In this article, we are going to discuss whether aged asphalt rejuvenation is beneficial and how it can be helpful to the environment. Soybean bio-oil is one of the vegetable-based oils that is gaining attention for its potential application in the rejuvenation of aging asphalt binders. Sunflower oil is another vegetable-based oil that is gaining popularity. The goal of this in-lab experiment was to characterize and quantify the diffusion and rheological properties of bio-oil-rejuvenated aged asphalt binder (BRAA) manufactured with soybean oil. In the research effort, an element analyzer (EA), gel permeation chromatography (GPC), and a Fourier infrared (FTIR) spectrometer were utilized to compare the chemical structure of soybean oil. Molecular models of BRAA were built by basing them on the chemical structure of the bio-oil. T he diffusion parameters were then calculated using molecular dynamic simulations of these models. Similarly, a dynamic shear rheometer (DSR) test apparatus was used to evaluate and quantify the rheological properties of the old asphalt binder that had been rejuvenated with 0%, 1%, 2%, 3%, 4%, and 5% soybean oil, respectively. Laboratory investigations revealed that bio-oil has the ability to raise the diffusion coefficients and phase angle of aged asphalt binder. Similarly, the concomitant decrease in complex shear modulus has a favorable effect on the properties of BRAA at low temperatures. 
The BRAA components' diffusion coefficients are as follows: 1.52 x 10-8, 1.33 x 10-8, 3.47 x 10-8, 4.82 x 10-8, and 3.92 x 10-8 for a 4.0 percent bio-oil dosage. Similarly, the equivalent decrease in complex shear modulus from 1.27 x 107 Pa to 4.0 x 105 Pa suggests that BRAA's low-temperature properties have been improved. In general, the study adds to the current body of research on the potential use of bio-oil derived from soybeans as a rejuvenator of aging asphalt binders. Asphalt pavements cover more than 80% of the roads that comprise highways around the world. Asphalt pavements are extensively utilized because they have many desirable features and advantages, such as good sliding and wearing resistance, driving comfortability, low noise, ease of maintenance, and the subgrade's deformation adaptability. Asphalt pavements are popular due to their features and benefits. When asphalt pavements are put into service, the asphalt binder contained inside the asphalt ages over time due to exposure to varying traffic loads and changing climatic conditions. This is not a desirable phenomenon. In recent years, there has been a substantial amount of research into the physical and rheological properties of aged asphalt binders. Despite the fact that each asphalt binders have its own distinct set of anti-aging properties, the mechanism by which asphalt ages is essentially the same. For example, as the aging duration of an asphalt binder increases, the penetration decreases, the penetration index rises, the softening point rises, the ductility falls, and so on. Also, as a function of aging time, the viscosity, complex shear modulus (G*), and creep stiffness (S) of the asphalt binder should increase, while the phase angle () and unrecoverable creep compliance (Jnr) should decrease. 
Finally, this indicates how aging causes an unwanted increase in the stiffness and embrittlement of the asphalt binder, which invariably results in a reduction in asphalt pavement performance, as demonstrated by distresses such as cracking, moisture damage, aggregate raveling, and so on. As a result, asphalt pavements will almost certainly require resurfacing, overlaying, maintenance, and/or rehabilitation over the duration of their service lives in order to preserve their characteristics and performance qualities. In the case of old asphalt binders, rejuvenators are typically used as part of the pavement maintenance and rehabilitation scheme to rejuvenate, restore, and recycle the aged asphalt binder, which may include reclaimed asphalt pavement (RAP) and sealing materials. Asphalt binder rejuvenated with leftover soybean oil has the potential to be just as good as, if not better, traditional mineral oil rejuvenators. According to the estimates of numerous research institutions in the sector, worldwide soybean production in 2020 will total 6030.80 million tons. This type of oil, on the other hand, contains a high percentage of polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens, and it has a low volatility rate during the mixing and building processes. Because of the increased awareness of environmental and public health issues, it is likely that the use of base oils as a rejuvenator of traditional PAHs will be regulated or even discontinued in the future. Traditional petrochemical products may be phased out in the future by environmentally friendly and renewable materials. Bio-oil as a bio-binder has several advantages, including low volatility and toxicity, as well as the potential for development into rejuvenators for aging asphalt binders. Xiong and colleagues have published a review of biochar-based catalysts for chemical synthesis, biofuel production, and pollution control. 
