THE USE OF POLYMER COMPOSITES IN BRIDGE REHABILITATION

ABSTRACT

As the use of Fibre Reinforced Polymer (FRP) composite material systems continues to rise all over the world, there is need to explore the possibilities of adopting this composite materials for the repairs and the restoration of deficient reinforced  concrete structures in Nigeria. The fibre reinforced polymer [or fibre reinforced  plastics (FRP)] composites is one of the  innovative  technologies that continues  to  win the attention of engineers in the recent times. The existence of deficient  reinforced concrete structures in Nigeria is worrisome and has contributed to the numerous cases of building collapse with the  disastrous consequences of deaths and economic waste. As Nigeria strives to improve standards on every side as  to  meet up with the Millennium Developmental Goals (MDGs), efforts must be geared towards reducing deaths in the country, especially in the building sector. For this, the need for researches into innovative methods of repairs and restoration remains very vital in the life of Nigeria. This article explores the potentials of externally bounded  FRP composites and how it can be gainfully applied in Nigeria to strengthen our deficient RC structures and help the building industry to reduce the perennial and embarrassing cases of structural collapse. Results of laboratory tests were used to confirme the potentials of FRP composites in strengthening damaged beams.

 

 

CHAPTER ONE

INTRODUCTION

Composite materials combine and maintain two or more distinct phases to produce a material that has properties far superior than either of the base materials. Composite materials have been used in construction for thousands of years. Straw has been used to reinforce bricks for over 2000 years and this method is still used today. There is also evidence of the use of metal to reinforce the tension face of concrete beams in Greece nearly 1000 years ago.

Polymer composites are multi-phase materials produced by combining polymer resins such as polyester, vinylester and epoxy, with fillers and reinforcing fibres to produce a bulk material with properties better than those of the individual base materials. Fillers are often used to provide bulk to the material, reduce cost, lower bulk density or to produce aesthetic features. Fibres are used to reinforce the polymer and improve mechanical properties such as stiffness and strength. High strength fibres of glass, aramid and carbon are used as the primary means of carrying load, while the polymer resin protects the fibres and binds them into a cohesive structural unit. These are commonly called fibre  composite materials.

Polymer composites have enjoyed widespread use in the construction industry for many years in non-critical applications such as baths and vanities, cladding, decoration and finishing. In 1999, the construction sector was the world’s second largest consumer of polymer composites representing 35% of the global market [1]. In recent times fibre composite materials have been increasingly considered for structural load bearing applications by the construction industry and have established themselves as a viable and competitive option for rehabilitation and retrofit of existing civil structures, as a replacement for steel in reinforced concrete and to a lesser extent new civil structures.

Statement of problem

While the need to renovate some aging infrastructures and historic buildings with lighter and environmentally friendly materials becomes increasingly evident in the advanced world, the need to restore recent structures  is common  in Nigeria. Cases  of buildings resulting defective right from the very end of construction phase is very rampant in Nigeria. In the developed world, the necessity for rehabilitation in the characteristically conservative civil construction industry arises  from deterioration/aging of structures, adaptation of existing structures to new design standards, mistakes in design/construction, accidental overloading, and a change in the functionality requirements of the structure. Apart from these generally known causes of structural distress, the Nigerian factor remains a prominent issue  to  contend with (Ede, 2010). All these factors contributing to the rampant cases of defective reinforced concrete structures in Nigeria eventually lead to collapses  with  the accompanying adverse effects. It has been verified that when the defects in structures are not excessive, repairs instead of complete substitution can be a viable solution. Based on the amount of capital invested in building many structures, it is  often uneconomical to simply replace them with a new one without considering the available options (Täljsten, 2002; Schnerch and  Rizkalla,  2004  and  Goodman, 2005).

Objective of the study

The main objecyive of the study is to examine the use of polymer composites in bridge rehabilitation. It will conduct a Laboratory  tests  results were used to confirm the potentials of FRP composites in strengthening damaged beams.

