Karwon Composites supplies matched structural strengthening systems: wrap fabric, primer, saturant, plate and rod.
Carbon fibre reinforced polymer has become the standard answer when an existing concrete structure has to carry more load than it was designed for, and it is specified badly more often than almost any other composite application.
The most common failure is not a material failure. It is ordering the wrong form of the material. Three products dominate this field, they look interchangeable on a supplier list, and they solve different structural problems.
The three forms and what each one does
Pultruded plate, sometimes called laminate or strip. A flat, rigid CFRP section, typically supplied on a roll in widths from 50 mm upward. Bonded to the tension face of a beam or slab with a structural adhesive. All the fibre runs along the length, so it does one job extremely well: adding tensile capacity in flexure.
Near surface mounted rod, round or rectangular. A pultruded CFRP section bonded into a groove cut into the concrete cover rather than onto the surface. Same function as plate, better protected from impact, fire and vandalism, and it develops bond over a larger surface for its cross section.
Unidirectional wrap fabric. Dry carbon fabric, all fibres in one direction, saturated with resin on site and wrapped around a member. Flexible, conforms to curved and irregular surfaces, and can be applied in multiple layers and multiple orientations.
The single question that decides between them
Are you strengthening in flexure, or confining in compression?
If a beam or slab needs to carry more bending moment, you are adding tensile capacity to the tension face. That is plate or near surface mounted rod. The member is straight, the load path is along its length, and a rigid section bonded flat is the efficient answer.
If a column needs to carry more axial load, or needs ductility for seismic performance, you are confining the concrete. Confinement works by wrapping fibre around the section so it resists the concrete's tendency to expand laterally under compression. That requires fibre running around the perimeter, continuously, following the shape.
A rigid plate cannot wrap a column. This is where most specifications go wrong, and it usually goes wrong because a supplier quoted what they had rather than what the drawing required.
If you have a drawing showing carbon applied around a column and a quotation offering pultruded plate, the quotation is wrong. Not more expensive, not lower specification. Wrong.
Why thickness is the wrong question for wrap
Buyers routinely ask for CFRP strips at a stated thickness for a column wrapping job. It is a reasonable question that does not apply to the product.
Wrap fabric is specified by areal weight in grams per square metre and number of layers. Cured thickness is an output of those two things plus the resin content achieved on site, not an input you can order to. A 300 gsm fabric in four layers and a 600 gsm fabric in two layers deliver similar fibre in the hoop direction and behave quite differently in handling, saturation and edge finish.
If a drawing states a thickness for a wrap system, someone has copied it from a plate specification. Go back and ask for areal weight and layer count, because that is what the structural calculation will have been done in.
What a complete strengthening system contains
CFRP strengthening is not a material purchase. It is a system, and every component has to be compatible with the others. Buying the fabric from one source and the resin from another is where site problems begin.
Primer. Applied to the prepared concrete. Penetrates the surface, stabilises the substrate and provides the bonding surface for what follows. Skipping it is the most common cause of debonding.
Saturant resin. The resin that wets out the dry fabric and transfers load between fibres and into the substrate. This is a specific product with a specific viscosity, formulated to impregnate fabric on a vertical surface without draining.
Putty or levelling filler. Fills surface defects and pores so the fabric is not bridging voids.
Fabric. The unidirectional carbon reinforcement itself.
Plate adhesive, where plates rather than fabric are used. A thixotropic structural paste, an entirely different product from a saturant.
Here is the distinction that causes the most trouble on site: a structural paste adhesive is not a saturating resin. They are both epoxies, they are both structural, and they are not interchangeable. A paste adhesive is formulated to hold a rigid plate against concrete at a controlled bond line thickness. It will not impregnate a dry fabric properly, and a consultant reviewing the submittal will reject it.
If a supplier quotes you a paste adhesive for a wet layup fabric job, that is a signal to look more closely at everything else in the quotation.
Specifying a job so it can be quoted accurately
Supply these and any competent supplier can price the job in one pass.
- What is being strengthened, and in what mode. Column confinement, beam flexure, slab flexure, shear strengthening.
- Member dimensions and quantity. For columns, section shape and size, height to be wrapped, and number of columns. Corners matter: sharp corners must be radiused before wrapping or the fibre will fail at the corner rather than in tension.
- Fabric areal weight and layer count, from the structural calculation.
- Fibre orientation. Hoop only, or hoop plus longitudinal.
- Total surface area, and state clearly whether that figure is net member surface or total fabric to be supplied. These differ substantially once overlap allowances, wastage and anchorage laps are included, and a quotation built on the wrong one will be short.
- Environmental exposure. Interior, exterior, marine, buried. This drives the protective topcoat, which is often omitted from enquiries entirely.
- Whether a matched system is required. Most consultants and most tender documents require all components from one system with published compatibility. Mixing sources will usually fail the submittal.
The overlap allowance nobody budgets for
Wrap fabric requires a lap at the closure of each wrap to develop the full tensile capacity around the section, plus additional laps where a roll runs out. On a column job with many small sections, laps can add a significant percentage to the fabric quantity over the bare geometric surface area.
Calculate the fabric quantity from the wrapped perimeter including laps, not from the drawn column surface. Under ordering on a strengthening job is expensive, because a partial second delivery arrives after the crew has demobilised.
Where this is used in the UAE
Structural strengthening is one of the steadier applications for carbon in this region, and it is driven by things that keep happening: buildings changing use, mechanical plant getting heavier, parking structures being asked to carry more, corrosion damage in coastal structures reducing effective steel area, and design code updates applied to existing stock.
It is also an application where the material cost is small relative to access, scaffolding and downtime. That changes the buying logic. The expensive failure is not paying more per square metre. It is having the wrong product delivered and losing a week.
Karwon Composites supplies matched structural strengthening systems into the UAE: unidirectional wrap fabric, primer, saturant resin and plate adhesive, supplied together as a system rather than as separate line items. We also supply pultruded plate and near surface mounted rod for flexural work.
Send us the drawing and the structural calculation, and we will tell you which form the job actually needs, including when it is not the more expensive one.