Frequently Asked Questions

How is the required number of CFRP layers calculated for a strengthening application?

The number of CFRP layers required is determined by structural engineering calculations based on the additional load the member must carry, the geometry of the member, the properties of the existing concrete and reinforcing steel, and the properties of the CFRP system (as certified by the manufacturer in ETA or ICC-ES approval documents). ACI 440.2R and fib Bulletin 90 are the most commonly referenced international design guidelines for FRP strengthening. In India, there is no dedicated Indian Standard for FRP strengthening design, so international guidelines are used with approval from the structural engineer of record and the building authority. Adding more CFRP layers than the design requires does not proportionally increase capacity due to failure mode shifts — the design must be optimised for the specific failure mode.

Does the CFRP wrap prevent inspection of the concrete underneath it?

Yes. Once the Nitowrap CWS carbon fibre laminate has been applied and the epoxy has cured, the concrete surface beneath it is not directly visible for inspection. This is a consideration for long-term maintenance — any future deterioration of the concrete substrate (new cracking, carbonation front advancement, rebar corrosion) will not be detectable by visual inspection through the CFRP. Acoustic tap testing and, in critical applications, advanced inspection methods (ultrasonic tomography, ground-penetrating radar) may be used to detect delamination or substrate deterioration below the CFRP laminate. A long-term monitoring plan should be specified for critical strengthened structures.

Is the Nitowrap CWS system resistant to fire and elevated temperatures?

The Nitowrap EP epoxy saturant resin softens at elevated temperatures — the glass transition temperature (Tg) of structural epoxy is typically 60 to 80 degrees C for standard formulations. If the CFRP laminate is exposed to temperatures above the Tg (for example, in a building fire), the epoxy will soften and the CFRP reinforcement will lose its bond to the concrete and its structural contribution. For fire-critical applications, the CFRP laminate must be protected by a fire-rated intumescent coating or fire protection board that limits the temperature at the CFRP surface to below the Tg for the required fire resistance period. Consult the fire design engineer for the appropriate fire protection system when Nitowrap CWS is used in fire-rated structural elements.