Rubber Binder Research Articles

Performance Assessment of Bioasphalt Mixtures Containing Guayule Resin as an Innovative Biobased Asphalt Alternative

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of 0.65–0.69 kJ/m2 compared to 0.46 kJ/m2 for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, 400 J/m2). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered 591 J/m2 at its performance grade low temperature (−16°C) and 409 J/m2 at −22°C compared to 429 J/m2 for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Investigation on aging and rejuvenation of asphalt rubber binders considering liquid and particle effect

The aging and rejuvenation behaviors of asphalt rubber (AR) binder are of great importance, while most studies investigated the two processes by regarding the AR binder as a whole. Therefore, the AR binder was regarded as a two-phase system in this study to further clarify the aging and rejuvenation mechanisms behind. The liquid phase and particle phase of AR binders were separated using a physical sieving method, and the liquid effect (LE) and particle effect (PE) were then defined. Results showed that compared with the LE, the PE played a dominant role in affecting the unaged AR binders, especially for those prepared with crumb rubber of larger sizes and higher dosages. After aging, the LE of AR binders remarkably increased while the PE slightly decreased. Specially, at this status, the LE even accounted for a significantly larger proportion of the whole modification effect than the PE. The LE of the rejuvenated AR binders significantly decreased due to the softening effect of the rejuvenator. The PE also slightly reduced after rejuvenation because of the further degradation of crumb rubber. On the other hand, the proportion of asphaltenes and resins increased while the proportion of aromatics and saturates decreased during the aging, and the changes in fractions were on the contrary after the rejuvenation. The statistical analysis revealed that the rheological properties of liquid phases were dominantly affected by chemical fractions for all the unaged, aged and rejuvenated AR binders.

Nafion as a facile binder additive stabilizes solid electrolyte interphase on graphite anode

Graphite is dominantly used as the anode material for lithium-ion batteries. However, it still suffers from a limited cycling life and poor rate capability due to the unstable solid electrolyte interphase (SEI). Herein, a simple and viable method with Nafion as an additive to the commercial carboxyl methyl cellulose-styrene butadiene rubber (CMC/SBR) binder is proposed to construct a superior interfacial film to suppress the continuous decomposition of electrolyte solvent molecules on the graphite surface. Nafion helps to break the solvation shell and form a thin and uniform solid electrolyte interphase film on the surface of the graphite anode with fast Li+ diffusion. Benefiting from the synergetic merits form the inner original SEI and the outer Nafion, the graphite anodes exhibit long cycling life with a capacity retention rate of 73.85% after 350 cycles, and a high rate capability of 333.4 mAh g−1 at 1C and 327.6 mAh g−1 at 6C. The facile strategy of binder additives to stabilize SEI is inspiring the design of high-performance electrodes.

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.

Rheological Modeling of Bituminous Mixtures Including Polymer-Modified Binder and Fine Crumb Rubber Added through Dry Process

In recent years, both dry and wet processes to include waste rubber (WR) in bituminous mixtures have had little success in Italy due to technical and economic reasons. However, the necessity to recycle this waste material and the increasing interest in low-noise emitting pavement is encouraging researchers and stakeholders to explore new solutions. In this context, a hot-mix asphalt (HMA) manufactured with polymer-modified bitumen and fine WR added through a dry method has been recently developed. This paper deals with the rheological characterization and modeling of this innovative HMA, in comparison with two reference mixtures, with ordinary polymer-modified bitumen and with an asphalt rubber binder produced through a wet process. The complex modulus was measured through uniaxial cyclic compression tests at different temperatures and frequencies. The Huet-Sayegh rheological model was used to simulate the experimental data. The results showed that the time-temperature superposition principle is valid, despite the presence of polymers and WR. The Huet-Sayegh model allows a good fitting of the dynamic modulus and loss angle data to be achieved. The viscous response of the mixture including polymer-modified bitumen and rubber powder is higher than the other HMAs, which is mainly associated with the nature of the modifiers, the binder content in the mix and the less severe short-term aging.

