Composite applications that incorporate other materials into a system or mix various types of fibers and resins are often referred to as hybrid composites. Today, several composite manufacturers and academics are combining fiber reinforced polymer (FRP) materials with other materials to create new systems with enhanced properties. Here are just a few examples:
Cement-Filled FRP Pipes
Pioneered by researchers at several U.S. universities, hybrid FRP/cement-bridge columns, pilings, and decks have been successfully incorporated into low-maintenance civil engineering projects. A pioneer in hybrid FRP/cement technology, Dr. Amir Mirmiran, professor and dean of the College of Engineering and Computing at Florida International University (FIU) in Miami, says, “We started about 15 years ago to demonstrate that we could introduce composites into civil engineering and construction projects. Because the name of the game was economy, we focused on hybrid construction with concrete because it combines the advantages of composites with the high compressive strength and low-cost of concrete,” he recounts.
Mirmiran has gone through two generations of these hybrid bridge columns, the first used a pipe filled with unreinforced concrete, for use in non-seismic areas. The second generation was reinforced with steel in the pipe for use in earthquake-prone areas. Researchers at FIU are now working on the third generation, which eliminates steel by using ultra-high-performance concrete (six times stronger than conventional concrete) in the lower 20 percent of the tube’s length, then filling the rest with conventional concrete. “Our tests show that Gen 3 should provide both the strength and ductility needed, even for seismic regions,” he says.
“Eliminating steel simplifies the construction tremendously because we don’t have to prepare the reinforcing cage first, embed it in the footing, then lower the tube onto the reinforcement before pouring the concrete. Now it’s a matter of placing the tube as designed then filling it with concrete for a much simpler, much cheaper construction, without worrying about corrosion.”
Another pioneer in this area is Prof. Amir Fam, Canada Research Chair in Innovative and Retrofitted Structures at Queens University in Ontario. He has worked with filament-wound composite tubes as “stay-in-place” closed forms for piles, columns and utility poles, as well as open forms for bridge decks for more than 15 years. “For closed forms, the advantage of using FRP pipes is that the properties can be engineered and controlled to achieve maximum flexural or axial strength for an application,” he explains.