Sika SikaWrap-231 C IN
High-strength unidirectional carbon fibre fabric for the Sika dry lay-up system, engineered to add flexural, shear and seismic capacity to concrete, masonry and timber with almost no added dead load.
What is it?
A 0-degree unidirectional carbon fibre fabric (230 g/m2) that becomes a bonded CFRP laminate once saturated with Sikadur-330 IN epoxy, forming external reinforcement on existing structures.
Where is it used?
Beams, columns, slabs and beam-column joints of RCC buildings, bridges, silos, chimneys and process structures needing extra load capacity or seismic upgrade.
Why use it?
It carries very high tensile stress along the fibres (~4,900 N/mm2 dry) while adding negligible weight and section, so members gain strength without heavy jacketing or downtime.
How is it applied?
Hand-applied dry lay-up: prime and level the substrate with Sikadur-330 IN, press the dry fabric into the wet resin along the load direction, then consolidate and over-coat with a second resin pass.
About Sika SikaWrap-231 C IN
SikaWrap-231 C IN is Sika’s India-grade carbon fibre fabric for externally bonded reinforcement, part of the wider family of fibre-reinforced polymer (FRP) strengthening systems used to upgrade structures that can no longer meet the demands placed on them. The fabric is woven so that virtually all the high-strength carbon filaments run in one direction (the warp, at 0 degrees), while a light heat-set glass weft simply holds those filaments straight and evenly spaced until the epoxy locks them in place. This unidirectional layout is deliberate: a strengthening designer decides the exact direction the added tension is needed and orients the fabric to match, whether that is along the span of a beam for flexure or wrapped around a column for confinement.
On its own the dry fabric does nothing structural; it becomes a load-bearing laminate only after it is saturated with Sikadur-330 IN, the two-part epoxy that both primes the concrete and impregnates the cloth. Once cured, fabric and resin act as a thin composite plate bonded to the surface, sharing load with the parent member through the adhesive bond. Because the whole system is a few tenths of a millimetre thick per layer and extremely light, it lets engineers add substantial capacity without enlarging the section, casting new concrete or shutting the structure down for long periods. For Indian consultants and applicators, Space Arc supplies the fabric alongside the matching Sika resins so the specified system is delivered complete rather than mixed across brands.
The technical insight
The mechanism is stress transfer through an adhesive bond. Carbon fibre is exceptionally strong and stiff in tension along its length but does almost nothing across it, which is why the fabric is unidirectional and why fibre orientation is a design decision, not a detail. When the epoxy cures, load in the concrete member is transferred by shear through the resin into the carbon, and the fibres pick up tension the cracked or under-reinforced concrete can no longer carry. Two numbers explain the payoff: a dry fibre tensile strength of about 4,900 N/mm2 and a modulus of elasticity around 250,000 N/mm2 (both to ISO 10618) mean the laminate is far stiffer and stronger than the steel it supplements, so a wrap only 0.127 mm thick per ply contributes meaningful capacity. The trade-off is that carbon fails in a brittle, linear-elastic way at roughly 2.1 percent elongation with no yield plateau, so designers size the system to strain limits well below rupture and never rely on it to yield gracefully like reinforcing steel. Everything therefore hinges on the bond: the substrate must be sound, clean and rough enough for the epoxy to develop full adhesion, because a debonded wrap sheds its stress back to the concrete instantly.