Determination of Mixing and Compaction Temperatures for the Rubberized Asphalt Binders Based on Shear Rate Dependent Viscosity

Despite the numerous advantages of using modified asphalt binders, there are a number of challenges associated with their use. One of these challenges is related with specifying the temperatures at which modified asphalt binders should be mixed and compacted. The Equiviscous method aims to calculate the Mixing and Compaction Temperatures (MCTs) of the unmodified binder. Nevertheless, the implementation of this method for modified asphalt binder results in very high MCTs, which may not be appropriate during the asphalt mixes construction. This paper investigates two alternative methods for the modified binder with Crumb Rubber (CR), referred to as the High Shear Rate (HSR) viscosity and Zero Shear Viscosity (ZSV) methods. Besides, the MCTs obtained from these methods are compared to the ones obtained using the Equiviscous method. For this purpose, one type of asphalt binder modified with three percent of CR has been used. The results have shown that the application of the ZSV method has resulted in more reasonable MCTs for the rubberized binder, which have been from 30 to 50 °C lower than the ones obtained using the Equiviscous method.

Waste Cooking Oil-Modified Epoxy Asphalt Rubber Binders with Improved Compatibility and Extended Allowable Construction Time.

The application of crumb rubber from end-of-life tires and waste cooking oil (WCO) in road pavements is of significant importance from an economic and environmental viewpoint. However, the incorporation of crumb rubber greatly shortens the allowable construction time of epoxy asphalt binders due to the high viscosity of the epoxy asphalt rubber (EAR) binder and poor compatibility between crumb rubber and asphalt binder. To lower the viscosity of asphalt rubber, extend the allowable construction time and improve the compatibility of EAR binder, waste cooking oil (WCO) was introduced. The effect of WCO on the viscosity–time behavior, thermal stability, dynamic modulus, glass transitions, crosslink density, damping ability, compatibility, mechanical properties and phase separation of WCO-modified EAR binders was investigated by using the Brookfield viscometer, thermogravimetric analysis, dynamic mechanical analysis, universal testing machine and laser confocal microscopy. The test results demonstrated that the incorporation of WCO declined the viscosity and extended the allowable construction time of the unmodified EAR binder. The inclusion of WCO improved the compatibility between asphalt and crumb rubber and the damping ability and elongation at the break of the unmodified EAR binder. The presence of WCO had a marginal effect on the thermal stability of the unmodified EAR binder. Confocal microscopy observation revealed that asphalt rubber particles aggregated in the epoxy phase of the unmodified EAR binder. With the inclusion of WCO, co-continuous asphalt rubber particles became more spherical.

Development and Optimization of Composite Cathode Materials for Use with Thin-Film Glassy Solid Electrolytes in Solid-State Batteries

The electrochemical properties and thermal behavior of thin-film glassy solid electrolytes (GSE) in the [Li2S - SiS2 - LiPO3] system make them viable candidates for inclusion in solid-state batteries. To properly assess these electrolytes in the full-cell format, compatible composite cathode materials must be developed. These materials must be electronically and ionically conductive, and form a stable interface in contact with the GSE. A composite blend of redox-active lithium iron phosphate (LiFePO4), a mixed-oxy-sulfide glassy electrolyte, carbon nanotubes, a lithium solvate ionic liquid (SIL), and styrene butadiene rubber binder (SBR) was utilized to create the cathode material. Mixing time and order of component mixing were controlled in order to optimize for ionic and electronic conductivities within the bulk composite powder. With the addition of the SIL and SBR, a composite cathode blend capable of stably cycling in contact with the GSE was created.

