Rubber Modified Asphalt Binders Research Articles

Effects of Silicone Rubber on Rheological Properties and Aging Characteristics of Asphalt Binder.

Silicone rubber (SR) is a kind of polymer insulation material with excellent performance. With the service life of silicone rubber products reaching the limit, how to dispose of waste silicone rubber is an urgent problem to be solved. In this paper, silicone rubber-modified asphalt binder (SRMA) was prepared by SR and 90# base asphalt binder. The simulated short-term aging and long-term aging tests of SRMA were carried out using the thin film oven aging test (TFOT) and pressure aging vessel test (PAV). The rotary viscosity test and dynamic shear rheological test (DSR) were applied to the rheological properties of SRMA before and after aging. The degradation degree and chemical composition changes of SR were explored by the toluene insoluble matter test, Fourier transform infrared spectroscopy (FTIR), and a Fluorescence microscope (FM). The results demonstrate that SR can significantly affect the aging resistance, fatigue life, and high-temperature stability of SRMA. As the content of SR rose, the elastic component in SRMA increased, leading to a nice performance in stability at high temperatures and fatigue resistance. However, excessive content (14%wt and 16%wt) had a negative influence on the performance of SRMA. So, the optimal content was speculated to be between 12% and 14%. Furthermore, SR and asphalt binder would be aged and degraded together in the aging process, and this phenomenon was more obvious during long-term aging.

Effect of waste engine oil and warm mix additive on the physical, rheological, and short-term aging attributes of Styrene–Butadiene Rubber-modified asphalt binders

Styrene-butadiene rubber (SBR) latex is used widely to increase the low-temperature resistance of asphalt binders. However, the high content of butadiene copolymer in SBR-treated asphalt causes oxidation and aging. Furthermore, following the SBR modification, the compatibility and thermal storage stability of SBR-modified asphalt is not satisfactory. Therefore, the best approach to improve the quality of short-term aged SBR-modified asphalt is to lower the manufacturing temperatures of the SBR-modified asphalt mixture. In this study, to reduce the preparation temperatures of SBR-modified asphalt mixes and improve their performance after short-term aging, several additives i.e., waste engine oil (WEO), warm mix agent i.e., ZycoTherm, and WEO/ZycoTherm combination (WEO+ ZycoTherm) were selected. The rheological properties and aging performance of binder samples were evaluated through the rational viscosity, dynamic shear rheometer, bending beam rheometer and Fourier transform infrared spectroscopy tests. The results showed that adding WEO together with ZycoTherm into an SBR-modified binder contributed to reducing the compaction and mixing temperatures. The chemical analysis showed that the three additives i.e., WEO, ZycoTherm, and ZycoTherm/WEO declined the aromaticity and chemical aging indicators of aged SBR-modified binders. Furthermore, it was demonstrated that both the ZycoTherm and WEO/ZycoTherm improved the asphalt resistance to rutting at elevated temperatures in both conditions i.e., before and after short-term aging. In addition, the findings revealed ZycoTherm /WEO compound yielded the best performance to improve the minimal-temperature cracking resistance of the SBR-modified binder, resulting in lower short-term aging temperatures. In summary, this study highlights the necessity of lowering preparation temperatures in asphalt mixes containing SBR to enhance binder resistance to rutting and cracking and reduce susceptibility to oxidation during short-term aging.

Effects of Aging on Rheological Properties and Microstructural Evolution of SBS Modified Asphalt and Crumb Rubber Modified Asphalt Binders

