In the last decade, civil engineers have experimented successfully with the use of composites for a variety of infrastructure projects. Among the notable applications have been decks for pedestrian and vehicular bridges, cables for cable-stay bridges and electric power transmission grids (not to mention power poles and towers), and liners for corroded underground pipe (a recent installation is chronicled on p. 54). Although composites are still “emerging” technologies in these areas and face stiff resistance from legacy materials, due in part to the difficulty of amending existing construction standards, composites have established a beach head and, as the following examples illustrate, continue to gain ground, sometimes in unusual and unanticipated ways.
BRIDGING A DEVELOPMENT GAP
Prof. Vistap Karbhari, a professor of material science and structural engineering at University of Southern California, San Diego (UCSD) and notable composites researcher with practical experience in several high-profile bridge construction projects in the past decade, has seen a huge increase in the use of composites in bridge construction, particularly in the areas of pultruded bridge decks and the use of composite rebar in place of steel as reinforcement for concrete. He credits the increase to greater acceptability of composite materials in the bridge-building community. On the other hand, Karbhari says he has seen few major innovations in recent years.
One exception, however, is an innovative all-composite bridge structure that made a striking appearance at last year’s JEC Show in Paris, France. FiberCore Europe (Rotterdam, The Netherlands), a commercial spin-off of the Rotterdam-based engineering and consultancy bureau, Composieten Team, displayed a carbon fiber-reinforced composite bridge that weighed just 12 metric tonnes (26,455 lb), which makes it about 30 times lighter than a comparable concrete bridge, according to FiberCore. The bridge is 24.5m/80.4 ft long and 5m/16 ft wide, yet the company’s design R&D engineer Jan Peeters says the bridge was load tested with 75 metric tonnes (nearly 164,400 lb) of weight and showed deflection of only 64 mm (2.52 inches). The bridge is, essentially, a large sandwich structure. Its corrugated honeycomb core is layed up in a sinusoidal pattern between composite skins that consumed 3 metric tonnes (6,614 lb) of commercial grade Panex 35 carbon fiber from Zoltek Inc. (St. Louis, Mo.). Fiber sizing and vinyl ester resin for the bridge project both were supplied by DSM Composite Resins AG (Schaffhausen, Switzerland). The bridge was molded using a proprietary tooling system developed for the project that, according to FiberCore, is easily adapted to produce structures in a wide variety of heights, lengths and widths. Peeters, therefore, contends that his carbon fiber bridges eventually could be cost-competitive with concrete because the tooling cost can be amortized over a large number of bridge projects. Following its brief stop at the JEC show floor, the structure was delivered to the Dutch municipality of Dronten and installed May 10, 2007. According to the company, engineers set the bridge in place in just 15 minutes (see photos, this page).
Later in 2007, FiberCore fabricated a 6m/19.7-ft wide bridge for a 6.6m/21.7-ft span to support auto traffic in Oostzaan, The Netherlands. The bridge comprised two 3.3m/10.8 ft decks that weigh 1,200 kg/2,646 lb each, resting on abutments at each end and meeting over a centered midspan support. According to FiberCore, the bridge is rated for 300 kN (67,442 lbf) loads. And on Feb. 29, this year, FiberCore oversaw the installation of another of its prefabricated bridges over a 10.5m/34.5-ft span on a bicycle/pedestrian path that a crosses a stream in Krimpen aan de Lek, The Netherlands.
FiberCore also has branched out into cladding elements. The company recently produced and installed composite end caps for a free bus lane in Hoofddorp, The Netherlands (see photo, this page) that bridges a 128m/420 ft span across the city’s highway A4. The 4m by 1.2m by 0.8m (13.1-ft by 3.9-ft by 2.62-ft) end caps provide aesthetically pleasing and corrosion-resistant design elements but add little weight to the bridge structure. According to FiberCore, the premanufactured end caps can be installed by as few as three workers, using a light-duty crane, with little disruption of traffic. FiberCore also offers similarly constructed modular composite sound barriers that run the length of an overhead bridge span, damping sound and thus isolating the area below the bridge from traffic noise.
Another recent concept — a lightweight, prefabricated bridge deck panel design also suitable for pedestrian/bike trail bridges — is the product of development work by Composite Advantage LLC, the National Composite Center (Dayton, Ohio), and core supplier WebCore Technologies (Miamisburg, Ohio). Scott Reeve, president of Composite Advantage, an NCC spinoff manufacturing company, expects to see a few vehicle bridge projects each year, which will help build data that, in turn, will build the comfort level of civil engineers comfort level. But he sees pedestrian bridges as a growth area for composites because the loads are moderate and less composite material and, as a result, less upfront expense, is required for construction.