Measurement and Analysis of Mechanical Properties of All-Solid-State Electrodes Fabricated By Dry Process with Saicas

Due to battery fire accidents while driving and charging an electric vehicle, research on improving battery safety as well as increasing the energy density has been extensively performed. For this purpose, an all-solid-state battery without the flammable liquid electrolyte is being more actively conducted. Among various solid electrolyte types, the sulfide-based solid electrolyte has been investigated as the most promising candidate owing to its high ionic conductivity and ductility. However, since sulfide solid electrolyte is too reactive to organic solvents like N-methyl pyrrolidone, a few nonpolar solvents (xylene or toluene) can be used to fabricate sulfide solid electrolyte. Thus, except for rubber binders such as nitrile butadiene rubber, other conventional adhesive binders are excluded from candidates. So, to solve this limitation fundamentally, a dry process without any solvents must be an attractive method for using the sulfide electrolyte in battery manufacturing process. For example, polytetrafluoroethylene (PTFE) is frequently used for fabricating all-solid-state electrode (ASSE) with sulfide electrolytes due to its wonderful fibrilization property. However, comparing to the wet process, it is more challenging to distribute all the electrode components uniformly in the dry process, where all the components are mixed through kneading the electrode dough. That is, to maximize the electrochemical performances of ASSEs, it is essential to evaluate the mechanical properties of ASSEs fabricated from dry process and to quantify them for optimization. However, most of research on ASSEs have been focused on their electrochemical performances up to now.Thus, in this work, we attempted to measure the mechanical properties of ASSEs with sulfide electrolyte using a surface and interfacial cutting analysis system (SAICAS). The ASSEs were fabricated through dry process while changing the PTFE binder content. Subsequently, both bulk and interfacial adhesive strengths were analyzed systematically and deliberately by a few μm resolution. Furthermore, to unveil the surface, bulk, and interfacial electrical properties are also measured using an electrode resistance measuring instrument (HIOKI RM2610). Thus, we can provide a correlation between binder content and mechanical/electrical properties of dry ASSEs. Finally, comparative results based on wet processed ASSEs will also be included in this work.

Porous asphalt mixture use asphalt rubber binders: Preparation and noise reduction evaluation

To prepare low-noise asphalt pavement with excellent noise reduction and road performance, a large amount of crumb rubber was added to asphalt binder to prepare high viscosity modified asphalt rubber, with Sasobit and waste cooking oil (WCO) selected as viscosity-reducing additives to reduce the viscosity. Moreover, the study took the prepared porous asphalt rubber mixture (PARM) as the research object and formed a systematic evaluation method for the noise reduction performance of the asphalt mixture. The temperature sweep test based on DSR, the dynamic creep test based on UTM, and the tire drop test were used to explore the damping performance of the asphalt mixture. Due to the softening effect of WCO and the high asphalt-aggregate ratio, the damping capacity of PARM with WCO is stronger. It is worth mentioning that the addition of crumb rubber can indirectly improve the damping performance of the asphalt mixture by increasing the asphalt-aggregate ratio. The impedance tube test results show that the air voids is the critical factor affecting the sound absorption performance of the asphalt mixture. The sound absorption coefficient of porous asphalt mixture (PAM) with the largest air voids is higher than PARM, and both are significantly higher than AC-13. In addition, the tire drop and pendulum instruments were designed to simulate and test tire pavement's vibration and friction noise. It can be found that the PARM mixed with WCO showed the best noise reduction effect.

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.

A Micro-Reference Electrode for Impedance and Potential Measurements in All-Solid-State Battery Pouch Cells