Bio-oil produced through rapid pyrolysis, cooling, and condensation has a chemical composition similar to petroleum asphalt binders but has a higher concentration of maltene. Chen et al. chose three samples of vegetable oil with physical properties equivalent to those of their virgin binders to demonstrate that bio-oil may successfully soften aged asphalt. According to a laboratory simulation, the use of bio-oil reduced the number of asphaltenes found in aged asphalt. As a result, because it makes old asphalt binders more malleable, bio-oil meets the fundamental features of an asphalt binder rejuvenator. Raouf investigated the physicochemical properties of three different types of bio-oils (oak, switchgrass, and maize straw) as potential components of bio-asphalt binders. The logarithmic linear relationship between the viscosity of the oak-based bio asphalt binder, the temperature at which it was sheared, and the rate at which it was sheared was found to be extremely similar to that of the petroleum asphalt binder. The bio-binder, on the other hand, was shown to be more sensitive to temperature variations than the traditional petroleum asphalt binder. Fini and colleagues investigated the characteristics of a bio-binder derived from pig manure. According to the findings, incorporating a bio-binder into an asphalt binder has the potential to improve the low-temperature capabilities and workability of a petroleum asphalt binder while having the reverse effect on the asphalt binder's high-temperature qualities 
. Furthermore, You et al. discovered that with the addition of 10% bio-binder, a bio-binder produced from swine manure has the potential to be employed as an asphalt binder modifier to reduce the cracking temperature of PG 64-22 asphalt binders by around 4.2-4.6 °C. reducing the temperature at which the asphalt binders cracked, was done (by weight of the asphalt binder). Zofka and Yut retrieved bio-oils from wasted coffee grounds in their study. They discovered that the bio-oils had no effect on the temperature susceptibility of the base asphalt binder and did not act as antioxidants in the asphalt binder. Furthermore, the bio-oils had no effect on the temperature susceptibility of the base asphalt binder. Jalkh et al. discovered that combining the extracted bio-oil with an asphalt binder restores the asphalt binder's linear behavior, accelerates the softening process of the blend matrix, and reduces its susceptibility to permanent damage at low-stress levels. The asphalt binder was combined with the extracted bio-oil, which led to these findings. Wen et al., on the other hand, discovered that the inclusion of waste cooking oil reduced the material's resilience to fatigue and rutting. Chen investigated the influence of used cooking oil and cotton seed oil on the high-temperature performance of regenerated asphalt binders using a dynamic shear rheometer (DSR) test instrument. 
Similarly, Tang used three bio-oils derived from maize stover, oak wood, and switch grass to compare and contrast their sensitivity to oxidative aging as well as their ability to regenerate aged asphalt binders. According to the findings of the investigations, bio-oils have the ability to minimize the effects of oxidative aging and revive old asphalt binders. A number of studies have studied the use of rejuvenators or modifiers derived from soybean oil, which shall be referred to as SBO throughout this article. Seidel investigated the rheological properties of asphalt binders modified with soy fatty acids at high temperatures (SFAs). He discovered that adding SFAs in minor proportions can result in asphalt binders that are less stiff and more workable. Elkashef et al. evaluated the physical and chemical parameters of an aged asphalt binder that had been regenerated with SBO using the DSR, BBR, FTIR, and GC-MS tests, respectively. According to the results of the testing, the SBO rejuvenator has the ability to significantly improve an asphalt binder's low-temperature and fatigue performance, including lowering the binder's temperature sensitivity. 
