# Permanent Deformation Mechanism of Steel Bridge Deck
## 2 Materials and Methods  
In accordance with the rutting test specifications outlined in the Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011) [36], a dense-graded asphalt mixture designated as AC-13 with a nominal maximum aggregate size of 13 mm was prepared. The target gradation of the designed asphalt mixture is illustrated in Figure 1, while the key technical properties of the asphalt binder and basalt aggregates are presented in Table 1 and Table 2, respectively.  
Figure 1: Synthetic gradation curve of AC-13.  
In order to determine the contact model parameters between asphalt mortar and coarse aggregates for numerical simulation, rutting tests were conducted using an automatic rutting tester at 30 \({}^{\circ}\)C and 45 \({}^{\circ}\)C, respectively. Rutting specimens with dimensions of 300 mm in length, 300 mm in width, and 60 mm in height were used in the tests, including a 10 mm thick steel plate. The specimen and test equipment of the wheel tracking test are shown in Figure 2. A load of 78 kg exerting a pressure of 0.7 MPa was applied to the slab specimen using a rubber wheel with a width of 50 mm. The rubber wheel oscillated 42 times per minute on the specimen, with each traversal measuring 230 mm. The total duration of the test was 60 min, and the equipment was paused after every 120 passes of the test wheel to record the rutting depth at that moment.  
In order to verify the reliability of the SACSS model established in this study, rutting tests were conducted using an automatic rutting tester at 30 \({}^{\circ}\)C and 45 \({}^{\circ}\)C under three different SAIB conditions. The proportions of the SAIB failure area were set as 0%, 17%, and 100%. Three specimens were prepared for each SAI condition. The specimen preparation procedure was as follows: Epoxy asphalt binder was uniformly coated at a dosage of 0.68 L/m\({}^{2}\) on steel plates previously treated with epoxy zinc-rich paint. The binder was applied selectively according to the designed layout to create different SAIB scenarios. In the regions designated for SAIB failure, an anti-adhesive isolating agent was applied instead of epoxy asphalt binder, whereas epoxy asphalt binder was used in the non-failure regions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Detection Index** & **Unit** & **Test Value** & **Specification Requirements** \\ \hline Penetration (25 \({}^{\circ}\)C, 100 g, 5 s) & 0.1 mm & 69 & 60\(\sim\)80 \\ Ductility (15 \({}^{\circ}\)C) & cm & \(>\)150 & \(\geq\)100 \\ Softening Point (R\&B) & \({}^{\circ}\)C & 47.0 & \(\geq\)46.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Asphalt technical index.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Properties**} & \multicolumn{3}{c}{**Sieve Size (mm)**} \\ \cline{2-4}  & 3\(\sim\)5 & 5\(\sim\)10 & 10\(\sim\)15 \\ \hline Apparent relative density & 2.717 & 2.958 & 2.927 \\ Bulk density & 2.667 & 2.858 & 2.859 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Technical properties of the aggregate.  
Figure 2: Wheel tracking test: (**a**) rutting specimen; (**b**) test equipment.  
The arrangement of SAI failure and non-failure areas is illustrated in Figure 3. Subsequently, the asphalt mixture with specified aggregate gradation was compacted onto the steel plates to produce SACSSs. Finally, the specimens were placed in the automatic rutting tester for rutting tests, and the maximum rut depths obtained under three different SAIB failure conditions at 30 \({}^{\circ}\)C and 45 \({}^{\circ}\)C were recorded in Table 3 and Table 4, respectively. It was observed from a macroscopic viewpoint that the SAIB failure aggravated the development of rutting.