## 1 Introduction
This high demand due to its excellent mechanical properties, durability, and light weight will significantly increase the amount of CFRP waste in the coming years, produced both in the manufacturing process and at the end of its useful life, estimated globally as reaching an annual quantity of 20,000 tons by 2025 [31; 32; 33; 34; 35]; as a result, good management of these products is necessary, which would make it possible to recover carbon fibers from waste and ensure their reintroduction as secondary raw materials instead of being disposed of in landfills or burning them in incineration plants, notably the two most widely used methods currently [36]. However, the relative environmental benefits of advanced recycling processes (i.e., pyrolysis, fluidized bed, and the chemical recycling process) provide superior environmental performance compared to conventional composite waste treatment technologies [37]. Mechanical recycling will be profitable if fiber recovery rates close to 100% are achieved and degradation of fiber mechanical properties is minimized, thereby ensuring the financial viability and environmental benefit of recycling fiber-reinforced polymer carbon [38]. Studies that have been carried out show that there are currently several recycling and re-manufacturing processes in an advanced stage, with commercial scale implementations of recycling processes, production of recycled CFRP with competitive structural performance, and demonstration components that have been manufactured [39]. One of the most widespread uses in building is the use of carbon fiber sheets or fabrics (CFRP) for the reinforcement of concrete structures because their physicochemical properties are even better than those of traditional materials and also they weigh very little [40]. The reuse of recycled CFRP in the form of fibers is one of the recycling alternatives for this kind of waste. These fibers, taken from CFRP sheets or fabrics and added to concrete either on their own or combined with other types of fiber, slightly improve its compressive strength, while its ductility, flexural toughness, impact resistance, and energy absorption capacity significantly improve. Previous studies show that increasing the volume fraction and length of the recycled carbon fiber improves the mechanical properties and impact resistance of the reinforced mix compositions, while reducing workability [41; 42; 43]. Otheraspects to bear in mind are that the workability of the concrete is reduced when the length and content of the fibers is increased and that an increase in porosity may be caused, particularly, when what are known as \"soft\" CFRP fibers are added [41; 42]. The addition of recycled CFRP fibers also increases the electrical conductivity of the concrete, which is a starting point for manufacturing multi-functional materials [44]. The recycled CFRP fibers made from polymers reinforced with carbon fibers ex-tracted from structural elements are obtained from semi-rigid sheets that have been appropriately cut in the shape of fibers or small irregular pieces. Research shows an improved performance with the addition of the small FRP pieces, with better flexural strength, although compressive strength is not improved when compared with concretes without additives. Similar behavior is seen in cement mortars [43; 45]. The need to recycle this type of waste has led researchers to study its behavior when hybridized with other recycled materials, such as tires, wherein the compressive strength of mixed compounds was observed as improving slightly, while ductility, resistance to bending, impact resistance, and energy absorption capacity were significantly improved [46]. Their behavior has also been compared with other recycled fibers, such as recycled glass fibers, wherein recycled carbon fibers were observed as having higher rates of gain in compressive strength than recycled glass fibers, while recycled glass fibers had higher rates of increase in flexural strength than recycled carbon fibers [47].