Repair & Rehabilitation of Concrete Structures - A Paradigm Shift

SK Singh
S. K. Singh, Senior Principal Scientist, CSIR-Central Building Research Institute, Roorkee, India
Concrete structures show distress signs and deterioration even at very early stages due to reasons such as physical and chemical factors, wear and tear, and failure of structures. Therefore, repair and rehabilitation of concrete is becoming inevitable, and an industry of importance equivalent to construction industry.

Fibre-reinforced polymer (FRP) composite materials with their high strength-to-weight ratio, is considered an innovative way for strengthening of concrete structures, while adding minimal additional weight to structures. Masonry structures are also strengthened with FRP, which is an integrated system based on fibers such as carbon, glass, aramid etc. and epoxy resins. This is an ideal technique as it combines the advantage of using non-corrosive and lightweight advanced composite materials in the form of FRP. In addition, by pre-stressing the Carbon Fiber reinforced polymer (CFRP), laminates are also used more efficiently in strengthening the structures by utilising its tensile capacity.

Gopal L Rai
Gopal L Rai, Managing Director, Dhirendra Group of Companies (DGC), Mumbai, India
An innovative mechanical anchorage system was developed to prestress the FRP laminates directly by jacking and reacting against the RCC structure. This paper describes the use of FRP and pre-stressed CFRP laminates for strengthening of RCC structures. There is an urgent need to bring all the stakeholders of this industry together for sharing knowledge in the innovations being made in repair techniques.


Repair and rehabilitation of rapidly deteriorating structures is a matter of concern for most countries in the world. Deterioration is observed in the form of cracking and corrosion (Riveros et al., 2018). It is very difficult to assess in totality the causes of damage, mapping the extent of damage, proper corrective prescription, prediction of residual life with and without repair measures, instrumentation, monitoring and maintaining the health, and, most importantly, to strike a cost benefit ratio of the repair. This makes the industry large and multifaceted and there is substantial amount of knowledge available on the issues.

Fibre reinforced polymer (FRP) composites such as glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) are being widely used for enhancing the load carrying capacity of reinforced concrete structural members (Jayasuriya et al., 2018 and Karatas et al., 2018). These composites consist of high strength fibers bonded in a resin matrix with the fibers as the main load carrying elements, whereas the resin or polymer matrix acts as a load transfer medium and protects the fiber from environmental damage.

Paradigm Shift

These FRP composites are heterogeneous, anisotropic and do not exhibit plastic deformation (Karatas et al., 2018). The provision of FRP around reinforced structures improves the bond strength between steel reinforcement and concrete by providing axial stress. It possesses good tolerance under various types of loadings, such as monotonic or cyclic (Boroujeni et al., 2018). The FRP wrapping prevents the entry of aggressive ions such as chloride ions, which delay the corrosion rates of reinforcement in concrete and slows down the degradation of structures. The confinement of FRP slows the degradation due to cracking, inhibits seepage of water through these cracks and helps in repair of cracks that are formed within the structures (Liang et al., 2019).

The effectiveness of FRP composites for rehabilitation work mainly depends on structural assessment, suitable design, its manufacturing and ion-site application. The performance of the FRP fabrics depends on the bond characteristics between the fabrics and the concrete structures. The bond governs the load transfer mechanism between the FRP fabrics and the structural matrix. Hence, the concrete crack spacing, crack width and reinforcement development length is controlled by FRP application (Meng et al., 2018).

The increasing application of these materials is owing to the advantages it offers with respect to the other conventional methods of strengthening. They are effective as strengthening materials due to their lightweight, non-corrosive, high tensile strength, high fatigue resistance, low density, high stiffness and durability. In addition, these materials can be made into any size and geometry and require less efforts in installation in comparison with other conventional materials of strengthening. The structures can be strengthened using these materials in relatively less amount of time without causing any hindrance to the normal functionality or affecting the aesthetics.

This method of strengthening is extensively studied, and various codes and guidelines are for the ease of application in actual structures (ACI 440 and CEB-FIP Report). FRP can be used for strengthening of concrete, masonry, timber and steel structures. Extensive research has been carried out on their successful use in strengthening of RCC slabs and beams to increase their flexural and shear capacity (Irwin et al., 2001) and increase of confinement in axially loaded columns. In addition, it has been found that application in masonry structures has reduced cracking and has increased the load carrying capacity and ductility.

