Enhancement of Anti-UV Aging Performance of Asphalt Modified by UV-531/Pigment Violet Composite Light Stabilizers

Abstract

Ultraviolet (UV) radiation accelerates the aging of asphalt pavements and shortens the service life of the pavement. To effectively mitigate the impact of UV aging on asphalt performance, a novel composite anti-UV aging agent, 2-hydroxy-4-n-octyoxybenzophenone/pigment violet (UV-531/PV), was developed. After UV-accelerated aging, the modified asphalt samples were characterized by conventional performance tests, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and a dynamic shear rheometer (DSR). The results show that UV-531/PV-composite-modified asphalt maintains excellent conventional properties after UV aging. The FTIR testing showed that the changes in carbonyl index (I_c=o) and sulfoxide index (I_s=o) of the composite-modified asphalt were significantly smaller than those of the matrix asphalt, indicating the less oxidation degree of the composite-modified asphalt. The GPC test results showed that the change in molecular weight of the composite-modified asphalt after UV aging was less than that of the matrix asphalt. DSR results showed that UV-531/PV-modified asphalt exhibited higher viscoelasticity and higher rutting resistance than unmodified asphalt. This study proposes a new method for preparing anti-UV aging asphalt, which can be used for micro-surfacing, fog sealing or ultra-thin overlay on road surfaces.

1. Introduction

Asphalt is a significant byproduct in refining petroleum or is found in natural beds, and is mainly used in paving, roofing, and waterproofing. Asphalt pavements, due to their cost-effectiveness and superior road performance, are the preferred choice in road construction. However, asphalt is prone to aging during refining, storage, transportation, and construction, which can lead to a series of issues such as cracking, rutting, potholes, and softening of the pavement, thus shortening its service life. The aging of asphalt pavements is primarily caused by thermal-oxidative aging and photo-oxidative aging [1]. Photo-oxidative aging mainly refers to the long-term ultraviolet irradiation that occurs throughout the service life of the mixture, due to the action of oxygen and UV radiation. When the chemical bond in asphalt is broken and the molecular structure is damaged, the asphalt material gradually loses its original flexibility and elasticity, and becomes brittle and hard, thus affecting the road performance of asphalt pavements [2].

A common method to prevent UV aging of asphalt is to add anti-aging modifiers such as UV absorbers, nano oxides, layered materials, and other inorganic and organic materials that shield or absorb UV rays [3,4,5]. For example, Jamal et al. added waste tire compound to asphalt and found that the waste rubber powder-modified asphalt had better resistance to ultraviolet radiation compared to the standard unmodified asphalt [6]. He et al. discovered that the inclusion of lignosulfonate-grafted layered double hydroxides in asphalt enhanced its resistance to UV aging [7]. Rajib et al. introduced biochar slag into pure asphalt and rubberized asphalt, and found that compared with pure asphalt, biochar did not significantly improve the UV aging resistance of rubberized asphalt [8]. Xiao et al. prepared organic montmorillonite/ethylene vinyl acetate/bitumen composites, which exhibited good rutting resistance, high elasticity, and superior crack resistance [9]. Tur Rasool et al. added highly recycled rubber (HRR) to SBS-modified bitumen, and studies showed that HRR can improve the aging resistance and physical properties of SBS-modified asphalt [10]. Yang et al. synthesized titanium dioxide/polystyrene-reduced graphene oxide, which was added to SBS asphalt and found to effectively inhibit the increase in carbonyl functional groups caused by UV aging [11]. However, these anti-aging agents have limitations in the UV absorption wavelength range and are prone to aggregation, which adversely affects their modification and anti-UV aging efficiency.

Light stabilizers extend the life of asphalt by absorbing UV energy, quenching singlet oxygen, and breaking down hydroperoxides into inactive substances [12]. Among different kinds of light stabilizers, UV-531 is popular in the market for its non-toxicity, good compatibility and low melting point. Zhong et al. prepared SiO₂-UV-531 material to enhance the migration and thermal stability of UV absorbers in polymer composites [13]. Zheng Gang et al. discovered that the addition of UV-531 not only improved the UV aging resistance but also enhanced both the high and low temperature performance of SBS-modified asphalt [14]. Souza et al. found that the combination of carbon black and hindered amine light stabilizer (HALS) minimized photodegradation phenomena [15]. Sun et al. discovered that hindered amine light stabilizers can effectively inhibit the UV aging behavior of asphalt. However, the UV aging resistance of the asphalt is related to the dispersibility of the light stabilizers [16] Hong et al. concluded that SBS-modified asphalt has excellent UV aging resistance at the optimal dosage of UV-531 [17]. However, UV-531, as an organic anti-aging agent, is prone to self-degradation, which reduces its protection against asphalt [18]. This problem, however, may be overcome by compounding UV-531 with other materials. High-performance pigments with high solvent resistance, light resistance, thermal stability, and reducing properties [19], are frequently used in various fields such as films, spinning, plastic resins, and automotive paints. However, to the best of our knowledge, there is currently no research on using high-performance pigments in asphalt to resist UV aging. Therefore, a composite of pigments and UV-531 can combine the advantages of both to improve the weather resistance of UV-531, thereby enhancing the UV aging resistance of asphalt.

