REPAIR & REHABILITATON OF STRUCTURES

REPAIR AND REHABILITATION OF STRUCTURES A Mini Project Report submitted to Jawaharlal Nehru Technological University, Anantapur. In partial fulfillment of the requirement for the award of the degree of BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING BY SILAR SHARFUDDIN (129X1A01A4) M SOWMYA PRAVALLIKA (129X1A0164) SAKE ASWINI (129X1A0191) Under the Guidance of Sri K.V.S GOPALA KRISHNA SASTRY ASSOCIATE PROFESSOR DEPARTMENT OF CIVIL ENGINEERING G.PULLA REDDY ENGINEERING COLLEGE (Autonomous) KURNOOL-518007 (A.P) Page | 1 DEPARTMENT OF CIVIL ENGINEERING G.PULLA REDDY ENGINEERING COLLEGE (Autonomous), KURNOOL-518007 (A.P) (2015-2016) CERTIFICATE This is certify that this Mini Project work titled REPAIR AND REHABILITATION OF STRUCTURES is a bonafied record work done by SILAR SHARFUDDIN (129X1A01A4) M SOWMYA PRAVALLIKA (129X1A0164) SAKE ASWINI (129X1A0191) Under my guidance and supervision in partial fulfillment of the requirements for the award of the degree of “BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING” of Jawaharlal Nehru Technological University, Anantapur. Prof.M.BASHA MOHIDDIN Sri K.V.S GOPALA KRISHNA SASTRY Head of the Department Associate Professor Department of C.E Department of C.E G.Pulla Reddy Engineering College G.Pulla Reddy Engineering College Kurnool-518007. Kurnool-518007. Page | 2 ACKNOWLEDGEMENTS We would like to acknowledge our deep gratitude to our guide Sri K.V.S Gopala Krishna Sastry, Associate Professor, for his valuable guidance and support. Our Special thanks to Prof. M Basha Mohiddin, Head of Civil Engineering Department for his encouragement during the project. We are grateful to our beloved Principal Dr. Srinavasa Reddy, for his kind co-operation in course of project work. We would like to thank Dr .P. Jayarami Reddy, Director of G Pulla Reddy Engineering College, Kurnool. Finally we thank all the unmentioned names and invisible hands who helped us in bringing this report to this present form. SILAR SHARFUDDIN M SOWMYA PRAVALLIKA SAKE ASWINI Page | 3 ABSTRACT MINI-PROJECT TITLE: “REPAIR AND REHABILITATION OF STRUCTURES” Reinforced cement concrete (RCC) as a construction material has come into use for the last one century. In India, RCC has been used extensively in the last 5060years.During this period, we have created large number of infrastructural assets in terms of buildings, bridges, sports stadium etc., which are lifeline for the civilized society. These have been created with huge investment of resources. We cannot even dream of recreating such assets out of limited national resources. It is there more essential to maintain them in functional condition. Since, deterioration of RCC is a natural phenomenon and has started exhibiting in large number of structures, a systematic approach is needed in dealing with such problems. Identification of the causes of deterioration and consequent repair/rehabilitation strategy at optimum cost needs a scientific evaluation and solution. Concrete constructions require proper care in the form of regular maintenance. If buildings remain for several years without proper attention then, various factors like water stagnation, paint peeling, plaster break- off, fungus growth, cracking of external surfaces will affect the building. Penetration of moisture into reinforced concrete components promotes corrosion process and further damages the concrete cover. It has been observed that the deterioration phenomena of RCC are not realized by majority of practicing civil engineers. As a result, the factors considered necessary for durability of RCC buildings are many times not given due importance during construction and/or during maintenance. The durability provisions have been given emphasis in the revised `Code of Practice on Plain and Reinforced Concrete' (IS: 456-2000). In the international scenario also, deterioration of RCC had been drawing attention of the practicing civil engineers for quite some time. They have accordingly, made certain advancement in the field of protection, repairs, rehabilitation, strengthening and retrofitting of the existing RCC structures taking advantage of the advancement in the materials science, more particularly the polymer science. The knowledge Page | 4 in this area among the Civil Engineers, in India is still at infancy stage and needs development and systematic dissemination. Our Mini-Project focuses with the latest techniques in repair and rehabilitation of structures .The various causes of structural failure and the principles of rehabilitation of structures are discussed. Major repairs that are to be carried out in Brick walls, Plaster walls, RCC members are explained in detail. Now-adays, for Reinforced Cement Concrete repair options like Shortcrete/Guniting, Form and pump method, RCC jacketing, Plate bonding etc., are widely used. For foundations Shoring and Under-Pinning and for repair of cracks, methods like Stitching, Routing and Sealing and Resin injection are used. Page | 5 INDEX SL .No CONTENTS PAGE No. 1 INTRODUCTION 1 2 PRESENT REPAIR PRACTICES-OVERVIEW 3 3 CAUSES OF DETERIORATION OF STRUCTURES 5 4 CONDITION SURVEY AND NON-DESTRUCTIVE TESTING 4.1 Objective 6 4.2 Stages of Condition survey 5 RATIONAL APPORACH TO ANY REPAIR AND REHABILITATION WORKS 5.1 Disstress Identification 8 5.2 Analysis of Problem and Solution 9 6 CLASSIFICATION OF DAMAGES 10 7 REHABILITATION& RENOVATION- THE WORK 8 7.1 Principles of Rehabilitation 11 7.2 Rehabilitation Work involving steps 11 7.3 General areas of Repair Work 12 TYPES OF REPAIR & REHABILITATION WORKS FOR DIFFERENT STRUCTURAL COMPONENTS 9 8.1 Repair for Plaster of walls 13 8.2 Repair of Brick walls 14 8.3 Repairs for Cracks 16 8.4 Types of Cracks 16 METHODS OF REPAIR AND REHABILITATION WORKS FOR WALLS/SLAB. 9.1 Stitching 18 9.2 Routing and Sealing 19 Page | 6 10 11 9.3 Resin Injection 21 9.4 Drilling and Plugging 23 9.5 Grouting 24 9.6 Overlays 24 RCC STRUCTURES REPAIRS 10.1 Guniting/Shortcrete 26 10.2 Form and Pump Technique 28 10.3 RCC Jacketing 30 10.4 Plate bonding 31 10.5 Dry Pack and Epoxy Bonded Dry Pack 32 10.6 Propping and Supporting 33 10.7 Fibre Wrap Technique 35 FOUNDATION REHABILITATION METHODS 11.1 Shoring 37 11.2 Underpinning 42 12 CONCLUSION 46 13 REFERENCES 47 Page | 7 LIST OF FIGURES FIGURE No. DESCRIPTION 8.1 Chipping off of plaster from a wall. 8.2 Deteriorated brick Wall 8.3 Types of cracks 9.1 9.2 9.3 9.4 9.5 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 The repair steps of cracks by Stitching. Routing and Sealing Bond Breaker Epoxy injection into Cracks Drilling & Plugging Recommended Layout for delaminated concrete. Pneumatically applying concrete on repair surface. Layout of Dry mix Shortcrete Layout of Wet mix Shortcrete Form Work technique for RCC column RCC Jacketing for RCC column. Tension face plates Dry Packing and Epoxy Bonded dry pack. Propping & Supporting for RCC column. Typical arrangement of Propping & Supporting a column to relive at form load. Fibre Wrap technique for improving load carrying capacity of a column. Horizontal Shoring Typical single flying Shoring Dead or Vertical Shoring Components of Dead Shoring Components of Inclined Shoring. Unsymmetrical Flying Shores arrangements. Pit under Pinning – Supporting the existing walls. Repair of damaged foundation. Helical Pier system- Damaged Foundation. Helical Pier System- Repaired Foundation. PAGE No 14 15 17 19 20 21 22 23 25 26 27 28 29 30 31 32 33 34 36 38 39 39 40 41 41 42 42 43 44 Page | 8 1. INTRODUCTION Large stocks