Frequently Asked Questions

What is the difference between Nitoplate CPS (pultruded plate) and Nitowrap CF (woven fabric) for beam strengthening?

Both are CFRP strengthening systems for externally bonded flexural reinforcement, but they differ in form and application. Nitoplate CPS is a factory-produced pultruded solid plate with precisely controlled properties and stiffness — bonded as a strip to the beam soffit using structural adhesive. Nitowrap CF is a woven dry fabric that is wet-laid on the concrete surface and impregnated with epoxy saturant on site. Pultruded plates are preferred for flexural strengthening where the high stiffness of the plate (controlled by pultrusion) is important for limiting deflection, and where the installation quality needs to be independent of site lay-up variability. Wet-laid fabrics are preferred for complex geometries (column wrapping, corners, curved surfaces) where a rigid plate cannot conform to the shape. Both systems are designed by a structural engineer for the specific application.

How is the bond between the Nitoplate CPS plate and the concrete surface achieved?

The Nitoplate CPS plate is bonded to the concrete using Nitoplate EP two-component epoxy structural adhesive, which is mixed and applied to both the concrete surface and the back face of the plate. The plate is then pressed into the adhesive bed and held in place until the adhesive cures to full strength (typically 24 hours at 20 degrees C). The concrete surface must be prepared by grinding to remove all laitance and loose material, and must be dry, clean, and sound (minimum pull-off strength typically 1.5 MPa). The quality of the bond is critical to the structural performance — any unbonded area reduces the effective tensile anchorage of the plate. Acoustic tap testing of the bonded plate after adhesive cure is used to detect any hollow or unbonded areas.

Is there a minimum concrete strength required for Nitoplate CPS strengthening to be effective?

Yes. The load capacity of the externally bonded plate system is limited not only by the plate and adhesive properties but also by the strength of the concrete substrate. If the concrete has low tensile or pull-off strength, failure will occur in the concrete below the adhesive layer rather than in the plate — called a concrete substrate failure mode — and the full tensile strength of the plate will never be mobilised. Most strengthening design guidelines (ACI 440.2R, fib Bulletin 90) require a minimum concrete compressive strength of 20 to 25 MPa and a minimum pull-off strength (adhesion in direct tension) of 1.5 MPa before strengthening is applied. If the existing concrete is below these thresholds, it must be repaired or strengthened before the CFRP plate system is applied.