This study involved the preparation of a composite light stabilizer material by melt blending the light stabilizer UV-531 with a high-performance pigment [20]. Accelerated UV-simulated aging experiments were conducted on the modified asphalt. The anti-UV aging performance of asphalt was analyzed through routine performance tests (ductility, penetration, and softening point [21,22]). FTIR and GPC were used to analyze the changes of functional group content and the molecular weight of asphalt before and after aging. The rheological properties of asphalt before and after aging were analyzed by dynamic shear rheometer (DSR), and the aging resistance and fatigue cracking properties of asphalt were studied.

2. Experimental Section

2.1. Materials

The Chuanhai Brand No. 70 matrix asphalt (SK-70A, Zibo, China) was used, and its basic properties are shown in

Table 1. Physical properties of SK-70A asphalt.

Items	Test Values	Test Methods
Penetration (25 °C, 0.1 mm)	66	T0604
Softening point (°C)	47	T0606
Ductility (10 °C, cm)	39	T0605
Viscosity (60 °C, Pa·s)	207	T0602

. UV-531 (Nona Technology Co., Ltd., Wuhan, China) and the pigment violet (2BR) (Kunshan Kairos International Trade Co., Ltd., Kunshan, China).

The UV-accelerated aging device was assembled in our laboratory. The UV lamp was provided by experts from Nanjing Hua Qiang Special Light Source, with a power of 30 W and a wavelength of 340 nm.

2.2. Preparation of Modified Asphalt

The mechanism is as follows: the ultraviolet agent absorbs the energy of ultraviolet rays to reduce the damage of ultraviolet rays to asphalt, and the anti-ultraviolet additives do not react with asphalt, so asphalt modification is generally carried out by physical mixing.

UV-531-modified asphalt: Weigh 240 g of matrix asphalt and heat it in a 130 °C oven for 30 min until molten state and take it out. Stir it with a Fluke agitator (Shanghai Fluke Technology Development Co., Ltd., Shanghai, China) at 1000 rpm for 5 min. Add 1.44 g UV-531 (0.6% relative to matrix asphalt) to the asphalt, agitating at a speed of 1500 rpm for 10 min and at 275 rpm for 5 min.

Pigment Violet (PV) modified asphalt: The preparation process is the same as above. 0.3% (relative to the asphalt) of PV is used.

Compound modified asphalt: The preparation process is the same as above. Add 0.6% UV-531 to the asphalt, stir at a speed of 1500 rpm for 10 min, then add 0.3% pigment violet, continue stirring for 15 min, and at 275 rpm for 5 min.

2.3. UV Aging Test

At present, there are three main forms of asphalt ultraviolet aging: direct ultraviolet aging of asphalt, thermal oxygen pretreatment ultraviolet aging, and hydrothermal ultraviolet coupling aging, which are used to simulate outdoor sunlight radiation, asphalt production and use processes, and complex natural environments in actual use [23]. According to the method described in the literature, the UV-accelerated aging test was carried out on asphalt by direct UV aging in a self-made aging test chamber in the laboratory. Weigh 15 ± 0.1 g of modified asphalt into a Petri dish with a diameter of 14 cm. Heat the Petri dish in an oven at 130 °C for 20 min so that the asphalt is evenly spread on the surface of the Petri dish and the thickness of the asphalt film is about 1 mm. Finally, put the samples into a UV-accelerated aging device with a wavelength of 340 nm and a radiation intensity of 300 W/m² for ultraviolet aging experiments, and keep the temperature at room temperature all the time. The UV aging time was 0 h, 48 h, 84 h, 108 h and 144 h, respectively.

