repair of corrosion affected

8/11/2019 Repair of Corrosion Affected

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REPAIR OF CORROSION AFFECTED

REINFORCED CONCRETE STRUCTURES


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WHAT IS CORROSION?

The process of formation of rust over the surface of

reinforcing bar and resulting in the depassivation ofsteel is known as corrosion.


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CORROSION PROCESS:

In concrete, the presence of abundant amount of calcium hydroxide

and relatively small amount of alkali elements, such as potassium and

sodium .

When concrete structure is often exposed to atmosphere, chloride

ions from these will slowly penetrate into the concrete, the chloride

ions will eventually reach the steel and then accumulate to beyond a

certain concentration level.


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CAUSES OF CORROSION IN REINFORCED

CONCRETE STRUCTURES

CARBONATION

CHLORIDE ATTACK


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CARBONATION

Reduction of ph in cover concrete which causes loss of

passive oxide layer

Low pH caused by reaction of Calcium Hydroxide

in concrete with atmospheric Carbon Dioxide


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CHLORIDE ATTACK

Caused by chlorides breaking up passive oxide layer

The moisture in concrete pores will act as electrolyte, and thearea adjacent to concentration of chloride ions on the

reinforcement steel will become cathode initiates corrosion.


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MATERIALS FOR REPAIR

Cement/Sand mortars.

Polymer Latex.

Epoxy Resins.

Polyester Resins.


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STRUCTURAL REPAIRS BASED ON EXTENT OF DAMAGE

1. Repairs to spallen concrete portions (Steel and concrete) Cement based repairs

Resin based repairs.

2. Large volume repairs.

Poured concrete.

Preplaced concrete.

3. Sealing of cracks

Cracks with no further movement expected.

Cracks with further movement expected

4. Surface coating


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1. Repair of a severely corrosion damaged member, where cover

Concrete has spallen and reinforcement has been exposed.

Step 1The repair process is started by cutting away all the loose and

deteriorated concrete until the hard core is reached, preferably

behind the corroding Reinforcement.

Step 2

All exposed reinforcements must be thoroughly cleaned. Loose

rust or any contamination is removed by abrasive blast cleaning

Step 3Severely corroded steel bars are replaced with new bars of the

same type and size, either welded or tied to the existing bars.


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Step 4

After the corrosion affected bars are replaced in position,

immediately a protective primer is applied.

Step 5

In order to build up the section, either cement based repair or resin

based repair is carried out.

Cement based repairs

Step 6The slurry (bonding coat) is applied to all concrete surfaces to which

bond is required and the patching mortar is applied, while the slurry

is still tacky.


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After the prepared surfaces have been coated with bonding agent

or a coating of neat cement slurry, the repair material consisting

of 1:3 cement and sand is applied in layers not exceeding 20mm

thick.

Resin based repairs

Step 7

As usual, the priming coat is applied over the prepared surfaces.

The interval between coats should not be too long, otherwise

there will be bond failure.


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Remove of all defective concrete and expose corroded

reinforcing bars to their full circumference

Remove the corrosion product from reinforcing bars until

they shine

Apply anti-corrosion protective priming coat to

protect reinforcing bars

Patch with repair mortar and resurface to required

thickness

Apply protective coating and follow up with

decorative painting


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2. Large volume repair

In case of large volume repair, the member is repaired by using

Poured concrete or Preplaced concrete.

Poured concrete

Defective concrete is first removed and loose concrete is chippedaway from the face and around the reinforcement.

The reinforcement is protected by applying corrosion inhibiting

paint like cement based polymer slurry or a resin based slurry.

Depending on the thickness to be poured, aggregate of maximum

20mm or 10mm size is adopted in the concrete mix, with suitable

shrinkage compensating agent.


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Preplaced concrete

The technique is best suited for certain types of repair,

particularly in under water work.


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3. Sealing of cracks

For this, the cause of crack has to be determined. I f the cause ofthe crack is such that it is unlikely to recur, then i t can be

fi l led with a rigid mater ial. But, if the crack is caused

due to movement and is l ikely to continue then any attempt

to seal the crack against further movement may cause a new

crack along the side of the old one.

Repair of cracks where no further movement is

expected

The procedure for carrying out this type of repair is as follows:


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Step 1

The crack is thoroughly cleaned using compressed air.

Step 2Superficial seal is applied over the crack at the surface by using a

fast setting polyester resin or a thermoplastic material into which

injection nipples are fixed at intervals.

Step 3

Injection is started at the lowest point and when resin reaches the

next higher point, the injection gun is moved up to the next and

the lower point is sealed. The process is continued until the whole

crack gets sealed.


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Repair of cracks where further movement is

expected

When a crack is subjected to continuing movement,

it is necessary to reduce the strain in it to reasonableamount. This can be easily done by widening the crack at

the surface and sealing it with an elastic material, such

as polysulphide rubber.


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4. Surface coatings

It is necessary,

After the completion of repair work, to treat both the repaired

areas and the rest of the structure with some coatings

To reduce the permeability of concrete, to moisture, carbon

dioxide, and other aggressive agents.

To give aesthetic look to the structure by coating the patches.


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Some of available repairing materials in India by

Dr.Fixit


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Fig shows the structure where cover concrete has spallen and reinforcement has been

exposed.


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Fig shows the structures which are affected by corrosion.


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Conclusion

Although many repair materials have been introduced

in the construction industry in the recent past, careful

judgment should be exercised by the engineers, while

selecting them. The decision should be governed bythe results of the insitu testing carried out on the

corrosion affected or damaged structure.

Maintenance is better than Repair


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REFERENCES:

Concrete technology by M.S. Shetty

Properties of concrete by A.M.Neville

The Repair of Concrete Structuresby

RTL.Allen,S.C.Edward & J.D.N.Shaw.

Dr.Fixit product guide.

Rebuild Vol-2 by Dr .Fixit,

cpwd.gov.in/Units/handbook.pdf

www.sedigest.in/article/repair-and-rehabilitation-buildings

tp://ceres.udc.es/ITS_Caminos/Optativas/.../REHABILI

TACION.pdf
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