*3.1. High-Temperature Rutting Resistance*

The G\* and δ of asphalt are the main parameters of the high-temperature rheological property of asphalt. The greater the G\*, the greater the shear deformation resistance and vice versa. The δ can evaluate the ratio of elastic components and viscous components. The greater the δ, the greater the viscous components. Conversely, the smaller the δ, the greater the elastic components. Figure 3 shows that the G\* and δ of asphalt after multiple aging through heat, UV and aqueous solution. As can be seen from Figure 3a, the G\* and δ of asphalt aged with TFOT increased and decreased, respectively, indicating the increase in shear deformation resistance and elastic components. The trend was further deepened after UV aging, manifesting the effect of UV was accumulated on the sample after thermal-oxygen aging. As can be seen from Figure 3b, the G\* of asphalt samples declined after immersion in water, saline solution and acid solution, while the G\* of asphalt samples increased after immersion in alkali solution. The δ of asphalt decreased after immersion in the four kinds of solutions. This could be explained by that there were some oxidation products on the surface of samples (UV 5d), and the existence of moisture resulted in dissolution and migration of these, leading to the reduction of the shear deformation resistance during immersion in three kinds of solution except alkali solution [38]. However, the reduction of other components might lead to an increase in the relative content of crystalline wax, resulting in an increment in the elastic components [39]. Chloride ions in saline solution could promote the emulsification of asphalt, and the esterification reaction between acid and olefin in asphalt generated long chain isomerized alkanes. The chemical reactions increased the content of saturates, resulting in the further reduction of the shear deformation resistance. Among these, the effect of salt solution on the high-temperature rheological property of asphalt was greater than that of water and acid solution, which might be due to the crystallization of salt in asphalt [40]. Moreover, the saponification of alkali solution with asphalt accelerated the asphalt oxidation to generate more asphaltenes, resulting in an increasing of the shear deformation resistance and elastic components [41]. After aging cycle of UV and water, the G\* and δ of asphalt are illustrated in Figure 3c. The order of G\* from small to large was the following order, (UV 5d + water 5d) < (UV 5d) < (UV 10d) < (UV 15d) < (UV 5d + water 5d + UV 5d). It suggested that the effect of water and UV on shear deformation resistance was opposite due to asphalt dissolution and migration, but water can increase the sensitivity of the shear deformation resistance to UV. The order of δ from small to large is the following: (UV 5d + water 5d + UV 5d) < (UV 15d) < (UV 10d) < (UV 5d + water 5d) < (UV 5d); manifesting water can also increase sensitivity of the viscoelasticity to UV.

Figure 4 shows the RAI of asphalt after the multiple aging. From Figure 4a, it can be seen that the RAIs of TFOT and UV aging were greater than 1 and increased with the increase of UV time. It indicates that the thermo-oxidative aging and UV aging have a positive effect on the rutting resistance of asphalt, and the positive effect could be accumulated. The RAI increased over temperature, suggesting that effect degree of thermal-oxygen and UV on the rutting resistance increased with the increment of temperature. Figure 4b,c illustrates the data graphs with the G\*/sinδ of sample (UV 5d) as the G ∗ virgin/ sin δvirgin. From Figure 4b, it can be seen that the RAIs of asphalt samples exposed to water, saline solution and acid solution were less than 1, while that of sample immersed in alkali solution was greater than 1. This demonstrates that the first three solutions had a negative impact on the rutting resistance of asphalt, while alkali solution improved the rutting resistance of asphalt. The RAIs of samples suffered the aqueous solutions except the alkali solution and were not affected by temperature, indicating they had similar effects on the rutting resistance at different temperatures. Additionally, the RAI of the asphalt treated by alkali solution