of existing structures and infrastructure are deteriorated with use and time and might have passed their design life and require retrofitting and rehabilitation. The cost of retrofitting various infrastructures is estimated in the lakhs of rupees. To overcome the ill effects caused by these deteriorated buildings Repair and Rehabilitation works are carried out from time to time. Many of the existing structures were designed to codes that have since been modified and upgraded. Change in use or higher loads and performance demands require modifications and strengthening of structural elements. Concrete construction is generally expected to give trouble free service throughout its intended design life. However, these expectations are not realized in many constructions because of structural deficiency, material deterioration, unanticipated over loadings or physical damage. Premature material deterioration can arise from a number of causes, the most common being when the construction specifications are violated or when the facility is exposed to harsher service environment than those expected during the planning and design stages. Physical damage can also arise from fire, explosion as well as from restraints, both internal and external, against structural movement. Except in extreme cases, most of the structures require restoration to meet its functional requirements by appropriate repair techniques. The human body becomes deteriorated upon ageing. To a certain extent, the problem can be remedied by taking necessary preventive steps at the appropriate time. This is exactly the case with buildings. As time passes, the condition of buildings also becomes deteriorated. Unless corrective measures are taken, it may so happen that the safety of the building itself may be jeopardized. There are other factors that necessitate renovation. These are accidents, environmental factors, alteration to structures, etc. The construction associated with already-constructed structures is called renovation. Some people call the process of rehabilitation "Forensic Engineering." The role of the engineer is just like that of a doctor trying to diagnose the disease of a patient and then recommending corrective treatment. Maintenance of constructed structures includes preventive care, repairs, and rehabilitation. Page | 9 Rehabilitation of structures is a multi-disciplinary activity. The concerned engineer should know the design aspects, environmental factors, construction procedure, and about building materials. The rehabilitation of existing structures is a more complicated and sophisticated assignment than new construction Page | 10 2. PRESENT REPAIR PRACTICES-OVERVIEW: Since 1950s, the construction activity in India has been increasing geometrically without matching increase in the availability of quality inputs, in terms of materials and skilled workmen. The gap between the quality planned and the quality achieved continues to become wider. The factors contributing to damages/distresses in buildings have, thus, become intrinsic right from the construction stage. Often these are concealed under external renderings and the defect takes time to manifest itself. Why Repair of structures arise?  Understanding gap between Quality Planned and Quality achieved in past, present.  We do take cube test but How far its significance is taken during progress of work how far is the co-relation maintained with such results.  Construction documents have specifications and instructions but they remain on paper sometime due to lack of understanding.  Procedures for Periodic Inspections of building and maintenance are not followed or maintained.  Budget estimates are prepared by un-experienced engineer or someone else.  Buildings remain several years without any attention. Construction documents contain adequate specifications and instructions required to execute quality works. However, they remain as written document without achieving the desired level of results, because of lack of understanding of their significance by the field engineers. Standard cube test results are taken as a measure of quality in the construction. Whereas the factors such as method of placing, compaction and curing of concrete, which have significant influence on the quality achieved in the hardened concrete, are given scant attention. Many a times, the quality of concrete as placed and hardened in position has no correlation to the cube test results, which are used for quality control measures. Procedures, mandatory or otherwise, for periodic inspection of buildings and structures and documenting defects, like cracks, excessive deflections, corrosion of reinforcement etc., in logical manner, and recording of structural repairs already carried out, are generally not followed or maintained. In some buildings, Page | 11 only visual inspection is carried out for preparing maintenance budget estimates and this exercise is often left to the engineers who have no experience in such problems. The engineers responsible for maintaining buildings often begin repair activity without adequate understanding of the factors responsible for the defects. The repairs strategy adopted is Replacement of damaged materials without dealing with the real problems .Many engineers unintentionally attempt treating the symptoms, instead of dealing with the cause and effect phenomenon. Such an approach may offer a quick action with minimum inconvenience to the occupants. But in this process, there is a strong possibility that the source and cause for the distress remain unattended and continue to cause problem even after the superficial repairs have been executed. If structural defects are deal with in this fashion, it remains only as defects camouflaged beneath finishes, which gives a false sense of safety to the occupants allowing the problem to continue without getting treated. A rational approach to any repair and rehabilitation work is to consider the source of the problem and the symptoms together. Page | 12 3. CAUSES OF DETERIORATION OF STRUCTURES: A structure becomes deteriorated for the following reasons Site Selection and Site Development Errors: Failures often result from unwise land use or site selection decisions. Certain sites are more vulnerable to failure. The most obvious examples are sites located in regions of significant seismic activity, in coastal regions, or in flood plains. Other sites pose problems related to specific soil conditions such as expansive soils or permafrost in cold regions. Design Errors: These failures include errors in concept that lack of structural redundancy, failure to consider a load or combination of loads, deficient connection details, calculation errors, misuse of computer software, detailing problems including selection of incompatible materials, failure to consider maintenance requirements and durability, inadequate or inconsistent specifications for materials or expected quality of work and unclear communication of design intent. Construction Errors: Such errors may involve excavation and equipment accidents; improper sequencing; inadequate temporary support; excessive construction loads; premature removal of shoring or formwork; and non-conformance to design intent. Material Deficiencies: While it is true that most problems with materials are the result of human errors involving a lack of understanding about materials, there are failures that can be attributed to unexpected inconsistencies in materials. Operational Errors: Failures can occur after occupancy of a facility as the result of owner/operator errors. These may include alterations made to the structure, change in use, negligent overloading and inadequate maintenance. Page | 13 4. CONDITION TESTING: 4.1) Objective: SURVEY AND NON-DESTRUCTIVE • It is examination of concrete for the purpose of identifying and defining area of distress. • Identify cause of distress and sources. • Access extent of distress due to corrosion, fire, earthquake, any other reasons. • Access residual strength of structure and inhabitability. 