Asphalt Rubber Research Articles

Evaluation and Correlation Analysis of the Rheological Properties of Ground Tire Rubber and Styrene Butadiene Styrene Compound-Modified Asphalt.

With the increase in highway traffic volume, many waste tires are being produced, which puts serious pressure on the global ecological environment. Processing waste tires into powder and adding them to asphalt is an important and effective way to solve this noticeable environmental challenge. In this paper, to produce ground tire rubber (GTR) and styrene-butadiene-styrene (SBS) compound-modified asphalt, GTR was put into SBS-modified asphalt (GTRSA). Subsequently, some ordinary property tests, frequency sweep tests, and multiple stress creep recovery tests were conducted to investigate the conventional properties and rheological properties of GTRSA. Moreover, the 2S2P1D (two springs, two parabolic elements, and one dashpot) model was adopted to analyze the consequences of adding GTR content on the rheological properties of GTRSA. Finally, the Pearson correlation coefficient was employed to reveal the connection between the conventional properties and the rheological properties. The results show that GTR has a great impact on improving the rutting resistance, thermo-sensitive performance, shear resistance capability, stress sensitivity, and creep recovery performance of GTRSA. Adding 20% GTR can improve the creep recovery rate to 80.8%. The 5 °C ductility index suggests that GTR makes a difference to the low-temperature properties. The rheological properties and conventional properties had a strong linear link.

Rheological Properties of Desulfurized Crumb Rubber Modified Warm Mix Asphalt

In order to study the rheological properties of warm mix asphalt modified by desulfurized rubber powder with different meshes, the desulfurized rubber powder was mixed with matrix asphalt at the best content. Dynamic shear rheological test (DSR) was used to study the high temperature rheological properties of asphalt modified by waste rubber powder. Multi-stress creep test (MSCR) was used to study the high temperature deformation resistance of asphalt modified with waste rubber powder. The low temperature rheological properties of Sasobit and crumb rubber modified asphalt with different mesh numbers were evaluated by bending beam rheological test (BBR). The test results show that compared with the base asphalt, the complex modulus and rutting factor of CRMA 60 are significantly improved, and the effect is more obvious than that of CRMA 40 and CRMA 80. With the addition of Sasobit, the high temperature performance of WCRMA first increased and then decreased. With the addition of Sasobit, the creep stiffness modulus of WCRMA decreases, the creep rate increases, and the low-temperature properties first increase and then decrease. From the atomic force microscope (AFM), it can be seen that Sasobit promotes the compatibility between rubber powder and asphalt, and the performance of asphalt modified by 60 mesh rubber powder is best. When the mass fraction of Sasobit is 2.5%, WCRMA has the best comprehensive performance.

Utilization of response surface methodology for predicting and optimizing the physical properties of rubberized asphalt modified with nanosilica and waste denim fiber

Utilization of response surface methodology for predicting and optimizing the physical properties of rubberized asphalt modified with nanosilica and waste denim fiber

Evaluation of Three Federal Highway Administration Targeted Overlay Pavement Solutions for Asphalt Pavements Based on Their Performances and Potential to Increase Pavement Service Life

The Federal Highway Administration Targeted Overlay Pavement Solutions (TOPS) program presents innovative overlay solutions for both asphalt and concrete pavements. The objective of this study was to conduct a comparative evaluation of three TOPS types for asphalt pavements, namely, Asphalt Rubber Gap-Graded, Stone Matrix Asphalt and High-Performance Thin Overlay as regards performance, how they extend pavement service life, and whether they can be used interchangeably. Asphalt binders from two sources were used in each of these three TOPS types, thus, providing a total of six TOPS mixtures. All TOPS passed the mixture performance tests where the test had a State Transportation Agency (STA) specified or a preliminary criterion, and the test results indicated that all three TOPS types can be used interchangeably. More specifically, all six TOPS mixtures met the Massachusetts Department of Transportation’s TOPS pilot specification criteria for rutting, moisture damage, and intermediate-temperature cracking. They also passed the mixture performance tests for reflective cracking and raveling based on criteria established by other STAs. AASHTOWare® Pavement Mechanistic-Empirical Design predictive models for bottom-up fatigue cracking indicated that 2 in. of a TOPS mixture placed on an existing in-service pavement can extend pavement service life between 11.2 and 14 years depending on the type of TOPS and source of binder. The maximum difference in service life between the six TOPS was slightly less than 3 years, although most of them were within 2 years of each other. Furthermore, none of the three TOPS types could be chosen to be the best TOPS.

