## 2 End-of-Life of CRC
### Use of Recycled Fibers and Concrete  
After being separated from their sizing, the recycled carbon fibers can be used in different scenarios. For some scenarios, the sizing does not have to be removed. Separated carbon fibers can serve as reinforcement in fiber concrete (FC). In FC, unlike fiber-reinforced concrete (FRC), the fibers lay unoriented in the concrete matrix. They are added during the mixing process of the concrete. In comparison to steel FC, with carbon FC, 18% better mechanical properties can be achieved with about \(\frac{1}{4}\) of the material input. The demand of FC is very high. Germany has a 50 kt/a need of steel FC. By substituting 10% of these steel fibers by rCF, 2/3 of Europe's annual CF waste could be recycled ([PERSON], 2019). Another possibility for rCF is the development of nonwovens as concrete or plastic reinforcement ([PERSON] et al., 2020). rCF nonwovens are ideal reinforcements for sophisticated composites [43]. As reinforcement for concrete, the nonwoven is unsuitable due to difficulties in soaking the nonwoven properly in concrete. The generated benefits do not justify the processing expense ([PERSON] et al., 2020). Further, a staple fiber hybrid yarn at Technische Universitat Dresden was tested in composite test pieces and reached a tensilestrength of over 80% of comparable pure carbon fiber composite. Because the rCF processed into a yarn can be oriented in the load direction, this method more effectively exploits the mechanical properties of the rCF. The yarn can be used in lightweight construction as, e.g., reinforcement in plastic composites for the automotive industry, where rCF's conductive properties can be beneficial [44]. As another alternative for carbon fiber utilization, carbon fiber-reinforced plastics (CFRPs), as a substitute in calcium carbide production, have been investigated on an industrial scale [45]. Calcium carbide (CaC\({}_{2}\)) is an important commodity chemical used for organic synthesis and nanotechnology [46]. In the production process, CFRP waste can replace up to 20% of the needed carbon source [45]. Further, the use of CFRP in the arc furnace steel production as a substitute for carbon sources has been investigated. The results are promising; nevertheless, the process has to be researched further on industrial scale [45,47]. If material recycling for carbon fibers is no option, thermal recycling can be considered [36]. The landfilling of carbon fibers with EP matrix is not allowed in Germany. The matrix must be removed. Considering the expensive removal process, landfilling is unfavorable in an economic and environmental way [3]. The recycling of concrete has been researched for a long time. The concrete fraction resulting from the FRC separation process is crushed to particle sizes of 3-56 mm and classified. For use in concrete production, it can be crushed and separated into 0-16 mm fractions. Subsequently, up to 45% volume fraction can be added in the production of new concrete parts for dry surroundings without further examination (Exposure-class XC1). Theoretically, concrete can be recycled like this many times [3]. Another common way of recycling is utilizing concrete aggregate as a filling material in road construction or in the construction of buildings, mines, and dams [3]. A promising approach for a closed life cycle in building industry is \"urban mining\". Materials in buildings at its EoL, which are still usable, are reused as a whole building part. [PERSON] et al. (2019) investigated the reuse of 1 m\({}^{2}\) CRC facade panels. First, the panel is deconstructed as a whole. Subsequently, it is transported to a processing plant where it becomes dismantled, refurbished, and re-mantled. After the return to a construction site, the facade panel is assembled again. The strategy of reuse is regarded as a flexible and sustainable solution [48]. The literature shows a clear necessity of sustainable EoL scenarios for CRC.