FRP Bridge Evolution: TxDOT Advances Viability of Customer FRP Bridge Beams in New Hybrid Structural Construction Research Project
By Jim Williams, MFG Construction Products
Project Profile
In its continuing research of new structural highway construction technologies, the Texas Department of Transportation (TxDOT) has expanded its implementation of custom fiber-re-inforced polymer (FRP) composite bridge beams for a new drainage ditch bridge (FM-1684) in Refugio County, Texas.
The Refugio County Bridge, 35 miles from Corpus Christi, will be the state’s second FRP hybrid-bridge endeavor, following the successful construction of the San Patricio County Bridge about three years ago. The county has a humid subtropical climate (averages 37 inches of rain annually) which results in corrosive salt and brackish water. Therefore, although more costly upfront, TxDOT specified the FRP beams to advance the research of the long-term corrosion and structural performance benefits of FRP materials vs. traditional steel or concrete beam solutions.
 With the FRP beams specified by TxDOT, Molded Fiber Glass Construction Products (MFG), which had produced the previous FRP beams at San Patricio, manufactured eight customized flanged U-Shaped beams whose depth and composite structure would provide optimal deflection under load. Once completed, the beams would weigh approximately 5, 000 pounds each and sit on abutments where the concrete deck would be poured onto it.
FRP Challenge/Forming Process
MFG fabricated the beams in its Texas location utilizing a Vacuum Infusion Process (VIP) versus the previous project’s hand lay-up to optimize the physical properties of the beam and facilitate production. This process was selected because vacuum infusion provided a number of benefits including; consistent fiber-to-resin ratio, less wasted resin, unlimited set-up time and much lower emissions. The VIP utilizes a vacuum bag to de-bulk or compact the parts’ complete laminate ply schedule of reinforcements and or core materials that are laid onto the mold.
For the Refugio beams, a male mold was produced to the beam design and then dry sheets of stitched glass fabric and chopped strand mat were laid over the U-Shaped mold. This process was applied in a series of layers to achieve the appropriate 1.5-inch beam thickness, and then a plastic film was laid on top to serve as a vacuum bag. Once a complete vacuum was achieved, liquid resin was then introduced into the laminate via carefully placed tubing. The vacuum then draws the resin through the fibers, filling all the voids and eliminating any remaining air along the flow-front.
According to Rich LaFountain, MFG Business Unit Leader/Open Molding, “The trick is to get the bag to draw down correctly so that wrinkles don’t develop in the individual layers of fabric which could affect the ultimate strength of the composite.”
Assembly/Installation
Once completed, the beams were cured, trimmed and assembled with shear transfer members (brace bars) that included flange plates/tubes across every 16 inches in a 50-foot beam. Holes were drilled into the vertical sides and brace bars (2-inch diameter) were inserted through the beam at the top of the webs (lips) on either side. The beams were placed at 4-foot to zero-inch center-to-center spacing with the concrete reinforced deck placed on top.
The deck was then tied to the beams with horizontal pipe (2.6 inches deep by 2.3 inches wide) close to the top of beams. The concrete deck pour was deep enough to engage the brace pipe for optimal strength to tie the beams to the deck. The goal was to achieve composite action between the beams and the deck; creating an inflecture-solid connection between the deck and beams.
Acoustic Emission Testing
Prior to installation, in April 2007, Beam Nos. 1 and 2 were given the Acoustic Emission Evaluation Test by The University of Texas at Arlington’s Guillermo Ramirez, PhD and Paul Ziehl PhD from the University of South Carolina. The tests monitored emission during the background check prior to loading, during load holds and during the background check after completion of loading.
The test threshold was 40 dB and the evaluation threshold was 48 dB. The main sensors used were type R15I (resonant in the range of 150 kHz) manufactured by Physical Acoustics (PAC). Broadband sensors were used for supplemental evaluation. Activity from the R15I sensors was monitored and recorded with a 24-channel Transportation Instrument; also manufactured by PAC.
According to Dr. Ramirez, “The test verifies the performance of the beams under the load criteria set forth by the project specifications. The beams performed well during load testing, passing the major criteria selected for the Acoustic Emission test. In fact, the beams’ stiffness tested better than expected substantiating their ability to sustain in service loads.” Ramirez added, “The beams looked very nice, with no visible flaws. The method of fabrication resulted in a very good product.”
