0005 India Regulation on Coating

i

For Official use only

GOVERNMENT OF INDIA

MINISTRY OF RAILWAYS

(Railway Board)

TECHNICAL LITERATURE ON CORROSION/CARBONISATION

PROTECTION IN CONCRETE STRUCTURES

MARCH– 2008

BS-88

ISSUED BY

RESEARCH DESIGNS AND STANDARDS ORGANISATION

LUCKNOW - 226011

ii

iii

CONTENTS

0 INTRODUCTION 1

1.0 CARBONATION OF CONCRETE 1

2.0 CHLORIDE ATTACK

4

3.0 CORROSION CONTROL 7

3.1 METLLURGICAL METHOD

9

3.2 CORROSION INHIBITORS 9

3.3 COATINGS TO REINFORCEMENT

12

3.4 METALLIC COATINGS 15

3.5 RE-ALKALIZATION

17

3.6 CHLORIDE REMOVAL 18

3.7 CATHODIC PROTECTION 18

3.8 COATINGS TO CONCRETE

21

4.0 REFERENCES 29

1

0. Introductions

Corrosion of steel in concrete is a complex phenomenon. There are different

factors affecting the process of corrosion in concrete. The increase in volume of

reinforcement after corrosion is one of the adverse effects on the structure apart from

reduction in cross section area of reinforcement. Corrosion has been found one of the

important reason causing weakness to concrete structures. Lot of research has been done

on this subject in India and abroad to prevent the process of corrosion in concrete

structures. Before discussing the methods to avoid or reduce corrosion, it will be more

appropriate to understand some of the fundamentals of process of corrosion of

reinforcement in concrete. The ingress of water and oxygen is must to start process of

corrosion. The excess of Ca (OH) 2 as a result of hydration process of cement in concrete

provides a passive environment around reinforcement to prevent corrosion. The pH value

of normal concrete with OPC remains in the range of 13 to 17. Any chemical reaction

with in concrete to reduce this pH value poses a potential threat for start of corrosion of

reinforcement apart from other damages to concrete microstructures. Following are few

commonly known processes causing deterioration to concrete.

1. Carbonation of concrete

The microstructure of concrete is such that it has capillary pores to the extent of

28%. The extent of pores depends upon quality of concrete and the presence of water at

the time of mixing of concrete. Making more dense concrete with less w/c ration reduces

the amount of pores. These pores are created due to evaporation of excess free water

during strengthening of concrete mass. These pores are inter connected and goes inside

the concrete mass from surface of concrete structures.

Carbonation of concrete is a process by which carbon dioxide from the air

penetrates into concrete through pores and reacts with calcium hydroxide to form calcium

carbonates. It has seen that the conversion of Ca(OH)2 into CaCO3 by the action of CO2

results in a small shrinkage.

We shall see another aspect of carbonation, as CO2 by itself is not reactive. In the

presence of moisture, CO2 changes into dilute carbonic acid, which attacks the concrete

and also reduces alkalinity of concrete (i.e. ph value reduces).

Air contains CO2. The concentration of CO2 in rural air may be about 0.03 percent

by volume. In large cities the content may go up to 0.3 percent or exceptionally it may go

up to even 1.0 per cent. In the tunnel, if not well ventilated the intensity may be much

higher.

The pH value of pore water in the hardened concrete is generally between 12.5 to

13.5 depending upon the alkali content of cement. The high alkalinity forms a thin

passivating layer around steel reinforcement and protect it from action of oxygen and

water. As long as steel is placed in a highly alkaline condition, it is not going to corrode.

Such condition is known as passivation.

2

In actual practice CO2 present in atmosphere in smaller or greater concentration,

permeates into concrete and carbonates the concrete and reduces the alkalinity of

concrete. The pH value of pore water in the hardened cement paste, which was around

13, will be reduced to around 9.0. When all the Ca (OH)2 has become carbonated, the pH

value will reduce up to about 8.3. In such a low pH value, the protective layer gets

destroyed and the steel is exposed to corrosion.

The carbonation of concrete is one of the main reasons for corrosion of

reinforcement. Of course oxygen and moisture are the other components required for

corrosion of embedded steel.

Rate of Carbonation:

The rate of carbonation depends on the following factors.

The level of pore water i.e. relative humidity.

Grade of concrete

Permeability of concrete

Whether the concrete is protected or not

Depth of cover

Time

Fig 1 Depth of Carbonation with respect to strength (grade) of concrete

It is interesting to know that if pore is filled with water the diffusion of CO2 is

very slow. But whatever CO2 is diffused into the concrete, is readily becomes dilute

carbonic acid reducing the alkalinity of concrete.

On the other hand if the pores are rather dry, that is at low relative humidity the

CO2 remains in gaseous form and does not react with hydrated cement. The moisture

penetration from external source is necessary to carbonate the concrete.

3

Fig 2 Depth of Carbonation for protected and un-protected concrete Depth of

carbonation with age and grade of concrete

Table 1

Age-years Depth of Carbonation (mm)

M20 M40

2 5.0 0.5

5 8.0 1.0

10 12.0 2.0

50 25.0 4.0

The highest rate of carbonation occurs at a relative humidity of between 50 and 70

per cent.

The rate of carbonation depth will be slower in case of stronger concrete for the

obvious reason that stronger concrete is much denser with lower W/C ratio. It again

indicates that the permeability of the concrete, particularly that of skin concrete is much

less at lower W/C and as such the diffusion of CO2 does not take place faster, as in the

case of more permeable concrete with higher W/C ratio. Fig 1 and table 1 shows th4e

depth of carbonation in various grades of concrete.

It is now well recognized that concrete needs protection for longer durability.

Protective coating is required to be given for long span bridge girders, flyovers, industrial

structures and chimneys. The fig.2 shows carbonation depth of protected and un-

protected concrete.

Depth of cover plays an important role in protecting the steel from carbonation.

The table 2 shows relationships between W/C, depth of cover and time in years for

carbonation depth to reach the reinforcement.

Table 2 Approximate relations between W/C, depth of cover and time in years for

carbonation depth to reach the reinforcement.

WC Depth of cover (mm)

Ratio 15 20 25 30

0.45 100+ 100+ 100+ 100+

0.50 56 99 100+ 100+

4

0.55 27 49 76 100

0.60 16 29 45 65

0.65 13 23 36 52

0.70 11 19 30 43

Time in years for carbonation

Fig 3 Concrete is under continuous attack by aggressive envoi mental agencies. Good

concrete and sufficient cover is the answer for durability

Measurement of depth of carbonation:

A common and simple method for establishing the extent of carbonation is to treat

the freshly broken surface of concrete with a solution of phenolphthalein in diluted

alcohol. If the Ca(OH) 2 is unaffected to CO2 the colour turns out to be pink. If the

concrete is carbonated it will remain uncoloured. It should be noted that the pink colour

indicates that enough Ca(OH) 2 is present but it may have been carbonated to a lesser

extent. The colour pink will show even up to a pH value of about 9.5.

2. Chloride Attack:

Chloride attack is one of the most important aspects for consideration when we

deal with the durability of concrete. Chloride attack is particularly important because it

primarily causes corrosion of reinforcement. Statistics have indicated that over 40 per

cent of failure of structures is due to corrosion of reinforcement.