increased with temperature, manifesting it had greater effects on the rutting resistance at high temperatures. From Figure 4c, it can be seen that the RAI of samples (UV 5d + water 5d) was less than that of samples (UV 10d), while the RAI of samples (UV 5d + water 5d + UV 5d) was greater than that of samples (UV 15d). It indicates that the effect of water on asphalt rutting resistance was less than UV, but it could increase the sensitivity of rutting resistance to UV. The RAI of samples (UV 5d + water 5d), (UV 10d) and (UV 15d) were not affected by temperature, manifesting water and UV had similar effects on the rutting resistance at different temperatures after UV aging for 5d. The RAI of samples (UV 5d + water 5d + UV 5d) increased with temperature, demonstrating that water made the rutting resistance more sensitive to temperature. *Materials* **2022**, *15*, x FOR PEER REVIEW 8 of 19 to UV. The order of δ from small to large is the following: (UV 5d + water 5d + UV 5d) < (UV 15d) < (UV 10d) < (UV 5d + water 5d) < (UV 5d); manifesting water can also increase sensitivity of the viscoelasticity to UV.

**Figure 3.** G\* and δ of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water.

Gvirgin \*

**Figure 3.** G\* and δ of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water.

Figure 4 shows the RAI of asphalt after the multiple aging. From Figure 4a, it can be seen that the RAIs of TFOT and UV aging were greater than 1 and increased with the increase of UV time. It indicates that the thermo-oxidative aging and UV aging have a positive effect on the rutting resistance of asphalt, and the positive effect could be accumulated. The RAI increased over temperature, suggesting that effect degree of thermaloxygen and UV on the rutting resistance increased with the increment of temperature. Figure 4b,c illustrates the data graphs with the G\*/sinδ of sample (UV 5d) as the

/sinδvirgin. From Figure 4b, it can be seen that the RAIs of asphalt samples exposed to water, saline solution and acid solution were less than 1, while that of sample immersed in alkali solution was greater than 1. This demonstrates that the first three solutions had a negative impact on the rutting resistance of asphalt, while alkali solution improved the rutting resistance of asphalt. The RAIs of samples suffered the aqueous solutions except the alkali solution and were not affected by temperature, indicating they had similar effects on the rutting resistance at different temperatures. Additionally, the RAI of the asphalt treated by alkali solution increased with temperature, manifesting it had greater effects on the rutting resistance at high temperatures. From Figure 4c, it can be seen that the RAI of samples (UV 5d + water 5d) was less than that of samples (UV 10d), while the RAI of samples (UV 5d + water 5d + UV 5d) was greater than that of samples (UV 15d). It indicates that the effect of water on asphalt rutting resistance was less than UV, but it could increase the sensitivity of rutting resistance to UV. The RAI of samples (UV 5d + water 5d), (UV 10d) and (UV 15d) were not affected by temperature, manifesting water and UV had similar effects on the rutting resistance at different temperatures after UV aging for 5d. The RAI of samples (UV 5d + water 5d + UV 5d) increased with temperature, demonstrating that water made the rutting resistance more sensitive to temperature.

**Figure 4.** RAI of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water. **Figure 4.** RAI of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water.

#### *3.2. Low-Temperature Cracking Resistance 3.2. Low-Temperature Cracking Resistance*

Figure 5 shows that the S- and m-value of asphalt after the multiple aging of heat, UV and water. It can be seen that the S of asphalt increased and the m-value gradually decreased with the decrease of test temperature. It indicated that the low-temperature ductility and relaxation rate of the asphalt gradually decreased with the decreasing of temperature and the asphalt started to become hard and brittle. After thermal-oxygen aging, the S of samples gradually increase, while the m-value declined, manifesting the lowtemperature, cracking resistance was weakened. The addition of UV aging deepened the change trend, meaning that thermal-oxygen and UV could accumulatively weaken the low-temperature cracking resistance. After the multiple aging of UV and aqueous solution, the S of asphalt exposed to water, saline solution and acid solution decreased and the Figure 5 shows that the S- and m-value of asphalt after the multiple aging of heat, UV and water. It can be seen that the S of asphalt increased and the m-value gradually decreased with the decrease of test temperature. It indicated that the low-temperature ductility and relaxation rate of the asphalt gradually decreased with the decreasing of temperature and the asphalt started to become hard and brittle. After thermal-oxygen aging, the S of samples gradually increase, while the m-value declined, manifesting the low-temperature, cracking resistance was weakened. The addition of UV aging deepened the change trend, meaning that thermal-oxygen and UV could accumulatively weaken

