Rubber Modified Asphalt Binders Research Articles

Cracking Resistance of Recycled Rubber Asphalt Binder Composed of Warm-Mix Additives.

Warm-mix asphalt technology has been applied to recycled rubber asphalt binder (RAB), which forms warm-mixed crumb rubber-modified asphalt binder (W-RAB) as a “green” material for environmental conservation and to enhance road performance. Furthermore, low-temperature cracking is one of the major distresses for asphalt pavement, which drastically restricts ride quality and service level. Therefore, the main objective of this study is to comparatively analyze the low-temperature properties of W-RABs based on thermal stress and the simple fractional model. W-RABs were obtained by mixing 60 mesh recycled rubber (CR) and two different types of warm-mix additives, namely viscosity reducer (1, 2, and 3%) and surfactant (0.4, 0.6, and 0.8%). First, Hopkins and Hamming’s numerical algorithm and the Boltzmann superposition principle were used for obtaining thermal stress . Subsequently, critical cracking temperature was derived using the single asymptote procedure (SAP) theory. Second, the simple fractional viscoelasticity model was used to calculate the creep compliance, damping ratio, and dissipation energy ratio, and the results were compared with the Superpave protocol results obtained with bending beam rheometer (BBR) tests. The results showed that a combination of CR and warm-mix additives could slightly improve the thermal crack resistance of the asphalt binder. The addition of 0.6% surfactant yielded the optimum performance, while only a high dosage (3%) of viscosity reducer provided a marked improvement in efficiency, which decreased with a decrease in temperature. This study recommends the use of RAB composited with 0.6% surfactant for areas with extremely low temperature.

Effect of Activation Modes on the Property Characterization of Crumb Rubber Powder from Waste Tires and Performance Analysis of Activated Rubber-Modified Asphalt Binder.

The rubber molecular chain in waste vulcanized tire rubber will be crosslinked to form a network structure that would be difficult to degrade in asphalt. Crumb rubber treated by desulfurization activation could form active groups on the surface by interrupting the crosslinking bond to improve the compatibility between crumb rubber powder and asphalt. To explore the influence of activation modes on crumb rubber powder and the corresponding rubber-modified asphalt binder, crumb rubber powder was firstly activated through three commonly used activation methods and asphalt binder samples modified by activated crumb rubber powder were also prepared. The basic properties of activated crumb rubber powder were characterized by infrared spectroscopy, and conventional tests were used to study the conventional physical properties of the asphalt binder. The infrared spectroscopy and elemental analysis showed that the crumb rubber powder was mainly composed of alkanes, alkenes, sulfonic acids, aromatics, and a little silica rubber and antioxidant zinc oxide, which is suitable for asphalt modification. The simple heat activation treatment method is not enough to greatly destroy the cross-linking structure of crumb rubber powder, but the “C=C” bond was destroyed more seriously. Under the action of adjuvants, the polysulfide cross-linking bond could be broken in crumb rubber powder. The heat treatment and chemical treatment could not achieve the purpose of reducing the viscosity and improving the compatibility of rubber asphalt binder through desulfurization activation. The mechanochemical treatment would help to improve the performance of crumb-rubber-powder-modified asphalt binder. The data correlation analysis based on the grey relational degree can provide a reference for the selection of activated crumb rubber powder for different application requirements in the asphalt modification procedure.

The Effects of Activation Treatments for Crumb Rubber on the Compatibility and Mechanical Performance of Modified Asphalt Binder and Mixture by the Dry Method

Compatibility and mechanical performance of crumb rubber (CR)-modified asphalt and mixtures prepared by the dry method are poor at present, which limits the application of dry-mixed asphalt rubber in paving engineering. To solve this problem, various activated treatments for CR were performed, and the modified asphalt binder was prepared by the dry process in this study, aiming to activate the CR as the modifier and improve the compatibility of CR-asphalt blends. The effects of pre-treating methods of high temperature, pre-swelling, and microwave treatment on rutting resistance and compatibility of the asphalt binder and asphalt mixture were evaluated. Furthermore, the dynamic shear rheometer (DSR) of temperature sweep, Brookfield rotary viscosity, physical properties, rutting resistance, and microstructure of modified asphalt were measured. The results indicated that the three treatments have a pronounced effect on the high temperature performance of the crumb rubber-modified asphalt (CRMA) binder in the dry process and modified asphalt storage stability improvement. The high-temperature and microwave pre-treatment for CR lead to the largest complex modulus, viscosity, and rutting factor. Moreover, high-temperature, pre-swelling, and microwave treatment for CR significantly increases the dynamic stability of dry-mixed asphalt mixtures, which indicates the enhanced resistance to permanent deformation. In microscopy, homogeneous and compatible states were obtained for asphalt modified by high temperature-treated CR and pre-swelled CR, in which the strong interaction occurs among rubber molecules and the asphalt component. The microstructure of dry CR-asphalt blends sheds light on the mechanical performance. Consequently, activated CR modification for the asphalt binder by the dry process in this study is a promising technology, and other properties need to be verified in the future.

