# The Recycling of Carbon Components and the Reuse of Carbon Fibers for Concrete Reinforcements
## 4 Results and Discussion
### Yarn Tensile Tests  
The tensile tests were carried out in accordance with [20; 21]. The individual yarns were cut to a length of 400 mm. A total of five yarns were tested for each type of wetting. For testing, the yarns were glued to aluminum sheets. The aluminum sheets served to introduce the load. According to [20], the free length of the yarns must not be less than 200 mm. The loading speed of the yarns during the tensile test was set to 3 mm/min. The measurement of the strain was carried out with a MultiXtens extensometer. The results of the yarn tests are presented in Figure 6.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number** & **Breaking Stress** & **Fiber Diameter** & **Tension** & **Strain** & **Young’s Modulus** \\  & **[cN]** & **[\(\mu\)m]** & **[GPa]** & **[\%]** & **[GPa]** \\ \hline
1 & 7.5 & 5.82 & 2.82 & 1.20 & 228.21 \\
2 & 7.07 & 5.47 & 3.01 & 1.30  
The rupture loads, as well as fracture behavior, vary depending on the impregnation. The average rupture load of the epoxy resin-impregnated yarn is 1.5 kN. For the polymer-impregnated yarns, failure occurred at 1.1 kN and for the geopolymer-impregnated yarn at 0.65 kN. The individual test curves are shown in the diagram. All results were shown in Table 3. All yarns failed between the load application points within the free span. Therefore, the tests are valid according to [20] and can be assigned to the type of failure I. In all tests, the yarn failed at the point with the smallest diameter. Direct determination of the stress-strain curve is not derivable. The background is that due to the manufacturing process of the yarn, the diameter is not constant. This has the consequence that an exact yarn tension cannot be determined. The average manually measured yarn diameter is approximately 1.5 mm. Since all yarns are made from a continuous yarn, a first comparison of the values is nevertheless possible. As was already the case with the single-fiber tests, fluctuations in the individual breaking loads could also be observed in the fiber tests. In the case of yarns impregnated with an epoxy resin, the tensile forces range between 649.17 N and 1463.64 N. The displacement ranges were between 1.09 mm and 2.14 mm. The yarns impregnated with a polymer were able to withstand forces between 691.51 N and 1069.04 N before failure occurred. The measured displacement ranged from 1.43 mm to 1.94 mm for the yarns impregnated with geopolymer. The breaking load for these yarns ranged between 430.39 N and 649.55 N. The displacement varied from 1.35 mm to 2.28 mm. The correlation coefficient of Figure 6 is 0.34. The standard deviation of the conducted experiments is listed in the following Table 4.  
The fluctuations can also be attributed to the production of the yarn at this point. Due to varying diameters, the yarns failed under different loads. The curves shown in the diagram also reveal that the yarns impregnated with epoxy resin have the least amount of displacement. Thus, the elongation of the yarns with epoxy resin, of the three examined, is the lowest. This leads to the result that the epoxy resin-impregnated yarns have the highest stiffness of the examined impregnation. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Force** & **Displacement** \\  & **[N]** & **[mm]** \\ \hline Standard deviation & 72.03 & 0.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Standard deviation of the yarn tensile tests.