m-value increased, while the opposite pattern appeared in samples suffered from alkali solution. This might be because the dissolution and migration of polar components in asphalt led to the softening of asphalt and enhancement of flexibility, leading to better cracking re-

in alkali solution, hardening the asphalt samples and weakening the crack resistance at low

the low-temperature cracking resistance. After the multiple aging of UV and aqueous solution, the S of asphalt exposed to water, saline solution and acid solution decreased and the m-value increased, while the opposite pattern appeared in samples suffered from alkali solution. This might be because the dissolution and migration of polar components in asphalt led to the softening of asphalt and enhancement of flexibility, leading to better cracking resistance at low temperatures. However, the polar components increased during immersion in alkali solution, hardening the asphalt samples and weakening the crack resistance at low temperature [42]. The rangeability order of S from small to large was the following: (UV 5d + water 5d) < (UV 5d) < (UV 10d) < (UV 15d) < (UV 5d + water 5d + UV 5d); and that of m-value was the opposite. It suggested that the effect of water was positive on cracking resistance, but water could increase the sensitivity of the cracking resistance to UV. *Materials* **2022**, *15*, x FOR PEER REVIEW 11 of 19 temperature [42]. The rangeability order of S from small to large was the following: (UV 5d + water 5d) < (UV 5d) < (UV 10d) < (UV 15d) < (UV 5d + water 5d + UV 5d); and that of mvalue was the opposite. It suggested that the effect of water was positive on cracking resistance, but water could increase the sensitivity of the cracking resistance to UV.

**Figure 5.** S and m-value of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water.

#### *3.3. Element Composition* samples were investigated to discuss the change mechanism in properties, as illustrated in Table 3. For 70 A, the elemental content of C and H was higher than that of N, S and O.

*3.3. Element Composition*

*Materials* **2022**, *15*, x FOR PEER REVIEW 12 of 19

Asphalt is a complex compound with a variety of polymeric hydrocarbons and their non-metallic derivatives, whose main constituent elements are carbon, hydrogen, oxygen, sulfur, nitrogen, etc. The effect of heat and UV on the element composition of asphalt samples were investigated to discuss the change mechanism in properties, as illustrated in Table 3. For 70 A, the elemental content of C and H was higher than that of N, S and O. After TFOT, the content of O increased, while that of others reduced, manifesting that oxidation reaction occurred to introduce oxygen atoms in air into the asphalt, therefore the relative content of other elements decreased. Moreover, the change trend of element composition increased gradually with the extension of UV aging time, indicating that the influence of UV accumulates gradually over time. The n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* of asphalt after the multiple aging are displayed in Figure 6. The n(H)/n(C) declined, while the *f<sup>A</sup>* and *C<sup>I</sup>* increased after TFOT. The results showed that heat could decrease saturated hydrocarbon and increase the aromatic ring substance and its condensation degree, causing the existence of the more complex ring structure. The polymer molecule with the kind of aromatic ring as the main chain could not be rotated internally, resulting in the increasing of rigidity and the weakening of flexibility. As a result, the high-temperature rutting resistance was improved and the low temperature cracking resistance was weakened, as reflected in the DSR and BBR results. The trend was further driven by UV aging. Table 4 illustrated the comparison of rangeability in *C<sup>I</sup>* after different aging methods. It could be seen that the rangeability caused by TFOT was greater than that caused by UV 5d, and the rangeability gradually decreased with the extension of UV aging time, indicating that the sensitivity of elemental composition to UV decreased with the deepening of aging. After TFOT, the content of O increased, while that of others reduced, manifesting that oxidation reaction occurred to introduce oxygen atoms in air into the asphalt, therefore the relative content of other elements decreased. Moreover, the change trend of element composition increased gradually with the extension of UV aging time, indicating that the influence of UV accumulates gradually over time. The n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* of asphalt after the multiple aging are displayed in Figure 6. The n(H)/n(C) declined, while the *f<sup>A</sup>* and *C<sup>I</sup>* increased after TFOT. The results showed that heat could decrease saturated hydrocarbon and increase the aromatic ring substance and its condensation degree, causing the existence of the more complex ring structure. The polymer molecule with the kind of aromatic ring as the main chain could not be rotated internally, resulting in the increasing of rigidity and the weakening of flexibility. As a result, the high-temperature rutting resistance was improved and the low temperature cracking resistance was weakened, as reflected in the DSR and BBR results. The trend was further driven by UV aging. Table 4 illustrated the comparison of rangeability in *C<sup>I</sup>* after different aging methods. It could be seen that the rangeability caused by TFOT was greater than that caused by UV 5d, and the rangeability gradually decreased with the extension of UV aging time, indicating that the sensitivity of elemental composition to UV decreased with the deepening of aging. **Table 3.** Element content of asphalt after the multiple aging of heat and UV (%).

