhance the rate of corrosion At high temperature organic chemicals are

saturated with water as temperature decreases water gets condensed Oxygen is needed

for maintaining iron oxide film

2 VELOCITY - High velocity of corrosion medium increases corrosion Corrosion pots

are formed rapidly because chemicals are brought to surface high rate The corrosion

pots are easily stiffled amp carried away by expansion of the new surfaces for corrosion

3 OTHER FACTORS- The core of corrosive chemical in distillation column

evaporationthe concrete can change continuously so difficult to predict the corrosion

rate the presence of moisture that collects during cooling can turn innocious chemical

in to dangerous corroswes

techniques - The techniques presently available for examining RCC

structures for corrosion are as follows

1Visual investigation 2Weight loss

3Cover meter 4Chloride analysis

5Resistivity 6Water absorption

7Moisture content 8Cement content

9Pit depth 10Concrete strength

These tests are designed to check one or more of the factors

leading to corrosion such as-

-Poor quality of concrete

-Moisture content

-Reduced Electrical Resistance

-Poor cover to reinforcement

-Chlorides

-Less cement or widely varying cement content

-Carbonation

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

FACTORS INFLUENCING CORROSION - 1 TEMPERATURE - Rise in temperature rate reduces the solubility of oxygen or air The

released oxygen enhance the corrosion Increase in temperature induces phase change

which enhance the rate of corrosion At high temperature organic chemicals are

saturated with water as temperature decreases water gets condensed Oxygen is needed

for maintaining iron oxide film

2 VELOCITY - High velocity of corrosion medium increases corrosion Corrosion pots

are formed rapidly because chemicals are brought to surface high rate The corrosion

pots are easily stiffled amp carried away by expansion of the new surfaces for corrosion

3 OTHER FACTORS- The core of corrosive chemical in distillation column

evaporationthe concrete can change continuously so difficult to predict the corrosion

rate the presence of moisture that collects during cooling can turn innocious chemical

in to dangerous corroswes

techniques - The techniques presently available for examining RCC

structures for corrosion are as follows

1Visual investigation 2Weight loss

3Cover meter 4Chloride analysis

5Resistivity 6Water absorption

7Moisture content 8Cement content

9Pit depth 10Concrete strength

These tests are designed to check one or more of the factors

leading to corrosion such as-

-Poor quality of concrete

-Moisture content

-Reduced Electrical Resistance

-Poor cover to reinforcement

-Chlorides

-Less cement or widely varying cement content

-Carbonation

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

These tests are designed to check one or more of the factors

leading to corrosion such as-

-Poor quality of concrete

-Moisture content

-Reduced Electrical Resistance

-Poor cover to reinforcement

-Chlorides

-Less cement or widely varying cement content

-Carbonation

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

visual - Corrosion in reinforcement results in three stages of sign

1Cracking along the bars

2Spalling

3Disintegration

Cracks along the bar is the first sign which is likely to be ignored as

these cracks are small in size amp discontinuousHowever this is the right

time to attend to the defect

When spalling occurs or cracks widen substantiallythe reinforcement

bars are rusted substantially

Repairs to structures where spalling and disintegration has occurred are

more difficult and expensive

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

PREVENTION OF CORROSION IN

REINFORCEMENT RCC can be protected from corrosion in three ways-

bull Seal the surface of the concrete to prevent ingress of chlorides and moisture

bull Modify the concrete to reduce its permeability thus retarding the flow of concrete moisture and chlorides to reach the reinforcing steel

bull Protect the reinforcing bars to reduce the effects of chlorides when they do reach the steel

More and more designers are specifying multiple levels of protection for structure that are subjected to the risk of corrosion It is common to specify epoxy coated reinforcing steel amp silica fume concrete for post tensioned structures

Corrosion controlling steps in reinforcement are stated in subsequent sections-

a) Good concrete practise

b) Latex modified concrete

c) Silica fume concrete

d) Epoxy coated reinforcement

e) Providing membranes and sealers

f) Cathodic protection

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Good Concrete Practice It require following considerations-

