Aged Asphalt Binders Research Articles

Study of the inter-diffusion characteristics and cracking resistance of virgin-aged asphalt binders using molecular dynamics simulation

• Inter-diffusion behavior between virgin and aged asphalt binders were investigated. • The degree of blending between virgin and aged asphalt binders were determined at the molecular level. • The cracking patterns of partial blending and total blending were distinguished. • The relationship between degree of blending and cracking resistance of blended asphalt were explored. To investigate the inter-diffusion characteristics and cracking resistance of blended asphalt binders, the virgin-aged asphalt models were developed through the molecular dynamics (MD) simulation. Based on the mass density profiles of virgin and aged asphalt binders, the effect of temperature on the inter-diffusion coefficients was analyzed. According to the spatial distribution of atoms, different blending states including partial blending and total blending were distinguished. The cracking resistance of blended asphalt binders was characterized by the fracture energy obtained from the stress-displacement responses. Relationship between degree of blending and cracking resistance was explored. Results show that high temperatures can increase the inter-diffusion coefficients of virgin and aged asphalt binders by enhancing the intramolecular potential energy and Van der Waals (VdW) interaction energy. Compared to aged asphalt binder, the virgin asphalt binder may be more susceptible to temperature. Under tensile loading, the crack always initiates in the blending zone of partially blended asphalt binders. However, for the totally blended asphalt binder, the crack is more likely to occur at localized defect locations which is randomly distributed. The ability of blended asphalt binder to withstand deformations becomes better, but the maximum tensile strength decreases a lot as the temperature increases. There is a positive correlation between the degree of blending and fracture energy of blended asphalt binders, indicating that the asphalt binder with a higher degree of blending has better cracking resistance. The results of MD simulations can help determine how much aged binder can be mobilized to blend with virgin binder and help select appropriate virgin binders or other additives that can improve the blending between virgin and aged asphalt.

Evaluation of Waste Tire Pyrolytic Oil as a Rejuvenation Agent for Unmodified, Polymer-Modified, and Rubber-Modified Aged Asphalt Binders

This study evaluated tire pyrolytic oil (TPO) derived from waste tire pyrolysis as a rejuvenating agent for three types of aged asphalt binders (unmodified, polymer-modified, and crumb rubber–modified). Gas chromatography–mass spectrometry (GC–MS) was performed to identify chemical compounds present in TPO. The rheological characteristics of all binders were examined through the complex viscosity–frequency profile, zero-shear viscosity, failure temperature, Black space diagrams, Cole–Cole plots, Superpave fatigue parameter, Glover–Rowe parameter, and linear amplitude sweep (LAS) tests. Mass loss was also determined for the rejuvenated binders. All binders were subjected to Fourier transform infrared (FTIR) analysis, and sulfoxide and carbonyl indices were computed. Atomic force microscopy (AFM) was conducted to study the effect of TPO on the micromorphology of the binders. The normalized Euclidean distance approach was used to rank the rejuvenated binders with respect to the proximity of their rheological and FTIR characteristics to that of the unaged binder. The use of TPO as a rejuvenating agent enabled the aged binders to achieve properties comparable to those of the unaged asphalt binder. The AFM-based rejuvenation index (RI) indicated a good potential of TPO as a rejuvenator. The results of the binder rheological parameters and the FTIR indicators investigated in the study indicated that a 9% dosage of TPO as a rejuvenating agent was the most effective.