2.4. Characterization Methods

2.4.1. Characterization of Asphalt Conventional Performance

Asphalt conventional performances, including softening point, ductility (10 °C), and penetration (25 °C) were measured based on T0606-2011, T0605-2011, and T0604-2011 in the Test Specification for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011), respectively.

2.4.2. FTIR Test

Ultraviolet radiation can destroy chemical bonds in asphalt, generate free radicals, and cause changes in the content of functional groups in asphalt [24]. Therefore, FTIR testing was used to characterize the C=O and S=O content in the asphalt molecule to explore the aging of asphalt. The samples were dissolved in tetrachloromethane and dropped onto compressed KBr plate. FTIR spectra were measured by using a Bruker Vertex 70 device (Bruker Corporation Germany, Massachusetts, US). I_C=O and I_S=O were calculated using a total area of 2000–600 cm⁻¹ [25].

$${\mathrm{I}}_{\mathrm{c}=\mathrm{O}}={\displaystyle \frac{{\mathrm{A}}_{1700{\mathrm{c}\mathrm{m}}^{-1}}}{{\mathrm{A}}_{2000-600{\mathrm{c}\mathrm{m}}^{-1}}}}$$

(1)

$${\mathrm{I}}_{\mathrm{S}=\mathrm{O}}={\displaystyle \frac{{\mathrm{A}}_{1030{\mathrm{c}\mathrm{m}}^{-1}}}{{\mathrm{A}}_{2000-600{\mathrm{c}\mathrm{m}}^{-1}}}}$$

(2)

2.4.3. GPC Test

Asphalt is a polymer organic mixture, and its structure and molecular weight may change greatly after aging. Thus, asphalt samples were dissolved in tetrahydrofuran (THF) and measured using GPC (WATERS1515). The formula used to calculate M_n and M_w, as well as the PDI, are as follows:

$$\mathrm{M}\mathrm{n}={\displaystyle \frac{\sum _{\mathrm{i}}{\mathrm{n}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}}{\sum _{\mathrm{i}}{\mathrm{n}}_{\mathrm{i}}}}=\sum _{\mathrm{i}}{\mathrm{x}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}$$

(3)

$$\mathrm{M}\mathrm{w}={\displaystyle \frac{\sum _{\mathrm{i}}{\mathrm{n}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}^2}{\sum _{\mathrm{i}}{\mathrm{n}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}}}={\displaystyle \frac{\sum _{\mathrm{i}}{\mathrm{m}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}}{\sum _{\mathrm{i}}{\mathrm{m}}_{\mathrm{i}}}}=\sum _{\mathrm{i}}{\mathrm{w}}_{\mathrm{i}}{\mathrm{M}}_{\mathrm{i}}$$

(4)

$$\mathrm{P}\mathrm{D}\mathrm{I}={\displaystyle \frac{\mathrm{M}\mathrm{w}}{\mathrm{M}\mathrm{n}}}$$

(5)

where: Mn = number-average molecular weight; Mw = weight-average molecular weight; PDI = polydispersity.

2.4.4. Dynamic Shear Rheometer (DSR) Test

According to the SHRP specification, the rheological properties of asphalt before and after aging were tested using DSR (Bohlin CVO 100D ADS) (Thermo Fisher Scientific, Waltham, MA, USA) to evaluate its ability to resist UV aging [26]. Temperature scans were performed on samples with different degrees of aging according to the T0628-2011 standard [27]. The diameter and thickness of the sample were 25 mm and 1 mm, respectively. The temperature scanning range was 5~85 °C, the heating rate was 5 °C/min, and the stress was 0.14 kPa.

The UV wavelength absorption ranges of PV, UV-531, and the UV-531/PV composite are characterized by using a LAMBDA 650 UV-vis spectrophotometer (Youke Instruments Co., Ltd., Shanghai, China) with a wavelength range of 200 to 800 nm.

3. Results and Discussion

3.1. UV-Vis Spectra Analysis of Anti-UV Agents

The UV-vis spectra of PV, UV-531 and UV-531/PV composite were measured to explore the wavelength range of UV absorption. Figure 1 shows that UV-531 can absorb ultraviolet light with wavelengths ranging from 240 nm to 340 nm, and PV can absorb ultraviolet light with wavelengths ranging from 200 nm to 375 nm and visible light from 490 nm to 630 nm. The UV-531/PV composites absorb ultraviolet light with wavelengths ranging from 200 nm to 383 nm and visible light from 490 nm to 630 nm. This result indicates that UV-531/PV composite increases the light absorption range of UV light. The UV rays in sunlight can only reach the Earth’s surface with short wavelength (290–320 nm) and long wavelength (320–400 nm), which are not completely absorbed when passing through the ozone layer in the atmosphere [28]. Therefore, for UV rays passing through the atmosphere, all three materials have an absorption effect on UV rays in sunlight. However, when PV is combined with UV-531, its UV absorption wavelength range becomes wider, which is expected to have better resistance to UV aging of asphalt.

