Repair, Rehabilitation & Retrofitting

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eMAGAZINE Constrofacilitator

January 2023

Knowledge and b2b portal for construction and infrastructure

Volume-05 eM-01

REPAIR REHABILITATION RETROFITTING

Repair & Rehabilitation of Rcc Structures Structural Retrot Repair and rehabilitation materials Hire the Right Structural Rehabilitation Consultant Structural Retrotting of Chitpore bridge Types of Non-destructive testing used in structures

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REPAIR REHABILITATION RETROFITTING

Repair and Rehabilitation includes several systematic approaches that are lined up with various strategies to promote a desired level in attaining maximum life of the structure. These are achieved by selection of suitable methods and proper construction and maintenance of the structure. The objective of any repair / rehabilitation or strengthening works is to enhance the performance of the structure, extend the service life or increase the load carrying capacity. A rational approach to any repair and rehabilitation work is to consider the source of the cause of the deterioration and symptoms together because treating only the symptoms without adequate understanding of the cause of the problems leads to defects camouflaged beneath the finishes. In any circumstances, the repair of repairs has to be clearly avoided. By using suitable methods, we can minimize the losses and damages in the construction of reinforced cement concrete structures. Proper supervision is required for maintenance. Regular inspection and periodical inspections play a very good role in strengthening the structure. In this edition of eMag, we have covered topics such as Repair and Rehabilitation of RCC Structures, Di erent types of repair and rehabilitation materials, Structural Retrofitting of Chitpore bridge by Sanrachana, Di erent types of Non-destructive testing used in buildings and structures, Structural Retrofit – A corrosion consequence, Repair & Rehabilitation of Rcc Structures Damaged by Corrosion, How to Hire the Right Structural Rehabilitation Consultant, etc.

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04 Repair and Rehabilitation of RCC Structures 08

Different types of repair and rehabilitation materials

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Structural Retrofitting of Chitpore bridge by Sanrachana

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Different types of Non-destructive testing used in structures

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Structural Retrofit - A corrosion consequence

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Repair & Rehabilitation of Rcc Structures Damaged by Corrosion

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How to Hire the Right Structural Rehabilitation Consultant

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Constrofacilitator • January 2023

REPAIR AND REHABILITATION OF RCC STRUCTURES

Repair and Rehabilitation of RCC Structures

Er. Shamanth Kumar M, Managing Director, Skanda Group of Constructions

INTRODUCTION Cement concrete is one of the most important construction materials and it has end up being practically basic to the present day development. Concrete is strong enough mechanically, yet it is vulnerable to deterioration and thus gets damaged and even fails. This deterioration of the structures may be due to the weathering action, fire, soil failure, defects in construction and also due to natural calamities like flood, tsunami, earthquake etc. Sometimes, even engineers do not realize that the reinforced concrete structures require periodic maintenance. That's why the factors important for durability of concrete structures many times not given due importance for construction and maintenance. Due to these reasons, some measures are adopted to reduce the effect of deterioration which greatly enhances the durability of structures. According to the consideration of time and money, repair of the damaged part of structure is the most favorable. Repair is the technical aspect of rehabilitation which refers to the modification of a structure partly or wholly which is damaged in appearance or serviceability. Repair and rehabilitation extended the life time of concrete structure so there is no issue for spending the billions on the repair of concrete structures. Repair of deteriorated structures having situations or conditions which are totally different from those encountered in new construction, although every repair have unique conditions and special requirements. Hence, it is important to select more

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appropriate repair material for particular type of deterioration. Structure repair and rehabilitating is a technique by which the probability of the existing structure can be enhanced so that it will survive for a long period of time. This can be accomplished through the addition of new structural elements, the strengthening of existing structural elements and/or the addition of base isolators. Repair and rehabilitation for concrete structures can be classified broadly into two categories: a) repair in which damages due to deterioration and cracking is corrected to restore the original structural shape and size while the core is mostly intact and b) repair which is necessary to strengthen the load carrying capacity of members which have become structurally deficient over a period of time. The main purpose of repair is to bring back the architectural shape of the building so that all services start working and the functioning of building is resumed quickly. Repair does not pretend to improve the structural strength of the building. The ancient /historical buildings require repair to regain the some strength, durability and stability as it was before. The new technologies and new repair materials which have been extensively being used by the advanced countries are also being tried in developed country like India. Many construction materials are being used for the repair of existing structures. different repair materials which are used for the purpose of regaining the strength of structures have been discussed. It also highlights the various methods used for repair and rehabili-

