Aged Asphalt Research Articles

Assessing the effectiveness of bio-based oil in rejuvenating aged asphalt: a comprehensive physical, rheological, chemical, and mechanical examination

The utilization of reclaimed asphalt pavement (RAP) in flexible pavement construction and rehabilitation has gained significant traction, driven by the need to conserve limited natural resources. This study explores the effectiveness of bio-based oils derived from harvested crops as rejuvenators in asphalt mixtures containing 50% RAP. Comprehensive assessments were conducted, including penetration, softening point, viscosity and ductility tests, to determine the optimal rejuvenator dosage. Additionally, evaluations of rolling thin film oven (RTFO) aging, retained penetration and ductility, equivalent softening and breaking points, plasticity temperature range, stiffness modulus, complex modulus, and phase angle were performed. Fourier-transform infrared (FTIR) spectroscopy, Marshall immersion, and moisture susceptibility tests further validated the rejuvenator's efficacy in improving asphalt properties. The incorporation of 1.8% bio-oil significantly reduced the viscosity of the mixtures, enhancing workability. The rejuvenator effectively compensated for the loss of light components in aged binders, restoring the maximum and minimum temperature performance to levels comparable to virgin asphalt (VA). Mechanical testing revealed that bio-oil mitigated the aging effects of RAP asphalt, and the rejuvenated mixtures showed considerable improvements over both VA and non-rejuvenated RAP mixtures, where the rejuvenated specimens achieved 90.8 and 89.4% of retained strength index (RSI) values for 24- and 48-h immersion periods, respectively comparing with 88.9 and 86% post-immersion of VA for similar durations. These findings underscore the potential of bio-oil as a sustainable and eco-friendly solution for rejuvenating aged asphalts, paving the way for more sustainable asphalt production practices.

A bibliometric analysis of research on asphalt aging: trends, patterns, and impact

A bibliometric analysis of research on asphalt aging: trends, patterns, and impact

Performance Restoration of Aged SBS-Modified Asphalt in RAP via Dry-Process SBS modifier Diffusion at the Interface of Aggregate-Aged Asphalt-Virgin Asphalt

To address and recycle more RAP (Reclaimed Asphalt Pavement), dry-process SBS(Styrene-Butadiene-Styrene) modifier was applied in hot in-place recycling. Molecular simulation and laboratory experiments were conducted to investigate the diffusion behavior of dry-process SBS modifier on RAP surfaces and its effects on the properties of recycled asphalt and recycled asphalt mixtures (RAM). Molecular simulation results revealed that after the diffusion of dry-process SBS on RAP surfaces, the fractured and aged SBS molecules in the aged asphalt were replenished, leading to a 59.49% enhancement in the interface energy between aged asphalt and aggregates. Dry-process SBS exhibited bidirectional diffusion between RAP and virgin asphalt, with a preference for the intact SARA components of Virgin asphalt. The diffusion coefficient of the dry-process recycling system was significantly higher compared to conventional wet-process recycling, achieving a higher degree of fusion (DOB) between virgin and aged asphalt. Laboratory experiments demonstrated that dry-process recycling was more effective in restoring the performance of aged SBS-modified asphalt compared to wet-process recycling. At high RAP contents (80%, 100%), the asphalt mixtures from wet-process recycling failed to meet specifications for high-temperature permanent deformation resistance, low-temperature cracking resistance, and resistance to water damage. However, using 10% dry-process SBS modifier by mass of aged asphalt in RAP enabled 100% RAP content asphalt mixtures to meet specifications.

