Compatibility of Buton rock asphalt with petroleum asphalt and their multi-scale ultraviolet aging behavior

Introduction: Ultraviolet (UV) radiation is one of the primary environmental factors causing performance degradation of asphalt pavements, while the compatibility between modifiers and petroleum asphalt significantly influences the aging resistance of modified asphalt. This study aims to elucidate the compatibility between Buton rock asphalt (BRA) and petroleum asphalts as well as the influence of compatibility on UV aging behavior.

Methods: The compatibility of BRA (at a dosage of 30 wt%) with four base asphalts (Maoming Petrochemical 70# (70-A), Donghai 70# (70-B), Shuanglong 70# (70-C), and Panjin 90# (90-D)) was evaluated through physical property tests and dynamic shear rheometer (DSR) measurements. The thin-film oven test (TFOT) was employed to simulate short-term thermo-oxidative aging during construction, followed by multi-cycle variable-intensity UV aging to simulate long-term photo-oxidative aging during service. Viscosity, DSR, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) tests were used to analyze multi-scale ultraviolet aging behavior.

Results: 70-A exhibits the best compatibility with BRA, with its modified asphalt (70-A-MA) showing a softening point of 50.5 °C (an increase of 11.0%), moderate viscosity growth (37.1%), and good storage stability. The increments in viscosity aging index and rutting factor aging index of 70-A-MA are lower than those of 90-D-MA, and 70-A-MA maintains lower surface crack density. FTIR analysis shows that the total growth rates of carbonyl and sulfoxide indices for 70-A-MA (70.4% and 42.5%) are significantly lower than those for 90-D-MA (202.0% and 131.7%); GPC results indicate that the total large molecular size (LMS) content increase for 70-A-MA (30.0%) is also lower than that for 90-D-MA (68.2%).

Discussion: These results demonstrate that the type of base asphalt is a key factor influencing its compatibility with BRA. Modified asphalt with superior compatibility exhibits better chemical stability and less severe aging damage. This study provides scientific guidance for the selection of base asphalt in BRA modification applications.

1 Introduction

Asphalt pavements have become the predominant choice in road engineering due to their excellent service performance (He et al., 2023; Styer et al., 2024; Zhu et al., 2025). However, during long-term service, asphalt pavements are subjected to multiple factors, including traffic loading and environmental effects, which cause gradual performance deterioration and seriously affect pavement service life and driving safety (Duan et al., 2024; Soenen et al., 2022; Yang et al., 2023). As one of the primary environmental degradation factors in outdoor environments, ultraviolet (UV) radiation can induce photo-oxidative reactions in asphalt molecular chains, causing changes in chemical composition and microstructure, ultimately leading to a series of macroscopic performance deterioration phenomena, including decreased low-temperature cracking resistance and shortened fatigue life (Yu et al., 2019; Zheng et al., 2025). Therefore, gaining a thorough understanding of the UV aging mechanisms of asphalt materials and improving their aging resistance is of great significance for extending the service life of asphalt pavements.

Buton rock asphalt (BRA), as a natural asphalt modifier, has attracted widespread attention in road engineering due to its excellent high-temperature stability and aging resistance (Lv et al., 2019; Li C. et al., 2024). Previous studies have confirmed that the incorporation of BRA can effectively enhance the viscoelastic properties and high-temperature performance of asphalt (Su et al., 2022; Li C. et al., 2024). Current research on BRA-modified asphalt has made considerable progress. In regard to BRA-modified asphalt component compatibility research, Zhang et al. indicated that when the BRA content exceeds a certain proportion, the ash content in BRA becomes the primary factor responsible for the decline in low-temperature performance of the modified asphalt (Zhang et al., 2023). Su et al. found that when the BRA particle size is ≤ 13.6 μm, the compatibility of the modified asphalt is significantly improved, with low segregation and good storage stability (Su et al., 2022). Li et al. found that activation treatments (such as grinding and heating) can effectively enhance the molecular polarity of BRA. The BRA-modified asphalt prepared by the wet process showed significant improvements in both high-temperature performance and aging resistance. Moreover, when the BRA content is 30%, the modified asphalt achieves an optimal balance between service performance and anti-segregation properties (Li et al., 2020). In regard to BRA-modified asphalt aging behavior research, existing studies have shown that UV aging typically causes an initial improvement in the high-temperature performance of BRA-modified asphalt, but this may decline after excessive aging, while the low-temperature performance deteriorates significantly (Fan et al., 2019; Gao et al., 2022; Li L. et al., 2024). Lv et al. found that for BRA-modified asphalt, the unique honeycomb structure of BRA ash may influence stress distribution and crack propagation paths during the aging process, thereby exhibiting distinct microstructural evolution characteristics (Lv et al., 2019).

