Durability of Concrete Beams Prestressed with CFRP Bars

Abstract

The need for sustainable structures is the driving force for the growing international interest in using advanced materials such as fiber reinforced polymer (FRP) materials for civil infrastructure applications. To date, FRP materials have not realized their full potential within the construction industry. One of the contributing factors is the limited information regarding their long-term performance. In particular, since the service life of a civil engineering structure is typically 50 to 100 years, 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 and the University of Cambridge. The research investigates the durability of concrete beams prestressed with CFRP bars and compares the results with those of companion beams prestressed with steel wires. A total of 15 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). The experimental program illustrates that CFRP prestressed concrete beams exhibit comparable ultimate strength and fatigue strength properties in comparison to equivalent steel prestressed concrete beams. Furthermore, 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, indicating the excellent durability of CFRP in the marine environment. Provided that provision is made for the lack of CFRP ductility in comparison to steel, the research undertaken has indicated that CFRP prestressed concrete is a durable, appropriate option when designing structures for use in offshore environments.