Asphalt Rubber Binder Research Articles

Chemical and Rheological Evaluation of the Ageing Behaviour of High-Content Crumb Rubber Asphalt Binder.

High-Content Crumb Rubber Asphalt (HCRA) binder improves road performance and address waste tyre pollution, yet its ageing behaviour is not fully understood. In this study, 70# neat asphalt binder and HCRA with rubber contents of 35% and 50% were selected and aged through the Thin Film Oven Test (TFOT) and Pressure Ageing Vessel (PAV) tests. FTIR (Fourier Transform Infrared Spectroscopy) and DSR (Dynamic Shear Rheometer) were employed to investigate their chemical composition and rheological properties. The FTIR results show that HCRA's chemical test results are similar to those of 70#, but HCRA is more susceptible to ageing. I(C=C) strength decreases with age. The DSR results show that HCRA outperforms 70# neat asphalt binder in terms of viscoelasticity, high temperature performance and fatigue resistance, and exhibits greater resistance to ageing. The ageing index (AI) was obtained through a calculation using the formula, and overall, 70# neat asphalt binder is more sensitive to ageing behaviour and less resistant to ageing, and HCRA is particularly outstanding for fatigue resistance. A strong correlation is observed between chemical composition and some rheological property indicators. Therefore, we are able to predict the rheological properties using chemical composition indicators. This study provides insight into the ageing behaviour of a neat asphalt binder and an HCRA binder and demonstrates that the HCRA binder outperforms conventional asphalt in several performance areas. It also provides theoretical support for the consumption of waste tyres to prepare high content crumb rubber asphalt.

Effect of Amine Additive on Rutting Resistance of Rubberized Asphalt Binder

Rutting is the most common distress occurring on asphalt pavement due to traffic increases. Rubberized asphalt was then introduced as potential materials for rutting resistance. However, rubberized asphalt needs a high temperature for mixing and compaction that may not uphold the principle of sustainability. This study focused on modifying the asphalt binder by adding 0.5%, 1.0% and 1.5% of the total asphalt binder with 3-(Triethoxysilyl)propylamine as additive into rubberised asphalt binder to improve rutting resistance. The asphalt binder was tested for penetration, softening point, rotational viscosity and dynamic shear rheometer to ensure conformity to the standard specifications. The results found that incorporating this additive into rubberized asphalt binder improved its physical and rheological properties. By adding 1.5% amine into 5% NR asphalt binder, the viscosity was increased by 56.1%, the highest compared to others while, the binder that containing 0.5% amine shows the lower viscosity and achieve the specification of less than 3000 mPa-s and the G*/sinδ is greater than 1.0 kP at 76°C. In conclusion, asphalt binder containing 0.5% amine could be able to produce asphalt mixture with low mixing and compaction temperature and better rutting resistance.

Tracing the odor source of crumb rubber modified asphalt emissions and evaluating the deodorization effect of attapulgite

Crumb rubber modified asphalt (CRMA) is widely used in road construction due to its excellent performance. However, it generates significant odorous gases during paving. To analyze the odor contribution, both untreated crumb rubber and desulfurized rubber were involved in this study to prepare CRMA and desulfurized rubber modified asphalt (DRMA). Attapulgite was selected as an emission reduction agent to reduce the odorous emissions released from CRMA and DRMA. An indoor fume collection system and gas chromatography-mass spectrometry (GC-MS) analysis were used to trace the odor source and quantify the odorous emissions. A comprehensive olfactory thresholds database for CRMA emissions was further established to evaluate the odor level of various rubberized asphalt binders by using three-point comparative odor bag method, along with known olfactory thresholds of certain compounds reported in the literature. Dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), bending beam rheometer (BBR) and Brookfield viscosity tests were used to analyze the effect of attapulgite on rheological properties of CRMA and DRMA. Results indicated that odor emission rate of CRMA containing 1 %, 3 %, and 5 % attapulgite was decreased by 42.62 %, 63.29 %, and 71.06 %, respectively. Benzothiazole, derived from tire rubber vulcanization accelerator, can be reduced by 60.25 % with 1 % attapulgite, demonstrating excellent performance in terms of reducing target odor emissions. Although DRMA has a lower emission rate than that of conventional CRMA, the addition of 1 % attapulgite can further reduce the odor emission rate of DRMA by 37.92 %. The addition of attapulgite has less impact on the overall performance of CRMA and DRMA. Besides, it was found that attapulgite can reduce the viscosity of rubberized asphalt binders, which is beneficial for rubberized asphalt mixture paving and compaction. Considering odor reduction, performance, and economic factors, the optimal attapulgite content was determined to be 5 % for CRMA and 1 % for DRMA. This approach successfully reduces odorous emissions while maintaining the desirable properties of CRMA, making it a viable solution for environmentally friendly road construction.