The company’s most high-profile project, the 1,300m² (~14,000 ft²)composite deck for the 860-ft/262m long Anacostia River Walk bridge in Washington, D.C., represents the largest square footage bridge for which Composite Advantage has supplied the deck panels. The project has required about 100 13.7m/45-ft panels that comprise a 76.2 mm/3 inches thick sandwich construction of fiberglass skins over a core made from TYCOR G6 fiber-reinforced, closed-cell foam, manufactured by WebCore Technologies Inc. (Miamisburg, Ohio). Skin reinforcements, supplied by Vectorply Corp. (Phenix City, Ala.), are a combination of multiaxial and unidirectional stitched fabrics. The layup (70 percent fiber content) consists of 55-oz unidirectional fabric and 40-oz multiaxial fabric, with the majority of the fibers oriented along the width of the panel for maximum strength and stiffness transverse to the support beams. “We actually wrap the whole core in skins so you have glass fabrics on the ends, too,” Reeve explains. The glass skins and core reinforcement fibers are infused simultaneously to create sheer webs between the skins that deliver greater strength and stiffness, says Reeve. “We infuse from the inside out,” he says. The panels are vacuum bagged then infused with vinyl ester resin supplied by Reichhold Inc. (Research Triangle Park, N.C.). Infusion takes about 40 minutes and the panels cure ambiently in about four hours. The “one-shot” infusion process and relatively inexpensive, reconfigurable tooling contribute to the panel’s reportedly moderate cost. CT reported on the panel design for this bridge in the December 2007 issue (see “Related Content,” at left). Installation of similar panels for another pedestrian bridge is shown on this issue’s cover.
FROM PROTECTION TO RESTORATION
According to John Hammond, VP of business development at Hardwire LLC (Pocomoke City, Md.), a strong market driver for composites innovation in the infrastructure realm today is repair and rehabilitation. Hardwire’s primary focus, in the wake of the 2001 terrorist attacks on the World Trade Center in New York City, was armor systems for building protection. “Since 9/11 a lot of time has been spent evaluating priorities, and we are entering a phase that we are starting to execute projects.” Hammond notes that the company has worked with Defense Advanced Research Projects Agency (DARPA), the research arm of the U.S. Department of Defense (DoD), on its product development and has also worked with pultruder Strongwell (Bristol, Va.) to manufacture ballistic E-glass panels for building production. He points out, however, that Hardwire’s high-tensile steel reinforcements are not process specific, noting that the product can be processed by a variety of methods, from hand layup to vacuum infusion to pultrusion, depending on the application. That adaptability has enabled Hardwire to gain footholds in building restoration and seismic reinforcement.
“We are taking armor technology that we have been developing and have transferred it into the critical infrastructure world,” says Hammond, noting that the company recently worked with two Italian firms to develop systems for preservation of historic buildings.
In 2007, Fidia Srl – Technical Global Services (Perugia, Milano, Italy) signed an agreement to distribute Hardwire products in Europe. “Thanks to successful results of testing campaigns conducted at the University of Perugia-Italy and at the University of Bath-U.K. on masonry members strengthened with the Hardwire reinforcements,” says Fidia engineer Dr. Paolo Casadei, “such materials are ready for commercial applications.” According to Casadei, Hardwire materials have been used to rehabilitate several historical structures located in the central region of Umbria, Italy, which was hit in 1997 by a large earthquake.
The first application was for the rehabilitation of an historic Franciscan convent, founded in the late 1400s near the city of Orvieto in Tuscany, Italy, and now undergoing a complete restoration. Fidia worked with Perugia-based TEC.INN Srl, the first and, since 1986, a leading Italian contractor specializing in fiber-reinforced polymer retrofit solutions. Fidia designed and supplied materials for strengthening the entire masonry structure and, in particular, vaults and floors. Low- and medium-density Hardwire reinforcement fabrics that are impregnated with either epoxy resin or mortar have been installed both to strengthen the masonry vaults as well as create reinforced ring-beams, at the roof level, to resist horizontal seismic forces, as dictated by the recently approved Italian seismic code.
For the project, Hardwire manufactured braided cord, using its trademarked Hardwire ultrahigh-tensile steel wire. The Hardwire steel filaments, drawn pearlitic steel wire first developed for use as cord in steel-belted tires, benefit from a number of microstructural changes that occur during the wire drawing process, which reorient and align the wire’s “pearlite colonies” along the wire’s long axis, increasing the steel filament’s strength and ductility. Reportedly, the filaments retain much of their elasticity right up until breaking point, a property that is expected to help protect the convent from further damage in the seismically active region.
Two different Hardwire-reinforced products were used: SRP (Steel Reinforced Polymer), which consists of tapes made from braided Hardwire cord impregnated onsite with epoxy resin, and SRG (Steel Reinforced Grout), comprising braided cord that can be used with a conventional mortar matrix.
TEC.INN credited the SRG product, in particular, for allaying some official concerns about the fire resistance of polymer resins and providing for a less labor-intensive installation. Where epoxy impregnated systems require that rough surfaces be smoothed and filled prior to application to ensure a good bond, the mortar previously used to level stone surfaces for the epoxy also can be used as the SRG matrix.
