Use of Fiber Reinforced Polymers - Literature review Example

? Use of Fiber Reinforced Polymers (FRP) Table of Contents Table of Contents 2 Use of Fiber Reinforced Polymers (FRP) 3 Introduction 3 Composite components 3 Fibers 3 Glass fibers 4 Carbon fibers 5 Aramid fibers 5 Matrices 5 Types of fibre reinforced polymers 6 Glass fiber reinforced polymer 6 Carbon Fiber Reinforced Polymer 6 Aramid Fiber Reinforced Polymer 7 Advantages of Fiber Reinforced Polymers 7 Failure of RC beams bonded with FRP 9 FRP reinforced concrete shear wall punctures 10 Modes of failure 11 Structural application of FRP 11 Beam reinforcement 11 Strengthening of beams using Carbon fibre reinforced Laminates 12 Advantages of FRP used 12 Strengthening and rehabilitation methods 14 Column wrapping using FRP 15 CFRP Laminates for Shear Strengthening of Concrete Beams 16 Conclusion 16 Bibliography 18 Use of Fiber Reinforced Polymers (FRP) Introduction A fibre reinforced polymers (FRP) composite is a polymer that is reinforced by a fibre. The fibres are usually glass, carbon or Aramid. Fibre reinforcement enhances strength and stiffness. FRP can be categorized in a class of materials known as composite materials, which are made up of two or more materials. When these materials are put together, they retain both their chemical and physical characteristics. FRP differ from other construction materials such as steel or aluminum that are viewed as traditional construction materials (ACI 440.2R-08, 2008). FRP contains properties that are apparent in the direction of applied load while steel or aluminum has uniform properties in all directions. The text will look at FRP and its role in strengthening structures as compared to other construction materials. The paper has also outlined several other issues associated with FRP composite materials these include types of fiber-reinforced polymers advantages of Fiber Reinforced Polymers, failure of RC beams bonded with FRP, FRP reinforced concrete shear wall punctures, modes of failure, structural application of FRP, strengthening and rehabilitation methods, and column wrapping using FRP Composite components Fibers The choice of fibres will normally influence the properties of the composites. There are three types of fibres that are identified in engineering namely; carbon, glass and Aramid. The composite is named after the reinforcing fibre. For instance a composite that is reinforced by carbon, will be referred to as Carbon Fibre Reinforced polymer (CFPR). The three fibres have different properties and carbon is viewed as the most suitable for strengthening. All the three fibres are said to contain a higher stress capacity than ordinary steel. They are also linear elastic. Stiffness and tensile strain are the properties that differ between the fibre types. The three fibres are presented in figure 1. They are compared with an ordinary steel bar and a steel tendon Fig. 1 Properties of different fibres and typical reinforcing steel (ACI Committee 440 (1996) and Dejke (2001). The fibers used in FRP composite material have unique characteristics that make them desirable for strengthening purposes. Some of the characteristics include high levels of elasticity for application in reinforcement, high eventual strength and low disparity of strength among fibers. Other significant characteristics are enhanced stability to endure manipulation techniques and consistency in diameters and surface dimension in the fibers. Some of the fibers used in FRP composites include glass fibers, carbon fibers and Aramid fibers. Glass fibers These types of fibers find application mainly in the naval and industrial areas to manufacture composites of relatively high performance. They are beneficial due to their high strength. The glass fibers are composed of silicon (SiO2) having a tetrahedral structure (SiO4). The material is further strengthened with aluminum oxides and additional metallic ions. Between the two types of glass fibers, the S-glass fibers normally have an enhanced tensile strength compared to the E-glass. Fiberglass is manufactured through the process of spinning a batch composed of sand, alumina and limestone. The components are mixed and heated in a tank to form the fiberglass. The glass fibers are then produced as thin sheets known as mats. Carbon fibers Carbon fibers are the most effective reinforcing materials and consequently the most expensive of the available fibers. The fibers however deserve their prestige classification because they have excellent characteristics, which place them above other fibers. Carbon fibers are composed of minute crystallite of turbostratic graphite. These are similar to graphite lone crystals save for the layer planes, which do not appear in regular structural version. Aramid fibers Aramid fibers are very strong when used for reinforcement because they are tagged to be five times stronger than steel of equal weight. In addition, the fibers are light in weight, flexible and easier to use. The fibers are resistant to heat and can only be destroyed at temperatures above 400 degrees Celsius. Matrices