Modified asphalt-rubber green pavement (MARGPave) mixtures: Product development and performance assessment

The major objective of this study was to develop “Modified Asphalt-Rubber Green Pavement (MARGPave)” mixtures with dense- and gap-graded aggregate structures to accomplish performance attributes superior to the conventional asphalt-rubber mixtures. The scope encompassed production of one conventional dense-graded, one dense-graded MARGPave, one gap-graded MARGPave, and one gap-graded asphalt-rubber mixtures using the Superpave mix design, conduct of stiffness modulus tests, moisture sensitivity, and fatigue evaluation at varying temperature-frequency combinations, which generated over 300 data points. The dense-graded MARGPave mix exhibited three times higher fatigue life and increased durability than the conventional dense-graded mix. The gap-graded MARGPave mix had lower modulus at all temperatures by more than 50% than the dense-graded MARGPave mix due to 2% higher asphalt content and rubber inclusions. Likewise, the modulus of gap-graded MARGPave mix was higher than gap-graded asphalt-rubber mix across all temperatures and frequencies, indicative of the elastic nature of the MARGPave mix due to higher rubber content. Higher modulus at higher temperatures and lower modulus at lower temperatures were concurrently displayed by dense-graded MARGPave mix, which indicated that the material would be resistant against rutting and low-temperature thermal cracking, thereby able to outperform conventional materials with insignificant rate of change of viscosity with increasing temperatures, and the presence of rubber particles that would render the mix the necessary additional resilience to endure the mix performance for the entire design life. It is noteworthy that the procedure of blending asphalt binder, aggregates, and the modified asphalt-rubber product that replaces some portions of fine aggregates helped create MARGPave mixtures that was found akin to the semi-dry process technology. It is envisioned that the indigenously developed MARGPave mixtures will be best suited as a roadway construction and maintenance strategy that supports the engineering use of end-of-life tires, encouraging the waste-to-wealth concept.

Investigation of 6PPD-Quinone in Rubberized Asphalt Concrete Mixtures.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-quinone (6PPD-Q), a transformation byproduct of 6PPD used in tires as an antiozonant and antioxidant, was recently discovered as the chemical primarily responsible for the acute lethal toxicity of urban storm runoff to coho salmon. The asphalt concrete (AC) surface layer is the primary medium to contact 6PPD-Q immediately upon its release from tires, and the addition of recycled tire rubber (RTR) to the asphalt binder and mixture is a widely accepted practice in asphalt production. Therefore, it is urgent to understand the fate of 6PPD-Q at the asphalt concrete surface layer-water interface. This study analyzed the sorption and desorption of 6PPD-Q by compacted and crushed loose (loose particles, ∼5 mm) rubberized asphalt mixtures and their mobilization from compacted asphalt mixtures during simulated rainfall events. It should be noted that the crushed loose asphalt mixtures demonstrated the physicochemical properties of the asphalt materials, while the compacted asphalt mixtures represent in-service AC layers. Sorption of 6PPD-Q by crushed loose and compacted asphalt mixtures reached equilibrium within 12 days, with a sorption coefficient of 151.57-257.51 L/kg for compacted asphalt mixtures. Within 12 days, desorption of 6PPD-Q from crushed loose and compacted rubberized asphalt mixtures (20 g particles/L) to the double deionized (DDI) water and synthetic stormwater was 0.01-0.09 and 0.025-0.05 μg/L, respectively. Through the rainfall simulation experiments, 0.0015-0.0049 μg/L 6PPD-Q was detected in the runoff water, much lower than the lethal concentration (LC50) of 6PPD-Q of 0.095 μg/L and 308.67 μg/L for coho salmon and zebrafish larvae. Our results indicate that, while the release of 6PPD-Q from compacted rubberized asphalt mixtures is minor, the mixtures can serve as sorbents for tire-derived 6PPD-Q and retain this emerging contaminant.

