Long-term effects of leaked oil vibration corrosion on the high-temperature performance of rubber asphalt and asphalt mixtures

Experiments were conducted on rubber asphalt (RA) corroded by leaked oil for different durations in order to study the long-term damage of leaked oil on the high-temperature performance of RA pavement. Asphalt physical property test, dynamic frequency scanning, temperature scanning, MSCR test, FT-IR, GPC test and TG test, were performed to investigate the influence of leaked oil on the high-temperature performance of rubber asphalt and rubber mixture. Based on the Grey Relation Analysis, the macro factors of asphalt that affect the high-temperature stability of asphalt mixtures were explored, and the correlation was analyzed between these macro factors and micro characteristic indicators. Physical experiments have shown that the complex shear modulus of rubber asphalt plunges after oil corrosion. The creep recovery rate(R) of rubber asphalt decreases after the oil corrosion, while the non-recoverable creep compliance (J_nr) significantly increases. Microscopic experiments revealed that oil corrosion lowers the mass loss temperature of rubber asphalt, with more severe corrosion causing greater temperature reduction. The chromatogram curves shift toward smaller molecules, reducing large molecule content while increasing small molecule components. Grey correlation analysis shows that MSCR test indexes (R and J) can predict permanent deformation of asphalt mixtures. This study provides a theoretical basis for enhancing the oil corrosion resistance of rubber asphalt pavements.

1 Introduction

Oil leakage often occurs when vehicles run in poor condition on rubber pavement. The accumulation of leaked oil makes the RA pavement in these areas suffer more obvious erosion, threatening the performance of rubber pavement. Nevertheless, current scholarly inquiries have not conducted a comprehensive examination of the influence of automotive oil seepage on the functionality of rubber-modified asphalt and asphaltic combinations. Furthermore, the exploration into the underlying process of how oil causes degradation to rubber asphalt (RA) is scant. In order to avoid the corrosion damage of RA pavement caused by oil leakage during driving, it is imperative to conduct research on the corrosion of RA pavement by oil leakage in high-temperature environments.

The base oil in the leaked oil is also a petroleum refined product and has a similar composition to asphalt. The distinction lies in the dissimilarity of the proportion of light and high-molecular-weight constituents within engine oil compared to asphalt. According to the solubility principle, it can be seen that asphalt is easily dissolved in engine oil with more lightweight components after contact (Li and Shanqiang, 2016). Qiang et al. (2019a) believe that oil corrosion is the main cause of early damage to asphalt pavement. The process of oil corrosion may result in the depletion of highly polar aromatic hydrocarbons as well as polycyclic aromatic compounds. Following oil corrosion, the surface of the asphalt mixture is beset with a multitude of voids, which predisposes the asphalt pavement to premature deterioration, including issues like ravelling and the formation of potholes. A plethora of investigators have employed various methodologies to examine the degradation of asphalt and its mixtures. Wang et al. (2022) utilized orthogonal design to assess the impact of oil content, duration, temperature, and aggregate classification on the mixture’s susceptibility to oil corrosion. Research has shown that asphalt undergoes changes in its internal structure and properties after being corroded by oil. The asphalt transitions from a gel state prior to oil corrosion to a sol state subsequent to oil corrosion, resulting in a decline in the PI (Penetration Index) value and a reduction in the temperature sensitivity of the asphalt. Chen et al. (2013) used engine oil and diesel to corrode Marshall specimens and rut plate specimens respectively by brushing to study the effect of oil corrosion on the high-temperature performance of the mixture. The observation was made that the degree of reduction in the deformation-resistant capabilities of asphalt mixtures correlates with the length of time subjected to oil corrosion. Diesel fuel has a more severe corrosion damage to the stability of asphalt mixtures than engine oil. Investigators have undertaken numerous examinations to assess the severity of asphalt degradation due to oil corrosion, in order to precisely delineate the level and rate of corrosion affecting asphalt surfaces. Qiang et al. (2019b) utilized the decline in asphalt quality subsequent to oil exposure as a proxy for the severity of oil corrosion. Shanqiang and Li (2015), Li and Li (2016) simulated the actual condition of asphalt pavement affected by oil corrosion by determining the factors of oil corrosion. The dispersion test’s quality loss has been identified as a more precise method for assessing the impact of oil corrosion on asphalt surfaces. Song and Chen (2010) investigated the enhancement of TLA on asphalt’s resistance to oil corrosion and discovered that oil corrosion diminishes the high-temperature functionality of asphalt. However, an elevation in the quantity of TLA can mitigate the influence of oil corrosion on the high-temperature properties of asphalt.

In the study of anti-oil corrosion modified asphalt, Irfan et al. (2017) used ELVALOY™ 4,170 Copolymer as an asphalt modifier to improve the oil corrosion resistance of asphalt. The research indicated that at a content of 1%, the polymer-modified asphalt exhibits enhanced resistance to oil corrosion, with relatively minor changes observed in the indirect tensile modulus, elastic modulus, and rutting susceptibility following exposure to oil. Felice et al. (2008), Preeda et al. (2018) added polymeric materials and modifiers to asphalt to study their improvement effect on the oil corrosion resistance of asphalt. Studies have revealed that the improved resistance of polymer-modified asphalt to oil corrosion is due to its effective interaction with the asphalt components. Additionally, it has been noted that rubber asphalt exhibits an even greater resilience against oil corrosion than polymer-modified types.