In summary, existing studies have mainly focused on modifier-related factors such as BRA content, particle size, and activation processes. Actually, the final performance of BRA-modified asphalt does not depend solely on the characteristics of BRA itself but is also constrained by its compatibility with the base asphalt. Poor compatibility can lead to an unstable internal structure, thereby limiting the modification effectiveness of BRA (Qu et al., 2020; Su et al., 2022). Nevertheless, current studies lack systematic comparative investigations on the effects of base asphalt factors on their component compatibility. Additionally, although some literature has reported the macroscopic performance changes and certain chemical characteristics of BRA-modified asphalt after aging, few studies have linked initial compatibility with subsequent multi-scale (molecular, microscopic and macroscopic scale) aging evolution behavior, resulting in the intrinsic mechanism by which compatibility influences long-term durability remains unclear (Li R. et al., 2024).

Based on the above analysis, this study adopts a systematic approach to investigate the component compatibility and aging behavior of BRA-modified asphalt. Firstly, the compatibility between BRA (at a dosage of 30 wt%) and four base asphalts (Maoming Petrochemical 70# (70-A), Donghai 70# (70-B), Shuanglong 70# (70-C), and Panjin 90# (90-D)) is evaluated through physical property tests and dynamic shear rheometer (DSR) measurements to establish the baseline characteristics. Secondly, a comprehensive aging protocol is implemented, where the thin-film oven test (TFOT) is employed to simulate short-term thermo-oxidative aging during construction, followed by multi-cycle variable-intensity UV aging to simulate long-term photo-oxidative aging during service. Finally, a multi-scale characterization approach is adopted, utilizing viscosity measurements, DSR analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) to systematically analyze the ultraviolet aging behavior from macro-mechanical to micro-structural levels.

2 Materials and methods

2.1 Raw materials

To ensure the uniform distribution of Buton rock asphalt (BRA) in the base asphalt, 200-mesh BRA particles were selected for the tests in this study (Li et al., 2018; Su et al., 2022). Their main technical properties are shown in Table 1. The base asphalts used in this study include Donghai 70#, Maoming Petrochemical 70#, Shuanglong 70#, and Panjin 90#. They were selected to represent different production sources and penetration grades commonly used for pavement engineering in China. Their basic properties are presented in Table 2.

Table 1

Table 1. Main technical properties of Buton rock asphalt.

Table 2

Table 2. Basic properties of base asphalts.

2.2 Preparation of modified asphalt

The base asphalt was placed in an oven at 155 °C and heated until completely melted, followed by thorough stirring to ensure homogeneity. BRA was weighed at 30% by mass of the base asphalt and incorporated into the continuously stirred asphalt in two equal portions—half at the initial stage and the remaining half after 20 min. The entire blending process lasted 40 min, during which the temperature was maintained at 160 °C–170 °C and the stirring speed was controlled at 4500 r/min to ensure uniform dispersion of BRA particles (Li et al., 2018; Zeng et al., 2018; Su et al., 2022). For clarity and conciseness, the four prepared BRA-modified asphalts are hereinafter referred to using the abbreviations listed in Table 3.

Table 3

Table 3. Abbreviations for modified asphalts.

2.3 Experimental methods

Figure 1 illustrates the overall experimental workflow employed in this study. For each test category, three parallel specimens were prepared to ensure data consistency and statistical reliability, and the reported values represent the mean of these three measurements.

Figure 1

Figure 1. Schematic diagram of the experimental procedure.

2.3.1 Physical property test

Following Standard Test Methods of Asphalt and Asphalt Mixture for Highway Engineering (JTG 3410–2025), a series of physical property tests were conducted, including the penetration test at 25 °C (JTG 3410–2025 T0604, PT), softening point test (JTG 3410–2025 T0606, SP), and Brookfield viscosity test at 135 °C (JTG 3410–2025 T0625, BV) to investigate the effects of different base asphalts on the physical properties of BRA modified asphalt (Luo et al., 2023; Lei et al., 2024; Huang et al., 2025).

