Corrosion of steel reinforcement is the primary cause of durability problems in Reinforced- and Prestressed-Concrete (RC and PC) structures. The construction industry has only partially answered the rising demand for corrosion-resistant technologies. This IDEA project contributes to the development of corrosion-resistant tendons for PC application that, in addition to durability and mechanical performance, exhibits favorable constructability and cost characteristics. The project focus is on Glass Fiber Reinforced Polymer (GFRP) that retains immunity to corrosion and maintains a low material cost while showing high strain at failure and low modulus of elasticity (an advantageous feature in PC fabrication). The low creep-rupture strength exhibited by GFRP does not allow designing for high level prestressing. However, mild-prestressing presents the advantage to lower losses due to concrete creep during the service life of PC structures. Furthermore, it guarantees compatibility with simple prestressing chucks and conventional tensioning techniques.

Traditional GFRP solid rebars used in RC construction are typically not suited for prestressing due to their difficulty to be coiled, while a GFRP tendon is currently not available in the marketplace. This project considered and developed various GFRP material solutions that are coilable and may be used in prestressing applications (including the evaluation of traditional steel prestressing anchors and a nylon-wedge anchor). Among them, the use of thermoplastic (TP) resin (compared to a thermoset) that eases manufacturing of complex shapes such as 7-wire strands or bent bars by allowing thermoforming, post-heating, and staged manufacturing. It may have a disruptive impact on the composite reinforcement industry. In fact, the use of thermoplastic resin would allow the production of stocks of coiled FRP bars that could be subsequently heated, shaped, and cut to length as orders are received. This solution would speed up the delivery of complex shapes to the construction field and allow the manufacturing of higher-quality reinforcement. The project was carried out into two stages. Stage I focused on the development, testing, and characterization of GFRP coilable material systems for concrete prestressing. Stage II focused on the design, construction, and testing of demonstrative structures using pre-tensioned GFRP reinforcement. Of the four coilable material systems considered, vinylester-GFRP coilable bars coupled with nylon-wedge anchors proved ready for field deployment at a pull of approximately 30% of their guaranteed tensile strength. The other material systems investigated showed promising performance under laboratory conditions and have been developed at a prototypical stage. Experimental testing of the four coilable GFRP material systems showed different initial pull strengths. Displacement-controlled tests under sustained pull were performed to simulate the behavior of the reinforcement-anchor systems during pre-tensioning operations. Tests were conducted for different time durations ranging from 12 hours to 7 days. Results showed compatibility with traditional pulling procedures. Two demonstrative piles partially-prestressed using coilable vinylester-GFRP bars were constructed for installation at a bridge site in Broward County, FL. The last component of this study quantified the economic implications of the technology.

The final report is available.