The existing research on the corrosion of RA pavement by leaked oil mainly focuses on the short-term damage process, and a few methods for long-term impact research are performance testing through on-site core drilling sampling. The process by which rubber asphalt undergoes degradation due to oil seepage has not been comprehensively examined. Hence, this investigation employs laboratory simulation tests and vibratory acceleration to mimic the progression of pavement degradation induced by oil seepage, immersion, and corrosion, aiming to delve into the enduring effects of oil corrosion on rubber asphalt (RA) pavements. The mechanism of oil leakage on the high-temperature performance damage of rubber asphalt is revealed as the performance changes of rubber asphalt after being corroded by leaked oil are compared and analyzed, and micro experiments are conducted to study the changes in micro characteristics of asphalt caused by oil corrosion.

2 Methods and experiments

2.1 Raw materials

2.1.1 Rubber asphalt

The asphalt in this study is rubber asphalt produced by Foshan Zhongyou Gaofu Petroleum Co. Its basic performance indicators are shown in Table 1.

Table 1

Table 1. Technical indices of rubber asphalt.

2.1.2 Engine oil

The Engine oil used in this paper needs to go through a pre-treatment process to exclude the interference of the impurities mixed in the oil inside the vehicle’s fuel tank for this study, and the pre-treated oil is shown in Figure 1.

Figure 1

Figure 1. Engine oil.

2.2 Oil corrosion test

2.2.1 Simulation test parameters

Drawing upon prior expertise, the investigation takes into account four variables: the category of engine oil, the frequency of vehicle vibration, the temperature of corrosion, and the length of corrosion exposure. The impact of varying corrosion durations on asphalt performance is examined under steady conditions of vibration frequency and temperature. The settings of various parameters are as follows:

2.2.1.1 Corrosion temperature

To mimic the chronic degradation of RA pavement due to oil seepage at elevated temperatures, this study sets the corrosion temperature of the leaked oil at 50 °C, thereby approximating the effects of high-temperature oil exposure on asphalt surfaces.

2.2.1.2 Vibration frequency

Moving vehicle loads can cause vibration on the road surface. Undoubtedly, it will intensify the diffusion and shear motion of asphalt at the micro and micro levels, which inevitably accelerates the corrosion of leaked oil on asphalt and mixtures. Studies have shown that the vibration frequency generated by the asphalt pavement surface is about 12.5 Hz when passing vehicles at a speed of 90 km/h for asphalt pavement with a thickness of 18 cm and a surface modulus of 30 GPa–50 GPa (Cunwei, 2016). Oil leakage corrosion simulation is conducted in this study at a vertical vibration frequency of 12.5 Hz to make sure the results of the indoor oil corrosion simulation test closer to the actual results.

The apparatus employed is the WS-Z30-50 vibration table manufactured by Beijing Wavespectrum Science and Technology Co., Ltd., capable of generating a range of vibration patterns. The primary specifications are detailed in Table 2.

Table 2

Table 2. Basic indices of shaking table.

2.2.1.3 Corrosion time

After the conventional index comparison, it can be calculated that the indoor vibration simulation is 40 times of the actual outdoor corrosion as the highway travel speed is 90 km/h, and the minimum distance between the front and rear traffic is 100 m (State Council of China, 2025). The 18 h indoor simulated corrosion is equivalent to the actual road surface corrosion for 1 month (calculated as 30 days). Some scholars have found that the time required from oil leakage to the formation of significant softening, loosening and even potholes in asphalt pavement is often within half a year (Noureldin and Wood, 1989). Therefore, the asphalt softening process within half a year of oil soaking and corrosion is simulated in this study. According to the principle of equivalence between indoor and outdoor vibration effects: indoor vibration times × indoor vibration duration = outdoor vibration times × outdoor vibration duration, it can be assumed that 6 months of actual pavement corrosion corresponding to the indoor corrosion duration as shown in Table 3.

Table 3

Table 3. Equivalence between indoor corrosion hours and actual outdoor corrosion hours.

2.2.2 Simulation test method

In this study, the simulation of oil corrosion on asphalt is conducted using the engine oil vibration immersion method. To closely mimic the corrosion of the asphalt film by oil, the asphalt is initially placed in an oven and heated to 135 °C until it reaches a fully fluid state. Subsequently, it is poured into molds measuring 10 mm × 10 mm × 2 mm, which have been prepared to form square plates. As it cools naturally to room temperature, it is then removed from the mold and placed inside an airtight tank, after which the sealed pot is situated within a thermostatic water bath. Moreover, the oil is warmed in an oven to the desired test temperature before being transferred into the sealed pot. The constant-temperature water bath is positioned on the vibration table and secured in place. The horizontal vibration frequency of the WS-Z30 small precision vibration table is adjusted to 10 Hz, with an amplitude of 2 mm. Once the vibration table is activated, the oil vibrates and soaks into the asphalt, causing corrosion. The temperature of the thermostatic water bath is set to 50 °C. Furthermore, the seal pot is opened every 9 h to maintain parity between the air inside the pot and the ambient atmosphere. Upon reaching the designated corrosion time, the pot is taken out and rinsed twice with room temperature deionized water. Subsequently, the asphalt sample is transferred to a desiccator to dry for 48 h, thereby obtaining the asphalt sample that has been eroded by the oil. To enable comparative analysis, an original sample without vibration corrosion is established as a control group (hereinafter referred to as “0”). Finally, the vibrating corroded asphalt samples are used to conducted tests to characterize corroded asphalt’s performance changes after oil corrosion.