Focusing on the comparison of aging resistance between styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) and crumb rubber modified asphalt binders (CRMA), the influences of aging on rheological properties and microstructural characteristics of different modified asphalts were investigated in this work. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were carried out, and the variations in rheological properties for different modified asphalts after the rotating thin film oven test (RTFOT) were analyzed with the rutting factor aging index (RAI) and creep rate aging index (CAI). By using Fluorescence microscopy (FM) and Fourier transform infrared (FTIR) spectroscopy, the evolutions of microstructure and chemical composition for two modified asphalts were analyzed with carbonyl index growth rate (CIR) and sulfoxide index growth rate (SIR). Then, The relationships between CIR/SIR and RAI/CAI were established to show the correlation between the deterioration of macroscopic performance and the evolution of micro-structure. The results indicated that the aging degree of asphalt increases with elevated temperatures, leading to decreasing low-temperature performance while improving high-temperature performance. Nevertheless, SBSMA exhibited strong sensitivity to aging temperature. Under thermo-oxidative aging, the RAI and CAI of SBSMA were lower than those of CRMA, whereas the regularities of CIR and SIR were opposite, indicating that CRMA was superior to SBSMA in terms of anti-aging properties due to the rupture of the cross-linked network structure of SBSMA. However, CRMA experienced aging accompanied by full swelling, and thus, relatively minor performance declined. The CIR and SIR exhibited a better correlation with the RAI and CAI, illustrating that both CIR and SIR could characterize the aging degree of modified asphalts well.

Mechanism of physical hardening on the fracture characteristics of polymer-modified asphalt binder

This article aims to reveal the physical hardening mechanism of polymer-modified asphalt binder (PMA) and accurately assess its impact on the low-temperature fracture properties of asphalt binders. Base asphalt binder (BA), styrene–butadiene–styrene modified asphalt binder (SBSMA), and crumb rubber modified asphalt binder (CRMA) were used as the research objects. Molecular dynamics (MD) simulation and differential scanning calorimetry (DSC) test were used to investigate the physical hardening mechanism of PMA at the microscopic level. The fracture characteristics of PMA under physical hardening were analyzed based on the single-edge notched beam (SENB) test. The results show that under prolonged cold service conditions, the asphalt molecular mobility is weakened, the non-bond energy and the free volume are reduced, and the molecules undergo aggregation state transformation, leading to the physical hardening of asphalt materials. In the process of physical hardening of asphalt molecules in the micro-Brownian motion of the main active force from the aromatic and saturate fractions. Considering the effect of physical hardening, it is recommended that the method used to test the low temperature properties of asphalt binders should ensure a constant temperature for at least 24 h. The crack tolerance (Ct) is recommended as the evaluation index of low-temperature cracking resistance of PMA in cold regions. The Ct of BA, SBSMA, and CRMA are reduced by 52.88 %, 12.04 %, and 35.24 %, respectively, after 24 h of constant low temperature. This indicating that the polymer modifiers can improve the fluidity of asphalt molecules, inhibit molecular aggregation, and reduce the effect of physical hardening on asphalt binders. Thermo-oxidative aging can aggravate the physical hardening phenomenon of asphalt binder, and the higher the degree of thermo-oxidative aging, the more severe the physical hardening of asphalt binder. The related research results provide the theoretical basis and technical support for the accurate design and development of the low-temperature performance of asphalt binders for roads in cold regions.

Effects of aging behavior on macro and micro characterizations of surfactant–crumb rubber asphalt binders

Asphalt aging process degenerates the performance and shortens the lifetime of the pavement, while using warm mix additive and crumb rubber modifier can improve the main negative distress. In this study, aged crumb rubber modified asphalt binder (CRMAB) with and without surfactant (0.6% SK) additive were designed through rolling thin film oven and pressure aging vessel test. The dynamic shear rheometer, bending-beam rheometer, fourier transform infrared spectroscopy, and atomic force microscopy tests were conducted to identify the effects of aging behavior on the macro-rheological properties, chemical constituents, and morphological characteristics of CRMAB and surfactant–crumb rubber modified asphalt binder (S-CRMAB). The findings from micro and macro analysis showed that aging increases carbonyl, sulfoxide, and aliphatic components, decreases aliphatic branched components, causing higher high-temperature rheology, lower low-temperaturen and fatigue performance. However, SK improves its aging resistance and relaxation ability. Moreover, the appearance of uniform hills–valleys and “round and bright lamellar” structures on the surface of 3D and 2D topographic images of S-CRMAB, respectively, indicating the surface roughness decreases, and microstructural stability gets enhanced.

