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ByD.SHANKAR

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NEED FOR STRENGTHENING

Damages to structural parts due to aging of constructionmaterials or fire damages, corrosion of reinforcement.

Errors in construction due to insufficient design dimensionand insufficient reinforcing steel.

Load increases due to higher live loads, increase wheelloads, installation of heavy machinery.

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Assessment procedure for evaluating the damaged structure

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Physical Inspection

Study of documents

Estimate of load activity

Estimate of environmental effect

Diagnosis

Retrospective analysis

Diagnosis conformed

Assessing of Structural adequacy

Choice of course of action

Load testEstimate offuture use

yesNo

Material tests

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CORROSION

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CORROSIONThe corrosion of reinforcing steel in concrete is a major

problem faced by the civil engineers and surveyors. Today asthey maintain an ageing infrastructure.

Corrosion is the gradual distraction of material (usuallymetals),by chemical reaction with its environment.Rust staining, corrosion cracks and cover spalling are alsooccurred

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RUSTING OF BARS

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CORROSION OF STEEL

Difference in electrical potential occur+ve ferrous ions (fe++) at anode pass into solution

-ve free ions (e) combines with water and oxygen to formhydroxyl ion

These combine with ferrous ions to form ferric hydroxidewhich is converted to rust.

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DAMAGES DUE TO CORROSION

Loss of strength in the reinforcement.

Formation of brown patches on the concrete surface.

Formation of multiple wide cracks.Spalling of cover concrete.

Buckling of bars.

Bulging of concrete.

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PROTECTIVE COATING FOR

REINFORCEMENT Methods of coating

Cement slurry coating.

Phospatic jelly coating.

Epoxy coating.

Plastic coating.

Galvanizing.

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CEMENT SLURRY COATINGCement slurry coating provides short-term protection until

placement of concrete.

Coating is the mixture of cement, silica and polymer.

It is found to be impermeable to water, chlorides and CO 2.

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EPOXY COATINGEpoxy coating is formed by the application of an Epoxy resing

with curing agent,catalysts,pigments and flow control agents.

Epoxy coating provides long term protection against corrosion.

Cost of implementing this method is significantly high

compare to other method of coating.

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PLASTIC COATINGPlastic coating is very similar to epoxy coating, the Plastic

coating is very effective in the preventing corrosion of

reinforcement even in high alkaline or chloride contaminated

environment

The reduction in bond between plastic coated bars and the

concrete is quite substaintial.

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GALVANIZINGGalvanizing gives the protection to the reinforcement

against corrosion by means of metallic coating( ZINC).

This method reduces the effects of chlorides, but it is not

advisable to use in the highly chloride contaminated

environment.

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STRENGTHENING OF BUILDING

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Strengthing techniques Strengthing can be done by following techniques

Jacketing

Underpinning Shoring Resin injection Epoxy resin

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JACKETING CONCRETE COLUMN

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JACKETINGJacketing is the process of fastening a durable materialover the concrete and filling the gaps with grout.The material used for jacketing are metal,rubberferrocement, plastic .when jacket is provided around the periphery of thecolumn is called collar.

The main function the collar is to transfer the vertical loadto the column

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DISADVANTAGE OF JACKETINGIt can damage the existing columnIt takes More time consumption.

It is more expansive.

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Underpinning may be necessary for a variety

of reasonsThe original foundation is simply not strong or stableenough.

The usage of the structure has changed.

The properties of the soil supporting the foundation may

have changed .

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STRENGTHENING OF FOUNDATION

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Common methods in underpinning

i)Micropiles ii)Jetgrouting

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SHORINGShoring is the temporary structure for providing supportand stability during repair and alteration.Shoring can be used for various circumstance, they are

Alteration are carried out in adjacent building forremodelling , strengthening of foundation etc..The stability of structure is endangered due to unequalsettlement during construction

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SOME OTHER METHODSThis an be achieved(a) By grouting(b) By providing wire mesh(c) By connection between existing stone walls.

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GROUTING

Grouting is a process of group improvementattained by injecting fluid like material intosubsurface soil or rock.

A number of holes are drilled in the wall,(2 to 4 m 2). First water is injected in order to wash the wall

inside and to improve the cohesion between thegrouted mixture and the wall elements.

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Conti..Secondly a cement water mixture (1:1) is grouted at low

pressure (0.1 to 0.25 MPa) in the holes starting from the lowerholes and going up.

Alternatively, polymeric mortars may be used forgrouting. The increase of shear strength can be achieved.

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STRENGTHENING OF STONE WALLS In stone buildings of historic importance consisting offully dressed stone masonry in good mortar effectivesewing of perpendicular walls can be done by drillinginclined holes through them, inserting steel rods andinjecting cement grout.

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Thank You