Molecular model and its evolution during secondary regeneration of asphalt based on molecular dynamics

With the use of recycled asphalt pavement, numerous recycled pavements will suffer from damages which needs to be regenerated for the second time (i.e. secondary regeneration). The mechanism and impact of secondary regeneration may diverge from those observed during primary regeneration. To study the aging and regeneration mechanism of secondary regenerated asphalt, the molecule models of regenerant and asphalts under different aging states were established through the molecular dynamics (MD). The double-layer diffusion models were constructed to examine the fusion behavior of new and aged asphalts. Based on this, the dynamic viscosity, rotational viscosity, bulk modulus, and shear modulus of secondary regenerated asphalt were predicted. The findings indicate that the established molecular models have a strong correlation with real asphalt molecules. During secondary regeneration, the deepening of asphalt aging reduces the fusion velocity and efficiency between aged and new asphalts. The introduction of regenerant can enhance the diffusion velocity between the aged and new asphalts, yet it does not necessarily improve their fusion degree. During the process of secondary regeneration, the shear modulus of secondary aged asphalt can be effectively restored by adding regenerant, but the recovery of dynamic viscosity, rotational viscosity and bulk modulus presents poor trends when compared to the primary regeneration.

Evaluation of pine needle oil recycled asphalt: Rheological characterization and molecular dynamics simulation

The regenerant based on bio-oil has the potential to lower carbon emissions, conserve natural resources, and shows promising prospects for application. In this paper, pine needle oil (PNO) and dioctyl phthalate (DOP) were utilized as base materials for asphalt rejuvenator. The primary aim of this research was investigate the impact of the rejuvenator on the rheological characteristics of asphalt and the compatibility between the rejuvenator and aged asphalt. The rheological properties of the asphalt were evaluated by the bending beam rheometer (BBR) and the dynamic shear rheometer (DSR). The glass transition temperature of the asphalt was tested by differential scanning calorimetry (DSC). Finally, the glass transition temperature (Tg), mean square displacement (MSD), cohesive energy density (CED), and solubility parameter (δ) were calculated and analyzed through molecular dynamics simulation to clarify the mechanism of PNO and DOP on asphalt. In the tested temperature range, the creep stiffness modulus of the PNO compound DOP recycled asphalt had decreased by 43.7∼68.4 % compared with the aged asphalt, and the rutting factor had decreased by 59.6∼75.3 %, but it was still better than the original asphalt. This showed that the regenerant had significantly restored the rheological properties of the asphalt. At 413.15 K, the difference of solubility parameters between PNO and DOP was the lowest, which was 1.37 and 0.17 (J/cm3)0.5, respectively. At this time, the compatibility between the PNO regenerant and aged asphalt was the best. The addition of the PNO softened the aged asphalt, reduced the rutting factor, adjusted the composition of the aged asphalt, improved its colloidal structure, and thereby enhanced its low temperature performance. The PNO regenerant also improved the diffusion of the four components of the aged asphalt and positively influenced the diffusion and fusion process of the system. DOP molecules lowered the asphalt's glass transition temperature, increased the amount of free space available for the thermal motion of asphalt molecules, and improved the compatibility of the asphalt with the regenerant.

Investigation on the oxidation aging resistance of asphalt by rejuvenator-loaded porous CaCO3 microparticles

ABSTRACT To delay asphalt binder oxidation-aging, a slow-release strategy was proposed, wherein porous CaCO3 microparticles act as a sustained-release carrier. Porous CaCO3 microparticles act as rejuvenators to supplement the evaporated saturate and aromatic fractions during the asphalt pavements service life. Porous CaCO3 microparticles were designed and synthesised via a double-decomposition method, and a vacuum-assisted method was applied to load the rejuvenator into the nanopores. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and laser particle size analysis indicated the successful synthesis of porous CaCO3 microparticles and the realisation of loading for the rejuvenator. Furthermore, CaCO3 microparticles were added as alternatives to mineral fillers in the neat asphalt binder, and short – and long-term aging was conducted on the asphalt mastic. The aging resistance performance results suggested that the CaCO3 microparticles loaded with the rejuvenator exhibited good slow-release behaviour after 20 and 40 h of pressure vessel aging when the dose of the microparticles reached 30%–50%. In addition, the rejuvenator release mechanism investigated by molecular dynamics (MD) simulations demonstrated that the rejuvenator's diffusion coefficient in the aging asphalt system reached 32.9 × 10−7 cm2/s, an increase of about 24% compared to that of the unaged asphalt system and the binding energy of the asphalt rejuvenator after aging was 7.1 times the binding energy of the nanopore rejuvenator. This study indicates that rejuvenator-loaded porous CaCO3 microparticles are promising sustainable candidates for delaying oxidative aging in the asphalt pavement industry.