4.2) Stages of condition survey:  Prioritize distressed elements according to seriousness for repairs. a) Preliminary inspection b) Planning c) Visual Inspection d) Field and laboratory testing. A) Preliminary inspection: • History of structure from client, owner, occupants, General public in building. • Note records, previous repairs history and expenses done for the same. • All possible data and information. • Practical restriction and safety requirements. • Extent and quantum of survey work. • Time required (survey and execution). • Advise immediate safety measures. Information gathering: • • • • • • • • • • Period of construction. Construction details (drawings,arch,structural ). Exposure conditions. Designed and present use of structure. Previous changes in use Record of structural changes if done. Record of 1st occurrence of defect. Details of repairs carried out previously. Previous reports etc. Details from owner, photographs. Page | 14 B) Planning survey: • • • • • Field documents Plans and actual observations each room-wise. Previous report , advise if any and implementation done as per report. Grouping of structural elements (external, interior etc. ) Exposure conditions The data to be collected are:     Assumptions made in the design and verification of design calculation. Quality of materials used in the construction. Result of soil investigations, ground water analysis. Quality control and method of construction. C) Visual Indications of Distress Conditions:      Formation of cracks in the structure in different patterns Peeling of plasters Sapling of concrete Yielding of steel Rusting of exposed steel D) Tests to be done: The following tests are to be conducted on the samples taken from the structure and on the structural members.        Testing of concrete for ascertaining the compressive strength Sampling and testing of subsoil Chemical analysis of subsoil water X ray diffraction tests on concrete Hammer or ultrasonic tests on concrete Permeability tests Vibration studies. Page | 15 5. RATIONAL APPROACH REHABILITATION WORKS: TO ANY REPAIRS & • Identification of Cause of Deterioration. • Consequent Repairs and Rehabilitation strategy at optimum cost. • Scientific Evaluation and Solution for protection-repairs, rehabilitation, strengthening and retrofitting taking advancement in material science (polymers). 5.1) Distress Identification: The success of repair activity depends on the identification of the root cause of the deterioration of the concrete structures. If this cause is properly identified, satisfactory repairs can be done for the improvement of strength and durability, thus extending the life of the structure, is not difficult to achieve. Before attempting any repair procedure it is necessary to have a planned approach to investigate the condition of concrete and reinforcement. While the diagnosis of damage or deterioration in some cases is reasonably straight forward, it may not be so in many cases. Particularly difficult are cases in which the cause and effect phenomenon cannot be readily explained or when prognosis in terms of long-term performance of restored structure is to be made. This will require a thorough technical inspection and an understanding of the behaviour of the structural component, which is being repaired. Inspection calls for detailed mapping of affected areas, documentation of type and location of symptoms and their history and photographic evidences. It may also include the environmental factors which are likely to accelerate the damage process. Existence of concealed ducts, water lines, wet areas require special attention. Some areas impose severe limitations on access to damaged areas. A comprehensive inspection data helps in making an effective strategy for repair and rehabilitation. Non-destructive evaluation (NDE) of concrete and components are well known and extensively used. While they are very good tools for establishing quality levels in new constructions, applying these techniques to damaged structures requires certain level of experience and understanding of limitations of these methods. Solving the problem successfully is entirely dependent on the ability of a team of experts engaged to do this job. Both field and laboratory tests are available. It is important to select the appropriate Non-Destructive Evaluation (NDE) techniques and location of investigation. This is a specialised Page | 16 job and requires sophisticated instruments and trained personnel. A single technique may not be adequate and a combination of techniques has to be adopted to get a truly representative data on the condition of the building. 5.2) Analysis of the problem and solution: Based on the results of tests and field observations, it will be possible to arrive at the actual cause of the problem and suggest suitable remedial action. Various alternative methods of solutions may be looked into taking into account the safety, economy, and time required for the work. The most suitable method among the alternatives which are explained below may then be selected. Page | 17 6. CLASSIFICATION OF DAMAGES: Grade for Assessment of the building: Based on the inspection and observation the distress level of the selected buildings may be categorized as mentioned below: • G1 – No distress observed. • G2 – Minor distress observed in few structural members, which can be repaired under the advice of a structural engineer. • G3 – Medium distress observed in few structural members, which can be repaired / rehabilitated including strengthening with the advice of a structural engineer. • G4 – Severe distress observed in some of the structural members, which can be rehabilitated including strengthening with the advice of a structural engineer. • G5 – Severe distress is observed which could prove dangerous, hence evacuation at an early date is required. Page | 18 7. REHABILITATION AND RENOVATION-THE WORK: 7.1) Principles of rehabilitation: a) Elimination: Remove the materials that cause damage to buildings. This is no easy matter, because everything from the floor to the roofing may contain various undesirable materials in the form of additives and admixtures. b) Separation: Something just can't be eliminated, but can still be protected. Use sealants or foil backed drywall to separate structures from damage causing sources. c) Ventilation: Controlled, filtered ventilation may be the only way to insure that the air we bring indoors is ideal. High humidity air or extremely low humidity air can cause significant damage to concrete, plaster and brick walls. 