The Use of Polymer Composites in Bridge Rehabilitation
CHAPTER ONE
Objective of the study
The main objective 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.
CHAPTER THREE
METHODS & MATERIALS
Materials:
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Types of fiber reinforcement:
There are many different types of fibers that can be used to reinforce polymer matrix composites. The most common are carbon fibers (AS4, IM7, etc.) and fiberglass (S-glass, E-glass, etc.). As with the matrix, the fiber chosen will be determined by the end application.
Carbon (Graphite) Fibers
Carbon fibers are conductive, have an excellent combination of high modulus and high tensile strength, have a very low (slightly negative) CTE and offer good resistance to high temperatures. Carbon fibers are frequently categorized using tensile modulus. There are five categories of carbon fibers generally used in composites; low modulus, standard modulus, intermediate modulus, high modulus and ultra-high modulus. The exact cut-off for these categories will vary depending on the reference consulted, but in general, low modulus fibers have a tensile modulus of less than 30Msi and ultra-high modulus fibers have tensile modulus greater than 75Msi. As a point of comparison, steel has a tensile modulus of 29Msi. As the modulus increases, the fibers tend to get more brittle, more expensive and harder to handle. Further, the tensile strength of the fibers generally increases as the modulus increases from low to intermediate, but then tends to fall off in the high and ultra- high modulus fibers. I.e. the tensile strength of carbon fibers tends to be the greatest for the intermediate modulus fibers.
CHAPTER FOUR
RESULTS
TEST OF DAMAGED BEAM STRENGTHENED WITH CFRP COMPOSITE
For the verification of the potentials of FRP composite in damaged structure, laboratory tests were performed. An un-strengthened reinforce concrete beam and an FRP-strengthened reinforced concrete beam were tested. Four-point static loadings were applied to the beams to induce damage (1st crack). After the appearance of the first crack, one of the beams was strengthened with CFRP and one was left un-strengthened. Successively, the two beams were subject to different cyclic loadings of 30K, 100K and 300K cycles. Dynamic tests were performed at the beginning of the process on each of the beams and then repeated after each static and cyclic test to ascertain the corresponding stiffness of the beams at each damage scenarios.
Fiber reinforced polymer (FRP) composites have been in service as bridge decks or complete load bearing superstructures on U.S. public roads (or the complete load bearing superstructure) for over 13 years.
CHAPTER FIVE
CONCLUSION
From the analysis, the enormous potential of the FRP composite have been exposed. It is very evident that the material will be of great benefit to the Nigerian construction industry especially for the repairs of common heavy concrete structures without overloading with excessive weights. The result of this laboratory test can be easily replicated in bigger life structures.
This paper attests to the many potential applications of FRP composite materials in construction, although the need for brevity prevents all topics from being fully addressed. It can be said that the amount of experience with various forms of FRP construction materials varies in accordance with the perceived near-term economic and safety benefits of the materials. In the case of externally bonded reinforcements, for example, the immediate cost and safety benefits are clear, and adoption of the material by industry is widespread. In other cases where FRP materials are considered to be primary load-bearing components of structures, field applications still maintain a research flavor while long-term experience with the material accumulates. A number of careful monitoring programs of structures with primary FRP reinforcement have been set up around the world and should provide this experience base in the coming years.
Standards and codes for FRP materials and their use in construction are either published or currently being written in Japan, Canada, the United States, and Europe. These official documents are typically similar in format to conventional standards and codes, which should ease their adoption by governing agencies and organizations. The most significant mechanical differences between FRP materials and conventional metallic materials are the higher strength, lower stiffness, and linear-elastic behavior to failure of the former. Other differences such as the thermal expansion coefficient, moisture absorption, and heat and fire resistance need to be considered as well.
The education and training of engineers, construction workers, inspectors, and owners of structures on the various relevant aspects of FRP technology and practice will be crucial in the successful application of FRP materials in construction. However, it should be emphasized that even with anticipated moderate decreases in the price of FRP materials, their use will be mainly restricted to those applications where their unique properties are crucially needed.
REFERENCES
- ACI Committee 440 Report (2002). “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (ACI 440.2R-02).” American Concrete Institute, Farmington Hills, Michigan.
- Bakis C.E., Bank L. C., Brown V. L., Cosenza E., Davalos J.F., Lesko J.J., Machida A., Rizkalla S.H., Triantafillou T.C. (2002). “Fiber Reinforced Polymer Composites for Construction-State of the Art Review”. Journal of composites for Construction Vol.6 No.2, pp73-87.
- Ede A. N., Bonfiglioli B., Pascale G. and Viola E (2004). “A Dynamic Assessment of Damage Evolution in FRP-Strengthened RC Beams”. Proceedings of the International Conference on Restoration, Recycling and Rejuvenation Technology for Engineering and Architectural Application, G. Sigh and L. Nobile editors, 07-11 June 2004, Cesena – Italy.
- Ede, A. N. (2008). “Structural Damage Assessment of FRP-Strengthened Reinforced Concrete Beams under Static and Fatigue Loads”: PhD Thesis in Composite Materials for Civil Structures, Department of Innovative Engineering, University of Salento, Lecce – Italy.
- Ede, A. N. (2010). “Structural Stability in Nigeria and Worsening Environmental Disorder: the Way Forward”. The West Africa Built Environment Research Conference Accra Ghana, July 26-28, 2010, pp 489-498.
- Goodman F., 2005. “Cementitious Repair Materials for Concrete”, An ACI 546R-04 Concrete Repair Guide presented at the ACI Spring 2005 Convention New York City.
- Nanni Antonio, (1996). “FRP Materials”; Short Course, (13-14 January 1996) Department of Structural Engineering, University of Bologna-Italy.
