Types Of Rejuvenators Research Articles

Long-term effectiveness of vegetable-based rejuvenation agents across different aging stages of asphalt pavements

ABSTRACT The effectiveness of rejuvenation agents in reducing the stiffness of aged binder in Reclaimed Asphalt Pavement (RAP) material during the initial service life is well documented. However, their long-term efficacy remains under evaluation. This is partially due to the wide variety of rejuvenation agents, with varying chemical compositions, which impact the short- and long-term performance of the rejuvenated material. This paper addresses this concern by assessing the effectiveness of five types of vegetable-based rejuvenation agents across the ageing stages of asphalt mixtures during the service life of flexible pavements. The evaluation includes monitoring the rheological, chemical and performance-related properties of the rejuvenated binder blends (i.e., a combination of aged asphalt binder, virgin asphalt binder and rejuvenator) as ageing progresses. The results indicate that the benefit of rejuvenation decreases with time and that this reduction is a function of the type of rejuvenator. These results highlight that an appropriate selection of a rejuvenator should consider not only the improvement of the material during the production of the mixture and a good response and performance in the initial stage of the pavement operation, as is often the case, but also its capability to maintain these positive effects in later stages of its service life.

Nuclear Magnetic Resonance (NMR) Assessment of Bio and Crude Oil-Based Rejuvenation

Asphalt binders in pavements lose their stability through aging and eventually fail in the field. Using nuclear magnetic resonance (NMR) to monitor the primary longitudinal relaxation time of asphalt samples and the ratio of material that carries this primary relaxation time has been shown to indicate the impact of ultraviolet (UV) radiation on the aging of asphalt pavements. Longitudinal NMR relaxation was used to investigate two types of proposed asphalt rejuvenators, a bio-oil-based rejuvenator and a crude-oil-based rejuvenator. Two different binders with the performance grades (PG) 64-22 and 76-22 were considered for their interactions with the rejuvenators. After 72 h of exposure to intense UV radiation, specifically designed NMR relaxometry experiments were applied to compare the rejuvenation capabilities of the two rejuvenator samples. The crude oil-based rejuvenator was found to exhibit relaxation times similar to the binder samples while the bio-based material showed relaxation times that pointed to different nuclear hydrogen environments. Both rejuvenators reduced the primary relaxation time of the PG 76-22 binder, which indicates that their stiffness was reduced. Both types of rejuvenators also seemed to prevent the effects of UV aging. Two mechanisms of rejuvenation were identified by NMR relaxometry. The primary relaxation time can be used to indicate a change in stiffness while the primary ratio of the material is tied to oxidative aging. Oxidative aging creates distinct hydrogen environments due to asphaltene aggregation. The bio-based rejuvenator only reduced the binder’s stiffness, while the crude oil-based rejuvenator also reduced the aggregation of asphaltenes. Consequently, the bio-based rejuvenator could be classified as an asphalt softener, while the oil-based material acted like a true rejuvenator.

Quantifying the blending efficiency of warm mix asphalt-synchronous rejuvenated SBS-modified asphalt through a dynamic shear rheometer (DSR) testing approach

The degree of blending (DOB), which is controlled by the diffusion between virgin and aged/rejuvenated asphalt binder, has a major impact on the performance of the asphalt mixture incorporated with reclaimed asphalt pavement (RAP). Despite numerous studies investigating the DOB through experimental methods, the blending efficiency of warm mix asphalt (WMA) and synchronous rejuvenated SBS-modified asphalt (SBSMA) is still unexplored. In this study, a dynamic shear rheometer (DSR) testing approach was developed to quantify the blending efficiency of WMA modified SBSMA and synchronous rejuvenated SBSMA. The novelty of this approach lies in the innovative use of a DSR asphalt double-layer structure to determine the DOB in combination with a developed theoretical calculation framework. The individual and synergistic effects of WMA additive and rejuvenator type on the DOB of WMA modified SBSMA-Synchronous rejuvenated SBSMA were investigated, while the influence of blending temperature, blending time, and dosage of aged/rejuvenated SBSMA on the blending efficiency were systemically evaluated. Results indicated that the SBS repairing agent in the synchronous rejuvenator can dramatically increase the DOB, while the presence of WMA additive can further increase the DOB by improving the fluidity of the virgin SBSMA. Furthermore, increasing the blending temperature/blending time and decreasing the dosage of aged/rejuvenated SBSMA were also conducive to enhancing the DOB. In addition, a blending chart of the WMA modified SBSMA-Synchronous rejuvenated SBSMA was developed to facilitate the accurate prediction of the DOB at any given blending temperature and blending time.