Effect of Recycled Asphalt Mixture and Solid Waste-Based Solidification Materials on Performance of Cold-Regenerated Asphalt Mixture

In this study, an aging asphalt mixture was regenerated by a waste-based rejuvenator and cemented by solid waste-based solidification materials (SSMs). A splitting test, wheel tracking test, and three-point bending test were conducted to evaluate the properties of the regenerated asphalt mixture (RAM). The results reveal that the properties of the asphalt mixture were not diminished or were moderately enhanced by the 30% substitution of RAP. With the substitution of RAP to 100%, the splitting tensile strength, dynamic stability, and splitting strength ratio were decreased by 13%, 15%, and 5%, respectively. With the 100% substitution of SSMs for cement, the compressive strength, dynamic stability, flexural strain, and splitting strength ratios of the RAM were increased by 40%, 32%%, 14%, and 8%, respectively. The lightweight components can be supplemented, and low-temperature deformation and interlayer flowability can be improved by the incorporation of the rejuvenator. The generation of hydrated calcium silicate and ettringite for SSMs is greater than those of cement. The massive generation of ettringite has been observed to increase the solid phase volume by 120%, which may facilitate a more complete filling of the remaining pores in the RAM due to water evaporation. The regeneration and cement on green and the high performance of the rejuvenator and the SSM markedly enhanced RAM performance.

A Holistic View of Asphalt Binder Aging under Ultraviolet Conditions: Chemical, Structural, and Rheological Characterization

Asphalt, as a key binder material in road construction, is susceptible to ultraviolet (UV) radiation-induced aging, leading to embrittlement and reduced durability. Despite the significance of UV aging, research in this area remains limited compared to that on thermal aging. This paper comprehensively reviews the current state of research on UV aging in asphalt, focusing on its mechanism, evaluation indicators, and methods to delay or avoid UV aging. The structural components, rheological properties, and aging mechanisms of asphalt are discussed. Various UV aging simulation methods, including the use of UV chambers and accelerated aging tests, are presented along with their evaluation tests such as dynamic shear rheometry, rutting tests, Fourier infrared spectroscopy, and bending beam rheology. Key indicators used to assess UV aging, including physical properties, rheological parameters, and chemical composition changes, are summarized. The mechanisms underlying UV aging, particularly the changes in asphalt’s structural components and rheological properties, are examined. The impact of factors like radiation intensity, temperature, chemical composition, and asphalt film thickness on UV aging is discussed. Additionally, various additives and modifiers, including modified bitumen, UV shielding agents, UV absorbers, antioxidants, and nanomodifiers, are reviewed for their potential to mitigate UV aging. This paper concludes by highlighting the challenges in developing standardized test equipment and evaluation criteria, the limitations of organic modifiers, and the need for further research on nanomaterials to improve asphalt’s UV aging resistance.