We have already discussed that due to high alkalinity of concrete a protective

oxide film is present on the surface of steel reinforcement. The protective passivity layer

can be lost due to carbonation. This protective layer also can be lost due to the presence

of chloride in the presence of water and oxygen. In reality the action of chloride in

inducing corrosion of reinforcement is more serious than any other reasons. One may

understand that Sulphates attack the concrete whereas the chloride attacks steel

reinforcements.

Chloride enters the concrete from cement, water, and aggregate and sometimes

from admixtures. The present day admixtures are generally containing negligible quantity

of chloride or what they call chloride free. Chloride can enter the concrete by diffusion

from environment. The Bureau of Indian Standard earlier specified the maximum

chloride content in cement as 0.05 percent. But it is now increased the allowable chloride

content in cement to 0.1 per cent. I S 456 of 2000 limits the chloride content as (Cl) in the

concrete at the time of placing is shown in table 3.

CO2

SO2

H2O

5

Fig 4 Pink Colour indicates that Ca (OH) 2 is unaffected by carbonization. the

uncoloured portion indicates that concrete is carbonated.

Table 3 Limits of Chloride Content of Concrete (IS 456 of 2000)

Sl.No. Type of Use of Concrete Maximum Total

acid soluble

chloride content.

Expressed as

kg/m3

of concrete

1. Concrete containing metal and steam cured

at elevated temperature and prestressed

concrete

0.4

2. Reinforced concrete or plain concrete

containing embedded metal

0.6

3. Concrete not containing embedded metal or

any material requiring protection from

chloride

3.0

The amount of chloride required for initiating corrosion is partly dependent on the

pH value of the pore water in concrete. At a pH value less than 11.5 corrosion may occur

without the presence of chloride. At pH value greater than 11.5 a good amount of

chloride is required.

Limiting values of chloride contents, above which corrosion may be imminent, for

various values of pH are indicated in table 4. The total chloride in concrete is present

partly as insoluble chlorialuminates and partly in soluble form. It is the soluble chloride,

which is responsible for corrosion of reinforcement.

Table 4 Limiting Chloride Content Corresponding to pH of concrete

PH Chloride content g/litre ppm

13.5 6.7400 6740

13.0 2.1300 2130

6

12.5 0.6720 672

12.0 0.2130 213

11.5 0.0670 67

11.0 0.0213 21

10.0 0.0021 2

9.02 0.0002 0.2

Chloride Permeability Based on Charge Passed

(As per ASTM C 1202)

Chloride

Permeability

Charges passed

(Coulombs)

Type of Concrete

High ≤ 4000 High water-cement ratio ≤ 0.6

Moderate 2000 to 4000 Moderate W/C ratio (0.4 to 0.5)

Low 1000 to 2000 Water-cement ratio ≤ 0.4

Very Low 100 to 1000 Latex modified concrete

Negligible ≤ 100 Polymer Impregnated concrete

Corrosion of Steel (Chloride induced)

Corrosion of steel in concrete is an electrochemical process. When there is a

difference in electrical potential along the steel reinforcement in concrete, an

electrochemical cell is set up. In the steel, one part becomes anode and other part

becomes cathode connected by electrolyte in the form of pore water in the hardened

cement paste. The positively charged ferrous ions Fe++

at the anode pass into solution

while the negatively charged free electrons e- pass through the steel into cathode where

they are absorbed by the constituents of the electrolyte and combine with water and

oxygen to form hydroxyl ions (OH)-. These travel through the electrolyte and combine

with the ferrous ions to form ferric hydroxide, which is converted by further oxidation to

rust.The reactions are described below

Anodic reactions

Fe→ Fe++

+2 e-

Fe

++2(OH)

- →Fe (OH) 2 (Ferrous hydroxide)

4 Fe (OH) 2 + 2H2 O+O2→ 4 Fe (OH) 3 (Ferric oxide)

Cathodic reaction

4 e- + O2+ H2 O→ 4 (OH)

–

7

Fig 5 Simplified model representing corrosion mechanism

Fig 6 Shows that, depending on the oxidation state, metallic iron can increase

more than six times in volume.

Fig 7 Diagrammatic representation of damage induced by corrosion cracking,

spalling and delamination

It can be noted that no corrosion takes place if the concrete is dry or probably

below relative humidity of 60 percent because enough water is not there to promote

corrosion. It can also be noted that corrosion does not take place if concrete is fully

immersed in water because diffusion of oxygen does not take place into the concrete.

Probably the optimum relative humidity for corrosion is 70 to 80 percent.

The products of corrosion occupy a volume as many as six times the original

volume of steel depending upon the oxidation state. Fig. 6 shows the increase in volume

of steel depending upon the oxidation state.

The increased volume of rust exerts thrust on cover concrete resulting in cracks,

spalling or delamination of concrete. Refer Fig 7. With this kind of situation concrete

loses its integrity. The cross section of reinforcement progressively reduces and the

structure is sure to collapse.

3.0 Corrosion Control:

From the literature survey and case studies it has been reported that 40% of failure

of structures is on account of corrosion of embedded steel reinforcement in concrete.

Therefore corrosion control of steel reinforcement is a subject of paramount importance.

First and foremost for corrosion control is the good quality of concrete through

good construction practices. It is a very vast subject touches the fundamentals of

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choosing constituents material and good rules to be followed during various stages or

production of concrete, in particular the use of lowest possible water/cement ratio having

regard to workability. In view of the general availability of superplasticizers, it should be

used to cut down the W/C ratio to make dense concrete.

Fig 8

Proper mix design, use of right quality and quantity of cement for different

exposure conditions is to be adopted. Recently it has been realized that lower W/C ratio

which has been always associated with lower permeability is not enough to make

impermeable concrete contributing to high durability. Use of supplementary cementitious

materials such as fly ash, ground granulated blast furnace slag (ggbs), silica fume etc. are

required to be used as admixtures or in the form of blended cement in addition to lowest

possible W/C ratio to make concrete dense. These materials improve more than one

properties of concrete, which will eventually reduce corrosion of reinforcement. Tests on

mortar containing ggbs have shown that water permeability is reduced by a factor up to

100. It is also reported that 60 per cent ggbs educed the diffusion of chloride ions into the

concrete by as much as 10 times. Silica fume contributes to the all-round improvements

in the quality of concrete, which are responsible for reducing corrosion of steel

reinforcement. The improvement in the microstructure of hydrated cement paste is

ultimately responsible for protecting the steel reinforcement from corrosion.

Fig 9 Crack formed due to bursting pressure on account of rusting of reinforcements

Example of delamination of concrete cover

9

In short it can be said that if we make good concrete with low permeability and

improved microstructure, it will be durable by itself and also it can take care of the

reinforcement contained in it o a great extent. It is always not possible to make such ideal

concrete, particularly, in view of the complex environmental and exposure conditions.

Further the inherent long term drying shrinkage and micro cracks in concrete, the

problems become more serious. This demands certain other measures to control the

corrosion of steel reinforcement. They are listed and briefly explained.