Recycle of waste tire rubber powder in a novel asphalt rubber pellets for asphalt performance enhancement

Asphalt rubber has been considered as an ideal road construction material due to its excellent rutting resistance, fatigue performance, crack resistance, and noise reduction functions. However, the preparation of asphalt rubber requires special equipment and takes higher cost. In this paper, a kind of asphalt rubber modifier pellets (ARP) that can be directly injected was prepared using a screw extruder, so as to simplify the production process and reduce equipment energy consumption during the synthesis of asphalt rubber. Industrial modifier PelletPAVE as control group, firstly, scanning electron microscopy (SEM) was employed to examine the internal microstructure of the two types of modifier pellets, and the storability were further evaluated. The rotational viscosity, High and low temperature rheological behaviors and fatigue properties of asphalt with two modifier pellets were investigated by rotational viscometer, dynamic shear rheometer (DSR), and bending beam rheometer (BBR), respectively. Finally, Infrared spectroscopy was used to explore the mechanism of modification. The findings revealed that 50% crumb rubber, 40% asphalt, and 10% calcium hydroxide are the optimal material compositions for preparing asphalt rubber pellets. The modifier particles coated with anti-sticking agent can achieve the same storability as PelletPAVE. The viscosity of the modifier pellets modified asphalt prepared is marginally higher than that of the PelletPAVE modified asphalt. Incorporating modifier pellets to asphalt demonstrates superior fatigue and crack resistance than PelletPAVE, as well as lower high temperature performance. Action mechanism of modified asphalt with both types of modifier pellets is regarded as a physical process. The asphalt rubber pellets prepared in this study reveal the merits of easy transportation, convenient direct injection, and wide application field.

Investigation of rejuvenation mechanisms of reclaimed asphalt rubber pavement through mortar tests

ABSTRACT Conventional rejuvenation methods recover the rheological properties of aged bitumen by adding rejuvenators to supplement the content of light fractions of bitumen. However, these methods cannot fully restore the microstructure and advantages of aged asphalt rubber (AR) binder due to the dissolution of rubber particles. Aiming at discovering a more suitable rejuvenation strategy for reclaimed asphalt rubber pavement (RARP), this study investigates the rejuvenation mechanisms of RARP through a series of chemical and rheological tests at the mortar level. A chemistry-based method was proposed to estimate the rubber dissolution in RARP mortar. AR mortars containing 40% of RARP mortar (RARP40%) were prepared. Three rejuvenation schemes were adopted for RARP40%, namely recovering the light fractions, supplementing the swelling rubber content, and both recovering and supplementing, respectively. The results indicate that adding rejuvenator only can effectively soften the aged RARP binder but it fails to slow down the rheological evolution of RARP40% mortar in the secondary aging. The incorporation of AR binder with extra rubber content notably improved the aging resistance but significantly compromised the workability of RARP40% mortar. The compound rejuvenation scheme was the optimum solution that balanced the rejuvenation effectiveness, aging resistance and workability.

Laboratory testing and field application of devulcanized rubber/SBS composite modified asphalt

Styrene-butadiene-styrene copolymer (SBS) and recycled tire rubber are the typical polymers for asphalt modification. The dispersion of crumb tire rubber (CTR) dominates the composite effect of rubberized asphalt. And the multiscale of CTR in mixtures always challenges the design and construction of asphalt mixtures. The multiscale dispersion of CTR can be controlled by pre-devulcanization. In this study, lightly devulcanized rubber (LDR) with various dispersive scales in asphalt from microns to dozens of microns, and deeply devulcanized rubber (DDR) with micro-nano scales were prepared and analyzed, respectively. The devulcanized rubber (DR) was further compounded with SBS to prepare composite modified asphalt. The influences of rubber content on the structure and properties of modified asphalt and mixtures were investigated, and the dispersive structure model of asphalt mixture was also established. Furthermore, a high viscoelastic rubberized asphalt was prepared with 4% SBS and 20% DDR in the field plant and paved in a field project, a new first-grade national highway. The results showed that the devulcanization of CTR can help the dispersion of CTR in asphalt by improving the compatibility among CTR, SBS, and asphalt. And the dispersive scale and the content of DR can affect the binder content, high and low temperature performance of asphalt mixtures. The field project showed that the high viscoelastic rubberized asphalt exhibited similar mix design and construction process but better high and low temperature performance compared to SBS modified asphalt.

