Aged Binder Research Articles

Restoration of physical properties on an aged crumb rubber modified bitumen adding a bio-based recycling agent

Reclaimed asphalt pavement (RAP) is a popular practice in the pavement industry due to environmental and economic benefits. But, RAP must be processed and treated before being reused in new pavements for preventing premature failures. A widely adopted strategy consists of adding recycling agents, and specifically rejuvenators, to mitigate the aging of the RAP binder. From the circular economy perspective, also crumb rubber (CR) from end-of-life tyres have been used to prepare binders with enhanced properties. The actual possibility of using the RAP derived from removed and/or reprocessed pavements containing CR particles (CR-RAP) for the formulation of new suitable mixtures is still a little-explored topic. Moreover, the available rejuvenators tailored on RAP have not yet evidence of effectiveness in producing asphalt mixtures containing CR-RAP. For this purpose, unaged, aged and rejuvenated blends with and without CR were studied through a rheological characterisation to evaluate the potential restoration of their physical properties when a bio-based recycling agent is added. The results of viscosity, frequency sweep, creep-recovery and multiple stress creep recovery (MSCR) tests have highlighted on the one hand the significant contribution of CR in reducing the accelerated aging effects of the binder, on the hand the effectiveness of the rejuvenator in restoring, more clearly at low temperatures, the rheological behaviour of the binders (above all for CRMB) similar to the unaged condition.

Evaluation of asphalt-aggregate adhesive property and its correlation with the interaction behavior

The performance of the asphalt binder-aggregate interface is an essential guarantee of the stability and durability of asphalt pavements. The objectives of this paper are to investigate the effects of various factors (test conditions, material properties) on the interfacial adhesive properties of asphalt binder-aggregate systems and to analyze the correlation between the bond strength and interface interaction. For this purpose, the improved pull-off tests under various temperatures, loading frequencies and asphalt film thickness were carried out to determine the test conditions for interfacial adhesion failure. The interfacial bond strength of various asphalt binders-aggregates and the corresponding interaction values were tested according to the determined test conditions and the correlation between them was analyzed. The results show that the bond strength between asphalt binder and aggregate was negatively correlated with temperature and positively correlated with loading rate, and there was an optimal film thickness. Among the selected minerals and aggregates, calcite and limestone presented the best bonding properties with asphalt binder respectively. Asphaltenes and resins enhanced the bond strength of asphalt binder-aggregate, while saturates and aromatics weakened the bond strength of asphalt binder-aggregate. The short-term aging of asphalt binder was beneficial to the bonding of binder and aggregate, whereas the long-term aging of asphalt binder was detrimental. Among the material properties factors, the SARA composition had the most significant effect on interfacial bond strength. A significant correlation was found between the C value (the preferred interaction parameter) and the bond strength of the asphalt binder-aggregate interface.

Chemical and mechanical analysis of field and laboratory aged bitumen

To predict the performance of bituminous products during their service life, an accurate simulation of the aging behaviour is required. Several laboratory methods are available, yet the correlation to field aging is mostly missing. In this study, an unmodified bitumen was exposed to laboratory aging with the Pressure Aging Vessel (PAV) using one to five aging cycles and the Viennese Binder Aging (VBA) method, followed by a comparison to a field sample of the same base binder. Measurements with the dynamic shear rheometer (DSR) and Fourier-transform-infrared (FTIR) spectroscopy showed that the field aging level could not be reached neither with VBA nor with multiple PAV cycles, but a better approximation compared to the standard aging procedure was achieved. The FTIR spectra displayed a high degree of correlation between the VBA and field aged sample, especially regarding carbonyl formation in the aromatic fraction and the intensity of the sulphoxide band in the resin and asphaltene fractions. Additionally, the VBA sample showed more similarities to the field sample regarding fluorescence excitation–emission maps. Although both laboratory aging methods are an improvement to the standard procedure, the VBA method allowed for a better qualitative simulation of the chemical properties of the investigated field sample.