Metallurgical methods

Corrosion inhibitors

Coatings to reinforcement

Re-alkalization

Chloride removal

Cathodic protection

Coatings to concrete

3.1 Metallurgical Methods: Steel can made more corrosion resistant by altering its structure through

metallurgical processes. Different methods such as rapid quenching of the hog bars by

series of water jets, or by keeping the hot steel bars for a short time in a water bath, and

by such other process the mechanical properties and corrosion resistance property of steel

can be improved. There are many situations where stainless steel reinforcements are used

for long term durability of concrete structures.

3.2 Corrosion inhibitors:

Corrosion inhibitors, which come in powder, gel and liquid form, retard the rate

of the corrosion reaction. They are widely used in many industries to effectively reduce

the corrosion rate of steel and other metals. Commercial products for the control of

corrosion of steel reinforcement in atmospherically exposed concrete were first produced

in the 1970's. They increase the time to the onset of corrosion and then act to reduce

the rate of corrosion. They can be introduced into the concrete mix at the time of

construction/ repair or (in a suitable formulation) applied to the surface of an existing

concrete structure. There are three main types of inhibitors:

3.2.1 Anodic inhibitors, which retard the corrosion reaction at the anode: Corrosion

can be prevented or delayed by chemical method by using certain corrosion inhibiting

chemicals such as nitrites, phosphates, benzoates etc. At low dosage there is concern that

they will suppress generalized corrosion but may fail to eliminate all anodic sites. Of the

available materials, the most widely used admixture is based on calcium nitrite but have

proved to be deleterious at high chloride concentrations. It is added to the concrete during

mixing of concrete. The typical dosage is of the order of 10-30 litres per m3 of concrete

depending on chloride levels in concrete.

10

Fig 10 Corrosion inhibiting effects of calcium nitrite

As mentioned earlier, in the high pH of concrete, the steel is protected by a

passivating layer of ferric oxide on the surface of steel. However, the passivating layer

also contains some ferrous oxide, which can initiate corrosion when the chloride ions

reach the steel. The nitrite ions present in the corrosion-inhibiting admixture will oxidize

the ferrous oxide to ferric oxide, thus stabilizing the passivating layer even in the

presence of chlorides. The concentration of nitrite must by sufficient to cope up with the

continuing ingress of chloride ions.

Calcium nitrite corrosion inhibitor comes in a liquid from containing about 30 per

cent calcium nitrite solids by weight. The more corrosion inhibitor is added, the longer

the onset of corrosion will be delayed. Since most structures in a chloride environment

reach a level of about 7 kg of chloride iron per m3 during their service life, use of less

than 18 litres/ m3 of calcium nitrite solution is not recommended.

Fig. 10 shows that without an inhibitor the reinforcing steel starts to corrode when

the chloride content at the rebar reaches a threshold level of 0.7 kg/ m3. Although the

corrosion process starts when the threshold level is reacted, it may take several years for

staining, cracking and spalling to become apparent and several more years before

deterioration occurs. Adding calcium nitrite increases this corrosion threshold. When you

add 20-litres/ m3, corrosion will not begin until over 7.7-kg/ m

3 of chloride is present in

the concrete at the rebar.

3.2.2 Cathodic inhibitors

Which retard the reaction at the cathode and seek to prevent oxygen reaching the

reinforcing steel. At low dosages, they are effective at reducing corrosion rates but are

generally less efficient than the anodic type.

3.2.3 Bipolar inhibitors

They retard the corrosion process both at the anode and the cathode. These combine

the benefits of both anodic and cathodic inhibitors at relatively low dosages. In this category

organic Migratory bipolar corrosion inhibitors are the most widely used.

Migratory Bipolar Corrosion inhibitors are organic inhibitors. They protect the

steel at both the anodic and the cathodic sites. The Bipolar corrosion inhibitor chemistry

involves migration of its molecules by electron density distribution to both the anodic and

11

cathodic sites of the steel. By virtue of its high vapour pressure, very high affinity and

virtue of diffusion these inhibitors migrate towards the steel in concrete and get deposited

in a monomolecular layer. This is true even in dense concrete. This barrier coating then

raises the chloride threshold concentration for corrosion. Further more the inhibitor

within the concrete matrix reduces the rate of chloride ion migration towards steel. It also

dislodges previously absorbed chloride ions and water molecules on the steel surface.

The basic advantage of the product lies in the ease of use. Studies have proved

that addition of these types of corrosion inhibitors has no deleterious effect on the

properties of concrete. Concrete penetrating corrosion inhibiting admixture upon addition

into the concrete matrix plays a major role in inhibiting the corrosion process. The

European Committee for standardization (CEN) pr. ENV 1504-9 recommends application

of Concrete penetrating corrosion inhibitors as a proven corrosion control strategy.

SHRP-S-666 (Strategic Highway Research Programme) has recommended these types of

corrosion inhibitors for concrete structures subjected to chloride-induced corrosion.

General Building Corporation of Japan has evaluated this product in concrete extensively

and has reported rebar life extension by six times. Two codes available internationally for

testing these types of inhibitors are ASTM G 109 & JIS A 6205.

They are available, both as surface applied inhibitors and as admixed inhibitors.

Surface applied inhibitors are used by spraying on the complete surface of the structure

being repaired so that protection to the unexposed reinforcement is taken care of.

Admixed inhibitors are used in the fresh mortar/concrete being placed for strengthening

the structure.

Specification for surface applied Corrosion inhibitor

Base Bipolar Water based Organic inhibitor. Concrete penetrating type.

Colour Colorless Hazy liquid

Specific Gravity 1.01 – 1.02 at 25o C

Viscosity at 250C 11-12 sec by Ford B4 Cup.

pH Minimum 9.5

Dosage To be sprayed at the rate of 4m2 / ltr

Toxicity Non-toxic , Eco-friendly.

Evaluation Should pass JIS - 6205 standard

Specification for Admixed corrosion inhibitor

Base Bipolar Organic inhibitor. Concrete penetrating type.

Colour Brownish

Specific Gravity 1.05 – 1.08 at 25o C

Viscosity at 250C 11-12 sec by Ford B4 Cup.

pH Minimum 9.0

12

Dosage 3 kgs per cubic meter of concrete.

Toxicity Non-toxic, Eco-friendly.

Effect on concrete

properties

No adverse effect on physical properties in fresh & hardened concrete in

the absence of any other admixtures. However it is Essential to carry out

trial mix with desired admixtures along with Migratory Corrosion

Inhibitor.

Compatibility for Higher

Thermal Cycles

Compatible for higher thermal cycles No deleterious effects

even at high temperature. Effective even at higher temperatures.

Evaluation Should pass ASTM-G-109 standard & JIS - 6205

Should pass tropical climate test (thermal cycles)

Acceptance Criteria:

Migratory Bipolar Corrosion Inhibitor should be tested as per ASTM-G-109/ JIS - 6205

from reputed laboratories like CSIR & I.I.T.

Tropical Compatibility:

Material shall have evaluated test reports indicating significant reduction in corrosion rate

after minimum of 90 thermal cycles at 60oC followed by 8 weeks of accelerated

corrosion. (Linear polarization method)

The inhibitor shall be non-toxic & safe to plant and human life.