3.2. Effect of Anti-UV Agents on the Conventional Performance of Asphalt Before and After UV Aging

The conventional performances of asphalt are an important basis for the selection of asphalt in practical engineering. Figure 2 displays the conventional performance of matrix asphalt, UV-531-modified asphalt, PV-modified asphalt, and UV-531/PV-composite-modified asphalt without UV aging. Compared to the matrix asphalt, the conventional performance of UV-531-modified asphalt remains largely unaltered, and PV-modified asphalt exhibits a slight reduction in ductility and penetration. However, there is no significant difference in the softening point, penetration, and ductility between UV-531/PV-composite-modified asphalt and matrix asphalt. This suggests that compounding UV-531 with PV can reduce the adverse effects of PV and improve PV compatibility with asphalt [29].

Figure 3a displays the softening point values of four distinct types of asphalt after UV aging for different times. One can see that the softening point gradually increases with the aging time. After 108 h of UV aging, the softening point of the matrix asphalt increased from 49.0 to 51.3 °C, which is a 4.6% increase. Similarly, the softening point of UV-531-modified asphalt increased from 49.5 to 51.7 °C, which is a 4.4% increase. After 144 h of UV aging, the softening point of PV-modified asphalt increased from 50.3 to 51.3 °C, which is a 2% increase. However, the softening point of UV-531/PV-composite-modified asphalt only increased from 50.5 to 50.8 °C even after UV aging for 144 h, indicating that the composite-modified asphalt has better UV aging resistance.

Figure 3b displays the ductility values of four types of asphalt after UV aging for different times. A gradual decrease in ductility with increasing aging time was observed. After 108 h of UV aging, the ductility of the matrix asphalt decreased from 28.7 to 16.8 cm, a decrease of 41.5%. The ductility of UV-531-modified asphalt decreased from 28.5 to 19.7 cm, a decrease of 30.9%. After 144 h of UV aging, the ductility of PV-modified asphalt decreased from 23.8 to 19.7 cm, a decrease of 17.2%. After 144 h of UV aging, the ductility of the UV-531/PV-modified asphalt decreased from 27.6 to 25.4 cm, a reduction of 8.0%, which is much lower than that of the other three types of asphalt, also indicating that the composite-modified asphalt has better resistance to UV aging.

Figure 3c displays the penetration values of four distinct types of asphalt after UV aging. As the aging time increases, the penetration gradually decreases for all samples. For instance, after 108 h of UV aging, the penetration of the matrix asphalt decreased from 61.5 to 52.5, which is a reduction of 14.6%. Similarly, the penetration of UV-531-modified asphalt decreased from 62.8 to 54.28, a reduction of 13.6%. After 144 h of UV aging, the penetration of PV-modified asphalt decreased from 53.93 to 49.6, which is a reduction of 8%. After 144 h of UV aging of the composite-modified asphalt, the penetration decreased from 55.27 to 52.9, a reduction of 4.3%. The reduction in penetration was lower than that of the other three types of asphalt, indicating that the composite-modified asphalt has better resistance to UV aging. After 108 h of UV irradiation, both the matrix asphalt and UV-531 modified asphalt had undergone severe aging. Therefore, it is not recommended to extend the aging time any further. After 144 h of UV aging, the changes in the three indicators of the UV-531/PV-composite-modified asphalt were much smaller than those of the other three asphalt samples, indicating that the UV-531/PV-composite-modified asphalt has a more significant effect in preventing UV aging.

3.3. Functional Group Analysis of the Modified Asphalts After UV Aging

Strong UV irradiation can destroy the chemical bonds in asphalt, causing the chromogenic groups in the molecules to enter the excited state, generating a large number of reactive groups, intensifying the aging of asphalt, and oxidizing the unsaturated carbon chain in asphalt to carbonyl groups (C=O) and sulfur to sulfoxide groups (S=O) [30,31,32]. Therefore, the degree of aging of asphalt can be assessed by quantitative calculations of carbonyl and sulfoxide groups before and after aging. As can be seen from Figure 4, the FTIR spectra of the modified asphalt after UV aging has stretching vibration peaks at 1700 and 1030 cm⁻¹, corresponding to C=O and S=O groups, respectively [33].