Impact Assessment of Mixing Conditions on Rubberized Asphalt Binder

Abstract The objective of this study was to enhance the efficiency of the approach employed for preparing asphalt binders modified with waste rubber nanomaterial. A high-shear mixer has been utilized, with revaluation rates of 3000, 4000, 5000, and 6000 rpm. In addition, a mixing time of 30 minutes was employed. Four different waste rubber nanomaterial dosages were used: 0.5%, 1%, 1.5 %, and 2% by weight of asphalt cement, respectively. The asphalt binder was heated to 140 °C. The characteristics of the modified asphalt binder, including penetration grade, softening point temperature, temperature sensitivity, rotational viscosity, and ductility, were analyzed. The study demonstrated that incorporating waste rubber nanomaterial as a modifier improved the physical characteristics of the asphalt binder. Overall, the study revealed decreased penetration and increased softening point temperature and viscosity values. Additionally, the temperature sensitivity was enhanced. In addition, high shear mixing proved to be more efficient in achieving a thorough dispersion of waste rubber nanomaterial particles within the asphalt binder, resulting in a uniform composite binder. The tested samples demonstrated that adding a dosage of 1 % waste rubber nanomaterial enhanced the physical characteristics of asphalt, making it more suitable for the construction of highway pavements in hot weather conditions.

Effect of High Polymer, Crumb Rubber, and Epoxy-Modified Asphalt Binders on Laboratory Performance of Open-Graded Friction Course Mixtures

Open-graded friction course (OGFC) is a thin asphalt mixture surface layer. It is gap-graded with a high percentage of coarse aggregates that are nearly uniform in size, resulting in a high percentage of interconnected air voids and asphalt binder, which provides improved skid resistance, visibility, and decreased pavement–tire noise. However, construction personnel at the Louisiana Department of Transportation and Development reported that conventional OGFC mixtures have durability issues and shorter service life, compared with thin asphalt mixture lifts. Hence, effects of different asphalt binder types on the performance of OGFC mixtures were evaluated. Five types of asphalt binder were utilized: conventional styrene-butadiene-styrene (SBS) asphalt binder PG 76-22M; high SBS content asphalt binder PG 88-28; diluted epoxy asphalt (EA) binder with two different dosages (25% and 50%); and a hybrid modified asphalt binder prepared with SBS and crumb rubber modifier PG 76-22G. The optimal aggregate structures were determined based on minimum required air voids and voids in coarse aggregate. Physical and mechanical tests were conducted to assess the performance of OGFC mixtures, including draindown, permeability, loaded wheel track, and Cantabro abrasion loss. Results indicate that OGFC mixtures incorporating diluted EA binder exhibited lower draindown values than mixtures containing PG 76-22M and PG 88-28. Moreover, mixtures with PG 88-28 and 50% EA binders demonstrated improved resistance to rutting. Mixtures with 50% EA and PG 88-28 binders demonstrated improved durability, compared with mixtures with PG 76-22M for unaged and aged conditioning, as measured by Cantabro abrasion loss values.

