# A Study on the Properties of Recycled Aggregate Concrete and Its Production Facilities
## 4 Development of the Technology to Improve the Quality of the Mixed Aggregates
### Principle of Technology
#### 4.3.2 Compressive Strength  
This concrete compressive strength test was implemented to determine the difference in the compressive strength, before and after mixing (as shown in Figure 8). Before mixing and with a three-day material age, the front portion exhibited compressive strengths in the range of 11.1-12.5 Mpa, with an average of 11.8. In the back portion, the compressive strengths were in the range of 10.4-11.7 Mpa, with an average of 11.0 MPa. Thus, there was a difference in the compressive strengths of a 0.8 MPa between the front and back. After mixing, the front portion had a compressive strength range of 11.5-12.4 Mpa, for an average of 11.9 MPa. In the back portion, the range was 11.9-12.4 MPa, with an average of 12.2 MPa. Thus, there was a 0.3 MPa difference in the compressive strengths, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Division**} & \multicolumn{2}{c}{**Unit Volume**} & \multicolumn{2}{c}{**Absolute**} & \multicolumn{2}{c}{**Absorption**} & \multicolumn{2}{c}{**Assembly**} & \multicolumn{1}{c}{**Organic**} \\  & **Weight** & **Dry Density** & **Rate** & **Rate** & **Rate** & **Impurities** \\  & **(kg/m3)** & **(g/cm3)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline Natural Coarse & \multirow{2}{*}{1518} & \multirow{2}{*}{2.59} & \multirow{2}{*}{1.01} & \multirow{2}{*}{7.02} & \multirow{2}{*}{-} \\ Aggregate & & & & & & \\ \hline Recycled Coarse & \multirow{2}{*}{1485} & \multirow{2}{*}{2.51} & \multirow{2}{*}{5.85} & \multirow{2}{*}{6.26} & \multirow{2}{*}{0.53} \\ Aggregate & & & & & & \\ \hline Natural Fine Aggregate & 1552 & 2.61 & 1.03 & 2.95 & - \\ \hline Before Modified & \multirow{2}{*}{1305} & \multirow{2}{*}{2.21} & \multirow{2}{*}{4.89} & \multirow{2}{*}{2.48} & \multirow{2}{*}{0.92} \\ Recycled Fine Aggregate & & & & & & \\ \hline After Modified Recycled & \multirow{2}{*}{1384} & \multirow{2}{*}{2.33} & \multirow{2}{*}{3.62} & \multirow{2}{*}{2.74} & \multirow{2}{*}{0.49} \\ Fine Aggregate & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of natural aggregate and recycled aggregate. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Division**} & \multicolumn{2}{c}{**Unit Volume Weight of Mortar**} & \multicolumn{2}{c}{**Unit Coarse Aggregate Amount**} \\ \cline{2-7}  & **Front** & **Back** & **Difference Rate** & **Front** & **Back** & **Difference Rate** \\  & **(kg)** & **(kg)** & **(\%)** & **(kg)** & **(kg)** & **(\%)** \\ \hline Before & 16.17 & 15.84 & 2.04 & 2.89 & 2.69 & 6.92 \\ After & 16.15 & 16.07 & 0.49 & 2.87 & 2.75 & 4.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental results of Unit Volume Weight of Mortar and Unit Coarse Aggregate Amount. between the front and back. For a material with a seven-day age before mixing, the front portion had a range of 18.1-19.3 Mpa, with an average of 18.6 MPa. In the back portion, the range was 17.1-18.2 MPa, with an average of 17.8 MPa. Thus, there was a 0.8 MPa difference in the compressive strength, between the front and back. After mixing, the front portion had a range of 18.4-19.2 MPa, with an average of 18.8 MPa, and the back portion had a range of 17.0-19.2 MPa, with an average of 18.0 MPa. Thus, there was a 0.8 MPa difference in the compressive strengths between the front and back. For the material with a 28 day age before mixing, the front portion had a range of 23.3-25.3 Mpa, with an average of 24.1 MPa, and the back portion had a range of 21.9-23.3 Mpa, with an average of 22.7 MPa. Figure 8: The (**a**) 3-day, (**b**) 7-day, and (**c**) 28-day concrete strength before and after aggregate mixing. Thus, there was a 1.4 MPa difference in the compressive strengths between the front and back. After the mixture, the front portion had a range of 23.5-24.4 MPa, with an average of 24.1 MPa, and the back portion had a range of 23.8-24.8 MPa, with an average of 24.2 MPa. Thus, there was a 0.1 MPa difference in the compressive strengths between the front and back.