2.3.2 Rheological property test

In accordance with JTG 3410–2025 T0628, the complex shear modulus (G*) and phase angle (δ) of the asphalt binders were measured using a dynamic shear rheometer (DSR), and the rutting factor (G*/sin δ) was calculated accordingly. The test temperature ranged from 58 °C to 82 °C, with an angular frequency of 10 rad/s. The rutting factor was used to evaluate the differences in high-temperature rheological performance among the various BRA-modified asphalts (Al-Khateeb et al., 2022; Xie et al., 2023; Zhang et al., 2024a; Li and Li, 2025).

2.3.3 Storage stability test

Following JTG 3410–2025 T0661, the high-temperature storage stability of the modified asphalt samples was evaluated. The softening points of asphalt samples from the top and bottom sections of the storage tube were measured in accordance with JTG 3410–2025 T0606, and the difference between these two values was calculated as the stability indicator (Guo et al., 2024; Zhang et al., 2024b).

2.3.4 Laboratory accelerated aging simulation methods for asphalt

According to the guidelines of JTG 3410–2025 T0609, short-term aging of asphalt samples was simulated using the thin-film oven test (TFOT). To further replicate the photo-oxidative aging conditions experienced by asphalt pavements in Changsha (Hunan Province, China), variable-intensity ultraviolet (UV) irradiation was applied. Compared with the commonly used constant-intensity UV aging method, variable-intensity UV aging produces more pronounced aging effects even when the total radiant energy remains identical. This is because stronger UV radiation during peak-intensity periods exerts more substantial damaging effects on asphalt molecules, resulting in higher oxidation levels and more severe microstructural damage (Ju et al., 2024). Therefore, the variable-intensity UV aging protocol more realistically simulates the diurnal variation of solar radiation under actual service conditions. According to regional investigation, the strongest daily shortwave radiation in Changsha city (China) reaches 5600 W h/m², with a duration of approximately 14.5 h. Based on the radiation intensity equivalence principle, the UV exposure process was divided into five stages. Considering that UV radiation accounts for approximately 5% of total solar shortwave radiation and applying an indoor-to-outdoor acceleration factor of 20, the UV intensities were set at 111, 504, 700, 504, and 111 W/m², as illustrated in Figure 2 and Table 4. The UV aging temperature was maintained at 60 °C, corresponding to the maximum pavement temperature during summer (Xu et al., 2023; Ju et al., 2024; Zheng et al., 2025). To evaluate the effect of aging duration on asphalt performance, indoor UV aging tests of 3, 6, and 9 cycles were conducted, corresponding to approximately 2, 4, and 6 months of outdoor UV exposure, respectively.

Figure 2

Figure 2. Indoor ultraviolet aging conditions.

Table 4

Table 4. Laboratory single-cycle UV aging condition simulation.

2.3.5 Microstructural characterization methods for asphalt

A Nicolet iS50 Fourier-transform infrared spectrometer (FTIR) was used to investigate the changes in chemical functional groups of BRA-modified asphalt before and after aging. The wavenumber range was 600–4000 cm⁻¹, with 32 scans per measurement (Zhang et al., 2024c). An EVO 10 scanning electron microscope (SEM) was used to observe the microscopic morphology changes of BRA-modified asphalt before and after aging. Approximately 1 g of asphalt was taken from the sample surface, vacuum-coated with gold, and observed at a magnification of 500× (Taheri-Shakib et al., 2024). A PL-GPC50 gel permeation chromatograph (GPC) was used to investigate the evolution of molecular weight distribution of BRA-modified asphalt before and after aging (Meng et al., 2020).

2.3.6 Evaluation methods of asphalt aging behavior

2.3.6.1 Physical property aging behavior

The viscosity aging index (V_AI) was employed to characterize the physical aging behavior of the modified asphalt (Luo et al., 2023). The Brookfield rotational viscosity at 135 °C was measured for both unaged and aged samples following JTG 3410–2025 T0625. Subsequently, the V_AI for each aging stage was calculated using Equation 1.

${\mathrm{V}}_{\text{AI}}=\frac{\text{Aged}\text{viscosity}-\text{Unaged}\text{viscosity}}{\text{Unaged}\text{viscosity}}\times 100(1)$

2.3.6.2 Rheological property aging behavior

The rutting factor aging index (R_AI) was employed to characterize the rheological aging behavior of the modified asphalt samples (Liu et al., 2025). The R_AI for each aging stage was calculated using Equation 2.

