Aged Bitumen Research Articles

A novel approach for analyzing linear amplitude sweep (LAS) test data of asphalt binders

Fatigue cracking is one of the crucial distresses considered for the design of flexible pavements. The initiation of fatigue cracking occurs in the binder phase of an asphalt mixture. The linear amplitude sweep (LAS) test was developed to analyze the fatigue damage in the asphalt binder. AASHTO T391 provides a method to analyze the LAS test data by fitting a power equation between the fatigue parameter (G*sinδ) and damage intensity. This method has some inherent weaknesses of overfitting or underfitting of the data at different damage levels. This study proposes a new method where a total curve is divided into two parts that fit the data in two different equations and then sum them up. The first part comprises of the data up to cumulative damage corresponding to the maximum effective stress, and the second part consists of accumulated damage in the material till it reaches the maximum strain (30 %). This method is called the bifurcation method in this paper. LAS test data of 27 long-term aged bitumen samples having different physical properties is used to determine the number of fatigue life cycles (Nf) by these two methods, and results are compared in terms of mean absolute percentage error (MAPE), root mean square error (RMSE), and residual sum of squares (RSS). It is shown that there is a significant reduction in the errors when the data fitting was done using the proposed bifurcation method. Further, the ranking was allotted to the samples based on the number of fatigue life cycles (Nf) at three different strain levels (2.5 %, 5 %, and 10 %) at intermediate-temperature conditions estimated using two methods. The shift indicator parameter was used to analyze the variability in the ranking of the samples due to changes in the strain levels. The study concludes that the proposed bifurcation method fits the predicted values more accurately than the prescribed power law.

Simulation and investigation of the mild-moderate aging properties of SBS modified bitumen: Physical, microscopic and rheological properties

Styrene-butadiene-styrene block copolymer (SBS) modified bitumen (SMB) is unable to meet usage requirements after being exposed to sun-light, heat and oxygen. The researches show that it is difficult to restore bitumen effectively when the penetration of the aged bitumen is below 20 dmm. Therefore, the penetration of 20 dmm is taken as the dividing line in this paper. Higher than 20 dmm is considered as mild-moderate aging, while lower than 20 dmm is considered as severe aging. The traditional rotating thin-film ovens (RTFO) and pressure aging vessels (PAV) methods are similar to simulate the aging behavior of the upper layer of bitumen pavement, but they are difficult to simulate the aging in the depth direction of bitumen pavement. In this paper, the aging of the modified bitumen is simulated by extending the aging time and deepening the depth of the aging mold, and then it is graded according to the penetration. We aimed to investigate the differences in physical, microscopic and rheological properties of SMB with including 0 wt%, 1.5 wt%, 2.5 wt%, 3.5 wt%, 4.5 wt% and 5.5 wt% SBS content before and after aging. Through the physical performance, such as penetration, softening point, ductility and elastic recovery, it was observed that a high SBS content leads to strong anti-aging ability. Fourier Transform Infrared (FTIR), fluorescence microscopy (FM), scanning electron microscopy (SEM) and atomic-force microscope (AFM) revealed that a good network structure can be formed through absorbing light components when the SBS exceeds 3.5 wt%. After that, it was found that there is a positive correlation between aromatic index and penetration, as well as a positive correlation between butadiene index and softening point. Additionally, rheological frequency scanning and temperature scanning indicated that the modulus was increased and the phase angle was decreased with increasing SBS content or aging. After aging, the rutting resistance of SMB was enhanced but the cracking resistance was weakened. This research can establish a theoretical support and foundation for the regeneration of the mild-moderate aged SMB.