Research on the micro-mechanism and factors of hot recycled asphalt binder cracking

The poor low-temperature performance of recycled asphalt is the primary cause of the recycled asphalt disease. However, further strengthening is required to analyze the molecular-level cracking of recycled asphalt. This article presented a comprehensive investigation of the cracking phenomenon of recycled asphalt at both the macro and micro levels. This was achieved through the utilization of experimental tests and molecular dynamics simulations. In this study, pressure-aged asphalt was subjected to 40 h of aging. The aged asphalt was divided into three groups: 30% RAP (reclaimed asphalt pavement) recycled asphalt, 50% RAP recycled asphalt, and 70% RAP recycled asphalt. The three groups were then analyzed in terms of three major indexes. Linear amplitude scanning (linear amplitude sweep, LAS) was conducted on the three groups. The mechanical response law of asphalt was obtained, and it was found that the coefficient of strength of recycled asphalt increased with the increase of RAP dosage. At the same time, the fracture energy density decreased subsequently. Furthermore, the fracture energy density of aged asphalt was 7% lower than base asphalt's. Subsequently, this study examined the four fractions and C=O and S=O functional groups of five types of asphalt and constructed the molecular structures and models of stable base asphalt and aged asphalt. Subsequently, this article constructed a fusion model of new and old asphalt, analyzed the fusion process of new and old asphalt, and studied the factors affecting the blending degree of new and old asphalt. Finally, the factors affecting the cracking performance of rejuvenated asphalt, including the blending degree, the content of the four fractions, and the addition of the rejuvenator, were investigated. The impact of each influencing factor on the cracking performance of recycled asphalt was analyzed from multiple perspectives. In conclusion, the findings of this study provide a valuable guide for interpreting the tensile properties of reclaimed asphalt and the influence of rejuvenators.

Study on the Effect of Hot and Humid Environmental Factors on the Mechanical Properties of Asphalt Concrete.

To investigate the effect of hot and humid environmental factors on the mechanical properties of asphalt mixtures research, in this paper, the dynamic modulus of asphalt mixtures under the effects of aging, dry-wet cycling, and coupled effects of aging and dry-wet cycling were measured by the simple performance tester (SPT) system, and the dynamic modulus principal curves were fitted based on the sigmoidal function. The results show that under the aging effect, the dynamic modulus of asphalt mixture increases with the aging degree; the dynamic modulus of short-term aged, medium-term aged, long-term aged, and ultra-long-term aged asphalt mixtures increased by 9.3%, 26.4%, 44.8%, and 57%, respectively, compared to unaged asphalt mixtures at 20 °C and 10 Hz; the high-temperature stability performance is enhanced, and the low temperature cracking resistance performance is enhanced; under the dry-wet cycle, the aging effect of asphalt water is more obvious in the early stage, and dynamic modulus of resilience of the mixture is slightly increased. In the long-term wet-dry cycle process, water on the asphalt and aggregate erosion increased, the structural bearing capacity attenuation, and the dynamic modulus of rebound greatly reduced at 20 °C and 10 Hz. For example, the dynamic modulus of asphalt mixtures with seven wet and dry cycles increased by 3% compared to asphalt mixtures without wet and dry cycles, and the dynamic modulus of asphalt mixtures with 14 cycles of wet and dry cycles and 21 cycles of wet and dry cycles decreased by 10.8% and 16.5%, respectively, compared to asphalt mixtures without wet and dry cycles. The main curve as a whole shifted downward; the high-temperature performance decreased significantly; in the aging wet-dry cycle coupling, the aging asphalt mixture is more susceptible to water erosion, and the first wet-dry cycle after the mix by the degree of water erosion is relatively small, along with the dynamic modulus of rebound. The dynamic modulus of resilience is relatively larger, and the high-temperature performance is relatively better, while the low-temperature performance is worse.

Waste coffee biochar and bi-oil composite modified rejuvenated asphalt: Preparation, characterization, and performance evaluation

