Aramid FRP

A Sumida, T Okamoto and M Tanigaki, Experiences with aramid FRP in concrete structures , Proceedings 50th Annual Conference, Composites Institute, SPI, New York, 1995, Paper 21-D. 

Other non-metallic materials may be considered for forming honeycombs for specific applications. Glass FRP, aramid FRP and Kraft paper honeycombs have been used. 

Where the discussion is specific to these materials, the abbreviations carbon FRP and aramid FRP are used. 

Aramid FRPs have excellent impact resistance, particularly to ballistic impact. On a weight basis they are superior to glass fibre composites, which themselves offer good ballistic impact resistance, but they are more expensive. 

In most of the above composites, as polymer matrices, thermoset polymers have gained major industrial importance as matrix materials. The use of thermoplastic matrices for aramid FRPs is being increasingly studied recently. There are also a vast number of applications where aramid fibers are the sole constituent, e.g., in protective apparel, armor systems, ropes, etc. During the last decade the aramid containing FRP composites have developed into economically and structurally viable construction materials for buildings and bridges [4]. 

The discussion on the preparation and properties of p-aramid FRP composites should not omit the most famous application of these materials in ballistic protection. A great deal of the freely available information in this area is included in numerous patents and technical publications. Significantly less in number are the scientific articles, most frequently dealing with modeling studies. Even a brief overview on the p-aramid composites in ballistics would probably require a separate chapter. Due to space limitations, we wUl only mention here a recently reported phenomenon with big potential for more flexible and better protecting body armor in the future. 

Fibre-reinforced polymers (FRP) rebars, usually made of an epoxy matrix reinforced with carbon or aramide fibres, have also been proposed both as prestressing wires and reinforcement. Nevertheless, they are not discussed here, because these applications are still in the experimental phase and there is a lack of experience on their durability. In fact, while they are not affected by electrochemical corrosion typical of metals, they are not immune to other types of degradation. FRP are also used in the form of laminates or sheets as externally bonded reinforcement in the rehabilitation of damaged structures this application will be addressed in Chapter 19. 

Sumida, A., Reinforcement, retrofit of concrete structures with aramid fiber, in FRP Composites in Civil Engineering, Proceedings of the International Conference on FRP Composites in Civil Engineering, Hong Kong, China, December 12-15, 2001, Teng, J.G., Ed., Elsevier, Amsterdam, 2001, p. 273. 

Odagiri, T., K. Matsumoto and H. Nakai (1997). Fatigue and relaxation characteristics of continuous aramid fiber reinforced plastic rods. Non-Metallic (FRP) Reinforcement for Concrete Structures, FRPRCS-3, Sapporo, Japan, pp. 227-234. 

Fibre reinforced polymers (FRPs) are composed of a reinforcement material (glass, aramid or carbon fibres) surrounded and retained by a (thermoplastic or thermosetting) polymer matrix (unsaturated polyester, epoxy, vinyl ester, or polyurethane). FRPs were first used in the rehahiUtation of reinforced or pre-stressed concrete, but they have also been widely used in the reinforcement of timber structures. 

Carbon FRPs have a strain to failure which is typically about 1.5%. They also have totally elastic behavour up to failure and therefore their ability to absorb impact energy without damage is limited. To improve the impact performance, fibres with higher strain to failure, such as glass or aramid, may be incorporated. 

The use of fiber-reinforced polymer (FRP) composite materials in the reinforcement of concrete structures has shown important results. These interventions are based on the application of carbon fiber, glass, or aramid impregnated with thermosetting polymers. The effectiveness of these interventions is demonstrated both by extensive research in the laboratory and by applications to existing structures. 

Figure 8.2 shows a pull-off test on a masonry structure reinforced with aramid fiber-reinforced polymer (AFRP). The rupture in this test is due to the lack of adhesion to the substrate and this means that the fiber-reinforced polymer (FRP) does not work properly. Proper failure of the material as a result of a pull-off test would also cause the separation of part of the masonry support. 

In principle, all fibres available for FRP can also be used as reinforcement in prepregs, the most common ones being carbon and glass fibres. Polymeric fibres made from aramid or polyethylene are also quite coimnon, as are inorganic basalt fibres, or natural fibres like hemp or flax. Often, the fibres are directly impregnated to make unidirectional (UD) tapes. Alternatively, they can first be transformed into fabric products, such as woven fabrics or non-crimp fabrics (NCF), and then impregnated to create multi-directional prepregs. 

Commercially available pultruded bars are made of glass, carbon or aramid fibres, oriented in the axial direction and embedded in a polymeric matrix, usually made of vinylester or epoxy resin. The FRP bars most often used in civil engineering applications combine vinylester and glass fibres. 

Table 9.4 presents typical ranges of variation for several physical and mechanical properties of FRP bars made of glass (GFRP), carbon (CFRP) and aramid (AFRP) reinforcement. For the typical fibre content, all FRP reinforcing bars present low density, about one-sixth to one-quarter that of steel bars (again, the main competitor), which facilitates transport and... 

---