Chemo-rheological deterioration of bitumen due to UV ageing: correlations between accelerated UV ageing tests and 1-year outdoor exposure

Predicting the performance of asphalt roads after several years of service is complex due to multiple weather events that can contribute to road ageing. This study investigates the correlation between an accelerated ultraviolet (UV) ageing test and the ageing of polymer-modified binders after 1 year spent in outdoor conditions. The impact of natural ageing on several bituminous binders was investigated by rheological and chemical analyses. Plastomer-modified (ethylene vinyl acetate) bitumen seemed to be the most affected by environmental ageing as evaluated through rheological and chemical testing. Elastomer-modified (styrene butadiene styrene) bitumen appeared to be the most resistant to environmental ageing as expressed by non-load related cracking resistance and relaxation properties as well as low oxidation levels. The natural ageing test confirmed the results obtained via the accelerated UV ageing test considering the Glover-Rowe parameter (average R2 = 0.89). The 30-day accelerated UV test was estimated to fasten natural ageing of conventional and plastomer-modified bitumen by more than 10 times and up to 5 times for elastomer-modified bitumen compared to long-term outdoor exposure. If used with a suitable weather dataset, accelerated UV ageing is a promising method to predict the environmental-related ageing of conventional unmodified bitumen; however, adjustments are required for polymer-modified binders.

Effects of Laboratory Ageing on the Chemical Composition and High-Temperature Performance of Warm Mix Asphalt Binders

Warm asphalt mixtures can suffer from decreased short-term high-temperature performance; therefore, introducing additional modifiers can mitigate this risk. This study investigates the effects of a liquid organosilane warm mix additive (WMAd) and grade-bumping polyethylene-based additive added simultaneously to asphalt binders on their chemical composition and its relationship with performance characteristics. Previous studies found relationships between the formation of certain chemical species during bitumen ageing and the increase in their viscosity, stiffness and other performance characteristics—the present work intended to verify these relationships when the two mentioned additives are used. Two asphalt binders were investigated—a paving-grade 50/70 binder and a 45/80-55 polymer-modified bitumen. The chemical analysis was performed using Fourier-transform infrared (FTIR) spectroscopy in attenuated total reflectance mode and focused on the quantification of carbonyl, sulfoxide, polybutadiene and polystyrene structures in the asphalt binders subjected to laboratory short- and long-term ageing. Additionally, the relationships between asphalt binder performance and selected FTIR indices were evaluated using a dynamic shear rheometer. It was found that the investigated additives significantly affected the apparent contents of all evaluated chemical structures in the asphalt binders; however, these changes were not reflected in their performance evaluation.

Insight into synergistic effect of zinc oxide/expanded vermiculite composite (ZnO/EVMT) on bituminous mixture performances under different aging conditions

Zinc oxide/expanded vermiculite composite (ZnO/EVMT) with synergistic effect can effectively retard bitumen aging behavior, but the effect on road and mechanical performance of bituminous mixture under different aging conditions is unclear, which hinders its application and promotion. Based on the above, this study is meant to reveal the synergistic effect of ZnO/EVMT on bituminous mixture, with the ultraviolet absorber (UVA) compounding with antioxidant (AO) (label as UVA+AO, the same component ratio as ZnO/EVMT) and hydrated lime (HL) modifier serving as comparison. Then, the influence of ZnO/EVMT on the laboratory performances, including road performance and mechanical properties, of bituminous mixtures under four different aging conditions (unaged, long-term oven aging, long-term continuous and long-term all-weather photo-oxidative aging conditions) were investigated. Results show that under unaged condition, the addition of ZnO/EVMT can enhance road performance of bituminous mixture, and has similar effect to that of HL modifier and more positive effect than that of UVA+AO modifier. Under long-term oven aging condition, bituminous mixture containing ZnO/EVMT and HL have similar deformation resistance. ZnO/EVMT and the other two modifiers can enhance the low-temperature property, water stability and fatigue property of bituminous mixture, and ZnO/EVMT modified bituminous mixture has the highest low-temperature property and the lowest property change sensitivity. Under two long-term photo-oxidative aging conditions, ZnO/EVMT modified bituminous mixture generally exhibits higher creep deformation and deformation growth rate but lower mechanical performance changing rate than base bituminous mixture. Therefore, ZnO/EVMT can improve bituminous mixture road performance and reduce its aging sensitivity under different aging conditions. And the expected service life and durability of bituminous pavement will benefit from its promotion practice.