Effect of modifier on Low-Temperature reversible aging behavior of asphalt binder and its morphology analysis

• Rubber powder can alleviate the effect of reversible hardening on asphalt binders. • The addition of modifiers can reduce the reversible hardening degree of the asphalt binder. • Cone penetration test can be used to characterize the reversible hardening degree of the asphalt binder. • With the extension of conditioning time, the average area of asphalt binder “bee” structure increases gradually. Reversible aging of asphalt binders is one of the reasons for the premature failure of asphalt pavements. To better understand the effect of modifier types on the reversible aging in asphalt binder, styrene–butadienestyrene (SBS), styrene-butadiene rubber (SBR), crumb rubber (CR), and Nano-CaCO 3 were selected to prepare modified asphalt binder. Firstly, an extended bending beam rheometer (Ex-BBR) test and a cone penetration test (CPT) were carried out on base asphalt (BA) and modified asphalt binders under different conditions. Secondly, the reversible aging behavior of asphalt binders was characterized using a logistic regression model. Furthermore, the mechanisms of asphalt reversible aging were analyzed by atomic force microscopy (AFM) and molecular dynamics (MD) simulation. The results show that the addition of modifiers affects the reversible aging behavior of asphalt binders. Compared with SBS, SBR, and nano-CaCO 3 , CR can improve the mobility of asphalt molecules and mitigate the aggregation of asphalt molecules, thereby alleviating the impact of reversible aging on asphalt binder performance. After 72 h low-temperature conditioning, CR modified asphalt binder has the smallest grade loss of 1.7 °C. The low-temperature conditioning time can greatly affect the microstructure of the asphalt binder. With the increase of low-temperature conditioning time, the average area of the asphalt binder’s “bee” structures increases linearly. Furthermore, the reversible aging behavior of asphalt binders can be better understood using MD simulation.

Rheological properties of model wax doped asphalt binders

To better understand the effect of three kinds of pure wax in asphalt binder on the rheological properties of asphalt, model asphalts were prepared with eicosane, triacontane, and squalane. Multi-stress creep recovery (MSCR) test, linear amplitude scan (LAS) test, and low-temperature dynamic mechanical test (torsion bar) were employed as the primary performance evaluation methods of high-temperature rutting, medium temperature fatigue, and low-temperature thermoreversible aging of asphalt binder, respectively. The test results showed that at high temperatures, no matter what form of wax existed, it could hurt the rutting resistance of asphalt; however, the branched-chain alkanes reduced this adverse effect. Under medium temperature, triacontane had the most significant negative influence on the fatigue performance of asphalt, while eicosane and squalane improved the fatigue performance of asphalt. Finally, thermoreversible aging was observed in the waxes doped asphalts at low temperatures. The degree of thermoreversible aging mainly relied on temperature, time, and wax structure rather than stress-induced volume change or previous deformation history.

Comparing the Effect of Thermal-Oxidation and Photo-Oxidation of Asphalt Mixtures on the Rheological and Chemical Properties of Extracted Bituminous Binder.

The reliable and representative ageing of asphalt samples in the laboratory is critically important to research on asphalt durability, waste material recycling and rejuvenation treatments. However, standard laboratory ageing protocols omit ultraviolet radiation and moisture, and are also based on a universally applied oven temperature and ageing duration. The aim of this research was to demonstrate the importance of ultraviolet radiation in laboratory asphalt aging, motivated by the need for more realistic ageing protocols. Asphalt cores were thermally aged in a standard laboratory oven for 98 days, while other cores were aged for the same period in a weathering chamber that combined thermal–oxidative (heat) and photo-oxidative (ultraviolet irradiation) aging. The bitumen was then extracted from the top, middle and bottom of each asphalt core, and tested for rheological, chemical, and compositional properties. The results were used to compare the effects of the aging protocols, and the effects of depth below the pavement surface. It was concluded that accelerated laboratory asphalt ageing must include photo-oxidation, in combination with thermal oxidation. It was also concluded that both chemical and rheological properties were effective indicators of extracted asphalt binder aging, although the rheological testing was preferred.