Experimental Investigation on the Properties of Vulcanized Natural Rubber–Modified Asphalt Binder

Experimental Investigation on the Properties of Vulcanized Natural Rubber–Modified Asphalt Binder

Physical properties of crumb rubber modified asphalt binders and environmental impact consideration

The use of Crumb Rubber Modifier (CRM) with asphalt binders improves their properties by reducing their temperature susceptibility; depending on the way CRM and binder react with each other. The CRM particles tend to absorb some oils from asphalt binder and swell, resulting in a higher viscosity and thus stiffer binder. This paper discusses the effect of adding CRM to asphalt binder produced in Jordan by applying three different percentages of CRM on two asphalt binders, namely, Grade 60-70 and Grade 85-100. A total of 120 specimens were prepared to test their basic physical properties such as penetration, softening point, ductility, flash and fire points, and rotational viscosity. It was found that modified asphalt binders with higher crumb rubber content have lower ductility and penetration number, but higher softening point and viscosity values. Hence, this could be sign of rutting resistance and extended service life. Furthermore, different analytical methods were utilized to validate the experimental results. It was reported that only penetration displayed change in behavior for grade 60-70 and 85-100 asphalt binders. CRM content was found to be influential on all performance-related physical tests. Finally, the combined effect of asphalt-types and CRM content is statistically significant on softening point, ductility and rotational viscosity test results. On the other hand, the energy saving due to CRM incorporation coupled with other benefits including less cracking and maintenance makes rubberized asphalt very attractive and beneficial in highway construction. Rubberized asphalt technique reduced the environmental impact of highway construction by 5% to 10% compared to traditional practice.

Enhancement of rheological performance and compatibility of tire rubber-modified asphalt binder with the addition of graphene

Rubber segregation and workability are issues associated with tire rubber powder (TRP) modified asphalt binder, restricting its widespread application. Meanwhile, graphene nanoparticles have gained considerable interest in asphalt modification due to their outstanding properties. This work has explored the influence of graphene incorporation on the compatibility and rheological behavior of TRP-modified asphalt binder. Firstly, TRP-modified asphalt and two kinds of TRP/graphene composite-modified asphalt were prepared. Then, the rheological characteristics of the asphalts were investigated using the frequency sweep, temperature sweep, multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests. The compatibility and microstructure of the different modified asphalt binders were evaluated using the cigar tube test and scanning electron microscopy. Results showed that adding graphene to the TRP-modified asphalt resulted in a notable improvement in rutting performance, as evidenced by the increase in rutting parameter (G*/sinδ) and % recovery (R) and a decrease in non-recoverable creep compliance (Jnr). The graphene addition also enhanced the anti-aging performance of TRP-modified asphalt. The results obtained from the LAS test, including the damage-characteristic curves and the number of cycles to fatigue failure, suggested that the fatigue performance of the TRP/graphene composite-modified asphalt was higher compared to the TRP-modified asphalt. Similarly, the BBR test results with 12% TRP and 0.5% graphene demonstrated that the composite-modified asphalt was more resistant to low-temperature cracking. Finally, the incorporation of graphene can potentially reduce the degree of phase separation in TRP-modified asphalt binder and improve its compatibility.

Molecular dynamics simulation and experimental analysis on fluidity improvement of liquid rubber modified asphalt binder

Liquid styrene-butadiene rubber (LSBR) has been used as a modifier to improve high-temperature storage stability and cracking resistance of asphalt binder. However, the interaction mechanism between LSBR and asphalt binder at both micro and macro scales has not been well understood. In this study, the intermolecular dynamics, rheological and chemical properties of liquid rubber modified asphalt (LRMA) binder by laboratory experiments and molecular dynamics simulation. Five LSBR dosages (0, 0.5, 1.0, 1.5, 2.0, and 2.5% by weight of asphalt binder) were applied to prepare the LRMA binders. Frequency sweep, performance grading, and multiple stress creep recovery (MSCR) tests were conducted to assess the intermediate- and high-temperatures rheological properties of modified asphalt binders. Fourier transforms infrared (FTIR) spectroscopy was applied to evaluate the chemical properties. Molecular dynamics (MD) simulation was performed to evaluate compatibility and molecular mobility during self-healing process. The results indicated that the addition of LSBR improved the fluidity of asphalt binder at intermediate- and high- temperature, and also enhanced the susceptibility to temperature changes. FTIR results showed that LSBR could effectively delay aging of asphalt binder and ameliorate the service performance degradation. The MD simulation results indicated that the addition of LSBR could improve the solubility of different components in asphalt and the homogeneity of asphalt system. LRMA had a better capability to heal micro-crack than the unmodified asphalt binder. LSBR could improve the fluidity of base asphalt and aged asphalt. It is feasible and appropriate to use liquid styrene-butadiene rubber to improve fluidity of asphalt to meet the requirements of construction and production. Keywords: asphalt fluidity, molecular dynamics simulation, liquid styrene-butadiene rubber, self-healing, rheological property.