Application of machine learning models for prediction of rheological properties of wax-modified asphalt binders

Machine learning models have received increasing attention in recent years to predict the mechanical behavior of different materials used in pavement construction due to their ability to configure their parameters based on data obtained in the laboratory. This study aims to develop, calibrate, and assess the performance of three multi-predictor machine learning models (Knearest neighbors, decision trees, and bagging systems) to predict four rheological variables (complex viscosity, complex modulus, phase angle, and dynamic viscosity) for two types of asphalt binders (an asphalt specified by penetration and an asphalt rubber) modified with different Carnauba wax contents (0, 3, 5, and 10% by weight of asphalt binder). Laboratory tests were carried out using a dynamic shear rheometer within temperatures and frequencies of 10 to 180 °C and 0.1 to 10 Hz, respectively. The results show that the three models have average coefficients of determination (R2) greater than 0.986 and relative errors (RE) less than 4% for predicting the rheological variables within the established temperature and frequency ranges. In addition, the results suggest the feasibility of implementing any of the three models for the multi-prediction (a single calibrated model is used to predict four variables simultaneously) of rheological variables for different modified asphalt binders. Based on these encouraging results, future applications of the models can be envisioned to predict the thermodynamic and physical properties of asphalt binders and develop multi-predictors with the ability to predict the response of multiple asphalt binders and rheological binder behavior with various additives.

Use of Municipal Solid Waste Bottom Ashes in Rubberized Asphalt Mixtures

Abstract The increasing need of environment protection and preservation has been stimulating road agencies to progressively adopt sustainable technologies for the design, construction, and maintenance of their assets, with the consequent increasing use of recycled materials, industrial by-products, and wastes. In such a context, the experimental investigation presented in this paper moved from the idea of synergistically combining the use of bottom ashes originating from incineration of municipal solid waste (MSW) and crumb rubber from end-of-life tires. The performance-related properties of rubberized asphalt mixtures containing MSW bottom ashes in partial substitution of natural aggregates were evaluated by means of laboratory tests focused on the determination of workability, viscoelastic characteristics, anti-rutting potential, and resistance to crack propagation. Tests were carried out by considering an ash-amended rubberized asphalt mixture and, for comparison purposes, a standard gap-graded rubberized mixture (GGRM). Obtained results indicate that the rubberized mixture containing bottom ashes exhibited lower workability (16 % decrease in k parameter), reduced stiffness (decrease of dynamic modulus at 20°C of approximately 40 % and 60 % at 0.1 Hz and 10 Hz, respectively), and decreased anti-rutting potential (17 % decrease in flow number values) with respect to the standard GGRM. Conversely, the addition of bottom ashes was found to provide beneficial effects in terms of resistance to crack propagation (with fracture toughness values five times larger than those of the reference mixture). These outcomes suggest that the use of MSW bottom ashes must be carefully considered because environmental benefits may be counterbalanced by lower performance.

Research on performance and mechanism of terminal blend/grafting activated crumb rubber composite modified asphalt

Terminal blend rubberized asphalt (TB) has attracted wide attention due to its excellent storage stability and low viscosity characteristics. However, in the special preparation process, the desulfurization and degradation of crumb rubber (CR) weaken high-temperature performance of TB. In this study, the grafting activated crumb rubber (GACR) treated by the acrylamide was selected as a modifier for strengthening high-temperature performance of TB. With special advantages, it balanced the storage stability and other properties of TB. Firstly, the self-made asphalt preparation equipment was used for the preparation of TB. Secondly, the obtained TB and GACR were mixed to prepare TB/GACR composite asphalt (TB/GACR). Finally, the properties of TB/GACR were compared and evaluated. Test results show that TB/GACR has excellent rheological properties and maintains the advantages of storage stability of original TB. In addition, GACR was conducive to improving the anti-aging performance of original TB, and slowed down the formation of S = O in TB/GACR system and the transformation rate of light components to macromolecules during the aging process.