Table 2. I_C=O and I_S=O of the unaged and UV-aged asphalt.

Asphalt	C=O	S=O	IC=O	IS=O
Matrix asphalt (UV-0 h)	0.03	0.15	0.0076	0.0379
Matrix asphalt (UV-108 h)	0.4	0.32	0.1028	0.0804
UV-531/asphalt (UV-0 h)	0.0738	0.0503	0.0489	0.0333
UV-531/asphalt (UV-108 h)	0.2	0.364	0.0517	0.094
PV/asphalt (UV-0 h)	0.0143	0.1467	0.0026	0.027
PV/asphalt (UV-144 h)	0.2126	1.1572	0.0131	0.0712
UV-531/PV/asphalt (UV-0 h)	0.0178	0.0503	0.0118	0.0333
UV-531/PV/asphalt (UV-144 h)	0.028	0.0755	0.0154	0.0414

displays the values of I_C=O and I_S=O before and after the aging process of various types of asphalt. It can be seen that the I_C=O and I_S=O values of asphalt increase after UV aging. The I_C=O and I_S=O are 0.0076 and 0.0379, respectively, for the unaged matrix asphalt. After 108 h of UV aging, I_C=O and I_S=O increase to 0.1028 and 0.0804, respectively, illustrating that ultraviolet radiation destroys the molecular structure of asphalt and accelerates the aging rate of asphalt. In contrast, the I_C=O and I_S=O values of UV-531/PV-composite-modified asphalt before aging are 0.0118 and 0.0333, respectively. After a 144 h UV aging, the I_C=O and I_S=O values of composite-modified asphalt increase to 0.0154 and 0.0414, respectively. These data show that the growth rate of the I_C=O and I_S=O values of matrix asphalt is the highest, while the growth rate of the UV-531/PV-composite-modified asphalt is the lowest among the four types of asphalt. This suggests that the UV-531/PV composite can protect asphalt against structural damage and slow down the oxidation reaction of asphalt caused by UV light. The C=C double bond in asphalt can react with other additives to improve the properties of asphalt, such as anti-aging properties. After the UV aging test, the I_C=O values of the four asphalts increased, indicating that the asphalt had aged and the C=C bond was broken, resulting in the decline of the anti-aging performance of the asphalt. Among them, the composite-modified asphalt did not change much before and after UV aging, indicating that UV-531/PV greatly inhibited the oxidation and deterioration of matrix asphalt, thereby improving its oxidation resistance and UV aging resistance.

3.4. Analysis of Changes in Asphalt Molecular Weight

GPC is used to test the molecular weight and polydispersity index (PDI) of an asphalt sample before and after UV aging [34,35,36]. After UV aging, asphalt experiences intermolecular associates and polycondensation reactions, leading to a reduction in light components and an increase in heavy components. The severity of asphalt aging is directly proportional to the proportion of asphaltenes in the asphalt, which accounts for a greater proportion of the total molecular weight [37].

Figure 5 displays the GPC curves of matrix asphalt and UV-531/PV-composite-modified asphalt before and after UV aging. One can see that after UV aging for 108 h, the matrix asphalt experiences material outflow within 30 to 32 min, and the curve shifts to the left, indicating the presence of components with larger molecular weights in the system. The UV-531/PV-composite-modified asphalt before and after aging maintains a similar curve graph, indicating the composite-modified asphalt is more stable and less affected by UV aging. This phenomenon can be attributed to the mutual conversion of neighboring molecules. However, the rate of decomposition of small molecules into lighter components after absorption of heavier components is significantly lower than the conversion of lighter components into heavier components, leading to an increase in molecular weight [38].

Table 3. M_n, M_w, and PDI of matrix asphalt and UV-531/PV-composite-modified asphalt before and after UV aging.

