What Are Carbon Fiber Strips?
Carbon fiber strips — more precisely called pultruded CFRP plates or laminates — are pre-manufactured rigid strips of carbon fiber reinforced polymer produced through the pultrusion process. Unlike flexible carbon fiber fabric that requires on-site resin impregnation, strips arrive as ready-to-bond elements with factory-controlled fiber content and mechanical properties.
The pultrusion process pulls continuous carbon fiber tows through a resin bath and then through a heated die that shapes and cures the composite in a continuous operation. This produces strips with extremely consistent properties, high fiber volume fraction (typically above 65%), and straight, well-aligned fibers.
Product Specifications
We manufacture two main CFRP plate products:
Standard Modulus Plate (XQ-CFRP-1250)
- Thickness: 1.2mm
- Tensile strength: ≥ 2,400 MPa
- Elastic modulus: ≥ 160 GPa
- Fiber volume fraction: ≥ 65%
- Available widths: 50, 80, 100, 120, 150mm
- Standard length: 50m or 100m rolls
- Surface: Peel-ply textured for bonding
High-Modulus Plate
- Thickness: 1.4mm
- Tensile strength: ≥ 2,800 MPa
- Elastic modulus: ≥ 210 GPa
- Fiber volume fraction: ≥ 68%
- Available widths: 50, 80, 100, 120, 150mm
CFRP Strips vs Fabric: When to Use Each
Both CFRP strips and fabric can strengthen concrete beams in flexure, but they serve different situations:
Choose CFRP strips when:- The strengthening surface is flat (beam soffit or slab underside)
- You need fast installation with minimal site work
- Quality consistency is critical (factory-controlled vs site-dependent)
- The design requires high stiffness (elastic modulus of strips is typically higher at ≥ 160 GPa vs 230 GPa for in-situ laminate which sounds higher but the effective modulus of a wet lay-up system is lower due to resin content)
- The surface is curved or irregular
- You need to wrap around columns or corners
- Multiple layers with overlapping are required
- The application involves shear strengthening (fabric strips at 45°)
Bonding System: The Critical Interface
CFRP strips are bonded to the concrete substrate using our Plate Bonding Adhesive (XQ-PB), a thixotropic two-component epoxy paste specifically designed for this application.
Why a specialized adhesive matters:- Standard construction epoxy does not have the right rheology for plate bonding
- The adhesive must maintain uniform thickness (1-3mm) across the plate length
- It must not sag on vertical or overhead surfaces
- The adhesive's elastic modulus must be compatible with both the CFRP and concrete to avoid stress concentration at bond line edges
Design Considerations
The structural design of CFRP strip strengthening follows guidelines in standards such as ACI 440.2R, TR55, and fib Bulletin 14. Key design checks include:
- Flexural capacity increase: Based on strain compatibility analysis with the existing reinforcement
- Debonding prevention: The most common failure mode is intermediate crack debonding, not strip rupture. Design must limit the strain in the CFRP to prevent debonding.
- Anchorage: Strip ends must be properly anchored, either through sufficient bond length or mechanical anchorage
- Fire protection: CFRP loses strength above the glass transition temperature of the adhesive (typically 60-80°C). Fire protection coatings may be required.
Cutting and Handling
CFRP strips can be cut to length on site using a diamond cutting wheel or abrasive saw. Do not use shears or snips — they will crush the strip and delaminate the fibers. Wear dust protection when cutting, as carbon fiber dust is an irritant.
Strips are supplied in coils (for thin strips) or straight lengths (for thick strips). Store in dry conditions away from direct sunlight. Shelf life is unlimited for the strips themselves; only the adhesive has an expiration date.
View our CFRP plate products or get project support from our engineering team.