Analysis of Rheological Properties and Regeneration Mechanism of Recycled Styrene-Butadiene-Styrene Block Copolymer (SBS) Modified Asphalt Binder Using Different Rejuvenators.

The regeneration performance of an aged styrene-butadiene-styrene block copolymer (SBS) will be significantly influenced by different rejuvenators. The objective of this study was to comparatively investigate the regeneration effect of different SBS-modified asphalt regenerators on aged SBS-modified asphalt. Four types of different regenerant formulations were selected. The optimal rejuvenator content was determined firstly using conventional performance tests. The rheological properties of the aged SBS-modified asphalt binder were evaluated by multiple stress creep recovery (MSCR) experiments. Subsequently, the regeneration mechanism of the SBS-modified asphalt binder was investigated using thin-layer chromatography-flame ionization detection (TLC-FID) and Fourier transform infrared spectroscopy (FTIR). The results showed that the rejuvenator had a certain recovery effect on the penetration, softening point, and ductility of the SBS-modified asphalt binder after aging. The SBS-modified rejuvenating agent was the most favorable among the four types of rejuvenators, where a rejuvenator dosage of 12% showed the optimal rejuvenation effect. The addition of regenerators could appropriately improve the elastic deformation capacity of the aged asphalt binder. The epoxy soybean oil in the regenerant reacted with the aging SBS-modified asphalt binder, supplementing the lost oil in the aged SBS-modified asphalt binder, dispersing the excessive accumulation of asphaltene, and making the residual SBS swell again. The viscoelastic properties of the aging asphalt binder were improved by adjusting the content of components and functional groups to achieve the purpose of regeneration.

Influence of bio-based and refined rejuvenators on asphalt mixture with cold RAP

ABSTRACT In the recent years, research on the effects of rejuvenation on hot mix asphalt (HMA) with a high amount of RAP (Reclaimed Asphalt Pavement) has intensified. However, the vast majority of scientists focus on the technology of preheated RAP addition (e.g. in the parallel dryer). It was decided to investigate the effect of rejuvenators on asphalt mixtures containing non-preheated RAP (RAP cold addition into the mixer). Different types of rejuvenators were used in the research. The tests were carried out for the binder course and the base course. The optimal amount of cold RAP in the mixtures was determined and based on the initial tests of stiffness modulus and air void content, the amount of rejuvenators was adjusted for later tests. Tests of air void content, stiffness, resistance to water and frost and rutting resistance were carried out in the laboratory. Afterwards tests in the asphalt mixing plant were conducted for the rejuvenator with the best results for the base course. The results obtained confirmed the potential of using rejuvenators for mixtures with cold RAP addition into the mixer. It has been shown that bio-based rejuvenators are suitable for the use in different types of asphalt mixtures.

Prediction and modelling marshall stability of modified reclaimed asphalt pavement with rejuvenators using latest machine learning techniques