January 2023 • Constrofacilitator

REPAIR AND REHABILITATION OF RCC STRUCTURES

tation of structures.

c) Application of repair materials

REPAIR

When the concrete surface is prepared, a bonding coat such as cement slurry, epoxy, resin materials etc. must be applied to the whole exposed surface which was cleaned before without any delay.

Repair: Repair is the technical aspect of rehabilitation which refers to the modification of a structure partly or wholly which is damaged in appearance or serviceability. Stages of repair: The various stages for the repair of concrete structures are as follows: Ÿ Ÿ Ÿ Ÿ

Removal of damaged concrete. Pre treatment of surfaces and reinforcement. Application of repair materials. Repair Procedure

a) Removal of damaged concrete Ÿ

Ÿ Ÿ

Ÿ

Before the execution of repair in any structure, one most important factor is to remove the damaged concrete. The equipment's and tools used for the removal of damaged concrete mostly depend on the damage. Damaged concrete are normally removed by using hand tools sometimes it is impossible to use hand tools then it can be removed with a light or medium weight air hammer fitted with a spade shaped bit. Care should be taken while removing the damaged portion that it must not damage the unaffected concrete portions.

b) Pre treatment of surfaces and reinforcement: It involves the following steps: Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

Unsound material must be completely removed. Undercutting along with the formation of smooth edges. Surface cracks must be removed. Formation of a well defined cavity geometry with rounded inside corners. Uniform surface but rough for repair can be provided. Before the repair, dirt, oil and all other loose particles should be removed out from the cavities. It can be accomplished by blowing with compressed air, hosing with water, acid etching, wire brushing, scarifying or a combination. Brooms or brushes will also help to remove loose material.

January 2023 • Constrofacilitator

d) Repair procedure The repair of any damaged structure can be discussed under two categories such as: ordinary or conventional procedures and sometimes using special procedures including the latest techniques and newer materials. It must be done with one or more objectives which are as follows: Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

To increase the strength. To improve the performance of structure. To provide water tightness. To improve appearance of concrete surface. To improve durability. To prevent access of corrosive materials to reinforcement.

REPAIR MATERIALS Cement and steel are generally used for the repair of various types of damages. Besides these, some special materials and techniques are available for best results in the repair works. They are described below:Ÿ Ÿ Ÿ Ÿ Ÿ

Shotcrete. Epoxy resins. Epoxy mortar. Gypsum cement mortar. Quick setting cement mortar.

Shotcrete Shotcrete is a strategy for applying a mix of sand and Portland concrete which blended pneumatically and passed on in dry state to the nozzle of a pressure gun, where water is blended and hydration takes place only before expulsion. The material bonds splendidly to the arranged surface of masonry and steel. In adaptability of use to curved or irregular surfaces, its high quality after application and great physical attributes, make for a perfect way to accomplish included auxiliary capacity in dividers and

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REPAIR AND REHABILITATION OF RCC STRUCTURES

different components. There are some minor limitations of clearance, thickness, course of use, and so on. Epoxy resins These have high tensile strength as these are excellent binding agents. Epoxy resins are prepared chemically whose compositions can be changed according to the requirements. These are blended just before the application. The final product obtained is of low viscosity and can also be easily injected in small cracks. While for the filling of larger cracks, higher viscosity epoxy resin may be used. Epoxy mortar Epoxy mortar is a combination of epoxy resins with fine aggregates which has higher compressive strength, higher tensile strength and a lower modulus of elasticity than the Ordinary Portland Cement concrete. Epoxy cannot be used alone as it is a combustible material. Gypsum cement mortar The structural application of gypsum cement mortar is limited as it has lowest strength at failure.

