# A Study on the Properties of Recycled Aggregate Concrete and Its Production Facilities
## Mechanical Properties of the Recycled Aggregates Using Concrete and Durability Characteristics
### Physical and Mechanical Characteristics
#### 5.2.1 Air Volume  
The air volume increased in, both, the general strength territory and the high strength territory, as the replacement rate of the recycled coarse aggregate increased. The air volume increased slightly by 0.3%-0.5%, up to a replacement rate of 60%, which was not significant, compared to the air volume increase of ordinary concrete. However, at a replacement rate of 100%, the air volume increased by 1.1%-1.7%. In addition, during the replacement of the recycled fine aggregates, before modification, a replacement rate of 30% in the general strength territory and a high strength territory changed the air volume by \(-\)0.3%-0.1%, compared to the ordinary concrete. However, at a replacement rate of 60%, the air volume increased by 0.6%-1.6%. At a replacement rate of 100%, the air volume increased significantly by 2.0%-2.2%. In the replacement of the recycled fine aggregate, after modification, both, the general strength territory and the high strength territory exhibited, decreased in air volume, \(-\)1.4% to \(-\)0.5%, compared to that of ordinary concrete, at up to 60% of the replacement rate. A similar air volume to that \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mix ID**} & \multirow{2}{*}{\
\begin{tabular}{c} **W/C** \\ **(\%)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **S/A** \\ **Water** \\ \end{tabular} } & \multirow{2}{*}{**Cement**} & \multicolumn{4}{c}{**Sand**} & \multicolumn{4}{c}{**Gravel**} \\ \cline{5-10}  & & & & & **N.E * & **R.B. *** & **R.A. *** & **N.C. *** & **R.C. *** \\ \hline IIIIIA & & & & & & & 974.5 & 0 \\ IZIIIA & & & & & & & 682.2 & 292.4 \\ I3 IIIA & & & & & & & 389.8 & 584.7 \\ I4 IIIA & & & & & & 0 & 0 & 974.5 \\ IIIIIA2 & 44.3 & 47.1 & 146.5 & 330.5 & 607.9 & 260.5 & & & \\ IIIIIA3 & & & & & 0 & 868.4 & & & \\ IIIII2A & & & & & 607.9 & 260.5 & 974.5 & 0 \\ IIIII3A & & & & & 347.4 & 521.0 & & & \\ IIIII4A & & & & & 0 & 868.4 & & & \\ IIIIIIB & & & & & 0 & 895.9 & & \\ IIIIIB & & & & & & & 627.1 & 268.8 \\ IIIIIB & & & & & & & 358.4 & 537.5 \\ IIIIIB & & & & & & 0 & 0 & 895.9 \\ IIIIIB & & & & & 577.9 & 247.7 & & & \\ IIIII3B & & & & & 330.2 & 495.4 & & & \\ IIIIIB & & & & & 0 & 825.6 & & 895.9 & 0 \\ IIIIIB & & & & & 577.9 & 247.7 & & & \\ IIIIIIB & & & & & 330.2 & 0 & 495.4 & & \\ IIIIIIB4B & & & & & 0 & 825.6 & & & \\ \hline \hline \end{tabular}  
* N.F.: Natural fine aggregate; *** R.B.: Recycled fine aggregate before modification; *** R.A.: Recycled fine aggregate after modification; *** N.C.: Natural coarse aggregate; and *** R.C.: Recycled coarse aggregate.  
\end{table} 
Table 4: Concrete mixing table. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Division** & **Factors** & **Levels** & **Symbols** \\ \hline \multirow{4}{*}{Aggregate Type} & Recycled Coarse Aggregate, Recycled Fine & & \\  & Aggregate before Modify, Recycled Fine & 3 & I, II, III \\  & Aggregate after Modify & & \\ \hline Recycled Aggregate & & 0, 30, 60, 100 & 4 & 1, 2, 3, 4 \\ Replacement Ratio (\%) & & & & \\ \hline Target Strength (MPa) & 24, 35 & 2 & A, B \\ \hline Water Cement Ratio (\%) & 48.5, 44.6 & 2 & - \\ \hline Fine Aggregate Ratio (\%) & 47.5, 49.2 & 2 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental factors and levels. of ordinary concrete was displayed at the replacement rate of 100%. Thus, the recycled aggregate contained a massive number of air-gaps on the mortar attached to the surface and the finite cracks, and the air volume increased as the density decreased, or the rate of use of the recycled aggregate (with a high absorption) rate increased. However, for the recycled fine aggregate, with an oven dried density of 2.33 g/cm\({}^{3}\) and an absorption rate of 4.62%, the air volume did not increase. Therefore, if the recycled coarse aggregate and the recycled fine aggregate, before modifications are used, it is prudent to prepare for changes in the air volume, for the design's standard strength and a continuous concrete quality management.