By providing adequate cover to reinforcing steel ndash helps in increasing the time it takes for the chlorides to reach the steel

By providing adequate curing (not allowing the concrete to dry without curing in atleast 7 days) ndash reduces hydration ampincreases permeability amp shrinkage

Use of water reducing admixtures to give the concrete enough workability so that workers are able to compact concrete properly with ease

Maintain a low water cement ratio in concrete

Consolidate the concrete thoroughly using suitable vibrators

Use post tensioning to minimize cracking where appropriate

Include provision for immediate repair of cracks in the original specifications assuming that the concrete will crack Repair or seal the cracks before the new structure is put into service

Adoption of good concrete practices may not be enough for the required level of performance to face the severe exposure conditions But good concrete practices are the most critical steps in controlling corrosion and deterioration

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Use of latex modified concrete -

Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete It contains 15 latex solids by weight of cement and has a water cement ratio of 035

It modifies the pore structure of the concrete and reduces its permeability to a very low range

It has been associated with some cracking problems and it should be placed in the evening or at night to reduce cracking

Its relative cost is high but performance is good to excellent

Use of silica fume concrete-

It is an extremely effective pozzolanic material that reacts with calcium hydroxide produced in hydrated portland cement paste to form additional cementitious materials which results in reduction of permeability of the concrete

Typical silica fume concrete mixtures contain 410 kg of cement per cum 8 to 10 silica fume by weight of cement a water powder ratio less than 040

Adequate plasticiser is provided to produce good workability with 50-200mm slump

Performance is good to excellent

The silica fume concrete has a moderate cost

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Epoxy coated reinforcing bars-

Pre- cleaned reinforcing steel bars are protected with a coating

of powdered epoxy

The coating physically blocks chloride ions and the performance

of these bars ranges from poor to excellent depending on

effectiveness of coating

The relative cost of epoxy coated steel is moderate

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Methods of protection from corrosion-

Surface treatments-Applied coatings

Plating painting and the application of enamel are the most common anti-

corrosion treatments They work by providing a barrier of corrosion-resistant material

between the damaging environment and the structural material

Platings usually fail only in small sections and if the plating is more noble than the

substrate (for example chromium on steel) a galvanic couple will cause any exposed area

to corrode much more rapidly than an unplated surface would

For this reason it is often wise to plate with active metal such as zinc or cadmium

Painting either by roller or brush is more desirable for tight spaces spray would be better

for larger coating areas such as steel decks and waterfront applications

Flexible polyurethane coatings like Durabak-M26 for example can provide an anti-

corrosive seal with a highly durable slip resistant membrane

Painted coatings are relatively easy to apply and have fast drying times although

temperature and humidity may cause dry times to vary

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Cathodic protection Cathodic protection (CP) is a technique to control the corrosion of a metal

surface by making that surface the cathode of an electrochemical cell Cathodic

protection systems are most commonly used to protect steel water and

fuel pipelines and tanks steel pier piles ships and offshore oil platforms

Biofilm coatings A new form of protection has been developed by applying certain species of

bacterial films to the surface of metals in highly corrosive environments This

process increases the corrosion resistance substantially Alternatively

antimicrobial-producing biofilms can be used to inhibit mild steel corrosion

from sulfate ndash reducing bacteria

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Corrosion in non metals Most ceramic materials are almost entirely immune to corrosion The

strong chemical bonds that hold them together leave very little free chemical

energy in the structure they can be thought of as already corroded When

corrosion does occur it is almost always a simple dissolution of the material or

chemical reaction rather than an electrochemical process A common example

of corrosion protection in ceramics is the lime added to soda-lime glass to

reduce its solubility in water though it is not nearly as soluble as pure sodium

silicate normal glass does form sub-microscopic flaws when exposed to

moisture Due to its brittlenss such flaws cause a dramatic reduction in the

strength of a glass object during its first few hours at room temperature

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Forms of Corrosion GENERAL

1048707 Identified by uniform formation of corrosion products that causes a even thinning of

the substrate steel

LOCALIZED

1048707 Caused by difference in chemical or physical conditions between adjoining sites

BACTERIAL

1048707 Caused by the formation of bacteria with an affinity for metals on the surface of the

steel

GALVANICDISSIMILAR METAL

1048707 Caused when dissimilar metals come in contact the difference in electrical potential

sets up a corrosion cell or a bimetallic couple

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Methods of Corrosion Control BARRIER PROTECTION

