Advanced Techniques for Repair and Rehabilitation in Construction

8/12/2019 Advanced Techniques for Repair and Rehabilitation in Construction

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Advanced Techniques for Repair &

Rehabilitation in ConstructionAnurag Sharma (UC0306)

Karan Deshmukh (UC1106)

Saravanan Panneervel (UC3606)

Dhruv Bhavsar (UC 3706)


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Rehabilitation Strategies & Measures

Rehabilitation

Recover OriginalPerformance

Repair Damage &deterioration

Upgrade originalperformance

Stiffen existingstructure

Strengthenexisting

structure

Reduceirregularity

UsingSupplemental

damping device

Reduce Seismicresponse

Reduce Masses

Isolate existingstructure


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Repair Methods

Cosmetic repairs onlyimprove the visualappearance of componentdamage and may restorenon-structural properties(weather protection) but

any structural benefit isnegligible.

Structural repairsintends to restore structuralproperties.


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Strengthening Chemically Deteriorated

Concrete Structures


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What the method is

The structural integrity of chemically-deteriorated reinforced concretebeams was restored by repairing one set of beams by epoxide resin latexand another by polymer-based latex system.

The beams were exposed to Sodium Sulphate solution for 3.5 monthsunder alternate wetting and drying cycles to simulate severe corrosiveconditions.

Protection of concrete from the corrosive action of chemicals, wet gasesetc. is receiving considerable attention today.


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How the Beams were Strengthened

The impregnator used for strengthening the original concrete matrix is avital element in the rehabilitation method.

It provides additional binder into the deteriorated concrete and acts as acomposite filler to fill up voids, honeycombs, deteriorated cement paste

binder etc.

The impregnator penetrates into concrete merely by virtue of its lowviscosity (2 to 4 Cps) and strengthens the cement matrix.

This type of strengthening is adopted in most of the European countriesand the USA for strengthening bridge decks, RC structural elements,hydraulic structures etc.


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Modifications dueto the System of

Treatment

The most redeeming feature ofpolymer modification is thesignificant improvement intoughness.

Addition of both epoxy as well aspolymer latex increases the

toughness by as much as 5 timesas reflected by the area understress-strain curves of Figs 2 and3.


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Chemical Deterioration

One of the main reasons for the detrimental sulphate action is crystallisedgypsum which is formed in the pores of concrete as a result of the reaction

between the sulphate ions and the Ca(OH)2of cement.

This chemical and crystallisation process is accompanied by an increase involume and induces the pores of the concrete, particularly in the surfacelayer to expand and burst.

This eventually leads to deterioration of concrete.


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Effectiveness of Repairs

The repairs carried out using two different systems proved very effective inrestoring the strength and rigidity.

This can be entirely attributed to repair procedure and materials used.

Polymer modified cementitious systems have, by and large, proved to beeffective in repairs of RC structures.

They are cost effective too.

Polymer modification improves flexural and tensile strengths of cementmortar considerably whereas increase in compressive strength ismarginal.


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Effectiveness of Repairs

Most redeeming feature of these systems is the significant increase intoughness values over cement-based systems.

This property alone renders the system most useful for repairs since therepaired areas would not deteriorate under dynamic loadings and energydistribution would be far form throughout the section.

Due to this, microcracking was conspicuously absent and hence higherdurability could be achieved.


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Source: IIT-RourkeesPaper on Advanced Repair Techniques.


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Results The epoxy based system gave 33% higher M.R. compared to equal M.R. for

the latex system.

For lesser deterioration, the epoxy system gave 42% higher M.R. and 4%

for the latex system. In both cases of repairs, top coating of IPN polymer was providedthroughout the section to protect it further from chemical attack.


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Conclusions The repair process and materials used for rehabilitation of deteriorated

RC beams have proved to be effective. Rigidity and ultimate load capacityof the beam is not only restored but an increase of 13 to 15 percent inultimate load carrying capacity is recorded.

The structural integrity of the chemically deteriorated beam was restoredby the repair process as seen by the similar behaviour of the repairedbeam under loading.

The sectional reconstruction materials used in repairs are polymer-modified systems and among the two, epoxy based system has exhibited

better performance.