${\mathrm{R}}_{\text{AI}}=\frac{\text{Aged}\text{rutting}\text{factor}-\text{Unaged}\text{rutting}\text{factor}}{\text{Unaged}\text{rutting}\text{factor}}\times 100(2)$

2.3.6.3 Chemical functional group index aging behavior

The carbonyl aging index (C_AI) and sulfoxide aging index (S_AI) were employed to characterize the chemical functional group aging behavior of asphalt (Duan et al., 2025; Ju et al., 2024). Infrared absorption spectra at each aging stage were obtained using FTIR, and the C_AI and S_AI values were subsequently calculated using Equations 3, 4.

${\mathrm{C}}_{\text{AI}}=\frac{{\mathrm{A}}_{1700}}{{\mathrm{A}}_{2800\sim 3000}}(3)$

${\mathrm{S}}_{\text{AI}}=\frac{{\mathrm{A}}_{1030}}{{\mathrm{A}}_{2800\sim 3000}}(4)$

where A₁₇₀₀ represents the absorption peak area at the wavenumber of 1700 cm⁻¹, A₁₀₃₀ represents the absorption peak area at 1030 cm⁻¹, and A_2800-3000 represents the total absorption peak area within the wavenumber range of 2800–3000 cm⁻¹.

2.3.6.4 Molecular weight aging behavior of asphalt

The large molecular size (LMS) content was employed to characterize the molecular-level aging behavior of asphalt (Zhang et al., 2024b). The molecular characteristic curves at each aging stage were obtained using a PL-GPC50 gel permeation chromatograph, and each curve was evenly divided into 13 segments, with segments 1–5 defined as LMS. The LMS content was then calculated using Equation 5.

$\text{LMS}\%=\frac{{\mathrm{A}}_{\text{LMS}}}{{\mathrm{A}}_{\text{Total}}}\times 100(5)$

where A_LMS represents the area of the large molecular region in the molecular characteristic curve, and A_Total represents the total area of the molecular characteristic curve.

3 Results and discussion

3.1 Compatibility between Buton rock asphalt and base asphalt

3.1.1 Physical properties

As a natural hard asphalt modifier, the compatibility of BRA with different base asphalts can be preliminarily evaluated through conventional physical property indicators. Figure 3 presents the changes in penetration, softening point, and viscosity of the four base asphalts before and after BRA modification.

Figure 3

Figure 3. Comparison of the physical properties of asphalt before and after modification. (a) Penetration test results. (b) Penetration reduction ratio. (c) Softening point test results. (d) Softening point increase ratio. (e) Viscosity test results. (f) Viscosity increase ratio.

As shown in Figure 3, the incorporation of BRA significantly reduced the penetration of all base asphalts and notably increased their softening point and viscosity. However, the magnitude of these changes varied considerably among different base asphalts. Specifically, the penetration reduction rate ranged from 30.2% to 39.8%, with the 90-D system showing the largest decrease (39.8%), indicating that BRA had a more pronounced hardening effect on this base asphalt. Regarding the softening point increase rate, the 70-A system exhibited the highest increase (11.0%), while the other systems ranged from 4.2% to 5.7%, indicating that BRA was more effective in improving the high-temperature performance of 70-A. The viscosity increase rate showed considerable variation: the 70-B system exhibited the highest increase of 88.4%, while the 70-A, 70-C, and 90-D systems increased by 37.1%, 60.2%, and 50.2%, respectively, indicating that BRA had a more pronounced effect on enhancing the high-temperature deformation resistance of 70-B.

Further analysis revealed that the 70-A system exhibited favorable compatibility characteristics. With relatively moderate changes in penetration and viscosity, its softening point showed a more pronounced increase (11.0%) and was ultimately higher than that of the other asphalts, demonstrating better thermal stability. This indicates that the combination of 70-A and BRA did not remain at the level of simple physical dispersion, but rather formed a two-phase continuous structure with superior thermal stability, which can effectively enhance the high-temperature service performance of asphalt materials (Deng et al., 2021). The 70-B system exhibited high modification efficiency, with both its viscosity increase rate (88.4%) and penetration reduction rate (36.9%) ranking among the highest. This indicates that BRA particles underwent sufficient swelling and dispersion in this base asphalt (Liu et al., 2023). However, this excellent dispersibility did not effectively translate into improved thermal stability. Its softening point increase rate was the lowest among all samples (4.2%), indicating that its excellent high-temperature performance mainly originated from the inherent properties of the base asphalt itself, while the contribution of BRA was relatively limited. The 70-C system showed moderate changes in all indicators, exhibiting no obvious advantages or disadvantages in compatibility. The 90-D system exhibited the largest penetration reduction rate (39.8%) and a relatively high viscosity increase rate (50.2%), but only a limited softening point increase (5.7%). After modification, the softening point and viscosity of this system were both lower than those of the other 70# modified asphalts, indicating that the initial properties of the base asphalt have a significant influence on the final performance of the modified asphalt.