High and intermediate temperature performance of warm asphalt rubber containing conventional warm mix additives and novel chemical surfactant

Warm mix asphalt (WMA) technology is widely used to address the workability concerns of rubberized asphalt paving materials. In this study, a novel chemical surfactant – alube– is proposed for the production of warm asphalt rubber (WAR) binders. To assess its suitability, the high and intermediate temperature performances of the resultant alube-WAR binder (AWAR) was compared with those of two conventionally produced WAR binders, namely sasobit-WAR binder (SWAR) and rediset-WAR binder (RWAR). An economic evaluation of the WAR binders was also done in order to assess their cost-competitiveness. For the high-temperature performance study, the high-temperature viscosity, viscosity-temperature susceptibility (VTS), rutting resistance, and stress sensitivity were investigated, while for the intermediate-temperature performance, the fatigue resistance factor was evaluated. Different findings were obtained from the performance and cost investigation. Alube was found to successfully lower the high temperature viscosity of AR binder but not as effective as the two conventional WMA additives. The VTS property of AR binder was only improved by the organic WMA additive (sasobit), while the chemical additives (rediset and alube) showed negative effects. In terms of rutting resistance, AWAR was superior to RWAR and AR, but was outperformed by SWAR. Also, SWAR was the least susceptible to stress changes, while AWAR and RWAR showed comparable performance. Based on the G*sin δ test, the fatigue resistance of the AR binder improved after the incorporation of the chemical additives and deteriorated after sasobit was added, and the performance ranking was determined as RWAR > AWAR > AR > SWAR. Overall, only SWAR had a better high-temperature performance than AWAR, whereas for intermediate temperature performance, only RWAR was better. Furthermore, economic analysis showed that AWAR is the most cost effective of the three WAR binders. The findings of this study indicate that alube has the potential of being utilized as a WMA additive for AR binders and can be utilized in wide range of road projects due to its cost-effectiveness.

Comprehensive study on the degradation progress of crumb tire rubber during the preparation of terminal blended rubberized asphalt binder

Terminal blended rubberized asphalt binder (TB) technology, which blends crumb tire rubber (CR) with asphalt under high interaction conditions, offers a promising waste tire recycling solution for pavement construction. By precisely controlling the degradation progress of CR, it is possible to prepare TB with specific property requirements. However, the degradation progress of CR and its impact on TB property during the TB preparation process remain ambiguous. This hinders the potential for efficient preparation of TB with specific property requirements. This study aims to understand the degradation progress of TB by analyzing binders, soluble fractions, and insoluble fractions obtained at various interaction durations. Microscopic analysis characterizes the chemical composition, morphology, and molecular weight distribution of insoluble and soluble fractions, while macroscopic analysis evaluates the solubility, viscosity, compatibility, and mechanical properties of binders. The results reveal that the degradation of CR during the preparation of TB consists of a desulfurization reaction, depolymerization reaction, and release behavior (carbon black and fillers). Depending on the degradation progress of CR, the interaction process can be classified into three stages: initial (desulfurization reaction dominant stage), middle (depolymerization reaction dominant stage), and last (release behavior dominant stage). The desulfurization reaction of CR is almost completed in the initial stage. The depolymerization reactions and release behavior occur throughout the process. The most pronounced depolymerization reactions occur in the initial stage for natural rubber and in the middle stage for synthetic rubber, while the most significant release behavior occurs in the last stage. Accordingly, in the initial stage, TB shows a rapid evolution in macro properties due to the significant development of degradation reactions, specifically, the notable improvement in viscosity, compatibility, and low-temperature properties, as well as the substantial deterioration in high-temperature properties. In the middle stage, the degradation reaction develops further but slower, with TB exhibits a further but slower evolution in macro properties. In the last stage, the degradation reaction is almost completed, and TB shows a gradual stabilization of macro properties. The findings are expected to achieve precise control of CR degradation progression, which offers the possibility of efficient preparation of TB with specific properties, thus advancing the application of CR in pavement engineering.