Fig 1: Grouting

around precast connections, stopping leakages, placing adhesives and soil stabilization. It is a mixture of cement, water and some other material such as sand, pozzolons and water reducing admixtures. Procedure of grouting Ÿ

Ÿ

Ÿ

Quick-setting cement mortar This material is patented and was originally developed for the use as a repair material for reinforced concrete floors adjacent to steel blast furnaces. It is non-hydrous magnesium phosphate cement with two components, a liquid and a dry, which can be mixed in a manner similar to Portland cement concrete. METHODOLOGY FOR REPAIR AND REHABILITATION The methodology for repair and rehabilitation are as follows: Ÿ Ÿ Ÿ Ÿ Ÿ

Grouting. Guniting. Routing and sealing. Stitching. Drilling and Plugging.

1. Grouting: Grouting as shown in Fig. 1 is the technique by which the material can be placed into cavities or holes present in the structure. It is used for increasing the load bearing capacity of a structure, filling voids

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Ÿ

A mixture of cement sand grout is prepared by employing 1:2 along with the water cement ratio between 0.6 and 0.8 using a mechanical mixer. The mixture is sent down under pressure (of about 120 kg/cm²) through a 30-50 mm diameter pipe terminating into steel cages. As the grouting continues, the channel is raised slowly up to a stature of not more than 60 cm above its beginning level after which it is pulled back and set into the following cage for additional grouting by a similar methodology. After the process of grouting for a height of about 60 cm, this operation is repeated, if necessary, for the next layer of 60 cm and repeated continuously.

2. Guniting It is a process which utilizes dry material from the machine to the surface whichever needs to be repaired through the nozzle by applying high velocity and compressed pressure. It is also called as the dry-mix Shotcrete process as shown in Fig.2. Procedure of Guniting Ÿ

Ÿ

The cement is mixed with moist sand and afterward required amount of water is added as the admixture comes out from the gun. Quantity of water can be regulated with the help of a regulatory valve. Firstly, the surface on which repair work required must be washed and cleaned. Then the nozzle of

January 2023 • Constrofacilitator

REPAIR AND REHABILITATION OF RCC STRUCTURES

Ÿ

Ÿ

Then this groove must be cleaned by air blasting, sandblasting, or water blasting and further it was dried. On the dry groove, a sealant is placed which is further allowed to cure.

4. Stitching

Fig 2: Guniting

Ÿ

Ÿ

gun is kept at a distance of about 750 mm to 850 mm from the surface to be repaired and the velocity of nozzle varies from 120 to 160 m/s. Sand and cement are initially dry mixed in a mixing chamber and the dry mixture is taken through a pipe to a nozzle, where it is forcibly projected onto the surface to be coated. The purpose of regulatory value is to provide a mix of desired stiffness which will adhere to the surface against which it is projected.

When the tensile strength of any structure needs to reestablished across the major cracks, stitching as shown in Fig. 4 must be used. It involves the process of drilling the holes on both sides of the crack and grouting in Ushaped metal units with short legs (staples or stitching dogs).

3. Routing and sealing It is used for treating both larger and fine pattern. This treatment reduces the chances of moisture to reach the reinforcing steel or pass through the concrete which can cause surface stains or other problems. For floors, the sealant should be sufficiently rigid to support the anticipated traffic. Routing and sealing was done as shown in Fig. 3. Procedure for Routing and Sealing Ÿ

First a groove of depth ranging from 6 to 25 mm at the surface is prepared.

Fig 4: Stitching

5. 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 applicable only when cracks run in reasonable straight lines and are accessible at one end. This method is often used to repair vertical cracks in retaining walls. Conclusion Ÿ Ÿ

Ÿ

Fig 3: Routing and Sealing

January 2023 • Constrofacilitator

Repair and Rehabilitation is necessary to save hazardous failure of structures due to deterioration. It is recommended for old buildings which have some signs like cracks, corrosion of embedded materials, etc. Therefore, timely maintenance of structures is required. Selection & evaluation of right repair material and protective coatings will save enormous money & time by reducing the repair costs of concrete buildings/structures.