In the realm of sustainable road construction, bio-oil has emerged as a promising and eco-friendly alternative for rejuvenating aged asphalt. Nevertheless, challenges arise due to poor stability, diminished performance at elevated temperatures, and limited anti-aging properties. This study introduces an innovative approach by blending biochar, obtained from the pyrolysis of waste coffee grounds, into bio-oil to create a composite modified regenerator. Initially, the study conducts a microscopic characterization of the biochar using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Subsequently, the rheological properties of this composite rejuvenated asphalt are evaluated across low, moderate, and high-temperature ranges using bending beam rheometer (BBR), linear amplitude sweep (LAS), and multiple stress creep and recovery (MSCR) tests. Departing from the traditional emphasis on initial property restoration, it further delves into performance alterations after re-aging of rejuvenated asphalt through temperature sweep (TS) and Fourier transform infrared spectroscopy (FTIR) tests, providing a comprehensive assessment of the anti-aging characteristics of rejuvenated asphalt. Additionally, gel permeation chromatography (GPC) is employed to quantitatively analyze the changes in asphalt molecular weight distribution. The microscopic characterization reveals the development of a rough and porous structure within the biochar, facilitating enhanced adhesion and interaction between the rejuvenator and the asphalt binder. Moreover, bio-oil rejuvenated asphalt exhibits excellent low-temperature crack resistance and moderate-temperature fatigue resistance. Following the incorporation of biochar, notable enhancements in high-temperature rutting resistance and anti-aging properties are observed, validating the efficacy of the biochar with bio-oil composite modified regenerator. To achieve optimal performance outcomes, a biochar content of 6 % (as a proportion of aged asphalt), corresponding to a 1:1 ratio of biochar to bio-oil, is recommended. Under this condition, the properties of the composite modified rejuvenated asphalt demonstrate comparability to those of the original asphalt. In summary, this research underscores the potential for integrating waste coffee biochar material into infrastructure development, thereby promoting circular economy principles and advancing more sustainable construction practices.

Investigation of the aggregation behavior of rubber asphalt components induced by short-term Aging: A perspective from molecular dynamic simulations and microscopic tests

The distribution characteristics of different rubber asphalt components remain a subject of debate, particularly under the influence of asphalt short-term aging. This paper leverages the visualization advantages of molecular dynamics (MD) simulation and integrates them with microscopic testing methods to observe morphological variations and property changes in the aggregation of different components induced by short-term aging. Short-term aging of rubber asphalt is simulated using a thin-film oven test (TFOT). By conducting Fluorescence microscope (FM) and scanning electron microscope (SEM) tests, the aggregation behavior of components under changes in fluorescence phase and microstructure before and after short-term aging is revealed. MD simulation is employed to analyze the degree of aggregation between different components before and after short-term aging. SEM test results indicate that the structure becomes looser and forms distinct pits as the rubber asphalt ages. FM test results reveal that the particle size of rubber powder particles in aged rubber asphalt decreases and aggregates gradually. Concurrently, the asphalt phase in rubber asphalt becomes more uniform after aging. MD simulation results demonstrate significant aggregation between asphaltene-asphaltene molecules and asphaltene-rubber powder molecules in aged rubber asphalt. A higher degree of asphaltene aggregation leads to reduce asphalt penetration and increase softening point and viscosity. Furthermore, rubber powder molecular chains can inhibit “π-π stacking,” and “offset π-π stacking” of the asphaltene molecules. Therefore, the accumulation effect in aged rubber asphalt is mitigated compared with aged base asphalt. The research outcomes provided a foundation for further studies on the aging and rejuvenation of rubber asphalt.

Distribution pattern and assembly mechanism of microbial community to cause biological aging of asphalt materials in forest road domain

The biological aging of asphalt due to microorganism decomposition causes such distresses as loosening and spalling on asphalt pavement in forest region, which deteriorates the durability of asphalt pavement. To study the distribution regularities of microbial communities in forest road domain and reveal the assembly mechanisms of microbial communities, 16S rRNA full-length sequencing was utilized to analyze the collected samples from three forest areas. Results show that when compared with those in roadside slope, the evenness and diversity of microbial community in asphalt pavement are decreased, but the richness of microbial community is significantly increased. Mycolicibacterium is screened for a biomarker in asphalt pavement. Additionally, the increase in the relative abundances of Bacteroidetes and Proteobacteria, which are the dominant bacteria in asphalt pavement, reshapes the co-occurrence network relationship among the microorganisms. The total carbon (TC) plays an important role in regulating the composition of microbial community. The microbial community in roadside slope is dominated by stochastic processes, while the strong interspecies interactions and selection effect of asphalt on microbial community strengthen the role of deterministic processes in remodeling the microbial community structure in asphalt pavement. This study is of great significance for understanding the biological aging mechanism of asphalt pavement.