The above physical property analysis indicates that the modification effect of BRA is base asphalt system-dependent. The significant differences in modification effects indicate that the properties of base asphalt have a critical influence on BRA dispersion and modification effectiveness. From the overall performance perspective, 70-A achieved a favorable balance between high-temperature performance enhancement and viscosity control after modification, demonstrating superior compatibility.

3.1.2 Rheological properties

The rutting factor (G*/sin δ) is a key indicator for evaluating the high-temperature performance of asphalt (Duan et al., 2023; Zhang et al., 2021). As shown in Figure 4, the incorporation of BRA generally increased the rutting factor of all four base asphalts, which is consistent with the enhanced high-temperature performance trend observed in the physical property tests. Analyzing the absolute performance of the modified asphalts, the G*/sin δ values of the 70-A-MA and 70-B-MA systems remained at relatively high levels across the entire temperature range, indicating their superior high-temperature rutting resistance. These rheological characterization results are consistent with the conclusions from the aforementioned softening point tests, further verifying the excellent high-temperature stability of both systems.

Figure 4

Figure 4. Rutting factor of the modified asphalts.

The enhancement of the rutting factor by BRA is mainly attributed to its unique compositional structure and modification mechanism. BRA has high contents of asphaltenes and resins, which can increase the proportion of heavy components in the base asphalt and improve the elastic recovery capacity of the asphalt (Lv et al., 2019). In addition, the honeycomb structure of BRA ash/particles increases the contact area with the base asphalt, transforming the asphalt from a homogeneous body into a two-phase continuous structure system, thereby enhancing the cohesion and resistance to shear deformation of the asphalt (Lv et al., 2019; Zhang et al., 2024d). The differences in rheological performance among the modified asphalts from different base asphalts may be attributed to the variations in the stability of the two-phase structures formed after modification.

3.1.3 Storage stability

Based on the systematic evaluation of physical and rheological properties described above, 70-A-MA, which exhibited superior overall compatibility among the 70# modified asphalts, was selected as the primary research subject, while 90-D-MA was selected as the control group to investigate the differences in UV aging behavior between the two modified asphalts. This selection was primarily based on its distinctly different modification behavior compared to 70-A-MA, as evidenced by the largest penetration reduction (39.8%) but a limited softening point increase (5.7%), which facilitates the investigation of the potential relationship between compatibility and UV aging behavior. Additionally, including a 90# asphalt enables comparison across different penetration grades. Before conducting the aging tests, storage stability tests were performed to verify the compatibility between BRA and these two base asphalts. As shown in Table 5, after 48 h of high-temperature storage, the softening point differences between the upper and lower portions of 70-A-MA and 90-D-MA were 0.3 °C and 0.4 °C, respectively, both far below the specification limit of 2.5 °C. These results indicate that the modified asphalts prepared with BRA and the two base asphalts exhibit good storage stability and have formed macroscopically homogeneous and stable systems (Su et al., 2022).

Table 5

Table 5. Softening-point difference after 48 h storage stability test.

3.2 UV aging behavior of Buton rock asphalt modified asphalt

3.2.1 Viscosity

The viscosity aging index (V_AI) can directly reflect the degree of rheological performance degradation of asphalt sample during the aging process. Figure 5 presents the evolution of V_AI for the two modified asphalts at different aging stages.

Figure 5

Figure 5. Viscosity aging index of asphalt.

As shown in Figure 5, after short-term thermo-oxidative aging (TFOT), the two samples exhibited significant differences in aging resistance. The V_AI of 70-A-MA was only 11.5%, while that of 90-D-MA reached 21.3%. This result indicates that 70-A-MA possesses superior resistance to short-term thermo-oxidative aging. This difference may originate from the more stable colloidal structure of the 70-A base asphalt itself and the formation of a more stable two-phase continuous structure system with BRA.