Kinetics-based formulation of relationship between healing and ageing of asphalt binder

ABSTRACT Ageing and healing are both important characteristics of asphalt binder. The effect of ageing on healing is often studied, but the quantitative relationship between them is not clear. Thus, this study aims at explaining and formulating the inner relationship between healing and ageing based on a kinetics-based approach, expressed as healing and ageing activation energy, respectively. The healing activation energy is obtained based on the healing kinetics approach using recoverable strain energy (RSE). The ageing activation energy is calculated based on the kinetics-based ageing model. After that, further analysis is performed to explore the relationship between healing and ageing kinetic rates of asphalt binders, and the interpretation of the discovered relationship is proposed. The results indicate that the healing activation energy of aged asphalt binder has no big difference from the sum of ageing activation energy plus the healing activation energy of unaged asphalt binder. Define the ratio of initial temperature kinetic rate to the final temperature kinetic rate of healing/ageing as the healing/ageing rate ratio. It indicates that the product of the healing rate ratio of unaged asphalt binder and the ageing rate ratio of the same binder is close to the healing rate ratio of aged asphalt binder.

The classification and reutilisation of recycled asphalt pavement binder: Norwegian case study

With increased demand of asphalt pavement and limited binder and aggregate supply, the reutilisation of Recycled Asphalt Pavement (RAP) has gained more attention in pavement engineering from the environmental, sustainable, and economic views. Given this background, this study aims to classify and reutilise the recycled asphalt binder collected from Norwegian fields used for new asphalt pavement. For this purpose, three RAP binders (namely RAP-1, RAP-2, and RAP-3) extracted from the recycled asphalt pavement were categorised into two types of asphalt binders by comparing them with fresh asphalt binder 70/100 and long-term aged asphalt binder in terms of the physical, chemical, rheological, and mechanical properties. The specific treatments for the two types of RAP binder were proposed: Direct application of RAP-1 and RAP-2 binders as a replacement for fresh asphalt binder; and restoring RAP-3 binder by 4% rejuvenator to the same level as a fresh asphalt binder. Finally, the feasibility of three treated RAP binders for asphalt pavement was evaluated by analysing asphalt mixture performance. The results suggested that the three RAP binders can be applied to new asphalt pavements after proper treatments.

Study on the blending behavior of asphalt binder in mixing process of hot recycling

The blending behavior of aged and virgin asphalt binder is one of the most critical problems in the mixing process of hot recycling. To accurately measure the participation degree of aged asphalt and optimize the mixing process of hot recycling, a series of laboratory tests were designed by using magnetite aggregate and thin-layer chromatography with flame ionization detection (TLC-FID) for the first time. In this study, 24 different lab-mixing conditions were deliberately adopted to investigate the impact on the DoB of aged and virgin asphalt binders, including mixing amount of RAP, mixing amount of rejuvenating agent, mixing time, mixing temperature, mixing orders and the thickness of asphalt film. The results indicated that the aged and virgin asphalt cannot be completely blended in the mixing process and DoB is only about 40–60 % in general. The DoB decreases with the increase of asphalt film thickness and it decreases by 30 % when asphalt film thickness is 9 µm. DOB increased with the content of RAP and rejuvenating agent up to 70 % which same as mixing sequence. Although the mixing time and temperature can promote DOB, the mixing time and temperature should be controlled within 240 s and 170 °C, otherwise the accuracy of DOB will be affected.

Chemical and thermodynamic properties of palm oil-based materials and their impact on recycled binder blends

• We characterised chemical and thermodynamic properties of palm oil-based materials. • We assessed the impact of adding these agents to binder blends of an HMA with high RAP. • Surface free energy was used to assess the adhesion quality and durability of the bonds between aggregates and recycled binder blends with these agents. • Key chemical compounds present in the palm oil materials contributed to the rejuvenation effectiveness. • Palm oil-based materials are promising candidates to be used as rejuvenators in HMA with high RAP. Rejuvenators are agents added during the production of hot mix asphalts with high contents of reclaimed asphalt pavement (RAP) to restore some properties of the aged RAP binder. These materials can be obtained from numerous sources; hence, their chemical composition and physical properties vary greatly, which can have an impact on the final mixtures’ properties. This work assesses key chemical properties of crude palm oil and two of its solid by-products to understand their rejuvenation effect on a blend of a virgin and an aged RAP asphalt binder. The evaluation included thermogravimetry analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and chromatography analysis. Besides, surface free energy measurements (SFE) on the recycled binder blends (i.e., virgin asphalt binder, RAP asphalt binder and rejuvenator) and of two aggregate sources were used to evaluate the impact of the palm oils in the adhesive bonds’ quality and moisture sensitivity of the recycled binder blends-aggregates systems. Results indicate that the palm oil materials have good thermal stability and contain several large molecular size (LMS) compounds that contribute to the rejuvenation effect. Besides, recycled binder blends produced with the palm oil materials developed strong adhesive bonds in dry and wet conditions. Overall, results highlight the potential of palm oil and its solid by-products as rejuvenators for high RAP content asphalt mixtures.