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REPAIR AND REHABILITATION MATERIALS

Different types of repair and rehabilitation materials

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comprehensive assessment of primary health centre (PHC) and health sub-centre (HSC) buildings across Chennai conducted by the Directorate of Public Health and Preventive Medicine, has identified 1,400 buildings that require immediate maintenance and repairs. The report pointed out that nearly 11,000 buildings were under the DPH, of which roughly 1,400, including those of some PHCs, required immediate maintenance and repairs. Uttarakhand's Joshimath is sinking. Cracks on walls and buildings were first reported

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in 2021, as Chamoli experienced frequent landslides and flooding. As per reports, the Uttarakhand government's expert panel in 2022 found that several pockets of Joshimath are "sinking" owing to manmade and natural factors. The panel's findings stated that ground subsidence - a gradual settling or sudden sinking of the earth's surface due to the removal or displacement of subsurface materials - has induced structural defects and damage in almost all wards of the city. Studies have blamed natural factors such as worn-out rocks, the location of the city, and humaninduced rapid construction of buildings, hydropower projects, and national highways, etc. for the current situation.

This is the state of crisis across India. As Indian cities grow older, the passage of time takes its toll on the infrastructure including its buildings. Climate change is further worsening the matter, with more extreme weather events. Over time, buildings and structures have started showing signs of deterioration and need constant repair. While proper maintenance can prolong the life of buildings, negligence often leads to casualties. Timely detection of deterioration and preservation of buildings can go a long way in making our urban landscape more habitable and safer.

January 2023 • Constrofacilitator

REPAIR AND REHABILITATION MATERIALS

A structure or building over time may show signs due to upgrading of design standards, increased safety requirements, change in its function, increase in load use of low-quality concreting materials, lack of maintenance etc. The distressed structure or building needs to be restored to the required strength. This creates an ultimate necessity for repair and rehabilitation to make the existing structural members safe. In such scenarios appropriate method and material is a prerequisite to regaining their structural strength. While the specific requirements will vary from one project to another, certain properties or characteristics are necessary in a repair material. The repair material should be similar to the substrate in terms of its stiffness or flexibility, its thermal expansion properties, water absorption, and water vapor diffusion. The durability of a repair depends on a proper bond with the substrate and between layers of repair material. The essential parameters for deciding upon repair and rehabilitation materials are: Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

Low shrinkage properties Setting/hardening properties Good bond strength with existing substrate Compatible coefficient of thermal expansion Compatible mechanical properties to that of the substrate Minimal or no curing requirement Low air and water permeability Non-biodegradable

Different types of repair and rehabilitation materials

Polymer Modified Mortar

Where reinforcing bars of two sizes are lap-spliced in tension, it is better to use the larger of the tension lap splice length for the smaller bar. The length of a lap splice varies with concrete strength, type of concrete, the yield strength of the reinforcing bars, bar size, bar spacing, concrete cover, and the number of ties or stirrups. Preplaced-Aggregate Preplaced aggregate is produced by placing coarse aggregate in a form and then later injecting a portland-cement-sand grout, usually with admixtures, to fill the voids. As the grout is pumped into the forms, it will fill the voids, displacing any water, and form a concrete mass. Typically, preplaced-aggregate concrete is used on large repair projects, particularly where underwater concrete placement is required or when conventional placing of concrete would be difficult. Typical applications have included underwater repair of stilling basins, bridge piers, abutments, and footings.

Non-shrink Grouts

January 2023 • Constrofacilitator

Epoxy resins Epoxy resins are excellent bonding agents which are used as a repair material. The use of epoxy resins gives high strength in the repair works. Epoxy resins are composed of chemicals with proportions which when changed give results as per requirement. These epoxy components are

Discussed below are different types of materials used for the repair and rehabilitation of buildings and structures.