1048707 Provided by a protective coating that acts as a barrier between corrosive

elements and the metal substrate

Paint

Powder Coatings

Galvanizing

CATHODIC PROTECTION

1048707 Employs protecting one metal by connecting it to another metal that is more

anodic according to the galvanic seriesrsquo

Impressed Current

Galvanic Sacrificial Anode

Galvanic Zinc Application - Zinc Metallizing Zinc-rich Paints Hot-dip Galvanizing

CORROSION RESISTANT MATERIALS

1048707 Materials inherently resistant to corrosion in certain environments

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Cathodic Protection

Impressed Current- External source of direct current power is connected (or impressed)

between the structure to be protected and the ground bed (anode) Ideal impressed

current systems use ground bed material that can discharge large amounts of current and

yet still have a long life expectancy

Galvanic Sacrificial Anode- Pieces of an active metal such as magnesium or zinc are

placed in contact with the corrosive environment and are electrically connected to the

structure to be protected Example Docked Naval Ships

Galvanic Zinc Application

Zinc Metallizing (plating)- Feeding zinc into a heated gun where it is melted and

sprayed on a structure or part using combustion gases andor auxiliary compressed air

Zinc-rich Paints- Zinc-rich paints contain various amounts of metallic zinc dust and

are applied by brush or spray to properly prepared steel

Hot-dip Galvanizing- Complete immersion of steel into a kettlevessel of molten

zinc

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

Corrosion removal

Often it is possible to chemically remove the products of

corrosion to give a clean surface but one that may exhibit

artifacts of corrosion such as pitting For example phosphoric

acid in the form ofnaval jelly is often applied to ferrous tools

or surfaces to remove rust

Corrosion removal should not be confused

with Electropolishing which removes some layers of the

underlying metal to make a smooth surface For example

phosphoric acid (again) may be used to electropolish copper

but it does this by removing copper not the products of

copper corrosion

PREPARATION OF RCC FOR REPAIR

Preparing Of Rcc Element For Repair Includes Removal Of All Loose Materialscleaning Of

Deteriorated Area And Removal Of Corrosion From Reinforcement

Contaminated And Loose Concrete Must Be Removed By Hard Steel Brushing And Washing

Thoroughly Before Undertaking Any Repair Work

Proper Removal Of Loose Or Contaminated Concreterebar Cleaning And Surface

Preparation Are Crucial For Effective Repair

Many Repair Failures Are Caused By Improper Performance Of These Operations

The Following Are The Main Steps To Prepare Reinforced Concrete For The Repair

bullExposing And Undercutting Rebar

bullCleaning Reinforcing Steel

bullCompensating Reinforcement

bullEdge And Surface Conditioning

Exposing And Undercutting Rebar

The Following Procedure Is Used For Repairs Of Horizontalverticaland Over Head

SurfacesThey Are Also Applicable When Removing Concrete By Hydro-

demolitionpneumatic Or Hydraulicimpact Method

Various Steps Include

bullRemove Loose Or Delaminated Concrete Above Corroded Reinforcing Steel

bullUndercut All Exposed Corroded Rebar After The Initial Removals

UNDERCUTTING EXPOSES THE BLIND SIDE OF THE REBAR FOR CLEANING AND WILL ALLOW THE REPAIR MATERIAL TO FULLY INCAPSULATE THE REBAR SECURING THE REPAIR MATERIAL STRURALLY PROVIDE AT LEAST 15MM CLEARANCE BETWEEN EXPOSED REBARS AND THE SURROUNDING CONCRETE OR 15MM LARGER THAN THE LARGEST SIZE OF AGGREGATE IN THE REPAIR MATERIAL WHICH EVER IS GREATER