Electrochemical impedance spectroscopy (EIS) is a powerful and versatile tool to investigate interfaces in batteries. In order to disentangle the anode and cathode contributions from the full-cell impedance, a reference electrode (RE) is required. In the field of batteries based on liquid electrolytes, the concept of a RE has become a widespread tool for the EIS analysis of small-scale cells [1]. However, there are only very few reports on the use of a three-electrode setup with a reference electrode for all-solid-state batteries (ASSBs) [2,3], which is due to the complexity of integrating a RE with a suitable geometry in the typical ASSB test cells that are based on a compressed electrolyte pellet (further on referred to as bulk-type ASSB cells), since for artifact-free single-electrode impedance spectra, the RE should be placed between the electrodes and should be thin compared to the thickness of the pellet. In contrast to the widely used bulk-type ASSB cells, a recently available alternative construction is offered by the use of free-standing separator sheets based on a solid electrolyte / polymer binder composite (further on referred to as sheet-type ASSB cells),[4,5] in which case a micro-RE can be placed between two separator sheets, in analogy to the micro-RE concept used with batteries based on liquid electrolytes [1].In this study, we use sheet-type separators based on a composite consisting of Li6PS5Cl (LPSCl) solid electrolyte and a hydrogenated nitrile butadiene rubber (HNBR) binder to build ASSB pouch cells that include a gold wire micro-RE (µ-GWRE). We show that upon in-situ lithiation of the µ-GWRE a stable reference potential is obtained and that artifact-free single-electrode impedance spectra can be obtained, analogous to what we had found previously for a µ-GWRE in a lithium ion battery with liquid electrolyte.[1] Figure 1 shows both half-cell impedance spectra of an InLi | separator sheet | Li cell. The sum of both half-cell impedances (blue) is identical to the full-cell impedance (green) and now impedance loops or other common artefacts are observed for the InLi (black) and the Li (red) electrodes, indicating the viability of this setup to determine single-electrode impedances. Since the InLi electrode is commonly used as counter electrode (CE) for ASSB testing cells, we will also use this setup to investigate the potential stability of InLi alloys and their impedance evolution upon lithiation and delithiation. Acknowledgements: This work was carried out as part of the research project “Industrialisierbarkeit Festkörperelektrolytzellen”, funded by the Bavarian Ministry of Economic Affairs, Regional Development and Energy.

Sustainable Asphalt Rejuvenation by Using Waste Tire Rubber Mixed with Waste Oils

Waste materials such as waste tire rubber (WTR), waste cooking oil (WCO), bio-oils, waste engine oil (WEO), and other waste oils have been the subject of various scientific studies in the sustainable and waste research field. The current environmental concerns have been identified to protect natural resources and reuse waste materials. Accordingly, this work reviews the use of recycled waste tire rubber mixed with waste oils (waste cooking oil, waste engine oil) and bio-oils that can be extracted from waste oils to rejuvenate asphalt in reclaimed pavements. This new solution may reduce the massive amounts of WTR and waste oils and produce a more environmentally sustainable material. Reclaimed, aged asphalt has been rejuvenated to achieve various penetration capabilities and properties by blending asphalt with one or more waste materials to evaluate the binder using standard tests. Many solutions with promising results in improving the properties of asphalt mixtures have been selected for further characterization. This review highlights that the addition of WTR and waste materials to rejuvenated asphalt binders improves stability, enhances the viscoelastic properties, provides better fatigue and crack resistance performance, and enhances the compatibility of the rejuvenated rubber oil asphalt. Moreover, the flashing point, softening point, ductility, and penetration of aged asphalt and Poly(styrene-butadiene-styrene)-rubber-rejuvenated and waste-rubber-oil-rejuvenated asphalt were enhanced after applying the rejuvenator compound. On the other hand, adding waste oil to WTR and asphalt reduces the viscosity and enhances the storage stability compared to the asphalt rubber binder.

Blending efficiency of reclaimed asphalt rubber pavement mixture and its correlation with cracking resistance

