## 2 Materials and Methods
### CT Scanning and Digital Image Processing  
High-resolution CT scanning was conducted using an industrial micro-CT system (Model: CD-200 CGA), developed in December 2005 by Chongqing University, and located at the Engineering Research Center for Non-Destructive Testing, Ministry of Education, Chongqing, China.  
The cylindrical specimens for CT scanning were prepared according to the Marshall standard compaction method (T 0702-2011) [34], with a diameter of 101.6 mm and a height of 63.5 mm. All five CPAM formulations underwent X-ray computed tomography using a  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Group Number**} & **Binder-Aggregate Ratio (\%)** & **Penetration Strength (kg/cm\({}^{2}\))** & \multicolumn{2}{c}{**Moding Strength (kN)**} & \multirow{3}{*}{**Residual Rate**} & **Stability** \\  & **Aggregate Strength** & & & & **(\%)** & **Retention** \\  & **Ratio** & **(kg/cm\({}^{2}\))** & & & **Standard** & **(\%)** & **Index** \\  & **(\%)** & & & & **Deviation** & **(\%)** \\ \hline CPAM1 & 4.89 & 1.53 & 5.59 & 0.55 & 92.60 & 99.84 \\ CPAM2 & 4.73 & 1.32 & 9.24 & 1.03 & 94.14 & 99.36 \\ CPAM3 & 5.77 & 1.0 & 9.76 & 2.30 & 85.66 & 99.92 \\ CPAM4 & 5.61 & 1.92 & 2.94 & 0.78 & 75.52 & 80.91 \\ CPAM5 & 5.76 & 1.57 & 4.31 & 0.81 & 69.95 & 50.36 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Laboratory test results of five CPAMs.  
Figure 1: Gradation curves of five CPAMs.  
high-resolution micro-CT scanner. The scanning procedure consisted of continuous axial imaging at 0.7 mm intervals throughout the specimen height, generating 85 cross-sectional images per specimen. This scanning arrangement enabled complete three-dimensional characterization of the internal microstructure while ensuring optimal contrast differentiation among aggregate, binder, and void phases.  
The obtained CT images were processed through comprehensive digital image analysis to improve quality and enable precise phase identification. The processing sequence comprised four consecutive steps: (1) noise suppression using a hybrid median-Wiener filtering technique [35], (2) localized contrast enhancement of void and aggregate regions via piecewise linear transformation [36], (3) global image refinement through adaptive histogram equalization [37], and (4) phase segmentation utilizing an enhanced Otsu-maximum entropy thresholding algorithm [38].  
For aggregate image processing, morphological operations were conducted using \(5\times 5\) pixel structural elements with linear, cross, and quadrangular configurations, effectively eliminating smaller particles and resolving particle adhesion issues. Following this, aggregate boundaries were accurately defined using the Canny edge detection operator. The efficacy of this image-processing approach is clearly demonstrated in Figure 2, which shows the progressive improvement in aggregate identification and characterization.  
Extending beyond two-dimensional image analysis, this study employed advanced three-dimensional reconstruction techniques to fully characterize the internal structure of CPAM. The CT scan data were processed using RadiAnt DICOM Viewer (version 4.6.9, Medixant) to create three-dimensional volumetric reconstructions, with subsequent void network analysis performed through Avizo (version 9.0.0, Thermo Fisher Scientific) software's visualization module. This integrated methodology facilitated the generation of precise three-dimensional models representing the void architecture within cold patch specimens. The reconstruction process effectively captured the complex spatial distribution and void connectivity, as illustrated in Figure 3. Additionally, the three-dimensional visualization model yields quantitative data on void morphology and spatial organization, providing exceptional detail for microstructural examination.