The principle of most inhibitors is to develop a very thin chemical layer on the

surface of the reinforcement. There is a very wide range of corrosion protection

performance from different inhibitor formulations, even with generic classifications.

Independent evaluation and certification of performance is desirable. However,

such evaluations need to be representative of field concretes and conditions. As the

true effect of an inhibitor can only be evaluated from corrosion rate measurements

before and after application and by reference to a control area, such systematic

evaluations are lengthy processes and are in their early stages.

3.3 Coatings to Reinforcement:

3.3.1 Cement Polymer Composite coating system (CECRI Karaikudi): Central Electro-Chemical Research Institute, Karaikudi, developed the system

after years of research on cement-based coatings. Rebars embedded in concrete are

surrounded by an alkaline medium and as such cement based coating is more compatible.

Basically two coats are applied - Primer coat and Sealer coat. The primer and sealer

products: have thereto-plastic acrylic resin as basic raw material. The sealer product is

formulated with resin mixed with cement as a pigment. The principle of the system is

that the base metal contains 'p' electrons, which get released in corrosive environment

leading to formation of Iron Oxide (Fe203). To prevent oxidation, a surface coating

capable of nullifying the released electrons is provided. The sealer coat is compatible with

primer and alkaline environment.

13

System at a Glance:

No. Parameter Requirement Codal

Reference

1. Pre-treatment

(Surface reparation)

Sand blasting to the near white metal

2. Primer coat To be given within 4 hours of sand

blasting

3. Sealer coat Within 30minutes of primer coat, this

should be given. Thickness 150

microns ± 25 microns

4. Air curing Six hours before use in the work.

5. Continuity of coating No defects such as cracking, bulging,

peeling, no rust mark. Inspect visually.

6. Adhesion of coating –

Test Coated bars are bent @ 120 around a

mandrel. No peeling or cracking should be

observe don outer radius.

7. Stacking Stack bars on buffer material.

8. Cutting, bending, welding Coated bars can be cut and bent. Cut ends and

weld portion should be treated with same

formulation.

3.3.2 Fusion Bonded Epoxy Coating:

The System:

Fusion bonded epoxy is basically 100% solid finely ground fused powder

particles, which when heated; melt to form a continuous adherent film. Fusion

Bonded Epoxy Coating (FBEC) system for rebars is a fully automatized online

process and large quantities of rebars can be obtained by reproducible quality. In early

seventies, this system was originally developed in USA and around 1988, it started

in India. It involves coating of epoxy under factory conditions and such plants are

established in the country.

14

Fig 11

Pros and Cons of the System:

Though this system is being used in India for more than a decade and in USA for

more than 3 decades, there are opinions expressed in favour and against this system..

Briefly, some points are highlighted here for the benefit of decision makers.

Points in favour of the system:

Research carried out by The National Bureau of Standards (NBS) for Federal

Highway Administration, USA concluded that epoxy coated reinforcement by

fusion bonding process in excess of 102 microns in thickness would be capable

of protecting steel from corrosion. Similarly, research done in other countries

(Canada, Japan, UK) has shown that FBEC bars performed better compared to

uncoated bars.

In India, Central Road Research Institute conducted the test on coated bars in the

laboratory and in field for 3 years and evaluated that the performance of FBECR

bars is satisfactory.

It is possible to repair cut ends and damages to the fusion bonded epoxy coated

bard by touch-up methods. Within few hours, it can be used.

Points against the system:

There is no passivating primer film provided in case of FBEC rebars.

This coating introduces a medium of weakness in the path of an intimate bond

between rebar and alkaline concrete.

Investigation carried out on 40 bridges in Florida Key in USA has revealed that

disbandment can occur easily in the FBEC rebars which lacked passivation layer

of Fe2O3 and is a precursor to corrosion.

Higher co-efficient of Thermal Expansion of fusion bonded epoxies impose

large thermal stresses in epoxy coating leading to its early failure.

Cost of FBEC rebars is 30 to 50% higher than uncoated bars.

Lot of precautions and care is required in transportation, handling and placement of these

coated bars failing which there will be damages, cuts and abrasions which may lead

to corrosion.

3.3.3 IP Net Rebar Coating System (CBRI Roorkee)

CENTRAL BUILDING RESEARCH INSTITUTE [CBRI/CSIR] ROORKEE

LICENCED SYSTEM

It is Interpenetrating Polymer Network Coating System for Corrosion Protection of

Reinforcing Steel.System Composition. The coating system consists of a primer coat and

a topcoat of the same system. The Primer and Topcoat (both coats) have Epoxy phenolic

base with mixing proportion of 1: 1 of resin and hardener by volume.

METHOD OF APPLICATION OF COATING SYSTEM:

The application of the IPNet-RB coating system comprises the following sequence.

Properties: System shall conforms to

15

ASTM - D - 3963 - 86 A-1.4.5.1. (Adhesion test with reinforcing steel)

IS - 2770 (Part-1) (Pull-out test of coated bar with concrete)

ASTM - B - 117 - 64 Part 21 (Salt spray test)

ASTM-D- 2370-73 (Elongation).

The durability of the coated rebars is related to the coating quality. The more damages to

the coating is more prone to corrosion. Good job site practices can minimize the coating

damages. For this reason, standards from ASTM, NACE (USA) have laid down specific

procedures for stacking and transporting coating bars. Some important guidelines are

referred here.

Specifications for patch repairing of coating damages

a) Coating repairs is required when peeling off and other damages exist. Prior to repairs,

the damaged area shall be cleaned by removing loose or deleterious material. In case

where rust is present it shall also be mechanically removed to repair.

b) After this, primer coat shall be brush applied. After curing (4 hours) top coat shall be

applied and it is desirable to ensure a thickness of 150 microns.

The object of coating to steel bar is to provide a durable barrier to aggressive materials,

such as chlorides. The coatings should be robust to withstand fabrication of reinforcement

cage, and pouring of concrete and compaction by vibrating needle.

3.3.4 Simple cement slurry coating

It is a cheap method for temporary protection against rusting of reinforcement in

storage. Central Electro Chemical Research Institute (CECRI) Karaikudi have suggested

a method for prevention of corrosion in steel reinforcement in concrete. The steps

involved in this process are:

De-rusting: The reinforcements are cleaned with a de-rusting solution. This is followed

without delay by cleaning the rods with wet waste cloth and cleaning powder. The rods

are then rinsed in running water and air-dried.

Phosphating: Phosphate jelly is applied to the bars with fine brush. The jelly is left for

45-60 minutes and then removed by wet cloth. An inhibitor solution is then brushed over

the phosphated surface.

Cement Coating: Slurry is made by mixing the inhibitor solution with Portland cement

and applied on the bar. A sealing solution is brushed after the rods are air cured. The

sealing solution has an insite curing effect. The second coat of slurry is then applied and

the bars are air-dried.

Sealing: Two coats of sealing solution are applied to the bars in order to seal the micro-

pores of the cement coat and to make it impermeable to corrosive salts.