Despite significant number of studies on recycling of conventional reclaimed asphalt pavement (RAP) mixtures into new asphalt mixture construction, research on recycling reclaimed asphalt rubber pavement (RARP) is still quite limited. The special multiphase system of asphalt rubber (AR) binder may cause a more complicated blending condition during the recycling of RARP due to the existence of rubber particles, and the blending efficiency of RARP and virgin AR mixtures is still unclear. The main objective of this study is to investigate the mobilization tendency of aged AR binder during the recycling of RARP mixture considering both the potential mobilizations of bitumen phase and rubber particles, as well as their correlation with the cracking resistance of the RARP mixture. AR mixtures containing 40% RARP were prepared at three different mixing temperatures and one warm mix case with the inclusion of a foam-based additive. A special gradation design was used to track the mobilization of aged AR binder from RARP to virgin coarse aggregates. Mobilization indexes of bitumen and rubber were established based on Fourier transform infrared spectroscopy and thermal gravimetric analysis tests, while the cracking resistance of the RARP mixture was evaluated by the semi-circular bending test. The mobilization indexes indicated that rubber and bitumen were simultaneously mobilized, and a higher mixing temperature led to stronger mobilization tendencies. In addition, a positive correlation was found between both mobilization indexes and the cracking resistance of the RARP mixture. The foam-based WMA additive markedly improved the blending efficiency but compromised the cracking resistance of the RARP.

Laboratory Evaluation of Storage Stability for CRM Asphalt Binders

This paper conveys the laboratory investigation of the storage stability of CRM binder as a basic study. The CRM binder was produced through the wet process in the laboratory. The percentages of crumb rubber used for rubberized binder were 5%, 10%, 15% and 20%. The samples were prepared according to ASTM D7173. In order to evaluate the properties of each part of the binders, tests were carried out through the rotational viscosity and viscoelasticity, and the separation index was assessed with the G*/sin δ and %rec. In general, the results of this study revealed that (1) the conditioned CRM binders appeared to have higher viscosity in the bottom part compared to the middle and top parts.; (2) similar to the viscosity results, the CRM binders after conditioning showed the highest G*/sin δ value in the bottom part; (3) from the MSCR test, Jnr and % rec values are observed to have a similar trend with G*/sin δ results, although some of the data were not measured due to the higher load than the DSR test; and (4) it was discovered that the SI from G*/sin δ generally used was suitable for evaluating the storage stability of CRM asphalt binders, compared to the SI from % rec.

The Crystal Transformation of α‐HNIW Coated with Different Coatings

AbstractIn this article, varying coatings including rubber binders, plasticizers, and dopamine derivatives have been well coated on the surface of α‐HNIW via the application of water suspension and in‐situ coating method, and the influence of different coatings on the crystal transformation of α‐HNIW has been studied. SEM, DSC, and XRD have been performed for the characterization of the coated α‐HNIW. The results demonstrate that rubber binders have inhibitory effects on the crystal transformation of α‐HNIW, and the inhibitory effect is ranked as NR>BR>EPDM. While the four plasticizers have promoted the crystal transformation of α‐HNIW, and the promoting effect is ranked as DOS>IDP>DOA>RH. Dopamine derivatives have been innovatively used to coat α‐HNIW, which have formed a stable polymer film on the surface of α‐HNIW and result in delayed crystal transformation temperature. In the meanwhile, the inhibitory effect of dopamine derivatives is greater than that of rubber binders with a ranking as PDA>PNE>PLD>POHDA.

Effect of Carbon Nanofibers on Physical, Adhesion and Rheological Properties of Liquid Epoxidized Natural Rubber Modified Asphalt

This study aimed to evaluate the effects of carbon nanofibers (CNFs) on the performance of liquid epoxidized natural rubber (LENR)-modified asphalt. The physical, adhesion and rheological properties were determined by several tests such as penetration, elastic recovery, ring and ball softening point, Brookfield rotational viscometer, AFM and dynamic shear rheometer. LENR was used at concentrations of 3, 6, and 9%, while CNFs were used at contents of 0.3, 0.4, and 0.5% by weight of asphalt. Conventional test results showed that the increases in LENR and LENR/CNFs composite contents in binder leads to an increase in the hardness and consistency and a reduction in the temperature susceptibility of base asphalt. Adhesion results revealed that the addition of CNFs significantly increases the adhesion and bonding properties of base and rubberized binders. Rheological properties analysis exhibited that LENR improved the viscoelastic properties and permanent deformation resistance of asphalt at different temperatures and frequencies. On the other hand, it was found that the addition of CNFs significantly improves the stiffness, elasticity, and hardness of LENR-modified binders. The 6% LENR and 0.4% CNFs were found to be the optimum to enhance the physical, adhesion, and rheological properties of asphalt in this study. Thus, it can be stated that the addition of CNFs is promising to improve the performance of rubberized binders for high temperature applications.