The Development of a New Thermoplastic Elastomer (TPE)-Modified Asphalt

The use of (recycled) plastics and (waste) vulcanized rubber powder is the main polymer of raw materials, and composite organic additives are selected to fully combine with asphalt components. The physical and chemical reactions between different components are completed in dynamic mixing, establishing a morphology structure similar to thermoplastic elastomers (TPEs), and a thermoplastic highly asphaltized alloy material. TPE-modified asphalt not only significantly improves the high-temperature stability of the base asphalt, but also has the social and economic value of rational utilization of resources and turning waste into treasure. There are very few studies on the preparation of modified high-viscosity asphalt formulations using rubber and plastic as modifiers. In this study, rubber, plastic, and plasticizers were added to the base asphalt, and the TPE modifier formulations were developed through the research of new TPE modifier series and functional formulations, preparation process, and its modified asphalt properties. Meanwhile, the preparation method of the rubber–plastic alloy modifier was determined. The performance of the TPE-modified asphalt was verified through performance verification tests to evaluate the modification effect of the modifier on the base asphalt. The test results showed that the penetration, softening point, ductility, and viscosity indexes of the TPE-modified asphalt developed through the proposed formulation, and it met the specification requirements for high-viscosity modified asphalt. Rubber and plastic modifiers significantly improved the high-temperature stability of the base asphalt. In addition, the rubber–plastic modifier had a significant tackifying effect, with a dynamic viscosity of 60 °C and a Brinell rotational viscosity much greater than asphalt and rubber asphalt. The microscopic mechanism of the newly developed TPE-modified asphalt was analyzed by fluorescence microanalysis. The results showed that the rubber–plastic modifier fully swelled in the asphalt and was uniformly dispersed in the asphalt as a floc. The network structure of activated waste rubber powder-modified asphalt was more uniform and dense, resulting in good performance of the modified asphalt, and stable storage of modified asphalt was obtained. Through appropriate formulation, the comprehensive performance of the TPE-modified asphalt obtained met the requirements of pavement application and construction, providing a good theoretical basis for promoting TPE-modified asphalt.

Optimized Performance Design of Low Freezing Point Asphalt Mixture for Northern Mountainous Areas

Due to the lack of research on the applicability and optimization design of low freezing point asphalt mixtures in specific environments, especially for the harsh environments of low freezing point asphalt mixtures in mountainous areas during cold winter and high humidity in other seasons, there is a significant engineering demand. This paper carries out a study on the performance optimization design of low freezing point asphalt mixtures in northern mountainous areas. Through comparative analysis of low freezing point asphalt mixture technologies and analysis of the road performance of low freezing point asphalt mixtures, combined with the climate and driving characteristics of northern mountainous areas, the low freezing point asphalt mixture suitable for northern mountainous areas is selected. The research shows that the hygroscopicity of M low freezing point filler is significantly stronger than that of Z low freezing point filler, and since the humidity in northern mountainous areas is relatively high, selecting low freezing point fillers with lower hygroscopicity to prepare low freezing point asphalt mixtures can avoid safety accidents caused by excessively wet road surfaces. SBS modified asphalt and waste tire rubber powder modified asphalt can both produce low freezing point asphalt mixtures that meet the requirements of standard road performance, and both have good high and low temperature performance. When conditions permit, waste tire rubber powder modified asphalt low freezing point asphalt mixture is recommended as the first choice.

Characterization of Interlayer Bonding Mechanism Based on Interface Morphology in Double-Layered Asphalt Systems

The mechanism of interlayer bonding and its relationship with interface morphology in asphalt pavement is not well understood yet. This study aims at investigating the effect of interface morphology on the interlayer bonding performance of double-layered asphalt systems. Four double-layered asphalt systems were prepared with rubberized asphalt concrete (RAC), asphalt concrete (AC), and stone mastic asphalt (SMA) mixtures. To test the influence of different interlayer treatments, three conditions were studied: styrene-butadiene-styrene (SBS)-modified asphalt gravel seal (GS) coat (SBS-GS), rubber-modified asphalt gravel seal coat (RA-GS), and fiber-reinforced rubber–modified asphalt gravel seal coat (FR-GS). The influence of surface type and interface treatment on interface morphology and bonding properties were compared and analyzed using a series of indoor interlayer shear bonding tests under three temperature conditions in two phases. In addition, based on the three-dimensional (3D) scanning and reconstruction technique, the morphology of the nondestructively separated interface of double-layered systems with no interlayer treatment was obtained, and the mechanism of the influence of the interface morphology on the interlayer shear strength was analyzed in depth. The results showed that double-layered systems exhibited different macrotexture and roughness characteristics at interlayer surfaces, creating distinct interface morphology properties for each system type. Consequently, the interlayer bonding strength and performance of double-layered asphalt systems were affected accordingly. In this respect, the order of the interlayer shear strength of double-layered systems with different interlayer treatments at different temperatures ranked as RAC-13/RAC-20 > SMA-13/RAC-20 > SMA-13/AC-20 > AC-13/AC-20. It was demonstrated that the proposed interface area ratio (K) can be used for the characterization of the interface morphology and reflect the interlayer bonding state. Moreover, it was found that the interlayer treatment could influence the interface morphology to a certain extent and change the effective bonding between layers. As a result, the order of interlayer shear strength of different interlayer bonding treatments ranked as FR-GS> RA-GS > SBS-GS. Finally, aggregate gradation of the mixtures could also affect the morphological characteristics of the interface.