2.3 Characterization test

2.3.1 Performance test

The traditional physical properties of the corroded rubber asphalt are assessed using the 25 °C penetration and softening point tests to investigate the impact of oil corrosion on the standard characteristics of rubber asphalt.

2.3.2 Frequency sweep test

To examine the high-temperature deformation resistance of rubber asphalt following corrosion, a dynamic frequency scanning test is performed on the rubber asphalt samples both before and after oil corrosion. The specific parameters of the frequency scanning test are as follows: the test adopts a strain control mode. Its mechanical response can be ensured to be within the viscoelastic range due to the small load on the asphalt, so the test adopts a 1% strain level. Taking into account the actual temperature of asphalt pavement during summer, the temperature range for the test is set between 34 and 82 °C, with a temperature increment of 6 °C. The scanning frequency range utilized is from 0.1 to 10 Hz. The distance between the parallel plates is set at 1 mm.

2.3.3 Temperature scanning test

In order to reveal the service condition of rubber asphalt under high temperature environment after being corroded by engine oil, the temperature scanning test of asphalt before and after oil corrosion is conducted through DSR, with the test frequency set at 1.59 Hz and the strain at 1%. The scanning temperature range is set from 46 °C to 82 °C, with a temperature interval of 6 °C. At each temperature, a total of 100 data points are scanned.

2.3.4 MSCR test

Multiple stress creep and recovery (MSCR) tests are conducted in the research on rubber asphalt specimens to investigate the effect of leaking oil on the deformation resistance of asphalt under external forces and the recovery after unloading of external forces. The test is carried out in strain control mode, where the strain is fixed at 1%, and the temperature is set to 64 °C to mimic the stress deformation and recovery characteristics of the pavement under the high temperatures commonly experienced in summer. The spacing of parallel plates is set to 1 mm, and the diameter is chosen to be 25 mm. Two different levels of stress (0.1 kPa and 3.2 kPa) on the asphalt specimens are used to load for 1 s and unload for 9 s in a period of time. Load asphalt for 1 s to let the stress deformation occur. Unload for 9 s to make the asphalt deformation recover. The specimens are subjected to 10 cycles of cyclic testing process.

2.3.5 FT-IR test

Utilization of a Thermo Scientific™ Nicolet™ iS50 Fourier Transform Infrared (FTIR) spectrometer, is employed to quantify the alterations in the characteristic peaks of functional groups within the asphalt subsequent to oil-induced corrosion. The spectrometer is operated with a scanning resolution of 4 cm^-1, encompassing a spectral range from 4,000 to 400 cm^-1.

2.3.6 GPC test

Gel permeation chromatography (GPC) serves as a technique for assessing the molecular weight distribution within various substances. The GPC test can be employed to ascertain the relative proportions of the large molecular size (LMS) fraction, the medium molecular size (MMS) fraction, and the small molecular size (SMS) fraction within particular substances (Noureldin and Wood, 1989; Jiang et al., 2019). In this study, GPC tests are performed on asphalt samples both before and after oil corrosion to characterize the alterations in asphalt molecular weight resulting from oil corrosion.

2.3.7 TG test

Thermal analysis tests are conducted on asphalt with different degrees of corrosion using a thermogravimetric analyzer to analyze the stability of asphalt at different temperatures. The asphalt sample has gone through thermogravimetric analysis using Shimadzu Model DTG-60(H) Differential Thermal Analyzers. The heating rate is 20 °C/min, and the volume flow rate is set at 100 mL/min.

3 Results and analysis

3.1 General physical properties

Scholars have found that the greater the penetration, the poorer the ability to resist external force deformation (Victor et al., 2020). A penetration test is carried out on asphalt samples eroded by leaked engine oil at various time intervals, with the test temperature maintained at 25 °C. The depth to which the needle penetrates the asphalt sample over a period of 5 s is recorded as the needle penetration value. The results of the penetration test for rubber asphalt prior to and following oil corrosion are depicted in Figure 2A.

Figure 2

Figure 2. Effect of oil corrosion on (A) RA needle penetration and (B) RA softening point.

As observed in Figure 2A, the needle penetration of the rubber asphalt undergoes a marked change after exposure to oil corrosion. As the duration of oil corrosion extends, the penetration of the asphalt continues to rise. After corrosion, the variation amplitude of rubber asphalt increases by 4 mm, 7.1 mm, 9.9 mm, 11.8 mm, 13.1 mm, and 13.9 mm compared to the original sample. In the 6th month of corrosion, the penetration of rubber asphalt still meets the specification requirements of 3–6 mm although the penetration significantly increases. This is because the lightweight and heavy components of asphalt in rubber asphalt are relatively small, and the components of asphalt become softer after being corroded by engine oil, which increases the number of rubber particles exposed to the surface. This has a significant impact on penetration testing, as the presence of rubber particles hinders needle penetration.

Scholars have demonstrated that the higher the softening point of asphalt, the greater its resistance to deformation at a given temperature, and a higher temperature is necessary to reach the corresponding level of softening (Chen et al., 2019). Softening point testing was conducted on corroded rubber asphalt samples, and the test results are shown in Figure 2B.

