Fiber Reinforced Polymer Composites : A Novel Way for Strengthening Structures

To meet up the requirements of advanced infrastructure, new innovative materials/ technologies in construction industry has started to making its way. Any technology or material has its limitations. To meet the new requirements, new technologies have to be invented and put to use. With structures becoming old and the increasing bar corrosion, old buildings have started to demand additional retrofits to increase their durability and life.

Use of FRP for confinement has proved to be effective retrofitting and strengthening application. The confinement in seismically active regions has proved to be one of the early applications of FRP materials in infrastructure applications. Confinement may be beneficial in non-seismic zones too, where, for instance, survivability of explosive attacks is required or the axial load capacity of a column needs to be increased due to higher vertical loads, e.g. if new storey's have to be added to an existing building or if an existing bridge deck has to be widened. In any case, confinement with FRP may be provided by wrapping RC columns with prefabricated jackets or in situ cured sheets, in which the principal fiber direction is circumferential. Beams, Plates and columns may be strengthened in flexure through the use of FRP composites bonded to their tension zone using epoxy as a common adhesive for this purpose. The direction of fibers is parallel to that of high tensile stresses. Both prefabricated FRP strips, as well as sheets (wet-layup) are applied. Hence, FRP composites are finding ways to prove effective and economical at the same time.

Dr. Gopal Rai,
R & M International, and
Yogesh Indolia,
21 SHM Consultant, Mumbai

Introduction

In today's growing economy, Infrastructure development is also raising its pace. Many reinforced concrete and masonry buildings are constructed annually around the globe. With this, there are large number of them which deteriorate or become unsafe to use because of changes in use, changes in loading, change in design configuration, inferior building material used or natural calamities. Thus repairing and retrofitting these structures for safe usage of these structures has a great Market.

There are several situations in which a civil structure would require strengthening or rehabilitation due to lack of strength, stiffness, ductility and durability. Some common situations where a structure needs strengthening during its lifespan are:
  • Seismic retrofit according to current code requirements.
  • Upgraded loading requirements; damage by accidents and environmental conditions.
  • Initial design flaws
  • Change of usage.
Depending on the desired properties, usage and level of damage in structural members, these can be repaired and/or strengthened by several widely used methods some of widely used repair techniques are presented below.

Concrete jacketing can be applied to locally damaged or heavily damaged structures. When concrete is slightly damaged, the loose concrete is removed the surfaces are roughened and the dust is cleaned. Now depending on the amount of concrete removed, some additional ties or reinforcement can be added and jacketing is carried out i.e. new concrete is filled. Non shrinkage concrete or concrete with low shrinkage properties should be used. Special attention is paid to achieve a good bond between old and new concrete.

Jacketing should also be applied in cases of heavily damaged columns or in cases of insufficient column strength. This is actually a strengthening procedure but can be used for repair purposes. The additional concrete and reinforcement added contribute to increase in strength.

Concrete jacketing has a lot of limitations. The jacket should be of minimum 100mm thickness. The sizes of members are increased and the free available usable space becomes less. Also adding a huge dead mass and increasing the stiffness which reduces the efficiency of the structure. Its durability has also been often found to be limited. Furthermore the whole process is slow and takes lot of time for completion.

Jackets may also be made of steel. It is a popular technique to use steel plates bonded with epoxy to external surfaces of columns, beams and slabs. This technique is simple and effective as far as both cost and mechanical performance is concerned but suffers major disadvantages. Corrosion of steel plates hurdles its use in structures in/near river, lake and sea. Furthermore difficulty in manipulating heavy steel plates in tight construction sites, need for scaffolding, and limitations in available plate lengths which results in need of joints. Sometimes steel's high young's modulus causes it to take large portion of axial load resulting in premature buckling.

The conventional jackets, sheets, plates may be replaced with FRP fabrics, sheet and laminates in view of above limitations.

A Fiber Reinforced Polymer (FRP) composite is defined as a polymer (plastic) matrix, either thermo set or thermoplastic, that is reinforced (combined) with a fibre or other reinforcing material with a sufficient aspect ratio (length to thickness) to provide a discernable reinforcing function in one or more directions. FRP composites are different from traditional construction materials such as steel or aluminium. FRP composites are anisotropic (properties apparent in the direction of the applied load) whereas steel or aluminium is isotropic (uniform properties in all directions, independent of applied load). Therefore, FRP composite properties are directional, meaning that the best mechanical properties are in the direction of the fiber placement.

Composites are composed of:
  • Epoxy - The primary functions of the resin are to transfer stress between the reinforcing fibers, act as a glue to hold the fibers together, and protect the fibers from mechanical and environmental damage. The most common resins used in the production of FRP grating are polyesters (including orthop- hthalic-"ortho" and isophthalic-"iso"), vinyl esters and phenolics.
  • Reinforcements - The primary function of fibers or reinforcements is to carry load along the length of the fiber to provide strength and stiffness in one direction. Reinforcements can be oriented to provide tailored properties in the direction of the loads imparted on the end product. The largest volume reinforcement is glass fiber.
  • Fillers - Fillers are used to improve performance and reduce the cost of a composite by lowering compound cost of the significantly more expensive resin and imparting benefits as shrinkage control, surface smoothness, and crack resistance.
  • Additives - Additives and modifier ingredients expand the usefulness of polymers, enhance their processability or extend product durability.
The following are major pros and cons of using Composites:

This section of the article is only available for our subscribers. Please click here to subscribe to a subscription plan to view this part of the article.