Results
“In addition to the lightweight FRP beams allowing for rapid onsite deployment, its material strength over time will reduce maintenance costs on the overall construction of the bridge,” said Roy Tijerina, superintendent for Haas-Anderson Construction.
A post-construction assessment by TxDOT/Federal Highway Administration Division Bridge Engineer Peter Chang noted, “The funding to promote the new fiberglass girder technology was allocated by TxDOT as a research project. With the load testing calculated and installation complete, the beams are actually stronger than we anticipated, thus proving the research positive.”
CRYO Industries Announces Price Increases for Acrylite and Acrylite Plus Acrylic Polymers
CYRO Industries, now part of the Methacrylates business unit within the Chemical Business Area of Evonik Industries, has announced a price increase for acrylic polymers. The increase will begin with shipments on or after Nov. 15 for all grades of CYRO Industries’ Acrylite acrylic polymers and Acrylite Plus impact acrylic polymers by $0.06 per pound.
The increase was onset by increased costs of key raw materials this fall, on top of the steady rise in prices throughout this year. And, the company does not anticipate these high costs abating any time soon.
The company ensured customers that the entire global Methacrylates team is working diligently to identify and implement productivity programs in an attempt to minimize continuous cost pressures.
Adhesive Offers Strength, Toughness and Chemical Resistance
 Bond EP30D-12 is a versatile two-component elastomer featuring superior strength, toughness and unusually superior chemical resistance developed by Master Bond, Inc. EP30D-12 combines the recognized advantageous performance characteristics of epoxy resins such as adhesive strength and chemical resistance with those of the polyurethane’s, including toughness, abrasion resistance and flexibility. The outcome is a product with high physical strength properties, such as a 7,500 psi tensile strength, a notable flexibility of 440 percent elongation at break combined with superior chemical resistance and durability manifested in low water absorption, low moisture permeability and high hydrolytic stability.
EP30D-12 is processable in both thick and thin sections. Because of the low viscosity of the blended mixture, the compound flows easily and smoothly even around intricate geometries. Parts more than one inch thick can be cast without undue exotherm development. EP30D-12 system cures with minimal shrinkage in five to six hours at ambient temperatures to a tough elastomer with remarkably good resistance to thermal cycling and chemicals including water, inorganic salts, alkalis and acids as well as many organic chemicals. Adhesion to metals, glass, concrete, ceramics, wood, vulcanized rubbers and many plastics is excellent over the temperature range of -60°F to more than 250°F (-50˚C to 120˚C). EP30D-12 is recommended for high performance bonding, sealing, casting, potting and encapsulation applications in the electronic, electrical, construction, metalworking, automotive and chemical process industries. It is available in premixed bi-packs and cartridge/gun packaging for convenient dispensing as well as in pint, quart, gallon and 5 gallon container kits.
Pecora Introduces NST Non-Staining Technology
To eliminate the high cost associated with silicone staining in porous substrates, Pecora has introduced a new line of silicone products: NST Non-Staining Technology. An innovation in sealant technology, Pecora's NST Non-Staining Technology, including 864NST, 890NST and 895NST, is the industry's first complete line of non-staining silicones.
Architects, builders and contractors benefit greatly from the revolutionary properties of the non-staining line of products.
Architects and specifiers can choose an NST sealant with the confidence that regardless of the substrate it will not be damaged by the silicone. And, because the NST silicones are available in a variety of modulus, as well as any color you can imagine, the sealant decision process has been made even easier.
Contractors and builders can use this revolutionary new line of products knowing that their projects will be seen in years to come for the quality of their workmanship instead of unsightly staining from the sealant. In addition, the NST silicone line provides the practical benefits of improved adhesion and reduced dirt pick-up.
Pecora's Non-Staining Technology removes the possibility of damage to a valuable substrate resulting in costly repair work and to an architect's or contractor's very reputation. “NST gives a specifier confidence,” said Chris Sajbel, Pecora's new Western Regional Sales Manager. “With Pecora there is no worry that the substrate will remain its original color and free from dirt pick-up.”
