## 1 Introduction
One of the recycling possibilities has been the separation of these constituents by cutting and then managing them separately [33; 34]. Polymers and balsa wood can be easily managed in this way, but GFRP recycling still remains complicated [35]. One possible route whose validity has been researched is a thermal and chemical process to separate the glass fibers from the polymer matrix [36], but the mechanical properties of fiberglass are significantly degraded, which hinders their use [37]. Another research avenue has been the mechanical crushing of GFRP, which yields GFRP fibers that can be used as a concrete component and eliminates the need to separate the GFRP constituents [33; 38]. These GFRP fibers provide load-bearing capacity to concrete [39]. The authors of this research are currently going a step further and are evaluating the suitability of the simultaneous crushing of all the constituents of wind-turbine blades. This mechanical treatment leads to raw-crushed wind-turbine blade (RCWTB) [40], and simplifies the recycling process, as all the constituents of the wind-turbine blades can be managed simultaneously [33; 36]. This waste is composed not only of GFRP fibers, but also of polymer and balsa-wood particles, with an approximately spherical shape [40]. Its use in contents of up to 6% by volume for the production of concrete of conventional workability has been successful, even improving its flexural strength [41]. Thus, the next step in this line of research is to propose the use of this waste for the manufacture of SCC. However, a preliminary evaluation of how the reduced RCWTB content affects the flowability of SCC is needed in order to later advance the formulation of a suitable SCC when adding this waste [17; 42]. This aspect, which has yet to be covered in the concrete-science literature to date, is evaluated in this scientific paper. The evaluation of SCC flowability through laboratory tests is the most common way to know the impact of the use of an alternative raw material on fresh SCC. Nevertheless, this experimental evaluation requires time and specific equipment [43]. Fluid simulation tools such as computational fluid dynamics (CFD) can soften that analysis, apart from allowing it to deepen the flowability of SCC in terms of viscosity [44]. CFD can model any fluid as homogeneous and divide it into uniform small elements to which mathematical equations describing the fluid motion are applied [45]. The solution of those equations simulates fluid movement and flow patterns [2]. When applied to SCC, CFD can focus on flowability, pumping processes, and fiber movement within the cement paste [46]. Nevertheless, the non-Newtonian behavior of SCC has to be considered for a successful simulation [47]. Although different constitutive laws can be used for that, the Bingham equation is usually chosen due to its simplicity and faithful similarity to real behavior [48]. The fresh performance of SCC containing up to 3% by volume of RCWTB is analyzed both experimentally and through CFD in this research. Simulations are conducted based on experimental measurements of the free flow of SCC to elucidate the effect of RCWTB on the viscosity of SCC and to define its relationship with the free-flow experimental results. From that point, the passing ability of SCC is also modeled through CFD with the aim of evaluating the suitability of this methodology to explain it. Finally, the mechanical properties of the SCC mixes are briefly addressed to offer an overview of SCC behavior. The goal is initially approaching the behavior of conventionally designed SCC with RCWTB to provide a new path for the re-evaluation of wind-turbine blades.