Figure 2B indicates that as the corrosion time increases, the softening point of the asphalt exhibits a downward trend, with a more rapid decrease in the initial stage followed by a slower decline rate as time progresses. As the corrosion time prolongs, the changing rates of rubber asphalt’s softening point are −10.82%, −18.90%, −25.00%, −29.12%, −31.40%, and −32.77%, respectively. A negative sign indicates a decreasing trend in the softening point. The softening point indicator is used to characterize the temperature sensitivity of asphalt. The softening point of rubber asphalt decreases to varying degrees after oil corrosion, indicating that the temperature sensitivity of rubber asphalt deteriorates after oil corrosion. As a result, it cannot withstand the action of force at higher temperatures while maintaining small deformation.

3.2 Frequency sweep analysis

Asphalt has obvious frequency sensitivity. At a lower frequency, the complex shear modulus (G*) of asphalt is also low. With the increase of frequency, the dynamic shear modulus of asphalt will correspondingly increase (Liu et al., 2011; Witczak and Bari, 2004). For the convenience of analysis, the data was logarithmized by taking both the horizontal and vertical coordinates as logarithms (Log10) to obtain the master curve modulus of rubber asphalt under different degrees of corrosion at different frequencies. The results are shown in Figure 3.

Figure 3

Figure 3. Effect of oil corrosion on the master curve of complex shear modulus of RA.

It can be noted that the complex shear modulus of rubber asphalt undergoes a significant decline after oil corrosion, as evidenced by the variation trend in the master curve of the rubber asphalt’s complex shear modulus under various corrosion durations depicted in Figure 3. At the same frequency, the complex shear modulus of rubber asphalt after oil corrosion exhibits a decrease of one order of magnitude compared to that of rubber asphalt which has not been subjected to oil corrosion. After 6 months of corrosion, the modulus of rubber asphalt decreased by 1.04 orders of magnitude. At the third month of corrosion, the modulus of rubber decreased by an order of magnitude of 14.25% compared to before corrosion, while at the sixth month of oil corrosion, the modulus decreased by an order of magnitude of 20.88%. It is noteworthy that oil corrosion has a pronounced effect on the trend of the master curve of asphalt. As the extent of oil corrosion intensifies, the relationship between the dynamic modulus and frequency of asphalt shifts progressively from a linear correlation to a nonlinear correlation. For asphalt that has been subjected to oil corrosion, when the asphalt is in the low-frequency region, the rate of change in dynamic modulus with respect to frequency diminishes. When asphalt is in the high-frequency region, the amplitude of its dynamic modulus changes more significantly with increasing frequency. Indeed, from this observation, it is evident that oil corrosion can substantially influence the frequency sensitivity of asphalt. After oil corrosion, the frequency sensitivity of asphalt is better in the low-frequency region, while the frequency sensitivity in the high-frequency region is less affected by oil corrosion. In summary, the harm inflicted by oil corrosion on asphalt predominantly leads to a significant reduction in the asphalt modulus by several orders of magnitude. The enhancement of low-frequency frequency sensitivity is inadequate to illustrate the positive effect of oil corrosion on asphalt, since the dynamic modulus is a measure of asphalt’s resistance to deformation. Oil corrosion softens asphalt, reduces dynamic modulus, and weakens its deformation resistance.

3.3 Temperature scanning analysis

A rheometer was utilized to perform a dynamic temperature scanning test on asphalt after oil corrosion, aiming to simulate the impact of the internal environmental temperature on the rheological properties of asphalt in-service rubber pavement. Some studies indicate that the modulus of asphalt decreases exponentially as the temperature rises (Hui et al., 2018). In order to facilitate the analysis, the Exponential function G* = aebT + c is used to fit the asphalt before and after oil corrosion, where G* is the complex shear modulus, T is the test temperature, a, b and c are undetermined coefficients. And the larger the coefficients a, b and c are, the larger the overall modulus of asphalt is. The fitting results are shown in Figure 4.

Figure 4

Figure 4. Effect of oil corrosion on RA modulus temperature susceptibility.

As depicted in Figure 4, it is evident that with the rise in temperature, the modulus of asphalt exhibits a trend of exponential decrease. As the corrosion time increases, the coefficient a continuously decreases, indicating that the rubber asphalt gradually softens after corrosion and its modulus continuously decreases. It is worth noting that the corroded rubber particles are still hard, manifested as the smallest reduction in modulus of rubber asphalt after corrosion since the rubber particles in RA are not affected by engine oil corrosion and do not soften.

“a/|b|” is used in this paper to characterize the effect of oil corrosion on the RA modulus. The coefficients a, b, and a/|b| values of the RA fitting function before and after oil corrosion are listed in Table 4.

Table 4

Table 4. Coefficient changes of RA fitting function before and after oil corrosion.

Based on the data presented in Table 4, it is observed that with the extension of oil corrosion duration, the ratio of a to the absolute value of b in rubber asphalt diminishes. The data indicate that asphalt’s modulus is substantially influenced by oil corrosion, with a marked reduction observed in the modulus following exposure to oil. At the 180th day of corrosion, the a/|b| value of rubber asphalt decreased by 82.12%. The reason for the decrease in modulus is that the components of corroded asphalt are affected, and the asphaltene and resin responsible for providing asphalt hardness are decomposed and failed by oil corrosion, resulting in a decrease in modulus of asphalt after oil corrosion, manifested as softening of asphalt and easy deformation under small forces.