The matrix is a secondary material in FRP. Its role is to transfer the forces between the fibres and protects the fibre from the environment. There are two types of matrices namely: the Thermoplastic polymers and thermosetting polymers. In civil engineering, thermosetting resins (thermo sets) are almost exclusively used compared thermoplastic. Of the thermo sets, vinyl ester and epoxy are the most common matrices. Epoxy is mostly favored above vinyl ester but is also more costly. Types of fibre reinforced polymers The different types of fibre-reinforced polymer are: glass fibre, carbon, aramid, ultra high molecular weight polyethylene, polypropylene, polyester and nylon. The change in properties of these fibres is due to the raw materials and the temperature at which the fibre is formed. Glass fiber reinforced polymer Glass fiber is made from a mixture of silica sand, limestone, folic acid in addition of other ingredients. The mixture is heated and melts at about 1260 degrees Celsius. The molten glass flows through fine holes in a platinum plate, the glass plates are cooled, gathered and wound. Then the fibres are woven into different forms for use in composites. Fig 2 Glass fiber reinforced polymer sheet Carbon Fiber Reinforced Polymer Carbon fibres have a high modulus of elasticity. The ultimate elongation is 0.3-2.5 % where the lower elongation corresponds to the higher stiffness and vice versa. Carbon fibres do not absorb water and are resistant to many chemical solutions. They with stand fatigue excellently, do not stress corrode and do not show any creep or relaxation, having less relaxation compared to low relaxation high tensile steel strands. Carbon fiber is electrically conductive and, therefore might cause galvanic corrosion when in direct contact with steel beams. Fig 3 Carbon Fibre Reinforced Polymer Aramid Fiber Reinforced Polymer Aramid is the short form for aromatic polyamide. A well-known trademark of aramid fibres is Kevlar although there exists other brands too. The module of the fibres is 70-200 GP with ultimate elongation of 1.5-5% depending on the quality. Aramid has high fracture energy and is therefore used for helmets and bulletproof garments. Aramid fibres are sensitive to elevated temperatures, moisture and ultraviolet radiation and therefore not widely used in civil engineering applications. Further aramid fibers do have problems with relaxation and stress corrosion (Smallman and Bishop 1999). Advantages of Fiber Reinforced Polymers FRP products have several advantages compared to the steel or aluminum products. Compared to aluminum or steel, it provides stiffness to material almost five times. The materials have high fatigue endurance limits and higher high fatigue endurance limits compared to the steel ones. They also have high abilities to resist corrosion and effects of earthquakes. In particular, the FRP products have the following characteristics/advantages: Specific gravity: the specific gravity of FRP materials is lower than that of steel. CFRP composite has a specific gravity, which is equal to the specific weight of steel. This gives the FRP products an advantage over the steel products because of higher strength to weight ratio. This makes the FRP products better materials to use for reinforcement compared to steel products (Han and Chung, 2011). Resistant to corrosion: FRP composite materials have higher resistance to corrosion resulting from chemicals compared to steel products. This is because the materials are composed of corrosion-resistant materials mainly glass and carbon fibers. This gives them an advantage over steel rods and bars. The FRP composite products find useful applications in ports and marine industrial sectors due to this advantage. In addition to resistance to corrosion, the materials are also not affected by earthquakes (Han and Chung, 2011). Modulus of elasticity: steel products have a lower modulus of elasticity in comparison to that of the FRP materials. This gives the FRP materials the advantage of having the appropriate flexibility required in reinforcement. The FRP materials are thus easier to apply and can be used in diverse fields (Han and Chung, 2011). Insulation: FRP products have unique insulation characteristics that make their application easier compared to the steel materials. The FRP products lack magnetic and electrical conduction properties. This property allows the application of FRP rods in concrete in places such as hospitals where the consideration of magnetic waves and electrical conductivity is critical. Other areas where the FRP find application as opposed to the steel rods include in the construction of magnetic train routes, airport runways and radar systems (Han and Chung, 2011). Thermal expansion properties: FRP composite materials have significant thermal expansion properties because the properties are different from those of steel. This makes them easier and flexible to use. Resistance: FRP materials have enhanced tensile strength, which makes them appropriate to use in construction of earthquake resistant structures. Their