With traditional silicone sealants, the fluids responsible for flexibility are able to migrate away from the cured sealant to create two kinds of damage to the building substrate, staining and residue rundown.
Staining is present when the fluid is absorbed into porous substrates such as marble, granite and limestone, causing permanent discoloration in the stone.
Residue rundown occurs when the fluid is not absorbed into the substrate, but migrates from the sealant, runs down the face of a building, and causes a streaking effect as it collects dirt.
Pecora's NST Non-Staining Technology removes the fluid causing the damage while maintaining the flexibility necessary to accommodate a building's constant movement.
FDA-Compliant Fluorosint HPV Tops Out Range of Enhanced PTFE-Based Engineering Plastics
 Stock shapes manufacturer Quadrant Engineering Plastic Products (Quadrant EPP) has extended its Fluorosint range of proprietary high performance PTFE-based shapes for machining with a grade that can operate in extreme environments at temperatures anywhere from -240°C to 260°C.
Fluorosint HPV is intended for applications such as seals and bearings that demand high wear resistance and low friction. Finished products may come up against mating surfaces such as 316 stainless steels (austenitic stainless steels with superior corrosion resistance), aluminium, mild steel, brass and even other plastics. It is available in the form of rod, tube and sheet, and can also be supplied in near net-shape form.
The Fluorosint family is the result of a proprietary process and composition yielding properties not normally attainable in reinforced PTFE. In particular, the materials offer an excellent combination of low frictional properties and high dimensional stability.
Ed Alvarez, advanced market manager, said Fluorosint HPV has properties above and beyond those of Quadrant’s two existing Fluorosint family members. Fluorosint FFM-500 offers excellent deformation resistance and very low CLTE (Coefficient of Linear Thermal Expansion) for a PTFE compound,” he said. “However, to attain these properties, the 500 grade gives up some of its wear-life properties in some applications. Another traditional grade, LF-207, has better wear performance and is FDA compliant, but does not have the dimensional stability under load and other properties of the 500 grade.
Our target was to develop a PTFE product that combines the best of these existing grades, with enhanced wear resistance, dimensional stability and a lower coefficient of friction.”
Fluorosint HPV has a dynamic coefficient of friction (dry vs. steel) of 0.14 to 0.15, and a K-Factor (an indication of wear resistance) of 25,000. Rockwell hardness is R 54. Parts can be used with or without external lubrication, allowing them to wear evenly without any erratic motion in low speed start-stop applications that require zero stick-slip. It is highly suitable for dynamic seals and bearings, and is ideal for non-lubricated, high bearing load components intended for use in extreme environments where metals fail due to erosion and corrosion.
Wear behavior is superior to bronze, powdered metals and steel, and the new product has the additional advantage over metals that it does not rust. Its ability to function without the need for lubricants helps keep products clean and is also a cost saver. The wear resistance of the material offers the benefit of extending time between maintenance and replacement of bearing and wear components.
Alvarez said the product outperforms traditional PTFE based materials not only in terms of friction and wear, but also in resistance to deformation and chemical attack. It can be used in both alkaline and acidic environments.
Fluorosint HPV is also FDA compliant, making it a suited choice for bearings and seals in food processing equipment. A major advantage is that it is not affected by steam or aggressive cleaning agents.
“Fluorosint HPV out-performs many other engineering polymers,” said Alvarez. “Most nylon, PET and PBT bearing-grade products are limited to light load applications. Dimensional stability of many nylon bearings is compromised by high water absorption, while thermoplastic polyesters can’t match fluoropolymers for temperature resistance and load bearing capabilities.”
The negligible moisture uptake of Fluorosint HPV means parts exhibit negligible swell across their operating range, allowing engineers to specify very tight clearances for bearings. Tighter clearances reduce the likelihood of debris entering the bearing housing and abrading the internal components of equipment– once again extending maintenance intervals.