Non-Shrink Grout is a pre-blended, pourable, non-metallic, Portland-cementbased material used for grouting steel columns, bearing plates, precast concrete and anchors. Non-Shrink Grout can repair an uneven foundation, distributes the weight of the unit, and prevents shifting after settling and leveling the unit. It is applied for patching of honeycombs, tie-bolt holes, accidental damage, break-outs, and pack-filling of gaps and voids.

Polymer-modified mortar reduces the rate of water evaporation, allowing the crystal structure to keep growing and building strength during these critical early curing stages. This reduced water evaporation is especially important in thin applications, where the surface area for evaporation is high, relative to the volume of the mortar. It acts as an adhesive to enable the modified mortar overlay to stick to a variety of surfaces such as concrete, masonry, brick, wood, rigid polystyrene and polyurethane foam, glass, and metals.

Alkaline Rust Converting Primer It is applied on rusted steel surfaces to form a complex compound. During the application of primer, the deoxygenating agent is formed which makes the rusted steel surface more corrosion-resistant.

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REPAIR AND REHABILITATION MATERIALS

mixed just before their application. The product formed by the addition of epoxy resin has low viscosity and it can be injected in small cracks also. The epoxy resins having higher viscosity could be used for surface coating or for filling the larger cracks or holes also. Epoxy mortar Epoxy mortar is a polymer-based bonding paste that comprises materials such as epoxy resins, solvent, binder, mineral fillers and some additives. Epoxy mortar with or without the aggregate will provide an impermeable environment and barrier that will protect reinforcing steel against corrosion. It is used as an adhesive and paste for structural repair. It can also be used to fill gaps, cracks and vents in driveways, patios and plazas

Sealants Concrete sealants are used to protect or repair cracks to seal joints. Sealants ensure structural integrity against the passage of harmful liquids, gasses, and other undesirable substances which would impair the quality of concrete. Its function is to improve thermal and acoustical installations, damp vibrations, or prevent unwanted matter from collecting in crevices.

and drying shrinkage These are utilized in concrete to minimise the plastic shrinkage cracking and drying shrinkage cracking. They also lessen the permeability of concrete and therefore reduce the flow of water. It has become a popular reinforcement material. Its application is not restricted to precast concrete, shotcrete, and tunnel Linings. It is also primarily used in industrial flooring and paving.

Carbon fiber-reinforced polymers

Anti-carbonation coatings

Quick-Setting Cement Mortar This quick-setting cement mortar is used as a repair material for reinforced concrete floors that are adjacent to steel blast furnaces. This mortar is a non-hydrous magnesium phosphate cement with two components, a liquid and a dry. It features low dry shrinkage, fast hardening speed, and high strength. It is used to repair sewers and culverts, floors, bridges etc.

Anti-carbonation coating protects reinforced concrete and other masonry cementitious substrates that are directly exposed to atmospheric conditions like UV radiation, high humidity, heavy rain, industrial pollution, & carbonation. It penetrates into the porous concrete substrate, producing an exterior masonry impermeable coating. It is used for bridges, flyovers, subways, underpasses, parking garages, tunnels, chimneys, industrial structures, stadiums, and RCC water tanks.

.Carbon fiber reinforced polymers are composite materials made of thin, strong crystalline filaments of carbon that are used to strengthen the material. Carbon fiber can be thinner than a strand of human hair and gets its strength when twisted together like yarn. Then it can be woven together to form cloth and if needed to take a permanent shape, carbon fiber can be laid over a mold and coated with resin. It has very high tensile strength and is also very lightweight. When bonded to the exterior of a concrete column, beam, or slab, it can add significant strength without adding weight that would increase the load on foundations and other structural members.

