## 3 Materials and Methods  
### Specimens' Specifications  
As discussed above, the crack spacing and propagation in SF RCARC beams was investigated. In this section, the properties of materials' and specimens' characteristics are described briefly. The NCA was characterised according to the [PERSON] et al. investigation [58]. In this research, RCA and NCA were used in specimens. The RCA came from demolished buildings and RCA was incorporated at 0%, 50% and 100% by weight. The used NCA and RCA are demonstrated in Figures 5 and 6, correspondingly. Additionally, the grading graph of the aggregates is demonstrated in Figure 7. The characteristics of the aggregates were determined and are shown in Table 1.  
Figure 5: Recycled coarse aggregate (RCA). Figure 6: Natural coarse aggregate (NCA). Figure 7: Grading curve of the aggregates employed in the current investigation. Cement was mixed with the RCA, NCA and SFs, and then a solution of water and high-performance super-plasticiser was added to the mix until the SFs were uniformly distributed in the concrete mixture. The SFs were used at 0%, 1% and 2% (by volume). In addition, the NCA was substituted by RCA at 0%, 50% and 100% by mass. The concrete mix design properties and the compression and tension strengths for the various concrete mixes are specified in Table 2.  
In Table 2, SF and RCA in the denomination of the mixes indicate the SF and RCA contents, e.g. 1 SF-50 RCA means 1% SFs by volume and 50% RCA by mass. Rebars with diameters of 20 mm, 10 mm and 8 mm were employed as tensile, compressive and shear rebars, correspondingly. The rebars were investigated in the direct tension setup and their specifications are shown in Table 3. To make the mixes, SFs with two bent ends were used. The tensile strength, modulus of elasticity and failure strain of the SFs were 200 GPa, 2 GPa and 3%, correspondingly. It should be stated that the length and equivalent diameter of the SFs were respectively 60 mm and 0.9 \(\pm\) 0.03 mm, as shown in Figure 8. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Physical Properties**} & \multicolumn{2}{c}{**Aggregate Type**} \\ \cline{2-3}  & **NCA** & **RCA** \\ \hline Apparent density (g/cm\({}^{3}\)) & 2.8 & 2.7 \\ \hline Bulk density (g/cm\({}^{3}\)) & 2.7 & 2.6 \\ \hline Water absorption (wt\%) & 1.44 & 1.19 \\ \hline Crush index (\%) & 30.00 & 48.9 \\ \hline Porosity (\%) & 3.9 & 3.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and chemical properties of RCA and NCA. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Specimens**} & **05F-** & **05F-** & **05F-** & **15F-** & **15F-** & **15F-** & **25F-** & **25F-** & **25F-** \\  & **0 RCA** & **50 RCA** & **100 RCA** & **0 RCA** & **50 RCA** & **100 RCA** & **0 RCA** & **50 RCA** & **100 RCA** \\ \hline Water (kg/m\({}^{3}\)) & 165 & 165 & 165 & 165 & 165 & 165 & 165 & 165 & 165 \\ Cement (kg/m\({}^{3}\)) & 400 & 400 & 400 & 400 & 400 & 400 & 400 & 400 & 400 \\ SFs (kg/m\({}^{3}\)) & 0 & 0 & 0 & 78 & 78 & 78 & 156 & 156 & 156 \\ RCA (kg/m\({}^{3}\)) & 0 & 420 & 840 & 0 & 385 & 765 & 0 & 345 & 685 \\ NCA (kg/m\({}^{3}\)) & 840 & 420 & 0 & 765 & 385 & 0 & 685 & 345 & 0 \\ NFA (kg/m\({}^{3}\)) & 950 & 950 & 950 & 950 & 950 & 950 & 950 & 950 & 950 \\ Average tensile stress (MPa) & 3.78 & 4.29 & 4.04 & 5.00 & 6.12 & 4.10 & 5.01 & 4.68 & 4.99 \\ Tensile stress coefficient & 0.17 & 0.04 & 0.09 & 0.01 & 0.27 & 0.04 & 0.27 & 0.09 & 0.13 \\ Average compressive resistance (MPa) & 38.4 & 35.0 & 37.1 & 36.8 & 35.7 & 35.7 & 36.9 & 35.7 & 35.6 \\ Compressive strength coefficient of variation & 1.56 & 1.08 & 1.65 & 1.33 & 1.19 & 0.85 & 1.38 & 1.00 & 0.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concrete mixes’ compositions and strengths.