Repairof RCC

8/11/2019 Repairof RCC

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REPAIR OF CORROSION AFFECTEDREINFORCED CONCRETE STRUCTURES


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Introduction

What is corrosion?

Causes of corrosion Materials for repair

Repair based on extent of damage

Some procedures of repair.

Sealing of cracks.

Conclusion

SCOPE OF SEMINAR


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IntroductionReinforcing concrete structures deteriorate under attack

from various external elements.

Particular concern toady is the corrosion of thereinforcing steel, which is affected mainly through carbonationand chloride attack.

Corrosion affected RC structures are more prone tocracking, incurring costs of repairs. This gives rise to need for

proper repair of structures using the cost effective materialsavailable.


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WHAT IS CORROSION?

The process of formation of rust over the surface ofreinforcing bar and resulting in the depassivation ofsteel is known as corrosion.


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CORROSION PROCESS:

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, at which the protective film is destroyed

and the steel begins to corrode, when oxygen and moisture are

present in the steel concrete interface.


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CAUSES OF CORROSION IN REINFORCEDCONCRETE STRUCTURES

CARBONATION

CHLORIDE ATTACK


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CARBONATION

Reduction of pH in cover concrete which causesloss 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 aselectrolyte, and the area adjacent to concentrationof chloride ions on the reinforcement steel willbecome 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

DAMAGE1. 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 coverConcrete has spallen and reinforcement has been exposed.

Step 1The repair process is started by cutting away all the loose anddeteriorated concrete until the hard core is reached, preferably

behind the corroding Reinforcement.

Step 2All 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 thesame 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 5In order to build up the section, either cement based repair or resin

based repair is carried out.

Cement based repairs

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

bond is required and the patching mortar is applied, while the slurryis still tacky.


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After the prepared surfaces have been coated with bonding agentor a coating of neat cement slurry, the repair material consistingof 1:3 cement and sand is applied in layers not exceeding 20mmthick.

Resin based repairs

Step 7As usual, the priming coat is applied over the prepared surfaces.The interval between coats should not be too long, otherwisethere will be bond failure.


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2. Large volume repair

In case of large volume repair, the member is repaired by usingPoured 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 maximum20mm or 10mm size is adopted in the concrete mix, with suitableshrinkage compensating agent.


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Preplaced concrete

The technique is best suited for certain types of repair, particularly in under water work. In this method formwork iserected in the normal way but it is first filled with clean specified

coarse aggregate. Later cement grout is pumped into the formsfrom bottom until all the voids are filled as the air or water Ivented at the top.

This method offers quality concrete without segregation withminimum during shrinkage.


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3. Sealing of cracks

For this, the cause of crack has to be determined. If the cause ofthe crack is such that it is unlikely to recur, then it can befilled with a rigid material. But, if the crack is causeddue to movement and is likely to continue then any attemptto seal the crack against further movement may cause a newcrack along the side of the old one .


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Repair of cracks where no further movement is

expectedThe procedure for carrying out this type of repair is as follows:Step 1The crack is thoroughly cleaned using compressed air.

Step 2Superficial seal is applied over the crack at the surface by using afast setting polyester resin or a thermoplastic material.

Step 3Injection is started at the lowest point and when resin reaches thenext higher point, the injection gun is moved up to the next andthe lower point is sealed. The process is continued until the whole

crack gets sealed.


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Repair of cracks where further movement isexpected

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 atthe surface and sealing it with an elastic material, suchas polysulphide rubber.


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4. Surface coatings

It is necessary,

After the completion of repair work, to treat both the repairedareas and the rest of the structure with some coatings

To reduce the permeability of concrete, to moisture, carbondioxide, 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 beenexposed.


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Fig shows the RC Columns which are affected by corrosion


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Fig shows the structures which are affected by corrosion .


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Conclusion RCC Structures are subject to deterioration through differentmechanisms.

Periodic maintenance of structures is essential. Although many repair materials have been introduced in theconstruction industry in the recent past, careful judgment should beexercised by the engineers, while selecting them.

The decision should be governed by the results of the insitu testingcarried out on the corrosion affected or damaged structure.


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REFERENCES

Ashwini K. Sinha, 2013, repair & rehabilitation of RCCstructures damaged by corrosion, Corrosion & WaterManagement Consultants , New Delhi.

A.M.Neville Properties of Concrete, Fifth Edition,

published by Pearson Education Ltd, 2012 Allen.R.T.L , Repair Of Concrete Structures, John Willey &Sons,1994M.S. Shetty Concrete Technology, Seventh Edition,

published by S. Chand publishing, 2010 www.sedigest.in/article/repair-and-rehabilitation-buildings

www.civil-resources.blogspot.in/2010/06/repair-of-

corrosion-affected-reinforced.html
http://www.cwmcindia.com/http://www.cwmcindia.com/http://www.cwmcindia.com/http://www.cwmcindia.com/


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Repairof RCC

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