Improving storage stability and rheological performance of asphalt rubber modified with nanosilica and Sasobit

In this study, nanosilica (NS) and Sasobit were incorporated into asphalt rubber (AR) binder to produce Si/Sa-AR binder. Various conventional rheological tests were performed to determine the rheological properties of Si/Sa-AR binder. Microscopic tests and four components test were performed to investigate the interaction mechanism of Sasobit and NS with the AR binder. The results show that the combination of AR binder with Sasobit and NS improves the resistance of asphalt to fatigue cracking and permanent deformation. Microscopic images of the AR binder show a ‘dendritic’ structure consisting of multiple swollen crumb rubber (CR) particles and a three-dimensional (3D) network structure, which is reflected in the excellent rheological properties of AR. The addition of Sasobit and NS breaks up the ‘dendritic’ structure while improving the 3D network structure. NS promotes the formation of a homogeneous multiphase system of the modified asphalt binder, which in turn improves the storage stability.

Exploring Progress and Future Trends in Reducing Traffic Noise: A Scoping Review on the Influence of Pavement Characteristics

This scoping review seeks to summarize current research on reducing traffic noise, focusing on how pavement characteristics affect road-tyre mechanical vibrations, which contribute significantly to urban noise pollution. The present study analyzes numerous research investigations on novel asphalt mixtures and rubber binders to identify current trends in pavement design that help reduce noise. Issues such as the longevity of noise-reducing pavements and the trade-off between noise reduction and other practical needs such as safety and cost-efficiency are examined. This assessment emphasizes the impact of new technologies, such as the Internet of Things (IoT), on improving pavement performance and reducing noise levels. Future directions stress the importance of a multidisciplinary approach involving material science, urban design, and acoustic engineering to create sustainable and effective solutions for traffic noise pollution. This review provides valuable input to the scholarly discussion on reducing traffic noise and also presents useful guidance for politicians and engineers aiming to improve urban livability by decreasing noise levels.

Can rubberized-asphalt comprising tire-derived aggregates produced through dry process be an alternative subsurface road material?

The major objective of this study was to investigate the suitability of utilizing tire-derived aggregates (TDA) at varying contents for the design of rubberized-asphalt base / subsurface layers through the dry process, along with (i) understanding the cracking potential and mechanical stress-strain response of the different materials under cyclic and confining stresses through triaxial resilient modulus (MR), dynamic modulus |E*|, and static semi-circular bend test, and (ii) assessing bonding strength of TDA with binder-aggregate matrix through moisture susceptibility test. The scope encompassed preparation of ten base course mixtures: one unbound granular base (UGB), three cement treated base (CTB), two asphalt treated base (ATB), and four rubberized-asphalt treated base (RATB) and obtaining mechanical performance at varying temperature-frequency combinations totaling 2636 data points. Triaxial MR tests indicated that CTB mix displayed highest modulus followed by ATB and RATB mixes, which was then followed by the UGB mix mainly ascribed to cement / asphalt treatment of the unmodified control subsurface material. Further, a finite element modeling study helped optimize the confinement levels to obtain realistic |E*| of ATB and RATB mixes. |E*| test results depicted that RATB mixtures would be rut-resistant at higher temperatures as they performed similar to the ATB mixes as well as crack-resistant at low to intermediate temperatures with significantly lower |E*| than ATB mixes, attributed to slower rate of change of viscosity with changing temperature in conjunction with enduring viscoelastic property (1.5–3 times higher phase angle than ATB) ascribed to high asphalt binder content and resilient nature of the rubber particles. Albeit the fracture toughness of ATB was twice higher than RATB, the latter had higher fracture energies, mainly due to the resiliency rendered by the rubber inclusions in concert with the extra viscous effect provided by the rubber-asphalt binder conglomerate. Based on the performance-based ranking, RATB mixes performed better than control mixes, and thus were adjudged as the most suitable alternative subsurface / base course materials in a pavement system. It is envisioned that this research will advance the current understanding of utilizing TDA in asphalt base / subbase courses using the dry process, and further assist in judging the viability of using rubberized-asphalt as potential sustainable alternatives to conventional systems to develop futuristic resilient pavement infrastructures with a strong emphasis on recycling of end-of-life tires, conservation of materials, and circular economy.