7.2) Rehabilitation work involves the following steps: a) Access arrangements: Special gadgets may be required to get access to that part of the structure where the work is to be carried out. The access arrangements may be in the form of suspended platforms, scaffoldings, jacking arrangements, anchoring systems, etc. b) Materials required: In choosing the materials, the following points may be kept in mind: Timely availability of the material, safe handling, adverse effect on the structure, surface preparation required availability of the equipment and financial implications. c) Sequence of operations: The process of rehabilitation has to carry out in such a manner that the safety of the structure is not jeopardized. Therefore it is necessary to plan the operations properly and then carry out it accordingly. Page | 19 7.3) General areas of repair/rehabilitation work:  Repair, removal, replacement and maintenance of mechanical supports, sanitary treatment plant and pipelines.  Repair and modifications to diffuser ports, aeration systems, and discharge pipelines.  Repair of columns and beams.  Installation and maintenance of dewatering structures.  Pile restoration and wood pile concrete encapsulation.  Anode installation for cathode protection.  Repair and replacement of trash-rack and debris screen. Page | 20 8. DIFFERENT TYPES OF REPAIRS AND REHABILITATION WORKS FOR DIFFERENT STRUCTURAL COMPONENTS: 8.1) Repair for Plaster of walls: Should you repair or replace? It is usually better to go in favour of repairing plaster walls, regardless of what they look like. But honestly, this is not always possible. Basically, if:  There is more than 1 large hole per 4 x 8 Sq. ft , or  There are more than 3-4 cracks in 100 Sq.ft, or  The cracks are more than 1/4" wide Then replace the section of wall. It will take more time and failed attempts to repair this wall than it is worth. Old plaster should be cherished - it is stronger and more sound proof than current walls made of gypsum board or sheetrock. Even cracking or crumbling plaster walls should be repaired, not replaced. a) Plaster Damage (Non-Structural Problems) Plaster is pretty tough stuff, but like any wall, it's going to get banged or gouged, and age will take its toll.  Impact Damage can be serious problem in an old house. Over the years, the walls are going to get banged and dented as shown in the figure (8.1). Generally we have to replace the plaster 6-12" from the visible hole to reach plaster that is still keyed to the lath tightly.  Nearly every wall has a few nail holes. These can usually be fixed with a tiny bit of spackle applied with the finger. Not perfect, but they will be unnoticeable when the wall is painted.  Water is the enemy of plaster. Brownish stains on the walls or ceilings are evidence for bowing out of plaster. Water-damaged plaster can be very friable.  Old walls and old houses often have cracks. Stress cracks are a sign of possible structural shifting, extreme temperature changes, incorrect plaster mix, improper curing or leaks. Diagonal cracks over doorways signal settlement, or a nearby source of vibration, such as a highway or railroad.  Bulging plaster is an indication that the plaster keys have broken off and allowed the plaster layers to separate from the lathe behind them. Bulging can be repaired with plaster washers. Page | 21 Figure (8.1) Chipping off of plaster from a wall b) Repairs  For repair of minor cracks, use fiberglass mesh tape then go over with a wide trowel and joint compound. There are also plaster patch compounds available that are excellent.  For larger cracks and holes, we need to remove all the debris and enlarge the crack until we reach solid plaster and fill the crack with joint compound or plaster patch. If we choose to put wallboard over the plaster, use the following tips:       Apply wallboard horizontally. Use the largest boards available. Use screws, not nails, 12" apart in ceilings, 16" on walls. Use a floating joint - the wall holds up the ceiling sheets. Use corner clips at all corners. Use fiberglass meshes tape, not paper, and special compound that is available for plaster walls. . 8.2) Repair of Brick Walls: Basically, brick is durable and long-lived as long as the mortar joints are sound. Brick houses are susceptible to moisture - more so than wooden framed houses but require very little maintenance. Page | 22 a) Problems with Brick (Structural Problems):  Deteriorated pointing affects many old houses. Mortar starts to disintegrate between the bricks, which can cause the entire wall to collapse, or single bricks to crumble is as shown in the figure (8.2).  Dirty or stained brickwork can be caused by moisture, time, and dirt along with rain or sprinklers.  Efflorescence results from bricks getting wet, which leaves deposits of salts that are drawn out of the masonry as the moisture evaporates the brickwork and find the source of the moisture.  Spalled brickwork is also common. Once bricks have been wet, the expansion of freezing water breaks off the top surface of the brick, leaving the inner surface exposed. After a time, most of these bricks will crumble completely. Figure (8.2) Deteriorated brick Wall b) A couple of Don'ts for brick:  Don't assume that old mortar needs to be replaced. Old mortar is usually of higher lime content than the newer replacement mortar we are likely to find to repoint, and the high Portland cement content of new mortar can damage old walls beyond repair.  Don't seal bricks with a water repellent (i.e., water seal) - it can mean that any moisture that is already in the brick stays in the brick, and interior moisture may not be able to escape. Page | 23  Don't use hydrochloric acid to clean brick, it can cause discoloration or mottling that is permanent  Never sandblast old brick. Sandblasting can damage the hard surface of fired brick and open the bricks up to water damage.  Never use expansion joints in historic masonry - they can pulverize brick and ruin mortar joints. c) Repair Work: i) Cleaning Brickwork  For normal dirt and grime, simply use plain water, rinsing with a hose and scrubbing with a stiff bristled brush.  For stubborn stains add 1/2c ammonia to a bucket of water.  Don't use a power washer except as a last resort - if we have a crumbling brick problem, this will make it worse (old windows don't stand up to high pressure water very well). ii) Removal of Organic Growth A moist brick will often lead to growth a variety of molds and mosses.  First, scrape the moss off the surface with a non-metallic spatula (the same kind used on Teflon).  Second, apply a wash of 1 part bleach to 4 parts water to kill the spores.  After a couple of days, scrape again and rewash. It will probably take a few applications to kill everything off. 8.3) Repair for Cracks in Structure: a) What is Crack? A line on the surface of something along which it has split without breaking apart. b) What happens if crack is not properly treated? If crack is not properly treated, it will affect the strength of wall/slab which ultimately leads to failure of that component. 8.4) Types of Cracks: The different types of cracks are as shown in figure (8.3). Page | 24 Figure (8.3) Types of cracks Page | 25 9. METHODS OF REPAIR AND REHABILITATION FOR SLAB/WALL CRACKS: 1) Stitching 2) Routing and sealing 3) Resin injection 4) Drilling and plugging 5) Grouting 6) Overlays 9.1) Stitching: Stitching involves drilling holes on both sides of the crack and grouting in Ushaped metal units with short legs (staples or stitching dogs) that span the crack is as shown in figure (9.1). Stitching may be used when tensile strength must be reestablished across major cracks. The stitching procedure consists of drilling holes on both sides of the crack, cleaning the holes, and anchoring the legs of the staples in the holes, with either a non-shrink grout or an epoxy resin-based bonding system. In this technique, the crack is bridged with U-shaped metal units called stitching dogs before being repaired with a rigid resin material. A non- shrink grout or an epoxy resin based adhesive should be used to anchor the legs of the dogs. Stitching is suitable when tensile strength must be reestablished across major cracks. Stitching dogs should be of variable length and orientation. a) Repair Steps: Step 1: Mark and Drill holes on both sides of the cracks. Step 2: Chase a Groove between the drilled holes. Step 3: Insert U-shaped M.S bars in the holes and span across the crack. Step 4: Grouting the holes with either epoxy or non-shrink grout. Page | 26 Figure (9.1) The repair steps of cracks by Stitching b) Benefits of Cracked Stitching:  Quick, simple, effective and permanent.  