Causes distresses concrete buildings
Figure 1 : Causes of distresses in concrete buildings

Repair & Rehabilitation Industry In India

Any concrete structure exhibits signs of distress and deterioration at an early age of construction due to various reasons, leading to repair works as shown in Fig. 1 (Suryawanshi, 2012).

As repair is inevitable in any structure, the repair industry is present in every nook and corner of India. However, the industry is not well organized. Thus, the exact figure of annual cost to stakeholders of the industry is not available. However, cost involved is found to be greater than that of the developed western countries.

Approach Towards Repair and Retrofitting of Structures

The engineering analysis, design and constructability are necessary steps for finalization of repair and retrofitting strategies, keeping in mind the following aspects (Chander, 2014), which define the basic approach towards developing a repair system.

Functionality Aspect: The basic function / operation of the structure should not be hampered.

Structural Safety Aspect: The susceptibility of the structure to an earthquake event has to be within acceptable standards.

Importance Level Aspect: Historic buildings / structures with immense archeological importance are sometimes beyond the cost factor for retrofitting. Such structures have to be rehabilitated without changing its aesthetics and architectural features.

Construction Methodology Aspect: The retrofitting has to be performed using latest construction techniques that have a minimal impact on the normal functioning of the buildings.

Economy Aspect: The entire cost of construction has to be practical and logical towards extended life of the structure.

Skilled Labour Availability: The repair & retrofitting practices need unusual construction method and is a highly technical job that and calls for utmost care while implementing. A very skilled workmanship must be provided to implement the suggested measures.

Based on the above aspects, the repair method adopted may be surface repair, protection, waterproofing, rehabilitation, strengthening etc. To implement this successfully, skilled expertise and specialized training is necessary. In India, the same contractor works on all kinds of works, which includes execution of new construction work, repair work and protection works. In addition, unskilled and semi-skilled labourers are involved in repair works due to non-availability of skilled labour. This leads to repair works of sub-standard quality. In addition, it is important to use state of the art equipment and technologies for different types of repair jobs.

Various Principles Adopted in Repair and Retrofitting

Coating Jacketing
As a first step of condition assessment, which includes visual survey, mapping of distress, detailed non-destructive testing etc., to establish the root cause of damage / distress is performed, based on which, the assessment and the owners’ repair objectives and requirements, one of the following repair principles is adopted at the site. These measures may be for protection / repair of concrete or rebar. Each principle may apply various methods to achieve the same objective as listed in Table 1 (BS-EN:1504) and a few of the repair techniques are shown in Fig. 2 to Fig. 5. However, most of the repair measures suggested do not have a standard specification or code provision for its execution in India.

Repair filling

Passive and Active Strengthening System

Strengthening of structures can be done using a passive or an active strengthening system. In case of active system, external forces are introduced in the member, which counteracts the effects of internal forces. In case of passive system, strengthening will come into picture when additional loads were applied. Concrete jacketing, bonding steel plates and FRP wrappings on structural members are examples of passive strengthening system. This system is relatively easy in application but does not utilize the materials full properties.

Table 1: Various principles adopted in repair of concrete


1 Protection against ingress

Hydrophobic impregnation


bandaging of cracks

Filling of cracks

Transferring of cracks into joints

Erecting external panels

Applying membranes

2 Moisture control

Hydrophobic impregnation
Erecting external panels

Electrochemical treatment

Concrete restoration

Hand applied mortar
Recasting with concrete or mortar
Spraying concrete or mortar

Replacing elements

Structural strengthening

Adding/replacing embedded/external reinforcing bars
Adding reinforcement anchored in pre-formed or drilled holes
Bonding plate reinforcement
Adding mortar or concrete
Injecting cracks, voids or interstices
Filling cracks, voids or interstices
Pre-stressing (post-tensioning)

FRP jacketing
5 Physical resistance


Adding mortar or concrete

Resistance to chemicals


Adding mortar or concrete

Preserving or restoring passivity

Increasing cover with additional mortar or concrete
Replacing contaminated or carbonated concrete
Electrochemical re-alkalisation of carbonated concrete
Re-alkalisation of carbonated concrete by diffusion