CONTINUE REMOVING CONCRETE ALONG CORRODED BARS UNTIL CORROSION FREE LOCATION ALONG THE BAR ARE REACHED AND WHERE THE BARS ARE WELL BONDED TO THE SURROUNDING CONCRETE

DO NOT DAMAGE THE REBARrsquoS BOND TO THE SURROUNDING CONCRETE IF NON CORRODED REINFORCING STEEL IS EXPOSED DURING THE PREPARATION PROCESS

UNDERCUT THE REBAR IF THE BOND BETWEEN THE REBAR AND SURROUNDING CONCRETE IS BROKEN

SECURE THE LOOSE REINFORCEMENT IN PLACE BY TYING IT TO OTHER SECURED BARS OR BY OTHER APPROPRIATE METHODS

CLEANING REINFORCING STEEL REMOVE ALL HEAVY CORROSION AND SCALE FROM THE BAR TO PROMOTE MAXIMUM

BOND OF THE REPAIR MATERIAL

IT CAN BE DONE PREFERABLY BY ABRASIVE BLASTING METHOD AS ALREADY EXPLAINED

A TIGHTLY BONDED WITH LIGHT RUST ON THE SURFACE OF REBAR IS USUALLY NOT DETRIMENTAL TO BOND

MANUFACTURERS RECOMMNEDATIONS SHOULD BE FOLLOWED FOR REBAR PREPARATION IF PROTECTIVE COATING IS TO BE APPLIED TO THE REBAR

COMPENSATING REINFORCEMENT IF REINFORCING STEEL HAS LOST SIGNIFICANT CROSS SECTIONA STRUCTURAL ENGINEER

SHOULD BE CONSULTED

IF REPAIR ARE REQUIRED TO THE REINFORCING STEEL THE BAR CAN BE REPLACED COMPLETELY OR SUPPLEMENTARY BARS CAN BE PLACED OVER THE AFFECTED SECTION

SUPPLEMENTARY BARS MAY BE MECHANICALLY SPLICED TO OLD BARS OR PLACED PARALLEL TO OLD BARS APPROXIMATELY 15MM FROM EXISTING BARS LAP LENGTHS SHALL BE DETERMINED IN ACCORDANCE WITH LATEST IS SPECIFICATIONS AND OTHER DESIGN GUIDELINES

EDGE AND SURFACE CONDITIONING THE SURFACE CONDITIONING STEPS ARE USED FOR HORIZONTAL VERTICAL AND OVERHEAD

SURFACES

THEY ARE ALSO APPLICABLE TO CONCRETE REMOVAL BY HYDRODEMOLITION AND ELECTRIC PNEUMATIC OR HYDRAULIC IMPACT BREAKERS

AFTER REMOVING DELAMINATED CONCRETE AND UNDERCUTTING REINFORCING STEEL REMOVE ADDITIONAL CONCRETE AS REQUIRED TO PROVIDE THE MINIMUM REQUIRED THICKNESS OF THE REPAIR MATERIALAT EDGE LOCATION PROVIDE RIGHT ANGLE CUTS TO THE CONCRETE SURFACE WITH EITHER OF THE FOLLOWING METHODS

SAW CUT 12MM OR LESS AS REQUIREDAVOID CUTTING REINFORCING STEEL

USE POWER EQUIPMENTSUCH AS HYDRODEMOLITION OR IMPACT BREAKERS AVOID FEATHER EDGES

REPAIR CONFIGURATION SHOULD BE KEPT AS SIMPLE AS POSSIBLE PREFERABLY WITH SQUARED CORNERS

REMOVE BOND INHIBITING MATERIALS SUCH AS DIRT CONCRETE LAITANCEAND LOOSE AGGREGATES BY ABRASIVE BLASTING OR HIGH-PRESSURE WATER BLASTING WITH OR WITHOUT ABRASIVE CHECK THE CONCRETE SURFACE AFTER CLEANING TO ENSURE THAT THEY ARE FREE FORM LOOSE AGGREGATES AND DELAMINATIONS