Steel fibers Steel fibers are usually used in concrete to control cracking due to plastic shrinkage

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January 2023 • Constrofacilitator

REPAIR AND REHABILITATION MATERIALS

Its advantages include; Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

High strength with low weight Minimal change to structure's shape, weight or appearance Corrosion resistance Thermal compatibility Flexible wrap allows tailoring to the desired shape Excellent fatigue behavior Faster repair than conventional methods Welding and heavy equipment are

not needed Minimal disruption and noise during preparation or installation

It is used for; Ÿ Ÿ Ÿ Ÿ

Structural reinforcement of building beams, columns and floor slabs Reinforcement of bridges, jetties and deck structures. Corrosion and reinforcement of commercial and industrial buildings Pipe structure reinforcement

Conclusion It is always better to appoint a specialist structural surveyor to monitor the situation before any works are deemed necessary. It is essential, therefore, that contractors with the necessary competencies and products from experienced manufacturers for getting desired repair and rehabilitation results.

Badrinath highway develops cracks amid Joshimath crisis Cracks measuring one-to-two metres have developed on the Badrinath national highway in Joshimath, where expanding fissures in hundreds of residential and commercial buildings amid land subsidence have triggered panic and forced the relocation of hundreds of families. District authorities, however, said the cracks aren’t “a cause of concern” and will be repaired before the annual pilgrimage to Badrinath, which usually starts in May. Over 863 houses of the around 4,500 buildings in Joshimath — known as the gateway to Badrinath and Hemkund Sahib pilgrimage sites — have developed cracks since October 2021. At least 181 of the buildings in the town have been placed in the unsafe zone, and 275 families have been moved out to safer areas, district authorities have informed. A small crack that has appeared on the Badrinath highway is load induced but it isn’t a cause of concern, Chamoli district magistrate Himanshu Khurana said on Saturday, citing experts of the Central Building Research Institute. Local residents, however, said the cracks have appeared at different spots. “The Badrinath highway has cracks at different spots up to Marwari flyover over the Alaknanda river. The government should get them repaired immediately,” said taxi driver Rajendra Saklani. Atul Sati, convener of the Joshimath Bachao Sangharsh Samiti, too, said: “A large part of Badrinath highway is in the grip of the land subsidence.” Taking note of the matter, state disaster management secretary Ranjit Kumar Sinha said that the local administration

January 2023 • Constrofacilitator

has been keeping a close watch on the land subsidence on the highway and the road will be repaired before the pilgrimage season. The agencies concerned have been instructed to repair the road, he said, adding that it would be done before the Char Dham Yatra. The Char Dham Yatra is an annual tour of the four Hindu shrines located in Uttarakhand -Yamunotri, Gangotri, Kedarnath and Badrinath. Hemkund Sahib, one of the most sacred sites for Sikhs, is also connected to the Char Dham Yatra. The pilgrims visit all four places one-by-one in a clockwise direction starting from Yamunotri, then Gangotri, Kedarnath and lastly Badrinath. The four shrines remain shut for around six months every year, opening in summer and closing with the onset of winter. This year, however, land subsidence in Joshimath and now cracks on the highway could pose a threat to the yatra, which is scheduled to begin in April or May.

The issue will be discussed in a high-level meeting to reduce the burden of pilgrims and vehicles on the gateway town in Chamoli district, an official privy to the matter said. “Thousands of pilgrims stay in Joshimath as they halt in the town on the way to Badrinath, and a discussion in this regard to reduce the burden of pilgrims and vehicles on the sinking town would come up during a high-level meeting,” said Ajendra Ajay, chairman of the Badrinath-Kedarnath temple committee. Meanwhile, the Uttarakhand government on Saturday wrote to the Border Roads Organisation (BRO) to consult the Geological Survey of India (GSI) and the Indian Institute of Technology (IIT), Roorkee, on resuming the work on Helang-Marwari bypass under the Char Dham all-weather road project that was halted by the district administration in the first week of January after protests by local residents. Source: hindustantimes.com

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CASE STUDY

Structural Retrofitting of Chitpore bridge by Sanrachana

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epair and retrofitting of vulnerable bridges is a necessity in the city of Kolkata. The bridges in the city of Kolkata are as old as its culture and heritage, one such bridge is the Chitpore bridge. As per getbengal.com in 1843, it was constructed under the engineering leadership of Captain John Thomson, who was the Superintendent of Canals and Agent for Iron Suspension Bridges. It spans 99 feet and has a roadway that is 24 metres wide. It was popularly referred to as the Bagbazar Bridge. It is one of the earliest examples of the bowstring