During the UV aging stage, with the extension of UV irradiation time, the V_AI values of both modified asphalts showed a continuous increasing trend, which is consistent with the general principle that the degree of aging deepens with time accumulation (Shen et al., 2023). However, although the total V_AI increase for both materials was approximately 8.5%, they exhibited different aging patterns. Specifically, 70-A-MA showed a decreasing aging rate trend, with V_AI increments of 3.7%, 2.9%, and 2.1% at each stage from TFOT to UV-9. This gradually slowing aging process indicates that a certain oxidative protective layer may have formed on the sample surface, hindering further penetration of UV radiation and oxygen, thereby protecting the internal material and demonstrating good long-term durability (Li C. et al., 2024). In contrast, 90-D-MA showed an increasing aging rate trend, with V_AI increments of 1.6%, 2.6%, and 4.3% at each stage. This aging phenomenon may be attributed to the intensified deterioration of the internal structure as aging progresses, leading to enhanced sensitivity to external environmental factors.

3.2.2 Rheological properties

To thoroughly evaluate the aging behavior from a viscoelastic perspective, this study tested the rutting factor (G*/sin δ) of samples at different aging stages, and its evolution is shown in Figure 6.

Figure 6

Figure 6. Rutting factor and its aging index of asphalt. (a) Rutting factor. (b) Rutting factor aging index at 64 °C.

As shown in Figure 6a, the rutting factor of all samples decreased with the increasing temperature, exhibiting typical temperature-dependent characteristics of viscoelastic materials. At all aging stages, the rutting factor curve of 70-A-MA consistently remained above that of 90-D-MA, indicating that it maintained superior high-temperature rutting resistance both before and after aging, which is consistent with the aforementioned compatibility evaluation conclusions. Meanwhile, both thermo-oxidative aging and UV radiation cause an overall upward shift in the rutting factor curves of the two asphalts, directly reflecting the hardening phenomenon induced by aging.

To quantitatively characterize this hardening process, the 64 °C rutting factor aging index (R_AI) was introduced for analysis (Xu et al., 2023), as shown in Figure 6b. The results revealed different aging pathways between the two materials. For 90-D-MA, after short-term thermo-oxidative aging (TFOT), its R_AI value sharply increased to 79.4%, while during the subsequent 9 cycles of UV aging, the increment was only 4.3%. This indicates that the performance degradation of this system mainly occurred during the thermo-oxidative phase simulating construction conditions. In contrast, 70-A-MA showed stronger resistance to short-term thermo-oxidative aging (with an R_AI of only 52.4% after TFOT), but during the subsequent UV aging stage, its R_AI exhibited a continuous and gradual increasing trend, with a total increment of 10.8%.

The differences in aging pathways between the two systems may originate from the differences in their initial performance and structural stability after modification. The 70-A system showed a higher increase in softening point and a moderate increase in viscosity after modification, exhibiting a favorable balance between high-temperature stability and flowability; the relatively small performance changes after aging indicate that its structure is relatively stable under thermo-oxidative conditions. The 90-D system showed the largest decrease in penetration and limited increase in softening point after modification; although its initial hardness was relatively high, its structural toughness may be insufficient, leading to more drastic index changes during aging and a more evident hardening trend.

3.2.3 Microscopic morphology

To reveal the influence mechanism of compatibility on aging behavior at the microscopic scale, this study systematically characterized the surface morphology of samples at different aging stages using SEM, and the results are shown in Figure 7.

Figure 7

Figure 7. Scanning electron microscopy (SEM) results. (a) 70-A-MA. (b) 90-D-MA. (c) 70-A-MA-TFOT. (d) 90-D-MA-TFOT. (e) 70-A-MA-UV3. (f) 90-D-MA-UV3. (g) 70-A-MA-UV6. (h) 90-D-MA-UV6. (i) 70-A-MA-UV9. (j) 90-D-MA-UV9.

As shown in Figures 7a,b, in the unaged state, both 70-A-MA and 90-D-MA exhibited relatively smooth and uniform continuous-phase surface characteristics, with no obvious cracks or macroscopic defects observed. This indicates that in the unaged stage, both modified asphalts possessed good macroscopic homogeneity, and BRA was uniformly dispersed in the base asphalt.

After short-term thermo-oxidative aging, as shown in Figure 7c, periodic wave-like wrinkle structures formed on the surface of 70-A-MA, with relatively uniform distribution. In contrast, the surface of 90-D-MA exhibited coarse and irregular wrinkles (Figure 7d). This morphological difference indicates that the two systems exhibited different shrinkage behaviors under thermal stress.

