## 5 Results and Discussion
### Moisture Damage Resistance  
Asphalt concrete in the service process is subject to temperature and precipitation, rainwater infiltration, and moisture in the concrete of the freezing and thawing cycles is prone to degradation of pavement performance, in severe cases, easily producing potholes, exfoliation, and other defects [39]. Hence, the moisture damage resistance of HSACs and ESACs was compared and evaluated. The test results are shown in Figure 8.  
Both \(RS\) and \(TSR\) of the concrete in Figure 8 were below 100%, indicating that irreversible damage to the internal structure of the specimen occurred under the combined  
Figure 8: Moisture damage resistance test results: (**a**) Immersion Marshall test and (**b**) Freeze–thaw splitting test.  
Figure 7: Beam bending test results.  
effects of moisture and temperature, causing a deterioration in its stability and splitting strength. The water immersion Marshall test results demonstrated that the variation of TPS content did not influence the \(RS\) significantly. The \(RS\) of HSAC exceeded 95%, which was higher than the requirement of \(\geq\)85% in the specification (JTG/T3364-02-2019) [24]. Similarly, the \(RS\) of ESAC did not exhibit a monotonic variation with increasing EP content. The \(RS\) of ESAC35, ESAC40, ESAC45, and ESAC50 were 92.4%, 92.9%, 92.3%, and 93.1%, respectively, which were still much higher than 85%, although the test results were lower than the HSAC.  
Conversely, the freeze-thaw splitting test results indicated that the variation of modifier content had a significant effect on the \(TSR\) of the concrete. Specifically, the \(TSR\) of both HSAC and ESAC gradually rose with increased modifier content. For HSAC, the addition of TPS dramatically improved the viscosity of the binder, enabling it to have superior adherence with the aggregate, effectively preventing the adverse effects of moisture, high temperature, low temperature, and other combined factors on the performance of concrete [40]. Meanwhile, the increase in TPS content caused the more evident improvement mentioned above. For ESAC, the enhancement of the cross-linked network structure within the binder positively affected the moisture damage resistance of the concrete, and the cohesion between asphalt and aggregate was strengthened with the increase in EP content [22]. Notably, the enhancement of \(TSR\) for HSMA13 and ESAC50 visibly slowed down compared to other concretes, with increasing values of 0.2% and 0.5%, respectively, suggesting that the excessive addition of modifiers was limited in improving the moisture damage resistance of concrete. The specification (JTG/T3364-02-2019) requires that the \(TSR\) of asphalt concrete should be \(\geq\)80% [24], and there is no doubt that all the concretes achieved this target. The results revealed that the moisture damage resistance of HSAC and ESAC was satisfactory, and HSAC was superior. Furthermore, it should be noted that the water immersion Marshall test was limited for evaluating the moisture damage resistance of concrete, and this test could not well-reflect the difference in performance between different concretes. Consequently, the freeze-thaw splitting test should be preferably chosen for the analysis of the moisture damage resistance.