Electrochemical chloride extraction

Increasing resistivity

Hydrophobic impregnations

9 Cathodic control Limiting oxygen content (at the cathode) by saturation or surface coating

Cathodic protection

Applying an electrical potential

Control of anodic areas

Active coating or barrier of the reinforcement

Applying corrosion inhibitors in or to the concrete

The Active system, even though not relatively easy in application, utilizes the materials properties completely. Such a system generally improves the performance of the structure and increases its serviceability by reducing cracks and deflections. Examples of such a system includes external post tensioning system, bonding prestressed FRP laminates on the structural member, etc. The nature of strengthening system to be applied depends on the magnitude of deficiency in the member. In addition, a combination of both the methods can be used for improvement in the structural performance (Mandara et al., 2002).

Prestressed FRP System

FRP composites and non-prestressed laminates are externally wrapped / bonded on the structural members to enhance load carrying capacity. This application is advantageous in several ways: It helps in enhancement of tensile strength in the direction of fibers and lowers the density of FRP composites. It develops high resistance against corrosion and harsh environmental conditions. Its application is user friendly as well. It requires the least number of equipment and is applied in a short period. However, only a partial strength of the FRP laminates is utilized by the structure. Only 30 - 35% of the tensile strength is utilized during the serviceability stage of structures. The cause for such an issue is the premature debonding failure of FRP laminates from concrete surfaces that limits the development of tensile stresses (Peng et al., 2016 and Serega et al., 2018).

Typical load deflection
Figure 6: Typical load-deflection curves by prestressed & non-prestressed laminates
(El-Hacha et al., 2001)
In order to improve the performance of FRP laminated structures under service load conditions, it is essential to actively strengthen it. This can be done by an innovative way of application of FRP by prestressing the laminates, which would enhance their strength and counter the applied loads. The technique of prestressing requires proper mechanical anchorage on concrete surface so that the shear stress does not significantly exceed the tensile strength and cause debonding (El-Hacha et al., 2001; El-Hacha et al., 2013; Serega et al., 2018 and Hong et al., 2016).

Prestressed FRP laminates on the tensile face of the flexural member improves its serviceability. It helps in increasing the fatigue life and durability of RC structures on which it is applied. It also helps to close the existing cracks, delay the formation of new cracks and reduce structural deformation within the structures (Guo et al., 2018; Rojob et al., 2018 and Hosseini et al., 2014). Prestressing is hence a useful technique as it easily overcomes the defects of passive reinforcement of FRP laminates on structures. Fig. 6 shows the typical load-deflection curves for RCC beams strengthened with non-prestressed and prestressed FRP composite laminate system.

Various techniques were developed to induce stressing in the CFRP composites for flexural strengthening (Fig.7), shear strengthening, confinement and axial load strengthening. This pre-stressing can be induced either on the surface of the structural members or on the outside. The amount of prestressing forces to be applied is carefully designed as it affects the strengthening behaviour. In case of high prestressing forces, the failure in members is possible. Hence, it is required to apply proper amount of force at the ends of the laminates.

wrap on girder
Figure 7: Application of non prestressed FRP laminates in slabs & wrap on girder

Prestressing forces should not exceed 50% of the ultimate strength of the laminates (CEB-FIP Report). Minimum level of prestressing should be 25% of the ultimate strength to improve the strength properties (El-Hacha, 2001). Mechanical anchors in the form of metallic plate can be used to provide sufficient anchorage to the laminates. Gradient anchors can also be used for the same. Prestressing of CFRP laminates can be done indirectly by cambered beam system or by inducing prestress against external steel frame, followed by bonding on the structural member to be strengthened (El-Hacha, 2001). But tensioning of CFRP laminates against the beam to be strengthened is one of the most widely used methods of prestressing. In this method, the FRP laminates are bonded on the member to be strengthened followed by application of prestress in the beams with the help of prestressing jacks at the ends of laminates. It is kept in the stretched position till the curing of the adhesive is complete. After this, the hydraulic jacks are removed and the laminate transfers the stresses to the concrete. Proper anchorages need to be placed at the ends to avoid debonding failures. This method of strengthening is highly effective.