Aged Asphalt Rejuvenation
Researchers have focused their attention on the interfacial interaction that happens between a rejuvenator and an aged asphalt binder in order to discover how the rejuvenator interacts with the asphalt binder. Regarding rejuvenation techniques and the use of bio-oil rejuvenators such as SBO, one of the most important technical concerns is the diffusion mechanism that happens between the rejuvenator and the aged asphalt binder. This is regarded as one of the most critical technical issues. Karlsson was able to successfully describe the internal diffusion behavior of microencapsulated rejuvenators in aged asphalt binders using FTIR-ATR tests. Their evaluation accomplished this. Ding investigated the diffusion that happens between the original asphalt binders and the aged ones using molecular dynamic (MD) simulations. Girimath et al. tested a bio-oil composed of aromatic chemical compounds and molecules containing oxygen. This bio-oil has the ability to improve the properties of asphalt binders, which is a highly desirable characteristic. Yang et al. investigated bio-binders using gel permeation chromatography (GPC) and discovered that the components of bio-oil are comparable to those of asphalt binders. The MD simulation results were successfully validated using GPC (gel permeation chromatography), and the related results suggested that the diffusion of large molecules inside the asphalt binder is an important role in the diffusion of asphalt binders. 
The diffusion coefficient concept was used by Xiao, Zadshir, and Xu in conjunction with MD simulations to explore the diffusion behavior of rejuvenators and asphalt binders. In addition, laboratory experiments (including DSR, FTIR, and others) were performed to validate the results of the MD simulations. According to the study's findings, MD simulations combined with laboratory testing were able to successfully model and quantify the behavior of rejuvenator diffusion, as well as its impact on the molecular structure and thermodynamic properties of asphalt binders found in RAP materials. The molecular structure of bio-oil was determined using an element analyzer (EA), gel permeation chromatography (GPC), and a Fourier infrared spectrometer in this work (FTIR). The objectives of these measurements were to improve RAP use and acquire a better knowledge of the diffusion and rheological properties of bio-oil-rejuvenated aged asphalt (BRAA). Molecular models of BRAA were created, and MD simulations were used to determine the diffusion parameter values. Throughout the study effort, a DSR test apparatus was used to measure and quantify the rheological properties of BRAA. For the purposes of this inquiry, both molecular dynamic simulations and laboratory tests were performed. The purpose of this study was to investigate the diffusion and rheological properties of soybean bio-oil, which was utilized to revitalize an aged asphalt binder (BRAA). 
The following are some conclusions and recommendations based on the study's data and findings: BRAA had much lower emissions of volatile organic compounds (VOC) and was more environmentally friendly than the base asphalt binder. The molecular weight of the soybean-derived bio-oil was discovered to be between 280 and 282 g/mol. Depending on your preference, this molecular weight could be represented by the chemical formulae C18H32O2 or C18H34O2. The bio-oil tested, sourced from soybeans, was soluble in the aged asphalt binder, with the potential to increase its viscoelastic characteristics and diffusion, as well as promote regeneration. The bio-oil tested, sourced from soybeans, was soluble in the aged asphalt binder, with the potential to increase its viscoelastic characteristics and diffusion, as well as promote regeneration. The bio-oil suggested the potential for the materials that were tested. For a bio-oil dose of 4.0%, the diffusion coefficients of the BRAA components were as follows: 1.52 x 10-8, 1.33 x 10-8, 3.47 x 10-8, 4.82 x 10-8, and 3.92 x 10-8. The BRAA regeneration mechanism suggests that the chemical diffusion of the bio-oil improved molecular movement within the old asphalt binder, including the addition of aromatics and saturates to build a new stable asphalt binder. According to the study's findings, bio-oil derived from soybeans has the potential to be an efficient regeneration agent for rejuvenating old asphalt binders, with a preliminary optimum dosage of 4.0 weight percent. 
However, while the study results appear feasible, further research should include experimentation with various base asphalt binders and other laboratory tests, such as cracking and moisture evaluation, as well as field validation. Future research should look into the use of FTIR indices as a quantitative measure of absorption and an indicator of rejuvenation effects to augment the conclusions and findings reported in this study. This will enable a more thorough presentation of the results and findings. Despite this, the research contributes to the state of the art by supplementing and expanding the already existing material. This is accomplished by providing a reference point for the usage of soybean oil as a potential regenerant agent to rejuvenate aging asphalt binders.