The primary problem with the experimental evaluation of Marshall stability (MS) of reclaimed asphalt pavement (RAP) is the inherent complexity and variability involved in the process. Traditional experimental methods for predicting MS can be time-consuming, labor-intensive, and costly. In the present research, an effort has been made to assess the most appropriate machine learning model for the prediction of MS of RAP. The study addresses the problem of accurately predicting MS by using a variety of input parameters derived from experimental work. The data for models was split in 7:3 for training and testing of models. Bitumen content (BC %), virgin binder percentage (VB %), virgin binder performance grade (VB-PG), RAP percentage (RAP %), RAP binder percentage (RAPB %), RAP binder PG (RAPB-PG), rejuvenator type (Rej type) and rejuvenator percentage (Rej %) were applied as input parameters for MS prediction. Several machine learning models including random tree (RT), M5P, Gaussian process (GP), support vector machine (SVM), and random forest (RF) were utilized for determining the most appropriate prediction model. Seven metrics were used for assessing the performance of these models, such as CC, MAE, RMSE, RA, RRSE, WI, and NSE. Based upon these metrics, the RF model is found to outperform the other applied models with the values of CC = 0.9959 and 0.9763, MAE = 0.3129 and 0.7847, RMSE = 0.3976 and 1.0492, RAE = 9.0062 and 21.8247, RRSE = 9.3624 and 23.6832, WI = 0.998 and 0.984 and NSE = 0.991 and 0.944 for training and testing stages, respectively. Also, box plots and sensitivity analysis confirm the superiority of the RF model over other models. Finally, the sensitivity analysis suggests the importance of bitumen content in the prediction of MS of reclaimed asphalt pavement modified with rejuvenators.

Mechanical, economic, and environmental assessment of recycling reclaimed asphalt rubber pavement using different rejuvenation schemes

Asphalt rubber (AR) is a prevailing sustainable paving material, but the recycling of reclaimed asphalt rubber pavement (RARP) faces the lack of proper rejuvenation strategies and the uncertainties in its economic and environmental values. To fill these gaps, this study assesses the comprehensive performance of RARP-included mixtures using different rejuvenation schemes through mechanical tests, life cycle cost analysis (LCCA), and life cycle assessment. The addition of rejuvenators increased the rutting depth of RARP mixture but their effects on the cracking resistance varied from different types of rejuvenators. The supplement of swollen rubber content was more effective in improving the cracking and aging resistances. Recycling 40 % of RARP into new AR mixture can save 24.5 % of greenhouse gas (GHG) emissions and 35 % of cost within the geographic scope of Hong Kong. The use of rejuvenator increased the GHG emission and cost, while incorporating extra rubber could further reduce the cost.

Do different chemical and rheological properties act as effective and critical indicators for efficiency evaluation of rejuvenated bitumen?

This study investigates the impacts of rejuvenator type/dosage and the aging degree of bitumen on the chemical and rheological properties of rejuvenated bitumen, and propose critical chemo-rheological indicators for evaluating rejuvenation efficiency. Moreover, the potential connections between essential chemical and rheological indices of rejuvenator-aged bitumen blends are explored. Results indicate that chemical indices show linear relationships with rejuvenator dosage and vary depending on the rejuvenator type and aging level of bitumen. All rejuvenators can regenerate certain rheological parameters of aged bitumen to varying degrees, but cannot restore the crossover modulus (Gc). Various rheological indices exhibit different correlations with rejuvenator dosage and sensitivity degrees to the discrepancy in rejuvenator type and aging degree of bitumen. Critical chemical and rheological indicators are proposed based on their sensitivity levels to influence factors, with the aromaticity index (AI), carbonyl index (CI), and sulfoxide index (SI) as effective chemical indices and the complex modulus (G*), crossover frequency (fc), and high-temperature master curve area (AMH) as critical rheological indices for rejuvenation efficiency evaluation. The study finds that the magnitude of rejuvenation efficiency for four rejuvenators is Bio-oil > Engine-oil > Naphthenic-oil > Aromatic-oil, and the linear correlations between the critical chemical and rheological indices, together with their rejuvenation percentages, are significantly affected by the rejuvenator type and aging level of bitumen.

