Carbon Fibre Strengthening

Carbon fibre strengthening is the fastest way to increase the capacity of an existing structure without enlarging its sections. With conventional jacketing the column grows thicker, formwork goes up, and after the pour you wait 28 days. With carbon fibre the applied thickness is a matter of millimetres and the system is ready to take load within a few days.

Zahan İnşaat carries out carbon fibre work as an authorised Sika dealer, using certified system products. That detail matters: the carbon fabric and the epoxy resin must be a compatible system from the same manufacturer. Mixing brands makes the bond performance impossible to document.

Where is carbon fibre strengthening used?

The application is decided by which capacity of the member falls short:

• Column wrapping — increases the ductility and axial capacity of a column. It is the most frequent requirement to come out of a seismic performance assessment.
• Beam flexural reinforcement — carbon laminate bonded to the soffit of a beam raises its bending moment capacity.
• Beam shear reinforcement — fabric wrapped in a U around the beam web increases shear capacity.
• Slab reinforcement — when the use of a floor changes and loads rise (archive, storage, machinery), laminate strips are applied to the slab.
• Masonry walls — in historic and masonry buildings, carbon mesh and fabric add in-plane strength.
• Chimneys, silos, minarets — wrapping works very efficiently on slender members with a circular section.

Application steps

Applied incorrectly, carbon fibre behaves like paper. What determines the result is not the fabric itself but the preparation beneath it.

• 1. Surface preparation — render and loose cover are removed and the concrete surface is opened up by grinding or blasting.
• 2. Repair — segregation, voids and corroded reinforcement are made good with repair mortar; corners are rounded to a radius of at least 25 mm.
• 3. Primer — an epoxy primer is applied to saturate the pores.
• 4. Filler — surface irregularities are levelled with epoxy putty.
• 5. Bonding — the carbon fabric is laid in saturating resin and rolled to expel air.
• 6. Protection — a coating or render is applied against UV and fire.
• 7. Testing — the bond is documented with a pull-off test.

Carbon fibre or reinforced-concrete jacketing?

The two are not rivals; they answer different problems. Carbon fibre comes to the fore where the capacity shortfall is limited, where the building must stay in use during the work, and where the section cannot be enlarged. Where the shortfall is large, where an irregularity has to be corrected, or where new shear walls are needed, reinforced-concrete jacketing is required. On most of our jobs the two are used together: the critical columns are jacketed and the rest are reinforced with carbon fibre.

What the scope covers

• Column and beam wrapping
• Slab and shear wall laminate reinforcement
• Carbon fabric overlay on masonry walls
• Surface preparation, epoxy system and pull-off testing