Multiscale investigation of waste soybean oil rejuvenated asphalt binder utilising experimental methodologies and molecular dynamics simulations

ABSTRACT To demonstrate the rejuvenation effect of waste soybean oil (WSO) on aged asphalt binder (AB) and realise the efficient combination of laboratory evaluation and numerical simulation. The rheological properties and molecular dynamics simulation of WSO rejuvenated binders were investigated. The results demonstrated that the WSO provided sufficient light components in the AB and reduced the stiffness. The WSO rejuvenated binders were transformed into a sol–gel structure, this resulted in excellent rheological properties. The WSO improved the anti-fatigue performance of rejuvenated binders. The WSO provided sufficient aromatics and a small amount of saturates for the AB. The blending mechanism of WSO and AB was physical blending. The atomic force microscopy micromorphology images showed that the bee-like structure of WSO rejuvenated binders was reduced in quantity compared with that of AB. The dosages of 3–6 wt% of AB content was determined to be the optimum content of WSO. The molecular dynamics results indicated that as the amount of WSO increased, the total volume and the occupied volume increased, while the free volume decreased. The volume fusion parameters increased significantly with an increase in the WSO content. This showed that WSO effectively improved the diffusion capacity of rejuvenated binders.

Evaluation of bio-based and petroleum-based rejuvenator based on cracking susceptibility of hot mix asphalt with high RAP content

Highly aged asphalt binder in RAP is a potential source of inferior performance, especially the cracking resistance of HMA. Use of rejuvenators is a suitable way to incorporate more RAP by offsetting the stiffness of the aged binder. In this study, bio-based and petroleum-based rejuvenators were evaluated based on cracking susceptibility of the hot mix asphalt prepared with low (15%) and high (30%) RAP content. Less amount of plant-based rejuvenator (15% by weight of RAP binder) was required to lower the RAP binder grade to a certain level in comparison to petroleum-based one (35%). Cracking susceptibility of the mix was determined by semi-circular bend test performed at intermediate and low temperature as well as by overlay test. It was observed that use of rejuvenator can successfully restore the cracking resistance of the mix with low RAP content from 93% to even 112% of the control mix. For mix with high RAP content the cracking potential cannot always be restored at the level similar to the control mix but can be improved from 56% to 144% of control mix properties. Petroleum-based rejuvenator is less susceptible to aging and performed significantly better to resist cracking for long-term aged mix in all the test performed in this study. However, use of maximum amount of rejuvenator should be limited because it can adversely affect the rutting as well as cracking resistance of the mix.

Performance Evaluation of Extracted Asphalt Binders from Field Cores Containing Recycled Components: Load- and Non-Load-Associated Cracking Resistance

Modifying asphalt mixtures with recycled components is common practice due to their environmental and economic merits. However, due to the oxidized air-blown asphalt binders in recycled asphalt shingles (RAS) and aged binders in reclaimed asphalt pavement (RAP), adopting RAP and/or RAS as recycled components in asphalt mixtures influences the performance of the overall asphalt binder in these mixtures. The percentages of recycled components and performance grade (PG) of virgin asphalt binders (VABs) in the asphalt mixtures govern the performance of the overall asphalt binder. Therefore, the main idea of this study was to investigate the effect of the percentages of RAP/RAS and PGs of the VABs on the load- and non-load-associated cracking resistance of the extracted asphalt binders (EABs) from field cores. Rheological tests were performed on the EABs to assess the load-associated cracking (fatigue cracking) and non-load-associated cracking (low-temperature and block cracking) resistance. The VAB's PGs, mixtures' ages, and the percentages of RAP/RAS affected the EABs' cracking resistance. When compared to EABs from mixtures with lower amounts of RAP, employing RAS in the asphaltic mixtures improved EABs' resistance to fatigue and block cracking. However, using RAS deteriorated EABs' resistance to low-temperature cracking. Increasing the RAP's percentage in the asphaltic mixtures decreased the cracking resistance of the EABs. Strong relationships were established between EABs' load- and non-load-associated cracking resistance.