Quantitative determination for effective rubber content in aged modified asphalt binder

During the aging process, the desulfurization and degradation process of crumb rubber modified asphalt binders (CRMA) consistently occurs. In this paper, a toluene insoluble test, an electrochemical titration method, viscosity, FTIR and GPC were developed to determine the effective crumb rubber content of CRMA after exposure to various aging conditions. Centering on efficiency and accuracy, these five methods were compared with the Pearson coefficient method. The results show that when the degree of aging was severe, the desulfurization and degradation of rubber were aggravated, causing the CC bond in the rubber to break and an increase in the large molecular weight of the asphalt binder. The effective rubber content in the aged CRMA was 7.7–14.2% less than the unaged CRMA. At the same time, the correlation coefficients among the five methods were all above 0.90, but the electrochemical titration and FTIR had priority over the other methods.

Aging characteristics of crumb rubber modified asphalt binder and mixture with regenerating agent

At present, the research hotspots of recycled asphalt mainly focus on the recovery of performance, but less attention has been given to the secondary aging of recycled asphalt. Therefore, this article mainly studied the effects on the physical properties of initial aging, regeneration and secondary aging of crumb rubber modified asphalt (CRMA) and mixtures. The results show that a rubber regenerating agent (RA) can restore the performance of aged CRMA to its original level, and the optimal RA content was 8%. During the secondary aging, RA-CRMA also experience performance degradation similar to virgin CRMA due to the loss of light components and the degradation of rubber. However, on the whole, the aging index of RA-CRMA and mixture was better than that of virgin CRMA and mixture, indicating that RA improved the aging resistance of CRMA. Further, the Pearson correlations between the various aging indexes of binder and mixture were significant, and the state of secondary aging can be quickly determined through a simple binder experiment.

Investigation of the Rheological and Bonding Characteristics of Crumb Rubber-Modified Asphalt Binders Mixed with Warm Mix Asphalt Additive and Antistrip Agent

Investigation of the Rheological and Bonding Characteristics of Crumb Rubber-Modified Asphalt Binders Mixed with Warm Mix Asphalt Additive and Antistrip Agent

Composition optimisation and performance evaluation of waterborne epoxy resin emulsified asphalt tack coat binder for pavement

ABSTRACT To ensure the effective bonding of each structural layer of pavement and improve the service quality and durability of pavement, the waterborne epoxy resin (WER) emulsified asphalt (WEREA) tack coat binders were prepared by using polyurethane-epoxy resin. The basic properties of WEREA, such as tensile strength, adhesion to aggregate, high temperature heat resistance and low temperature impact resistance were studied. Its composition and ratio were optimised. The waterproof, bonding and durability performance of WEREA used in pavement tack coat were evaluated. The results show that WEREA prepared by polyether polyurethane modified E-51 epoxy resin (PUD-E51) has higher early and late strength. Its tensile strength was 1.75 MPa after curing for 7 days. The basic properties of WEREA, including adhesion to aggregate, heat resistance and impact resistance were better than those of SBS modified asphalt and crumb rubber modified asphalt binder. The tack coat of WEREA cannot seep under the dynamic water pressure of 0.6 MPa for 30 min. According to the interlaminar shear strength, the recommended spraying amount of the WEREA tack coat was 1.0 kg/m2. The WEREA could guarantee the effective bonding of each structural layer of the pavement, and improve the durability of the tack coat and pavement.