**Figure 5.** S and m-value of asphalt after the multiple aging of heat, UV and solution. (**a**) multiple aging of heat and UV; (**b**) multiple aging of heat, UV and solution; (**c**) aging cycle of UV and water.

Asphalt is a complex compound with a variety of polymeric hydrocarbons and their non-metallic derivatives, whose main constituent elements are carbon, hydrogen, oxygen, sulfur, nitrogen, etc. The effect of heat and UV on the element composition of asphalt

**Table 3.** Element content of asphalt after the multiple aging of heat and UV (%). **Samples C H N S O**


**Figure 6.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *CI*) of asphalt after the multiple aging of heat and **Figure 6.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* ) of asphalt after the multiple aging of heat and UV.

UV.


after immersion in different aqueous solution. The n(H)/n(C) declined, while the *f<sup>A</sup>* and *C<sup>I</sup>*

**Samples Δ***C<sup>I</sup>* Virgin/TFOT 0.0009 TFOT/UV 5d 0.0007 UV 5d/UV 10d 0.0004

**Table 4.** Rangeability of *C<sup>I</sup>* after the multiple aging. UV 10d/UV 15d 0.0001

**Table 4.** Rangeability of *C<sup>I</sup>* after the multiple aging.

*Materials* **2022**, *15*, x FOR PEER REVIEW 13 of 19

Table 5 illustrated the element composition of asphalt samples after the multiple aging of UV and aqueous solution. Compared with UV 5d, the C and H remain essentially unchanged and the N and S declined to a certain extent, while the content of O increased after immersion in different aqueous solution. The n(H)/n(C) declined, while the *f<sup>A</sup>* and *C<sup>I</sup>* increased after immersion in different aqueous solution, as shown in Figure 7. It indicated that the oxidation during immersion caused the existence of molecules with high condensation degree, in which the water-soluble heterocyclic compounds containing N and S (including anhydrides, lactones and cyclic lactams) were easier to dissolve and migrate [42]. This resulted in the situation where N and S decreased but C and H remain essentially unchanged. The presence of solute could accelerate the trend, and the order of the effect degree is as follows: alkali > acid > salt > water. increased after immersion in different aqueous solution, as shown in Figure 7. It indicated that the oxidation during immersion caused the existence of molecules with high condensation degree, in which the water-soluble heterocyclic compounds containing N and S (including anhydrides, lactones and cyclic lactams) were easier to dissolve and migrate [42]. This resulted in the situation where N and S decreased but C and H remain essentially unchanged. The presence of solute could accelerate the trend, and the order of the effect degree is as follows: alkali > acid > salt > water. **Table 5.** Element content of asphalt after the multiple aging of UV and aqueous solution (%).