Reducing Compaction Temperature of Asphalt Mixtures by GNP Modification and Aggregate Packing Optimization.

Compaction of hot mix asphalt (HMA) requires high temperatures in the range of 125 to 145 C to ensure the fluidity of asphalt binder and, therefore, the workability of asphalt mixtures. The high temperatures are associated with high energy consumption, and higher NOx emissions, and can also accelerate the aging of asphalt binders. In previous research, the authors have developed two approaches for improving the compactability of asphalt mixtures: (1) addition of Graphite Nanoplatelets (GNPs), and (2) optimizing aggregate packing. This research explores the effects of these two approaches, and the combination of them, on reducing compaction temperatures while the production temperature is kept at the traditional levels. A reduction in compaction temperatures is desired for prolonging the paving window, extending the hauling distance, reducing the energy consumption for reheating, and for reducing the number of repairs and their negative environmental and safety effects, by improving the durability of the mixtures. A Superpave asphalt mixture was chosen as the control mixture. Three modified mixtures were designed, respectively, by (1) adding 6% GNP by the weight of binder, (2) optimizing aggregate packing, and (3) combining the two previous approaches. Gyratory compaction tests were performed on the four mixtures at two compaction temperatures: 135 C (the compaction temperature of the control mixture) and 95 C. A method was proposed based on the gyratory compaction to estimate the compaction temperature of the mixtures. The results show that all the three methods increase the compactability of mixtures and thus significantly reduce the compaction temperatures. Method 3 (combining GNP modification and aggregate packing optimization) has the most significant effect, followed by method 1 (GNP modification), and method 2 (aggregate packing optimization).

Rejuvenation of aged asphalt binders by waste engine oil and SBS blend: Physical, chemical, and rheological properties of binders and mechanical evaluations of mixtures

Due to the poor cracking performance of aged binders, the use of reclaimed asphalt pavement (RAP) in road pavements is limited. When applying a greater RAP percentage, the use of a rejuvenator is necessary. The rejuvenator's unfavourable softening impact, on the other hand, causes the pavement to be vulnerable to rutting. As a result, RAP binders with optimized rutting and fatigue cracking properties are required. Therefore, this study was carried out to evaluate the simultaneous effects of 70% waste engine oil (WEO) and 30% SBS copolymer as a compound rejuvenator (WS-rejuvenator) on the performance of asphalt binders and mixtures containing RAP binders of 30% and 50%. The physical, chemical and rheological properties of asphalt binders were evaluated using the conventional tests, SARA (Saturate, Aromatic, Resin, and Asphaltene) analysis, FTIR test, thermal gravimetric analysis (TGA), DSR, and BBR. The mechanical properties of mixtures were examined using the Marshall, indirect tensile strength, moisture damage, rutting, and aggregate coating tests. The findings showed that WS-rejuvenator at 5% and 10% recovered the physical characteristics of asphalt binders containing 30% and 50% RAP, respectively. Furthermore, WS-rejuvenator was able to compensate for the light components of the RAP binder that were lost over time. As a consequence, the behavior of the RAP binder at high, moderate, and low temperatures was recovered to that of the virgin binder. By mixing the RAP binder with the compound rejuvenator, the oxygenation indices were effectively reduced. The TGA revealed that the thermal stability of regenerated binders was equivalent to that of the virgin binders. In addition, the mechanical properties of regenerated mixes were enhanced in comparison to the control mixture. In summary, the adoption of RAP and WEO-SBS rejuvenator in asphalt mixtures show promising outcomes to enhance greener pavement materials application in the future.