Investigation of the intelligent anti-aging bitumen using microcapsule clean-product secreting waste cooking oil through polyacrylamide-gel in porous-shell structure

The aging of bitumen is an urgent problem in pavement engineering materials. The objective of this work was to fabricate an intelligent anti-aging bitumen using a clean microcapsule product that secretes waste cooking oil through polyacrylamide (PAM)-gel in a porous shell structure. The microcapsule had a composite shell with cross-linked hexamethoxymethylmelamine as a skeleton with a porous structure and gel PAM filled in pores as the channels of the liquid waste cooking oil as core material. Aged bitumen was mixed with various microcapsules, and their physical and chemical properties were investigated. The testing results indicated that shells had successfully microencapsulated the oily rejuvenator without defects and damages. FT-IR results showed that the HMMM had been cross-linked and PAM also deposited in shells. SEM morphology showed that PAM was removed from the shell material after alcohol elution, and the shell still kept the spherical shape with a porous structure. Penetration experiments have demonstrated that PAM in the porous structure of the shell material can serve as a secretion channel for core material. Microcapsules had perfect thermal stability and homogeneous dispersion in bitumen, and there was no interface separation phenomenon. The test results showed that the bitumen/microcapsules samples gradually became softer and increased viscosity based on the viscosity changes, softening point, and penetration parameters. The tensile test also proved that adding microcapsules reduced the tensile strength of aged bitumen and increased the tensile elongation with the extension of time, which was entirely attributed to the action of the secreted rejuvenator molecules. The complex shear modulus (G*) values of bitumen/microcapsules samples gradually decreased with anti-aging time increasing at the same temperature. The phase angle values (δ) show that its value gradually decreases after the anti-aging process, indicating that the elastic composition of bitumen increases.

Rheological Performance and Differences between Laboratory-Aged and RAP Bitumen.

Traditional recycled asphalt pavement (RAP) binder extraction is not a cost-effective and sustainable option for a quick field study because it requires the use of a huge amount of solvent. Hence, most of the studies on asphalt pavement are carried out with laboratory-aged bitumen in accordance with well-established procedures, i.e., the pressure aging vessel (PAV). Unfortunately, some studies highlight the differences between bitumen aged in the laboratory and in service because it is difficult to reproduce extreme conditions such as real conditions, both atmospheric and load; and this also affects the choice and use of rejuvenators, sometimes compromising the interpretation of results. This study aims to compare the thermo-rheological behavior of a 70/100 bitumen aged with the PAV and two different binders extracted by RAPs. The rheological performances of bitumens were compared in temperature and by dynamic oscillatory tests and steady-state tests, resulting in strength and viscosity values higher for samples with RAP binders compared to the PAV sample. The same bitumens were tested with the addition of a 3% w/w of soybean oil (SO). The results show a decrease in the moduli and viscosity at all the temperatures investigated when SO is added to the laboratory-aged bitumen, while no appreciable differences are evident on naturally aged samples added with SO. Differences were evaluated in terms of cross-over frequency and rheological parameters. Furthermore, the SO effect showed substantial differences, especially in viscosity values, indicating that the study of regenerated or modified bitumen from aged bitumen still requires study, as current standard techniques and procedures cannot emulate real aging conditions well.

Use of antioxidants to retard aging of bitumen: A review.

Oxidative aging of bitumen is an inevitable and irreversible phenomenon. Exposure to detrimental factors such as sunlight, oxygen, and UV radiations accelerates the aging of bitumen and bituminous pavement. The aging process induces hardening and embrittlement in bitumen, leading to premature pavement failure. Therefore, for constructing sustainable long-lasting pavements anti-aging additives are used. Among the available additives, the use of antioxidants has emerged as a promising solution to mitigate the aging of bitumen. The current review aims to summarise the existing literature for a comprehensive understanding of the effectiveness of these additives as aging inhibitors. It provides an overview of the chemical pathway involved during bitumen oxidation and various quantification techniques to measure the effect of aging. This review also highlights the potential use of antioxidants in bitumen and elaborates on the working mechanism of different types of antioxidants to prevent bitumen aging. Further, the effect of modification in bitumen at micro, macro, and mixture levels are discussed. Additionally, cost analysis and future prospects on the use of antioxidants for bitumen are presented.

