Cathay Composite’s CC-Quantum
Strengthening Systems

Fibre Reinforced Polymer

Fibre-reinforced polymer (FRP) composites have been used for structural strengthening for several years. During this period, acceptance of FRP composites as a mainstream construction material has grown, and so has the number of completed FRP strengthening projects. As a result, the use of FRP for strengthening and retrofit is gaining more popularity among design professionals over conventional strengthening techniques, such as installation of supplemental structural steel frames and elements.

FRP strengthening of existing structures can involve complex evaluation, design, and detailing processes, requiring a good understanding of the existing structural conditions along with the materials used to repair the structure prior to FRP installation. The suitability of FRP for a strengthening project can be determined by understanding what FRP is and the advantages it offers, but more importantly, its limitations

FRP Application

FRP systems provide a very practical tool for strengthening and retrofit of concrete structures, and are appropriate for:

  • Flexural strengthening,
  • Shear strengthening, and
  • Column confinement and ductility improvement.

FRP systems have also been successfully used for seismic upgrading of concrete structures. These applications include mitigating brittle failure mechanisms such as shear failure of unconfined beam-column joints, shear failure of beams and/or columns, and lap splice failure. FRP systems have also been used to confine columns to resist buckling of longitudinal steel bars. These FRP schemes increase the global displacement and energy dissipation capacities of the concrete structure and improve its overall behaviour.

Because of the resistance to corrosion, FRP composites can be utilized on interior and exterior structural members in all almost all types of environments.

FRP System

The most common FRP systems for concrete strengthening applications are carbon fibre based (CFRP). Carbon has superior mechanical properties and high tensile strength, stiffness, and durability. The use of prefabricated CFRP bars and plates is typically limited to straight or slightly curved surfaces; for example, the top side or underside of slabs and beams. Prefabricated FRP elements are typically stiff and cannot be bent on site to wrap around columns or beams.

FRP fabric, on the other hand, is available in continuous unidirectional sheets supplied on rolls that can be easily tailored to fit any geometry and can be wrapped around almost any profile. FRP fabrics may be adhered to the tension side of structural members (e.g. slabs or beams) to provide additional tension reinforcement to increase flexural strength, wrapped around the webs of joists and beams to increase their shear strength, and wrapped around columns to increase their shear and axial strength and improve ductility and energy dissipation behaviour.

The adhesive systems used to bond FRP to the concrete substrate may include a primer that is used penetrate the concrete substrate and improve bond of the system; epoxy putty to fill small surface voids in the substrate and provide a smooth surface to which the FRP system is bonded; saturating resin used to impregnate the fabric and bond it to the prepared substrate; and protective coating to safeguard the bonded FRP system from potentially damaging environmental and mechanical effects. Most epoxies for FRP strengthening systems are adversely affected by exposure to ultraviolet light, but can be protected using acrylic coatings, cementitious coatings, and other types of coatings.

The resins and fibre for a FRP system are usually developed as one system, based on materials and structural testing. Mixing or replacing a component of one FRP system with a component from another system is not acceptable and can adversely affect the properties of the cured system.

The bond between FRP system and the existing concrete is critical, and surface preparation is essential to most applications. Any existing deterioration or corrosion of internal reinforcement must be resolved prior to installation of the FRP system. Failure to do so can result in damage to the FRP system due to delamination of the concrete substrate.