## 2 Materials and Methods  
### Laboratory Test of CPAM  
This investigation selected five commercially available CPAM formulations (designated CPAM1-CPAM5) widely implemented in highway maintenance across China's diverse climatic regions. The selected materials represent typical formulations used in both northern and southern regions, ensuring comprehensive coverage of varying environmental conditions and construction practices. As these materials were used in their original pre-mixed state and stored for extended periods, the bitumen binders were not separately extracted or tested, and their properties are not available. Preliminary field investigations revealed that CPAM4 and CPAM5 exhibited inferior field performance compared to other formulations, particularly in terms of durability and service life. A comprehensive laboratory evaluation was conducted, measuring six critical performance indicators: aggregate gradation, binder-aggregate ratio, penetration strength, molding strength, residual rate, and stability retention index. Referring to the American Association of State Highway and Transportation Officials (AASHTO) standards [14], three penetration tests (TP43-94) and three rolling sieve tests (TP44-94) were performed on each of the five CPAMs, with the average of three test results representing the penetration strength and residual rate. Following the Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011) [34], six Marshall strength tests (T 0710-2021) and six water immersion Marshall tests (T 0709-2021) were carried out on each CPAM at room temperature, and the average of six test results was adopted as the molding strength and stability retention. Additionally, in accordance with the combustion furnace method (T 0735-2021) and sieving method (T 0725-2000) specified in JTG E20-2011 [34], two sets of samples from each CPAM were tested, and the average of three sets of samples was used to determine the asphalt content and mineral aggregate grading. Standard Marshall specimens were used for most of the performance tests, including water stability, residual stability, and cohesion tests. These specimens were cylindrical in shape with a diameter of 101.6 mm and a height of 63.5 mm, prepared in accordance with relevant testing standards. An exception was made for the penetration test, which did not require the preparation of standard Marshall specimens. Instead, the materials for the penetration test were compacted into molds according to the specific requirements of that test method. By maintaining consistent specimen dimensions for the majority of the tests, the reliability and comparability of experimental results were ensured. The quantitative test results, as shown in Table 1 and Figure 1, offer fundamental baseline data for follow-up microstructural analysis and performance correlation studies. These specific parameters were selected due to their well-documented relevance to field performance and their capacity to distinguish between material formulations under different service conditions. Figure 1 reveals that CPAM2 and CPAM3, which exhibit higher forming strength, contain a greater proportion of coarse-grained mineral materials (9.5-13.2 mm). Conversely, CPAM1 and CPAM5, with lower molding strength, show reduced coarse-grained mineral content. This suggests that optimal coarse-grained material content enhances CPAMs' molding strength. Table 1 demonstrates that CPAM4, despite its higher coarse aggregate content, displays inferior performance across all parameters, indicating that simply increasing coarse aggregate content cannot improve CPAM performance. Comparative analysis of CPAM3 and CPAM5, which have similar total coarse aggregate content, reveals comparable performance but lower cohesion in CPAM3. Experimental results indicate this difference stems from CPAM3's reduced mineral content in the 2.36-4.75 mm grading range, confirming that varying coarse aggregate gradations significantly influences CPAM performance.