Laboratory evaluation of synergistic blending with SBS-modified bitumen and rejuvenator to enhance the performance of recycled bitumen with a high content of RAP materials

Reclaimed asphalt pavement (RAP) stands as a pivotal construction material widely used in asphalt pavement rehabilitation. The prevailing focus and trajectory revolve around increasing the proportion and utility of RAP materials. However, the potential for temperature and fatigue cracking increases with the dosage of RAP materials. In this study, SBS modified bitumen (SBSMB) and four rejuvenators were combined synergistically with aged asphalt to enhance the performances of the recycled bitumen with high RAP content and consequently augment the value of the RAP material, all while ensuring compatibility between the SBSMB and aged base bitumen. Initially, the base bitumen was aged using a pressure aging vessel (PAV) test. Subsequently, a selection of virgin bitumen (VB), SBSMB, and four rejuvenators were utilized to revitalize the aged bitumen. A comprehensive battery of tests, encompassing conventional tests, temperature sweep, frequency sweep, multiple stress creep recovery (MSCR), bending beam rheometer (BBR), and linear amplitude sweep (LAS), were carried out to characterize the rheological properties. Finally, Fourier transform infrared spectroscopy (FTIR) was employed, along with the determination of polystyrene index (IPS) and polybutadiene index (IPB), to evaluate the compatibility between SBSMB and aged base bitumen. The results underscore that the incorporation of SBSMB and rejuvenator comprehensively enhances high-temperature performance and fatigue cracking resistance while effectively reinstating low-temperature cracking resistance. Furthermore, the values of IPS, IPB, and IPS/IPB exhibit an increase with the addition of a rejuvenator, indicating its potential to improve the compatibility between SBSMB and aged base bitumen. Thus, this research proposes a more cost-effective and environmentally sustainable approach to bolstering conventional asphalt pavement performance and grade.

Performance of asphalt mixtures containing high reclaimed asphalt pavement and waste steel rolling oil

Reducing costs, dealing with environmental problems, and preserving more natural resources are among the main incentives for reusing asphalt instead of road reconstruction. However, asphalt reuse involves the addition of some modifiers to the asphalt mixture. In this respect, rejuvenators investigated in the previous studies did not perform properly against all failures. Besides, they had problems such as lacking access to the required amount for road construction and high production costs. Regarding the high-temperature resistance and antioxidant properties of the waste steel rolling oil (WSRO), for the first time, the effect of using this lubricant was investigated on the recovery of bitumen aging and the performance of asphalt mixture containing high amounts of reclaimed asphalt pavement (RAP). To this end, the conventional (penetration and softening point) tests and rotational viscosity test were conducted to determine the optimal amount of rejuvenator. In addition, FTIR and FESEM tests were carried out for chemical and morphological investigation. SCB and dynamic creep tests were performed on a balanced mix design to examine the performance against cracking and rutting. Moisture sensitivity was also investigated by performing an indirect tensile test. The results show that a uniform texture was created in the aged bitumen modified with WSRO, and there was a decrease in functional groups that represent the occurrence of aging. Therefore, WSRO can restore aging and improve rutting and cracking performance. Resistance to moisture sensitivity also improved. Overall, the results show a performance improvement in the mixture containing high RAP content mixed with WSRO as a waste rejuvenator. However, more studies encompassing rheological, economic and environmental aspects, are needed to conclude about the practical use of this material.

Assessing correlations between two linear amplitude sweep (LAS) standards for evaluating the fatigue properties of aged bitumen

ABSTRACT Linear amplitude sweep (LAS) is an accelerated and well-established testing method to evaluate bitumen fatigue. However, there are different versions of LAS procedures employed. Significant differences in loading modes, damage failure criteria and calculations exist between existing standards, leading to the inconsistency in the performance characterisation of bitumen. This study investigated the fatigue performance of six different bitumen at various ageing levels using two versions of the LAS standards (TP101-14 and T391-20). The stress–strain curves, damage characteristic curves, prediction of fatigue life and cracking length were analysed and compared. It was seen that conclusions drawn from the old version of LAS standard (TP101-14) were unclear as no distinct trends related to change in fatigue life could be observed for binders with progressively increased ageing levels, regardless of the strain levels used for analysis. The new version of LAS (T391-20), however, showed acceptable consistency. The trends indicate that at low strain levels, the fatigue life increases with ageing levels, while opposite trend was observed at higher strain levels. Moreover, the cracking length as defined in the T391-20 standard increases with progressively increased ageing. The new version of LAS standard (T391-20) is recommended for characterising the fatigue performance of aged bitumen.

