Repair Procedures Durai Maruthu

8/11/2019 Repair Procedures Durai Maruthu

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Various repair procedures recommended by

ACI Committee-224 are listed below:

Resin injection Stitching

Bonding of external reinforcement

Routing and sealing

Drilling and plugging Chemical grouting

Flexible sealing

Portland Cement grouting.


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Resin Injection

Cracks as narrow as 0.05mm can be bonded by injection of

epoxy. This technique consists of drilling holes at close

intervals along the cracks and injecting epoxy under pressure

in a controlled manner to fill the cracks, thereby restoring the

structure to its original design capability and preventing

further downgrading of the structure. This repair technique is

widely used in the repair of building, bridges, dams and other

types of structures.


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Fig. 1 Diagram of crack injection


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Fig. 2 Use of T- injection ports flush on concrete

surface


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Fig. 3 Use of injection ports in

drilled holes


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Stitching

This technique is used when the tensile stress must be established

across the major cracks. This method involves drilling holes on both

the sides of the crack. Grouting is done after stitching U shaped

metal units with variable length, which are called dogs across the

cracks and along the lengths. Stitching the cracks tends to stiffen the

structure locally. The dogs should be of variable lengths and so located

that the tension transmitted across the crack does not revolve on single

plane, but is spread over the area. The legs of the dogs are anchored

with the help of either a non shrink grout or an epoxy resin based

bonding system.


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Fig. 5 Repair of crack by stitching


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Epoxy adhesives have the distinct advantage of being

able to bond dissimilar materials. In areas of high

shear stress, additional reinforcing bars in the form of

shaped stirrups may be bonded externally to concrete.

The main advantage in strengthening structures by

this method is to achieve higher shear strength

between the steel resin adhesive interface.


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Routing and Sealing

It is the simplest and most common technique

applicable for sealing both fine pattern cracks and

larger isolated defects to prevent water from reaching

the reinforcing steel. The routing operation consistsof preparing a groove at the surface that is

sufficiently large to receive an approved sealant. A

minimum surface width of 6mm (0.25in) is desirable

for repairing. The surface of the routed joint shouldbe cleaned with an air jet and allowed to dry before

placing the sealant.


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Fig.4 Repair of crack by routing and sealing


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Drilling and Plugging

This technique is applicable when cracks run instraight lines and are accessible at one end. Thismethod is most often used to repair vertical cracksin retaining walls. A hole of 50mm to 75mm

diameter is drilled along the crack. The hole mustbe large enough to intersect the crack along its fulllength. The drilled holes are then cleaned andfilled with grout. The grout key preventstransverse moment of the sections of concrete

adjacent to the crack. The key will also reduceheavy leakage through the crack and loss of soilfrom behind the retaining wall.


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Fig. 7 Repair of crack by drilling and

plugging


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Fig.6 Examples of external

prestressing


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Chemical Grouting

Chemical grout consists of a solution of two

or more chemicals, which form a gel or a

solid precipitate of foam. Cracks in

concrete as narrow as 0.05mm can be filled

with chemical grout. The advantage of

chemical grout is that it can be applied in

most environments. But it needs a highdegree of skill for satisfactory applications.


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Flexible Sealing

Active cracks are first routed out and cleaned by sandblast or buy

air/water jet or both. Then the routed portion is filled with a suitable

flexible sealant. A bond breaker as shown in fig 2.10 is provided at the

bottom of the sealant, to undergo the volume changes. The bond

breaker may be a polyethylene strip, pressure sensitive tape or other

material, which will not bond to the sealant before or during curing.

This method is a very economical one and may be used in the repair of

interior of tanks, roofs or other areas, not subjected to traffic or

mechanical loads. Repair of crack using flexible sealant is shown in fig

2.11.


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Portland Cement Grouting

Portland cement grout may be used to repair wide cracks, particularly

in gravity dams and thick concrete walls. The repairing procedure

consists of cleaning the cracked concrete surface, installing the built-

up seats (grout nipples) astride the crack and sealing the crack

between the seats with a cement grout. Grout mixtures contain cement

and water, or cement, sand and water depending on the crack width.

However, the water cement ratio must be kept as low as practical to

maximize the strength and minimize shrinkage. Water reducers or

other admixtures may be used to improve the properties of the grout.


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Autogenous healing:

The inherent ability of concrete to heal crackswithin itself is termed as autogenous healing.

The mechanism where by healing occurs is the

carbonation of calcium oxide and the calciumhydroxide in the cement paste by thecarbondioxide present in the surrounding air andwater.

The resulting calcium carbonate and calciumhydroxide crystals precipitate, accumulate andgrow out from the cracks.

Repair Procedures Durai Maruthu

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