Value Engineering with MCI®-2019 for Concrete Maintenance and Repair
True value engineering saves money without reducing service life or affecting the quality of construction or materials. Ideally, it adds value to the project. MCI®-2019 is one such value engineering solution that can extend the service life of existing

Read more ...

Agrani Milestone Use Carbon Fiber Laminates to Strengthen Slab
Ramendra Bahadur Sinha, Managing Director, Agrani Milestone, explains the remedial measures and challenges faced during slab strengthening of a deflected slab at IIT. NBCC India Limited undertook the strengthening of a deflected slab at a G+2 storey IIT building

Read more ...

Waterproofing Challenges & Remedial Measures in High Rise Buildings
High-rise buildings need special attention when it comes to waterproofing as the challenges inherent in them are peculiar in nature. Unfortunately, there is a lack of knowledge on the remedies and products available in the market as water- proofers continue to

Read more ...

Importance of Waterproofing Structures
The longevity of structures depends on how much resistance the building element will offer to water ingress. Water leakage not only reduces the durability but also hampers the serviceability or usability of the structure; hence, a good waterproofing system will

Read more ...

Terrace Waterproofing Solutions for Energy-Efficient Buildings
Terrace waterproofing is particularly important and is considered a priority as the roof is always exposed to harsh climatic conditions and weather changes. Rajeev Gupta, Business Head, ECMAS Construction Chemicals Pvt. Ltd. An effective waterproofing solution

Read more ...

Structural Rehabilitation of Reinforced Concrete Structures
Cement concrete is one of the most important construction materials and is practically basic to present-day developments. It is strong enough mechanically, yet vulnerable to deterioration. It thus gets damaged and even fails. This deterioration may be due to the weathering

Read more ...

Thermax - HDPE-SBS Waterproofing System for Basement Waterproofing
Gradual shift in lifestyle has driven the idea of modern construction towards developing underground spaces and buried structures to bring efficiency in use of space. However, the improved efficiency comes with an increase in challenges like infiltration

Read more ...

Waterproofing in Hilly Areas with Sub-Zero Temperatures
Industry experts Kunjan Popat, General Secretary, Waterproofing Association of India; Ramendra Bahadur Sinha, Managing Director, Agrani Enterprises, and MS Sudish, Director, SIWIN Institute of Waterproofing and Insulation, share the challenges

Read more ...

Dow Sealants for Sustainable Infrastructure
Durability is a key requirement for modern infrastructure projects – highways and roads, bridges, airports and airfields, walkways and plazas, parking structures and stadiums. Miles of concrete must

Read more ...

FAIRMATE FAIRCURE WC - White Pigmented Concrete Curing Aid
Buildings have major environmental impacts over their entire life cycle. Resources such as ground cover, forests, water, and energy are depleted to give way to buildings. Today, India has demonstrated

Read more ...

Repair and Rehabilitation of A Minor Bridge in Shravasti District  (UP), India
Scour is a natural phenomenon caused by the erosive action of flowing stream on alluvial beds. Failure of bridge due to scour at their foundations, which in this case consisted of abutments and pier, one 1.2 dia

Read more ...

Faircoat Anti-Carbonation Coating Protects Concrete Structures Like Flyovers, Bridges & Buildings
To protect concrete structures like Flyovers, Bridges, Parking areas, Big Commercial and Residential Buildings, the normal decorative exterior paint will not serve the purpose as these paints are not vapour permeable

Read more ...

Repair Strategy of Stoplog Sill Beams During Operation Stage of 510 MW Teesta-V Power Station in Sikkim
Repair Strategy of Stoplog Sill Beams During Operation Stage of 510 MW Teesta-V Power Station in Sikkim Running Power Stations serve as a boom to the economy of the country and any generation loss due to construction

Read more ...

Concrete Protective Liner by Russian company Hydropolymer
Concrete protective liner is a multipurpose solution for waterproofing and protection of concrete surfaces against corrosion and destruction. The product warranties long-term and reliable protection of structures

Read more ...

Necessity of Health Monitoring of Structures Constructed Before 2000 across India
Sangeeta Pandey, Chief Manager (Civil), Power Grid Corporation of India Ltd., Patna, PVS Sudhakar, Sr. General Manager (Civil), NOFN Works, Power Grid Corporation of India Ltd., Vishakhapatnam & Dr. Achintya, Professor of Civil

Read more ...

WATERPROOFING Importance of Filling Cracks, Joints & Voids
Samir Surlaker, Director, Assess Build Chem Private Limited discusses some new joint treatments and injection systems in waterproofing. It is a myth that waterproofing treatments can be carried out by application of single material

Read more ...

Construction Chemicals in Repair and Rehabilitation of Structures
Years of research plus decades of practical experience have enabled FAIRMATE to develop detailed solutions to restore and rehabilitate concrete structures with structural rehabilitation, retrofitting and strengthening of RCC structures

Read more ...

Repair and Maintenance Techniques for Building Facades
Sunny Surlaker, Head Technical Services, Assess Build Chem writes on the selection ideologies, materials and methods for defect remediation in Concrete Buildings. The building façade or the envelope is the primary line of

Read more ...

Condition Evaluation of Fire Exposed Concrete Foundation
This article provides some basic information on effects of fire on concrete, various condition evaluation methods, and show findings from a case study of a fire exposed concrete foundation in California, and informs construction

Read more ...

Concrete Repair Bonding Agents Panacea or Snake Oil?
There is considerable controversy within the concrete repair industry regarding the use of bonding agents as a pretreatment method for the repair of deteriorated concrete. This paper examines the use of bonding agents

Read more ...