## 3 Results and Discussion
### Water Stability Performance
#### 3.3.2 Freeze-Thaw Splitting Test  
The implementation of the freeze-thaw splitting test requires more stringent conditions--freeze-thaw cycles--than the implementation of the immersion Marshall test. In this study, in order to comprehensively evaluate the water damage resistance of the WER-EA mixtures, the freeze-thaw splitting strength ratio (\(TSR\)) was selected as a supplementary index, and its calculation method is shown in following equations:  
\[R_{\text{T1}}=0.006287P_{\text{T1}}/h_{1} \tag{11}\]  
Figure 12: Marshall residue stability results of asphalt mixtures immersed in water.  
\[R_{\rm T2}=0.006287P_{\rm T2}/h_{2} \tag{12}\]  
\[TSR=\frac{R_{\rm T2}}{R_{\rm T1}}\times 100 \tag{13}\]  
where \(R_{\rm T1}\) represents the splitting tensile strength of the specimens at room temperature, MPa; \(R_{\rm T2}\) stands for the splitting tensile strength of the freeze-thaw specimens, MPa; \(P_{\rm T1}\) represents the test load value of the specimens at room temperature, N; \(P_{\rm T2}\) stands for the test load value of the freeze-thaw group specimens, N; \(h_{1}\) indicates the height of the specimens at room temperature, mm; \(h_{2}\) represents the height of the specimens in the freeze-thaw group, mm; and \(TSR\) represents the freeze-thaw splitting strength ratio, %.  
The \(TSR\) values of the four WER-EA mixture specimens are shown in Figure 13. The characterization of the water damage resistance of the mixtures was similar to that of the \(IRS\) value, that is, the better the water damage resistance of the specimen, the higher the \(IRS\) value. The AASHTO specification set the limits that the TSR for 70# should be larger than 75%. According to the results, the addition of the WER system could alter the \(TSR\) value of the emulsified asphalt mixture such that it changes from not meeting the limit of the specified value to meeting the requirements of the specified value.  
As can be seen in Figure 13, the \(TSR\) value of the emulsified asphalt mixtures was increased by 4-10% in the three WER systems, and the \(TSR\) value of E44 was the lowest among the mixtures, at only 4.61%. The TSR value of the E20-T and E51-T mixtures differed by only 2.1%.  
Based on the results of the two experiments, the \(IRS\) value and \(TSR\) value of the WER-EA mixtures were significantly higher than those of the control group, which was consistent with the corresponding \(VV\) values in Table 11. This phenomenon is related to the presence of highly stable, highly cross-linked, three-dimensional interpenetrating polymer networks (IPNs) in WER-EA mixtures, which allow the components of the mixture to interlock with each other and make the mixture more resistant to the pressure generated by the ingress of moisture.  
In addition, the \(TSR\) value and \(IRS\) value of the E20-T mixture were higher, that is, E20-T had a better comprehensive effect on the improvement of water damage resistance in the emulsified asphalt mixture. Thus, the use of WER with a low epoxy value is more conducive to the formation of a more stable and cross-linked interpenetrating polymer network in a WER-EA mixture, which can resist the damage caused by a rainy environment in summer.  
Figure 13: Freeze–thaw splitting strength ratio of asphalt mixtures.