Frequently Asked Questions

What types of structural strengthening can be achieved with Nitowrap CF-CS and how is the design carried out?

Nitowrap CF-CS can provide three main types of structural strengthening for reinforced concrete structures. Flexural strengthening is achieved by bonding carbon fibre fabric to the tension face of beams and slabs — the carbon fibre in the tension zone supplements the existing steel reinforcement, increasing the bending capacity of the section. Shear strengthening is achieved by bonding carbon fibre strips or wraps around the web of beams in the shear span — the carbon fibre acts as additional shear reinforcement, equivalent to adding stirrups. Confinement strengthening of columns is achieved by wrapping carbon fibre around the full perimeter of the column — the confined concrete develops significantly higher compressive strength and ductility, increasing both the axial load capacity and the ability to withstand cyclic loading in earthquakes. The structural design of CFRP strengthening must be carried out by a structural engineer using the applicable design guidelines (ACI 440.2R or ISIS Canada guidelines are the most widely used), considering the existing structural capacity, the required increased capacity, and the CFRP material properties.

Is Nitowrap CF-CS installation complex and what special skills and equipment are required?

Nitowrap CF-CS installation requires trained applicators and must be carried out under the supervision of an experienced structural strengthening contractor. The critical steps in installation are: structural preparation of the concrete surface (grinding or grit blasting to expose clean aggregate, removal of all laitance and contamination, rounding of sharp corners at least 25 to 30 mm radius to prevent carbon fibre fabric from breaking at corners); application of the epoxy primer coat and allowing to cure to the correct tack; mixing the epoxy saturant resin; applying the saturant to the concrete surface; laying the dry carbon fibre fabric into the wet saturant and working the resin into the fabric to fully wet out all fibres; applying a top coat of saturant; and protecting the freshly applied laminate from contamination and damage until fully cured (typically 24 to 48 hours at 25 degrees Celsius). Quality control testing of the completed laminate includes pull-off adhesion testing and visual inspection for debonds or dry spots. Space Arc Engineering provides technical guidance and product supply for Nitowrap CF-CS strengthening projects.

How does the performance of Nitowrap CF-CS compare to conventional steel plate bonding for structural strengthening?

Both externally bonded CFRP (Nitowrap CF-CS) and externally bonded steel plates are proven methods for strengthening existing concrete structures. CFRP strengthening with Nitowrap CF-CS has several significant advantages over steel plate bonding in most applications: carbon fibre fabric weighs approximately 200 to 600 g per square metre versus steel plate at 7,850 kg per cubic metre — CFRP adds negligible dead load while steel adds significant weight; carbon fibre is 100 per cent corrosion-resistant, requiring no protective coating and maintaining its properties indefinitely in outdoor or humid exposure, while steel plates require surface treatment and corrosion protection that may need maintenance; CFRP fabric can be shaped around curved surfaces and corners far more easily than rigid steel plates; and the tensile strength of carbon fibre (3,500 MPa or more) far exceeds that of steel plate (250 to 350 MPa), allowing the same strengthening effect with a much thinner composite layer. Steel plate bonding may still be preferred where impact resistance is a concern or where the structural engineer requires the specific stiffness characteristics of a steel plate section.