Study on Rheological Properties of Waste Cooking Oil and Organic Montmorillonite Composite Recycled Asphalt

Pre-treated waste cooking oil (WCO) and organic montmorillonite (OMMT) were employed for the recycling of aged asphalt, which resulted in the improvement of the design of WCO asphalt rejuvenators and the enhancement of high-temperature performance of WCO-recycled asphalt. The effect of the rejuvenator and the properties of recycled asphalt were evaluated by viscosity, dynamic shear rheometer (DSR), bending beam rheometer (BBR) and scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) tests. The results indicated that aged asphalt could be obviously softened and restored to the level of original asphalt by adding 6% WCO. However, the high-temperature properties of recycled asphalt would be declined by adding too large a dose of WCO rejuvenator. The high-temperature performance of recycled asphalt was significantly improved by the WCO-OMMT complex rejuvenator, and the viscosity and rutting factor of recycled asphalt were increased. Light components of aged asphalt could be supplemented by WCO of the complex rejuvenator. The volatilization of small molecules could be slowed down by the peel structure formed by OMMT and small molecules of the asphalt, which resulted in the proportion of small molecular substances (SMS) being increased by 4% and improvement of the colloidal structure of aged asphalt. The high-temperature and low-temperature performance of recycled asphalt can be improved concurrently by the combination of 6% WCO and 1% OMMT, and this was evidenced by the fact that the high-temperature and low-temperature PG were all upgraded by one level.

Influence of Variable Intensity Ultraviolet on the Performance of SBS Modified Asphalt

Previous scholars studied UV aged asphalt performance under constant UV intensity. This study proposed a method of UV aged asphalt based on the time-varying UV intensity, which is more capable of realistically simulating the UV aging of asphalt under natural conditions. The softening point, viscosity, and DSR tests were used to analyze changes in conventional and rheological properties of UV aged asphalt and compared them with RTFO (Rolling Thin-Film Oven) aged asphalt. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) tests were analyzed for the microscopic characteristics. The aging index was also used to evaluate the percentage of asphalt aging attributable to each UV aging cycle. The results show that the softening point is more susceptible to UV radiation, with UV-6 cycles exceeding the softening point increment of RTFO. On the contrary, the viscosity is more susceptible to thermo-oxidative aging, and the viscosity increment of RTFO is 39.3% higher than that of UV-12 cycles. Based on DSR's test results, the rutting factor magnitude of RTFO was between 9-12 UV aging cycles The phase angle results indicate that thermo-oxidative aging is more likely to convert asphalt to elastomer than RTFO asphalt. UV aging process of asphalt produced sulfinyl and, carbonyl and other polar functional groups, asphalt intermolecular forced to enhance the production of a harder oxidation layer, the asphalt surface began to appear cracks. As aging time increases, the cracks become longer and deeper. Practical image recognition technology can identify the areas of the cracks. The crack area follows a linear pattern during cycles 3 to 9, while the growth rate slows down during cycles 9 to 12.