A longtime fixture in repair/rehab segment, Fyfe Co. LLC (San Diego, Calif.) also offers structural strengthening systems in a variety of configurations that incorporate carbon, aramid, glass or hybrid fabrics. Currently the company’s Tyfo Fibrwrap Systems are being used to strengthen, upgrade or repair existing structures that are made from traditional materials, such as wood, concrete and steel, according to Scott Arnold, Fyfe Co.’s general manager. The majority of the company’s work, according to Arnold, is done with unidirectional carbon-reinforced polymers — in seismic upgrades, general strengthening or to facilitate change of use (e.g., to change a building from a business office to a residential condominium). A recent example is a seismic retrofit of the Pasadena City Hall in Pasadena, Calif. (see photos, below).
Fyfe Co.’s Fibrwrap fabrics are impregnated in the field, and the wetout fabric is applied by hand. The epoxy-based matrix emits virtually zero volatile organic compounds (VOCs) so retrofit or repair work can be done without health risk to building occupants. Although the cost per square foot of material is higher than that of conventional materials, Arnold points out that the use of composite products enables economies elsewhere. Installations typically require no heavy equipment, and installers can work in tight spaces. Further, the flexibility of the overwrap materials can negate the need to remove plumbing pipe, electrical conduits or HVAC ductwork to access and complete a job.
Recently, Fyfe Co. developed and patented an anchorage system now used to improve the overall efficiency of its strengthening system.
Holes (typically 3/8-inch) are bored in the member, and the Tyfo anchors (Tyfo SCH anchors, reinforced with carbon fibers, or SEH anchors, reinforced with glass fibers) are embedded in the substrate and bonded in place with epoxy in the same way standard steel anchors are applied. Anchors typically consist of a 3-inch/76-mm stud that is inserted into the hole and a 3-inch/76-mm-radius flange on the exterior that can be bonded to the composite overwrap. However, anchor size can vary, and anchors can be passed all the way through a structural member if it is being wrapped on both sides or the application requires continuity of tensile capacity through the member. In this case, the system transfers tension forces from the fiber-reinforced polymer (FRP) sheathing on the member’s surface to the anchors and then to the sheathing on the opposite side of the member to create a continuous tension member in situations where Fyfe Co. previously has been able to create one, says Arnold.
FibrWrap Construction (Ontario, Calif.) recently used the Fyfe Co. composite anchors to complete a project in a parking structure at the Van Nuys, Calif. airport to confine and add shear strength to beams in the structure after a construction error was discovered. The Tyfo SCH composite anchors were designed to provide the required confinement around the beam. Afterward, the Tyfo SCH-41 System was bonded to the anchors to deliver additional shear strength requirements.
THE WORK AHEAD
While headway is being made when it comes to the acceptance of composite materials in infrastructure, those who use them say standards and industry education still lag behind the need.
Composites use in infrastructure is far from a commodity business, says Fyfe’s Arnold. “There is still a lot of technical backup that needs to be done on a project-by-project basis. There is not always a code in a book to tell me whether or not a project is justified.”
The lack of standardized material properties, says Karbhari, continues to make growth difficult. “We should define what we are using so the user has a good idea of what we are talking about when we use a term,” he says.
Toward that goal, Fyfe Co. has been working with organizations, including the International Code Council (ICC, Washington, D.C.) and American Water Works Assn. (AWWA, Denver, Colo.), in an effort to advance the codification of its products.
It also is important, says Arnold, to educate engineers about what the materials can and can’t do. “I’ve noticed a perception among some engineers that these materials have ‘magic’ to them,” he says, noting that composites “are often asked to do things that [engineers] would not ask a traditional tension member to do. These materials are governed by the same law of physics as traditional materials.” If acceptance and use is to increase, he says, it is important that the materials are used in validated environments.
Arnold notes that Fyfe Co.’s president, Ed Fyfe, is spearheading research into fire resistant composite materials approved for columns and overhead applications in an effort to alleviate fire concerns when composites are used for structural strengthening. Fyfe Co. developed the Tyfo Advanced Fire Protection (AFP) System, which has received the Underwriters Laboratories (UL, Northbrook, Ill.) certification, meeting the requirements of ASTM E-119 and ASTM E-84 (ASTM International, W. Conshohocken, Pa.). The AFP is applied over the FRP strengthening systems to insulate the FRP from fire because extremely high temperatures can cause epoxy resins to soften or burn, which, in turn, can compromise the FRP’s structural strengthening properties.
Karbhari concludes that while composites have much to offer the repair market, standardization and education are a big part of the battle in the infrastructure market. The path to wider use, he says, is a practical partnership between industry and academia. Scientists and engineers in the field should be teaching classes and establishing composites centers of excellence. “We haven’t done a very good job of educating future generations about composites,” he admits. “To truly put composites on par with other materials, we need the same amount of emphasis at the academic level as we see for timber, concrete and steel.”