A Nature-Inspired Design for Sequestering Polycyclic Aromatic Hydrocarbons in Asphalt-Surfaced Areas

Asphalts for pavement and roofing are known to emit volatile organic compounds (VOCs), contributing to air pollution, including the formation of ozone and secondary organic aerosols, which further worsen air quality. These emissions become more pronounced with higher sun intensity and higher temperature, accelerating the loss of essential components and the aging of bitumen. Consequently, the durability and functionality of bitumen are compromised. In this study, we investigate the efficacy of nitrogen-carrying functional groups in biochar at retaining VOCs in bitumen and prolonging the service life of asphalt surfaces. Biochar derived by hydrothermal liquefaction of red microalgae, rich in N-functional groups, is compared with low-N biochar obtained through acid-washing. Laboratory tests demonstrate that bitumen modified with high-N biochar exhibits greater resistance to aging after 200 h of ultraviolet radiation exposure compared to bitumen modified with low-N biochar. The values of an aging index based on the crossover modulus and an aging index based on the crossover frequency indicate greater susceptibility to aging in neat bitumen compared to biochar-modified bitumen, and bitumen modified with high-N biochar showed the lowest aging index. Compared to neat bitumen, measurements of carbonyl and sulfoxide as aging indicators showed an improvement of 12.9% for high-N biochar in slowing bitumen aging, while low-N biochar provided only a 3.1% improvement. Dynamic vapor sorption analysis showed 35% less mass loss in bitumen with high-N biochar compared to bitumen with low-N biochar. These improvements can be attributed to the increased retention of VOCs in bitumen facilitated by the N-functional groups in high-N biochar. Modeling with density functional theory shows the mechanisms by which biochar rich in N-functional groups exhibits enhanced adsorption of VOCs. This modeling highlights the importance of biochar's nitrogen functional groups in biochar's electronic structure and molecular structure in retaining VOCs in the bitumen matrix. The study outcomes promote sustainability and resource conservation in the construction industry and align with goals of carbon neutrality.

Recovering the properties of aged bitumen using bio-rejuvenators derived from municipal wastes

Ageing of bitumen leads to significant performance deterioration of asphalt pavements and leads to material properties that are not conducive to recycling. Aiming to maximise the reusability of bitumen, this study investigated the feasibility of rejuvenating aged bitumen using bio-based rejuvenators synthesised from municipal wastes. Two bio-rejuvenators were used in this study, namely Rej-A which was a crude polymer with bio-waste pyrolysis dense fractions and Rej-B which was a filtered pyrolysis wax further derived from Rej-A. The bio-rejuvenators, virgin, aged, and rejuvenated bitumen were characterised using a comprehensive testing programme of gas chromatography and mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), and frequency sweep tests. It was observed that both bio-rejuvenators produced in this study can effectively recover the rheological properties of aged bitumen, improving its fatigue performance, e.g. the fatigue lives (at 15 % strain level) of Rej-A and Rej-B rejuvenated bitumen were 5.4 times and 3.0 times of that for aged bitumen when the dosage was 14 %. The rejuvenated bitumen was more sensitive to strain while less sensitive to temperature compared with virgin bitumen. Overall, Rej-A outperformed Rej-B in recovering the properties of aged bitumen. However, Rej-A was thermally unstable, undergoing 15.6 % mass loss when heated to 160 °C.