REPAIR OF CORRODED RCC ELEMENTS

REPAIR OF CORRODED REINFORCEMENT INCLUDES FOLLOWING MAIN STEPS

CHIP OFF ALL LOOSE AND CRACKED CONCRETE IN RCC ELEMENT

REMOVE CONCRETE IN COVER COMPLETELY TO EXPOSE CORRODED REINFORCEMENT

REMOVE ALL LOOSE AND DETERIORATED CONCRETE BY WIRE BRUSH

CLEAN THE REINFORCEMENT THOROUGHLY TO REMOVE ALL RUST OF CORRODED STEEL BY SAND BLASTING OR CHEMICAL WASH

WASH AND SATURATE ALL CAVITIES IN ADJOINING CONCRETE WITH CLEAN WATER AND REMOVE ALL FREE WATER BEFORE PLACING REPAIR MORTAR

FILL ALL CRACKS WITH EPOXY RESINS AND APPLY BOND COAT JUST PRIOR TO PLACING PATCH REPAIR MORTAR OR CONCRTE

APPLY PATCH REPAIR MORTAR OR CONCRETE OR GROUT ON THE DAMP CAVITY SURFACE

IN CASE OF LOSS OF STEEL SECTIONADDITIONAL STEEL REINFORCEMENT MAY BE TIED TO THE EXISTING BARS PRIOR TO APPLICATION OF BOND COAT

FILL THE CAVITY WITH REPAIR MORTAR OR CONCRETE AND CONSOLIDATE THOROUGHLY WITH ROD AND MALLET OR VIBRATION

ALTERNATIVELY FILLPREPACKED AGGREGATE CONCRETE IN THE CAVITIES AFTER APPLYING BOND COAT ANAD FINISH WITH PRESSURE GROUTING WITH REPAIR MORTAR

APPLY A PROTECTIVE COATING ON THE FINISHED SURFACE OF THE REPAIRED ELEMENT

CORROSION DUE TO DAMPNESS

CORROSION DUE TO WATER AND DUE TO AGE

UNDERCUTTING EXPOSES THE BLIND SIDE OF THE REBAR FOR CLEANING AND WILL ALLOW THE REPAIR MATERIAL TO FULLY INCAPSULATE THE REBAR SECURING THE REPAIR MATERIAL STRURALLY PROVIDE AT LEAST 15MM CLEARANCE BETWEEN EXPOSED REBARS AND THE SURROUNDING CONCRETE OR 15MM LARGER THAN THE LARGEST SIZE OF AGGREGATE IN THE REPAIR MATERIAL WHICH EVER IS GREATER

CONTINUE REMOVING CONCRETE ALONG CORRODED BARS UNTIL CORROSION FREE LOCATION ALONG THE BAR ARE REACHED AND WHERE THE BARS ARE WELL BONDED TO THE SURROUNDING CONCRETE

DO NOT DAMAGE THE REBARrsquoS BOND TO THE SURROUNDING CONCRETE IF NON CORRODED REINFORCING STEEL IS EXPOSED DURING THE PREPARATION PROCESS

