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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
http://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildingshttp://www.sedigest.in/article/repair-and-rehabilitation-buildings8/11/2019 Repair of Corrosion Affected
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