3.3.1. Rutting Resistance

The wheel track test is used to study the rutting resistance of 1.0% and 2.0% ER-100 reinforced LCA-AMs and the original asphalt mixture. The specimens were cured at 25 ◦C for 72 h. The results are shown in Figures 7 and 8, where it can be seen that the accumulated deformation (rutting depth) of the asphalt mixture increases gradually with the increase of the number of load cycles, and the rutting depth growth rate of ER-100-reinforced LCA-AM is less than that of the LCA-AM without ER. After the same number of load cycles, the rut depth of ER-reinforced LCA-AMd is much smaller than that of the LCA-AM without ER. At the loading times of 45 min and 60 min, the rut depth of the LCA-AM with 1.0% ER is 21.2% or 25.5% smaller than that of the original asphalt mixture; the rutting depth of 2.0% ER-reinforced LCA-AM is 57.3% (59.9% smaller than that of the LCA-AM without ER). Meanwhile, the dynamic stability of ER-reinforced LCA-AMs is much higher than that of the LCA-AM without ER. The results indicate that ER can significantly enhance the high-temperature stability of LCA-AMs. The reason is that, after the curing of the ER, part of the strength of the asphalt mixture is provided by the ER, and the ER can form a spatial skeleton structure in the asphalt mixtures, which have greater strength and stiffness. Therefore, it can greatly improve the rutting resistance of the mixtures.

**Figure 7.** Rutting depth increase curve of asphalt mixtures.

3.3.2. Low-Temperature Crack Resistance

LCAs can decrease the formation temperature of asphalt mixtures by decreasing the viscosity of asphalt binders. However, if the reduction in viscosity is too large, it results in a reduction in the mechanical properties of the asphalt mixture (even at low temperature), which can easily break down during low-temperature crack resistance tests. In order to improve the low-temperature crack resistance of LCA-AMs, −10 ◦C and 0 ◦C SCB tests were conducted to evaluate the low-temperature cracking resistance of LCA-AMs with different dosages of ER. The results are shown in Figure 9 and Table 11, and the comparison of fracture energy of LCAs-AM is shown in Figure 10. According to Figure 9 and Table 11, the fracture energy and fracture toughness of LCA-AMs increase first and then decrease with the increase of ER dosages, and the LCA-AM with 0.6% ER has the highest fracture energy and fracture toughness. After curing, the ER acts as part of the skeleton structure in LCA-AMs. Therefore, a low content of ER can enhance the significantly increase the low-temperature crack resistance of LCA-AMs.

However, with the gradual increase of ER dosages, the increasing effect of the ER on the stiffness (mechanical performance) is much more obvious, and it may be too big and have a negative effect on the low-temperature crack resistance of LCA-AMs. The ER content in the LCAs-AM does not need to be high. The results show that one can significantly increase the low-temperature crack resistance of LCA-AMs by controlling the ER content in LCA-AMs.

**Figure 9.** Displacement and load curve of SCB tests: (**a**) −10 ◦C; (**b**) 0 ◦C.


**Figure 10.** Low-temperature fracture energy with different ER contents.

#### 3.3.3. Water Sensitivity

Immersion Marshall Test

The residual Marshall stability (RMS) of LCA-AMs with different dosages of ER were studied using the immersing Marshall test. The results are shown in Figure 11. From Figure 11, the Marshall stability of LCA-AMs with ER is higher than 8 kN both before and after the immersion condition. The RMS of LCA-AMs increases with the increase of ER dosage, and all the RMS of LCA-AMs are more than 80%. The results even satisfy the requirements of the specification of HMA.

**Figure 11.** Immersion Marshall stability and RMS of LCA-AMs with ER.

Freeze-Thaw Splitting Test

The freeze-thaw splitting ratio (TSR) of LCA-AMs with the different dosages of ER were studied using the freeze-thaw splitting test. The results are shown in Figure 12. It can be seen from Figure 12 that the TSR of LCA-AM without ER is lower than 75%. However, all the TSRs of LCA-AMs with ER are higher than 75%, and meet the requirements of HMA. The TSR increases first and then decreases with the increase of ER dosage, and the TSR of LCA-AMs with 1% ER is the highest. Therefore, due to the enhancement effect of ER, LCA-AMs have a good anti-water damage performance.