The above is a patent method evolved by CECRI and license is given to certain

agencies. Somehow or other this method has not become very popular. Some experienced

consultants and engineers doubt the efficacy of this method.

3.4 Metallic coatings (Galvanized reinforcement): Although coatings can be provided by number of metals such as nickel, copper,

lead, tin etc., coating provided by using zinc is more suitable and economical. This

process is known as "Hot Dip Galvanizing" and involves steps such as picking,

16

rinsing, flux solution dipping, drying and coating.

Galvanizing of reinforcement consists of dipping the steel bars in molten zinc.

This results in a coating of zinc bonded to the surface of steel. The zinc surface reacts

with calcium hydroxide in the concrete to form a passive layer and prevents corrosion.

Fig 12 Galvanization process adopted for corrosion resistance

Minimum mass of zinc coating shall be provided as given in the following table:

S. No. Environment Mass of zinc coating – minimum

grams/m2 of surface

Reference

1. Aggressive surrounding

such as marine areas,

chemical plants

915 (125 microns) ICJ Paper January

2004 by Mr.

Pugazhendy

17

2. Normal 610 (85 microns) - do -

Zinc coating covers up any scratches/holidays that may occur in the coating due to electro-

chemical property of zinc. Galvanized bars can be bent without cracking or peeling up of

coating due to ductility of zinc. Bond characteristics and weld-ability of zinc coated bars

remain unaffected.

Testing of Galvanized Bars:

Following tests shall be carried out to determine suitability of galvanized bars and before using

them in concrete:

S.No. Test Criteria for

Acceptance

Reference Remarks

1. Hammer Test (Hammer Wt.215 gms) Should not peel off IS – 2629

2. Knife Test (Sharp Edge) No scratches and no

peel off

IS – 2629

3. Thickness Test Zinc coating should

conform to specified

thickness

IS – 3203

4. Preece Test (copper sulphate test for coating

uniformity)

No copper deposits IS – 2633

5. Hydrogen evolution test for purity of zinc

coating wt.

Coating mass to be as

specified

ASTM – A –

123

6. Stripping test 15% HCL solution Coating as specified IS - 6745

IS - 4759

3.5 Re-alkalization:

This electro-chemical technique provides a means of restoring the alkalinity to

carbonated but otherwise sound concrete. It involves the passage of a direct current

between the reinforcement (the cathode) and an anode applied temporarily to the

surface of the concrete. This process generates hydroxyl ions at the steel surface,

which locally regenerates the alkalinity of the concrete raising its pH upto about 12.

This helps restore the passivating surface oxide layer to the reinforcement.

Under the applied voltage, alkali ions are drawn from the anode into the

concrete. The use of sodium or potassium carbonate electrolyte is claimed to make the

treatment more resistant to further carbonation. Several forms of anode may be

employed. These are commonly either some form of mesh (titanium or steel) or

electrolytic tanks (for vertical surfaces)/baths (for deck slab applications). Sprayed

cellulose impregnated with the electrolyte is used with the mesh anode system.

The introduction of sodium ions, when using sodium carbonate as an

electrolyte, may exacerbate any potential the concrete has for ASR. In these cases,

plain water has been used as an electrolyte. It is understood that a lithium electrolyte has

been proposed and tested but is still a subject of research. The process typically takes

18

between three and five days but sometimes may take several weeks. Successful

treatment can be established by means of an acid/alkaline indicating solution. However,

it should be noted that phenolphthalein changes colour at a pH of about 9.5 (unless a

modified solution of phenolphthalein is used). This is not a passivating condition

and an indicator (Universal indicator) with a colour change closer to pH 12 may

be required to demonstrate that a passivat ing condition has been achieved.

As with cathodic protection and desalination, consideration must be given to

hydrogen evolution at the reinforcement. The re-alkalization process applies some 20

- 50 VDC between the anode and the steel that must be expected to achieve steel

potentials at which hydrogen evolution could take place. It seems unlikely that re-

alkalization would need to be applied to pre-stressed concrete structures.

Re-alkalization requires electrical continuity of the steel in the areas to be

treated, a reasonable level and uniformity in the conductivity of the concrete, no

short circuits between the cathode and the anode and no electrically insulating layers

in he cover zone/bar surrounds. The process requires fewer concrete repairs than the

patch repair alternative. It is also able to treat the whole surface of the zone in

question. There has been strong growth in the use of re-alkalization in recent years

(since the late 1980's) presumably because of its greater convenience and cost

advantage over patch repairs.

3.6 Chloride removal:

Negatively charged chloride ions (Cl-) can be repelled from reinforcement and

move towards an external anode by making the steel cathodic and passing a direct

current through the concrete. This process is known by various names such as electro-

chemical chloride extraction, desalination and chloride removal. It is similar in

operation to cathodic protection by utilizes a temporary anode and a much higher

electrical power density. The cathode reaction generates hydroxyl ions that locally

enhance the alkalinity of the concrete in the vicinity of the reinforcing bars and

encourages their re-passivation. Treatment periods are in the order of 3 to 6 weeks.

Electrolytes employed include water and saturated calcium hydroxide.

The anode types employed are essentially the same as those used for

Realkalisation protection, namely either mesh systems or liquid electrolyte systems

contained within tanks. Sprayed cellulose impregnated with the electrolyte is used with

the mesh anode system. These use either titanium or a steel mesh (which is consumed

during the treatment).

As with other electro-chemical systems, it is necessary to have electrical

continuity across the zone to be treated, no electrical short circuits between anode

and cathode together with a reasonable level and uniformity in the conductivity of

the concrete. The approach minimizes the amount of concrete repair work necessary. It is

claimed hat the technique can be used to treat the whole of the concrete surface and, on

the basis of life cycle costs, that it should be applicable to a wide range of structures. Care

needs to be exercised in relation to potential problems (as with the other electro-chemical

methods, namely hydrogen evolution in the member concerned).

3.7 CATHODIC PROTECTION:

The chloride extraction and re-alkalization repair techniques are temporary

19

processes. Cathodic protection is a similar technique but permanent. It is now well

established and is increasingly becoming accepted as a practical long-term solution for the

rehabilitation of reinforced concrete structures suffering from chloride induced corrosion.

The basis of cathodic protection is to eliminate corrosion by reducing the potential

of the steel to a more electronegative state, thereby converting the whole of the steel

reinforcement into a large cathode. This is achieved by passing a small direct current

between an external anode material and the steel reinforcement material. The anode

material is connected to the positive pole of a rectifier and the negative to the steel

reinforcement. The production of electrons (cause of corrosion), which are consumed

by the oxygen and water in reduction reactions, does not occur at the steel reinforcement.

Instead the system forces electrons into the steel to be consumed in these reactions and thus

protect its integrity. The production of hydroxyl ions at the steel surface (cathodic

reactions) causes the concrete to revert back to an alkaline state thus stopping the

corrosion process.

Cathodic protection of reinforcing steel can be achieved by using sacrificial

anodes or an external direct impressed current source. However, sacrificial anodes

may not be suitable in the atmospheric zones due to the high electrical resistivity of the

concrete.