THE IMPACT OF CRUMB RUBBER CONTENT ON THE RHEOLOGICAL FEATURES OF ASPHALT CEMENT

Asphalt modified with reused rubber from vehicle tires was considered subject to a severe challenge in two directions, the first is the possibility of waste disposal to maintain sustainable infrastructure, and the second is the clear and tangible ability to enhance the characteristics of asphalt mortars and mixes. The need for asphalt cement and mixtures improvement has become unavoidable as a result of the main failure sorts related to the flexible pavement, which are represented by the cracking and rutting, that result from fatigue in the road due to the excessive application of loads and the high tire pressures of vehicles nowadays. The binder may be able to lessen asphalt paving issues and enhance the pavement's overall functionality. Following up on earlier research, it was found that rubber is one of the key components in enhancing the durability and temperature tolerance of modified asphalt cement. The aim of this study is to track the improvement in the rubber-modified asphalt binder as it was observed that the introduction of tire fracture rubber improved the quality of asphalt cement in addition to increasing the cracking factor (G*/Sin), which indicates a greater resistance to cracking. Furthermore, it is believed that the use of rubber crumbs to enhance the properties of asphalt cement will improve the sustainability of asphalt pavement economically and environmentally.

Volumetric Dilatometer Study of Thermoreversible Aging Properties in Crumb Rubber–Modified Asphalt Binders

Abstract The primary objective of this paper is to investigate the thermoreversible aging mechanism of crumb rubber–modified asphalt binders (CRMAs). In order to achieve this goal, an extended bending beam rheometer (Ex-BBR) test and volumetric dilatometer test were conducted. Additionally, isothermal crystallization kinetics (Avrami theory) and thermal stress calculation using the Hopkins and Hamming algorithm were employed to process the test data. The low-temperature properties of the asphalt specimens were characterized through calculations of creep stiffness (S), creep rate (m-value), grade loss (GL), thermal stress, and Avrami index (n). The experimental results indicate that thermoreversible aging is present in all asphalt samples during the long-term isothermal hardening process. This aging is characterized by continuous macroscopic volume shrinkage, accumulation of thermal stress, a crystallization process, and a process akin to crystallization (i.e., crumb rubber adsorbed oil at low temperatures). It was observed that CRMAs exhibit more severe thermoreversible aging and faster physical hardening rates due to their unique properties at a constant low temperature when compared with base asphalts. However, it was also observed that CRMAs can reduce the thermal stress by reducing the volumetric shrinkage coefficients and S. It is important to note that the volumetric shrinkage coefficients are not constant, which are related to the base asphalts, crumb rubber, and conditioning time. Therefore, it is not appropriate to use a single empirical constant to calculate thermal stress. Instead, multiple coefficients may need to be incorporated to account for the variability in shrinkage behavior.