**Table 5.** Element content of asphalt after the multiple aging of UV and aqueous solution (%). **Samples C H N S O**


**Figure 7.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *CI*) of asphalt after the multiple aging of UV and aqueous solution. **Figure 7.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* ) of asphalt after the multiple aging of UV and aqueous solution.

The element composition of asphalt was observed after the aging cycle of UV and water, as shown in Table 6. Compared to the sample (UV 10d), the sample (UV 5d + water The element composition of asphalt was observed after the aging cycle of UV and water, as shown in Table 6. Compared to the sample (UV 10d), the sample (UV 5d + water 5d) had the same content of C, higher content of H and O and the lower content of N and

5d) had the same content of C, higher content of H and O and the lower content of N and S. The sample (UV 5d + water 5d + UV 5d) had the lower content of C and H, the same

S. The sample (UV 5d + water 5d + UV 5d) had the lower content of C and H, the same content of N and the higher content of S and O than the sample (UV 15d). Figure 8 describes the n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* of asphalt after the aging cycle. The sample (UV 5d +water 5d) had the smaller n(H)/n(C), the greater *f<sup>A</sup>* and *C<sup>I</sup>* than the sample (UV 10d), meaning that the effect of water on element composition was less than UV. Compared to the sample (UV 15d), the n(H)/n(C) of sample (UV 5d +water 5d + UV 5d) was smaller but the *f<sup>A</sup>* and *C<sup>I</sup>* were greater. In addition, it could be seen from Table 4 that the rangeability of *C<sup>I</sup>* between the sample (UV 5d + water 5d and UV 5d) and the sample (UV 5d + water 5d) was 1.25 times that between the sample (UV 10d) and the sample (UV 5d), demonstrating that water could increase the sensitivity of element composition to UV. that the effect of water on element composition was less than UV. Compared to the sample (UV 15d), the n(H)/n(C) of sample (UV 5d +water 5d + UV 5d) was smaller but the *f<sup>A</sup>* and *CI* were greater. In addition, it could be seen from Table 4 that the rangeability of *C<sup>I</sup>* between the sample (UV 5d + water 5d and UV 5d) and the sample (UV 5d + water 5d) was 1.25 times that between the sample (UV 10d) and the sample (UV 5d), demonstrating that water could increase the sensitivity of element composition to UV. **Table 6.** Element content of asphalt after the aging cycle of UV and water (%).

5d) had the smaller n(H)/n(C), the greater *f<sup>A</sup>* and *C<sup>I</sup>* than the sample (UV 10d), meaning

**Samples C H N S O** UV 5d 82.86 10.21 0.72 4.37 1.84 UV 5d + water 5d 82.86 10.21 0.71 4.34 1.88 UV 10d 82.86 10.20 0.72 4.36 1.86 UV 15d 82.67 10.17 0.72 4.34 2.10 UV 5d + water 5d + UV 5d 82.61 10.16 0.72 4.35 2.16 UV 5d + water 5d 82.86 10.21 0.71 4.34 1.88 UV 10d 82.86 10.20 0.72 4.36 1.86 UV 15d 82.67 10.17 0.72 4.34 2.10 UV 5d + water 5d + UV 5d 82.61 10.16 0.72 4.35 2.16

*Materials* **2022**, *15*, x FOR PEER REVIEW 14 of 19

**Figure 8.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *CI*) of asphalt after the aging cycle of UV and water. **Figure 8.** Important indexes (n(H)/n(C), *f<sup>A</sup>* and *C<sup>I</sup>* ) of asphalt after the aging cycle of UV and water.