Assessment of the Aging Process of Finished Product–Modified Asphalt Binder and Its Aging Mechanism

Styrene-butadiene-styrene-modified asphalt binder (SBSMA), crumb rubber–modified asphalt binder (CRMA), and high-viscosity-modified asphalt binder (HVMA) have been widely used in porous asphalt concrete. However, the aging of the modified asphalt binder significantly affects the performance of the porous asphalt concrete. The main aim of this research is to quantitatively assess the aging degree of finished product–modified asphalt binders of SBSMA, CRMA, and HVMA at high, medium, and low temperatures, and to explore the aging mechanism at the microscopic level. This study used rolling thin-film oven and pressurized aging vessel to simulate the aging of asphalt binders. Dynamic shear rheometer, bending beam rheometer, Fourier transform infrared spectrometry, thin-layer chromatography with flame ionization detection, and scanning electron microscopy were employed to investigate how aging affects the rheological and microscopic properties of finished product–modified asphalt binder. The results showed that at high temperatures, short-term aging significantly impacted HVMA [change rate of the rutting factor (CRRF)=18.9%], while long-term aging had an enormous influence on CRMA (CRRF=179.5%). Short-term aging had the greatest effect on the fatigue property at medium temperature of CRMA [change rate of Nf(CRNf)=59.9%], followed by SBSMA (CRNf=46.1%) and HVMA (CRNf=26.2%). However, the effect of long-term aging on the fatigue properties of HVMA (CRNf=99.2%) is the largest, followed by that of CRMA (CRNf=95.8%) and SBSMA (CRNf=56.6%). At low temperature, compared with CRMA and HVMA, aging had the greatest influence on the low-temperature rheological properties of SBSMA. In addition, the three finished product–modified asphalt binders exhibited similar changes in microscopic level after aging.

Short-Term Aging Performance and Simulation of Modified Binders Using Adaptive Neuro-Fuzzy Inference System

The influence of polymer/nanocomposites (Acrylete-Styrene-Acrylonitrile (ASA)/ Nanosilica (Si)) asphalt binder aging and performance characteristics was investigated. ASA was used at 5% while nanosilcia was blended in 3, 5 and 7% concentrations by the weight of asphalt. Temperature sensitivity, aging resistance and viscoelastic properties of the asphalt binders were evaluated by conducting physical and dynamic shear rheometer (DSR) testing procedures. The tests were performed under unaged and short-term aged conditions by simulating the aging of asphalt in a Rolling thin film oven (RTFO). Additionally, the Adaptive Neuro-Fuzzy Inference System (ANFIS) modelling technique was adopted to predict the short-term aged behaviour of asphalt binders by using the viscoelastic properties of asphalt in an unaged state. The experimental outcomes from the DSR tests showed that the complex modulus (G*) was increased and the phase angle (δ) was reduced for the modified binders, indicating an improvement in the viscoelastic properties compared to the control asphalt binder. Furthermore, the considerably small difference in the G* and δ between the binders in unaged and RTFO aged states indicated that the modifiers had a positive effect in terms of improving the aging resistance of the asphalt binders. Moreover, the ANFIS model prediction capacity, which was assessed by the Coefficient of Determination (R2) and Mean Squared Error (MSE) and Mean Average Percentage Error (MAPE) was shown to be capable of accurately predicting the short term-aging behaviour of asphalt binders from the asphalt binder viscoelastic properties in an unaged state with an R2 value of 0.977, MSE of 0.00032 and MAPE of 0.286.