Evaluation of Effect of Thermoplastic Polyurethane (TPU) on Crumb Rubber Modified (CRM) Asphalt Binder.

Crumb rubber binder with thermoplastic polyurethane (TPU) has been experimented with to characterize the performance properties considering the workability, rutting, fatigue cracking and cracking resistance at low temperatures depending on the temperatures and aging states. Physical and rheological properties were evaluated to proceed with the study by applying Superpave asphalt binder testing and multi-stress creep recovery (MSCR). Based on the targeted experiments, the binder samples were produced at three aging states (original, short-term aged and long-term aged) using a rolling thin film oven (RTFO) and pressure aging vessel (PAV). The results revealed that (i) the addition of TPU into CRM binders has a potential effect on increasing viscoelasticity at the original condition, (ii) CRM binders containing TPU showed improved anti-aging performance based on results of RTFO residues and (iii) the inclusion of TPU made it possible for CRM asphalt binder to improve its fatigue and cracking resistance at low temperature.

Separation mechanism of asphalt rubber and improvement with microwave irradiation

This study aims to analyse the separation mechanism of asphalt rubber (AR) binder and the principle of improving storage stability by microwave irradiation. Based on an in-depth analysis of the terminal settling velocity of crumb rubber (CR) particles, Scanning electron microscopy and Fourier transform infrared spectroscopy were used to investigate the physical and chemical properties of CR with different particle sizes and microwave times. Separation and dynamic shear rheometer (DSR) tests were performed to evaluate the storage stability of the AR binders quantitatively. The results showed that the increase in the surface irregularity of CR particles had an obvious benefit for improving storage stability, which can directly reduce the particle terminal settling velocity, especially at low Reynolds numbers. CR with higher irregularity was also conducive to material exchange and reduction of density difference. The irregularity of the CR particles and the strength of the C-N functional group increased with microwave time roughly, which was beneficial for enhancing storage stability. Changes in the physical and chemical properties were more evident in the #20 CR particles after microwave irradiation. Separation and DSR tests showed that the storage stability improved with increased microwave time. The improvement of the AR binders with #20 coarse CR was relatively more remarkable, while the improvement of the AR binders with #80 fine CR was smoother. Notably, the CR density may be lower than the asphalt density.

Adhesion and segregation characteristics of crumb rubberized binders based on solution-soaked methods

The increasing waste tires have posed a great challenge to the environment. Meanwhile, the potential advantages of using waste tire crumb rubber (CR) as the modifier of paving asphalt materials have attracted the attention of many researchers. However, the weak compatibility between the asphalt matrix and CR called researchers to make further attempts. In this study, the soaking pretreatments of CR in various solutions were used to boost the interfacial compatibility of CR to the asphalt and further improve the performance of rubberized asphalt, by chemically activating the CR surface. It was found that the three peaks appeared at a wavenumber of 2914 cm−1, 2847 cm−1, and 1429 cm−1 after solution soaking pretreatments, which represented the CH2 played an important role in the process. Besides, the lowers the area of these peaks, the greater the CR-asphalt compatibility. Furthermore, soaking the CR in the heated water slightly decreased the adhesion strength of rubberized asphalt and increased the segregation degree between the CR and asphalt. On the other hand, soaking the CR in potassium permanganate and the mixed solutions of sodium hydroxide and potassium permanganate significantly increased the adhesion strength of rubberized asphalt and decreased the segregation degree between the CR and asphalt.