Where it is used
- Flexural strengthening of RCC beams and slabs where reinforcement is deficient or loads have increased
- Shear strengthening of beams and beam-column joints using U-wraps or full wraps
- Seismic retrofitting and confinement of columns to improve ductility and axial capacity
- Strengthening bridge girders, decks and piers for higher live loads or load-rating upgrades
- Rehabilitation of silos, chimneys, water tanks and process structures subject to cyclic or pressure loading
- Reinstating capacity in members damaged by corrosion, impact, fire or design/construction defects
- Upgrading masonry and brickwork elements and, where designed, timber members
- Change-of-use strengthening where an existing structure must carry heavier equipment or occupancy
Key advantages
- Very high tensile strength (~4,900 N/mm2 dry) delivers large capacity gains from a thin laminate
- Adds negligible dead load and almost no section, so clearances and foundations are unaffected
- Corrosion-proof carbon will not rust like steel plate bonding, suiting aggressive and marine environments
- Flexible dry fabric drapes around corners, curves and columns that rigid plates cannot follow
- Fast hand lay-up means minimal disruption and quicker return to service than concrete jacketing
- Unidirectional weave lets the designer place strength precisely where the structure needs it
- Part of a complete, compatible Sika system (fabric plus Sikadur-330 IN) for predictable performance
- Supplied in continuous ≥50 m rolls, reducing joints and offcuts on larger strengthening jobs
Limitations & considerations
- Strength acts only along the fibre direction; the fabric contributes little across the weave and must be correctly oriented
- Performance depends entirely on the epoxy bond, so a weak, dusty or laitance-covered substrate will cause premature debonding
- Carbon is brittle and fails suddenly at ~2.1% elongation with no yield warning, so it must be designed to conservative strain limits
- Requires competent concrete: a substrate pull-off (tensile) strength of at least 1.0 N/mm2 is needed
- Application, curing and long-term performance are sensitive to temperature and moisture limits of Sikadur-330 IN
- Externally bonded CFRP has limited inherent fire resistance and usually needs protective encasement or a rated coating where fire is a design case
Selection & best practice
Success is decided at the substrate. Remove all laitance, curing compounds and loose material by grinding or blasting, repair spalls and expose a sound, slightly roughened profile, then confirm a minimum tensile pull-off strength of 1.0 N/mm2 before any resin goes down. Round off sharp column corners to a suitable radius so the fabric is not stressed over an edge. Mix Sikadur-330 IN in full, correct ratios and apply within its pot life and the permitted temperature window, working on a dry surface. Lay the dry fabric into the wet resin strictly along the design fibre direction, then work it firmly with a ribbed roller from the centre outwards to drive out air voids and fully wet the fibres, allowing proper laps between sheets. Budget roughly 0.8-1.2 kg/m2 of resin for the first layer and 0.5-0.8 kg/m2 for each subsequent layer, and let each layer take up before the next. Protect the cured laminate from UV and, where fire or impact matters, over-clad it. This is engineered structural work, so it should be executed by trained applicators strictly to the strengthening designer’s drawings.
Specifications
| Fibre type / orientation | High-strength carbon, unidirectional (0 degrees), glass weft |
| Areal weight | 230 g/m2 (+/- 12 g/m2), carbon fibres only |
| Dry fibre tensile strength | 4,900 N/mm2 (ISO 10618) |
| Modulus of elasticity in tension | 250,000 N/mm2 (ISO 10618) |
| Elongation at break | 2.1% (ISO 10618) |
| Dry fibre density | 1.80 g/cm3 |
| Dry fibre thickness | 0.127 mm (based on fibre content) |
| Impregnation resin | Sikadur-330 IN (primer and laminating resin) |
| Roll size / packaging | 500 mm wide, length >= 50 m, one roll per box |
Industry use cases
Bridges & Infrastructure
Load-rating upgrades and strengthening of girders, decks and piers for heavier traffic or revised codes, without widening the section or closing the structure for long.
Commercial & Residential Buildings
Restoring or increasing beam and slab capacity for change of use, added floors or heavier equipment, and confining columns during seismic retrofits.
Industrial & Process Plants
Reinforcing silos, chimneys, tanks and support structures subject to pressure, vibration or cyclic loads, where the corrosion-free wrap suits harsh exposure.
Repair & Rehabilitation
Reinstating members weakened by corrosion, impact, fire or original design shortfalls, giving engineers a quick, low-intrusion alternative to concrete jacketing.
Heritage & Masonry
Discreet strengthening of masonry, brickwork and, where designed, timber elements where added thickness or heavy jacketing would be visually or structurally unacceptable.
Frequently asked questions
Can SikaWrap-231 C IN be used on its own?
How much load can the wrap add to a beam or column?
How do I decide which way to lay the fabric?
What condition must the concrete be in first?
How much Sikadur-330 IN resin will I need?
Does it need fire protection?
How we position Sika SikaWrap-231 C IN
SikaWrap-231 C IN sits at the workhorse end of Sika’s carbon fabric range and is always paired with Sikadur-330 IN, its dedicated primer/saturant; where a designer needs a higher fibre volume or thicker laminate, heavier SikaWrap grades or Sika CarboDur pultruded plates are the natural step up within the same Sika family, and Sikadur-30 is the companion adhesive for plate bonding. As an authorised distributor of multiple brands, Space Arc can also supply an equivalent Fosroc CFRP fabric system where a project or consultant specifies Fosroc, and can advise on companion concrete-repair mortars needed to reinstate the substrate before wrapping.
Fosroc Nitowrap CW — A specifier standardised on Fosroc, or matching an existing Fosroc-detailed repair, may prefer Nitowrap CW as the equivalent unidirectional carbon fibre wrap, used with its own Nitowrap primer and saturant.
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