The grout combination provides an excellent bond within the substrate.  Masonry remains flexible enough to accommodate natural building movement.  Non-disruptive structural stabilization with no additional stress. 9.2) Routing and Sealing: Routing and sealing of cracks can be used in conditions requiring remedial repair and where structural repair is not necessary. This method involves enlarging the crack along its exposed face and filling and sealing it with a suitable joint sealant as shown in the figure (9.2). This is a common technique for crack treatment and is relatively simple in comparison to the procedures and the training required for epoxy injection. The procedure is most applicable to approximately flat horizontal surfaces such as floors and pavements. However, routing and sealing can be accomplished on vertical surfaces (with a non-sag sealant) as well as on curved surfaces (pipes, piles and pole). Page | 27 Figure (9.2) Routing and Sealing a) Features:  This is the simplest and most common method of crack repair.  It can be executed with relatively unskilled labor and can be used to seal both fine pattern cracks and larger isolated cracks.  This involves enlarging the crack along its exposed face and sealing it with crack fillers.  Care should be taken to ensure that the entire crack is routed and sealed. Routing and sealing is used to treat both fine pattern cracks and larger, isolated cracks. A common and effective use is for waterproofing by sealing cracks on the concrete surface where water stands, or where hydrostatic pressure is applied. This treatment reduces the ability of moisture to reach the reinforcing steel or pass through the concrete, causing surface stains or other problems. The sealants may be any of several materials, including epoxies, urethanes, silicones, polysulfide, asphaltic materials, or polymer mortars. Cement grouts should be avoided due to the likelihood of cracking. For floors, the sealant should be sufficiently rigid to support the anticipated traffic. Satisfactory sealants should be able to withstand cyclic deformations and should not be brittle. The procedure consists of preparing a groove at the surface ranging in depth, Page | 28 typically, from 1/4 to 1 in. (6 to 25 mm). A concrete saw, hand tools or pneumatic tools may be used. The groove is then cleaned by air blasting, sandblasting, or water blasting, and dried. A sealant is placed into the dry groove and allowed to cure. A bond breaker may be provided at the bottom of the groove to allow the sealant to change shape, without a concentration of stress on the bottom as shown in the figure (9.3). Figure (9.3) Bond Beaker The bond breaker may be a polyethylene strip or tape which will not bond to the sealant. Careful attention should be applied when detailing the joint so that its width to depth aspect ratio will accommodate anticipated movement. 9.3) Resin injection: Cracks as narrow as 0.002in (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 is as shown in the figure (9.4). 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. If the cause of the cracks cannot be removed, then two options are available. Page | 29 One is to rout and seal the crack, thus treating it as a joint, or, establish a joint that will accommodate the movement and then inject the crack with epoxy or other suitable material. With the exception of certain moisture tolerant epoxies, this technique is not applicable if the cracks are actively leaking and cannot be dried out. Wet cracks can be injected using moisture tolerant materials, but contaminants in the cracks (including silt and water) can reduce the effectiveness of the epoxy to structurally repair the cracks. Figure (9.4) Epoxy Injection into cracks The use of a low-modulus, flexible adhesive in a crack will not allow significant movement of the concrete structure. The effective modulus of elasticity of a flexible adhesive in a crack is substantially the same as that of a rigid adhesive because of the thin layer of material and high lateral restraint imposed by the surrounding concrete. Epoxy injection requires a high degree of skill for satisfactory execution, and application of the technique may be limited by the ambient temperature. a) Repair Steps: i) Clean 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. Page | 30 ii) Seal the surfaces: Surface cracks should be sealed to keep the epoxy from leaking out before it has gelled. Where the crack face cannot be reached, but where there is backfill, or where a slab-on-grade is being repaired, the backfill material or sub base material is sometimes an adequate seal. 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. When 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. 9.4) Drilling and plugging: Drilling and plugging a crack consists of drilling down the length of the crack and grouting it to form a key. This technique is only applicable when cracks run in reasonable straight lines and are accessible at one end. This method is most often used to repair vertical cracks in retaining walls. A hole [typically 2 to 3 in. (50 to 75 mm) in diameter] should be drilled, centered on and following the crack as shown in the figure (9.5). Figure (9.5) Drilling and Plugging Page | 31 The grout key prevents transverse movements of the sections of concrete adjacent to the crack. The key will also reduce heavy leakage through the crack and loss of soil from behind a leaking wall. If water-tightness is essential and structural load transfer is not, the drilled hole should be filled with a resilient material of low modulus in lieu of grout. If the keying effect is essential, the resilient material can be placed in a second hole, the fiat being grouted. 9.5) Grouting a) Portland cement grouting: Wide cracks, particularly in gravity dams and thick concrete walls, may be repaired by filling with Portland cement grout. This method is effective in stopping water leaks, but it will not structurally bond cracked sections. The procedure consists of 1) cleaning the concrete along the crack. 2) Installing built-up seats (grout nipples) at intervals astride the crack 3) Sealing the crack between the seats with a cement paint, sealant, or grout. 4) Flushing the crack to clean it and test the seal and, 5) then grouting the whole area. Grout mixtures may contain cement and water or cement plus sand and water, depending on the width of the crack. However, the water-cement ratio should 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. For small volumes, a manual injection gun may be used and for larger volumes, a pump should be used. After the crack is filled, the pressure should be maintained for several minutes to insure good penetration. 