Fiber Reinforced Polymer (FRP) is comprised of a polymer (such as epoxy, vinyl-ester, or polyester) that is reinforced with a fiber (such as carbon, glass, Kevlar, basalt, etc.); thus the name Fiber Reinforced Polymer or FRP. The fibers are the main source of strength and stiffness in FRP. The resin serves two primary purposes: a) it distributes the load among all fibers, and b) it protects the fibers from environmental effects such as abrasion, etc. FRPs have physical properties that are different when measured along different axes or directions. By orienting the fibers in the desired direction, one can achieve the required strength in each direction.
The original technique of use of FRP for repair and retrofit of structures was pioneered in the late 1980s by Professor Ehsani and his associates at the University of Arizona. That technique used at that time is what is known as the wet layup system. In the wet layup system, fabrics of carbon or glass are saturated with epoxy resin in the field and applied to the structure (similar to wallpaper); by the next day when the epoxy cures, the FRP will have a strength about three times that of steel!
For over two decades the construction community continued to use either the fabrics in a wet lay-up application or carbon strips. These materials by nature have limitations and they had prevented structural engineers from offering cost-effective high quality solutions to several applications.
In 2009, Professor Ehsani introduced the next generation of FRP products called SuperLaminates that overcome the shortcomings of the above mentioned wet layup and narrow carbon strips. As discussed below, these products make many applications that have challenged the engineering and construction professionals for decades possible. In some cases, the solutions would not have been possible without the development of super laminates.
SuperLaminates are constructed with specially designed equipment. Sheets of carbon or glass fabric up to 60 inches (1.5m) wide are saturated with resin and passed through a press that applies uniform heat and pressure to produce the laminate. SuperLaminates shown below offer three major advantages over conventional laminates. First, by using unidirectional or biaxial fabrics, the laminate may provide strength in both longitudinal and transverse directions. This is a tremendous advantage that opens the door to many new applications. Secondly, they are much thinner than conventional laminate strips; with a typical thickness of 0.025 inches (0.66 mm), they can be easily coiled into a circle with a diameter of 12 inches (300 mm) or smaller. Lastly, the number and pattern of the layers of fabrics can be adjusted to produce an endless array of customized products that can significantly save construction time and money.
Why did we develop SuperLaminate™ ?
Nearly two decades ago, Professors Ehsani and Saadatmanesh introduced the concept of repair and retrofit of structures with Fiber Reinforced Polymer (FRP) to the construction industry in a paper published at the ACI Concrete International. During this time the application of FRP products has seen significant growth worldwide. However, the form of these materials has remained virtually unchanged.
In the original concept, referred to as the wet layup method, fabrics of carbon or glass are saturated in the field with resins such as epoxy and they are bonded to the exterior surfaces of structural elements such as beams, columns and walls. The materials cure in less than a day, resulting in a reinforcing skin that is 2-3 times stronger than steel. The technique is somewhat labor intensive and requires trained installers to make sure the fibers in the fabric are aligned properly during the installation and that no air bubbles are trapped under the fabric. Samples of the saturated fabric are made each day on the job site and sent to a laboratory for testing to verify the strength of the installed products. However, these results become available in a few days, often after the project is near completion and remedial measures are difficult to implement.
In response to the above shortcomings, we have developed a new “form” of FRP products called SuperLaminate™ which are produced in our manufacturing facility. In this case, one or more layers of glass or carbon fabric are saturated with resin and passed through specially designed equipment that applies uniform heat and pressure. The result is a very thin solid laminated sheet; typical sheets are 0.01-0.025 inches thick X 50 inch wide X 150 feet long. The tensile strength of the laminate is about 155,000 psi. Basically, we have moved 70%-80% of the construction activity away from the field to our production facility. This results in savings in construction time, while improving the quality of the finished installation. Unlike the wet layup method, here the strength of the laminates can be tested prior to installation and if there are any defective products, they can be rejected.
The unique strength and stiffness of SuperLaminate™ allows it to be inserted into pipes, spanning over gaps caused by corrosion of the host pipe and creating a new strong pipe inside the old pipe or culvert. These engineering characteristics that can be tailored to meet the specific project requirements, make SuperLaminate™ ideal for demanding applications such as high pressure gas and water pipes where other conventional repair techniques may fail to meet those challenges. Please click here to learn more about the advantages of this product.
SuperLaminate™ is a very versatile product. Its strength and stiffness allow it to be coiled in the field to create a shell of virtually any size in minutes, like an extremely strong and durable Sonotube. Applications include repair and strengthening of deteriorated and corroded columns, underwater piles, utility poles, encapsulation of underwater piles in the tidal or splash zone. It also offers unique solutions in post-disaster restoration of columns and piles following earthquakes, hurricanes, blast loading, etc.
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- Concrete Repair Bulletin – ‘Trennchless Emergency Repair of Mile Long Penstock with FRP’
- Concrete Repair Bulletin – ‘Restoration of Large Diameter Prestressed Concrete Cylinder Pipelines’
- Restoration of a Deteriorated Reinforced Concrete Chimney with FRP