## 2 Materials and Methods
### Methods  
From each concrete, specimens were cast to characterize the mechanical response to uniaxial compression and residual flexural tensile strength. Therefore, from each concrete, 3 cylinders of \(\mathcal{O}\)150/300 mm and 3 prisms measuring 150 \(\times\) 150 \(\times\) 600 mm\({}^{3}\) were produced, whereas for R9-3 and R9-9, \(\mathcal{O}\)100/200 mm cylinders were used for testing, due to the availability of R9 recycled aggregates. For the result comparison, a conversion ratio of \(f_{c\text{150/eq}}\) = \(f_{c\text{100/0.9}}\) was used [24]. Batching was performed in a laboratory concrete pan mixer (Collomatic 65/2 K-3) with a capacity of 35 l. The aggregates and cement were first mixed for 1 min. Then, 95% of the mixing water was added within 30 s, and mixing was continued for another 1 min. The plasticizer was dissolved in the remaining 5% of the mixing water and added within 30 s, followed by a further 1 min of mixing. Finally, the fibers were added for 1 min of mixing. Where the RA was used, the aggregate and cement were included separately, and after the aggregate was mixed for 1 min, additional water was added, and the mixing continued after the cement was added [25; 26; 27]. For all mixes, the slump was tested, and then, the specimens were cast into molds and compacted on a vibrating table. Each specimen was molded in three stages, keeping the shaking time at around 15 s each time. After 24 h, the specimens were unmolded, marked, and placed in a curing chamber for 28 days. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Fraction** & **Fines Content (\%)** & **24 h Water Absorption (\%)** & **Oven-Dry Density (kg/m\({}^{3}\))** \\ \hline Natural Aggregate & 0/4 mm & 8.1 & 1.56 & 2590 \\
4/12 mm & 0.5 & 0.57 & 2690 \\
12/20 mm & 2.4 & 0.61 & 2680 \\ \hline Recycled Aggregate (R3) & 4/12 mm & 6.1 & 6.64 & 2270 \\
12/20 mm & 2.6 & 3.63 & 2440 \\ \hline Recycled Aggregate (R9) & 4/12 mm & 5.2 & 7.04 & 2250 \\
12/20 mm & 4.9 & 6.68 & 2260 \\ \hline \end{tabular}
\end{table} 
Table 1: Physical properties of the aggregate. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Concrete** & \begin{tabular}{c} **Cement** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} \(w_{\text{eff}}\)\({}^{1}\)** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} \(w_{\text{add}}\)\({}^{2}\)** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Plast.** \\ **(\%com.)** \\ \end{tabular} & \begin{tabular}{c} **NA (kg/m\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **RCA (kg/m\({}^{3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Fiber (kg/m\({}^{3}\))** \\ \end{tabular} \\ \hline N-3 & & & & 0.80 & 782.6 & 265.9 & 706.4 & & & 3.00 \\ N-9 & \multirow{2}{*}{\(350\)} & & & 2.73 & 770.5 & 261.8 & 695.5 & & 9.00 & \\ \cline{2-2} RF-3 & & & 0.80 & 782.6 & 265.9 & 706.4 & & & 3.00 \\ RF-9 & & & 2.73 & 770.5 & 261.8 & 695.5 & & & 9.00 \\ \hline R3-3 & & & & 1.26 & 638.6 & & & 478.9 & 478.9 & 3.00 & \\ R3-9 & \multirow{2}{*}{\(385\)} & & & 2.53 & 632.1 & & & 474.1 & 474.1 & 9.00 & \\ \cline{2-2} R9-3 & & & 29.27 & 1.49 & 638.6 & & & 478.9 & 478.9 & 3.00 & \\ \cline{2-2} R9-9 & & & 3.00 & 632.1 & & & 474.1 & 474.1 & 9.00 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mix design of the tested concretes. For the axial strain-stress testing, a compression testing machine (IBERTTEST MEH 3000, Madrid, Spain) was used. Before the stress-strain test, the specimen was polished to keep the top and bottom sides of the cylinder flat. During the test, three linear variable displacement transducers (LVDTs) were mounted at 120\({}^{\circ}\) relative to each other, as in Figure 4. In order to avoid the eccentricity of loading, all the concrete specimens were subjected to three compression cycles of up to 30% of the peak load (11 MPa) before testing. The applied load and deformation were measured to derive the stress-strain behavior of the concrete specimens. The residual flexural tensile strength was tested according to EN 14651 [28].