Evaluation of rutting resistance and moisture susceptibility of high RAP content asphalt mixtures containing bio-based rejuvenators

Hot Mix Asphalt (HMA) incorporating high Reclaimed Asphalt Pavement (RAP) contents can potentially have good rutting resistance due to the higher stiffness of the aged RAP-binder. The use of rejuvenators to enhance the workability and performance of high RAP mixes is becoming a common practice. However, the impact of rejuvenators on the rutting resistance and moisture susceptibility of high RAP mixes has not been studied exhaustively. The Hamburg Wheel-Tracking (HWT) test was used in this study to evaluate the asphalt mixture performance in terms of their resistance to permanent deformation and moisture damage at two conditioning temperatures of 44℃ and 50℃. Highly recycled asphalt mixes containing 50% RAP were prepared with various bio-based rejuvenators and a soft binder to compare with a control mix with 20% RAP content. Different HWT data analysis methods were used to quantify the mix performance. The results indicated that the rejuvenated high RAP mixes showed increased rut depth and higher possibilities of stripping compared to the control mix and the 50% RAP mix without rejuvenators. Regardless of the rejuvenator type and dosage, both the control and the rejuvenated high RAP mixes experienced severe stripping due to the increase in testing temperature. The 50% RAP mix performed best at both test temperatures. Therefore, caution is warranted concerning the adverse effects of rejuvenators or soft binders on the rutting performance and moisture susceptibility of high RAP mixes. Furthermore, traditional HWT parameters could be misleading due to the confounding effects of post-compaction and moisture-induced deformation. Parameters developed by the novel HWT data analysis methods could separately evaluate the rutting resistance and moisture susceptibility.

Performance and cost evaluations of 100% recycled hot asphalt mixtures for pothole patching applications in flexible pavements

Fixing the potholes using bituminous patching mixtures is a critical and costly pavement maintenance activity. The patching mixture's quality significantly affects patch durability and performance; always using the best material available is advisable. This study investigated the feasibility of using 100% hot recycled asphalt pavements (RAP) as a possible patching material by comparing the performance results with cold patching mixtures (CPM) as well as Superpave hot mix asphalt (SHMA) mixtures. Four different RAP mixtures, two fine-graded and two coarse-graded, from two distinct sources, are obtained. RAP mixtures were handled in a laboratory environment to obtain the hot recycled patching materials. Three different rejuvenators were incorporated into hot-recycled pavement material (HRPM) at manufacturer-recommended dosages to determine the best rejuvenator type. Performances of the mixtures are evaluated in terms of linear viscoelastic characterization, permanent deformation, and low-temperature thermal cracking potentials using dynamic modulus, flow number, and indirect tensile strength tests, respectively. The results show that RAP mixtures with any RAP source, gradation, and rejuvenator type outperformed CPM in performance tests and behaved similarly to SHMA mixtures.

Maintenance of systems with critical components. Prevention of early failures and wear-out

We present a model for inspection and maintenance of a system under two types of failures. Early failures (type I), affecting only a proportion p of systems, are due to a weak critical component detected by inspection. Type II failures are the result of the system ageing and preventive maintenance is used against them. The two novelties of this model are: (1) the use of a defective distribution to model strong components free of defects and thus immune to early failures. (2) the removal of the weak critical part once it is detected with no other type of rejuvenation of the system which constitutes an alternative to the minimal repair. We study the conditions under which this model outperforms, from a cost viewpoint, other two classical age-replacement models. The analysis reveals that inspection is advantageous if the system can function with the critical component in the defective state for a long enough time. The proportion of weak units and the quality of inspections also determine the optimum policy. The results about the range of application of the model are useful for decision making in actual maintenance. A case study concerning the timing belt of a four-stroke engine illustrates the model.

Influence of combined aging on the mechanical and physical properties of reclaimed asphalt pavement mixtures blended with rejuvenator agents

Recently, reclaimed asphalt pavement (RAP) with high RAP contents with rejuvenator agents have been implemented in Japan. However, a unified view of the durability of RAP mixtures with rejuvenators has not been established. Therefore, this paper aims to assess the durability of RAP mixtures blended with different types of rejuvenators through combined aging, compared with that of hot mixed asphalt (HMA) mixture. Mechanical and physical properties of RAP mixtures with rejuvenators subjected to a combination of moisture, heat, and oxidation were investigated. Saturation aging tensile stiffness conditioning was used to simulate the combined aging. Four types of RAP mixtures were prepared by employing two types of oil-based rejuvenators with two RAP contents. HMA mixtures were also prepared. The test results demonstrated that the RAP mixtures did not exhibit a reduction in the retained stiffness, whereas the HMA mixtures exhibited a significant drop in stiffness with conditioning. In addition, the RAP mixtures exhibited a longer residual service life than the HMA mixtures after conditioning. Detailed analyses revealed differences in the stiffness and fatigue behaviors of the RAP mixtures with different types of rejuvenators. Finally, certain aspects of the deterioration mechanisms of RAP mixtures with rejuvenators were discussed.