tensile strength is far much higher compared to that of steel. The tensile strength for FRP materials containing carbon fibers is MPa2200 while those containing glass fibers have a tensile strength of MPa 1100. Failure of RC beams bonded with FRP In their lifetime, structures are subjected to various damages. Such damages can be induced by either `load higher than the design services or due to environmental conditions. The composites of FRP have been used so much for purposes of repair and retrofitting. This is because they provide unique advantages compared to conventional steel bars/plates. There have been many attempts for numerical simulation of concrete beams strengthened by FRP composites (Jerome et al. 1997). This has resulted to a complex problem and the interaction of the different interfaces between concrete steel FRP and adhesive layer has not been successful in simulating debonding failures under dynamic loads. Another essential part of the simulation is the bonding/debonding behavior of the adhesive layer. From the results of a wide range of experiments tests, debonding failures in flexural strengthened RC beams may be classified into two; end debonding and intermediate crack. End debonding is a failure that starts from one end of the plate due to local stress concentration and intermediate crack induced bonding in which debonding starts from either a flexural crack or a shear crack (Teng et al. 2002). Fibre- reinforced composite material are expansively used in weight sensitive and stiffness critical structures like those normally found in motor racing and aerospace where strength to weight ratio is very crucial to be ignored. They are characterized by stiffness, high in-plane strength, low density and toughness. The environmental impacts on the FRP and the following failure, has led to the increased stress on the study of diverse fracture surfaces. The moisture and the stresses’ presence associated with the moisture induced expansion may lower tolerance or damage the structural durability. There are two types of changes in the mechanical properties of the thermoset polymers namely reversible and irreversible (Teng et al. 2002). Delimitation among layers is a serious problem in applications of fibre reinforced composite laminates. The papers try to study the failed surfaces and uncover the mechanism that occurred using the microscopic techniques. By carefully observing the fracture surface of the composite, the factures influencing their failure and the type of environment they were in can be could be determined (Teng et al. 2002). FRP reinforced concrete shear wall punctures Structures need frequent strengthening due to wear through a process referred to as strengthen infrastructure construction. Retrofitting processes also serve as strengthening measures of beams against external destruction forces such as seismic forces. Several techniques use the FRP composites as reinforcement materials courtesy of their exceptional characteristics, which include enhanced strength, lightweight, resistance to corrosion resulting from chemicals and ease of application (Han and Chung, 2011). RC beams bonded with FRP however, fail in some instances due to a number of issues associated with the materials themselves and others with the application. Some of the problems causing the failures of such beams include a decrease of adhesion between steel and concrete resulting from extreme corrosion and heavy steel plate construction issues with the contractors. Another problem causing the failure of such material is the premature aging of the concrete component of the material (Han and Chung, 2011). Modes of failure Structural failure occurs in FRP materials when: The tensile forces stretch the matrix more than the fibres. This makes the material to shear at the interface between the matrix and the fiber. The tensile forces near the end of the fibres exceed the tolerance of the matrix. It separates the fibers from the matrix. The tensile forces can also exceed the tolerances of the fibres causing the fibres themselves to fracture leading to material failure (Erhard 2006). Structural application of FRP FRP can be used to strengthen the beams, columns and slabs in the buildings. FRP helps to strengthen the structural members after they have been damaged. There are two ways in which the beams can be strengthened. The first way is to paste FRP plates to the bottom of a beam. In doing this, the strength of the beam is increased as well as the deflection capacity of the beam and stiffness. The second way can be by pasting FRP strips in U shape around the sides and bottom of a beam, this result in a higher shear resistance. Beam reinforcement The use of fibre reinforced composites for rehabilitation of beams and slabs started with the on set of the pioneering research performed at the Swiss Federal laboratories for materials testing research (Meier 1987). Since then, there was a shift and a number of work has its focus on timber and reinforced concrete structures. The cost of FRP can be a set back in its use since its material is very