Effect of Warm Mix Asphalt (WMA) Antistripping Agent on Performance of Waste Engine Oil-Rejuvenated Asphalt Binders and Mixtures

Evaluating the performance of rejuvenated asphalt mixes is crucial for pavement design and construction, as using a rejuvenator not only boosts recycling and contributes to positive effects on the environment but also increases the sensitivity to rutting and moisture. This study was executed to evaluate the effect of a warm mix asphalt (WMA) antistripping agent, namely nano-ZycoTherm, on the moisture-induced damage and rutting potential of asphalt mixtures containing 30% and 60% aged (RAP) binder and rejuvenated with 12% waste engine oil (WEO). For this purpose, the rutting resistance of asphalt mixes in wet and dry conditions was examined utilizing a loaded wheel tracker. In addition, the impacts of moisture on the performance of the mixtures were evaluated using different experiments, such as modified Lottman (AASHTO T283), resilient modulus, dynamic creep, aggregate coating and wheel tracking tests. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analysis were performed to identify the functional groups, which would be significant in terms of moisture damage, and to assess the thermal stability of binder samples, respectively. The results revealed that the rejuvenation of aged binder with WEO increases the moisture susceptibility of the mixtures; however, the addition of ZycoTherm was found to enhance the moisture resistance of WEO-rejuvenated mixtures. Furthermore, the results indicated that the WEO-rejuvenated mixtures modified with ZycoTherm exhibited a better rutting resistance in a wet condition compared to that of WEO-rejuvenated and conventional HMA mixtures. However, the rejuvenated mixtures modified with ZycoTherm showed poorer rutting performance in a dry condition. In summary, the adoption of the WMA antistripping agent, RAP binder and WEO rejuvenation techniques demonstrated satisfactory outcomes in terms of rutting resistance and moisture susceptibility, and also, these techniques are much less expensive to implement.

Laboratory and Field Testbed Evaluation of the Performance of Recycled Asphalt Mixture Using High-Penetration Asphalt

The application of recycled asphalt pavement (RAP) on a large scale is highly promoted to meet the current needs of carbon neutrality and sustainable development purposes. However, a majority of RAP mixture productions are currently relying on the restoring effects provided by the rejuvenators. Therefore, the study focuses on the feasibility of using high penetration asphalt binder (HPAB) in RAP mixture as a replacement for conventional rejuvenators. In this study, a recycled asphalt pavement mixture containing HPAB (RAP-H) was developed to resolve the cracking issue of RAP pavement in winter seasons owing to the rigid behavior of aged binders. To verify the applicability of the RAP-H mixture, the results of the quality standard test and mechanical performance test were compared with the reference RAP mixture having rejuvenator (RAP-R). Through the fatigue cracking test, by using Overlay Tester (OT) device, it was found that all specimens did not reach 93% load reduction after 1000 OT cycles, indicating a satisfied stress-bearing capacity. Additionally, the highest dynamic modulus of 27,275 MPa was found in the modified HPAB mixture, and this result is 4.4% higher than that of the reference mix. In the full-scale testbed, the long-term field applicability of the proposed approach was verified through field test construction. The measurement in practice reveals that the elastic modulus of RAP-H back-calculated from the FWD (Falling Weight Deflectometer) test is increased by more than 50% compared to RAP-R, which resulted in excellent performance characteristics of the HPAB pavement layer. In addition to the efficiency in the surface layer, an improved elastic modulus of the sub-base and subgrade layers in the HPAB section was found to be at 28.6% and 19.5%, respectively, compared to the RAP-R mix. In general, the performance of RAP-H satisfied all of the domestic and international quality and performance standards. The field test results confirmed the possibility of field application by showing performance higher than conventional recycled asphalt pavement.