Research on the Fatigue Properties of Rejuvenated Asphalt Prepared by Waste Cooking Oil Pre-Desulfurized Crumb Tire Rubber.

Fatigue cracking has hitherto been a crucial constraint on the development of reclaimed asphalt pavements attributed to the performance of rejuvenated asphalt binder. Therefore, it is extremely significant to evaluate the fatigue performance of rejuvenated asphalt precisely and objectively and to improve the fatigue life of rejuvenated asphalt binders. With preceding research in our group, this paper investigated the fatigue properties of waste rubber/oil (WRO) rejuvenated asphalt and universal rejuvenated asphalt by dynamic shear rheometer test (DSR). The applicability of common fatigue life evaluation indexes and the response to internal and external influences on the fatigue performance of rejuvenated asphalt were analyzed. It is demonstrated that Np20 corresponding to the mutagenesis of phase angle is physically significant and independent of the parameters including rejuvenator type, loading mode and loading level, which was recommended as the evaluation index for fatigue life of rejuvenated asphalt in this paper. The fatigue performance of both WRO and universal rejuvenated asphalt is found to decrease with loading frequency and loading level, but the fatigue life of WRO rejuvenated asphalt is comparatively superior to the latter, particularly at high loading frequencies and levels. Influenced by waste tire crumb rubber (WTCR), increasing the proportion of WTCR can improve the fatigue life of rejuvenated asphalt. When compared to other rejuvenated asphalt, RWRO@55 rejuvenated asphalt shows better fatigue performance and its fatigue life rebounds at high loading frequency. Consequently, the recommended mastic-oil ratio is 5:5. However, when the rheological recoverability compensation is considered, the fatigue lifetime evaluation of rejuvenated asphalt will be changed significantly, and therefore the fatigue performance evaluation of rejuvenated asphalt should consider the influence of rheological recoverability to develop a comprehensive evaluation system.

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

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

Prediction of the Rejuvenator Diffusion Coefficient in Aged Asphalt Based on Free Volume Theory

A method for predicting the diffusion behavior of rejuvenators in aged asphalt was developed based on free volume theory to avoid the influence of experimental conditions or speculative simulation models on results. Three types of rejuvenators (straight saturate, cyclic saturate, and naphthene aromatic) with different molecular structures and AAA-1 aged asphalt were selected to verify the model. According to the prediction of diffusion coefficients of typical types of rejuvenators, the influencing factors of the diffusion behavior of rejuvenators were comprehensively analyzed. The results show that the prediction method can predict the diffusion coefficients of rejuvenators in aged asphalt and avoid experimental error through standardized methods. The diffusion coefficient of the rejuvenators is affected by the interaction of temperature, rejuvenator dosage, and rejuvenator type. At normal temperature, it is easier for the naphthene aromatic to diffuse in aged asphalt than the cyclic saturate and straight saturate. The increase of temperature makes the saturate-based rejuvenators more active, and the cyclic saturate shows the highest diffusion coefficient at high temperature. A similar trend occurred when the rejuvenator dosage was increased. According to the molecular chemical characteristics, rejuvenators with small or light molecules have the advantage of diffusion at high temperature, while at normal temperature, it is recommended to select the rejuvenator with a benzene ring structure.