Strengthening of Slab Using Prestressed FRP System

Excessive deflected slab
Figure 8: Excessive deflected slab (Courtesy: M/s DGC, Mumbai)
A case study of strengthening of slab panels of a reinforced concrete framed commercial building having G+11 storeys situated in Thane district of Maharashtra, is discussed in this section. The construction of the building was carried out in two stages with the G + 8 storeys being constructed in the first phase followed by addition of two more storeys after a gap of two years. The top two floor levels showed signs of cracking and excessive deflection in the flat slab panels. The deflection varied from 20 mm to 100 mm with crack pattern running along the column drop region and progressing further in the column strip. A few slabs were found severely distressed. The grade of concrete in slab was established through core tests. It was observed on inspection that at column drop interface region the negative moment reinforcement was terminated abruptly, and cracks were observed in this region. Also, at the negative moment regions of middle strip regions there was no reinforcement provided.


After carrying out an analysis of the RCC structure, it was decided to provide prestressed CFRP laminate in alternate manner at the negative moment regions at the tension face with a pre-stressing force of 50 kN. The properties of the materials used in strengthening are as per Table 2. The details of prestressing are shown in Fig. 8 to Fig. 12. After carrying out the strengthening of the slab it was subjected to load testing using water load. The slab was subjected to loading as per specifications given in IS 456: 2000. The loading was applied in stages so as to avoid any untoward mishap due to distress in structure. After full loading was applied, the readings of deflections and strain were measured, and after keeping the load on the slab for 48 hours the readings were further monitored. To check the rebound of the slab, the dewatering was done in stages and readings was recorded at consecutive intervals of time. The recovery observed in strengthened flat slab panel even after 48 hours loading post strengthening is 80.97% thereby indicating that the proposed method of strengthening has worked effectively.

Prestressing operation in slab

Strengthening of Brick Masonry Building With FRP System

The FRP systems are also being used to confine and strengthen masonry structures. A residential building, about 45 years old, was distressed. After preliminary visual inspection, the requirement for strengthening of structural member with repair of building’s other non-structural member were finalized. Fig. 13 shows ongoing retrofitting work of the building, step wise.

Performance of Repair Works

Repair/retrofitting is a complex process due to various factors involved. It is important that the engineer who addresses the issues understands the nature of the structure and its importance. The root cause of damage before suggesting a repair methodology; and understanding that life and performance of the repair work not only depend on the materials or workmanship, but also on the compatibility between the existing structure and the new materials used for repair. Due to the lack of specialists and specifications, many a times repair work does not meet the performance criteria and in turn leads to repair of repairs. Thus, the field of repair and rehabilitation of structures has not gained the confidence of people and is always looked down upon. A survey also shows that of the total repair works carried out, 50% of the works performed unsatisfactorily.

Futuristic Vision

Repair and retrofitting of structures have never been performed on a large-scale basis in India. Therefore, there are no established guidelines available for this purpose. Existing building codes do not address this problem adequately. It is the need of the day to have a vision to improve the status and performance of the repair and rehabilitation industry in India. The main objective shall be to create a repair/rehabilitation code to establish assessment, design, materials and construction practices to raise the level of repair/protection performance, establish clear responsibilities and provide building officials with means to issue permits for such work.

Table 2: Material properties of FRP composite system
Type of laminates Thickness of laminate (mm Width of laminate (mm) Ultimate Tensile strength (MPa) Ultimate strain (%)
Alternate Prestressed CFRP laminates 1.4 100 3200 1.5

There are challenges in the existing structures due to non-visible damage and unknown structural conditions, which affect the assessment of causes of distress. The lack of specific requirements for variations in repair practice and materials affects the choice of materials and hence the failure in compatibility of the old to new material, which further affects the performance and life of the repair work. Lack of safety and reliability checks or performance standards leaves the building officials with no directions, post repair.


Taking into consideration all the practical difficulties and shortcomings in repair and rehabilitation of structures, it may be proposed to develop standard guidelines for the process from diagnostics to implementation stage, along with performance standards for its acceptance.


masonry building
Figure 13: Retrofitting of brick masonry building (Courtesy: M/s DGC, Mumbai)
ACI 440.2R-08. 2008. Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures. American Concrete Institute.