Molecular Simulation Study on the Aging Mechanism of NEPE Propellant Matrix

Polyethylene glycols (PEG) and toluene diisocyanate (TDI) are often used as the main components of binders and curing agents in solid propellants, and their aging is an important issue in the storage and use of propellants. To study the aging behavior and aging mechanism of nitrate ester plasticized polyether propellant (NEPE) matrix during storage, the transition states of aging reactions of binder and curing agent were optimized at the (U)B3LYP/6-311G(d,p) level of theory, and the rate coefficients over the temperature range of 298-1000 K were calculated by CVT theory. The results showed that there were five kinds of aging reactions for binder, which included decomposition, nitration, H abstraction, oxidation, and crosslinking reactions. Among them, theenergy barriers of oxidation and H abstraction reactions were relatively low (79.3-91.2 kJ·mol-1) and the main reaction types of binder aging. The main aging reaction of curing agent was decomposition. Compared with the aging reactions of binder, the energy barriers of curing agent are higher (196.6-282.7 kJ·mol-1) and the reaction is more difficult to occur. By comparing the energy barriers and rate constants of different reactions, it is found that the aging of NEPE propellant matrix can be divided into two stages. In the first stage, the propellant matrix mainly undergoes H abstraction and oxidation reaction, and as the reaction proceeds, the products crosslink to form -O-O-, -C-C-, and -C-O-C- bonds. At this time, the long chain molecules of the propellant matrix crosslink, and the molecular weight increases. This stage corresponds to the rising stage of mechanical properties in the aging process of the propellant. In the second stage, the propellant matrix mainly undergoes decomposition and nitration, resulting in degradation, the reduction of molecular weights, and the appearance of holes and microcracks in the matrix. This stage corresponds to the decline of mechanical properties in the aging process of the propellant. The above simulation results are in good agreement with the aging experimental phenomena, revealing the microscopic mechanism of the changes in the macroscopic properties of NEPE propellant during the aging process, and providing a theoretical basis for the related research on the aging properties and anti-aging technology of NEPE propellant.

A laboratory investigation on benefits of WCO utilisation in asphalt with high recycled asphalt content: emphasis on rejuvenation and aging

ABSTRACT Waste cooking oil (WCO) is being investigated as a rejuvenator to utilise higher amount of reclaimed asphalt pavement (RAP) in asphalt mixtures. Past studies have evaluated the potential of WCO as rejuvenator without considering the performance of the rejuvenated binder after the secondary aging (long-term aging). The studies did not reveal any optimum amount of WCO required for the appropriate rejuvenation for incorporation of particular amount of RAP binder or aged binder. In this study, the potential of WCO is evaluated as rejuvenator of the binders incorporating higher aged binder by considering the anti-aging effect of WCO on the performance of rejuvenated binder after secondary aging. The study proposes a concept to determine the optimum dose of WCO for binders with different percentage of aged binder based on Equi-viscous concept and rutting criteria for short-term aged binder.Optimum dosages for the rejuvenated binders with 45, 60 and 75% RAP binder were found to be 6.45, 7.07 and 7.59%, respectively. The rejuvenated binders with different RAP contents and optimum WCO dosage showed lower susceptibility against fatigue and rutting. Further, the study concludes that the WCO can perform dual function as rejuvenator and also as an anti-aging additive.

Oxygen Diffusion Coefficients of Asphalt Mixtures and Their Impacts on Mixture Aging

The oxidative aging of asphalt binder affects the long-term performance of flexible pavement. Apart from the intrinsic property of asphalt binder, binder aging in an asphalt mixture is also affected by the mixture’s oxygen transport efficiency, which can be characterized by the oxygen diffusion coefficient. In this study, the diffusion coefficients ( Ds) of compacted asphalt mixtures of different designs were determined. The same mixture samples were also aged in one dimension for a relatively long period of time. Asphalt binders from different slices of the aged specimens were extracted and recovered, and their aging states were determined. Influences of Ds and air void content on binder aging gradient and binder aging extent in the mixture samples were systematically examined and compared. The results indicate that, as compared with air voids, Ds is more closely related to the aging susceptibility of asphalt binders in asphalt mixtures. It may serve as a useful and convenient parameter in mixture design optimization, modeling and prediction of in situ pavement aging, and quality control and quality assurance (QC/QA) in pavement construction.