Insight into the compatibility behaviors between various rejuvenators and aged bitumen: Molecular dynamics simulation and experimental validation

The compatibility potential of rejuvenators plays an important role in improving the blending degree of rejuvenated bitumen. This study aims at estimating the efficiency of molecular dynamics (MD) simulation in predicting the compatibility between rejuvenators and aged bitumen, and exploring the influence of rejuvenator type, aging degree of bitumen, and temperature on the compatibility potential. The thermal storage stability of rejuvenated binders is evaluated to validate the compatibility prediction. Afterward, the underlying mechanism for the storage stability difference between rejuvenators and aged bitumen is explained with the atomic-scale parameters. The results revealed that the ranking on predicted compatibility and experimentally measured thermal storage stability for four rejuvenators is the same as AO > BO > NO > EO. Furthermore, the thermodynamic parameters of solubility parameter difference Δδ, Flory-Huggins parameter χ, and mixing free energy ΔGm are efficient for estimating the compatibility potential of various rejuvenators with aged bitumen. Moreover, the separation index (SI) parameters based on rheological and chemical indices are available to assess the phase stability of rejuvenated bitumen. At the molecular scale, the compatibility and phase stability issues between rejuvenators and aged bitumen are complicated and related to different aspects of intermolecular interaction, dispersion degree, and molecular mobility.

Performance Evaluation and Characterization of Extracted Recycled Asphalt Binder With Rejuvenators

Rejuvenators are used in the asphalt industry to improve the performance and durability of aged binders and facilitate the use of recycled asphalt materials. The purpose of this study was to evaluate the impact of rejuvenator type and dose on the laboratory performance of asphalt binders. For this study, recycled asphalt pavement (RAP) and extracted RAP binder were obtained from an airfield reconstruction project located in Atlantic City, NJ. One petroleum-based (aromatic extract) and three organic-based (corn oil, tall oil, and modified vegetable oil) rejuvenators were evaluated in this study. Each rejuvenator was used at two different rejuvenator doses (6% and 12% by total RAP binder weight) and was aged at three different levels. Performance grade testing, frequency sweep tests, critical temperature differential (ΔTc ), and Fourier transform infrared spectroscopy (FTIR) tests were conducted. Results showed that the use of rejuvenators lowered the high and low performance grade of extracted RAP binders, in particular organic-based rejuvenators had a greater impact on the performance grade. ΔT c was also improved through the use of rejuvenators. In fact, the extracted RAP binder exceeded the high severity ΔTc threshold (−5°C), whereas the rejuvenated RAP binders improved ΔT c to values greater than the low severity threshold (−2.5°C). Similar findings were observed from the Glover-Rowe parameter as well, in which rejuvenated RAP binders improved the cracking resistance of the extracted RAP binder. When assessing the aging susceptibility, modified vegetable oil and corn oil rejuvenators showed the smallest change in performance between aging levels.

Chemical characterizations and molecular dynamics simulations on different rejuvenators for aged bitumen recycling

Molecular dynamics (MD) simulation is an advanced tool to explore the interaction mechanism between aged bitumen and rejuvenators at the nanoscale. However, the general MD molecular structures of rejuvenators led to the lower quantify and inaccuracy of the simulation outputs. This study aims at developing more realistic molecular models to represent the generic rejuvenators for MD simulation of aged bitumen recycling. Four types of rejuvenators (bio-oil, engine-oil, naphthenic-oil, and aromatic-oil) are characterized in terms of element analysis, functional groups distribution observed from Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy, and average molecular weight. Afterward, the average molecular structures of rejuvenators are determined and validated. Further, the MD simulations are performed to predict the energetic, dynamic, volumetric, and structural properties of various rejuvenators. Based on the chemical characteristics, the average chemical formula of bio-oil, engine-oil, naphthenic-oil, and aromatic-oil is derived as C19H36O2, C22H44, C26H48, C30H40. From MD simulations, the ranking of density and glass transition temperature for four different rejuvenators is AO > NO > BO > EO, which is same as the experimental results. It proves that the established average molecular structures of four rejuvenators are reasonable. Various rejuvenators display different thermodynamics and structural properties. The aromatic-oil exhibits the highest potential energy, cohesive energy density, and solubility parameter. Besides, the order of expansion coefficient and diffusion coefficient of the four rejuvenators is the same as BO > EO > NO > AO, while the viscosity presents the opposite sequence. Moreover, the fractional free volume values follow EO > BO > NO > AO. The occurrence probability between bio-oil and aromatic-oil molecules is higher than engine-oil and naphthenic-oil. This study develops the representative average molecular models for generic rejuvenators and helps understand the difference in chemo-physical and thermodynamics properties among various rejuvenators.