#### *3.4. Chemical Structure*

*3.4. Chemical Structure* The change of element composition and chemical structure are the fundamental reason for the change of rheological properties. The effect of multiple aging on chemical structure were characterized by FTIR test. Figure 9 illustrates that the *IC=O* and *IS=O* of asphalt after the multiple aging of heat and UV. The *IC=O* of virgin asphalt was close to 0, while the *IS=O* was far greater than the *IC=O*. It shows that the virgin asphalt was not oxidized and some parts of S element belong to S=O of asphalt itself [43]. Compared with the virgin, the *IC=O* of samples increased by 0.06, 0.11, 0.15 and 0.17, while the *IS=O* samples increased by 0.21, 0.35, 0.45 and 0.53 after TFOT aging, UV 5d, UV 10d and UV 15d. The The change of element composition and chemical structure are the fundamental reason for the change of rheological properties. The effect of multiple aging on chemical structure were characterized by FTIR test. Figure 9 illustrates that the *IC=O* and *IS=O* of asphalt after the multiple aging of heat and UV. The *IC=O* of virgin asphalt was close to 0, while the *IS=O* was far greater than the *IC=O*. It shows that the virgin asphalt was not oxidized and some parts of S element belong to S=O of asphalt itself [43]. Compared with the virgin, the *IC=O* of samples increased by 0.06, 0.11, 0.15 and 0.17, while the *IS=O* samples increased by 0.21, 0.35, 0.45 and 0.53 after TFOT aging, UV 5d, UV 10d and UV 15d. The coupling of thermaloxygen and UV could accumulate to promote the asphalt oxidation. It indicated that asphalt aging increased polar functional groups, such as C=O and S=O, which had permanent

coupling of thermal-oxygen and UV could accumulate to promote the asphalt oxidation.

the intermolecular friction resistance of asphalt [44]. The high-temperature rutting resistance was improved, and the low-temperature cracking resistance was weakened, which was shown in the DSR and BBR results. The rangeability of *IC=O* and *IS=O* under different aging methods was compared in Table 7. It could be seen that the rangeability

dipoles and generate electrostatic force, resulting in the increase in the intermolecular friction resistance of asphalt [44]. The high-temperature rutting resistance was improved, and the low-temperature cracking resistance was weakened, which was shown in the DSR and BBR results. The rangeability of *IC=O* and *IS=O* under different aging methods was compared in Table 7. It could be seen that the rangeability caused by TFOT was greater than that caused by UV 5d, and the rangeability gradually decreased with UV aging time, indicating the sensitivity of the asphalt oxidation to UV decreased with the deepening of the aging degree. Because in the short-term aging, asphalt aging to generate carbonyl and sulfoxide group. During UV aging, the carbonyl and sulfoxide groups decompose to form long chains or rings, and the aromatics and colloid converted to asphaltenes, promoting the further aging of asphalt [45]. Therefore, the preventing formation of C=O and S=O and the synthesis of long chain can delay the asphalt aging to contribute to the sustainable development of the asphalt pavement [46]. caused by TFOT was greater than that caused by UV 5d, and the rangeability gradually decreased with UV aging time, indicating the sensitivity of the asphalt oxidation to UV decreased with the deepening of the aging degree. Because in the short-term aging, asphalt aging to generate carbonyl and sulfoxide group. During UV aging, the carbonyl and sulfoxide groups decompose to form long chains or rings, and the aromatics and colloid converted to asphaltenes, promoting the further aging of asphalt [45]. Therefore, the preventing formation of C=O and S=O and the synthesis of long chain can delay the asphalt aging to contribute to the sustainable development of the asphalt pavement [46].

*Materials* **2022**, *15*, x FOR PEER REVIEW 15 of 19

**Figure 9.** *IC=O* and *IS=O* of asphalt after the multiple aging of heat and UV. **Figure 9.** *IC=O* and *IS=O* of asphalt after the multiple aging of heat and UV.