UNDERCUT THE REBAR IF THE BOND BETWEEN THE REBAR AND SURROUNDING CONCRETE IS BROKEN

SECURE THE LOOSE REINFORCEMENT IN PLACE BY TYING IT TO OTHER SECURED BARS OR BY OTHER APPROPRIATE METHODS

CLEANING REINFORCING STEEL REMOVE ALL HEAVY CORROSION AND SCALE FROM THE BAR TO PROMOTE MAXIMUM

BOND OF THE REPAIR MATERIAL

IT CAN BE DONE PREFERABLY BY ABRASIVE BLASTING METHOD AS ALREADY EXPLAINED

A TIGHTLY BONDED WITH LIGHT RUST ON THE SURFACE OF REBAR IS USUALLY NOT DETRIMENTAL TO BOND

MANUFACTURERS RECOMMNEDATIONS SHOULD BE FOLLOWED FOR REBAR PREPARATION IF PROTECTIVE COATING IS TO BE APPLIED TO THE REBAR

COMPENSATING REINFORCEMENT IF REINFORCING STEEL HAS LOST SIGNIFICANT CROSS SECTIONA STRUCTURAL ENGINEER

SHOULD BE CONSULTED

IF REPAIR ARE REQUIRED TO THE REINFORCING STEEL THE BAR CAN BE REPLACED COMPLETELY OR SUPPLEMENTARY BARS CAN BE PLACED OVER THE AFFECTED SECTION

SUPPLEMENTARY BARS MAY BE MECHANICALLY SPLICED TO OLD BARS OR PLACED PARALLEL TO OLD BARS APPROXIMATELY 15MM FROM EXISTING BARS LAP LENGTHS SHALL BE DETERMINED IN ACCORDANCE WITH LATEST IS SPECIFICATIONS AND OTHER DESIGN GUIDELINES

EDGE AND SURFACE CONDITIONING THE SURFACE CONDITIONING STEPS ARE USED FOR HORIZONTAL VERTICAL AND OVERHEAD

SURFACES

THEY ARE ALSO APPLICABLE TO CONCRETE REMOVAL BY HYDRODEMOLITION AND ELECTRIC PNEUMATIC OR HYDRAULIC IMPACT BREAKERS

AFTER REMOVING DELAMINATED CONCRETE AND UNDERCUTTING REINFORCING STEEL REMOVE ADDITIONAL CONCRETE AS REQUIRED TO PROVIDE THE MINIMUM REQUIRED THICKNESS OF THE REPAIR MATERIALAT EDGE LOCATION PROVIDE RIGHT ANGLE CUTS TO THE CONCRETE SURFACE WITH EITHER OF THE FOLLOWING METHODS

SAW CUT 12MM OR LESS AS REQUIREDAVOID CUTTING REINFORCING STEEL

USE POWER EQUIPMENTSUCH AS HYDRODEMOLITION OR IMPACT BREAKERS AVOID FEATHER EDGES

REPAIR CONFIGURATION SHOULD BE KEPT AS SIMPLE AS POSSIBLE PREFERABLY WITH SQUARED CORNERS

REMOVE BOND INHIBITING MATERIALS SUCH AS DIRT CONCRETE LAITANCEAND LOOSE AGGREGATES BY ABRASIVE BLASTING OR HIGH-PRESSURE WATER BLASTING WITH OR WITHOUT ABRASIVE CHECK THE CONCRETE SURFACE AFTER CLEANING TO ENSURE THAT THEY ARE FREE FORM LOOSE AGGREGATES AND DELAMINATIONS

REPAIR OF CORRODED RCC ELEMENTS

REPAIR OF CORRODED REINFORCEMENT INCLUDES FOLLOWING MAIN STEPS

CHIP OFF ALL LOOSE AND CRACKED CONCRETE IN RCC ELEMENT

REMOVE CONCRETE IN COVER COMPLETELY TO EXPOSE CORRODED REINFORCEMENT

REMOVE ALL LOOSE AND DETERIORATED CONCRETE BY WIRE BRUSH

CLEAN THE REINFORCEMENT THOROUGHLY TO REMOVE ALL RUST OF CORRODED STEEL BY SAND BLASTING OR CHEMICAL WASH

WASH AND SATURATE ALL CAVITIES IN ADJOINING CONCRETE WITH CLEAN WATER AND REMOVE ALL FREE WATER BEFORE PLACING REPAIR MORTAR