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bridge. Deterioration is a common problem in bridges and Chitpore Bridge is no exception. KMDA conducted structural inspection of Chitpore bridge The Kolkata Metropolitan Development Authority KMDA, conducted structural inspection of several bridges in Kolkata and came to a realisation that Chitpore bridge falls under the category of “vulnerable bridges and flyovers”. It needed immediate repair and restoration to avert any major mishap in the near future.

January 2023 • Constrofacilitator

CASE STUDY

Non- Destructive Test of Chitpore Bridge In August 2019, LASA was awarded consultancy services for Chitpore Bridge. The present condition of the bridge was soon surveyed and Non- Destructive tests were performed. The seemingly healthy bridge revealed active corrosion in selected areas. NDT test revealed that; Ÿ Ÿ

Ÿ Ÿ

In the vertical hangers, steel reinforcement has lost its diameter at several locations Spalled portions and discontinuous rebars were visible in hanger columns, under the deck slab and on cross beams The structural strength of sectional members was compromised by corrosion Pitting corrosion of the embedded steel in the vertical hangers and in the beams supporting the deck

Adding to its already distressed condition, nearby Tala Bridge was closed down, sending substantial traffic to Chitpore Bridge. To prevent a catastrophe, an immediate strengthening of the structural system was necessary. It had to be done fast with due diligence. That’s where Sanrachana came to the rescue.

Spalled portions show exposed and discontinuous rebars in hanger columns, under deck slab and on cross beams

Repair and Retrofitting of Chitpore Bridge executed by Sanrachana Sanrachana is one of the pioneers in the area of structural retrofitting & protection in India and has decades of experience in executing bridge repairs across the country. It has served clients on over 2000 projects involving commercial properties, industrial facilities, energy plants and public infrastructure of varying scale. Overview of work executed: Ÿ Ÿ Ÿ Ÿ

Sandblasting, anti-corrosion treatment Providing additional rebars, micro-concreting Strengthening of hangers, deck & cross beams with SRM carbon laminates & SRM C-wraps Post-tensioning 4 Mac-alloy bars with 5 tons each, to counteract tension on each hanger

The team started repair work with sandblasting in Chitpore to get clarity on underlying distressed concrete. Delamination and spalling were detected and removed with a hammer and chisel. The exposed rebars of the hangers were treated for corrosion. The section January 2023 • Constrofacilitator

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CASE STUDY

was rebuilt with high-strength micro concrete. The underside of the bridge was made accessible with platforms supported by a structural steel section.

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With basic repairs done, the team moved towards strengthening. The strengthening of hangers, decks & cross beams was done with SRM C-Lam carbon laminates & SRM C-wraps.

January 2023 • Constrofacilitator

CASE STUDY

The base of the hangers were armoured with a 1.2m cover block. Structural steel sections were used on the top of hangers above the RCC arch. Connecting these, high-strength Mc-alloy threaded bars were installed. The tensioning mechanism was to be operated from the top of the hangers.

Mechanism of post-tensioning Upon tightening the McAlloy bars, tension force is developed in it, because of which, a reaction force of compression is generated on the RCC hangers. With the application of protective coating, the work was completed. All the contract criteria were met by Sanrachana. ABOUT SANRACHANA STRUCTURAL STRENGTHENING PVT. LTD. The company is committed to taking responsibility of the structural retrofitting projects right from planning and design to execution giving due consideration to budgets, schedules, service life or any other unique structural requirement and completing the projects in a safe, planned and professional manner. They are a leading service provider in the field Structural Repairs, Rehabilitation, Strengthening & Retrofitting.

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NON-DESTRUCTIVE TESTING

Different types of Non-destructive testing used in structures

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on-destructive testing is used for inspecting, testing and evaluating the quality of materials and existing structures and the causes of damages. There are various NDT test methods to detect issues such as cracks, voids, inclusions, and porosity. This method can also be used to measure the thickness, hardness and the properties of materials.

Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

Purposes of Non-destructive Tests; Ÿ Ÿ

Estimating the in-situ compressive strength

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Estimating the uniformity and homogeneity Estimating the concrete strength and elasticity Identifying areas of lower integrity in comparison to other parts Detection of the presence of cracks, voids and other imperfections Chloride, sulphate, alkali contents or degree of carbonation Assessing the potential durability of the concrete Providing information for any proposed change of use of a structure Measuring the volume or density of the material and components of a concrete structure

Ÿ

Ÿ

To determine the strength of Old Concrete Structures (like Bridges, Building etc) Leakage testing and detection

Types of non- destructive testing There are different types of nondestructive methods, each of these methods can help you spot a material's defects in different ways. Few of the nondestructive methods are discussed below. Ultrasonic test Ultrasonic testing uses high-frequency sound waves called ultrasonic pulse January 2023 • Constrofacilitator

NON-DESTRUCTIVE TESTING

Concrete resistivity test

waves to detect flaws or other imperfections or defects in metal components, and it can also be used to identify and monitor changes like shifts in thickness within the components that may result in failure or other problems in the future. One of the most common uses of ultrasonic testing is to evaluate corrosion in pipelines and other enclosed structures or components. Ultrasonic testing is most commonly performed on metals and metallic alloys, but it can also be used to test concrete and composites. Rebound Hammer test The rebound hammer test measures the elastic rebound of concrete and is primarily used for estimation of concrete strength and for comparative investigation. The method could be used for assessing the likely compressive strength of concrete with the help of suitable correlations between rebound index and compressive strength, assessing the uniformity of concrete, assessing the quality of the concrete in relation to standard requirements, and assessing the quality of concrete.

riod of time to help reveal defects that extend below the component's surface. Penetration Tests The penetration test, typically utilising the Windsor Probe test system, consists of a device that drives a probe into the concrete using a constant amount of energy. The probe is made of a hardened steel alloy specifically designed to crack the aggregate particles and to compress the concrete being tested. Once fired, the length of the probe projecting from the concrete is measured. A test typically consists of firing three probes and averaging the projecting lengths.

Half-cell Potential test The half-cell potential test is used for assessment of the durability of reinforced concrete and helps in diagnosing reinforcement corrosion. A more negative reading of potential is generally considered to indicate a higher probability of corrosion.

The concrete resistivity test is used to evaluate the electrical resistivity of watersaturated concrete. The resistivity test of a given structure gives information about the risk of early corrosion damage, because generally a low concrete resistivity is correlated to rapid chloride penetration and to a high corrosion rate. Bulk resistivity and surface resistivity are two most popular methods used for concrete resistivity test. Bulk resistivity is performed by placing a metal electrode plate with conductive foam inserts at each end of a cylinder or core and measuring potential values between opposite ends. Surface Resistivity uses a four-probe Wenner electrode array to measure electrical resistance. The Wenner array consists of four equally spaced electrodes. The external electrodes apply low-frequency alternating current on the moist concrete surface, while the inside probes measure electrical resistance.

Carbonation depth test Carbonation depth test is used to determine the extent of carbon dioxide infiltration into the concrete. The process is similar to chloride ion testing where a sample is either removed, either by coring or drilling and the sample is tested by the application of a revealer. The revealer com-

Liquid penetrant test Liquid penetrant testing is one of the oldest methods of non-destructive testing. The testing method uses capillary forces to find surface cracks or pores and make them visible. It can detect surfacebreaking flaws such as cracks, laps, porosity. In this method, a penetrant is applied to the surface of the component to be tested. After the penetrant is applied, it is allowed to “soak in” for a prescribed peJanuary 2023 • Constrofacilitator

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NON-DESTRUCTIVE TESTING

monly used is phenolphthalein. When phenolphthalein comes into contact with high pH (>10) concrete the solution shows as bright pink. When the solution comes into contact with low pH (