Externally bonded CFRP fixes carbon-fibre laminates or fabric to a concrete member with resin. The system may add tensile capacity or confinement, but only if forces transfer reliably through the bond into the concrete. Structural design, concrete condition and anchorage therefore govern suitability.

When might CFRP fit?

An engineer may assess CFRP where changed loads, a change of use, damage or inadequate capacity calls for strengthening. A laminate bonded to the tension face can contribute to flexural strengthening. For shear strengthening or confinement, the engineer may choose a different configuration, such as flexible carbon-fibre fabric. These are different systems. Steel plates, concrete or mortar enlargement and external prestressing are alternatives with different effects on space, weight, fire, corrosion, construction and inspection.

Investigation and design

Assess the existing structure, loads, reinforcement, active damage and possible failure modes. Bonding requires a sound, suitable substrate. Delaminated cover, active corrosion, contamination, moisture or deterioration may first require repair or another strategy. Fire, temperature, moisture, UV exposure, edges, terminations and debonding also belong in the design assessment.

The engineer designs the strengthening as part of the whole structure and specifies product, direction, position, length and anchorage. This guide gives no design values or installation parameters. The method statement follows approved details and system instructions. Check material traceability, substrate acceptance, installation conditions, continuity and specified bond tests. A smooth finish does not prove bond or capacity.

Ask who designs the system and approves changes, which defects must be addressed first, and how anchorage and protection will be checked. Have a structural engineer assess the design and its suitability for the specific structure.

Concrete beam section with a composite laminate underneath and a detail of the bonded interface. Schematic bonded reinforcement; geometry, design and anchorage are project-specific.

Legend - 1. concrete · 2. adhesive · 3. CFRP laminate · A. interface

Sources

  1. CROW-CUR Aanbeveling 91:2021, third revised edition - Dutch guide for externally bonded carbon reinforcement; design and execution quality are essential. Source.
  2. ACI PRC-440.2-23, Design and Construction of Externally Bonded FRP Systems - Public preview describing design, execution and inspection. Source.
  3. fib Bulletin 90, Externally applied FRP reinforcement, 2019 - International design report covering bonded and near-surface mounted FRP. Source.
  4. AFGC, Reparation et renforcement des structures en beton avec materiaux composites, 2011 - French recommendations cover design, substrate, installation and site control; France/Eurocode context. Source.