Boroujeni, A. Y., & Al-Haik, M. 2019. Carbon nanotube – Carbon fiber reinforced polymer composites with extended fatigue life. Composites Part B: Engineering, 164, 537-545.

BS EN 1504 Part (I to X). 2004. Products and Systems for protection and repair of concrete structures – Definitions, requirements, quality control and evaluation of conformity. European Standards.

CEB-FIP Task group 9.3.2001. FRP reinforcement for concrete structures, externally bonded FRP reinforcement for RC structures”, fib CEB-FIP, Technical report bulletin 14.

Chander, S.S. 2014. Rehabilitation of Buildings. International Journal of Civil Engineering Research, 5(4), 333-338. Concrete Repair System.1996. A Guide to Concrete Repair. United States department of the Interior Bureau of the Reclamation Technical Service Centre.

El-Hacha, R., Wright, R. G. and Green, M. F. 2001. Prestressed fiber-reinforced polymer laminates for strengthening structures, Progress in Structural Engineering Materials, 3(2), 111-121.

El-Hacha, R. and Aly, M. Y. E. 2013. Anchorage system to pre-stress FRP laminates for flexural strengthening of steel-concrete composite girders, Journal of Composites for Construction, © l17, 324-335.

Guo, X., Yu, B., Huang, P., Zheng, X., & Zhao, C. 2018. J-integral approach for main crack propagation of RC beams strengthened with prestressed CFRP under cyclic bending load. Engineering Fracture Mechanics, 200, 465-478.

Hong, S., & Park, S. K. 2016. Effect of pre-stress and transverse grooves on reinforced concrete beams prestressed with near-surface-mounted carbon fiber-reinforced polymer plates. Composites Part B: Engineering, 91, 640-650.

Hosseini, M. M., Dias, S. J., & Barros, J. A. 2014. Effectiveness of prestressed NSM CFRP laminates for the flexural strengthening of RC slabs. Composite Structures, 111, 249-258.

Irwin, R. and Rahman, A. 2002. FRP strengthening of concrete structures – Design constraints and practical effects on construction detailing, New Zealand. Concrete Society Conference.

Jayasuriya, S., Bastani, A., Kenno, S., Bolisetti, T., & Das, S. 2018. Rehabilitation of Corroded Steel Beams Using BFRP Fabric. Structures, 15, 152-161.

Karataş, M. A., & Gökkaya, H. 2018. A review on machinability of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composite materials. Defence Technology, 14, 318-326.

Liang, H., Li, S., Lu, Y., Hu, J., & Liu, Z. 2019. Electrochemical performance of corroded reinforced concrete columns strengthened with fiber-reinforced polymer. Composite Structures, 207, 576-588.

Mandara. M, Piazza. M, Perdikaris. P and Schaur. C. 2002. Repairing and strengthening for new requirements: Use of Mixed Technologies, Improving Buildings Structural Quality by New Technologies Seminar, Lisbon .

Meng, W., Khayat, K. H., & Bao, Y. 2018. Flexural behaviors of fiber-reinforced polymer fabric reinforced ultra-high-performance concrete panels. Cement and Concrete Composites, 93, 43-53.

Peng, H., Zhang, J., Shang, S., Liu, Y., & Cai, C. S. 2016. Experimental study of flexural fatigue performance of reinforced concrete beams strengthened with prestressed CFRP plates. Engineering Structures, 127, 62-72.

Riveros, G. A., Mahmoud, H., & Lozano, C. M. 2018. Fatigue repair of underwater navigation steel structures using Carbon Fiber Reinforced Polymer (CFRP). Engineering Structures, 173, 718-728.

Rojob, H., & El-Hacha, R. 2018. Performance of RC beams strengthened with self-prestressed Fe-SMA bars exposed to freeze-thaw cycles and sustained load. Engineering Structures, 169, 107-118.

Seręga, S., Kotynia, R., & Lasek, K. 2018. Numerical modelling of preloaded RC beams strengthened with prestressed CFRP laminates. Engineering Structures, 176, 917-934.

Suryawanshi, C.S. 2012. Structural concrete repair – A durability based revised approach is needed. Indian Concrete Journal, 37 – 42.

