# Physical and Mechanical Properties of Reclaimed Asphalt
## 4 Results and Discussion  
### Physical Properties  
Following the grain size analysis for all tested blends, the grain size distribution for each of them is presented in Figure 4.  
As can be seen from Figure 4, all samples have a similar grain size distribution with slight differences. So, it is obvious that the RAP-VA blends (B-E) are comparable to VA (blend A) and that it is reasonable to proceed to the next steps of laboratory investigation. In addition, all the materials are considered to be well graded, since the coefficients Cu and Cc  
Figure 4: Grain size distribution of all examined blends.  
Figure 3: Mechanical behavior of granular material under triaxial testing [50].  
are within the specified limits. The values of Cu and Cc are shown in Table 2. In particular, the value of C\({}_{\text{u}}\) decreases with the increasing content of RAP, but is still well above the specified limit. The value of C\({}_{\text{c}}\) generally increases--within the limits--as the content of RAP increases. This means that the addition of RAP can also improve the gradation of VA, because the closer the Cc value is to the specified limits, the flatter the gradation curve becomes. Moreover, the values of the coefficients for the blends RAP-VA are close to those of the blend VA, which means that the addition of RAP does not significantly change the grain size distribution of the control blend (100% VA).  
As for the content of RAP, RAP contains mainly finer particles, as the material passes through sieves with openings of 10 mm and below. Moreover, it can be observed in the studied blends that when the sieve size exceeds 4 mm, the percentage of grains passed increases with the content of RAP. In contrast, when the sieve size is less than 4 mm, the percentage of grains passed decreases with the increasing content of RAP. In the first case, the grain size distribution of blend A (100% VA) is located at a lower position, while in the second case it is located at a higher position. It could be concluded that, as the percentage of RAP increases, the blend consists of finer particles, which could be due to the extraction process of the material, i.e., milling and grinding. This confirms that RAP is a fine material.  
Based on the compaction test, the values of dry density versus moisture content are estimated. As mentioned earlier, OMC corresponds to MDD. Detailed results for all blends can be found in Table 3. Since all OMC values were around 6% without varying significantly (an average OMC value of 6.3% with a coefficient of variation of 6.5%), a fixed OMC value of 6% was considered representative of all blends for the remainder of the laboratory study. Therefore, this value was used to repeat the compaction procedure prior to the CBR tests.  
It is worth noting that the OMC values derived from the tests are considered typical. For example, in the worldwide literature [22, 25, 28, 29], it is stated that the moisture content of the RAP-VA blends varies between 4.5 and 9%, while an OMC value of 5.5 to 7% is commonly used. Accordingly, MDD values are also considered typical. Many researchers [22, 25, 28, 29, 30] found that the MDD for RAP-VA blends ranges from 2050 to 2350 kg/m\({}^{3}\). Overall, it appears that the addition of RAP to VA does not significantly alter the physical properties of VA for use in unbound pavement layers. The gradation coefficients are within the limits and the OMC and MDD parameters have similar values for the VA and RAP-VA blends.