Investigating the synergistic anti-aging effects of Sasobit and recycled engine oil in styrene-butadiene rubber modified asphalt

During the preparation of asphalt mixtures, styrene-butadiene rubber (SBR) polymers are susceptible to thermal decomposition, which can significantly impair the binder’s low-temperature performance. This study explores the potential of combining warming agents with waste materials to enhance the low-temperature properties and aging resistance of the binder. Specifically, it examines the synergistic impact of Sasobit/recycled engine oil (Sasobit/REO) composites on the rheological and physical attributes of styrene-butadiene rubber asphalt binder (SBRAB). Utilizing fluorescence microscopy (FM), bending beam rheometer (BBR), and dynamic shear rheometer (DSR), the study assesses the aging resistance and modification mechanisms of Sasobit/REO on SBRAB. The findings indicate that the incorporation of Sasobit/REO composites more effectively reduces the mix preparation temperature than either component alone. The preparation of Sasobit/REO warm mix asphalt mixtures is feasible at temperatures 20°C lower than those required for traditional hot mixtures. These composites also enhance the performance of SBRAB at both high and low temperatures, counteracting the adverse effects associated with the individual use of Sasobit or REO. This reduced short-term aging temperature is beneficial in lessening the negative impact of high temperatures on SBRAB’s performance. Moreover, the addition of Sasobit/REO composites significantly improves the thermal cracking resistance of SBRAB mixtures. The study also demonstrates that Sasobit/REO enhances the short-term and long-term aging resistance of SBRAB, paving the way for the broader application of this novel warm mix additive in the asphalt industry.

Multiscale enhancement mechanism of low-temperature performance for degraded recycled waste rubber asphalt binders: MD simulation and microscopic investigation

Desulfurization and degradation are important processes to facilitate the storage of waste rubber asphalt and improve its utilization. However, this process is extremely complex and the mechanisms underlying the resulting performance enhancement remain unclear. This study aims to investigate the multiscale mechanism of rubber degradation and its impact on the low-temperature performance of degraded rubber modified asphalt (DRMA) binder through differential scanning calorimetry (DSC), bending beam rheometer (BBR), fluorescence microscopy (FM) and Fourier transform infrared spectroscopy (FTIR) tests and molecular dynamics (MD) simulations. The results showed that as the degradation of rubber powder deepens, lightweight components decomposed from the rubber are more easily dissolved into the virgin asphalt, thus improving its dispersion. In addition, the small molecular structure after rubber degradation penetrates and fills the aggregation space between asphalt molecules, effectively increasing the molecular activity of asphalt, thus enhancing the low-temperature performance of asphalt.

Foamed waste oil-activated rubberized asphalt binder: A sustainable recycling approach for improving foaming effect and performance

This study prepared foamed waste oil-activated rubberized asphalt (ORA) by activating crumb rubber (CR) with waste vegetable oil (WVO) to address the issue of undesirable foaming effect. Optimal foaming parameters for different rubberized asphalt were determined based on foaming characteristic experiments. Furthermore, rheological properties, fatigue resistance, and adhesion performance of various unfoamed or foamed rubberized asphalt were evaluated through dynamic shear rheometer, bending beam rheometer, pull-out tests. Finally, the analytic hierarchy process was utilized to select the optimum foamed rubberized asphalt. The results show that foaming pressure has a great influence on rubberized asphalt foaming effect, and is recommended at 300 kPa. Compared to conventional rubberized asphalt whether foamed or not, with the increase of activation degree, low-temperature performance, and fatigue resistance of ORA are significantly ameliorated, and the adhesion property of ORA first increases and then decreases, but detrimental to high-temperature performance. The foaming process and foaming agent addition are conducive to low-temperature performance but unfavorable to fatigue resistance and high-temperature property, and have little effect on adhesion performance. ORA (mass ratio of WVO to CR is 1:5) with foaming agent is determined as the optimum selection.