Comparative Investigation on the Properties and Molecular Mechanisms of Natural Phenolic Compounds and Rubber Polymers to Inhibit Oxidative Aging of Asphalt Binders

Using bio-based antioxidants and industrial wastes to inhibit asphalt aging is a sustainable practice in the pavement industry. To investigate the inhibitory effects and potential mechanisms of phenolic compounds and crumb tire rubber on the aging deterioration of asphalt binders, the aging characteristics of base asphalt, catechin modified asphalt, and crumb rubber modified asphalt were evaluated using Fourier transform infrared spectroscopy and reactive molecular dynamics simulations. The results showed that both catechins and crumb rubber exerted resistance to asphalt aging and that the former performed better. Specifically, catechins block asphalt aging at the chemical level by providing active H atoms to react with O2 and free radicals, thus preventing them from oxidizing asphalt molecules. In contrast, crumb rubber exerts its antiaging properties mainly in physical aspects, firstly by limiting the movement of asphalt molecules to reduce the contact and reaction of asphalt with O2 and secondly by counteracting the aging-induced asphalt hardening through its own degradation, thus partially restoring the mechanical properties of aged asphalt. This study provides molecular insight into the antiaging mechanisms of natural phenolic compounds and rubber polymers and is expected to provide theoretical guidance for the development of targeted antiaging technologies for asphalt binders.

Fatigue Behavior and Healing Properties of Aged Asphalt Binders

This study aims to investigate the fatigue behavior and healing properties of aged asphalt binders. Both 70# and SBS-modified asphalt binders were aged using a rolling thin-film oven test (RTFOT), and their physical properties were analyzed. Their fatigue behavior and healing properties were investigated using a dynamic-shear-rheometer time-sweep test. The influence of healing on fatigue behavior was evaluated in terms of the fatigue life ratio (FLR), and a new index was defined (accumulated dissipation-energy ratio, ADER) to evaluate the healing properties of aged asphalt binders. Aging reduced the penetration and ductility of both the asphalt binders, and large aging degrees increased their softening points. Small aging degrees slightly decreased the softening point of the SBS-modified asphalt binder but increased that of 70# asphalt binder. The former had a better thermal-oxidative aging resistance than the latter. Aging increased the complex shear modulus of the binders, resulting in a longer fatigue life under controlled-stress conditions. The fatigue life of aging asphalt binders obeyed a good (R2>0.90) double-logarithmic linear relationship with the stress level. Healing recovers the asphalt complex shear modulus and extends its fatigue life. Additionally, the FLR and ADER increased with a decrease in aging degree and an increase in the healing period.

Research on the Ability of Bio-rejuvenators to Disaggregate Oxidized Asphaltene Nanoclusters in Aged Asphalt.

A real rejuvenator must have the ability to disaggregate oxidized asphaltene nanoclusters. However, few studies pay attention to the topic, and there is a lack of comparison of the disaggregation ability of different rejuvenators. Thus, the disaggregation ability and regeneration mechanism of three bio-rejuvenators (waste cooking oil (WCO), waste wood oil (WWO), and straw liquefied residue oil (SLRO)) on oxidized asphaltene nanoclusters were studied in this paper. Laboratory tests and molecular dynamics (MD) simulation were used to compare the effectiveness of the three bio-rejuvenators and reveal its corresponding mechanism. It is found that these bio-rejuvenators have a softening effect on aged asphalt binder, but not all of them can disaggregate oxidized asphaltene nanoclusters. The introduction of WWO and WCO can effectively disturb the nanoclusters caused by the increase of polar functional groups during the oxidation process. The effect of WWO is more significant, but neither of them can restore the asphaltene dispersion to the virgin asphalt binder. SLRO has an adverse effect on the disaggregation of oxidized asphaltene nanoclusters. WCO, WWO, and SLRO showed different disaggregation mechanisms, including ″pull-out, intercalation, and compression″, respectively. WCO and WWO can increase the activation energy reduced by aging in a short aging time, and SLRO makes the activation energy lower. Such findings can help enterprises screen more reasonable rejuvenators to facilitate the recycling of reclaimed asphalt pavement (RAP) materials and promote the sustainable development of the construction industry.