**Figure 12.** Indirect tensile strength and TSR of LCA-AMd with ER.

#### 3.3.4. Fatigue Resistance

The repeated SCB test was conducted to investigate the fatigue resistance of LCA-AMs. The results are shown in Table 12 and Figure 13. The stress ratios of the fatigue test were 0.3, 0.4, 0.5, 0.6 and 0.7, respectively.

It can be seen from Table 12 that, at 25 ◦C, the peak load and fracture toughness of LCA-AM with 1.0% ER are the highest, while the LCA-AM with 0.6% ER has the maximum fracture work and fracture energy. Compared with the LCA-AM without ER, the fracture energy of LCA-AMs with 0.3%, 0.6% and 1.0% ER increase by 26.7%, 109.3% and 60.5%, respectively. It can be seen from Figure 13 that under the same loading frequency, the fatigue life decreases gradually with the increase of stress ratio. When the stress ratio increases from 0.3 to 0.7, the fatigue life of the LCA-AM without ER decreases by 83.7%, which shows that the fatigue resistance of the asphalt mixture has an obvious stress dependence. When the stress ratio is 0.3, the fatigue life of the LCA-AM increases gradually with the increase of ER content. Compared with the LCA-AM without ER, the fatigue performance of LCA-AM with 0.3% ER decreased by 12.5%, while that of LCA-AMs with 0.6% and 1.0% ER increase by 15.3% and 48.9%, respectively. When the stress ratio is 0.7, the fatigue resistance of 0.3%, 0.6% and 1.0% ER reinforced LCA-AMs increases by 22.6%, 11.8% and 6.0%, respectively. This shows that ER can significantly increase the fatigue resistance of LCA-AMs. The LCAs-AM with 0.6% and 1.0% ER are much better than the LCA-AM without ER.

**Table 12.** Results of repeated SCB tests of LCA-AMs.


**Figure 13.** Fatigue life of LCA-AMs with ER.

#### **4. Conclusions**

In this paper, an environmentally friendly LCA asphalt modifier additive was developed, which can used to decrease the construction temperature of asphalt mixtures. The design and preparation parameters of LCA-modified asphalt mixtures were determined. The volumetric properties, mechanical performance and mixture performance of LCA-AMs were studied as well. The main conclusions are as follows:


It is feasible to improve the mixture performance by the enhancement of low dosages of ER. LCAs can facilitate the low-temperature preparation of asphalt mixtures, with remarkable environmental benefits. LCAs should find wide application prospects in asphalt pavement engineering.

**Author Contributions:** Conceptualization, Y.L.; methodology, Y.L., J.F., A.C. and S.W.; validation, F.W.; data curation, Y.L., J.F., A.C., F.W. and Q.L.; writing—original draft preparation, J.F. and F.W.; writing—review and editing, Y.L., A.C., S.W., Q.L. and R.G.; visualization, R.G.; supervision, Y.L.; funding acquisition, Y.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors acknowledge the financial supported provided by the National Natural Science Foundation of China (No. 52108415), the National Key Research and Development Program of China (No. 2018YFB1600200), the Natural Science Foundation of China (No. 51778515), the Key Technical Innovation Projects of Hubei Province (No. 2019AEE023), the Plan of Outstanding Young and Middleaged Scientific and Technological Innovation Teams in Hubei Province Universities (No. T2020010), the Key R&D Program of Hubei Province (No. 2020BCB064), the Scientific Research Fund Project of Wuhan Institute of Technology (No. K2021032), the Science and Technology Project of the Department of Housing and Urban-Rural Development of Hubei Province, and the test help from Shiyanjia Lab (www.shiyanjia.com).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no competing financial interest.

#### **References**

