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The question of whether it is right to bond tendons made of glass, aramid, or carbon fibers to concrete has not yet been addressed directly. Paper discusses the various issues involved and concludes that, in many cases, these tendons should remain unbonded. All the new materials that have a stiffness high enough and creep low enough show linear elastic response right up to failure. This contrasts with steel, even very high-tensile steel, which shows a considerable reduction in stiffness at high loads. In bonded beams, when cracks form on the tension face of the concrete, very high strains are generated across the crack. With a steel tendon, local yield must occur, with a consequent reduction in cross-sectional area, which leads to debonding of the bar on either side of the crack. This allows the strain at the crack to reduce below its theoretical maximum value. In calculation, average steel strains are used, which ignore any local increase at the crack positions, but there are some controversial code rules that limit the (average) steel strain to less than the material can actually sustain. When new materials are used, the local yielding mechanism is no longer available, and the concept of using average strains is no longer justified. In concrete reinforced with FRP, the entire strain capacity of the fibers is available, and it is unlikely that fiber failure will occur before the concrete strains become unacceptable. But in prestressed concrete, much of the fiber strain capacity is absorbed in the prestress, leaving a tendon very sensitive to high strains in the vicinity of cracks. There is a move to increase the ductility of beams reinforced or prestressed with FRP by using FRP cages in the compression zone. This will increase the chances of a bonded tendon snapping before concrete crushing occurs. These mechanisms are not present in unbonded tendons, where high local strains do not occur, and indeed the change in stress in the tendon is small. It has been argued that, for steel tendons, this is an economic disadvantage; however, for FRP tendons, it is shown here to be beneficial.

Because fibers made of such materials as glass, carbon, aramid, and vinylon have very high resistance to corrosion, more attempts are being made to utilize continuous fiber reinforcing materials (CFRM) in reinforced and prestressed concrete structures instead of ordinary steel. However, CFRM are composite materials composed of millions of fibers and binding material, and have little plastic behavior. The mechanical behavior of reinforced concrete using CFRM is quite different from conventional reinforced concrete. As of the present, there is no general agreement relating to the methodology to be adopted in design or testing methods of such fibers. Realizing this problem, the Concrete Committee of the Japan Society of Civil Engineers (JSCE) organized a subcommittee on CFRM in 1989. The following results have been published as the committee report in 1992: design concept for concrete members using CFRM; test methods for durability of CFRM; concept for durability of CFRM; and a state-of-the-art report on CFRM for concrete structures. Paper describes the design concept for concrete members using CFRM.

The National Research Project on the use of new materials in the construction field, sponsored by the Ministry of Construction (MOC) of Japan in 1988, is scheduled to last for 5 years. The project is separated into two sections. One is infrastructure and the other is building engineering, which is further divided into two divisions, i.e., use of metallic and nonmetallic materials. Research on FRP reinforcement belongs to the latter division. Objectives of the research are to establish standard testing methods for materials and draw guidelines for structural design. To achieve these objectives, many basic experiments have been carried out on materials and structural members of reinforced concrete (RC) and prestressed concrete (PC) construction in cooperation with universities, private industry, and MOC. Such materials as carbon, aramid, and glass fibers, available presently in Japan, were used. The organization of the national research project, representative experimental results, and the outline of the guideline are introduced.

Aramid FRP rods, a composite of reinforced aramid fibers, are corrosion-free and used in various fields. Aramid FRP rods have been gaining attention for their use in prestressed concrete tendons. They have high tensile strength and excellent resistance. They are manufactured from aramid fibers and vinylester resin using a pultrusion process. The physical properties of aramid FRP rods were determined experimentally. Use of aramid FRP rods as prestressed concrete tendons requires a high-bond performance with grout or concrete, and a special anchoring system also had to be developed. Studies carried out in response to these requirements enabled the authors to conclude that aramid rods could make viable prestressed concrete tendons. A pretensioned road bridge (L = 12.5 m), a post-tensioned road bridge (L = 25.0 m); a ground anchor, and a prestressed concrete berth were constructed using aramid FRP rods.

The characteristics of CFCC, including mechanical properties, fatigue, relaxation, and anticorrosive properties, are described. Examples of actual bridges in which CFCC has been used as a reinforcement are shown. In summarizing the investigation of these characteristics and the results of such tests as adhesion with concrete, antifatigue characteristics, antialkali characteristics, relaxation, and temperature cycle tests, it was confirmed that CFCC is a material suitable for tension applications in PC bridges.