Evaluation of Warm Mix Crumb Rubber Modified Asphalt Mixture (WCRMA) on resisting permanent deformation

Crumb rubber (CR) is generated from the recycling of used or discarded car tires and has long been utilized in the paving industry. Crumb rubber can be used in asphalt mixes in two ways: dry process and wet process. However, compared to standard combinations, crumb rubber modified asphalt (CRMA) requires much higher mixing and compaction temperatures. As a potential substitute, using warm mix asphalt (WMA) technology significantly lower hot-mix asphalt (HMA) production and placement temperatures through viscosity reduction. In accordance, the objectives of the study are to produce warm mix crumb rubberized asphalt mixtures (WCRMA) using a dry process and to evaluate WCRMA’s performance in terms of rutting resistance. WCRMA is produced by adding 1, 3, and 5% Sasobit® of the total weight of the binder. The rutting performance of WCRMA was evaluated by Dynamic Creep test. The result showed that the asphalt mixes with the largest percentages of Sasobit® (5%) showed the lowest lowest accumulated strain and permanent deformation. The modified asphalt mixture performed better and had greater rutting resistance due to the replacement of fine aggregate with crumb rubber and the addition of Sasobit® compared to control sample.

Excellent low temperature performance for modified asphalt by finely dispersed sidewall tire rubber

Low temperature performance of rubber asphalt in cold regions still has challenges for facing cracking. In this study, the modified asphalt by finely dispersed degraded sidewall tire rubber (STR) was prepared to study its low temperature performance by bending beam rheometer, differential scanning calorimetry, Fraass brittleness temperature and ductility. Results showed that low test temperature and Fraass brittleness temperature of STR-modified asphalt could be down to −24.0 °C, both of which were better than that of current crumb tire rubber modified asphalt. The ductility at temperature of 5 °C was 22.3 cm, which was higher than those of other tire section rubber modified asphalt, such as tread tire rubber modified asphalt (TTRMA, 19.8 cm) and bead tire rubber-modified asphalt (BTRMA, 15.6 cm). This was owing to that STR-modified asphalt had low glass transition temperature (Tg) of −33.1 °C, which was lower than those of TTRMA (−32.9 °C) and BTRMA (−31.2 °C). Modification mechanism proposed that flexible butadiene rubber (Tg of −110.0 °C) in STR strongly promoted the relaxation of rubber molecular segments through molecular orientation and conformation switching when suffering stress concentration. Accordingly, the STR-modified asphalt had excellent low temperature performance, and could be practically used for flexible pavement in cold region.

Comparison of asphalt emulsion-based chip seal and hot rubber asphalt-based chip seal

The use of asphalt emulsion chip seal and hot rubber chip seal as pavement preservation techniques has been gaining popularity. This study aims to compare the laboratory performance of asphalt emulsion and hot rubber asphalt used in chip seal applications. Interlayer shear strength (ISS) and interlayer tensile strength (ITS) tests were designed to evaluate the bond quality of the chip seal samples prepared for both materials. The sweep test was used to estimate the aggregate loss of the chip seal on the asphalt pavement. The universal testing machines were used to evaluate the deterioration of the ISS and ITS values under cyclic load conditions, while the tensile and shear bond properties of chip seals under wet-freeze conditions were evaluated using freeze-thaw cycles. Results showed while both materials experienced a decline in their ISS and ITS values following repeated cycles of load and freeze-thaw, the hot rubber chip seal demonstrated significantly higher ISS and ITS values than the asphalt emulsion chip seal (48–111% and 36–102%, respectively). Moreover, the hot rubber chip seal exhibited better performance in terms of aggregate retention and cohesive strength. The aggregate gradation would affect the aggregate retention and cohesive strength. Nonetheless, both treatments are deemed acceptable for pavement maintenance. The weak bond between hot rubber asphalt or asphalt emulsion and aggregate could be attributed to cyclic load and freeze-thaw conditions.