chapter 4 repair, rehabilitation & retrofiiting

REPAIRS, REHABILITATION AND

RETROFITTING OF STRUCTURES

Prepared By:

Assistant Professor Ankit Patel

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REPAIR, RESTORATION AND RETROFITTING

Repair: To bring back the position of the structure to its previous condition so it gives performance same as previously.It doesn’t cover the strength aspect of the structures.Some examples of repair……. Decoration of structure,Painting,White Washing Checking the wiring of building Replastering of any wall if required Repairing of damaged flooring Repair of door and window Checking or repairing of pipe line connections, gas line connections

and plumbing serveries. Relaying disturbed roof tiles

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REPAIR, RESTORATION AND RETROFITTING

Rehabilitation: Rehabilitation of a building means returning a building or a structure to a useful state by means of repair, modification, or alteration.It is related to the strength aspect of structures.To Bring back the position and condition of the structure by considering the strength aspect. Some of the examples of Rehabilitation….. To fill the wide cracks using some suitable material Injecting epoxy like material in to cracks in walls,columns,beams,

etc. Removal of damaged portion of masonry and reconstructing it

using rich mortar mix. Addition of reinforcing mesh on both sides of the wall

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REPAIR, RESTORATION AND RETROFITTINGRetrofitting:Earthquake creates great devastation in terms of life, money and failures of structures.Earthquake Mitigation is an important field of study from a long time now.Seismic Retrofitting is a collection mitigation techniques for Earthquake Engineering.It is of utmost importance for historic monuments, areas prone to severe earthquakes and tall or expensive structuresIt is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes.The retrofit techniques are also applicable for other natural hazards such as tropical cyclones, tornadoes, and severe winds from thunderstorms. BITS Edu

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REPAIR, RESTORATION AND RETROFITTINGWhen is Seismic Retrofitting Needed ?The two circumstances are:-Earthquake damaged buildings, and Earthquake-vulnerable buildings(with no exposure to severe earthquakes)Some examples of retrofitting ……… Increasing the lateral strength in one or both directions, by

reinforcement or by increasing wall areas or the numbers of walls and columns

Giving unity to the structure by providing a proper connection between resisting elements.

Eliminating features that are sources of weakness, asymmetrical plan distribution of resisting members, abrupt changes of stiffness from one floor to the other.

Avoiding the possibility of brittle modes of failure by proper reinforcement and connection of resisting members. BITS Edu

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REPAIR METHODOLOGY

Evaluation Relating observation to causes Selecting methods and materials Preparation of drawings and specifications Selection of a contractor Execution of the work Quality Control

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MATERIALS FOR CRACK REPAIRThe various materials used for repairs of cracks are:

Cement Slurry Cement Mortar Epoxy resin Polymer Modified Cementitious Products

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CRACK REPAIR TECHNIQUES Epoxy-injection Grouting Routing and Sealing Flexible Sealing Stitching Providing additional Reinforcement Drilling and plugging Prestressing steel Grouting Dry packing Surface Coatings

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CRACK REPAIR TECHNIQUES Epoxy-injection GroutingCracks as narrow as 0.002 in. (0.05 mm) can be bonded by the injection of epoxy. The technique generally consists of establishing entry and venting ports at close intervals along the cracks, sealing the crack on exposed surfaces, and injecting the epoxy under pressure. Epoxy injection has been successfully used in the repair of cracks in buildings, bridges, dams, and other types of concrete structures. However, unless the cause of the cracking has been corrected, it will probably recur near the original crack. The general procedure are given below.

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CRACK REPAIR TECHNIQUESClean the cracks: The first step is to clean the cracks that have been contaminated; to the extent this is possible and practical. Contaminants such as oil, grease, dirt, or fine particles of concrete prevent epoxy penetration and bonding, and reduce the effectiveness of repairs. Preferably, contamination should be removed by vacuuming or flushing with water or other specially effective cleaning solutions.Seal the surfaces: Surface cracks should be sealed to keep the epoxy from leaking out before it has gelled. A surface can be sealed by applying an epoxy, polyester, or other appropriate sealing material to the surface of the crack and allowing it to harden. If a permanent glossy appearance along the crack is objectionable and if high injection pressure is not required, a strippable plastic surface sealer may be applied along the face of the crack.

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CRACK REPAIR TECHNIQUESWhen the job is completed, the surface sealer can be stripped away to expose the gloss-free surface. Cementitious seals can also be used where appearance of the completed work is important. If extremely high injection pressures are needed, the crack can be cut out to a depth of 1/2 in. (13 mm) and width of about 3/4 in. (20 mm) in a V-shape, filled with an epoxy, and struck off flush with the surface.

Install the entry and venting ports. Two methods are in general use:Fittings inserted into drilled holes: This method was the first to be used, and is often used in conjunction with V-grooving of the cracks. The method entails drilling a hole into the crack, approximately 3/4 in. (20 mm) in diameter and 1/2 to 1 in. (13 to 25 mm) below the apex of the V grooved section.

