Precast Inc. - July/August 2008 - (Page 10) What Is CFRP? In the United States, it has been only within the last 10 years that fiber-reinforced polymers (FRP), including carbon fiber reinforced polymers (CFRP), have emerged as a lightweight material alternative to steel reinforcing in precast concrete structures designed for corrosive environments. This relatively new, noncorrosive, nonmagnetic reinforcing material offers clear advantages for precast concrete structures built in aggressive environments. In harsh climates, the ingress of deicing salts and chemicals through hairline cracks can cause corrosion of the underlying reinforcing steel and significantly shorten the service life of concrete bridges and parking facilities. Long-term durability for America’s bridges is a critical concern of federal transportation agencies. In particular, strong and noncorrosive CFRP reinforcing has the potential to greatly increase the durability and service life of precast, prestressed concrete bridges. Possessing high longitudinal tensile strength (in the direction of fibers), FRP is a composite material that has fibers embedded in polymeric resin. This resin can be extruded into a variety of shapes, from reinforcing bars and stirrups to strands and tendons for both prestressing and post-tensioning of precast concrete. Unlike steel reinforcing, FRP bars do not yield but are elastic until failure and therefore must be designed for their lack of ductility. Used a decade earlier in Canada and Japan, these countries have developed design documents for FRP reinforcement in concrete. The American Concrete Institute (ACI) has recently published specifications for glass fiber reinforced polymer (GFRP) and CFRP reinforced concrete. In a follow-up article, Precast Solution magazine’s September-October 2008 issue will present current applications and service-life testing of CFRP reinforcing in a state-of-the-art article by Professor Nabil Grace, a world-renowned expert in CFRP research and precast, prestressed bridge concrete applications from Lawrence Technological University. which could have possibly damaged the prestressing or mild reinforcing. One of the most interesting differences for us between CFRP and steel reinforcing was the surprising light weight of the material. Unlike steel bar cages, zip-tie guns made quick fabrication and two workers could move CFRP reinforcing cages with ease. Would you work with CFRP reinforcing again? Absolutely! Why? After all is said and done, CFRP is not as different a medium to work with as we first anticipated. We had first thought that the strands would break easily, and that never happened. I think we broke one strand of the approximately 800 CFRP strands that we were tensioning. More importantly, because we can build more durable bridges with CFRP, we all win. If you were to do the project again, what would you do differently? (Laughing) Charge more! But seriously, we wouldn’t make the components as complicated – we’d make them easier for long-line production. For example, we’d have the diaphragm built in to the double tees instead of having a secondary pour for the diaphragms. For larger projects, casting the diaphragms afterward would have made our long-line production more efficient. Another thing we’d do differently would be to begin working as a team with the designers earlier. While the designers were open to suggestions, diligent and fantastic to work with, the sooner the producer can be involved in design – especially with new technology – the better. What advice can you offer to precast producers who are interested in CFRP reinforcing? Talk, meet and work with other producers who can provide information and lessons learned in working with CFRP. The most important things are to develop and test a prototype with your production people and to take advantage of any training you can get. I would be more than pleased to speak with or meet other precasters who would be working with CFRP reinforcement – now or in the future. Visit www.psi-hci.com for more information. BOOTH 1633 THE PRECAST SHOW How much more expensive is CFRP than conventional reinforcing? About seven times as much. Of course this was back in 2002 and we were purchasing the CFRP materials from Japan. Today, we have much higher steel prices that would change the economics significantly. 10 JULY/AUGUST 2008 | PRECAST INC. http://www.psi-hci.com http://www.concretecareers.com http://www.concretecareers.com
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