Evaluation of waste engine oil rejuvenation for highly short term aged asphalt binder

Evaluation of waste engine oil rejuvenation for highly short term aged asphalt binder

Changes in the nanoscale asphaltene particles and relaxation spectra of asphalt binders during aging and rejuvenation

Asphalt binder is a widely used engineering material. It is essentially a nanomaterial with colloidal particles suspended in an oily medium. As asphalt binder ages, the colloidal particles are subject to fundamental physicochemical changes such as agglomeration, which is translated into dramatic engineering property changes of the asphalt binder. In engineering practices, organic rejuvenators are often added to the aged asphalt binder, with the hope of breaking down the nanoparticles and restoring its original engineering properties. However, how the nanoparticles evolve during the aging and rejuvenation of asphalt binder remains hypothetical. This study revealed the fundamental changes of the colloidal particles in asphalt binder during aging and rejuvenation. Moreover, changes in the morphology of colloidal particles are connected to the relaxation spectrum of the asphalt binder. As a result, practitioners do not have to rely on complicated methods and equipment to observe asphalt binders at the microscopic level. Instead, they can employ commonly used engineering tests with a dynamic shear rheometer (DSR) to decipher what occurs at the nanoscale during asphalt binder aging and rejuvenation. This would greatly assist practitioners in material selection and design.

Thermal, chemical and rheological properties of asphalt binders extracted from field cores

The intermediate-temperature performance of extracted asphalt binders (EABs) is altered when recycled asphalt shingles (RAS) and/or reclaimed asphalt pavement (RAP) are included in asphalt mixes. This happened as a result of the RAP’s aged asphalt binder and the RAS’s oxidized air-blown asphalt. Thus, the rheological properties of EABs from field cores were examined at intermediate temperatures. The fatigue life and the Superpave fatigue cracking parameter were among the rheological properties. Thermogravimetric analysis and Fourier transform infrared were used to analyze EABs’ thermal and chemical characteristics, respectively. The relationships between EABs’ fatigue cracking resistance, thermal, and chemical characteristics were scrutinized. Ages of mixes, percentages of RAP and/or RAS, and intermediate performance grade (PG) temperatures of virgin asphalt binders (VABs) controlled the resistance of EABs to fatigue cracking. Considering VABs with the same intermediate PG temperatures, EABs from older mixes with higher RAS percentages had higher resistance to fatigue cracking than those from younger mixes with lower RAP percentages. When RAP percentages in asphalt mixes were increased, EABs’ resistance to fatigue cracking deteriorated. Thermal and chemical analyses along with rheological characteristics are suggested as indicators of EABs’ intermediate-temperature performance.

Impacts of Field and Laboratory Long-Term Aging on Asphalt Binders

Asphalt binder aging accelerates cracking of flexible pavement. Quantifying the extent of binder aging allows the formulation and selection of appropriate binders for flexible pavement applications. Asphalt binder aging depends on climatic exposure, asphalt concrete field-surface density, and binder chemistry. The aim of this work was to select a laboratory-aging protocol to represent realistic field aging in Illinois. Binders were extracted from field cores aged from eight to 31 years. Extracted binders were tested for rheology and chemical characteristics. Small- and large-strain rheological parameters were determined. In addition, chemical functional groups and molecular weight distribution of extracted binders were evaluated. Effects of aging across pavement depth were also investigated. Double pressure-aging vessel (PAV) was identified as a suitable laboratory long-term aging protocol to represent eight to 12 years of aging for flexible pavements in Illinois. Thresholds were proposed for selected small- and large-strain rheological parameters representing realistic field aging. These thresholds may be used for binder selection and procurement to ensure the binder’s long-term performance. Furthermore, chemical analysis on extracted binders showed that only specific carbonyl functional groups are affected by field aging.