Investigation of the cohesive behavior of water-intervened rejuvenated SBS-modified bitumen

When water interacts with bitumen, the diffusion and cohesion characteristics between the components of bitumen are negatively impacted. Molecular dynamics simulations were employed to construct various bitumen models, including bitumen–bitumen (without water), water-containing single bitumen, water-containing bitumen–bitumen, and bitumen–water–bitumen models. The primary research objectives were as follows: comparing the changes in the densities of bitumen models with and without water, analyzing the interlayer cohesive energies of bitumen models interacting with water, evaluating the hydrogen bonds in water-containing bitumen models, and characterizing the diffusion behaviors of bitumen components. The results indicated that when water interacted with the bitumen, it filled internal voids, leading to an overall increase in volume and reduction in density. The interaction energies between the rejuvenated bitumen models and water molecules decreased as the numbers of polar sites exposed to SBS molecules decreased. The numbers of hydrogen bonds between water molecules and rejuvenated bitumen models were similar to those in aged bitumen models. As the number of fractured SBS molecular chains gradually increased, the interlayer cohesive energy in the Methylene-bis(4-cyclohexylisocyanate) (HMDI)-rejuvenated bitumen model gradually increased. Water molecules significantly influenced the interactions at the rejuvenated bitumen–rejuvenated bitumen interface, weakening the cohesion characteristics between bitumen molecules. Water interactions significantly reduced the interlayer cohesive energy of the bitumen–water–bitumen model. Conversely, the recovery process improved the interlayer cohesion characteristics of the bitumen. The diffusion characteristics of the components of bitumen SARA were significantly greater under wet conditions than under dry conditions.

Enhancement of bitumen aging resistance by nanomicron porous eggshell loaded with waste engine oil prepared under mechanical force

Volatilization of lightweight components during long-term service is one of the main causes of bitumen aging. In this study, porous eggshell powder (EP) loaded with waste engine oil (LEPWEO) was prepared by the oil milling process, which released lightweight components during bitumen aging to improve bitumen aging resistance. The results showed that the pore volume of the EP was increased by 135.7 % after oil milling and waste engine oil (WEO) loaded in the pore was 16.41 wt%. Nano-pores and micron-pores were observed by transmission electron microscopy (TEM) and scanning electron microscope (SEM) tests, which were attributed to the crushing and compressive effects of mechanical force. Compared to unmodified bitumen, LEPWEO effectively retarded the aging of bitumen. And its carbonyl group, sulfoxide group, and microhardness change rates after long-term aging were reduced by 53.2 %, 90.0 % and 65.9 %, respectively. Moreover, LEPWEO had superior dispersibility and compatibility with bitumen. The contact angle of EP with bitumen was reduced from 30.4° to 12.7° after oil mill modification, which contributed to the uniform release of lightweight components. In this work, a porous biomass material with a lightweight composition is prepared by the oil milling process, which proposes a foundation for the application of retarded bitumen aging.

The Problem of Road Bitumen Technological Aging and Ways to Solve It: A Review

This paper discusses the main features of technological aging of bitumen, in particular, the mechanisms and transformations that accompany this process. The main laboratory methods for modeling the above processes are considered. It is described how the technical essence of the methods has changed from the first developments to the present. A number of compounds that can be used as inhibitors of technological aging, including antioxidants and plasticizers, as well as some “natural” substances that have these properties, are presented.

Anti-ageing and rheological performance of bitumen modified with polyaniline nanofibres

Asphalt pavements represent the great majority of roads worldwide. However, the bitumen physico-chemical properties change due to ageing processes during both the production and service life of the asphalt mixes. In recent years, a completely new trend has been observed in the road engineering industry oriented to extending the service life of roads, bringing direct economic, ecological and social benefits. This work presents the possibility of inhibiting ageing of road bitumen by using polyaniline nanofibers (PANI_NFs) as well as enhancing its rheological properties examined with Linear Amplitude Sweep (LAS) as well as Multiple Stress Creep and Recovery (MSCR) tests. These results show that the application of PANI_NFs maintains the primary penetration value of bitumen short-term and long-term aged road bitumen at 88 % and 52 %, respectively. Moreover, bitumen modification with PANI_NFs reduces the softening temperature increase by 33 % and 24 %, respectively, and the viscosity increase of road asphalt by 50 % and 25 %, respectively. PANI_NFs also stabilised the bitumen surface adhesion force, determined with AFM, consequently confirming the enhanced resistance to ageing processes. In addition, changes in the carbonyl index, sulphoxide index and aromaticity of bitumen demonstrated that PANI_NFs inhibit oxidation and aromatisation reactions of its components. The tests indicated a 4-fold decrease in the degree of bitumen component oxidation after short-term ageing and a 33 % decrease after long-term ageing. FTIR analysis also showed a reduction in the degree of bitumen component aromatisation process of 79 % and 76 % for short-term and long-term ageing, respectively. The LAS and MSCR test results also showed that PANI_NFs had a beneficial impact on the resistance of the bitumen to fatigue and rutting. Overall, the study results suggest that PANI_NFs consitute a promising modifier for bitumen in terms of ageing inhibition and performance characteristics.

