Types of FRP Composites

FRP composites are a laminate structure such that each lamina contains an arrangement of unidirectional fibres embedded in a thin layer of polymer matrix material. The fibres provide the strength and stiffness and the matrix binds and protects the fibres and transfers the stresses between them. Fibres used in FRP composites for civil engineering applications are continuous or long fibres, which are approximately 5-20 [xm in diameter. Continuous 

AF used in the construction industry are better known by the trade names Kevlar and Twaron. Each is a family of fibre types rather than a particular one. AF are approximately 12 pm in diameter. They have high strength and fatigue performance, intermediate modulus, good moisture and chemical resistance, and well known for their excellent impact resistance. 

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The question of whether delamination resistance can be quantitatively characterized using existing standard test procedures or whether modified or new standard procedures have to be developed also applies to other types of FRP composites. 

All three types of FRP composites used in construction have relatively very low coefficients of thermal expansion. It is nearly zero for CFRP in the fibre direction and AFRP even has... 

Williams, B., Shehata, E., and Rizkalla, S.H. (2003), Filament-wound glass fiber reinforced polymer bridge deck modules , J. Comp. Const., 7(3), 266-273 Xiao, Y, and Wu, H. (2003), Compressive behavior of concrete confined by various types of FRP composite jackets , J. Reinf. Plast. Comp., 22(3), 1187-1201 Zhao, L., Burgueilo, R., Rovere, H.L., Seible, F, and Karbhari, V. (2000), Preliminary evaluation of the hybrid tube bridge system. Report TR-2000/04 , Final Test Report submitted to California Department of Transportation under Contract No. 59AO032, San Diego, CA. 

Potyrala (2011) has provided a very useful table naming all-composite and hybrid bridges aronnd the world from the oldest to the newest. The table gives basic details and the type of FRP composites used. Some of the more recent examples of the construction of all-composite bridges throughout the world are in Spain and Rnssia. 

The literature published on fracture mechanics testing of FRPs in the last 40 years comprises a large database on delamination resistance or fracture toughness of different types of FRPs. An early review [51] compiled the data available at that time. Selected data from quasi-static mode I and mode II tests on FRPs were compared by O Brien [52], and quasi-static mode I test data from carbon—fibre epoxy and poly-ether-ether-ketone (PEEK) by Brunner [53]. Mechanical properties of FRP composites are compiled in the Composite Materials Handbook version F (2002) [9—11], but this does not comprise fracture mechanics data. Hence, there is no comprehensive and up-to-date database on the available data or literature. 

General FRP composites generally have very good resistance to fatigue, although the fatigue performance of FRP composite materials depends on the matrix composition and, to some extent, on the type of fibre (Curtis... 

Testing has shown that transverse fibre debonding for a number of FRP composites is strain related and independent of the type, proportion and orientation of the glass reinforcement. Thus with a knowledge of the material modulus, the stress to initiate transverse fibre debonding may be calculated for any particular material. Available test data indicate that the strain amplitude to debond varies approximately linearly from 0.3% strain at 10 cycles to 0.1% strain at 10 cycles. 

The ensuing sections introduce some of the fibers typically used in composite materials and their formation into fabric layers as well as other types of FRP. As the discussion goes into different material configurations, the reader has to keep in mind the importance of anisotropy in the selection of fibers and the formation of fabrics. 

The mechanical properties of FRP composites depend on the type of fibre nsed in their production and the fibre content in the final product. These aspects are likely to vary between competing composite products since there is currently no agreed standard specification for their production. Therefore, all design must be based on the actnal properties supplied by the manufacturer and laboratory test results. 

A relatively new repair technique for concrete structures, including prestressed structures, consists of externally bonding flexible sheets of FRP composites to the concrete surface. Depending on the type of application, the function of the externally bonded reinforcement... 

There are two types of FRP bridge concepts (1) the traditional bridge one with material substitution, and (2) the new material one. The number of bridges being built utilising the second concept with all-FRP composite material is small, although it is growing. 

An epoxy matrix is assumed for the FRP composite, although properties of polyester, vinylester, or other common matrices can be substituted. The distribution type and COVs for as-built composite modulus and ultimate tensile strength are given in Table 5.3. Mean values for ultimate tensile strength and modulus of elasticity of a lamina are calculated for a set of constituent materials for a specific fiber volume fraction assuming a 5% void volume fraction other statistical properties were obtained from Atadero et al. (2005) for wet lay-up, field-manufactured composites, in order to emulate the possible variation in properties of FRP composites cured under ambient conditions. 

The advantages of composites are inherent in their construction. A variety of resin/fiber systems can yield possible solutions for many types of situations. Depending on the product and application, FRP products for civil and mechanical applications can deliver the following benefits ... 

For commodity applications, there are four major classes of resins that are used in FRP applications. They are phenolic resin, epoxy resin, unsaturated polyester resin, and epoxy vinyl ester resins. A more complete description of these types of resins and their many variations can be found in Handbook of Thermoset Plastics. This is not a comprehensive list of resins used in composite manufacture, as commodity materials like polyurethanes and isocyanurate resins are sometimes used as well to make FRP parts. However, these materials are not covered in this chapter owing to their limited use, but, the principals of fire safety that apply for the resins described subsequently apply to these materials as well. 

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