Microscopic experimental and numerical research on rejuvenators: A review

Prompting high content of reclaimed asphalt pavement (RAP) to be used in road building and maintenance has drawn great attention. The application of rejuvenators is an efficient way to ensure the performance of recycled asphalt mixtures. However, as various types of rejuvenators emerging, limited understanding about rejuvenation poses challenges to put effective ones into use. For precisely evaluating the performance of rejuvenators, plenty of studies were conducted to ascertain the fundamental mechanism of rejuvenating from the microscopic view. This paper provides an overview of studies focusing on the change inside asphalt after adding rejuvenators. Chemical compositions of rejuvenators were collected as basic information. Both laboratorial experiments and molecular dynamic simulations were investigated to not only compare the effectiveness of several rejuvenators but also explain the rejuvenating mechanism. Finally, functional groups of rejuvenator structures were comprehensively examined to provide global understanding about how chemical compositions influence the efficacy of rejuvenators. This review highlights that the essential capacity of a true rejuvenator is to disturb asphaltene agglomerations. Besides, the molecular structures of rejuvenators will not only affect their deagglomerating abilities but also the performances of diffusion and durability. It has been found that gel-permeation chromatography (GPC) analysis is effective in evaluating the performance of rejuvenators, while Fourier transform infrared spectroscopy (FT-IR) and SARA (saturates, aromatics, resins and asphaltenes) analysis are only suitable for assessing asphalt oxidization. In addition, comparing some tests can only detect changes, molecular dynamic simulation can reveal the mechanism both of data and vision. The results of this work can provide comprehensive knowledge for the evaluation and development of rejuvenators.

Insights into permeability of rejuvenator in old asphalt based on permeation theory: Permeation behaviors and micro characteristics

Aiming to analyze the permeation behaviors and micro characteristics of rejuvenator in old asphalt, the rejuvenation fusion layer (RFL) of rejuvenator and old asphalt was first fabricated by permeation test. Then, the viscosity of RFLs was analyzed and its several influencing factors were explored via conducting the rotational viscosity test. On this basis, coupled with Fick’s law and composite material theory, the permeability coefficient (D) of rejuvenator in old asphalt was calculated and the influencing factors were investigated. Lastly, the micro-phase morphology, mechanical and chemical characteristics of RFL were analyzed via the AFM and FTIR tests. Results showed that the permeability of rejuvenator in old asphalt depended on permeation temperature, permeation time, rejuvenator type and asphalt layer thickness. The higher permeation temperature or longer time contributed to the permeation effect of rejuvenator in old asphalt. Moreover, based on the results, the mixing temperature should not be less than 150 °C and the mixing time should be about 12 s ∼ 18 s for the uniform mixing of RAP and rejuvenator in actual thermal rejuvenation engineering. The permeability of mineral oil rejuvenator in aged asphalt was stronger than that of bio-rejuvenator, and thinner aged asphalt layer made the rejuvenator more easily permeate. Further, the sampling layer exhibited the most remarkable influence on the permeability of rejuvenator in old asphalt, followed by rejuvenator type, permeation time and permeation temperature. The AFM test confirmed that the permeation effect of mineral oil rejuvenator in aged asphalt was superior to that of bio-rejuvenator from the micro perspective, and that under the permeation conditions of 130 °C and 6 h, the mineral oil rejuvenator can fully fuse with aged asphalt and show similar morphological characteristics (“bee” size and quantity) at different layers of RFLs. Further, the mineral oil rejuvenator greatly enhanced the micro mechanical properties of aged asphalt, demonstrating a favorable rejuvenation effect. FTIR test manifested that the functional group composition of the L-type rejuvenator was similar to that of the original asphalt, and that the L-type rejuvenator contained lower carbonyl contents compared to B-type and H-type rejuvenators and exhibited better permeability and rejuvenation effect.