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Carbon Fiber Reinforced Polymers

Dealing with maintenance and repair of deteriorated components and structures are part of everyday life for most municipal, commercial and industrial managers. The affects of degraded conditions are seen in closed highways, collapsed structures, burst pipes and unscheduled industrial plant outages. In addition personnel safety can be compromised and operating budgets can be significantly impacted. However, a new technology is now available that can increase the usable life of components and structures, while significantly reducing the economic burden normally associated with repair or replacement options. This technology is known as "Carbon Fiber Reinforced Polymers" or CFRP. CFRP utilizes carbon fibers and high strength epoxy resins to restore or enhance the structural and or pressure boundary capacity of equipment and structures. This process utilizes the high strength of the carbon fibers to add additional structural capacity to the existing member. The design determines the orientation of the fibers to add strength in the direction of static and dynamic loading conditions. The repairs to the affected items are performed in-place and completed during relatively short durations. Small crews perform the work and can do internal strengthening with access through only a manhole. The technology and engineering associated with CFRP repair methods provides an effective mechanism to rehabilitate structural steel, concrete, pressure piping, storm drains, potable water piping, pumps, heat exchangers, water boxes, bridges and numerous other items while minimizing the cost typically associated with direct replacement.

Process Description
A significant advantage of a CFRP Repair Solution versus a more traditional repair technique is the relative ease of installation. Small two or-three man crews with minimal equipment perform the work. The work is performed quickly and can often be completed during regularly scheduled shutdown times. These small crews can work around existing obstacles and do internal pipe strengthening with access only through a manhole.

Prior to the installation of the CFRP System, the substrate is repaired as required to eliminate any degradation of the base material. For concrete installations, this may include removing unsound concrete, repairing corrosion-damaged rebar, crack injection, addressing ongoing corrosion problems and general patchwork. For applications on steel, severely corroded areas must be returned to sound base metal and repairs made as necessary.

Following substrate repair, the surface of the member to be strengthened is prepared. The extent of surface preparation required depends on the type installation. There are two types of installations - Contact Critical and Bond Critical

Contact Critical installation involves confinement of the structural member such that the FRP is applied completely around the member and re-bonds to itself. Bond critical applications require a bond between the adhesive and the structural member. These include shear and flexural type applications where the material does not completely encase the member.

For contact critical applications, the surface must be clean, sound and free of any fins, sharp edges or protrusions that may damage the fibers. In addition, large voids should be filled with a system compatible repair material to allow continuous contact between the FRP and the surface of the substrate. Well-adhered paint does not need to be removed.

Bond Critical

For bond critical applications, surface preparation should be made according to American Concrete Institute (ACI) guidelines for concrete substrates. This includes the removal of laitance, dirt, existing coatings or other substance that would interfere with the bonding. Then the concrete surface shall be mechanically abraded to provide a roughened surface. A minimum concrete surface profile of 3 as defined by the Industrial Concrete Repair Institute (ICRI) should be achieved. Steel surfaces where bonding of the FRP is necessary are prepared such that a white metal finish is provided in accordance with the requirements of the Steel Structures Painting Council (SSPC).

In addition, all corners, edges or other abrupt changes in surface continuity must be rounded to ensure that the primary fiber will not be damaged or prevented from performing its design function. A ½ inch minimum radius is typically required and may be increased depending on project specific considerations. Chamfered corners can be rounded out using thickened epoxy. A system compatible primer should be applied to all surfaces to receive composites and then the application of the fibers may begin.

The materials to be applied are composed of unidirectional or multidirectional fiber fabrics that are impregnated with an epoxy resin at the job site. The type of reinforcement fibers and direction of orientation are a function of the specific design requirements that are determined as a result of all loading conditions.

The first step in preparing the composite material for installation is to combine the two-part epoxy and mix thoroughly per the manufacturer's instructions. Prior to or in parallel with this step, the reinforcement fibers are cut to the desired length and width as necessary to conform to the surface contours of the structure. Subsequently, the dry fibers are impregnated with the epoxy using manual wet out techniques or a saturation machine. The saturation machine consists of two heavy rollers and a reservoir containing the epoxy resin. The dry fibers pass through the epoxy bath and then through the rollers. The rollers are gapped such that the correct amount of epoxy is left on the fibers. This provides equal and consistent saturation of the fibers and ensures that a high level of product reliability is maintained. The saturated fibers are then re-rolled and brought to the site of the installation.

After saturation, the wet fibers are applied to the prepared substrate. Care is taken to ensure that the fibers are applied straight, in the correct direction, and that air bubbles are worked out of the system. Multiple layers are applied until the required thickness is achieved. Appropriate overlaps are provided as detailed by the design. All edges are sealed with a system compatible epoxy so no loose fibers are apparent. At this point a final top coat is applied to protect the surface the carbon fiber from any incidental damage or normal wear. In addition where the product is to be exposed to sunlight an ultra-violet protection coating may be applied where long-term exposure is a concern.