Types of cathodic protection systems:

3.7.1 Titanium mesh anode/cementitious overlay system:

This has been the system most widely used but other systems appear to have

been overtaking it recently with regards to usage. It is applicable above ground/water

level and provides even current distribution, which minimizes the risk of over

protection. If necessary multiple layers can be used to protect large surface areas of

steel. However, the cementitious overlay can be susceptible to de-lamination, if not

applied correctly. It also imposes extra weight on the structure and can be susceptible to

impact damage.

3.7.2 Slotted/grid anode system:

A dense titanium mesh ribbon or strip is installed in slots cut into the concrete

(generally 25mm x 25mm) and the slots are then backfilled with a cementitious mortar

compatible with the parent concrete). It has a low risk of de-lamination and life can

be enhanced by using a larger anode strip. Minimal concrete cover can affect the

uniformity of current distribution.

3.7.3 Internal anode systems:

The internal anodes are embedded in 12mm diameter holes drilled into the

concrete at depths of upto 300 to 400mm. depending upon the length of anodes required

and the structural component being protected. A graphite based backfill material or a

conductive gel is injected into the holes and the 3mm titanium rods are then inserted into

the anode backfill. The life of the system is basically controlled by the consumption of the

graphite backfill, which is estimated by the manufacturer as 20 years, although recent

use of the conductive gel suggests a life of at least 30 years. However experience is now

showing that anodes of this type in service seem to have difficulties in meeting the

20

lifetime expectations of the manufacturers. The system is especially cost effective on

large elements such as beams, piers and columns but is not suitable for thin sections.

Careful design is required to minimize cable requirements and to ensure optimum

spacing and critical positioning of anodes in the vicinity of the steel.

3.7.4 Electro-conductive tape grease/over-wrap system:

A conductive tape/grease system which provides a conductive path to the

concrete is wrapped around a column or pile followed by titanium mesh. A further

layer of conductive tape over-wraps the mesh anode to secure and provide a

contact surface for the outer face of the mesh anode. Mechanical protection is provided

by either polyethylene or fiberglass impact resistance jackets. This system is

difficult to install on large sections, is susceptible to impact loadings and appearance

becomes a problem.

3.7.5 Electro-conductive tape Qrease/Ranel system:

This system utilizes similar technology as the over-wrap system. However, it

is pre-fabricated fiberglass impact resistant panel, which can be bolted into position.

It is suitable for soffits, columns and beams and it is easy to install. The thickness of

panels and their aesthetic appearance are its negative attributes. The expected life of the

conductive gel also needs consideration.

3.7.6 Water/soil anodes:

In this case remote anodes consist of proven materials such as high

silicon cast it on, lead, silver or 3 - 6mm diameter titanium rod embedded in coke

breeze (conductive backfill) and secure din geo-textile bags in a trench. In shallow

waters, the anodes are dug into the mud whilst those installed in seawater are normally

located flush with piers and housed in a slotted PVC' pipe for protection from boat

damage. These anodes are powered by an independently controlled output from the

Transformer/ Rectifier and protect large areas of reinforcing steel in immersed

concrete structures. These systems are mainly used in conjunction with other

systems to address the problem of current dumping.

3.7.7 Sacrificial zinc anode systems:

Sacrificial zinc anodes can be clamped onto concrete columns, immersed

below the waterline or dug into the mud in order to provide protection to the

buried/submerged and tidal zones. The degree of polarization will vary as a result

of several factors including the amount of current output from the anodes, the rate of

polarization obtained in the submerged/buried section, tidal variations and tidal

resistivity. Over-protection of the steel reinforcement is not a concern as zinc anodes'

current output is self-regulating with low driving voltage of 0.9 to 1.1 volts.

3.7.8 Sprayed zinc CP systems:

This is a very simple system with a very low initial cost outlay. It requires

21

the application of 99.9% pure zinc by arc-spray method at a total thickness of about 400

microns. It is a sacrificial system, which has a life expectancy of 12 to 15 years that can

be extended by whip blasting and re-spraying additional zinc material. It can also

be installed as an impressed current system and a protective coating may be applied

over it to further extend the useful life of the system. Sacrificial zinc anodes are also

use din combination with these systems, which protect the submerged/ tidal zones and

minimize current dumping.

3.7.9 Impressed current systems:

These require electrical connections to distribute the impressed current across

the anode, a DC power supply and an associated control system together with

embedded monitoring probes providing data by which adjustments can be made to

the voltage and currents applied. An installation will normally be divided into a number

of zones, each with its own power supply. The design of the zones needs to take

account of a number of factors such as the -

Variation in moisture and chloride contents (and hence the conductivity, of

the concrete) across the structure.

Continuity of reinforcement in different areas,

Presence of joints in the structure,

Requirements for different anode types

Variation in reinforcement provision.

Commissioning is a very important stage in achieving an effective and

durable CP system. It provides the opportunity to perform a variety of tests and trials

establishing the initial behaviour of the CP system, make adjustments to current and

voltage supplies and to verify control criteria. Once it has been established that an

impressed current CP system is providing protection to all reinforcement, it is

essential that the operation of the system be monitored and that it be properly

maintained. Changes occur in the concrete over the first few months of operation

(increase in resistivity due to removal of chloride ions and drying out of concrete).

The objective of the monitoring is to ensure that all reinforcement remains effectively

protected. For concrete structures with old types of pre-stressing steel, the risk of

hydrogen-embitterment shall be analyzed when considered the implementation of

impressed current CP systems.

3.8 Coatings to Concrete: In the past it was believed that concrete by itself is a durable material, which

needs no protection or maintenance. This belief is no more hold good particularly on

account of environmental pollution, industrial fumes and contamination of ground water.

In addition to the coating of reinforcement by appropriate material, a surface coating to

the concrete member is given to increase the durability further. The coatings serve the

dual purpose of protection and decoration. Fig2 shows the reduction in depth of

carbonation of the protected concrete.

Giving protective coatings to major concrete structures such as bridges, flyovers,

industrial buildings and chimneys have become a common specification in India as in

22

other countries. Four km long bridge on national highway at Cochin was recently coated.

Almost all the flyovers at Mumbai are being coated for additional durability.

There are number of approved coating systems available in the country however

selection of coating depends on the severity of environment and the component of the

bridge.

3.8.1 Epoxy Painting System by CECRI System:

Central Electro-chemical Research Institute at Karaikudi has developed a coating

system for controlling corrosion. This system is applied on the concrete surface and

helps in controlling carbonation and weathering effects. The system comprises of 4

coats such as primer coat, middle coat and top coat all these are epoxy based. The fourth

coat is finish coat of polyurethane and is recommended wherever the surface or part

of the structure is exposed to ultra violet radiation.

Before application, the substrata is thoroughly cleaned to remove the dust,

hardened cement slurry, oily residues etc., by scrubbing with coarse wire brushes,

grinding or sweep blasting methods depending on site requirements. Residual

amounts of de-moulding agents, curing agents should be completely removed. Any

cracks, crevices or surface blemishes should be treated with sealant prior to primer

application. The subsequent coats shall be applied by brush or spray with an interval of

24 hours between the two coats.

