The WIRreFa project WIR‑B1‑III, funded by the German Federal Ministry of Education and Research under grant 03WIR6003B, ran from 1 December 2022 to 31 January 2024 and was carried out by CarboCon GmbH in cooperation with the wider WIRreFa consortium. Its goal was to close or reduce gaps in the circular use of recycled carbon fibres in construction, with a particular focus on applying existing solvolysis and pyrolysis technologies to produce new reinforcement products from waste carbon‑reinforced concrete.

The scientific work concentrated on developing a decision‑tree specification for the circular use of carbon fibres, which was updated throughout the project and expanded with new experimental data. The decision tree maps the recycling process into discrete steps and decision points, illustrating the current state of knowledge and highlighting research gaps. Experimental comparisons of recycled fibre strands with different impregnation levels revealed that, relative to commercially available carbon grids, recycled fibres would need several times more layers to achieve the same load‑bearing capacity, depending on the intended application and reinforcement design. A sensitivity analysis showed that the required reinforcement amount is strongly influenced by the tensile strength and elastic modulus of the recycled product; improving these properties would reduce the number of layers needed and lower the variability of strength.

Mechanical testing of prototype linear‑processed fibre products, produced in subcontracted facilities, demonstrated that the recycled fibres could reach mechanical performance comparable to primary glass and basalt fibre‑reinforced composites. These prototypes confirmed the feasibility of the proposed recycling chain and provided a basis for further mechanical evaluation in subsequent WIRreFa phases. An initial economic assessment, based on the costs of fibre strand production and the typical recycling processes used so far, indicated that the recycling route remains more expensive than conventional production when the recycled fibres exhibit lower performance. However, the assessment also identified key cost drivers and suggested that improvements in fibre quality could make the recycling route competitive.

The project’s work packages were organised into three of the six planned packages: AP 3 focused on updating the specification and incorporating new findings; AP 4 performed a preliminary design of reinforcement using recycled carbon fibres and assessed market opportunities and economic viability; AP 6 produced and demonstrated a prototype application of the processed fibres. All packages were largely completed on schedule, and the resulting prototypes and decision‑tree tool will be used for further mechanical testing and development within the WIRreFa programme.

In summary, WIR‑B1‑III produced a comprehensive decision‑tree framework for carbon‑fibre recycling, experimentally quantified the performance gap between recycled and commercial fibres, identified critical material properties through sensitivity analysis, and demonstrated that recycled fibres can achieve comparable mechanical performance when processed appropriately. The project also highlighted the current economic challenges of recycling and outlined pathways for cost reduction, thereby providing a solid foundation for future development of circular carbon‑reinforced construction materials.