9.6) Overlays: Slabs containing fine dormant cracks can be repaired by applying an overlay, such as polymer modified Portland cement mortar or concrete, or by silica fume concrete. Slabs with working cracks can be overlaid if joints are placed in the overlay directly over the working cracks. In highway bridge applications, an overlay thickness as low as 1-1/4 in. (30 mm) has been used successfully. Suitable polymers include styrene butadiene or acrylic latexes. The resin solids should be at least 15 percent by weight of the Portland cement, with 20 percent usually being optimum. Page | 32 10. RCC STRUCTURES REPAIRS:  Problems in RCC Structures (Structural Problems) 1) Flexure, Shear, Torsion, Shrinkage and Tension cracks. 2) Splitting, Diagonal, Horizontal cracks in Columns. 3) Rusting, Buckling, Bending, Twisting Distress in Steel structures. Recommended Layout for delaminated concrete is as shown in the figure (10.1). Figure (10.1) shows the Recommended Layout for delaminated concrete Methods of Repair for RCC Structures: 1) Shortcrete/Guniting. 2) Form and Pump Technique 3) RCC Jacketing 4) Plate bonding 5) Dry Pack and Epoxy Bonded Dry Pack 6) Propping and Supporting 7) Fibre Wrap Technique Page | 33 10.1) Shortcrete/Guniting: Shortcrete is the process of pneumatically applying concrete onto various surfaces at high velocity is as shown in the figure (10.2). There are two primary application methods: the wet process pumps mixed concrete through a hose to the nozzle where compressed air is added to provide high velocity for placement and consolidation; the dry process, commonly known as gunite, uses compressed air to blow pre-blended dry materials through a hose at high velocity to the nozzle, where water is added. The effects in most cases are almost identical. The materials used in both processes are generally the same as those used for conventional concrete are Portland cement, aggregates and water. Various additives can enhance strength and reduce cracking. As a result, shotcrete/gunite has high-strength, durability, low permeability, and excellent bonding characteristics. Shotcrete/gunite application also provides almost limitless possibilities for complex shaping and forming in new construction and renovation projects. a) Other key benefits include:     Little or no form work is required. Cost-effective method for placing concrete. Ideal for irregular surface applications. Allows for easier material handling in areas with difficult access. Figure (10.2) shows the pneumatically applying concrete on repair surface Page | 34 b) Types of shorcrete: i) Dry mix shorcrete (Guniting). ii) Wet mix shorcrete. i) Dry mix: (Guniting) Dry mixing involves premixing of binders and aggregates which are fed into special mechanical feeder metering the premixed materials into a hose. The mix is jetted out along with compressed air from a nozzle connected to the hose having a water ring outfitted to it as shown in the figure (10.3). This mix is injected to the repair spot. The resultant hardened properties include increased flexural, compressive strengths and more durability. Figure (10.3) Layout of Dry mix Shortcrete ii) Wet mix: Wet mix Shotcrete is a method that involves premixing of all ingredients including binder, water, aggregates and admixtures .The premixed repair materials are deposited into a pump which transports the materials to an exit nozzle where compressed air is introduced as shown in the figure (10.4). The repair material is propelled onto the substrate with compressed air. Admixtures can be used to enhance durability. Air entrainment is required for freeze thaw resistance. The effect is smooth and unnoticeable. Page | 35 Figure (10.4) Layout of Wet Mix Shortcerte 10.2) Form and Pump Technique The form and pump repair method is a two-step process of constructing formwork and pumping repair material into the cavity confined by formwork and existing concrete. The form and pump technique allows use of different materials. Repair materials are mixed and pumped into the cavity. When the cavity is full, pump pressure is exerted into the form causing the repair material to consolidate and make contact with existing concrete surfaces. a) Surface Repair of Vertical Location (Column): One of the most common methods of surface repair of vertical and overhead location is placement of formwork and casting of repair material into the prepared cavity as the in the figure (10.5). The repair material must be of low shrinkage and necessary flow ability. Rodding or internal vibration is necessary to remove air and provide intimate contact for placing concrete substrate. In some applications complete filling of the cavity may be difficult. In those cases a final step of dry packing the remaining cavity works well. b) Surface Repair of Overhead Location (Beam): There are many techniques available to restore damaged or deteriorated concrete structures. Each surface repair techniques offer advantages and limitations depending upon the conditions of the repair project. Form a pump Page | 36 technique is relatively new method which has been developed as a viable alternative to Shotcrete (gunite), hand placement and grouted preplaced aggregate techniques. Figure (10.5) Form Work Technique for RCC Column c) Advantages of Form and Pump Technique:  The use of almost any type of repair material- from fine grained mortar to course grained cement concrete.  Placement is not limited by depth of repair, or by size or density of reinforcements.  The pressurization process provides full encapsulation of exposed reinforcing steel.  The formwork protects the repair material during curing process. Page | 37 10.3) RCC Jacketing Reinforced concrete jacketing increases the member size significantly. This has the advantage of increasing the member stiffness and is useful where deformations are to be controlled. If columns in a building are found to be slender, RC jacketing provides a better solution for avoiding buckling problems as shown in the figure (10.6). Design for strengthening/repair work is based on composite action between the old and the new work. Strain compatibility calculations may have to be carried out carefully giving due accounts to factors such as creep. As the new jacket is to behave compositely with the parent member, the new jacket can take additional loads only with the increase in the stresses & strains in the old one. The problem arises if the;  Old concrete has reached limiting strain and is not likely to sustain any more significant strain.  Old concrete is weak and porous and started deteriorating due to weathering action and corrosion of reinforcement. The question then arises as to whether the composite action should be abandoned and the new jacket (plate or RC) designed to carry the entire load. It is perhaps best to design the strengthening in this manner, but detailing must be right to ensure transfer of load to the new jacket, if the old concrete fails. It is however, necessary to ensure perfect bond also between the old and new concrete by providing shear keys and effective bond coat with the use of epoxy or polymer modified cement slurry giving strength not less than that of new concrete. Figure (10.6) RCC jacketing for column Page | 38 10.4) Plate bonding Plate bonding is an inexpensive, versatile and advanced technique for rehabilitation, up gradation of concrete structures by mechanically connecting MS plates by bolting and gluing to their surfaces with epoxy as shown in figure (10.7).Plate bonding can substantially increase strength, stiffness, ductility and stability of the reinforced concrete elements and can be used effectively for seismic