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Fiber Reinforced Composite Material Composite Materials :

Combination of more than two types of materials that combines thebest features of each constituent so as to maximize certain properties

A wide range of properties are possibly obtained.

Fiber Reinforced Composite (FRC):

Fiber reinforced composites are composed of fibers and a matrix.

Fibers are the reinforcement and the main source of strength while thematrix 'glues' all the fibers together in shape and transfers stresses

between the reinforcing fibers.

Fibers include glass fiber, Carbon Fiber, Polypropylene fiber, natural fiber,

synthetic fiber.


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Applications Of FRC FRCs can be used in the concrete structures in the following forms:

Plates-at a face to improve the tension capacity.

Bars-as reinforcement in beams and slabs replacing the steel bars.

Cables-as tendons and post tension members in suspension andbridge girders.

Wraps -around concrete members to confine concrete and improve

the compressive strength.


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Advantages

The nonmetallic fibers have strengthsthat are 10 times more than that of steel

The ultimate strain of these fibers is alsovery high. In addition, density of thesematerials is approximately one-third

that of steel. Due to its corrosion resistance FRCs can

be applied on the surface of thestructure without worrying about itsdeterioration due to environmentalattack.

They in turn protect the concrete corefrom environmental attack


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Use of Carbon Fiber Composite (Plate) The load deflection graph of a post

strengthened beam has beencompared with that of anunstrengthened beam

It was observed that a 0.3 mm thickCFC laminate has doubled theultimate load of a 15O x 200 beamof 2m span

It is observed that the tensile failureof the laminate occurred suddenly

with a sharp explosive snap.

However, it was announced inadvance by cracking sound.


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FRCS AS WRAPPING ON CONCRETE ELEMENTS

If a concrete element is confined using a wrapping thefailure due to tensile cracks can be prevented

The compressive strength of the wrapped concrete elementis several times higher than the unwrapped concreteelement


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Wrapping is suggested around damaged concrete elements to improve thestrength of the members.

Wrapping can be applied to strengthen concrete beams in compressionand shear.


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Shotcrete


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What is Shotcrete? Shotcrete is the generic name for cement, sand and fine aggregate

concretes which are applied pneumatically and compacted dynamicallyunder high velocity.


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Shotcrete : A Brief History Shotcrete was invented in the early 1900s by American taxidermist Carl

Akeley, used to fill plaster models of animals. He used the method ofblowing dry material out of a hose with compressed air, wetting it as it wasreleased.

This was later used to patch weak parts in old buildings. In 1911, he wasgranted a patent for his inventions, the "cement gun", the equipment used,and "gunite", the material that was produced.

Until the 1950s when the wet-mix process was devised, only the dry-mixprocess was used.

In the 1960s, the alternative method for gunning by the dry method wasdevised with the development of the rotary gun, with an open hopper thatcould be fed continuously


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Dry Mix

The dry mix method involves placing the dry ingredients into a hopper and then

conveying them pneumatically through a hose to the nozzle. The nozzlemancontrols the addition of water at the nozzle. The water and the dry mixture is notcompletely mixed, but is completed as the mixture hits the receiving surface. Thisrequires a skilled nozzleman, especially in the case of thick or heavily reinforcedsections.


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Wet Mix

Wet-mix shotcrete involves pumping of a previously prepared concrete, typicallyready-mixed concrete, to the nozzle. Compressed air is introduced at the nozzle toimpel the mixture onto the receiving surface.


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Dry Mix v/s Wet Mix Advantages of the dry mix process are that the water content can be

adjusted instantaneously by the nozzleman, allowing more effectiveplacement in overhead and vertical applications without usingaccelerators. The dry mix process is useful in repair applications when it is

necessary to stop frequently, as the dry material is easily discharged fromthe hose.

In the wet mix, the wet-gun procedure generally produces less rebound,waste (when material falls to the floor), and dust compared to the dry-mixprocedure. The greatest advantage of the wet-mix process is that larger

volumes can be placed in less time.


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Steel fibre reinforced micro silica shotcrete Silica fume or micro silica is a by-product of the ferro silicon metal

industry and is an extremely fine pozzolan.