During the UV aging stage, the two asphalts exhibited significantly different microstructural evolution pathways. In the early stage of UV aging (UV3), as shown in Figures 7e,f, the surface of 90-D-MA had already developed a relatively dense crack network, while the number and density of cracks on the surface of 70-A-MA were relatively low. As shown in Figures 7g–j, the surface damage of both systems intensified, but the damage patterns differed significantly. The surface of 70-A-MA was mainly characterized by crack deepening and widening, dividing the surface layer into relatively large blocks, with warping observed in some regions. In contrast, the surface of 90-D-MA not only developed a denser crack network but also exhibited significantly increased surface roughness, with more prominent granular or cluster-like morphological features. These changes in surface morphology characteristics may be related to the oxidative aggregation of internal components of the material (Zhao et al., 2024).

In summary, the evolution pathway of microscopic morphology reveals the important role of compatibility in aging behavior. The excellent compatibility of 70-A-MA results in a more stable system that can more effectively resist the erosion of thermal stress and photo-oxidative stress, with a damage mode mainly characterized by surface cracking. In contrast, the relatively poorer compatibility of 90-D-MA leads to non-uniformity and instability of its internal structure during the aging process, ultimately resulting in more severe damage patterns.

3.2.4 Chemical functional group indices

FTIR can effectively characterize the chemical structural changes of asphalt during the aging process. As shown in Figures 8a,b, with the progression of aging, both asphalts exhibited gradually intensified characteristic absorption peaks near 1700 cm⁻¹ (carbonyl C=O stretching vibration) and 1030 cm⁻¹ (sulfoxide S=O stretching vibration). These two oxygen-containing functional groups are characteristic oxidation products of asphalt components, and their accumulation can be semi-quantitatively characterized by the carbonyl index (C_AI) and sulfoxide index (S_AI) (Zhang et al., 2024c). As shown in Figures 8c,d, at all aging stages, the C_AI and S_AI values of 70-A-MA were consistently lower than those of 90-D-MA, indicating stronger resistance to chemical oxidation.

Figure 8

Figure 8. FTIR test results. (a) FTIR absorption spectra of 70-A-MA. (b) FTIR absorption spectra of 90-D-MA. (c) Carbonyl index. (d) Sulfoxide index.

During the short-term thermo-oxidative aging stage, the carbonyl index growth rate of 70-A-MA was 37%, while that of 90-D-MA was 61%. This difference was more pronounced for the sulfoxide index, which is more sensitive to thermo-oxidation: the sulfoxide index growth rate of 70-A-MA was approximately 18%, while that of 90-D-MA was approximately 61%, about three times higher than the former. This data indicates that 90-D-MA underwent more intense oxidation reactions under high-temperature aerobic conditions. This difference in chemical reactivity is consistent with the aforementioned physical and rheological performance evaluation results, indicating that the rapid deterioration of its macroscopic properties is accompanied by intense oxidation at the molecular level.

During the UV aging stage, the carbonyl index growth rate of 90-D-MA reached 87.3%, and the sulfoxide index growth rate reached 44%, indicating strong photo-oxidation sensitivity. In contrast, 70-A-MA demonstrated stronger resistance to photo-oxidation, with carbonyl and sulfoxide index growth rates of only 24.3% and 21.1%, respectively, both lower than those of 90-D-MA. The lower chemical reaction rate of 70-A-MA can be attributed to the formation of a synergistic system with better compatibility and more stable structure between BRA and 70-A, which may slow down the chemical degradation of asphalt through UV shielding or inhibition of free-radical chain reactions (Shao et al., 2023; Li L. et al., 2024).

3.2.5 Molecular weight

The increase in LMS content is usually associated with oxidative polymerization of small molecules or molecular association caused by enhanced polarity, affecting the evolution of macroscopic viscoelasticity of the material (Zhen et al., 2023). To reveal the influence of compatibility on aging behavior from the perspective of molecular size distribution, gel permeation chromatography was used to determine the LMS content of samples at different aging stages, and the results are shown in Figure 9.

Figure 9

Figure 9. LMS content of asphalt under different aging processes.

As shown in Figure 9, during the TFOT stage, the LMS content growth rate of 70-A-MA was 18.2%, while that of 90-D-MA was as high as 31.8%, approximately 1.7 times higher than the former. The higher LMS content growth rate of 90-D-MA is consistent with the higher chemical reactivity revealed by FTIR during the TFOT stage, indicating that its molecular association effect induced by chemical changes is more intense. During the UV aging stage, the LMS content of 90-D-MA exhibited a continuous and rapid growth trend, with a growth rate of 27.6%. In contrast, the molecular weight evolution of 70-A-MA tended to be gradual, with a corresponding growth rate of only 10.0%. This difference indicates that the superior compatibility of 70-A-MA may help suppress oxidative polymerization reactions under long-term UV radiation, maintaining a relatively stable molecular size distribution.