Multiscale Evaluation of Asphalt Aging Behaviour: A Review

The performance of asphalt pavement will deteriorate gradually due to oxidation, also named the ageing of asphalt binders. In this study, the research progress on the multiscale evaluation of asphalt aging behaviour in the past decade was reviewed to further analyse the evolution law of asphalt aging behaviour and determine the asphalt aging mechanism. Firstly, artificial aging methods were introduced, the factors affecting asphalt aging behaviour were analysed, and the changes of asphalt properties before and after aging were identified. Secondly, the methods and research progress in terms of the evaluation of asphalt aging degrees were summarised from the macro-, mesoscopic-, micro-, and nanoscales. Finally, considering extensively studied rheological properties as an example, the correlations among the rheological properties of asphalt in the aging process and the conventional physical properties, chemical composition, microscopic properties, nano-molecular dynamics, and other parameters were analysed. The results show that various scales are interrelated, and the multiscale evaluation of asphalt aging can provide a more comprehensive prediction of the extent of asphalt aging. The correlation between multiple scales enables a thorough analysis of the mechanism of asphalt aging and the evaluation of asphalt aging behaviour at multiple scales.

Rheological Characterization of Ground Tire Rubber Modified Asphalt Binders with Parallel Plate and Concentric Cylinder Geometries

Recently, scrap tire rubber-modified asphalt binders and pavements have been the preferred choice of state DOTs and parties involved due to the desirable engineering, as well as economic and environmental impacts. Rheological and mechanical properties of rubber modifications have been the main focus of researchers for the last couple of decades. This paper investigates the rutting potential, fatigue cracking resistance, and continuous performance grade (CPG) changes of waste tire rubber-modified, original, and aged asphalt binders. The CPG of asphalt binders is determined at high, intermediate, and low temperatures. A Delta T Critical comparison of the binder was carried out to establish a relationship between measured parameters. Linear amplitude sweep (LAS) tests at equi-stiffness temperatures were conducted to discover the fatigue life of all binders while the multiple stress creep recovery test is performed to assess the high-temperature rutting performance of asphalt binders as per the Superpave performance grading system at accepted regional (58 °C) as well as high PG temperatures. In addition, parallel-plate geometry and concentric cylinder geometry were used with the Multiple Stress Creep Recovery (MSCR) test to discover the impact of discrete particles available in crumb/ground tire rubber-modified asphalt binders as per standards. The results show that rubber modifications improved the base binder’s rutting resistance and continuous PGs without adversely affecting the fatigue cracking resistance. Based on the mathematical expressions developed, 2.71%, 7.82%, 12.94%, and 18.05% (by weight of binder), GTR modifications improved the high PG of the modified binders one, two, three, and four grade bumps, respectively. Similar linear correlations with R2 0.872 and 0.6 were established for continuous low and intermediate PGs, respectively. MSCR test results revealed that both 9% and 20% GTR modifications were achieved to enhance the H-grade traffic level of the original binder to E-grade.

Understanding Bitumen Aging through Interrelationships and Aging Ratios

Aging of bitumen can lead to fatigue and non-load-associated cracking of asphalt pavements. Performance grade specifications include threshold limits for rheological properties from specific ranges of binder behavior after laboratory aging. Some specifications include aging ratios (ARs) to limit the rate at which properties deteriorate. This study compares the evolution of interrelationships and ARs of performance parameters in specific areas in Black Space to understand the relative susceptibility of the binder behavioral spectra to aging. Unmodified and polymer modified binders are aged with the rolling thin film oven and pressure aging vessel, and tested with the dynamic shear and bending beam rheometers. It is seen in the study that there are both related and unrelated aging trends in the distinct stiffness-related ranges. Correlations in parameter development significantly improve when binders are grouped by similar features such as modification type or origin. Binder source and modification type and degree greatly dictate aging trends in the high-stiffness range. In the low-stiffness range, the initial hardness of the binder is indicative of aging potential. The evolution of properties may be influenced by either modification or binder source in the intermediate domain. When considering ARs for specifications, combining complementary ARs may provide reciprocal insights into binder aging.