Nonlinear viscoelastoplastic kinetics for high-temperature performance of modified asphalt binders

Modified additives are widely used to improve the high-temperature performance of asphalt binders. However, the high-temperature performance of modified asphalt binders cannot be well evaluated by the existing methods. To address this issue, this study aims to develop a new nonlinear viscoelastoplastic kinetics method to evaluate the high-temperature performance of modified asphalt binders. Styrene-butadiene-styrene (SBS), rubber modified asphalt binders and their aged materials are employed. First, the non-recoverable creep compliance from the standard and modified Multiple Stress Creep and Recovery (MSCR) tests are used to evaluate the high-temperature performance of asphalt binders. Then, the viscoplastic strain and activation energy from creep-recovery tests are adopted to evaluate the high-temperature performance of asphalt binders based on nonlinear viscoelastoplastic kinetics method. Results show that the high-temperature performance results from the standard and modified MSCR tests are inconsistent. The viscoplastic strain of unaged SBS modified asphalt binders shows different trends compared with other asphalt binders. It rapidly increases at the initial loading stage, then follows by a reinforcement period, and finally maintains a steady growth rate, while the reinforcement period will disappear after aging. The viscoplastic activation energy from the nonlinear viscoelastoplastic kinetics method can characterize the stable high-temperature performance of asphalt binders, avoiding controversy caused by the number of cycles in MSCR tests.

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

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

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

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

The Impact of Crumb-Rubber on the Mechanical Characteristics of Modified Asphalt Mixture

By following up on the effect of rubber, which has recently been widely used as a direct additive to the asphalt binder or to the concrete mix as a percentage of the weight of the aggregate. The success of the effect of this type of admixture on improving the modified asphalt binder in addition to the modified concrete mix has been investigated. As it was noted the importance of following the asphalt properties due to the increasing use of crumb rubber modifiers in asphalt mixtures, there is a more position to check their rheological and physical properties comprehensively. In general, the performance of the asphalt rubber binder is affected by the rubber crumb content and mixing conditions. This research used 40/50 asphalt grade and Crumb Rubber additives with contents (5, 10, 15, and 20%). The main objectives of this study were to investigate the physical and rheological properties of rubber-modified asphalt binder and mixture. These purposes were achieved by testing HMA samples using the Marshall test approach to determine (Marshall stability and flow and void properties) and measuring the retained Marshall stability and DSR and Viscosity test. Sample testing showed that when recycled rubber was used as modifiers for asphalt mixes, the mixture became more stable, had a higher bulk specific gravity, and had less flow value and air voids. This infers that using recycled rubber can enhance the rutting resistance of bituminous mix.

Comparison and correlation between polymer modified asphalt binders and mastics in high- and intermediate-temperature rheological behaviors

Traditional evaluation parameters for multiple stress creep recovery (MSCR) test and linear amplitude sweep (LAS) test are difficult to deeply and theoretically characterize the high- and intermediate-temperature rheological behaviors of polymer modified asphalt (PMA) binders and mastics. In this paper, one neat asphalt and four types of PMA binders and mastics are selected (i.e., the rubber modified ones, SBS modified ones, thermoplastic elastomer modified ones and SBS/Rubber modified ones). Two new analysis methods, i.e. Burgers model and damage mechanics-based crack growth model, are applied in analyzing the high- and intermediate-temperature rheological behaviors of PMA materials respectively. The Burgers model results indicate adding filler decreases the viscous deformation, and leads to lower non-recoverable compliance in the MSCR test. The polymer modification transfers the delayed elastic deformation to elastic deformation, thus causing more excellent rutting resistance. The damage mechanics-based crack growth model analysis reveals that adding filler enhances the crack growth rate and crack length, thus sacrificing the fatigue resistance. By contrast, the polymer modification enhances the fatigue resistance regardless of polymer types. Notably, a two-stage pattern based on crack growth rate and energy release rate was further proposed to identify the crack initiation and propagation of PMA materials. Specifically, 30% rubber modified asphalt binders and mastics perform best in both rutting and fatigue resistance. Moreover, PMA binders and mastics have strong correlation based on the recovery percentage and delayed elastic deformation. The correlation of fatigue life between PMA binders and mastics is very significant, however there was no obvious correlation in terms of crack length.