In summary, 90-D-MA exhibited higher LMS content growth rates during both the thermo-oxidative and UV aging stages. The accumulation of large-molecule components is consistent with the increasing trend of oxidative functional groups observed by FTIR and is mutually corroborated by the surface morphology evolution characteristics observed by SEM. Conversely, the more gradual increase in LMS content of 70-A-MA throughout the aging process further confirms the chemical stability advantage provided by its superior compatibility. This system can effectively maintain structural stability during aging, which is the molecular-level basis for its excellent long-term durability.

4 Conclusion

This study systematically evaluated the compatibility between BRA and four petroleum asphalts and thoroughly investigated the aging behaviors of the two modified asphalts. The main conclusions are as follows.

1. BRA exhibits significantly different compatibility with various petroleum asphalts, with 70-A-MA showing superior component compatibility. The 70-A-MA achieves a softening point of 50.5 °C (11.0% increase), maintains high rutting resistance across all temperatures, and exhibits moderate viscosity growth (37.1%). Its excellent storage stability is confirmed by a softening point difference of 0.3 °C.

2. The two modified asphalts (70-A-MA and 90-D-MA) exhibit distinctly different aging behaviors linked to their compatibility levels. At the rheological level, 70-A-MA shows smaller increases in both viscosity and rutting factor aging index compared to 90-D-MA during aging, indicating lower rheological aging rates. At the microstructural level, SEM reveals that 70-A-MA develops fewer surface cracks, while 90-D-MA forms a dense crack network with significant surface roughening. At the chemical level, the better-compatible 70-A-MA demonstrates superior chemical stability. FTIR analysis shows that its carbonyl and sulfoxide index total growth rates are 70.4% and 42.5%, respectively, which are markedly lower than those of 90-D-MA (202.0% and 131.7%). GPC results indicate that the LMS content of 70-A-MA increases by 30.0%, compared to 68.2% for 90-D-MA. These multi-scale observations reveal a clear correlation: enhanced compatibility reduces chemical oxidation, limits microstructural damage, and preserves macroscopic performance during UV aging.

3. Short-term thermo-oxidative aging (TFOT) critically influences long-term UV resistance. The less-compatible 90-D-MA experiences more significant increases in viscosity and rutting factor during TFOT, which compromises its subsequent UV aging resistance. This finding emphasizes the importance of controlling short-term aging during BRA-modified asphalt preparation and construction to ensure optimal long-term performance.

5 Future research recommendation

Future research is recommended to focus on field validation of these laboratory findings through actual pavement tests to verify the applicability of the compatibility-aging relationship under real service conditions. Additionally, investigating the long-term performance of BRA-modified asphalt under combined environmental factors (temperature cycling, moisture, and UV radiation) may provide a more comprehensive understanding of durability in practical applications.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

CR: Conceptualization, Formal Analysis, Investigation, Methodology, Writing – original draft. DJ: Formal Analysis, Investigation, Methodology, Resources, Writing – review and editing. CZ: Writing – review and editing, Funding acquisition. MZ: Investigation, Resources, Writing – review and editing. WL: Funding acquisition, Project administration, Supervision, Writing – review and editing. SL: Methodology, Validation, Writing – review and editing. HD: Formal Analysis, Investigation, Visualization, Writing – review and editing.

Funding

The author(s) declared that financial support was received for this work and/or its publication. This work was supported by the National Natural Science Foundation of China (grant numbers 52408461), the Graduate Scientific Research and Innovation Project of Changsha University of Science and Technology (Grant No. CLKYCX24004), the China Railway Fifth Bureau Group Mechanized Engineering Co., (Grant 2024-Key project-14), Open Fund of Key Laboratory of Road Structure and Material of Ministry of Transport (Changsha University of Science and Technology, grant number kfj230404). The authors gratefully acknowledge this financial support.

Acknowledgements

The authors sincerely thank the reviewers and editors for their valuable comments and suggestions. The authors also gratefully acknowledge the financial support received for the conduct and publication of this work.

Conflict of interest

Authors DJ and MZ were employed by China Railway Fifth Bureau Group Mechanized Engineering Company Limited.

The remaining author(s) declared that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The author(s) declared that this study received funding from China Railway Fifth Bureau Group Mechanized Engineering Co. The funder had the following involvement in the study: investigation, providing resources, and preparation of the manuscript.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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