Frequently asked questions about carbon reinforced concrete

Carbon fibre reinforced concrete (also called carbon concrete or textile-reinforced concrete with carbon) is a composite material consisting of concrete and non-metallic reinforcement made from carbon fibres (often in the form of impregnated meshes/grids or bars). The carbon fibres provide the tensile capacity that plain concrete lacks. Unlike short fibres mixed into the concrete (which improve toughness but are not structural primary reinforcement), carbon concrete uses continuous, oriented carbon reinforcement (meshes or bars) placed where tensile stresses occur. This enables thinner, lighter, and more durable elements because carbon does not corrode.

Carbon offers higher strength-to-weight, corrosion immunity, and material savings, but is more expensive and less ductile in the classical sense.

Because carbon does not corrode, the large durability cover required for steel is unnecessary. Typical values from practice and guidelines:

• New-build elements: minimum around 10 mm (instead of ~55 mm for steel in many cases).
• Strengthening/repair layers: minimum layer thickness around 15 mm (instead of ~80 mm).
• Specific systems (e.g. CARBOrefit): as low as 3–5 mm between layers or to the surface depending on the grid type, governed mainly by bond requirements.

Cover is still needed for bond, anchorage, and fire protection. Always follow the product approval or the DAfStb guideline for non-metallic reinforcement.

The total cost of the element or structure is often more relevant than the pure reinforcement price per m². Because carbon is corrosion-free:

• Concrete cover can be strongly reduced
• Element thicknesses and concrete volumes drop significantly
• Handling and logistics become lighter
• Service life increases and maintenance decreases

In practice this frequently leads to lower overall costs compared with conventional steel-reinforced solutions, especially in rehabilitation (e.g. industrial floors), façades, or slender precast elements. Hitexbau has documented cases where carbon-concrete solutions were 20–30 % cheaper than full demolition-and-rebuild with steel concrete.

Recommendation

For a reliable price per m² for a specific HTC mesh, contact Hitexbau directly with details of the intended application, required grid type and estimated quantity. Project-oriented quotations and technical support are provided.

Carbon reinforced concrete can achieve fire resistance of up to 90 minutes (R90) when standard fire-protection measures are applied. Research at TU Dresden has shown that with suitable protection (e.g. fire-protection plaster, intumescent coatings or boards), the temperature in the carbon reinforcement stays low enough for the fibres to retain a significant part of their strength and continue contributing structurally.

Without additional protection, thin carbon-concrete sections heat up quickly and the reinforcement loses capacity at high temperatures (above approx. 600 °C). In practice, the same proven fire-protection methods already used in conventional construction are fully effective and can be applied without compromising the advantages of carbon reinforcement (slender sections, corrosion resistance and material savings).

For project-specific fire design, contact Hitexbau or a qualified engineer.

Cut with an angle grinder or tile saw fitted with a continuous diamond or carbide blade (preferably water-cooled). Avoid shears or coarse-tooth tools that crush or tear the fibres. Secure the mesh, cut slowly, and tape the cut line to reduce fraying. Wear cut-resistant gloves, eye protection and a dust mask, and use local extraction to control carbon dust.

Installation

1. Prepare and roughen the concrete substrate.
2. Apply a thin layer of fine-grained concrete or compatible mortar.
3. Embed the mesh into the fresh layer and press it fully in.
4. Immediately apply the cover layer.

Overlaps and cover thicknesses must follow the project design and the relevant product approval. The mesh is light and flexible, so it is easy to handle even for overhead or curved work. Always follow the manufacturer's instructions and use trained personnel for approved systems.

Hitexbau HTC carbon meshes are covered by both a European Technical Assessment and the German DIBt approval. Because the meshes are manufactured to the same construction principles, the DIBt approval applies across the HTC range used in the CARBOrefit® system.

European Technical Assessment (ETA) and CE marking

ETA-23/0269 (issued 20 April 2023 by TZÚS, based on EAD 260057-00-0303) covers specific HTC types as inorganic fibre grids for reinforcement of cement-, anhydrite- or resin-based screeds:

• HTC 18/18-40 (24K)
• HTC 25/25-80 (24K)
• HTC 21/21-40 (48K)
• HTC 21/21-80 (48K)
• HTC 34/34-40 (48K)

Holder: Alligard s.r.o. (Czech Republic). This ETA enables CE marking under AVCP system 2+ for the declared screed-reinforcement use (primarily shrinkage crack control).

DIBt general building approval

abZ/aBG Z-31.10-182 (CARBOrefit® – Verfahren zur Verstärkung von Stahlbeton mit Carbonbeton), valid until 31 August 2028, regulates the use of HTC carbon grids together with the compatible fine concrete for structural strengthening of reinforced concrete members.

The meshes are built exactly the same way, so the approval covers the HTC meshes employed in the system (including the types listed in the technical documentation such as HTC 10/15-80, HTC 21/21-80 and HTC 25/25-80-UW, and equivalent constructions). Design and execution in Germany therefore follow this DIBt approval and the associated planning documentation.

Additional national technical approval

Czech National Technical Approval No. 060-053547 (TZÚS) covers carbon reinforcement nets for industrial and road construction (multiple 12K–96K variants). Its validity has been extended to 31 December 2027.

Summary

For project-specific application, always refer to the current full approval documents and technical data sheets from Hitexbau.

Yes — provided the maximum aggregate size of the concrete is smaller than the mesh opening.

Hitexbau HTC meshes are available with different grid sizes:

• Many standard types are suitable for aggregates up to 8 mm.
• Larger meshes (e.g. HTC 50/50) are suitable for aggregates up to 16 mm and can therefore be used with conventional concrete mixes.

For thin strengthening layers (such as the CARBOrefit system), a fine-grained concrete or special mortar is normally used to ensure complete embedment and bond. In new construction or thicker elements, standard concrete is possible when the mesh geometry matches the aggregate size.

Always check the technical data sheet of the specific HTC product for the recommended maximum grain size and follow the relevant approval or design rules.

In France, design is based on the principles of Eurocode 2, adapted to the linear-elastic behaviour of carbon reinforcement (no yield plateau).

Main references

• AFGC guide “Utilisation d'armatures composites (à fibres longues et à matrice organique) pour le béton armé” (2021) — practical recommendations for characterisation, durability and design of composite reinforcements.
• Eurocode 2 (NF EN 1992-1-1) and its future Annex R (under preparation for the revised EC2) dedicated to non-metallic / composite reinforcement.
• For strengthening systems, the relevant product approvals or Avis Techniques and the associated design rules (e.g. CARBOrefit principles).

Key design points

• Use the design tensile strength of the carbon mesh (characteristic short-term strength reduced for long-term effects and partial safety factors).
• Verify both concrete compression failure and carbon tension failure.
• Apply the reduced concrete cover possible with non-corroding carbon (typically 5–15 mm).
• Check anchorage, overlaps and bond according to the product-specific values and the AFGC guide / future Annex R.
• Serviceability checks (crack width, deflection) follow adapted EC2 rules.

Characteristic material data (tensile strength, bond, reduction factors) are taken from the technical documentation of the specific HTC mesh. For project-specific support or design assistance, contact Hitexbau or a qualified structural engineer.

Yes — on demand. Please contact Hitexbau with your project details and the required file formats.