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CRACK REPAIR TECHNIQUESBonded flush fitting: When the cracks are not V grooved , a method frequently used to provide an entry port is to bond a fitting flush with the concrete face over the crack. The flush fitting has an opening at the top for the adhesive to enter and a flange at the bottom that is bonded to the concrete.

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CRACK REPAIR TECHNIQUESMix the epoxy: This is done either by batch or continuous methods. In batch mixing, the adhesive components are premixed according to the manufacturers instructions, usually with the use of a mechanical stirrer, like a paint mixing paddle. Care must be taken to mix only the amount of adhesive that can be used prior to commencement of gelling of the material.Inject the epoxy: Hydraulic pumps, paint pressure pots, or air-actuated caulking guns may be used. The pressure used for injection must be selected carefully. Increased pressure often does little to accelerate the rate of injection. If the crack is vertical or inclined, the injection process should begin by pumping epoxy into the entry port at the lowest elevation until the epoxy level reaches the entry port above. For horizontal cracks, the injection should proceed from one end of the crack to the other in the same manner. The crack is full if the pressure can be maintained. If the pressure can not be maintained, the epoxy is still flowing into unfilled portions or leaking out of the crack.

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CRACK REPAIR TECHNIQUESRemove the surface seal: After the injected epoxy has cured, the surface seal should be removed by grinding or other means as appropriate.

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CRACK REPAIR TECHNIQUES

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REPAIR BY ROUTING AND SEALING

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REPAIR BY PROVIDING EXTRA REINFORCEMENT

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REPAIR BY POST TENSIONING

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GROUTINGGrouting is a process of injecting mixture of cement, sand water at high pressure in the cracks, joints, voids etc.

Purpose of grouting:

To strengthen the porous Concrete To prevent the seepage in dam and water retaining structures To reduce uplift pressure below dam To fill the cracks in concrete structure

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GROUTINGProcedure for grouting:Drilling of Grouting holesFor drilling grouting holes, equipment's like jack hammer, diamond drill, shot drill etc are used. The choice of type of drilling equipment depends upon the type of stone, size of hole and depth of hole.Arrangement of grout pipesGrout pipes of 4 to 5 cm dia and 45 to 90 cm length are inserted in the grout holes. The space surrounding the pipe is filled with cement mortar. The top end of the pipe is connected to the pump.Cleaning of cracksBefore injecting grout mixture in the cracks, it is necessary to clean the cracks. Inserting grout in holesNormally grout is inserted in the holes at a pressure 0.65kg/cm2 per m depth hole BITS Edu

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GROUTINGTypes of grouting:1. Consolidation Grouting:This type of grouting is used for shallow depth grouting holes. Normally pressure below 3 kg/cm2 is known as low pressure grouting. 2. Stage grouting:When thick layers are to be grouted the total thickness of layer is divided into stages of 1m each and grouting of each layer is carried out one by one. Grouting of upper layer is started only after the grout in the lower layer had properly set.3. Curtain Grouting: This type of grouting is done to prevent the seepage of water below foundation of dam. Grouting holes are drilled in the upstream side of dam in the bed rock and impermeable grout wall is created.it will prevent seepage of water through dam foundation.

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CAUSES OF DAMAGE IN MASONRY BUILDING

Heavy Weight and very stiff buildings, attracting large seismic

inertia forces.

Very low tensile strength particularly with poor mortars

Low shear strength

Brittle behavior in tension as well as in compression

Weak connection between wall and wall

Weak connection between roof and wall

Stress connection at corners of doors and windows

Overall unsymmetry in plan and elevation of buildings

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UNDERWATER REPAIRS

INTRODUCTIONMany of the techniques available for above water repair can be used underwater with only minor modifications. The materials specified for use in air, however, are often completely unsuitable for underwater use.The major effects that underwater working has on repair operations are summarized as follows:

The cost & difficulty of underwater working requires that operations to be carried out at the repair site be minimized & made as simple as possible. The method of repair must be tailored to suit the available methods of access.

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INTRODUCTIONPreparation of the damaged area requires specially adapted techniques. Care must be taken to ensure that the area is not contaminated prior to application of the repair material.The material selected for the repair must be compatible with underwater use both during placing & curing. Many resin-based repair materials are not suitable for use underwater; cementitious systems are however in an ideal medium.Placement methods & formwork must be adopted that minimize mixing between repair material & water.


INTRODUCTIONChecking during the repair operation and regular inspection on completion is difficult and costly to achieve underwater.

The cost of underwater repair is far greater than for similar repairs carried out in the dry. The cost of failed repairs is also therefore high. Hence it is important that laboratory trials on both repair methods and materials be carried out to identify possible problem areas and ensure smooth site operations.


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UNDERWATER REPAIR

Preparation of damaged area: The preparation of damaged area

require removal of cracked concrete and cutting of corroded

reinforcement. The damaged concrete can be removed by high

pressure water jetting. Wherein hydraulic expanding cylinder are

inserted in to pre-drilled holes and pressurized until splitting of

concrete occurs.

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