# Determining the Compaction Temperature of Warm-Mix Anti-Rutting Asphal Mixture
## 4 Compaction Characterization of Warm-Mix Anti-Rutting Asphal Mixture
### Compaction Analysis Based on CT Scans  
There is a certain experimental error in measuring the voids of the warm-mix anti-rutting asphalt mixture by the saturated surface-dry method, because the Marshall specimens have closed voids. During the saturated surface-dry method test, it is difficult for water to fill all the voids in the specimen, making it difficult to accurately reflect the true distribution of the internal voids in the asphalt mixture. CT scanning technology has significant importance in the study of asphalt mixtures. It uses an X-ray source to scan and reconstruct images of the object being tested in a non-destructive state, the scanning principle is shown in Figure 8. It can obtain continuous cross-sectional images of the microstructure of the asphalt mixture, reflecting its two-dimensional distribution characteristics, providing real and accurate digital images for the study. Therefore, the voids of the asphalt-mixture specimens obtained through CT scanning technology are more accurate than the results obtained by the saturated surface-dry method. The following is a description of CT scans based on research needs:  
Specimen specifications: Cylindrical Marshall specimens with a diameter of 100 mm and a height of 63.5 mm. Experimental purpose: To scan and obtain cross-sectional images of the specimens and to calculate the voids of the specimens using software. Scanning plan: Four specimens were selected for scanning from each group of variables, totaling 80 specimens. Cross-sectional images at 7 mm, 17 mm, 27 mm, 37 mm, 47 mm, and 57 mm from the height direction of each specimen were taken as the research objects, as shown in Figure 9. The specimen scanning process is shown in Figure 10.  
Figure 8: X-ray tomography schematic. Figure 9: Section selection drawing. Specimens are scanned using a CT test machine (YXLON, Hamburg, Germany), capturing cross-sectional images with a pixel size of 1028 \(\times\) 1028. The cross-sectional images are then enhanced using the Avizo 3D software (2017.2), shown in Figure 11.  
Following enhancement, the images were imported into Image-Pro Plus (v.7.0) for binarization processing. Some of the processed images are shown in Figure 12.  
Extract each void (voids are the black shadow parts) from the images that have been binarized and export the data. The selected cross-section voids of each specimen were calculated, finally taking the average value of parallel specimens to obtain the average  
Figure 11: Process of image enhancement at 115 \({}^{\circ}\)C with different warm-mix dosages: (**a**) 0% warm-mix agent, (**b**) 1% warm-mix agent, (**c**) 2% warm-mix agent, and (**d**) 3% warm-mix agent. Figure 10: Diagram of the CT scan site process. voids under different compaction temperatures and warm-mix-agent dosages. The final results are shown in Table 8.  
Based on the data from Table 8, the measured voids of the warm-mix anti-rutting asphalt mixture are fitted, as shown in Figure 9.0  
Similarly, using the 4% voids of hot-mixed asphalt-mixture Marshall specimens as a reference, based on the principle of equal voids, the target voids of 4% is substituted into the calculated voids-compaction temperature-fitting equation for the warm-mix anti-rutting asphalt mixture with different warm-mix-agent contents:  
Figure 9.1  
Figure 9.2  
Figure 9.3  
Figure 9.4  
When adding 0%, 1%, 2%, and 3% warm-mix agent, the compaction temperatures for the warm-mix anti-rutting asphalt mixture are 176.32 \({}^{\circ}\)C, 148.51 \({}^{\circ}\)C, 144.30 \({}^{\circ}\)C, and 142.39 \({}^{\circ}\)C. Compared with the anti-rutting asphalt mixture without the addition of warm-mix agent, the addition of 1% warm-mix agent reduced the compaction temperature by 27.81 \({}^{\circ}\)C, 2% reduced it by 32.02 \({}^{\circ}\)C, and 3% reduced it by 33.93 \({}^{\circ}\)C. The compaction temperatures  
Figure 9.5 Calculation of voids–compaction temperature curves for warm-mix anti-rutting asphalt mixture.