Carbon Fiber Strengthening: When and How?

Carbon fiber reinforced polymer (CFRP) systems are one of the most common ways to strengthen existing reinforced concrete structures without demolition and without enlarging sections. Although very light, they have far higher tensile strength than steel and do not corrode.

When is it used?

• Columns, beams and shear walls found insufficient in a seismic performance assessment
• Slabs that must carry more load after a change of use
• Members that have lost capacity through rebar corrosion, fire or damage
• Sections with missing reinforcement due to design or construction errors

The decision to strengthen and its design must be based on a structural engineer's calculations; the number of layers, width and fibre direction are set by that calculation.

Fabric or plate?

Carbon fiber fabric (DEMCO CARBON WRAP) is flexible; it is used for column wrapping (confinement), shear strengthening and complex shapes. Carbon fiber plates (DEMCO CARBON LAMINATE) are rigid and are bonded to the underside of beams and slabs for flexural strengthening. Plates and fabrics can be tied to each other and to adjacent members with carbon fiber anchors.

Application steps

1. Surface preparation: plaster is removed, loose concrete is cleaned off, corners are rounded, and the surface is ground and dust-free.
2. Repair: cracks are injected with epoxy injection resin (DEMCO EPOX 120 INJECTION RESIN) and damaged areas are repaired with epoxy repair mortar.
3. Primer and levelling: an epoxy primer is applied and irregularities are filled with epoxy putty.
4. Lamination: the fabric is saturated with epoxy laminating resin (DEMCO EPOX 121 CARBON FIBER RESIN) and laid in place, with air removed by roller. Plates are pressed on with epoxy adhesive.
5. Protection: after curing, a protective coating or render against fire and UV is applied where needed.

Advantages

• Adds almost no weight to the structure and does not enlarge sections.
• Fast to install, often while the building stays in use.
• Does not corrode and lasts a long time.

For our complete system of carbon fiber fabrics, plates, anchors and resins, browse our structural strengthening products; contact us for data sheets and a quote.