Ageing of Crumb Rubber Modified Bituminous Binders under Real Service Conditions

Due to their environmental advantages, crumb rubber modified asphalt binders constitute an interesting alternative to conventional binders for road surfaces of a more durable and sustainable nature. However, in practice, they remain less commonly used than conventional polymer modified binders. This research aims to study the real ageing of crumb rubber modified asphalt binders during their service lives when exposed to various factors, including temperature gradients, the presence of water and oxidation. To this end, research was conducted on a selection of highways built with these binders and located in regions with severe climatic and traffic conditions. The binders from cores of highway surface layers were recovered and tested using the DSR (Dynamic Shear Rheometer) to determine the evolution of the rheological parameters. Crumb rubber modified asphalt binders were studied in comparison with traditional polymer modified bitumen. The analysis of the complex modulus and phase angle was conducted based on frequency and temperature sweep tests, while the evolution of the elastic recovery, Jnr, L-Index and T-Index were assessed from the multiple stress creep and recovery test. The results obtained indicate that crumb rubber modified binders show similar ageing and rheological parameters to those of conventional polymer modified bitumen, even under severe traffic and climate conditions. Furthermore, it was observed that, at high temperatures, the effect caused by real service life ageing was different to that obtained in the laboratory through the RTFO and PAV tests.

Impact and stretching standardized tests as useful tools for assessment of viscoelastic behavior for highly rubberized asphalt binder

• Impact and stretching tests are efficient tools for evaluating rubberized binder. • Brittle-tough transition of rubberized asphalt binder happened with 25% rubber. • Up to 40% rubber content modified asphalt binder was prepared. • Toughening mechanism of highly rubberized asphalt binder was summarized. Asphalt binder is generally identified as a brittle material at low service temperature or under high-speed load, and the brittleness becomes serious after weathering aging. Improving the toughness of asphalt binder through adding high-content of crumb tire rubber is an efficient method to solve this problem. Devulcanized rubber modified asphalt binder (DRMA) with different contents (15–40%) of devulcanized rubber (DR) were prepared and their conventional physical properties, toughness, rheological properties, and microstructure were characterized by DSR, dynamic mechanical thermal analysis, sol–gel analysis, gel permeation chromatography and optical microscopy. It was found that DRMA with 35% DR content still had a good processing property. According to the results of Charpy impact and stretching tests, the toughness of DRMA measured under dynamic or fast-speed loads dramatically increased with an increase of DR content. Remarkably, the brittle-tough transition of DRMA with approximately 25% DR content was identified. The toughening effect of DR on asphalt binder was explained in terms of the decreased temperature stress, the improved speed of stress dissipation, and the increased fracture energy of DRMA. These findings provided a perspective on the viscoelastic characteristics of DRMA under a dynamic load by simple adaptation of standardized tests dedicated for polymers.

Optimum preparation and rheological properties of liquid rubber modified asphalt binder

• The optimal preparation method of LRMA was provided. • As the increase of LR content, the high temperature performance decreased. • Low temperature cracking resistance of base asphalt can be enhanced by LR. • LR has greater improvement on fatigue resistance of base asphalt than CR. In order to overcome the limitations of crumb rubber modified asphalt (CRMA) in application such as the weak storage stability and construction workability, liquid rubber (LR) was adopted to improve the properties of base asphalt binder in this paper. The main research purposes are to explore the optimum preparation method and the rheological properties of liquid rubber modified asphalt (LRMA). Meanwhile, the modification effect of LR and crumb rubber (CR) on the rheological properties and micro characteristics of base asphalt binder was compared. Firstly, the optimum preparation method of LRMA was determined by analyzing the performance indexes of orthogonal experimental design. The results showed that the optimum combination of preparation parameters of LRMA is LR content of 8 wt%∼10 wt%, original CR of 60 mesh, reaction time of 1 h, and reaction temperature of 160 ℃. The modified asphalt binders containing 9 wt% LR and 9 wt% CR were prepared under optimum conditions. Next, scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), and differential scanning calorimetry (DSC) were carried out on base asphalt, LRMA, and CRMA. The results clarified that the thermal stability of LRMA are much better than that of CRMA. Moreover, the viscosity test results indicated that LRMA possesses excellent workability. Finally, the temperature sweep (TS), frequency sweep (FS), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests were conducted on three kinds of asphalt binder to analyze their rheological properties. The findings manifested that the addition of LR can slightly enhance the high-temperature rutting resistance of base asphalt binder, while has observably positive effect on the resistance to low-temperature cracking and fatigue.

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

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