Carbon Fibre Reinforced Polymer (CFRP) is used for structural strengthening of existing structures and easily fits any shaped structure including rigid strips/bars and plates for straight surfaces such as walls, floors and soffits or woven material for beams and columns.
CFRP consists of high strength continuous carbon fibres embedded in a polymer matrix. The fibres provide the main reinforcing elements while the polymer matrix (epoxy resins) protects the fibres, transfers loads between the fibres and is bonded to the prepared concrete substrate. Once cured it becomes an integral part of the structural element, acting as an externally bonded reinforcing system. Carbon fibre has superior mechanical properties and a high tensile strength, stiffness, and durability.
CFRP increases the shear and axial strength of columns to improve ductility and energy dissipation.
CFRP fabrics may be fixed to the tension side of structural elements to provide additional tension reinforcement to increase flexural strength or wrapped around beams to increase their shear strength or wrapped around columns to increase their shear and axial strength.
The primer penetrates the concrete and epoxy filler is used to provide a smooth surface for bonding while a saturating resin is used to impregnate the fabric and bond it to the prepared substrate a protective coating is applied.
Surface preparation is critical to the bond between CFRP system and the existing concrete.
Any existing deterioration or corrosion of internal reinforcement must be resolved prior to installation to prevent delamination of the concrete substrate.
The most common type of carbon fibre for concrete strengthening is continuous unidirectional fibre which runs the length of the fabric and because the fibre is the main load-carrying component, the type of fibre, orientation and thickness of the fabric determines the tensile strength and stiffness.
CFRP has a tensile strength from twice to five times that of mild steel one fifth the weight.
CFRP systems are used for strengthening of concrete structures equally for flexural strengthening, shear strengthening, and column confinement and ductility improvement.
The existing concrete substrate strength is important for bonded materials and must have sufficient strength to transfer the flexural or shear stresses.
Temperature and surface moisture of concrete affect the performance of the CFRP system and surface preparation to create a bond between the CFRP and the existing concrete is critical.
Curing of the CFRP system depends on time and temperature. The higher the temperature, the quicker it will cure but 24 to 72 hours can be taken as a guide.
Use of CFRP for strengthening building elements, bridges, tanks and tunnels has been proven to be more cost-effective than traditional strengthening techniques.