retrofitting. Figure (10.7) Tension Face Plates In this method the bolts, which are first used to hold the plates in position during construction, act as permanent shear connectors and integral restraints. The bolts are also designed to resist interface forces assuming the epoxy glue used as non-existent assuming it as destroyed by fire, chemical break down, rusting or simply bad workmanship. Since epoxy is prone to premature bonding, use of mechanical anchorage along with epoxy bonding is considered more reliable. Since the steel plates are unobtrusive, with this technique original sizes of the structural members are not increased significantly. This method is preferred where enlargement of the members is going to affect the head room, existing windows, doors and other fixtures. Page | 39 10.5) Dry Pack and Epoxy Bonded Dry Pack The Dry Pack Repair technique is application of dry cement sand mix. It consists of cement and clean sand (in proportion 1:2:5) with just enough water to be able to form a ball by hand. It is immediately packed into place before the bond coat has dried or cured, with suitably shaped hardwood dowel and hammer in 8 to 10 mm thick layers as shown in the figure (10.8). Figure (10.8) Dry Packing and Epoxy Bonded Dry pack If the epoxy is used as bonding material between the repair material and the substrate, the method is termed as Epoxy Bonded Dry Pack. Its application shall be limited to areas that are small in width and relatively deep but not less than 25 mm in depth. The application areas include core holes, holes left by removal of form-ties, cone-bolts, she bolt holes, narrow slits for critical repairs or for repairs expected to be exposed to severe service conditions. Dry pack shall neither be used for shallow depressions where lateral restraint cannot be obtained nor for filling behind steel reinforcement. Page | 40 10.6) Propping and Supporting Problem arises in deciding on propping and supporting the structure to give relief in stresses and strains in some of the existing weak members being strengthened. Mere vertical props sitting on some beams & slabs may not be enough. Propping and Supporting for columns is as shown in the figure (10.9). Figure (10.9) Propping & Supporting for Column For a Multi-Storey building the propping and supporting is carried out as shown in the figure (10.10). Page | 41 Figure (10.10) Typical Arrangement of Propping & Supporting a Column to Relieve at Form Load Page | 42 10.7) Fibre Wrap Technique The fibre wrap technique, also known as Composite Fiber System is an onintrusive structural strengthening technique that increases the load carrying capacity (shear, flexural, compressive) and ductility of reinforced concrete members without causing any destruction or distress to the existing concrete. There are two systems followed In adopting this technique: a) Bi-directional Woven Fabric: This system comprises of woven fabric presoaked in specially formulated epoxy and applied over prepared surface after application of epoxy primer. Woven fibre fabric is composed of bi-directional high strength fibers that are combined with specially formulated epoxy in a pre-determined proportion to form a composite material. This composite material is wrap applied onto the reinforced concrete or steel member as shown in the figure (10.11) for requiring strengthening or protection and left to cure at ambient temperature. The subsequent layer/s of unidirectional fiber fabric could be applied after giving the required overlap along the direction of fibres as per design requirements. b) Uni-directional E-glass Fibres: This system comprises of precut unidirectional E-glass fibre wrapped over epoxy primer applied prepared surface of member requiring structural strengthening and/or surface protection. Subsequent to its wrapping, it is saturated with epoxy using rollers and stamping brushes manually to remove air bubbles, if any and left to cure at ambient temperature. The subsequent layer/s of unidirectional fibre fabric could be applied after giving the required overlap along the direction of fibres as per design requirements. Though the underlying principle of the above two methods is more or less identical, but the Application techniques and basic materials adopted are at slight variance .Each of the above systems has their own merits. Enhancement in lateral drift ductility and horizontal shear carrying capacities of a concrete member can also be obtained by confinement of the member by this method. The flexural, shear and axial load carrying capacities of the structural members can be enhanced by appropriate orientation of primary fibres of the Page | 43 composites. The resulting cured membrane not only strengthens the reinforced concrete member but also acts as an excellent barrier to corrosive agents, which are detrimental to concrete and the reinforcement. Ingress of water, oxygen and carbon dioxide through the external surface of concrete member is prevented by the application of composite jacket. Figure (10.11) Fibre wrap technique for improving load carrying capacity of a column. The system is useful for its structural enhancement and protection capabilities under severe environmental conditions. It can be used for retrofitting of a wide variety of structures that include bridges, flyovers, chimneys, water tanks, buildings, large diameter pipes, industrial plants, jetties, sea-front and underwater structures. Page | 44 11. FOUNDATION REHABILITATION METHODS: The methods to repair and rehabilitate a structure having foundation distress generally involve shoring & underpinning work for structures that are out of plumb, or are sensitive to effects of small settlement etc. Methods 1) Shoring 2) Under Pinning 11.1) Shoring Shoring means support or propping. Before any shoring work is commenced, the building should be carefully surveyed & record of levels, cracks & tilts kept. The observations should be continued throughout the period of shoring & under pinning and till the time when detectable measurements have ceased. The terminology used is: a) Raking shores with the angle of shores generally 60 to 75 are usually used where external support is necessary. In case, the feet of raking shores are to be kept free, then flying shores can be provided which strut against another structure or wall. b) Flying shores merely provide a restraint against building or tilting. c) Dead shores are verified struts bearing on the ground at the required distance & supporting the vertical load of a wall wherever required in conjunction with flying shores or horizontal ties. The level of raking shores & flying shores are so arranged as to bear on the wall at floor or ground with a firm bearing. Folding wedges should be inserted at the foot of shores to take up yielding if any, of the ground & elastic shortening of the struts. Columns can be shored up individually by needle beams. The needle system has to be properly designed to suite the particular requirements. Suitable placing of jacks for exerting upward pressure can also be planned & designed. Page | 45 11.1.1) Types of Shoring  Horizontal shoring.  