NBM&CW February 2019

Preservation of Capex Towards Industrial Cooling Towers

Industrial Cooling Towers are used to remove heat through evaporation of water in a moving air stream being carried from various sources such as a machinery or some heated process material. Their main use is to remove Read More ...

India's Repair Industry Needs a Responsibility Criteria

In India, the repair industry is not organized, hence, the exact numbers on annual cost to owners/public funding for repair, protection & strengthening are not available. Today, India is placing new concrete to the tune of Read More ...

Rehabilitation of Overstressed Rigid Pavements

Due to shortage of resources like cement as well as finances, hardly any concrete roads were constructed in free India, though, in the long run they are cheaper than bituminous roads, was an established fact. Some internal Read More ...

Concrete Repair: Principles from EN 1504 and Practical Considerations

Many a times, even after taking all the due precautions and all quality control measures, Concrete structures deteriorate. One of the practical reasons is due to the fact, that at the time of planning or at the design table Read More ...

Repair & Rehabilitation to improve life-span of buildings

Across Indian cities, there are millions of old buildings that are in a dilapidated condition. In Mumbai alone, there are 14,375 dilapidated structures across the city and another 10,500 in the suburbs. Such structures pose an Read More ...

Repair/Rehabilitation of Structure

UPV Test in Progress
A structure, when it is constructed, has generally got a service life. The service life is dependent on the quality, workmanship of the construction and various other factors including materials, components, Read More ...

Remedial measures for reinforced concrete structures using cementitious materials

Remedial Measures for Reinforced Concrete Structures
An essential part of a successful repair of concrete structures, is to establish the underlying cause and extent of concrete deficiency, and deterioration mechanism. For a repair to be successfully completed, Read More ...

Latest Techniques for Repair & Rehabilitation- A Perspective

Latest Techniques for Repair Rehabilitation
For a successful repairing work of a structure, the most vital things to be considered are identification of the root cause, selection of the right products & methods, proper repairing of the damage by skilled Read More ...

Durable Repairs State-of-the-art Corrosion Mitigation Techniques

Steel Protected in Carbonated Concrete
Most of today's concrete construction relies on the composite interaction of concrete and steel, which is aided by the near equivalence of their thermal expansion characteristics Read More ...

Concrete Repair: Principles, Guidelines and Practical Considerations

Steps For Repair
India has witnessed a tremendous spurt in construction over the last couple of decades. Residential, Commercial, Industrial and Infrastructure construction and expansion has been progressing Read More ...

Polymers blend for repair applications (Epoxy resins & polymers)

Micrographs of Polymer Blends
Epoxy resins are widely used as highly cross linked materials in various repair applications where special performances such as good mechanical, thermal and electrical properties are required Read More ...

Concrete structures repair & Rehabilitation - Causes of Distress & its Solution

Concrete Degradation
CONCRETE DEGRADATION may have various causes & reasons. It can be damaged by factors like fire, alkali - aggregate reaction expansion, sea water effects, bacterial corrosion, calcium leaching, physical Read More ...

Soil Strengthening – Use of Pressure Injection Grouting as a means of Improving Load Bearing Capacity of Existing Foundations

Ejection of Underground Water
This Paper describes the procedure for improving the Load bearing capacity of the foundations by means of strengthening the soil under and around the foundations. Use of Injection grouting in the Read More ...

Retrofit of R.C. Beams & Columns

Finite Element
During the last week of March a few years ago, author was invited by a certain Company in an Indian city to review and advise upon measures to strengthen the ground floor and basement beams and columns Read More ...

Stainless Steel Rebar: A Necessity for Coastal Regions

Ferritic Stainless Steel
Both stainless steel and carbon steel derive their corrosion resistance from a naturally occurring chromium rich oxide film, which is present on its surface. This invisible film is inert, tightly adherent Read More ...

Rigid Pavement Repair and Maintenance Strategies

Rigid Pavement Repair
The rapid growth in road construction brought about considerable expansion of road infrastructure, which subsequently fell into disrepair through lack of maintenance. The damage is Read More ...

New Building Material & Construction World

New Building Material & Construction World
MGS Architecture

Modern Green Structures & Architecture

Modern Green Structures & Architecture

Lifting & Specialized Transport

Lifting & Specialized Transport

Indian Infrastructure & Tenders Week

Indian Infrastructure & Tenders Week