costly although it still remains competitive. The competitiveness is brought about by the fact that FRP is resistant to corrosion and at the same time have high ratios of strength and stiffness to destiny. In terms of weight, FRP is lighter compared to steel and therefore may require cheap labor; it can be handles physically compared to steel, which requires a crane to lift. It may be expensive to hire a crane compared to hiring a manual labor (Smallman and Bishop, 1999). Strengthening of beams using Carbon fibre reinforced Laminates The use of FRP has become more popular for strengthening structures than any other material. This is because they have high tension strength, low weight and are resistant against corrosion. Basically, there are two types of FRP; glass fibre reinforced polymer (GFRP) and Carbon fibre reinforced polymer (CFRP). CFRP is recognized as being more appropriate compared to GFRP. It is stated that CFRP has more strength than GFRP. The use of CFRP materials for strengthening steel structures has been on the rise as manifested in its use for strengthening bridges (Sen et al. 2001). Rizkallet. et al (2008) used CFRP strips to strengthen steel beams, selecting appropriate adhesive for bonding. An analytical method used to investigate the strengthening of steel was presented (Bocciarelli 2009). The method was used to evaluate the statistics of steel beams that were reinforced by CFRP in the elastic – plastic regime. Advantages of FRP used FRP is mostly used to strengthen devices. The content of this idea is related to the advantage of hardening timbers by the use of fiber-reinforced polymers (FRP). To be specific, for members loaded in tension vertically to the grain and in firmness similar to the grain. During the first part of the idea , the research looked forward to the numerical and experimental study of hardening members of glulam that were loaded with tension equal to that of the grain. Wood has a weak mechanical property when subjected to a tension equal to that of the grain. The tension strength equal to those of the grain can be achieved by adding flax fiber together with glass fibre –reinforced polymer (FRP). Three glulam species were tested in a tension equal to that of the grain (Han and Chung, 2011). When FRP was reinforced, it was noted that the stiffness and the tensile strength increased tremendously. When a Monte Carlo (MC) together with the first –order second-moment was used in a parameter study, there was a flax fibres mechanical variation. The variation looked like the driving parameter of the strength system. A numerical analysis was conducted to replica the unreinforced with flax fibre composite reinforced glulam (Han and Chung, 2011). In determining the softening of the specimen and the elastic response, models with two dimensions were used. Damage propagation and initiation was modeled by the use of crack model as the base. Traction separation law and cohesive elements were used. The tensile stresses vertical to that of the grain found from numerical model can be compared to those obtained from the experiments. Elements that are cohesive interface have been used successively in modeling the crack formation and the propagation in glulam under tension vertical to the grain. The stiffness of the timber products is usually the determining factor when designing timber structures. The stiffness necessity in the serviceability-limit state, both final and short term deformation, More so in the horizontal members , are factors mostly makes it a must to increase the members ‘ dimension. Normally this causes an increase in material use and therefore the production cost increases. This feature can be reduced by the use of carbon fibre-reinforcement (CFRP) (Han and Chung, 2011). In part two of the idea, the researchers were interested in the strengthening glulam members loaded in density parallel to the grain. The outcomes of the hardening glulam beams weighed down in bending with dissimilar amount of laminate on the tension and compression was investigated in the experiment. In beam analysis, small -scale compression test are not used because they do not give accurate material data. Moment capacity and stiffness are the only terms where the theory and the experimental results agree on by modifying the material which is made of wood for compressing data (Feih and Mouritz, 2012). Strengthening and rehabilitation methods The maintenance, rehabilitation and upgrading of structure members has proved to be a crucial a big problem in civil engineering. Structures that were constructed in the past used older design codes, which are structurally unsafe. Replacing such structures may be costly and at the same time take a lot of time. Today, instead of replacing such structures, strengthening has been accepted as a way of improving the load carrying capacity and possibly prolonging their time for service. One of the challenges that arise in strengthening the concrete structure is selecting the method that will enhance the strength and live time service of the structure (Feih and Mouritz, 2012). Structural