Eastman Chemical Company Launches New Polymer
 Eastman Chemical Company has released the Eastman TritanTM copolyester, a new-generation copolyester that is suited for a broad range of applications, including housewares, appliances and sheet applications. The result of new technology, this innovative material delivers the advantages of traditional copolyesters, such as clarity and chemical resistance, with higher heat resistance, improved design flexibility and ease of processing. These unique attributes offer differentiated performance for brand owners, designers, fabricators, processors and consumers.
“An introduction of this magnitude has not been seen in the plastics marketplace for many years,” says Dr. Gregory O. Nelson, executive vice president and polymers business group head, Eastman Chemical Company. “With its unique balance of properties, Tritan will open the door to a new era of product innovation for Eastman and our customers.”
Tritan's unique chemistry provides a higher glass transition temperature (Tg) than traditional copolyesters, allowing the material to deliver improved heat resistance. This new-generation copolyester can also be molded into various applications without incorporating high levels of residual stress. Combined with Tritan’s outstanding chemical resistance and hydrolytic stability, these features give molded products enhanced durability in the dishwasher environment, which can expose products to high heat, humidity and aggressive cleaning detergents.
The new material’s lower inherent residual stress gives designers a new level of freedom to create products with enhanced aesthetics and functionality attributes, as product designs do not need to be limited to minimize the effects of residual stress. This feature can allow brands to differentiate their products at retail and better meet consumer demand for enhanced product performance.
Tritan provides faster molding cycles than many other transparent plastics and can be used in injection molds designed for traditional polymers, including polycarbonate. As the material does not require an additional annealing step after molding, because of its lower inherent residual stress, these attributes may result in significant manufacturing advantages, including reducing energy use, improving processing times, lowering associated costs and increasing production rates.
With a 2-percent lower density than polycarbonate, Tritan also yields more parts per kilogram of resin, which may contribute to material savings. These savings are extended by the new copolyester’s durability, which can help to lengthen product lifetime and lower replacement costs.
While Tritan offers a higher glass transition temperature (Tg) than traditional copolyesters, sheet products manufactured with the new polymer do not require pre-drying. The durable and lightweight products can also be thermoformed faster and at lower temperatures than polycarbonate sheet. These unique forming attributes contribute to superior material distribution properties and open the decorating window when using pre-form decorative paints, inks and vinyl.
“Tritan is a revolutionary step forward in the plastics marketplace and is a direct result of the ingenuity and technical expertise that has come to be expected of Eastman,” Nelson said. “This new-generation copolyester will provide the plastics industry with an opportunity to better address evolving consumer needs with differentiated, higher performance products.”
High Speed for Hot Places
First High Speed Products in BASF’s Ultramid Plastics Line
 Three years after the market introduction of Ultradur High Speed, BASF’s very easy-flowing PBT, BASF has released its first Ultramid High Speed products. For now, these are the three highly filled polyamide 66 grades Ultramid A3WG8 High Speed, Ultramid A3WG10 High Speed and the optimum-warpage Ultramid A3WGM53 High Speed. The two first products are filled with 40 percent and 50 percent glass fibers, respectively, while the third one is filled with glass fibers and mineral. The incorporation of special nanoparticles into the plastic accounts for a marked improvement of these products not only in terms of the flow properties but also of the heat-ageing resistance at high temperatures. Currently, there are no polyamides with this extraordinary combination of properties on the market. Material for sampling will be available in early 2008.
Nanoparticles: Reducing Weight through High Flowability
After the incorporation of tailor-made nanoparticles in Ultradur, BASF’s PBT product line (PBT: polybutylene terephthalate), had led to a substantial improvement in the flow properties of the products, developers have now succeeded in transferring this concept to another engineering plastic, namely, polyamide (PA). They have created nanoparticles that are precisely harmonized with the polyamide matrix. As a result, the flowability of Ultramid A3WG8, A3WG10 and A3WGM53 has been raised by up to 100 percent. This pronounced enhancement of the flow properties, coupled with the high heat ageing resistance, predestines these new materials for the production of large components in the engine compartment such as cylinder head covers or intercooler end caps. In this area, processors can use the new products in order to save material and thus reduce weight by taking advantage of the good flow behavior since this allows the injection-molded parts to be thinner. The processing is likewise made easier since fewer injection points are needed. The first highly filled grades in the PA 6 family with a similar property profile are now also being developed. |