CHAPTER TWO

FIBER REINFORCED POLYMER (FRP) COMPOSITE SYSTEMS FOR STRENGTHENING CIVIL STRUCTURES: A GENERAL REVIEW

The use of Fibre Reinforced Polymer (FRP) composites in various engineering fields,

e.g.aerospace, automotive and marine engineering applications has attained an advanced level while the use in civil structural applications is constantly increasing (Bakis et. al., 2002;). High quality manufacturing techniques, decreasing cost, advancement in methods of analysis, design and testing of FRP materials have all contributed to the diffused application of this innovative material in the construction industry. Due to their superior material properties: corrosion and weather resistance, high mechanical strength and low weight, ease of handling, good fatigue resistance, and versatility of size, shape or quality, they are finding a wide range of application in structural rehabilitations (Bakis et. al., 2002; Quattlebaum et al., 2003;  and  Ede, 2008).

From the majority of experimental works conducted on structures strengthened with various FRP technological systems, it has been established that the performance of these structures are controlled by the quality of the bond between the FRP and strengthened structure (Teng et. al., 2002). Therefore the most important issue for    the repair of reinforced concrete structures is the efficiency of the bond between the FRP and concrete substrate.

In the past, the bonding of steel plates to deficient reinforced  concrete  (RC)  structures has been the most popular method  for  strengthening  RC  structures. Epoxy bonded steel plates have proved to increase the strength and stiffness of existing structures and also to reduce flexural crack widths in the underlying concrete (Oehlers, 1992). This technique is simple, cost-effective and efficient for strength, stiffness and ductility enhancement, but it  suffers  from deterioration of  the  bond at the steel-concrete interface caused by corrosion of steel. Other problems include difficulty in manipulating the heavy steel plates at the construction site, need for scaffolding, and limited delivery lengths for long  elements, increase  in dead loads  and the cross-sectional dimensions of the structure, intensive labour and down time.  All these pose significant problems for the efficiency of this method (Stallings et al., 2000). In the recent years, the use of fibre reinforced polymer composite plates or sheets to replace steel plates in structural strengthening has become very common.

The Fibre Reinforce Polymer (FRP) has gradually taking the place of steel plates in some field of structural rehabilitation. In fact, FRP sheets may be wrapped around structural elements, resulting in considerable increases in strength  and  ductility without excessive stiffness change. Furthermore, FRP wrappings may be tailored to meet specific structural requirements by adjusting the placement of fibres in various directions or stacking more layers together (ACI Committee 440 report, 2002).

Today, FRP is virtually used in almost all fields of applications and in particular in the following fields: aerospace/military, automotive, building/construction/ infrastructure, industrial plants/chemical processing, oil & gas/ petrochemical, electrical and household applications. The major advantages are high mechanical strength, low weight, corrosion and weather resistance, good fatigue properties, high impact strength, high insulation values, very low maintenance cost, resistance to water, frost and salt, easy integration of lighting, cables and conduits

Evolution of Fibre reinforced polymer (FRP) composite materials for civil constructions

Over the past sixty years, rapid advances in construction materials technology have enabled impressive gains in the safety, economy and reliability of civil structures built to serve mankind. This has been in tone with the other advances made to improve human health and general standards of living. The fibre reinforced polymer [or fibre reinforced plastics (FRP)] composites is  one of these new technologies that continue to win the attention of engineers engaged in civil constructions in the recent years. Historically, the fibre reinforced composites materials have been in use since the  1940s in the form of glass fibres embedded in polymeric resins made available from the petrochemical industries. The combination of high-strength, high-stiffness and low-density/ light-weight structural fibres with environmentally resistant polymers resulted in composite materials with mechanical properties and durability better than either of the constituents alone (Nanni, 1996).

At first, FRP composites made with high performance fibres such as boron, carbon  and aramid were too expensive to make much impact beyond niche applications  in  the high value added technological fields (e.g. aerospace and defence industries).

As the cost of FRP material continues to decrease and with the aid of intensive research and demonstration, projects on FRP civil structural applications have  become common. After over 50 years of service experience, this technology is now finding wider acceptance in the characteristically conservative civil construction industry (Bakis et. al., 2002).

The range of strengthening and retrofit has passed from RC structures to masonry, timber, metal and aluminium structures. The  type  of  structural  elements strengthened include beams, slabs, columns, shear walls, joints, chimneys, vaults, domes and trusses. An extensive detailing on FRP civil applications can be found in the literature (e.g. Crivelli Visconti, 1975; Nanni, 1995; Teng et.al.,  2002; Bakis  et.   al., 2002 and Ede, 2008).

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