Investigation on aging and rejuvenation of asphalt rubber binders considering liquid and particle effect

The aging and rejuvenation behaviors of asphalt rubber (AR) binder are of great importance, while most studies investigated the two processes by regarding the AR binder as a whole. Therefore, the AR binder was regarded as a two-phase system in this study to further clarify the aging and rejuvenation mechanisms behind. The liquid phase and particle phase of AR binders were separated using a physical sieving method, and the liquid effect (LE) and particle effect (PE) were then defined. Results showed that compared with the LE, the PE played a dominant role in affecting the unaged AR binders, especially for those prepared with crumb rubber of larger sizes and higher dosages. After aging, the LE of AR binders remarkably increased while the PE slightly decreased. Specially, at this status, the LE even accounted for a significantly larger proportion of the whole modification effect than the PE. The LE of the rejuvenated AR binders significantly decreased due to the softening effect of the rejuvenator. The PE also slightly reduced after rejuvenation because of the further degradation of crumb rubber. On the other hand, the proportion of asphaltenes and resins increased while the proportion of aromatics and saturates decreased during the aging, and the changes in fractions were on the contrary after the rejuvenation. The statistical analysis revealed that the rheological properties of liquid phases were dominantly affected by chemical fractions for all the unaged, aged and rejuvenated AR binders.

Assessing the effect of short and long-term aging on moisture damage of hot mix asphalt using two different methods

ABSTRACT The effects of short-term aging (STA) and long-term aging (LTA) on moisture damage mechanisms were investigated using mechanical and thermodynamic methods. PG58-22 and PG64-16 asphalt binders modified with Dodecylamine (DA) and Wetfix (WT) additives and limestone and granite aggregates were used. The moisture sensitivity was assessed using the indirect tensile strength (ITS) test via the modified Lottman test and the surface free energy (SFE) method. As asphalt binder becomes harder due to aging, ITS values increase in dry conditions. However, ITS values decrease due to the texture and mineralogical properties of aggregates, the reduction of mastic cohesion and asphalt binder-aggregate adhesion because of water infiltration and weakening of the mixture in wet conditions. The tensile strength ratio (TSR) test revealed that TSR values decrease due to aging. The cohesion free energy of the PG64-16 asphalt binder increased by 8.9% in the STA state and by 29.8% in the LTA state compared to the unaged state. This rise in PG58-22 was about the same as that in PG64-16. Asphalt binder aging in all the samples reduced the adhesion energy. These variations indicated that aging reduces the probability of cohesion failure and increases the probability of adhesion failure.

Adhesion characteristics and spectroscopic analysis of regenerated ultraviolet aged asphalt binder using waste vegetable oil

The adhesion characteristics between asphalt and aggregate are damaged severely after ultraviolet (UV) aging. Thus, the adhesion characteristics of UV-aged asphalt after regeneration should be investigated. The regenerated UV-aged asphalt was prepared according to different influencing factors (aging asphalt with UV for different amounts of time, different rejuvenator content, and different stirring temperatures and stirring times). Using the surface free energy (SFE) theory, the effects of the four influencing factors above on the adhesion characteristics of regenerated UV-aged asphalt were investigated. Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the functional group changes of different types of regenerated UV-aged asphalt. The results indicated that the regenerated asphalt under different preparation conditions exhibited different regeneration effects. The SFE showed that the asphalt’s adhesion improved after regeneration and its resistance to water damage increased. Further, an appropriate increase in the stirring temperature and stirring time improved the regenerated asphalt’s adhesion. It was concluded from the FTIR analysis that the homemade rejuvenator diluted the carbonyl and sulfoxide groups in the aged asphalt and restored some of the asphalt’s properties. In addition, the correlation between the SFE index and carbonyl group correction peak area was analyzed. The correlation between the peak area and the peeling work at different stirring temperatures was 0.98. Therefore, regenerated asphalt’s adhesion can be evaluated effectively with SFE and FTIR.