Characterisation of bitumen through multiple ageing-rejuvenation cycles

ABSTRACT The multiple recycling of bitumen offers the possibility of reusing it for repeated lifecycles and achieve a higher degree of circularity of materials used in pavement construction. Aiming to identify the prospect, this study aged bitumen in a laboratory setting and then rejuvenated it using a bio-based rejuvenator for four ageing cycles. The low temperature and fatigue performance of the bitumen in each cycle was comprehensively characterised using dynamic shear rheometer (DSR) based rheological measurements. The results illustrated that although rejuvenation cannot recover all properties of the aged bitumen to the level of virgin bitumen, using rejuvenators can largely improve most properties negatively affected by ageing. The optimal dosage of rejuvenators should be determined based on the balance of the properties. The use of rejuvenation indexes, such as the one employed in this study, can assure that the low-temperature and intermediate temperature performance can be met through multiple ageing-rejuvenation cycles. In terms of chemical changes, although ageing reduces the chemical or colloidal stability of bitumen, rejuvenation can recover this property to its initial level. Overall, the results obtained in the study suggest that using appropriate rejuvenators, bitumen can potentially be recycled through multiple lifecycles.

Long-term aging simulation of asphalt mixture: A comparative experimental study

In this study, the efficacy of the extended oven aging procedure outlined in NCHRP 973 for generating laboratory-produced reclaimed asphalt pavement (RAP) was explored. The study also sought to establish a correlation between the results obtained from the aged bitumen extracted from oven-aged asphalt mixture and PAV-aged bitumen. Both aging techniques, with varying durations, were applied, and a series of tests, encompassing penetration, softening point, rotational viscosity, bending beam rheometer, temperature sweep using dynamic shear rheometer, and FTIR, were conducted for comprehensive comparison. The outcomes revealed that the oven aging procedure has limited applicability for simulating the long-term aging of asphalt mixtures. At the temperature of 95°C, an increase in the oven aging duration had minimal impact on the degree of aging, especially beyond five days, as evidenced by various parameters such as penetration, softening point, viscosity, master curves of viscoelastic properties, aging index, and low-, intermediate-, and high-temperature characteristics of the different aged bitumens. Furthermore, a comparative analysis between PAV and bitumen extracted from oven-aged asphalt mixture indicated that bitumen aged for five days in the oven exhibited analogous properties to bitumen subjected to 1 cycle of PAV aging, encompassing chemical, rheological, and physical test results. In conclusion, while some researchers have suggested that performing 2 or 3 cycles of PAV aging may be necessary to simulate long-term aging, the findings indicate that oven aging of asphalt mixture cannot effectively simulate aging characteristics beyond 1 cycle of PAV aging.

Review of Lab-Accelerated Aging Techniques of Asphalt Mixes

Bitumen aging contributes to main pavement distress due to the changes in rheological, chemical, and physical characteristics of bitumen. Mainly, aging process can be divided into two categories, the first category namely short-term aging takes place during the heating up of bitumen and aggregate, mixing, transportation, laying down, and compaction. While the second category of aging takes place during the service life of pavement which is denoted as long-term aging. Consequently, researchers’ focus is to simulate bitumen aging in the lab by developing lab-accelerated methods to simulate the process of bitumen aging and studying the rate of change before and after aging. This article reviews these methods and compares the extent of the impact on lab-aged bitumen with old bitumen. The main outcome is, that the duration of exposure to high temperatures, which is the dominant method to accelerate aging process, resulted in inadequate changes in the structure of the bitumen molecule, hence, making it different from old bitumen. For that reason, using oxidants such as hydrogen peroxide showed more reliable results but requires more attention by researchers to achieve a standardized aging process of bitumen.