# Evaluation of Mechanical Properties of Recycled Material for Utilization in Asphalt Mixtures
## 3 Experimental Work
### Laboratory Tests
#### 3.2.7 Wet/Dry Strength Variation Test  
Strength is an important aggregate property which is related to the satisfactory resistance to crushing under the roller during construction, and adequate resistance to surface abrasion under traffic [56]. Therefore, aggregates used in pavement construction should be strong enough to resist crushing during mixing, laying process, compaction, consolidation and during its service life period when they are subjected to various loads applied by traffic [57]. In this research, the variation in strength of aggregate is evaluated by conducting the Wet-Dry Strength Variation Test on RCA, RAP and basalt in accordance with AS 1141.22 (2008), as shown in Figure 8. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample Number**} & \multicolumn{3}{c}{**Weak Particles (\%)**} & \multirow{2}{*}{**Australian Standards Aggregate**} \\ \cline{2-2} \cline{4-5}  & **RCA** & **RAP** & **Basalt** & \\ \hline Sample 1 & 0.21 & 0.05 & 0.29 & \\ Sample 2 & 0.25 & 0.03 & 0.16 & 1\% (max) \\
**Average Weak Particles** & \multirow{2}{*}{**0.23**} & \multirow{2}{*}{**0.04**} & \multirow{2}{*}{**0.23**} & For heavy and very heavy traffic \\
**Percentage (\%)** & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The Results of Weak Particle Test for Coarse Aggregates and Weak Particles Percentage Limits for Dense Graded Asphalet Based on Australian Standards. Figure 7: Crushing Value Test for Coarse Aggregates. (**a**) apparatus to crush aggregate; (**b**) compression machine ; (**c**) aggregates after crushing and sieving. This test determines the variation in strength of the aggregates tested after drying in an oven and then saturated yet with a dry surface. Based on the available standards, the wet/dry strength variation of less than 35% indicate a durable material but values as high as 60% could be used in undemanding circumstances. In this research, the wet/dry strength variation test was conducted on the RCA, RAP and basalt fraction passed through 13.2 mm and retained on 9.5 mm I.S sieve. Different loading was used in order to adjust the applied load for providing the fines within the range of 7.5% and 12.5%. The results of these tests for coarse aggregates are illustrated in Figures 9 and 10 under dry condition and saturated surface dry condition (SSD), respectively. The wet and dry strengths can be inferred from the test results shown in these figures. Based on the obtained data, the wet/dry strength variation was calculated as follows:  
\[\text{Wet/dry strength variation}=\frac{\text{D}-\text{W}}{\text{D}}\times 100 \tag{1}\]  
where D is the dry strength in kilonewtons, and W is the wet strength in kilonewtons. Figure 8: Conducting the Wet/Dry Strength Variation Test on Coarse Aggregate. (**a**) apparatus to crush aggregate; (**b**) compression machine. Figure 9: Results of Wet/Dry Strength Test for Coarse Aggregate (Dry Strength). The results of the calculations for wet strength, dry strength, and wet/dry strength variation for basalt, RAP and RCA are presented in Table 8.  
As the results of wet/dry strength test shows, the wet/dry strength variation of RCA is substantially more than the corresponding values for RAP and basalt. Therefore, as mentioned previously, it appears plausible to further investigate the feasibility of the application of RCA for the replacement of part of basalt in asphalt mixtures. Accordingly, the wet/dry strength variation test was also conducted on different mix of coarse aggregates (i.e., RCA, RAP and coarse basalt) considering different percentages of these materials. Figures 11 and 12 illustrate the results of the wet/dry strength test for several mixes of RCA, RAP and basalt in dry condition and saturated surface dry condition respectively. Based on the obtained results from these graphs, the wet strength (W) and the dry strength (D) can be determined and subsequently the wet/dry strength variation can be calculated as shown previously.