FILL ALL CRACKS WITH EPOXY RESINS AND APPLY BOND COAT JUST PRIOR TO PLACING PATCH REPAIR MORTAR OR CONCRTE

APPLY PATCH REPAIR MORTAR OR CONCRETE OR GROUT ON THE DAMP CAVITY SURFACE

IN CASE OF LOSS OF STEEL SECTIONADDITIONAL STEEL REINFORCEMENT MAY BE TIED TO THE EXISTING BARS PRIOR TO APPLICATION OF BOND COAT

FILL THE CAVITY WITH REPAIR MORTAR OR CONCRETE AND CONSOLIDATE THOROUGHLY WITH ROD AND MALLET OR VIBRATION

ALTERNATIVELY FILLPREPACKED AGGREGATE CONCRETE IN THE CAVITIES AFTER APPLYING BOND COAT ANAD FINISH WITH PRESSURE GROUTING WITH REPAIR MORTAR

APPLY A PROTECTIVE COATING ON THE FINISHED SURFACE OF THE REPAIRED ELEMENT

CORROSION DUE TO DAMPNESS

CORROSION DUE TO WATER AND DUE TO AGE

COMPENSATING REINFORCEMENT IF REINFORCING STEEL HAS LOST SIGNIFICANT CROSS SECTIONA STRUCTURAL ENGINEER

SHOULD BE CONSULTED

IF REPAIR ARE REQUIRED TO THE REINFORCING STEEL THE BAR CAN BE REPLACED COMPLETELY OR SUPPLEMENTARY BARS CAN BE PLACED OVER THE AFFECTED SECTION

SUPPLEMENTARY BARS MAY BE MECHANICALLY SPLICED TO OLD BARS OR PLACED PARALLEL TO OLD BARS APPROXIMATELY 15MM FROM EXISTING BARS LAP LENGTHS SHALL BE DETERMINED IN ACCORDANCE WITH LATEST IS SPECIFICATIONS AND OTHER DESIGN GUIDELINES

EDGE AND SURFACE CONDITIONING THE SURFACE CONDITIONING STEPS ARE USED FOR HORIZONTAL VERTICAL AND OVERHEAD

SURFACES

THEY ARE ALSO APPLICABLE TO CONCRETE REMOVAL BY HYDRODEMOLITION AND ELECTRIC PNEUMATIC OR HYDRAULIC IMPACT BREAKERS

AFTER REMOVING DELAMINATED CONCRETE AND UNDERCUTTING REINFORCING STEEL REMOVE ADDITIONAL CONCRETE AS REQUIRED TO PROVIDE THE MINIMUM REQUIRED THICKNESS OF THE REPAIR MATERIALAT EDGE LOCATION PROVIDE RIGHT ANGLE CUTS TO THE CONCRETE SURFACE WITH EITHER OF THE FOLLOWING METHODS

SAW CUT 12MM OR LESS AS REQUIREDAVOID CUTTING REINFORCING STEEL

USE POWER EQUIPMENTSUCH AS HYDRODEMOLITION OR IMPACT BREAKERS AVOID FEATHER EDGES

REPAIR CONFIGURATION SHOULD BE KEPT AS SIMPLE AS POSSIBLE PREFERABLY WITH SQUARED CORNERS

REMOVE BOND INHIBITING MATERIALS SUCH AS DIRT CONCRETE LAITANCEAND LOOSE AGGREGATES BY ABRASIVE BLASTING OR HIGH-PRESSURE WATER BLASTING WITH OR WITHOUT ABRASIVE CHECK THE CONCRETE SURFACE AFTER CLEANING TO ENSURE THAT THEY ARE FREE FORM LOOSE AGGREGATES AND DELAMINATIONS