strengthening may be necessary for different reasons; The strengthening may be necessary to allow many loads to be placed on the structure; this may happen when the use of structure changes and therefore need for a higher load capacity. Strengthening may be necessary in order to allow the structure resist loads that were not foreseen in the original design. Such a situation may happen when When there is a deficiency in the structure ability to carry the initial design loads, there may be need for strengthening. This comes up as a result of deterioration or corrosion of steel reinforcement (Feih and Mouritz, 2012). In order to select the method that will be suitable for structural strengthening, one has to consider many factors. Such factors include; The magnitude of the desired strength The cost; if the project is small and needs special materials, it may be not be cost effective and therefore not viable (Feih and Mouritz, 2012) The condition of the environment will determine what to be used. For instance the use of adhesives is not recommended in environments where there are high temperatures. On the other hand, the use of external steel methods may not be suitable in corrosive environments. Column wrapping using FRP In order to achieve higher strength, columns in building can be wrapped with FRP. The corrosion of the steel reinforcement is caused by chloride contamination. This can end up damaging structures such as bridges (Harichandran and Baiyasi 2000). Their main concern is the lack of a method that can either minimize or prevent corrosion of the steel. However, FRP provides a possible solution. FRP contains fibres that are oriented in the vertical direction which enhances the bending strength. In order to assess the effects of using fibres six experiments were conducted (Harichandran and Baiyasi 2000). Issues that were assesses include: Freeze – thaw durability Effect of the wrapping on the rate of corrosion in an accelerated corrosion test Effect of freeze – thaw and wet – dry cycles on the properties of FRP Impact resistant of FRP panels supported on a concrete substrate Effect of high temperature on wraps Field installation of wraps on corrosion – damaged bridge columns CFRP Laminates for Shear Strengthening of Concrete Beams The application of CFRP laminates in reinforcement efforts for concrete structures is an old trade and has been very effective. One type of CFRP laminate that has been in application since the 40s is the NSMR. In this process, steel reinforcement is inserted into spaces in concrete covers or alternatively in concrete covers that are used on the structure. Although this technique has not been very effective, it is better compared to the use of steel materials for the same purpose. The CFRO NSMR is resistant to corrosion and does not require very thick concrete covers in the application (Bisby, Green and Kodur, 2005). Another advantage of this technique is that CFRP laminates can be customized to suit the application in question. In addition, based on the kind of the laminate air voids available, the laminates can be excluded in the application. Some of the strengthening techniques using the CFRP Laminates include external bonding and near surface bonding. An advantage of strengthening a concrete structure using NSMR is that the lowered weight of the fiber makes it flexible to move without necessarily lifting the structure. The NSMR are also easier and faster to apply in construction works. The main disadvantage of this technique is that this form of reinforcement is prone to fire and impact sensitivity if not well safeguarded (Bisby, Green and Kodur, 2005). Conclusion This paper has outlined a number of issues associated with FRP composite materials. Some of the issues that have been outlined include FRP seem to the main solution for strengthening structures as way of improving them (Bisby, Green and Kodur, 2005). This is due to its components that make it cost effective other than rebuilding the whole structure. FRP is becoming the preferred option as construction materials compared to steel and aluminum. However there is still a problem in bonding RC with FRP and this raises some concern for researchers as to how this can be sought out. types of fiber-reinforced polymers advantages of Fiber Reinforced Polymers, failure of RC beams bonded with FRP, FRP reinforced concrete shear wall punctures, modes of failure, structural application of FRP, strengthening and rehabilitation methods, and column wrapping using FRP Bibliography ACI 440.2R-08, 2008, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, American Concrete Institute, Farmington Hills, MI, USA, Bisby, L.A., Green, M.F., and Kodur, V.K.R., 2005, Response to fire of concrete structures that incorporate FRP, Progress in Structural Engineering and Materials, 7, 3, 2005, pp. 136- 149 Boeciarelli, M. 2009. Response of statistically determined steel beam reinforced by CFRP in the elastic Plastia regime.Eng. struct.31:956 – 397 Erhard, G. 2006. Designing with Plastics. Trans. 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