Oil corrosion causes a sharp decrease in the modulus of asphalt, and the deformation resistance of asphalt in high-temperature environments is usually determined by the rutting factor (G*/Sinδ) for characterization (Kuang et al., 2019). Log(G*/Sinδ)-T is linear fitted in this study, and the fitting results are shown in Figure 5.

Figure 5

Figure 5. Log(G*/Sinδ)-T fitting results for RA before and after oil corrosion.

As shown in Figure 5, log(G*/Sinδ)- The linear fit of T exceeds 0.98, indicating log(G*/Sinδ) Strong linear correlation with temperature. It can be observed that the slope of the fitted straight line after oil corrosion significantly changes, and its absolute value shows a decreasing trend. The slope, indicative of the rate at which the asphalt rutting factor is influenced by temperature, shows a decline post-oil corrosion. This decline suggests a diminished alteration in the asphalt rutting factor due to temperature fluctuations post-corrosion, leading to an enhancement in temperature sensitivity. Consequently, a notable reduction in the asphalt rutting factor is observed.

Research have shown that the higher temperature at the lower limit of the rutting factor (G*/Sinδ1kPa), better the shape stability of asphalt that can withstand loads at higher temperatures (Jing et al., 2019). The temperature corresponding to the lower threshold of the asphalt rutting factor is utilized to delineate the high-temperature resilience of asphalt, facilitating a quantitative assessment of how the rutting factor alters as oil corrosion duration increases. As oil corrosion time extends, the rutting factor of rubber asphalt continues to comply with the specification criteria even after 180 days of exposure. In terms of deformation resistance, the rubber particles, post-oil corrosion, exhibit an effective retention of the asphalt’s resistance to deformation.

3.4 MSCR analysis

MSCR tests were conducted on rubber asphalt samples in order to study the impact of leaked engine oil on the deformation resistance of asphalt under external forces and its recovery performance after unloading. After organizing and analyzing the data obtained from the MSCR test, four indicators can be obtained: asphalt creep recovery rate (R), non-recoverable creep compliance (J), and stress sensitivity (R_diff and J_diff). The average strain of 10 cycles is taken as a representative value in order to quantify the changes in strain and recovery rate caused by oil corrosion on rubber asphalt, and the results are shown in Figure 6.

Figure 6

Figure 6. Stress-strain relationship of three asphalts in one cycle. (A) Rubber asphalt-100 Pa; (B) Rubber asphalt-3200 Pa.

Figure 6 shows that the deformation of asphalt under load after oil corrosion is significantly greater than that of asphalt without corrosion, and the degree of increase in this deformation becomes more significant with the increase of oil corrosion duration. The strain generated by rubber asphalt under 100 Pa stress loading for 1 s is 0.494, which increases to 0.846, 1.125, 1.361, 1.534, 1.667, 1.742 after 30–180 days of oil corrosion. It can be seen that the ability of rubber asphalt to resist stress deformation is greatly weakened after oil corrosion. This phenomenon becomes more pronounced as the stress increases. The irreversible deformation of rubber asphalt post-oil corrosion escalates to differing levels in correlation with the augmentation of oil corrosion duration. It is evident that the elastic characteristics of the asphalt subsequent to oil exposure have diminished, resulting in an impaired capacity to sustain effective deformation recovery and rebound.

A statistical examination is performed on the R, J, Rdiff, and Jdiff of rubber asphalt subjected to various stress influences. This analysis aims to precisely delineate the alterations in the asphalt’s deformation resistance and its capacity for recovery following exposure to oil corrosion.

According to Table 5, it can be seen that the creep recovery performance of rubber asphalt is greatly affected after being corroded by leaked oil. The creep recovery rate has decreased while the irrecoverable creep compliance has significantly increased. The recovery ability after oil corrosion is severely weakened, and by the 180th day of oil corrosion, the creep recovery rate of rubber asphalt under two different stresses is 83.83% and 67.82% of the original sample. The stress sensitivity of asphalt to oil corrosion has decreased, increasing from 0.594 to 0.671. The smaller the R_diff, the better the stress sensitivity, so the sensitivity has decreased. In terms of creep compliance, the permanent deformation difference of rubber asphalt under different stresses before oil corrosion is small, only 0.00038. However, after the 180th day of oil corrosion, it sharply increases to 0.00126, which is three times the flexibility before. It can be seen that oil corrosion has a strong weakening effect on the permanent deformation resistance of asphalt, and this weakening degree is more obvious when the applied stress increases. From the perspective of flexibility analysis, it can be found that the sensitivity trend is the same as that of recovery rate sensitivity. The sensitivity to permanent deformation after oil corrosion is 63.76% of the original rubber asphalt, and the sensitivity to permanent deformation is weakened. In summary, oil corrosion has a significant impact on the recovery rate and irrecoverable creep compliance of rubber asphalt. After oil corrosion, R_diff increases while J_diff decreases, and R_diff’s dependence on stress is enhanced, while J_diff is the opposite.

Table 5

Table 5. Effect of oil corrosion on the MSCR test index of rubber asphalt.

3.5 FT-IR analysis

Infrared scanning is an effective method for testing the types and content of functional groups in substances (Lamontagne et al., 2001; Zhen-gang et al., 2016). This method can be employed to investigate variations in the functional groups of diverse engine oils and their influence on the corrosion of asphalt. The findings from the infrared spectroscopy of the sample are depicted in Figure 7.