Evaluation on the diffusion-fusion properties and interfacial mechanical behavior of virgin and aged asphalt

To investigate the regeneration mechanisms of rejuvenated asphalt mixtures, molecular simulation techniques were employed to research virgin and aged asphalt's fusion characteristics and interface mechanical properties. The blended zone was identified based on relative density distribution, and a molecular-scale calculation method for the Degree of binder Blended (DOB) between virgin and aged asphalt was proposed. Finally, the influence of DOB on the mechanical properties of the asphalt-aggregate interface was evaluated through interface pull-out tests. The results revealed that the proposed molecular-scale DOB calculation method effectively assessed the blending effectiveness between virgin and aged asphalt. Higher degrees of asphalt aging made it more challenging for aged asphalt to fuse with virgin asphalt, while elevated temperatures facilitated diffusion fusion between them. Under tensile loading, initial cracks were primarily initiated from the rejuvenated asphalt's blended zone. This region represented the weakest area within the interface system and was prone to fracture under load. The increase in DOB significantly improved the interfacial properties of recycled asphalt, with the increase in DOB the interfacial tensile strength increased by 4%–14% and the fracture energy increased by 10%–19%. However, this enhancement effect diminished with an increased degree of asphalt aging. At the molecular scale, increasing DOB improved the interface strength and deformation resistance of rejuvenated asphalt. The molecular simulation results provide theoretical guidance for evaluating the fusion degree of aged asphalt in RAP materials and determining the utilization efficiency of aged asphalt.

Sustainability of Asphalt Mixtures Containing 50% RAP and Recycling Agents

The substitution of virgin asphalt binder with reclaimed asphalt pavement (RAP) has environmental and economic merits, however, cracking susceptibility arises due to the aged asphalt binder within RAP. The objectives of this study are to (1) enhance the cracking resistance of asphalt mixtures containing 50% RAP utilizing recycling agents (RAs) derived from six petroleum-based and bio-based materials, (2) conduct an environmental impact assessment (represented by global warming potential “GWP”) for high-RAP mixtures including RAs, and (3) estimate the cost effectiveness of including high-RAP content in asphalt mixtures. Based on the RAP asphalt binder performance grade (PG), base asphalt binder PG, and RAP content, the RA contents were determined to achieve a target asphalt binder of PG 76-22. A control mixture was benchmarked for comparison, specified for high-traffic volume roads, and contained PG 76-22 polymer-modified asphalt binder. The engineering performance of studied asphalt mixtures was evaluated using the Hamburg wheel-tracking (HWT), semi-circular bend, Illinois flexibility index, Ideal cracking tolerance, and thermal stress-restrained specimen tensile strength tests. It was found that petroleum-derived aromatic oil, soy-based oil, and tall oil fatty acid-based RAs demonstrated a successful restoration of aged RAP asphalt binder without compromising the permanent deformation resistance. The 50% RAP mixtures emitted less GWP by 41% and 42.9% using petroleum- and bio-oil RAs, respectively, and achieved a 31% cost reduction compared to the control mixtures.

Novel composite rejuvenators development and comparative analyses of epoxy versus diisocyanate rejuvenators in rejuvenating aged SBS-modified asphalt binders

Currently, many high-grade highways are undergoing expansion and remodeling phases. Utilizing recycled Styrene-Butadiene-Styrene (SBS) modified asphalt mixtures not only increases waste material utilization but also offers significant environmental benefits. In pursuit of high-quality rejuvenation of aged SBS-modified asphalt binders (SBSMA), this research leveraged aromatic oil (AO) as the component rejuvenator and introduced two novel SBS rejuvenators: ethylene glycol diglycidyl ether (GDE) and isophorone diisocyanate (IPDI). Furthermore, the study explores the mechanisms and effectiveness of both epoxy and diisocyanate rejuvenators, which are commonly used in SBS rejuvenation, specifically focusing on reconstructing cross-linked network structures within rejuvenated SBSMA. Findings indicate that during rejuvenation with diisocyanate rejuvenators and AO, the amide groups effectively react with carboxyl and ester groups in aged SBS, thus reconstructing the SBS modifiers. The rejuvenated SBS subsequently absorbs AO and light components, leading to swelling and the reconstruction of cross-linked network structures. Nevertheless, the rejuvenation efficacy of epoxy rejuvenators was relatively limited due to their low reactive nature or adverse side reactions that could degrade the rejuvenated SBS molecules, resulting in less effective reconstruction of the network structure. The specific differences in the reconstruction of network structures were reflected that diisocyanate rejuvenators improved the road performance of rejuvenated SBSMA under both high and low temperatures, reaching or even surpassing unaged SBSMA, while the performance of epoxy rejuvenators was closer to that achieved using AO alone. Overall, diisocyanate rejuvenators outperformed epoxy rejuvenators in repairing SBS, significantly enhancing the performance of SBSMA. This study provides valuable insights into achieving high-quality rejuvenation of SBSMA, which can significantly enhance the efficiency and quality of rejuvenation in high-grade roadways.

