Relaxation, creep, and fatigue behavior of carbon fiber reinforced plastictendons

Corrosion of steel tendons is a major problem in prestressed and post-tensi oned concrete structures. Fiber reinforced plastics (FRPs) are a promising alternative to steel due to their high tensile strength, light weight, and resistance to electrochemical corrosion. Different types of FRP tendons hav e been developed to potentially replace steel tendons in areas where corros ion is a problem. However, before field application of FRPs as prestressing elements, their long-term behavior must be investigated. This paper presen ts relaxation, creep, and tension-tension fatigue test result of two carbon fiber reinforced plastic (CFRP) tendons, namely, Leadline PC-D8 8-mm-(5/16 -in.)-diameter, and 1 x 7-7.5-mm-(5/16-in.)-diameter carbon fiber composite cable (CFCC). Twelve Leadline and 12 CFCC tendon specimens were tested in air at temperatures of -30, 25, and 60 C to determine their relaxation beha vior. In addition, the relaxation behavior of 24 Leadline and 24 CFCC sampl es was examined in chemical solutions simulating aggressive field condition s. The loss of tensile force for the 3000 hr test duration at stress ratios of 0.4 and 0.6 was generally less than 10 percent, and it depended primari ly on the initial stress level and the type and temperature of the environm ent. Preliminary investigation of creep behavior of Leadline and CFCC in air and in chemical solutions was also conducted. Six samples of Leadline and six samples of CFCC were subjected to sustained load at room temperature in air , in alkaline, and in acidic solutions, for a period of 3000 hr. Creep beha vior of both tendons was good; however, the creep strains were higher in so lutions than in air. Furthermore, 190 samples of Leadline and CFCC were tes ted in tension-tension fatigue to examine the effect of repeated loading on the modulus of elasticity, Poisson's ratio, and the tensile strength of th ese types of tendons. Fatigue strength was generally good and depended on t he stress range and initial stress level.