REPAIR OF CORRODED RCC ELEMENTS

REPAIR OF CORRODED REINFORCEMENT INCLUDES FOLLOWING MAIN STEPS

CHIP OFF ALL LOOSE AND CRACKED CONCRETE IN RCC ELEMENT

REMOVE CONCRETE IN COVER COMPLETELY TO EXPOSE CORRODED REINFORCEMENT

REMOVE ALL LOOSE AND DETERIORATED CONCRETE BY WIRE BRUSH

CLEAN THE REINFORCEMENT THOROUGHLY TO REMOVE ALL RUST OF CORRODED STEEL BY SAND BLASTING OR CHEMICAL WASH

WASH AND SATURATE ALL CAVITIES IN ADJOINING CONCRETE WITH CLEAN WATER AND REMOVE ALL FREE WATER BEFORE PLACING REPAIR MORTAR

FILL ALL CRACKS WITH EPOXY RESINS AND APPLY BOND COAT JUST PRIOR TO PLACING PATCH REPAIR MORTAR OR CONCRTE

APPLY PATCH REPAIR MORTAR OR CONCRETE OR GROUT ON THE DAMP CAVITY SURFACE

IN CASE OF LOSS OF STEEL SECTIONADDITIONAL STEEL REINFORCEMENT MAY BE TIED TO THE EXISTING BARS PRIOR TO APPLICATION OF BOND COAT

FILL THE CAVITY WITH REPAIR MORTAR OR CONCRETE AND CONSOLIDATE THOROUGHLY WITH ROD AND MALLET OR VIBRATION

ALTERNATIVELY FILLPREPACKED AGGREGATE CONCRETE IN THE CAVITIES AFTER APPLYING BOND COAT ANAD FINISH WITH PRESSURE GROUTING WITH REPAIR MORTAR

APPLY A PROTECTIVE COATING ON THE FINISHED SURFACE OF THE REPAIRED ELEMENT

CORROSION DUE TO DAMPNESS

CORROSION DUE TO WATER AND DUE TO AGE

REPAIR OF CORRODED RCC ELEMENTS

REPAIR OF CORRODED REINFORCEMENT INCLUDES FOLLOWING MAIN STEPS

CHIP OFF ALL LOOSE AND CRACKED CONCRETE IN RCC ELEMENT

REMOVE CONCRETE IN COVER COMPLETELY TO EXPOSE CORRODED REINFORCEMENT

REMOVE ALL LOOSE AND DETERIORATED CONCRETE BY WIRE BRUSH

CLEAN THE REINFORCEMENT THOROUGHLY TO REMOVE ALL RUST OF CORRODED STEEL BY SAND BLASTING OR CHEMICAL WASH

WASH AND SATURATE ALL CAVITIES IN ADJOINING CONCRETE WITH CLEAN WATER AND REMOVE ALL FREE WATER BEFORE PLACING REPAIR MORTAR

FILL ALL CRACKS WITH EPOXY RESINS AND APPLY BOND COAT JUST PRIOR TO PLACING PATCH REPAIR MORTAR OR CONCRTE

APPLY PATCH REPAIR MORTAR OR CONCRETE OR GROUT ON THE DAMP CAVITY SURFACE

IN CASE OF LOSS OF STEEL SECTIONADDITIONAL STEEL REINFORCEMENT MAY BE TIED TO THE EXISTING BARS PRIOR TO APPLICATION OF BOND COAT

FILL THE CAVITY WITH REPAIR MORTAR OR CONCRETE AND CONSOLIDATE THOROUGHLY WITH ROD AND MALLET OR VIBRATION

ALTERNATIVELY FILLPREPACKED AGGREGATE CONCRETE IN THE CAVITIES AFTER APPLYING BOND COAT ANAD FINISH WITH PRESSURE GROUTING WITH REPAIR MORTAR

APPLY A PROTECTIVE COATING ON THE FINISHED SURFACE OF THE REPAIRED ELEMENT

CORROSION DUE TO DAMPNESS

CORROSION DUE TO WATER AND DUE TO AGE

CORROSION DUE TO DAMPNESS

CORROSION DUE TO WATER AND DUE TO AGE