Moisture damage mechanism of asphalt mixtures containing reclaimed asphalt pavement binder: A novel molecular dynamics study

Reclaimed asphalt pavement (RAP) stands at the forefront of sustainable practices in road construction and rehabilitation. However, concerns regarding the moisture susceptibility of aged RAP binder have arisen due to its potential hazard to pavement durability. So far, the underlying mechanisms of how moisture infiltrates into the mixture and results in binder stripping remain controversial and scarcely investigated. To address this challenge, a novel molecular dynamics (MD) simulation method has been developed to explore the nanoscale stripping mechanisms, considering the effects of asphalt oxidative aging and rejuvenation. The results indicate that hydrogen bonding interactions between water and the aggregate surface reduce the contact distance compared to the distance between asphalt and aggregate. Under pore water pressure, moisture diffuses into the interface, occupying the van der Waals adhesion sites of asphalt molecules and consequently causing detachment. Asphalt oxidative aging, on one hand, increases the oxygen concentration and hydrophilicity, thereby increasing moisture susceptibility from the energy perspective. On the other hand, it increases the intermolecular friction between aged asphalt molecules, leading to reduced flexibility and age hardening, consequently triggering asphalt premature detachment and diminishing its coating quality on the aggregate surface. Rejuvenators can restore the moisture sensitivity of severely aged asphalt, with a mechanism involving two aspects: firstly, reducing the agglomeration and proportion of polar components in asphalt, thereby weakening its hydrophilicity; secondly, lubricating aged asphalt molecules to restore their flexibility and surface coating properties. Findings from this study contribute to revealing the moisture-induced damage mechanism when recycling RAP binder.

An efficient and robust method for evaluating the low-temperature performance of asphalt binder based on DSR testing

The BBR test has received growing concerns regarding its applicability to field studies and special materials due to the large amount of long-term aged asphalt binder used in preparing asphalt binder beams and the time-consuming beam preparation and testing process. In recent years, the application of a dynamic shear rheometer (DSR) to investigate the low-temperature performance of asphalt binder has attracted widespread attention because it uses significantly less asphalt binder for testing and allows for easy specimen preparation. The objective of this study was to develop an efficient and robust method to evaluate the low-temperature performance of asphalt binder based on DSR testing. Frequency sweep tests were performed on twelve asphalt binders at temperatures ranging from 0 to 25 °C using the 8-mm parallel plate geometry. Two conversions were applied to frequency sweep test data in order to predict the flexural creep stiffness and m-value of asphalt binder, namely the conversion from frequency domain to time domain and the conversion from shear loading to bending loading. The 1S2P1D model was employed to construct the master curves of storage modulus and loss modulus. Afterwards, the flexural creep stiffness was predicted using the shear creep compliance master curve model, which was derived from the 1S2P1D model using the inverse Laplace transform, and the Poisson’s ratio, which was assumed to be constant. It was found that the predicted values of S(60) and m(60) were comparable to the counterparts measured by the BBR, which well demonstrated the feasibility of the proposed DSR-BBR conversion method. In comparison to existing analysis methods, the proposed conversion method strictly complied with the linear viscoelastic theory, and it enabled efficient and robust predictions because the prediction model of flexural creep stiffness had the same parameters as those of the 1S2P1D model, thus avoiding multiple data fittings.