Application:

Concrete surface to be painted shall be allowed maturation time of minimum

28 days before applying primer coating. Primer coating shall be applied to the cleaned

surface after surface preparation within the pot life. After air-curing, intermediate and

top coatings should be applied with time lag as per manufacturer's specifications. The

coating shall be applied by brush or air-less spray gun.

The paint application should aim to achieve minimum dry film thickness as

specified by CECRI. Some typical thickness used are as under:

Primer 100 microns

Middle coat 100 microns

Top coat 120 microns

Finishing coat 40 microns

The DFT (Dry film thickness) shall be measured on 100x100mm steel plate

attached with epoxy on the concrete surface at the rate one per l0m2.

3.8.2 Epoxy Phenolic IP Net (Inter-Penetrating Polymer Network)

Protective Coating system (CBRI Roorkee):

MATERIALS

1. The coating materials shall meet the standards specified by various codes and

formulation set forth by the patenter.

23

2. A written certification shall be furnished to the Department that properly identifies the

number of each batch of coating material used in the work, material, quantity represented,

date of manufacture, name and address of manufacturer and a statement that the coating

material used must meet the requirements specified by CBRI-Roorkee.

3. The coating material shall be stored in the manner as per recommendations of the

manufacturer until ready for use. The coating material shall be used within the

manufacturer’s written recommended shelf life.

4. When a representative sample of the material is to be sent to outside laboratory, then

the sample shall be packaged in an airtight container and identified by batch number. The

sample will be got tested at Tenderer/ Contractor’s cost.

SPECIFICATION OF COATING MATERIAL

S. No. Description Primer coat Middle coat Top coat

1. Base

Interpenetrating

Polymer

(Epoxy phenolic)

Interpenetrating

Polymer

(Epoxy phenolic)

Interpenetrating

Polymer

(Aliphatic

Polyurethane)

2. Pot life 1 Hour for 2 lt.mix 1 Hour for 2 lt.mix 1 Hour for 2 lt.mix

3. Curing Air curing Air curing Air curing

4. Colour Clear Yellow/Grey Yellow/Grey

5. Shelf Life One year in tightly

sealed container One

One year in tightly

sealed container

One year in tightly

sealed container

6.

Dry film

thickness

(Microns)

55-65 per coat 90-100 per coat 40-50 per coat

7. Coverage 5-6 sq.mt/lt. 4-5 sq.mt/lt 6-7 sq.mt/lt

8. Recommended

No. of coats One One One

9. Recoatibility

Subsequent coat shall

be applied after 6

hours to 7 days

4 hours to 7 days.

Ensure the surface is

dust and deposit free

prior to application.

N. A.

10. Mix proportion

Base:1 PBV*/

Curing Agent:1 PBV*

*PBV-parts by

volume

Base:1 PBV*/

Curing Agent: 1PBV*

*PBV-parts by

volume

Base:1 PBV*/

Curing Agent: 1PBV*

*PBV-parts by

volume

Material should conform to following properties:

a. Tensile strength: Minimum tensile strength of the coating must be 15 N/mm2 and it

should be determined as per ASTM D-2370-73

b. Elongation: Minimum elongation of the coating must be 15% and it should be

determined as per ASTM D-2370-73

24

c. Specific permeability: The maximum value must be 0.15 mg/cm2/mm/24hr and it

should be determined as per ASTM D-1653-74

d. Adhesion with concrete: The minimum adhesion with concrete by pullout method

must be 2.5N/mm2 and it should be determined as per BS-3900-E-10-79

SURFACE PREPARATIONS

In order to have better bonding, the concrete surface should be clean, dry and

mechanically sound. The surface of the concrete structure to be coated shall be cleaned of

all traces of mould oil, laitance, salt deposits by mechanized means. The surface should

be thoroughly scrubbed using power tools/sweep blasting. Finally, the surface should be

washed with clean water jet to remove any salt deposits. The surface should be dried. All

the protrusions should be removed and cracks, joints should be sealed with sealant.

APPLICATION OF COATING

1. Mix the base and curing agent in prescribed proportion by volume thoroughly and

allow it to remain in a container for ten minutes.

2. A primer coating of IPN polymer shall be applied to the cleaned surface after surface

preparation within the pot life.

3. After air curing, intermediate and top coating should be applied with time lag as per

manufacturer’s specification.

4. The coating shall be applied by airless spray or other approved means.

COATING THICKNESS

During the application of IPNet systems clean, abraded steel plates of

approximately 10cm x 8cm shall be adhered to the concrete surface by means of putty/

adhesive in such a way that these can be detached. IPNet system can be applied over the

plates in the course of application over the concrete surface. Dry film thickness (DFT)

can be measured using magnetic electrometer. DFT measurement should be done at every

500-to 600-sqm areas or as per the direction of Engineer-in-charge.

For acceptance purpose, at least 60% of all recorded total thickness measurement

of the coating after curing shall be 200 ± 10 microns (minimum). Thickness measurement

below 200 ± 10 microns shall be considered cause for rejection. The upper thickness limit

does not apply to repaired areas of damaged coating.

PERMISSIBLE COATING DAMAGE AND REPAIR OF DAMAGED COATING

1. All coating damage shall be repaired with patching material by the contractor at his

own cost.

2. Repaired areas shall have a minimum coating thickness of 200 ± 10 microns

3. Repair of damaged coating shall be done in accordance with the patching material

manufacturer’s written recommendations within the accepted rates.

25

3.8.3 Wet surface compatible Substructure coating system (CECRI Karaikudi):

MATERIALS

1. The coating materials shall meet the standards specified by various codes and


2. A written certification shall be furnished to the Department that properly identifies the


date of manufacture, name and address of manufacturer and a statement that the coating

material used must meet the requirements specified by CSIR/CECRI Karaikudi.

3. The coating material shall be stored in the manner as per recommendations of the



4. When a representative sample of the material is to be sent to outside laboratory, then




The coating system shall be moisture compatible for applying in wet/dry conditions as

well as foundations and subsoil structures.

The coating system shall conform to the following:

Base Quick curing two component moisture compatible

Resin System

Drying time (touch dry) 2 hours

D.F.T. in two coats 300 – 350 microns

Chemical resistance Excellent against chlorides, salts, sulphate, alkalies

Salt spray test Should pass as per ASTM-B-117

1000 hrs minimum

Adhesion 3.0 KN minimum as per ASTM-D-4541

Resistance (Impedance) 108 ohms

Surface preparation As per manufacturers specification or as per relevant

IS codes



mechanically sound. The surface of the concrete structure to be coated shall be

cleaned of all traces of mould oil, laitance, salt deposits by mechanized means. The

surface should be thoroughly scrubbed using power tools/sweep blasting. Finally, the

surface should be washed with clean water jet to remove any salt deposits. All the

26

protrusions should be removed and cracks, joints should be sealed with sealant as per

Central Electrochemical Research Institute, Karaikudi (CECRI).


1. Mix the base and curing agent in prescribed proportion by volume thoroughly and

allows it to remain in a container for ten minutes.

2. First and Top Coat should be applied with time lag as per manufacturer’s

specification.



