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Long-Term Behavior of Anchorage for Carbon Fiber Reinforced Polymer Strands Using Highly Expansive Material

Investigation of long term characteristics of the Highly Expansive Material (HEM) anchorage for CFRP strands is very important. In the post-tensioning type of prestressed concrete structures, considerations should be made for the loss of prestressing force due to the pull-out displacement which is caused by the creep of the HEM. The long-term characteristics of the HEM anchorage were investigated by creep test on five specimens. From the creep test, some important characteristics of HEM anchorage were observed, for example, time-dependent change of pull-out displacement at the loaded end, unit shear "q" distributions and the tensile force distributions "Tp". An analytical relationship on how the long-term behavior of prestressing force can be predicted by using the measured values for the time-dependent change of pull-out displacement at the loaded end is presented. Also from the simulated results of this relationship, it was found that the loss of prestressing force is negligible in practice when the CFRP strand is 10 meters long. Normally the expansive pressure of HEM at prestressing is 50MPa. However, when the expansive pressure is 100MPa, the pull-out displacement at the loaded end and the loss of prestressing force can be reduced to more than the half of one with 50 MPa.