Vertical shoring or dead shoring  Inclined Shoring or flying shoring a) Horizontal Shoring:     It consists of Horizontal beam or strut Wall plates Cleats Straining beams Used to support two adjacent buildings. The above components are clearly seen in the figures (11.1) and (11.2). Figure (11.1) Page | 46 Figure (11.2) b) Vertical shoring or dead shoring Vertical shoring consists of Dead shore, Sole plates, Needles, Props as shown in the figures (11.3) and (11.4). Purpose: Used for rebuilding of walls. Figure (11.3) Dead or Vertical Shoring Page | 47 Figure (11.4) Components of Dead shoring. c) Inclined Shoring It consists of 1)Rakers 2)Needles 3)Cleats 4)Braces 5)Sole plate Purpose:  Used to strengthen a wall. The above mentioned components are shown in figures (11.5) and (11.6). Page | 48 Figure (11.5) Components of Inclined shoring .Figure (11.6) Page | 49 11.2) Underpinning:  DEFINITION Underpinning is the process of strengthening and stabilizing the foundation of an existing building or other structure. Foundation underpinning is a means of transferring loads to deeper soils or bedrock. Figures (11.7) and (11.8) shows the supporting of walls of structure and then repairing the foundation. a) Purpose of under pinning 1) To obtain additional foundation capacity. 2) To modify the existing foundation system. 3) To create new foundations through which the existing load may be wholly or partially transferred into deeper soil . 4) To arrest the excessive settlement. 5) To improve the future performance of the existing foundations. Figure (11.7) Pit Under Pinning-Supporting the existing walls Figure (11.8) Repair of damaged foundation Page | 50 b) Underpinning is required when: • Construction of a new project with deeper foundation adjacent to an existing building. • Change in the use of structure. • The properties of the soil supporting the foundation may have changed or was mischaracterized during planning. • To support a structure this is sinking or tilting due to ground subsidence or instability of the super structure. Methods for underpinning: • Pit Underpinning • Push Piers System • Helical Pier System {figures (11.9) and (11.10)} • Pile Underpinning • Other Methods • Chemical Grouting • Micro-fine Grouting • Micro-piles Figure (11.9) Helical Pier System-Damaged Foundation Page | 51 Figure (11.10) Helical Pier system-Repaired Foundation If underpinning is necessary to arrest settlement, it is essential that the underpinned foundation should meet the requirements of correct allowable bearing pressures. Depending on the cause of settlement, shallow underpinning may be satisfactory in some cases, whereas in some cases the underpinning has to be taken down to a deeper & relatively incompressible stratum. Underpinning material are metals in case of comparatively shallow underpinning. Underpinning by piles or piers is suitable, only if the new bearing stratum is deep. Underpinning piles are normally provided in pairs, one on each side of the load bearing walls or in groups around the sides of columns. Micro-piles are a useful means of underpinning. They can be installed from the ground surface without deep excavation and the equipment in installing the piles is suitable for working in confined spaces. The rotary drilling results in less damage & loss of ground, as compared to the percussion method. Proprietary jacked piles with pre-cast segments are another means of underpinning. In the proprietary `pre-test' methods of underpinning the underlying ground is preloaded before the load of the structure is finally transferred by means of jacking between the tilted existing structure & the new underpinning. There are various patented systems of jacking, involving inter connection of jacks with centralised pumping plant etc. Underpinning by injection of the ground with cement or chemicals to fill voids or to permeate and strengthen the ground is sometimes used. Various forms of grout can be introduced into granular soils or cavernous rock Page | 52 formations to increase their strength to reduce their compressibility grouts ,however, cannot be induced to permeate clays or clayey silts, though by means of high injection pressure and using closely spaced points the "hydro-fracture" technique can be used to uplift the mass of clay or self & there by provide a means of raising a structure. However, it may be worthwhile in many cases to take the foundation down to a deeper & more incompressible stratum say by piles rather than try to compensate & stop the settlement by grouting. At the end, it is worthwhile bearing in mind that a foundation is not an entirely nor an end in itself. The ability to discern differences in type of framing etc. is also an essential attribute of an expert investigator. In certain, cases, the results of fresh site investigates would indicate that the settlement may continue but at a deceasing rate. In that case, a possible solution could be to keep on monitoring and when the rate of settlement has decreased sufficiently, the building could simply be "patched up". It is worth noting that damage investigations include both the design & operation (and lifetime usage) assessment, which involve "looking backwards in time" as are time dependent. As stated earlier the concept of time scale is important. In any case, for a good & effective damage investigation, proper causation statement is essential. They need to cover information about the damages, technical details, facts about what & when precise explanation of the causes of damages etc. causation is about opinion & fact meshed together so that they explain what happened. There must be clarity and it must be based on evidence. This will then load to the appropriate repair & rehabilitation strategy, always bearing in mind that foundation is not an isolated entity but a part of the structure as a whole. Page | 53 CONCLUSION 1) Periodic maintenance of structures is essential. 2) Each and every problem should be properly analyzed and then the appropriate repair methods undertaken. 3) Primary design of the building reflects its performance in long run. 4) Each repair technique is suitable only for the particular application for which it is meant for. 5) Cost should not be significant planning factor in rehabilitation though it is a deciding factor. 6) Due to moisture, walls get patch off and brick walls losses its strength, so the mentioned repair works for bricks and plaster of walls is well recommended. 7) Due to some adverse conditions cracks will form in walls and slab which disturbs the functioning of structure, so the earlier mentioned methods are very useful for repair of cracks and rehabilitation of structure. 8) RCC structures gets deteriorated due to corrosion of steel which ultimately results in improper functioning of structure ,so above mentioned methods like RCC jacketing, Plate Bonding Guniting/Shortcrete etc., are very useful in rehabilitation of structures. 9) Form and Pump technique which has become the alternative for grouting, guniting now-a-days is also cost effective in large scale operations. 10) Due to improper settlement of underlying soil the foundation damaged by which all the overlying structure may get disturbed, so for the repairs of foundations methods like Shoring and Underpinning are recommended. Page | 54 REFERENCES 1) HANDBOOK ON REPAIR AND REHABILITATION OF RCC BUILDINGS PUBLISHED BY DIRECTOR GENERAL (WORKS), CENTRAL PUBLIC WORKS DEPARTMENT, GOVERNMENT OF INDIA, NIRMAN BHAWAN. 2) INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY ON REPAIR AND REHABILITATION OF STRUCTURES (2014). 3) JOURNAL ON “REPAIR AND REHABILITATION OF RCC STRUCTURES” BY P P AMBEDKAR M.E, CIVIL (Construction & Management). 4) S N SINHA, RCC DESIGN, TATA MCGRAW-HILL PUBLICATIONS LTD-2002. 5) B SIVAGNANAM “REHABILITATION” INDIAN CONCRETE JOUNRAL, DECEMBER-2002, VOL 76. 6) ALLEN R.T.C, REPAIR OF CONCRETE STRUCTURES,JOHN WILLEY & SONS (1987). Page | 55 Page | 56