Development of dynamic shear-rheology-based method to improve evaluation of swelling degree of recycled crumb rubber in asphalt rubber

Inappropriate disposal of substantial scrap tires has become an unavoidable and imminent environmental concern. Asphalt rubber (AR) facilitates the value-added recycling of scrap tires into eco-friendly and durable pavement, showcasing immense potential for pollution alleviation and resource conservation. In preparing AR, the swelling effect of rubber plays a dominant role in the gel-like network formation and performance enhancement of the modified asphalt. Accordingly, it is crucial to accurately evaluate the rubber swelling degree for guiding AR preparation and mixture design. Existing research mainly relies on measuring the volume of expanded rubber particles to assess the rubber swelling degree, which requires sophisticated instruments or a cumbersome process of extracting the crumb rubber. In this study, a method was proposed to conveniently evaluate the swelling degree of crumb rubber based on the dynamic shear rheological indicators. Firstly, the base asphalt was mixed with crumb rubber at different levels of time to prepare AR binders with varying swelling degrees. The mechanical properties (i.e., elastic recovery) and physical properties (i.e., volume expansion) were measured and analyzed to investigate the impacts of swelling time on AR properties. Secondly, the rheological properties of AR with different swelling degrees were measured via temperature sweep (TS) test, multiple stress creep recovery (MSCR) test, and linear amplitude sweep (LAS) test. Thirdly, the particle effect (PE) and interaction effect (IE) values were calculated, and the swelling degrees were determined based on the variations of PE values. Relationships between swelling degrees and PE-related indicators were established to facilitate the development of the new evaluation method. Finally, the swelling degrees evaluated by the newly developed method were compared with volume expansion to validate its reliability. The results from different rheology tests were also used to verify the feasibility of the proposed method, and the prediction of swelling degree against the swelling time was established. The findings of this research provide references for evaluating the swelling degree of crumb rubber conveniently and accurately.

Effect of microwave pretreatment on characteristics of asphalt binders modified with scrap non-tire automotive rubber and waste derived pyrolytic oils after prolonged thermal storage

The use of waste automotive rubber and pyrolytic products has recently gained interest in asphalt binder modification, and it also presents an appealing solution towards waste re-utilization and sustainable asphalt binder modification. Further, composite modification of asphalt binders is now often attempted to achieve a wider range of benefits in the asphalt binder performance through the modifiers. For the petroleum crude-based asphalt binders after their modification with different additives, viz. polymers, rubbers, and oils, the phase separation behavior, usually assessed in terms of storage stability, plays a very important and crucial role in its long-term performance. A modified asphalt binder must possess adequate storage stability to assure homogeneity during storage and hauling at elevated temperatures to achieve the desired performance after construction. The present study firstly evaluated the long-term phase separation behavior/storage stability of asphalt binders modified with waste non-tire rubber granules (ethylene-propylene-diene monomer (EPDM) type) alone and then for composite rubberized asphalt binders formulated with EPDM rubber along with tire pyrolytic oil (TPO) and plastic pyrolytic oil (PPO) after microwave pretreatment. To assess the standard and the long-term phase separation behavior in terms of storage stability, formulated rubberized asphalt binders were subjected to thermal storage at two different scenarios: (a) for 2 and 4 days at163 °C, and (b) for 2, 4, 7, 10, and 14 days at 135 °C. The phase separation behavior and performance of rubberized asphalts post long-term storage were evaluated in terms of chemo-rheological, microstructural, and rubber dissolution tests. A total of 28 asphalt binders with variable modification and thermal storage periods were characterized and evaluated. Both storage temperature and duration were found to play a critical role in dictating the storage stability and chemo-rheological performance of the rubberized asphalts, and the prolonged storage stability of rubberized binders correlates well with their rutting and fatigue performance. The pretreatment of rubber granules with pyrolysis oils using microwave irradiation facilitated the achievement of a composite modified asphalt binder with good storage stability and rheological performance.