Silica fume, added in quantities of 8 to 13% by weight of cement, can allowshotcrete to achieve compressive strengths which are double or triple the

value of plain shotcrete mixes.

The result is an extremely strong, impermeable and durable shotcrete.Other benefits include reduced rebound, improved flexural strength,improved bond with the existing structure and the ability to place layers ofup to 200 mm thick in a single pass because of the shotcrete's 'stickiness'.

However, when using wet mix shotcrete, this stickiness decreases theworkability of the material and superplaticizers are required to restore thisworkability.


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Steel fibre reinforced micro silica shotcrete Steel fibre reinforced shotcrete was introduced in the 1970s and has since

gained world-wide acceptance as a replacement for traditional wire meshreinforced plain shotcrete.

The main role that reinforcement plays in shotcrete is to impart ductilityto an otherwise brittle material.


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Mesh reinforced shotcrete


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Shotcrete


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Foundation Repair


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PRO-LIFT FOUNDATION REPAIR

The Pro-Lift System is a proven, powerful, and permanent solution for foundation repairs. ThePro-Lift System uses the latest technology and the best method at every step of the foundationrepair process.

Different foundation problems also require different solutions. If your foundation is onlysuffering from minor seasonal movement, it has the equivalent of a cold and might only needwatering. If your foundation has suffered from permanent settlement, you might need

foundation repairs.

It serves 2 purposes:

1. The piling serves as a platform upon which we set a jack to raise the settled portion of thefoundation.

2. the piling transfers the weight of the building from the unstable surface soils to deeper more

stable layers.


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Pro-Lift Pressed Pilings with rigid steel

connectorsAdvantages All the advantages of other pressed pilings.

Custom-fitted for your home with all theadvantages of the Pro-Lift System.

The rigid steel connectors help preventhorizontal movementduring and afterinstallation.

The performance of Pro-Lift pilings isgauranteed for the life of your home.

Guarantee is backed by the TexasFoundation Warranty Trust

Disadvantages

Depth can only be verified by checkingcontractor records (cylinder counts, initialand final length of connector, etc.)

Normal Pile.

Pro-lift System


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Pro-Lift Concrete Piers 8 to 20 feet deep and belledto twice the shaft diameter

Advantages

A permanent solution when properlydesigned and installed.

A bell at the bottom greatly increases loadbearing capacity.

Depth can be visually verified.

Alignment can be verticle or angled.

Disadvantages

Proper installation requires expensive soilsampling and lab work.

Installation requires a minimum of 10 days.

Can require the use of heavy equipment. Can be very destructive to landscaping.

Extremely difficult to install inside ofbuildings.


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Pro-Lift Multi-wall Steel Pilings.

Advantages All the advantages of single-walled steel

pilings, plus:

Double-walled pipe provides extra stiffness,ensuring a straight shaft.

The load of the structure bears straightdown on the piling, ensuring a straight and

vertical shaft.

The entire piling is buried and out of sight.

The concrete top assembly will not rust.

The performance of Pro-Lift pilings isguaranteed for the life of your home.

Guarantee is backed by the Texas

Foundation Warranty Trust.


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Bibliography Mahar, J.W., Parker, H.W. and Wuellner, W.W. 1975.Shotcrete practice

in underground construction.

State-of-the-Art in Techniques for Rehabilitation of Buildings, 11 WCEE,Acapulco, Mexico, Paper no. 2179, Elsevier

BIS (1993). IS:13935-1993 Repair and Seismic Strengthening of Buildings-

Guidelines, Bureau of Inidan Standards, New Delhi.

Termpaper of IIT Bombay Recent Advances in technology of repair ofconcrete structures available atwww.krishnaconchem.com.

Termpaper of IIT-Rourkee -Advanced Repair Techniques available at

www.krishnaconchem.com. Shotcrete Repair in Paper Millby Marc Ferland, Jean Froncois & Alan

Chaisse.
http://www.krishnaconchem.com/http://www.krishnaconchem.com/http://www.krishnaconchem.com/http://www.krishnaconchem.com/


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QUESTION based on PRESENTATION What are the various advanced techniques of repair

& rehabilitation of structures? Give a brief note withtheir salient features, methods of application & areasof application.

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Advanced Techniques for Repair and Rehabilitation in Construction

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