Figure 7

Figure 7. Infrared spectra of rubber asphalt before and after oil corrosion.

As shown in Figure 7, rubber asphalt exhibits characteristic peaks at 2922 cm^-1, 2853 cm^-1, 1611 cm^-1, 1460 cm^-1, and 1375 cm^-1. The data reveal that there is no significant alteration in the characteristic peak functional groups and the types of molecular structures of both the oil and rubber asphalt, suggesting that no pronounced chemical reactions occur during the oil corrosion process of asphalt. Nevertheless, the intensity of the characteristic peaks of asphalt has been altered following oil corrosion. The intensity of the characteristic peaks for rubber asphalt at 2,922 cm^-1, 2,853 cm^-1, 1,460 cm^-1, and 1,375 cm^-1 exhibit an increase as the oil corrosion intensifies. The trend of characteristic peaks at 1611 cm^-1 is opposite. This is due to the superposition of the spectra of oil and asphalt. The characteristic peaks of 2922 cm^-1, 2853 cm^-1, 1460 cm^-1, and 1375 cm^-1 in the oil spectrum are stronger, while 1611 cm^-1 is weaker. When the leaked oil corrodes into the interior of the asphalt, the blending effect of the two causes the intensity of the characteristic peaks in the oil corroded asphalt spectrum to overlap and weaken. This further indicates that the corrosion process of asphalt by oil corrosion is mainly physical dissolution, and the oil dissolves the asphalt components, causing changes in the asphalt composition. Furthermore, the soaking of engine oil into the asphalt leads to the intensity of the asphalt’s spectral characteristic peak drawing closer to that of the engine oil’s characteristic peak.

To assess the influence of oil corrosion on rubber asphalt, a quantitative evaluation was performed by examining the alterations in the area of characteristic peaks of rubber asphalt subjected to varying degrees of oil corrosion (Zhao et al., 2023). The areas of the characteristic peaks for rubber asphalt prior to and following oil exposure are presented in Table 6.

Table 6

Table 6. Area of characteristic peaks of rubber asphalt at different degrees of oil corrosion.

From Table 6, it can be seen that the impact of leaked oil corrosion on the same characteristic peak strength of rubber asphalt varies. After 6 months of corrosion, the characteristic peak strength of rubber asphalt at 2922 cm^-1, 2853 cm^-1, 1460 cm^-1, and 1375 cm^-1 increased, but decreased at 1611 cm^-1. It can be seen that oil corrosion has a significant impact on the methyl and methylene groups of asphalt. Due to the strong intensity of these five peaks in the oil composition, and the enhancement of the peaks in the same position of asphalt after oil corrosion, it can be seen that after oil corrosion, the oil is immersed in the asphalt, and the content of broken chain small molecules is relatively increased, while the large molecular components are lost. After oil corrosion, the content of C=C functional groups in asphalt decreases. Due to the stable and non deformable structure of C=C, the amplitude of change in peak area at this point can be considered as the degree to which the deformation resistance of asphalt is affected by oil corrosion. By comparing the characteristic peak area changes at 1611 cm^-1 of rubber asphalt before and after oil corrosion, as well as the situation where the small molecule content increases while the large molecule content relatively decreases, it can be concluded that the movement between rubber asphalt molecules after corrosion becomes simpler, manifested as a decrease in their resistance to deformation.

3.6 GPC analysis

Studies indicate that the properties of asphalt exhibit no substantial association with its number average molecular weight. However, the weight average molecular weight is closely linked to the performance characteristics of asphalt (Ma et al., 2021). Previous studies have shown a high correlation between the molecular weight of compounds in asphalt and their performance (Sung et al., 2009; Sheng et al., 2014). To examine the alterations in the molecular weight (Mw) of asphalt following oil exposure, a comparative analysis of the weight-average molecular weight of rubber asphalt pre- and post-oil corrosion is essential, as depicted in Figure 8A.

Figure 8

Figure 8. Lolecular weight of asphalt before and after oil erosion: (A) change; (B) change mule.

Figure 8A shows tha the Mw of rubber asphalt decreases after oil corrosion. After 180 days of oil corrosion, the rubber asphalt decreases from 3260 g/mol to 2540 g/mol, a decrease of 22.09%. It can be seen that the overall weight of asphalt molecules decreases after oil corrosion, and this decrease in molecular weight is bound to cause changes in high-temperature performance. Due to the fact that the performance of asphalt is not only related to the size of its molecular weight, the distribution of molecular weight also affects the expression of its performance (Balamurugan et al., 2018). As shown in Figure 8B.

As shown in Figure 8B, oil corrosion can significantly affect the distribution of asphalt molecular components. After being affected by oil corrosion, the chromatogram curves of rubber asphalt move towards small molecules. For rubber asphalt, after oil corrosion, peak 1 clearly moves to the left and downwards, and the magnitude of the movement is closely related to the corrosion time. In the early stage of oil corrosion, the two peaks shift significantly to the left, but in the later stage, the amplitude of peak 1 shifts significantly smaller. After oil corrosion, the peak 2 of asphalt significantly moves upwards and increases significantly, while the peak 3 of asphalt after oil corrosion is not obvious. The increase in molecular relative content is more reflected at the 102.5 position, indicating that after rubber asphalt is corroded by oil, the molecules break and form small molecules mainly distributed at 102.5. It can be seen that rubber particles have a certain inhibitory effect on the formation of small molecules in asphalt, which is because the rubber particles distributed in the asphalt phase have not yet fully swelled and developed. When asphalt macromolecules are affected by oil corrosion and fracture to form small molecules, rubber particles can continue to absorb them and swell and develop.