COATING THICKNESS

1. Measurement of coating thickness shall be made using thickness measuring gauge

and Elcometer. The minimum total thickness of coating (1st& Top coat) must be 300-

350 microns

2. For acceptance purpose, at least 60% of all recorded total thickness measurement of

the coating after curing shall be 300-350 microns (minimum). Thickness

measurement below 300 microns shall be considered cause for rejection. The upper

thickness limit does not apply to repaired areas of damaged coating.



own cost.

2. Repaired areas shall have a minimum coating thickness of 300-350 microns



3.8.4 Solvent/Water based Acrylic Elastomeric Coating

3.8.5 MATERIALS

a. The coating materials shall meet the standards specified by various codes and


b. A written certification shall be furnished to the Department that properly identifies the


date of manufacture, name and address of manufacturer

c. The coating material shall be stored in the manner as per recommendations of the



d. When a representative sample of the material is to be sent to outside laboratory, then



27


S.

No. Description Primer coat Middle coat Top coat

1. Base Aqueous based

Acrylic

Aqueous based

Acrylic

Aqueous based

Acrylic

2. Curing Air curing Air curing Air curing

3. Colour Clear Pigmented Pigmented

4. Shelf Life One year in tightly

sealed container

One year in tightly

sealed container

One year in tightly

sealed container

5. Coverage 7-8 sq.mt/lt. 4-5 sq.mt/lt 4-5 sq.mt/lt

6. Recommended

No. of coats One One One

7. Recoatibility

Subsequent coat shall

be applied after 24

hours to 7 days

24 hours to 7 days.

Ensure the surface is

dust and deposit free

prior to application.

N. A.

8. Dry Film

Thickness Total DFT in Three Coats 225±20 microns

Material should conform to following properties:

1. Specific Gravity IS-345 1.32 to 1.40

2. Solid Content IS-345 70% ± 3

3. UV Resistance ASTM-G-53 Should Pass

4. Adhesion ASTM-D-4541-02 Should Pass

5. Bend Test (Conical Mandrell) ISO-6860 Should Pass

6. Difusion Against Carbon

Dioxide Tested like ASTM-E-96 Should Pass

7. Resistance to water immersion ISO-2812-2 Should Pass

8. Electrochemical Polarisation

Test Tafel Extrapolation Should Pass



mechanically sound. The surface of the concrete structure to be coated shall be cleaned of

all traces of mould oil, laitance, salt deposits by mechanized means. The surface should

be thoroughly scrubbed using power tools/sweep blasting. Finally, the surface should be

washed with clean water jet to remove any salt deposits. The surface should be dried. All

28

the protrusions should be removed and cracks, joints should be sealed with sealant as per

manufacturers recommendation.


1. Thoroughly mix the entire contents of the packaged tin prior to use.

2. A primer coating of the coating shall be applied to the cleaned surface after surface

preparation.

3. After air curing, intermediate and top coating should be applied with time lag as per

manufacturer’s specification.

4. The coating shall be applied by airless spray or other approved means.

COATING THICKNESS

During the application of the coating, clean abraded steel plates of approximately

10cm x 8cm shall be adhered to the concrete surface by means of putty/ adhesive in such

a way that these can be detached. The coating can be applied over the plates in the course

of application over the concrete surface. Dry film thickness (DFT) can be measured using

magnetic electrometer. DFT measurement should be done at every 500-to 600-sqm areas

or as per the direction of Engineer-in-charge.

For acceptance purpose, at least 60% of all recorded total thickness measurement

of the coating after curing shall be 225 ± 20 microns (minimum). Thickness measurement

below 225 ± 20 microns shall be considered cause for rejection. The upper thickness limit

does not apply to repaired areas of damaged coating.

COATING CONTINUITY

The coating shall be visually inspected after curing for continuity of the coating

and shall be free from holes, voids, contamination, cracks and damaged areas discernible

to the unaided eye.



own cost.

2. Repaired areas shall have a minimum coating thickness of 225 ± 20 microns


manufacturers written recommendations within the accepted rates.

Bridge piers and girders are of considerable dimensions. Freshly made concrete

members contain plenty of water in the pore structures. It takes long time to dry. Such

freshly made concrete structures should not be coated with epoxy or other materials,

which will seal off and prevent the internal moisture from going out in consonance with

atmospheric conditions. The moisture trapped inside the concrete can do untold harm to

the durability of concrete in addition to damaging the protective coating itself. For better

durability, the concrete should be able to “breathe” i.e. water vapour should be able to

migrate from inside to outside and from outside to inside. But water as it is, should not be

able to enter from outside to inside. The protective coating given to the concrete should

be of the above characteristics.

Therefore, it is pointed out that the epoxy coating, which does not allow the

concrete to breathe, should not be used for coating concrete members.

Instead, the protective coating should be based on acrylics which retains the

breathing property of concrete, while protecting the concrete from other harmful

environmental agencies, in particular entry of water and carbonation.

29

In addition, epoxy based coating material is not resistant to ultra violet rays when

exposed to sunlight and also it is not flexible. Whereas the coating material based on

acrylic polymer is resistant to ultra violet rays of sun and is flexible.

Coating is not only required for bridges, flyovers and industrial structures, it is

also required for very thin members like fins, façade, sun breakers and other delicate

concrete structures where specified amount of cover can not be given. Therefore, acrylic

based protective cum decorative coatings can be given for additional durability of such

concrete members.

a

REFERENCE :-

Specifications for Road & Bridge Works issued by MORT & H and published by Indian Road Congress.

IRC – Highway Research Board – Special Report on “State of Art : Corrosion & Corrosion Protection of Pre-stressed Concrete Bridges in Marine Environment.”

Biggest world map was drawn on cooling

tower in Germany using Emce Colour -

flex for protection of concrete subjected to

aggressive acidic environment

Acrylic based protective cum

decorative coating given to J-J

Flyover at Bombay. particularly

being in coastal region.

30

Steel Corrosion in Concrete by Aron Bentur, Sidney Diamond & Neal S.Berke published by E&FN Spon – London.

Corrosion of Reinforcement in Concrete Construction by C.L. Pagci P.B. Bamforth, J.W. Figg (U.K.).

Corrosion Reinforced Steel in Concrete by Tonini-Gaides - ASTM Special Publication 713.

Concrete bridge Practice (Construction, Maintenance & Rehabilitation by Dr. V.K. Raina.

FIP Recommendations – Corrosion Protection of Unbonded Tendons.

FIP Guide to Good Practice – Maintenance of Pre-stressed Concrete Structures.

IS 12594 : 1988 HOT – DIP Zinc Coating on Structural Steel Bars for Concrete Reinforcement.

CRRI Paper on “Critical Evaluation of Fushion Bonded Epoxy Coated Reinforcements and other Protective Coating on Reinforcement” by M.V. Bhaskar Rao.

FIP Guide to Good Practice – Practical Construction.

Technical Report by Mr. P. Xercavins. PX consultants, France ( Formerly Technical Director of STUP, France).

Corrosion Handbook, a Joint Publication of The Electrochemical Society of India and Associate (Data) Publishers Pvt. Ltd.

Report on Investigation of Sharavathi Bridge, by STUP Consultants Limited/Hyder Consulting Limited, U.K. and STATS, U.K.

Documents

0005 India Regulation on Coating