Stage-aging characteristics and stages division of crumb rubber modified asphalt binder

Currently, the aged crumb rubber-modified asphalt binder (CRMA) pavements have recycling demands; however, the understanding of the aging behavior of CRMA remains limited. Furthermore, few studies have been conducted to divide the aging stage of CRMA, which is an essential basis for the study of recycling. To solve the above problems, this study aims to analyze the stage-aging characteristics and divide the aging stages of the CRMA to understand better the aging and recycling mechanism of CRMA. The evolution characteristics of the rheological performance of aged CRMA were assessed by high-temperature performance indicators. In addition, thermal gravimetric analysis (TGA) is employed to investigate the degradation degree of crumb rubber modifier (CRM). Finally, the rheological-performance results are combined with the TGA results to divide the aging stages. The results demonstrate that the CRM in CRMA degrades in aging, which shows an initial rapid degradation, then slows down. The process of CRM degradation is accompanied by changes in CRM composition; the natural rubber content of CRM decreases the most significantly, followed by synthetic rubber and filler. The evolution of the properties of aged CRMA is characterized by stages due to CRM degradation, and the CRMA is divided into three aging stages. In addition, the gray correlation entropy analysis demonstrates that the MSCR test is more sensitive to the degradation of CRM in CRMA; it can be used to characterize the stage-aging process of CRMA. In summary, this study's results might fill a significant gap in understanding the aging mechanism of CRMA and provide the basis for recycling the aged CRMA.

Molecular dynamics simulation and experimental validation on the interfacial diffusion behaviors of rejuvenators in aged bitumen

This study aims to multiscale investigate the effects of rejuvenator type, temperature, and aging degree of bitumen on the diffusion behaviors of rejuvenators (bio-oil BO, engine-oil EO, naphthenic-oil NO, and aromatic-oil AO) in aged binders. The molecular dynamics (MD) simulation method is performed to detect the molecular-level diffusion characteristics of rejuvenators and predict their diffusion coefficient (D) parameters. At an atomic scale, the mutual but partial interfacial diffusion feature between rejuvenators and aged bitumen molecules is observed. Moreover, Fick's Second Law well fits the concentration distribution of rejuvenator molecules in aged bitumen. The magnitude for D values of four rejuvenators varies from 10-11 to 10-10 m2/s, and the diffusive capacity order is BO > EO > NO > AO. Meanwhile, diffusion tests and dynamic shear rheometer (DSR) characterizations are employed to validate the MD simulation outputs. The experimental results in magnitude and order of D values agree well with MD simulation outputs. Lastly, the increased aging degree of bitumen exhibits a negative impact on the molecular diffusivity of BO, EO, and NO rejuvenators, while the D value of AO molecules enlarges as the aging level deepens. The underlying mechanism may be composed of the free volume fraction in aged bitumen and the intermolecular force between rejuvenator and aged bitumen molecules, which differs remarkably for various rejuvenators.

Characterization of Base Oil Effects on Aged Asphalt Binders Considering Bicycle Road.

Demand for various bicycles and sharing systems has constantly been growing worldwide as they improve the quality of life and promote eco-friendly transportation. Accordingly, it is inevitable that bicycle roads should be expanded. As bicycle roads have a relatively lower load applied than automobile roads, adopting a design method that uses a high reclaimed asphalt pavement (RAP) content can be beneficial. However, much uncertainty still exists about the relation between the mixing method and application in field sites, without appropriately considering the quality control of the rejuvenator. Therefore, this study aims to demonstrate the effect of base oil as a rejuvenator on aged binders, considering the use of a high RAP content for bicycle roads. To prepare the aged binder, a rolling thin-film oven (RTFO) and pressure aging vessel (PAV) were used to imitate the life cycle of asphalt pavement from production to service life, and then three contents of aged binder (0%, 50%, and 100%) were added and mixed with fresh PG 64-22 base binder. Finally, each type of prepared aged asphalt binder was blended with three different base oil contents (0%, 5%, and 10%). The results indicated that (1) the addition of base oil effectively decreased the viscosity of aged binders, (2) aged binders containing base oil showed less G*/sin δ compared to originally aged binders, and (3) the application of base oil improves the cracking properties of the aged binder by decreasing stiffness. In conclusion, the most striking observation from the data analysis from the Superpave test and statistical results was the effect of reducing the asphaltene portion based on the use of base oil in the aged binder. Therefore, using base oil in RAP can enable the application of a high RAP content to the bicycle road.