## 4 Discussions  
Based on the results of the investigation of the effects of recycled aggregate quality on bond and shear behaviors of RC beams, using a recycled aggregate concrete, the following points can be discussed. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**References**} & \multicolumn{2}{c}{**Section (mm)**} & \multirow{2}{*}{\(a\)/\(d\)} & \(\rho\) & \(f_{c}\) & \(V_{u,exp}\) & \(V_{u,com}\) & \(V_{u,exp}\)/\(V_{u,com}\) & **Class** \\ \cline{2-9}  & **b** & **d** & & **(\%)** & **(MPa)** & **(kN)** & **(kN)** & **(kN)** \\ \hline \multirow{3}{*}{[PERSON] et al. [24]} & 170 & 270 & 2.0 & 1.10 & 31.6 & 66.65 & 60.79 & 1.09 & N \\  & 170 & 270 & 2.0 & 1.10 & 39.66 & 59.98 & 65.01 & 0.92 & H \\ \hline \multirow{6}{*}{[PERSON] et al. [12]} & 200 & 300 & 2.5 & 1.90 & 31.8 & 75.5 & 83.36 & 0.91 & N \\  & 200 & 450 & 2.5 & 1.90 & 31.8 & 106.9 & 112.92 & 0.95 & N \\  & 200 & 600 & 2.5 & 1.90 & 31.8 & 125.9 & 140.19 & 0.90 & N \\  & 300 & 450 & 2.5 & 1.90 & 31.8 & 156.7 & 171.41 & 0.91 & N \\  & 400 & 600 & 2.5 & 1.90 & 31.8 & 256.4 & 280.38 & 0.91 & N \\  & 200 & 300 & 2.5 & 1.90 & 34.9 & 72.9 & 85.98 & 0.85 & H \\  & 200 & 450 & 2.5 & 1.90 & 34.9 & 96.4 & 116.47 & 0.83 & H \\  & 200 & 600 & 2.5 & 1.90 & 34.9 & 125.1 & 144.61 & 0.87 & H \\  & 300 & 450 & 2.5 & 1.90 & 34.9 & 159.8 & 176.81 & 0.90 & H \\  & 400 & 600 & 2.5 & 1.90 & 34.9 & 256.6 & 289.21 & 0.89 & H \\ \hline \multirow{6}{*}{[PERSON] et al. [25]} & 200 & 260 & 2.31 & 1.10 & 32.5 & 71.9 & 64.9 & 1.11 & N \\  & 200 & 260 & 2.31 & 1.10 & 34.8 & 57.15 & 66.40 & 0.86 & L \\  & 200 & 260 & 2.31 & 1.10 & 44.1 & 65.4 & 71.85 & 0.91 & L \\  & 200 & 260 & 2.31 & 1.10 & 42.4 & 81.4 & 70.92 & 1.15 & L \\ \hline \multirow{6}{*}{[PERSON] et al. [11]} & 200 & 309 & 2.59 & 1.62 & 34.4 & 110.1 & 81.68 & 1.35 & N \\  & 200 & 300 & 1.50 & 1.00 & 43.5 & 195.7 & 95.99 & 2.04 & M \\ \cline{1-1}  & 200 & 300 & 2.00 & 1.50 & 43.5 & 174.1 & 94.65 & 1.84 & M \\ \cline{1-1}  & 200 & 305 & 3.93 & 2.46 & 43.5 & 106.3 & 86.22 & 1.23 & M \\ \cline{1-1}  & 200 & 300 & 1.50 & 1.00 & 36.9 & 187.2 & 90.87 & 2.06 & L \\ \cline{1-1}  & 200 & 300 & 2.00 & 1.50 & 36.9 & 165.6 & 89.60 & 1.85 & L \\ \cline{1-1}  & 200 & 309 & 2.59 & 1.62 & 36.9 & 104.0 & 83.65 & 1.24 & L \\ \cline{1-1}  & 200 & 305 & 3.93 & 2.46 & 36.9 & 83.8 & 81.62 & 1.03 & L \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Shear strength of the RC beam using a recycled aggregate concrete, from the literature. Concrete made with lower quality recycled aggregate always has a lower slump due to its higher water absorption capacity and excessive moisture loss from the aggregate, during a one-day drying period, before the concrete is mixed, resulting in a compressive strength comparable with natural concrete, without any attenuation in strength. The bond strength of the concrete with the low-quality recycled coarse aggregate is always the lowest, but the bond strength deterioration could be ignored for the high- and medium-quality recycled aggregate concrete. In some cases, the bond strength of the concrete with the high- and medium-quality recycled coarse aggregate replacement is higher than that of the natural aggregate concrete. In addition, the bond between the concrete and different diameters of deformed rebar (13 and 19 mm) have highly similar bond behaviors and ultimate bond stresses, when the embedment length is maintained at the same ratio of four times the steel diameter. Shear strength of recycled concrete beams decreases as the effective depth decreases. In contrast, the ultimate shear strength of natural concrete beams increases, even for smaller beam size. The estimated shear strength of all beams are larger than the experimental results, except for beam NS60 and HS60, having \(V_{u,cap}/V_{u,com}\) of 1.27 and 1.04, respectively. The effect of high-quality of recycled aggregate on shear strength should not be considered.