Sample	Aging Time (h)	Mn	Mw	PDI
Matrix asphalt	0	1165	1339	1.1495
	108	1310	1657	1.2647
UV-531/PV modified asphalt	0	1136	1335	1.1753
	144	1122	1354	1.2067

shows that M_n, M_w, and D of the matrix asphalt increased after UV aging. Prior to aging, the M_n, M_w and D of the asphalt were 1165, 1339, and 1.1495. After UV aging for 108 h, the M_n, M_w and D values were changed to 1310, 1657, and 1.2647, respectively. This represents an increase of 12.4% for M_n, 23.7% for M_w, and 10.2% for PDI. For UV-531/PV-composite-modified asphalt, before aging M_n, M_w, and PDI were 1136, 1335, and 1.1753, respectively. After a 144 h UV aging, M_n decreased by 1.2%, while M_w increased by 1.4% and PDI increased by 2.6%, with Mn and Mw values of 1122 and 1354, respectively, and PDI value of 1.2067. The results indicate that after 108 h of UV aging, the matrix asphalt exhibited significant signs of aging. The molecular weight of the asphalt increased dramatically, resulting in poor molecular dispersion within the asphalt. This is because chemical reactions such as oxidation and polymerization occur during the aging process of asphalt, which increases the average molecular weight of asphalt. In addition, the molecular weight of asphaltene in asphalt material is larger, and the increase in molecular weight indicates that the asphaltene content increases, which is also the reason why asphalt becomes hard and brittle after aging [39]. However, the molecular weight of UV-531/PV-composite-modified asphalt did not change significantly after 144 h of UV aging. Additionally, the dispersion of molecules remained stable, indicating that the addition of UV-531/PV inhibited intermolecular polycondensation and association reactions [37]. Therefore, the UV-531/PV-composite-modified asphalt exhibits strong resistance to UV aging.

3.5. Rheological Property Analysis

The rheological properties of the modified asphalt after aging can be studied using a DSR. The DSR test was carried out at temperatures ranging from 0 to 80 °C on asphalt samples to analyze the effects of temperature and UV aging on the complex modulus G* of asphalt. The complex modulus G* is composed of two parts: G′ (the recoverable elastic part of the asphalt) and G″ (the non-recoverable viscous part). As asphalt ages, the elastic portion typically transforms into a viscous portion [40].

Figure 6 shows that as the temperature increases, G′ decreases. This may be because the elastic part of the asphalt converts to the viscous part under the influence of temperature, which reduces its viscous property. Furthermore, within the experimental temperature range, the addition of UV-531/PV composite improved the storage modulus of asphalt. This suggests that UV-531/PV composite can enhance the fatigue resistance properties of asphalt at room temperature and the permanent deformation resistance properties at high temperature [41]. By comparing the data of matrix asphalt (Figure 6a) with the data of UV-531/PV-composite-modified asphalt (Figure 6b) before and after aging, it is evident that the value of G′ increased for both types of asphalt after the UV aging. The difference in G′ between the two types of asphalt was observed to be matrix asphalt > UV-531/PV-composite-modified asphalt. The severity of the aging degree of asphalt is directly proportional to the increment of G′. Compared to the unaged sample, the G′ of the matrix asphalt increased by 45.1%, while the G′ of the UV-531/PV-composite-modified asphalt increased by 19.2%. This suggests that the UV-531/ PV-composite-modified asphalt aged less than the matrix asphalt. The UV-531/ PV has a dual role: to shield the asphalt from UV light and to slow down the reduction of elastic components during asphalt aging.

Figure 7 shows a decreasing trend of G″ with increasing temperature. Additionally, the loss modulus of asphalt improved with the addition of UV-531/PV composite in the range of temperature studied. This suggests that the addition of UV-531/PV composite enhanced the elasticity and viscosity of the asphalt [42]. When comparing the data of the matrix asphalt in Figure 7a with the UV-531/PV-composite-modified asphalt in Figure 7b, it is evident that the G″ values have increased after the UV aging test, indicating a corresponding increase in viscosity. However, the increasing trend of the UV-531/PV-composite-modified asphalt is gentler compared to the matrix asphalt. These results indicate that the UV-531/PV-composite-modified asphalt is more effective in resisting UV aging.

4. Conclusions

In summary, a novel UV-531/PV composite system has been developed to improve the anti-UV aging performance of asphalt. The results illustrate that the UV-531/PV composite system can extend the UV absorption wavelength range. Upon the addition to asphalt, the UV-531/PV-composite-modified asphalt exhibits good UV aging resistance. FTIR results indicate that the changes in the I_C=O and I_S=O values of the UV-531/PV-composite-modified asphalt before and after aging are much smaller than those of the matrix asphalt. The GPC results indicate that the molecular weight and polydispersity index of UV-531/PV-composite-modified asphalt largely remain unchanged after UV aging. The DSR test showed that incorporation of UV-531/PV improved the elasticity and the recovery rate of the asphalt. In summary, the UV-531/PV composite system-modified asphalt has better resistance to UV aging and can be used for micro-surfacing, fog sealing or ultra-thin overlay on road surfaces.