The LMS, MMS, and SMS relative contents of asphalt with different degrees of oil corrosion are obtained through area method statistics and normalization, as shown in Figure 9.

Figure 9

Figure 9. Effect of different corrosion time on molecular weight of asphalt.

From Figure 9, it can be observed that as the oil corrosion time increases, the LMS content of rubber asphalt decreases after oil corrosion, while the SMS and MMS content actually increases. The primary cause for this occurrence is the intrusion of engine oil components into the asphalt matrix via the corrosion process. Engine oil typically possesses a higher concentration of low molecular weight species, resulting in a reduction of the LMS (lighter molecular species) content within the asphalt post-corrosion by engine oil. Furthermore, the intercalation of engine oil among the larger molecules within the asphalt diminishes the intermolecular frictional forces. As the oil corrosion time increases, the amount of engine oil immersion also increases, and the mutual constraint between molecules decreases, ultimately leading to the loss of asphalt large molecules. Consequently, it is evident that the high-temperature deformation resistance of asphalt is severely compromised due to oil corrosion, as indicated by the outcomes.

3.7 TG analysis

Thermogravimetric analysis can accurately control the ambient temperature and heating rate, and measure the quality of the sample to be measured in real time. The volatile amount of asphalt can be obtained through the temperature quality response relationship. Thus, the thermal stability performance, phase state, and material structure of asphalt at specific temperatures can be inferred. Therefore, TG analysis is an effective means to study the thermal stability of asphalt materials (Hassan-Firoozifar et al., 2011). Figure 10 illustrates the obtained experimental findings.

Figure 10

Figure 10. Effect of oil corrosion on the thermal stability of rubber asphalt.

Figure 10 shows that when the temperature rises to 800 °C, the remaining mass of rubber asphalt is 17.48%, while the mass of this part decreases after corrosion, with reduction rates of 15.26%, 14.16%, and 12.32%, respectively. This is because when the temperature rises to 800 °C, the heavy components in the asphalt are not completely Pyrolysis, but the macromolecular components in the asphalt are lost after oil corrosion. In addition, small molecules of oil are immersed in the asphalt, causing the molecular weight distribution of the asphalt to move to the direction of small molecules. Hence, the data indicate that following oil corrosion, upon the heating of asphalt, there is an accelerated loss of mass and an increased rate of decline, with a decrease in the residual mass observed at 800 °C.

In order to quantify the impact of oil corrosion on the weight loss rate of asphalt, this article attempts to observe the corresponding relationship between differential thermogravimetry (DTG) and temperature changes. The corresponding relationship is shown in Figure 11.

Figure 11

Figure 11. (A) Effect of oil corrosion on DTG curves of different Rubber asphalt. (B) DTG illustration.

As depicted in Figure 11, the degradation in asphalt quality is primarily attributed to two distinct stages, with the phenomenon of segmented loss in asphalt quality after oil corrosion being particularly pronounced. Before oil corrosion, there are fewer lightweight components in asphalt, while after oil corrosion, there are more small molecular components in asphalt. The first stage of loss of quality after oil corrosion becomes obvious, and as the degree of oil corrosion deepens, the rate of asphalt in the first stage continues to increase. On the contrary, the response rate of asphalt in the second stage decreased after oil corrosion, with rubber asphalt decreasing from 7.7%/min before oil corrosion to 5.1%/min. The rate of the second stage is significantly slowed down. The modified rubber powder helps to inhibit the corrosion of oil on the macromolecular components in asphalt, so the reduction range becomes smaller.

To measure the alteration pattern of oil corrosion on the relative content of asphalt constituents, the DTG curve was integrated to calculate the area for each stage (refer to Figure 11B).

The effect of oil corrosion on the relative content of rubber asphalt components is characterized by normalizing the area ratio change. The area ratio data of normalized rubber asphalt samples are shown in Table 7.

Table 7

Table 7. Area change of different bitumen before and after oil corrosion.

From Table 7, it can be seen that after being corroded by engine oil, the proportion of small molecule content in rubber asphalt significantly increases, while the relative content of large molecule components decreases. The increase in the relative content of small molecules after oil corrosion is due to the appearance of cracks or pores on the surface of asphalt after being corroded by engine oil, resulting in the immersion of smaller molecular weight oil into the interior of asphalt. Furthermore, the macromolecular constituents of asphalt are influenced by oil corrosion, with a pronounced thermal motion effect. Due to this thermal impact, the macromolecular components undergo loss, which consequently results in a substantial increase in the area of the first stage and a marked decrease in the area of the second stage.

3.8 Relation analysis

The grey relation analysis method is a method of conducting grey system statistical analysis on multiple factors. This method uses the sample data of each factor as a comparison basis to describe the correlation (Zhang-Liang et al., 2020; Zhang et al., 2025). To investigate the relationship between oil corrosion and the rutting resistance of asphalt mixtures under high-temperature conditions, as well as the overall asphalt performance, this study utilizes the permanent deformation data obtained from high-temperature creep tests of the mixtures and the dynamic stability data from the rutting wheel rolling tests as the standard data series. Additionally, various high-temperature performance indicators of the asphalt binder are employed as the analysis data series for grey relational analysis. This approach aims to quantitatively examine the correlation between the asphalt properties and the high-temperature performance of the mixtures. The findings of this analysis are presented in Figures 12A,B.