Effect of aging on damping properties of rubberized asphalt binder and rubberized porous asphalt mixture

The purpose of the study is to explore the effect of aging on the damping properties of rubberized asphalt binder and rubberized porous asphalt mixture (RPAM), and to reveal the attenuation mechanism of damping properties. The effect of aging on the damping properties of asphalt binder was analyzed through temperature scanning test. Fourier transform infrared spectroscopy, gel permeation chromatography, and fluorescence microscopic test were conducted to analyze the aging mechanism of damping properties from the perspectives of chemical composition and morphology. The dynamic modulus test and free vibration damping test were used to investigate the effect of aging on the damping properties of asphalt mixtures. Results showed that aging led to a decrease in the damping properties of asphalt mixtures. Compared to porous asphalt mixture, RPAM had lower sensitivity to aging, so its damping properties was less prone to decay. The effect of aging on asphalt binders obtained from the temperature scanning test was consistent with the results of asphalt mixtures, indicating that the decrease in damping properties of asphalt mixtures was attributed to the deterioration of damping properties of asphalt binders. The results of chemical composition and phase morphology indicated that the proportion of large molecules in the asphalt binder increased significantly during the aging process. The decrease in intermolecular mobility led to a decrease in the damping properties of asphalt binder. Significantly, crumb rubber can prevent the aging of asphalt binder, thereby delaying the attenuation of damping properties of RPAM.

Development of Plug Joint with Polymer-Modified Rubber Asphalt as Filling Material

Rising traffic volume, heavy loads, and construction activities have raised concerns about expansion joint device damage. This study focuses on developing an innovative expansion joint using polymer-modified rubber asphalt as the filling material to enhance its service life. Styrene–butadiene–styrene (SBS) emerged as a suitable modifier for rubber-modified asphalt, significantly improving elasticity and adhesion. Through the strategic combination of 3- and 2-block linear SBS, the elasticity and adhesion properties were significantly improved, resulting in the formulation of a well-suited polymer-modified rubber asphalt binder. The developed asphalt binder exhibits impressive elastic recovery (61.1% to 66.1%), surpassing commercial products, with enhanced constructability and workability (15% to 21% viscosity reduction). The carefully engineered mastic asphalt mixture showcases self-leveling characteristics at a moderate 210 °C, addressing historical constructability challenges. Settlement is 40% less than traditional hot mix asphalt for surface layers, with improved moisture and stripping resistance, enhancing existing asphalt plug joint durability and workability. Collectively, this novel mixture, comprising polymer-modified rubber and mastic asphalt, showcases the potential to enhance the durability of existing asphalt plug joints while ensuring superior constructability and workability.

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.

Influence of Warm Mix Asphalt Additives on the Physical Characteristics of Crumb Rubber Asphalt Binders

This investigation is centered around the application of warm mix asphalt (WMA) technologies to address workability concerns linked to rubberized asphalt binders. The primary aim of incorporating crumb rubber (CR) and WMA additives is to establish a robust paving method that fosters energy conservation, efficient waste management, noise reduction, and improved overall performance. The current study aims to comprehensively characterize and differentiate the physical attributes of rubberized asphalt binders by employing three distinct WMA additives: Sasobit, Cecabase RT and Rediset WMX. These additives are introduced into eight unique asphalt binders. Laboratory assessments are carried out to evaluate the workability and physical properties of these binders. The evaluation encompasses penetration, softening point, penetration index, penetration viscosity number, storage stability, ductility, viscosity, and stiffness modulus analyses. The findings indicate that the rubberized asphalt binder enhanced with Sasobit demonstrates the highest levels of both hardness and softening point in comparison to asphalt binders supplemented with alternative WMA additives. The evaluation of storage stability underscores the satisfactory stability across all modified asphalt binders. Both the unmodified and modified binders meet the requirements stipulated by the ductility test; the rubberized asphalt binder modified with Rediset falls short. The rubberized asphalt binder improved with Sasobit displays the most notable enhancement in workability. Furthermore, the blend of crumb rubber and Sasobit binder reveals the highest stiffness modulus values under conditions of intermediate and high temperatures with 1.88 and 0.46 MPa, respectively. In summation, the rubberized asphalt binder incorporating crumb rubber with Sasobit showcases superior improvements in both stiffness and workability compared to counterparts modified with Cecabase RT and Rediset WMX.

