# Evaluation of Mechanical Properties of Recycled Material for Utilization in Asphalt Mixtures
## 3 Experimental Work
### Results and Discussions  
As presented in the previous sections, in this research, the properties of RCA, RAP, basalt and mix of these aggregates were evaluated by conducting a series of tests. The test results are summarized in Table 10.  
In addition, to have better comparisons between the aggregate properties, the test results on different aggregates as well as the standard limits are also illustrated in Figure 13.  
As shown in Figure 13, the results of preliminary tests on coarse aggregates indicate that all properties of RCA, except for water absorption and wet strength (which are shown in bold in Table 10), are within the limits specified by relevant Australian Standards and hence deemed appropriate for use as aggregate in the asphalt mixture. However, for some parameters such as Flakiness Index and Particle Shape which are two dominant characteristics having significant impact on asphalt mixture strength and stability; RCA displays smaller value in comparison with basalt and RAP. This can be one of the strong points of RCA as flakiness index and particle shape are the two important properties for proper compaction, deformation resistance, and workability of asphalt mixture [58]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test**} & \multirow{2}{*}{**Test Method**} & \multicolumn{3}{c}{**Aggregate**} & \multirow{2}{*}{**Typical Limit Based on**} \\  & & **RCA** & **RAP** & **Basalt** & **Australian Standards** \\ \hline Particle Distribution Test & AS 1141.11.1 & As & presented in relevant Figures and Tables & - \\ Flakiness Index Test & AS 1141.15 & 6.91 & 10.42 & 19.03 & 25\% (max) \\ Particle Shape Test & AS 1141.14 & 6.16 & 9.47 & 18.34 & 35\% (max) \\ Water Absorption & AS 1141.6.1 & **6.30** & 1.78 & 1.64 & 2\% (max) \\ Particle Density & AS 1141.6.1 & 2.370 & 2.541 & 2.640 & - \\ Particle Density on Dry Basis & AS 1141.61 & 2.212 & 2.431 & 2.530 & - \\ Particle Density on SSD Basis & AS 1141.61 & 2.351 & 2.474 & 2.571 & - \\ Aggregate Crushing Value & AS 1141.21 & 29.21 & 7.40 & 8.91 & 35\% (max) \\ Weak Particles & AS 1141.32 & 0.23 & 0.04 & 0.23 & 1\% (max) \\ Wet/Dry Strength Test & AS 1141.22 & **26.6** & 7.4 & 8.5 & 35\% (max) \\ Wet Strength & AS 1141.22 & **119.7** & 398.2 & 359.2 & 150 kN (min) \\ Dry Strength & AS 1141.22 & 163.1 & 429.8 & 392.9 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary of the Test Results for the Evaluation of Coarse Aggregate Properties. Figure 13: Comparison of Different Aggregate Properties with Standard Limits. In addition, as can be observed in Table 10 and Figure 13, the water absorption of RCA is higher than the corresponding value of RAP and basalt and the Australian Standards limit, because it is well known that water absorption requires linked and open cracks in the structure of aggregate and RCA contains cracks due to the crushing processes. Moreover, the great amounts of impurities in RCA can increase the water absorption of RCA. The high water absorption of RCA may result in high bitumen absorption in asphalt mixtures, and hence plays an important role in asphalt mixture design. Accordingly, since this research aims to investigate the feasibility of the application of RCA for the partial replacement of coarse virgin aggregate (basalt) and in combination with other recycled aggregate (RAP) in asphalt mixtures, the particle density and water absorption tests were conducted on different mix of coarse aggregates while considering different percentages of these materials. The results of these tests are presented in Figure 14.  
As can be observed in Figure 14, increasing RCA in the mix does not make any substantial change in mix density in comparison with water absorption. In other words, by increasing RCA from 0% to 100% in the mix, the density decreases by 7%, whereas water absorption increases by 74%. In addition, although wet/dry strength variation of RCA meets the requirements of Australian standards, the test results show that this value is higher than the corresponding value of RAP and basalt.