Figure 12

Figure 12. Relationship between RA high temperature performance index and RA mixture. (A) Permanent deformation (B) Dynamic stability.

As indicated by Figures 12A,B, there is a strong correlation between the high-temperature creep deformation of asphalt mixtures and the creep recovery rate, as well as the irrecoverable creep compliance of the asphalt. This suggests that these asphalt properties play a significant role in determining the rutting resistance of asphalt mixtures under high-temperature conditions. The observation suggests that the R and J metrics, as determined through MSCR assessments, are capable of serving as predictors for the irreversible deformation of the mix. Figure 12B illustrates a strong correlation between the dynamic stability of the mixture and the softening point. Furthermore, there is a positive correlation observed between the creep recovery rate of rubber asphalt and the dynamic stability of the corresponding mixture. In essence, the softening point is a reliable parameter for forecasting the dynamic stability in rubber asphalt mixtures. Additionally, the creep recovery rate serves as a predictor for assessing the dynamic stability of asphalt mixtures that have been modified.

Due to the high correlation between the high-temperature stability of asphalt mixtures and the softening point, R_0.1, and J_0.1 of asphalt, in order to study the impact of asphalt microscopic properties on its high-temperature performance, the softening point, R0.1, and J0.1 were used as standard numerical sequences, and various microscopic characteristic indicators of asphalt were used as analytical numerical sequences to study the microscopic factors affecting asphalt high-temperature performance. The results of grey relation analysis are shown in Figures 13A–C.

Figure 13

Figure 13. The correlation degree of asphalt microscopic properties with (A) softening point of asphalt; (B) R_0.1; (C) J_0.1.

Observations from Figures 13A–C reveal that the predominant factors influencing the softening point and creep recovery rate of asphalt are the residual mass following asphalt combustion, the molecular weight (Mw), and the largest molecule size (LMS) as determined by thermogravimetric analysis. The transformation of functional groups at 1,375 cm^-1, along with the alterations in mass loss during the initial phase of thermogravimetric measurement, notably influence the non-recoverable creep behavior of asphalt. The process of oil corrosion on asphalt alters the high-temperature characteristics of the asphalt by modifying its molecular weight, distribution of molecular weights, and the functional groups at 1,375 cm^-1, consequently impacting the stability of asphalt mixtures under high-temperature conditions.

4 Conclusion

This article primarily focuses on investigating the enduring effects of oil seepage on rubber asphalt (RA) surfaces. The realistic process of engine oil’s vibrational corrosion is mimicked utilizing an indoor setup involving oil leakage submersion and vibrational acceleration. A suite of experiments was carried out to examine the influence of oil corrosion on the high-temperature characteristics of rubber asphalt. The findings of the research indicate that:

1. The predominant effect of oil contamination on the high-temperature rheological behavior of rubber-modified asphalt is a tenfold decrease in its modulus, which leads to a softened asphalt state, an augmentation in the non-recoverable creep compliance, and a decrease in the rate of creep recovery, consequently diminishing its capacity to resist deformation.

2. Following oil contamination, the proportion of small molecular weight (SMS) constituents within the rubber asphalt rises, concurrently with a decline in the large molecular weight (LMS) fraction. The process of oil corrosion adversely affects the thermal stability of rubber asphalt, resulting in a reduction of the temperature at which mass loss occurs in the rubber asphalt compared to the uncorroded asphalt.

3. With respect to the high-temperature behavior of rubber-modified asphalt, the critical elements that influence the softening temperature and the rate of creep recovery in asphalt are the leftover mass following asphalt combustion, the molecular weight (Mw), and the large molecular size (LMS) as measured during thermogravimetric analysis. Oil corrosion of asphalt changes the macroscopic high-temperature performance of rubber asphalt by affecting its molecular weight, molecular weight distribution, and 1375 cm^-1 functional groups.

This study reveals the significant deterioration of the high-temperature rheological properties of rubber asphalt due to oil corrosion. Future work will focus on preparing the corresponding asphalt mixtures and systematically evaluating their high-temperature stability and rutting resistance through tests such as the rutting test, thereby providing a direct basis for developing oil-corrosion-resistant pavement materials.

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

XZ: Conceptualization, Funding acquisition, Methodology, Supervision, Writing – original draft, Writing – review and editing. AF: Conceptualization, Data curation, Methodology, Writing – original draft, Writing – review and editing. PR: Data curation, Writing – original draft, Writing – review and editing. JL: Data curation, Writing – original draft. PG: Writing – original draft. TL: Data curation, Writing – original draft, Writing – review and editing.

Funding

The author(s) declare that financial support was received for the research and/or publication of this article. This research was supported by the Key Science and Technology Project of the Transportation Industry in 2022 (Project No. 2022-ZD7-129).

Conflict of interest

Authors XZ, AF, PR, JL, and PG were employed by China Railway Communications Investment Group Co., Ltd.

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

Generative AI statement

The author(s) declare that no Generative AI was used in the creation of this manuscript.

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