Effect of Crumb Rubber Modifier Particle Size on Storage Stability of Rubberized Binders

This research study aimed to assess the influence of different particle sizes of crumb rubber modifier on phase separation when mixed with virgin asphalt binder (PG 64-22). Both Superpave and multiple stress creep recovery (MSCR) tests were conducted to determine the optimal particle size. Three sizes of crumb-rubber particles (≤0.5 mm, ≤1 mm, and 1–2 mm) were individually incorporated into the binder at a weight proportion of 10%. The findings revealed that an increase in particle size resulted in higher viscosity, which reduced workability. However, the use of particles with a size of ≤0.5 mm effectively decreased viscosity. Furthermore, larger particle sizes enhanced resistance to rutting and improved the lifespan of the pavement. Multiple shear creep recovery (MSCR) tests confirmed that larger crumb-rubber particles exhibited a higher load-bearing capacity. Additionally, phase separation studies demonstrated that larger particle sizes were associated with increased phase separation. Notably, particles with a size of ≤0.5 mm performed exceptionally well in reducing phase separation across all combinations. In conclusion, crumb-rubber particles with a size of ≤0.5 mm were identified as the most effective in minimizing phase separation when blended with virgin asphalt binder. These findings provide solid scientific evidence related to the effects of crumb-rubber particles on the storage stability of rubberized asphalt binder and have significant implications for future research in this field.

Sustainable production of eco-friendly rubberized asphalt binders through chemically crosslinking with polymer modifier

The incorporation of waste tire rubber into asphalt pavement can facilitate the development of sustainable transportation infrastructure. Recently, terminal blend (TB) rubberized asphalt incorporating polymers has gained popularity due to its improved performance and eco-friendliness. However, the crosslinking mechanism between terminal blend (TB) rubberized asphalt and supplemented polymer modifier is not well understood. The present paper aims to investigate the crosslinking mechanism between degraded rubber, styrene-butadiene-styrene (SBS) polymer and crosslinking agent, and to clarify the effect of crosslinking reaction on the properties and production of eco-friendly rubberized asphalt. In this paper, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), dynamic shear rheological (DSR), multiple stress creep recovery (MSCR) and bending beam rheometer (BBR) tests were employed to investigate the chemical and physical properties of TB rubberized asphalt after incorporating various contents of SBS and crosslinking agent. FTIR test indicates that the conjugated olefins released from crumb rubber have the possibility to react with sulfur. However, sulfur alone fails to greatly improve the rheological performance of TB rubberized asphalt, for the level of crosslinking reaction between sulfur and TB rubberized asphalt is weak. Therefore, it is necessary to further add SBS polymer to enhance the crosslinking reaction. Further study showed that there are two types of crosslinking reactions when involving conjugated olefins. Type I is the reaction of sulfur with conjugated olefins provided by the degraded rubber, which helps the conjugated olefins to crosslink themselves, resulting in increase of the amount of trans olefins. Type II is that sulfur bridges the SBS polymer and degraded rubber through the chemical link between the opened trans olefins double bonds located in SBS and opened conjugated olefins from degraded rubber, which leads to reduction of the amount of trans olefins. Type II crosslinking reaction can effectively improve the high temperature performance of TB rubberized asphalt. The findings of this study not only provides valuable insights into the interaction mechanism of eco-friendly rubberized asphalt, but also promote the recycling of waste tire rubber.

MODIFICATION OF PETROLEUM BITUMENS WITH RUBBER WASTE

This article provides an overview of the modification of petroleum bitumen with rubber waste, considers various technologies for the production of rubberized asphalt binders: dry process, wet process with high viscosity and wet process without mixing, shows their advantages and disadvantages.