## 3 Results and Discussions
### Influence of RAP Particle Size on Emulsification-Separation
#### 3.3.3 Emulsification-Separation Effects of Different RAP Gradation Levels  
A total of 300 g of pretreated RAP of different sizes was removed from each aggregate size, and 300 g of oversized aggregates with a diameter of 16 mm or more was taken. A total of 1500 g of RAP was emulsified and separated, and the optimum separation conditions in Section 3.2 were selected to determine the change in mass, thereby obtaining the increase or decrease in conditions for each aggregate. We defined the ratio of the mass change of each agglomerate of the aggregate before and after emulsification as the rate of change. A positive rate of change meant that the mass of this grade of aggregate was decreasing; a negative rate of change meant that the mass of this grade of aggregate was increasing.  
Figure 8: Grading curves of emulsification–separation of different sizes of RAP: (**a**) 13.2 mm; (**b**) 9.5 mm; (**c**) 4.75 mm; and (**d**) 2.36 mm.  
Figure 9: Evaluation of emulsification–separation of different sizes of RAP.  
In Figure 10, the quality of RAP aggregates above 9.5 mm is shown to be significantly reduced, especially the 16 mm RAP, with a sieve removal rate of 100%, and the 13.2 mm RAP, with a sieve removal rate of 88.11%. The sieve removal rate of the 9.5 mm RAP barely changed, with a rate of only 8.54%; correspondingly, aggregates below 9.5 mm increased, with the 4.75 mm aggregate increased by 31.73% and the 2.36 mm aggregate almost doubled, its sieve removal rate reaching 103.27%. From the rate of change of each grade, it can be preliminarily concluded that an aggregation larger than 9.5 mm contains numerous 4.75 and 2.36 mm aggregates, especially fine aggregates of 2.36 mm, with a very significant change rate. Aggregates of 2.36 mm can easily produce 4.75 mm clusters during processing because aggregates below 4.75 mm contain more asphalt, which is easily rebonded during the separation process. Therefore, no 2.36 mm RAP was added for subsequent separation, and only RAPs with a particle size above 4.75 mm were studied in mixed separation. To further explore the optimal separation, we used 500 g each of the same quality of 13.2, 9.5, and 4.75 mm coarse aggregates for emulsification-separation.  
Figure 11 shows that the sieve removal rate of the 9.5 mm aggregate reached about 40%, which was almost five times higher than the 8% rate for the average mixed processing of aggregates. Thus, it can be proved that the selection of coarse aggregate agglomerates with larger particle sizes makes it easier to open the agglomerates for separation.  
As seen in Figure 12 and Table 7, when only 9.5-13.2 mm RAP was used, mixed in a 1:1 ratio for processing, the PL was only 18.06, the FMR reached 0.99, and the asphalt content was reduced to 1.6%, thus indicating that the mixing and separation effect is excellent when treating coarse aggregates of 9.5 mm or more. When only 4.75-9.5 mm RAP was used, the PL was only 15.67, the FMR was as low as 1.00, and the asphalt content was reduced to 1.8%, indicating an excellent separating effect. The filling area between the emulsification-separation sieve grading curve and the extraction grading curve was calculated. According to the results, the treatment effect for 9.5-13.2 mm RAP was the best, with an area of only 14.85. The separation effect for 4.75-9.5 mm RAP was also excellent, with an area of 26.48. The separation effect of mixed processing was significantly improved compared to single particle size processing. Based on the above conclusion, the 1:1 treatment of 13.2 and 9.5 mm RAPs yielded the best results.  
Figure 10: Changes in mass after emulsification–separation of various RAP sizes.