DURABILITY AND FATIGUE BEHAVIOR OF HIGH-STRENGTH CONCRETE BEAMS PRESTRESSED WITH CFRP BARS

The need for sustainable structures has motivated an international interest in the use of fiber reinforced polymer (FRP) materials as internal reinforcement for concrete infrastructure applications. One of the contributing factors affecting the widespread use of FRP materials is the limited information regarding their long-term performance. In particular, knowledge of the long-term durability of FRPs is of prime importance. The research work presented in this paper is the result of a research collaboration between North Carolina State University (NCSU) and the University of Cambridge (UC). The research investigates the durability of concrete beams prestressed with carbon FRP (CFRP) bars and compares the results with those of companion beams prestressed with steel wires. A total of fifteen beams have been constructed and tested under different mechanical and environmental conditions. The parameters included in the program were the level of sustained stress in the bars and wires (55 and 70 percent of the ultimate bar or wire strength), the environmental exposure condition (air exposure and continuous exposure to 15 percent by mass salt water spray at 54 °C temperature), the length of time under sustained load (9 and 18 months) and the method of testing (with or without application of cyclical loading prior to static testing to failure). Test results show that the beams prestressed with steel wires did not survive the environmental exposure over 12 months whereas the beams prestressed with CFRP bars survived up to the end of the 18 month long extreme environmental exposure