# Evaluation of Mechanical Properties of Recycled Material for Utilization in Asphalt Mixtures
## 3 Experimental Work
### Results and Discussions
As the wet/dry strength variation is related to the principal mechanical properties which are required for asphalt aggregate, it is of high importance in asphalt mixture design. Therefore, wet/dry strength variation test was also conducted on different mixes of coarse aggregate. Figure 15 shows the comparison of wet strength, dry strength, and wet/dry variation in different mixes of RCA, RAP and basalt. As illustrated in this figure, the wet/dry strength variation of mix of RCA/basalt increases by increase of the percentage of RCA in the mix, so that the increase of RCA from 0% to 100% will result in 20% increase in wet/dry strength variation. The results of these two tests (i.e., water absorption and particle density test, and wet/dry strength variation test) on mix of coarse aggregates are summarized in Table 11.  
Figure 14: Comparison of Water Absorption and Particle Density of Different Mixes of Coarse Aggregates. The results of tests on mix of coarse aggregate showed that in all cases of RCA ratios, RCA increase causes a decrease in wet and dry strength and an increase in water absorption. This will necessitate the proper selection and optimum combination of RCA and other aggregates. The coefficient of variation is used as an indication to measure the heterogeniety of test results. The results of calculation of standard deviation (SD) and coefficient of variation (CV) for each set of aggregate mixes are presented in Table 12.  
As can be observed in Table 12, the coefficient of variation for each data set reveals that the test results dispersion is low and the tests are conducted consistently. Furthermore, regression analysis is typically applied to the water absorption test results for different combination of RCA and basalt, to show the typical amount of RCA and basalt in a blend to give 2% water absorption which is the standard limit of water absorption based on Australian standards (Figures 16 and 17). \begin{table}
\begin{tabular}{c c c} \hline
**Mix** & **Coefficient of Variation** & **Standard Deviation** \\ \hline Basalt (100\%) + RCA (0\%) & 2.14 & 0.035 \\ Basalt (75\%) + RCA (25\%) & 1.71 & 0.050 \\ Basalt (50\%) + RCA (50\%) & 3.52 & 0.131 \\ Basalt (25\%) + RCA (75\%) & 4.42 & 0.204 \\ Basalt (0\%) + RCA (100\%) & 2.47 & 0.156 \\ \hline \end{tabular}
\end{table} 
Table 12: Coefficient of Variation and Standard Deviation for Mix of Coarse Aggregates. Figure 15: Comparison of the Wet Strength and Dry Strength of Different Mixes of Coarse Aggregates. As illustrated in Figures 16 and 17, the standard water absorption limit of 2% can be achieved by mixing of almost 8% and 92% of RCA and basalt, respectively. However, based on the available references [59], typically, the amount of binder absorbed by aggregate is 0.3 to 0.7 times the water absorption of the aggregate. In addition, according to this standard, if the sample absorbs between 2% and 4% of its mass, it should be carefully examined by other tests. If the sample absorbs in excess of 4% of its mass, it will rarely prove to be an adequate aggregate for asphalt production. Based on the water absorption results, it can be observed that the combination of 25% RCA and 75% basalt would provide water absorption of 2.93%, and also water absorption of the combination of 50% RCA and 50% basalt would be 3.71%, which are still in the range of aggregate water absorption that suggest further research. Figure 16: Regression Analysis for Determination of Optimum Basalt Amount. Figure 17: Regression Analysis for Determination of Optimum recycled construction aggregate (RCA) Amount.