**Table 7.** Rangeability of *IC=O* and *IS=O* after the multiple aging.


UV 5d/UV 5d + water 5d 0.03 0.07 UV 5d + water 5d/UV 5d + water 5d + UV 5d 0.10 0.45 After the multiple aging of UV and aqueous solution, the *IC=O* and *IS=O* of asphalt are illustrated in Figure 10. After immersion in water, saline solution, acid solution and alkali solution, the *IC=O* increased by 25.31%, 50.38%, 67.08% and 136.42%, while the *IS=O* increased by 7.22%, 21.02%, 29.60% and 90.27%. This increment was greater than the increment when UV and aqueous solution are treated asphalt simultaneously, indicating that sequential treatment has a greater impact on asphalt than simultaneous treatment [18]. Aqueous solution could accelerate the asphalt oxidation after UV aging, and the order of After the multiple aging of UV and aqueous solution, the *IC=O* and *IS=O* of asphalt are illustrated in Figure 10. After immersion in water, saline solution, acid solution and alkali solution, the *IC=O* increased by 25.31%, 50.38%, 67.08% and 136.42%, while the *IS=O* increased by 7.22%, 21.02%, 29.60% and 90.27%. This increment was greater than the increment when UV and aqueous solution are treated asphalt simultaneously, indicating that sequential treatment has a greater impact on asphalt than simultaneous treatment [18]. Aqueous solution could accelerate the asphalt oxidation after UV aging, and the order of the effect degree is as follows: alkali > acid > salt > water. Figure 11 shows the *IC=O* and *IS=O* of asphalt after aging cycle of UV and water. The sample (UV 5d + water 5d) had the lower *IC=O* and *IS=O* than the sample (UV 10d), denoting water had the less effect on chemical structure than UV. However, the *IC=O* and *IS=O* of sample (UV 5d + water 5d + UV 5d) were greater than that of sample (UV 15d). Moreover, from Table 7, it can be seen

the effect degree is as follows: alkali > acid > salt > water. Figure 11 shows the *IC=O* and *IS=O* of asphalt after aging cycle of UV and water. The sample (UV 5d + water 5d) had the lower

structure than UV. However, the *IC=O* and *IS=O* of sample (UV 5d + water 5d + UV 5d) were greater than that of sample (UV 15d). Moreover, from Table 7, it can be seen that the rangeability *IC=O* and rangeability *IS=O* between sample (UV 5d +water 5d + UV 5d) and sample (UV 5d + water 5d) was 2.5 and 4.5 times as much as that between the sample (UV 10d) and the sample (UV 5d), respectively. It shows that water could increase the sensitivity of

asphalt chemical structure to UV. That agreed with the result of existing studies [47].

that the rangeability *IC=O* and rangeability *IS=O* between sample (UV 5d +water 5d + UV 5d) and sample (UV 5d + water 5d) was 2.5 and 4.5 times as much as that between the sample (UV 10d) and the sample (UV 5d), respectively. It shows that water could increase the sensitivity of asphalt chemical structure to UV. That agreed with the result of existing studies [47]. *Materials* **2022**, *15*, x FOR PEER REVIEW 16 of 19 *Materials* **2022**, *15*, x FOR PEER REVIEW 16 of 19

2

**Figure 10.** *IC=O* and *IS=O* of asphalt after the multiple aging of UV and aqueous solution. **Figure 10.** *IC=O* and *IS=O* of asphalt after the multiple aging of UV and aqueous solution. **Figure 10.** *IC=O* and *IS=O* of asphalt after the multiple aging of UV and aqueous solution.

.

.

**Figure 11.** *IC=O* and *IS=O* of asphalt after the aging cycle of UV and water. (**a**) *IC=O*, (**b**) *IS=O*.**Figure 11.** *IC=O* and *IS=O* of asphalt after the aging cycle of UV and water. (**a**) *IC=O*, (**b**) *IS=O*.

**Figure 11.** *IC=O* and *IS=O* of asphalt after the aging cycle of UV and water. (**a**) *IC=O*, (**b**) *IS=O*.