Laboratory and Field Evaluation of Pre-Treated Dry-Process Rubber-Modified Asphalt Binders and Dense-Graded Mixtures

Pre-treatment of ground tire rubber is emerging as a popular method to incorporate rubber particles in dense-graded asphalt mixtures. This study investigates the effects of a chemically engineered Dry-Process Ground Tire Rubber (DP-GTR) modification in asphalt binders and mixtures. The DP-GTR is comprised of rubber particles measuring 400 to 600 µm in diameter (minus #30 mesh) coated with a non-elastomeric liquid. No change in aggregate gradation is necessary in DP-GTR modification of asphalt mixtures. In this study, the effects of DP-GTR modification on binder properties were measured by dynamic shear rheometer, Multiple Stress Creep and Recovery (MSCR), and bending beam rheometer tests. Additionally, mixture properties measured by three cracking tests: Disk-shaped Compact Tension (DC[T]) test, Illinois Flexibility Index, and indirect tensile asphalt cracking test and one rutting test (Hamburg wheel track test) were evaluated. Results showed: (a) 10–12°C bump on binder high temperature performance grade with 10% DP-GTR modification by weight of binder; (b) improvement in non-recoverable compliance in MSCR test indicated higher rut resistance; (c) increase in DC(T) fracture energy at low temperatures; (d) decrease in rut depth; and (e) decrease in flexibility index and cracking test index. Field performance of the chemically treated DP-GTR sections located in different states was examined to address discrepancies observed in the cracking tests. The cracking and rutting performance of all the field sections was good-to-excellent, suggesting that some of the currently popular simple cracking tests may not be able to properly assess the cracking resistance inherent in GTR-modified asphalt mixtures.

Aging Properties and Mechanism of Microwave-Activated Crumb Rubber Modified Asphalt Binder

Although crumb rubber modified asphalt (CRMA) has a better performance than matrix asphalt (MA) in road engineering, the application bottlenecks of this material lies in its high viscosity, poor workability and bad storage stability. Microwave technology is one of the solutions to the above problems. The objective of this study was to investigate the physical and chemical changes before and after aging of CRMA which was prepared by microwave activated crumb rubber, and the aging mechanism of microwave-activated crumb rubber modified asphalt (MACRMA). Through penetration, softening point, ductility, viscosity and DSR test, the high and low temperature performance and temperature sensitivity of MA, CRMA and MACRMA before and after aging were studied. These tests results revealed that microwave treatment can improve the anti-rutting ability and the anti-aging performance of rubber asphalt. According to gel permeation chromatography (GPC) test, the distribution changes of the internal molecular content of the three asphalts were determined during the aging process. Its test results showed that aging effect accelerated the conversion of small molecules to large molecules in asphalt, and the value of large molecular size (LMS) increases more after long-term aging. The microwave activation made the swelling reaction more intense, thereby delayed the conversion of LMS in the rubber asphalt. In addition, LMS has a high correlation with test indicators. The fourier transform infrared spectroscopy (FTIR) test was used to measure the functional group changes of each asphalt. The FTIR spectra indicated that microwave activation is mainly a process of physical change. The carbonyl and sulfoxide functional group indices of MACRMA were lower than those of MA and CRMA, which also confirmed that MACRMA has a better anti-aging ability.

The Effect of Activation Method of Rubber on the Performance of Modified Asphalt Binder.

Poor storage stability is a key problem restricting the rapid development and wide application of rubber-modified asphalt binder, and activation of rubber has shown good prospects to solve this problem. In this study, two activation methods, coating by polyamide 6 and grafting by acrylamide, were introduced to treat crumb rubber. Then the activated rubber was added to base asphalt binder to prepare modified asphalt binder. The chemical structure and morphology of rubber powder before and after activation and of asphalt binder before and after modification were characterized by Fourier transformation infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The conventional and rheological properties and storage stability were analyzed to reveal the influence of activation method on the performance of asphalt binder. The results showed that after being activated, the surface of the rubber is loose and rough. A chemical reaction did not occur during activation by polyamide but occurred during activation by acrylamide. The activation of the rubber effectively improved the high- and low-temperature performance, and the softening difference decreased by 79.8%. This is because the interaction between rubber and asphalt binder was enhanced through activation of rubber, and grafting activation had better effect due to the chemical reaction between the basic amide groups of acrylamide and acid groups of asphalt binder.

Heterogeneous visco-hyperelastic numerical modelling of crumb rubber-modified asphalt binders

ABSTRACT Three-dimensional numerical finite element (FE) biphasic models verified against the experimental data were developed aiming to study the accuracy of FE modelling in the prediction of viscoelastic properties of crumb rubber-modified asphalt binders. In the numerical models, crumb rubber-modified asphalt binders are considered as a heterogeneous composite material consisting of the original asphalt binder and rubber particles which respectively have viscoelastic and hyperelastic behaviours. Three different dosages of crumb rubber including 10, 15 and 20 wt% of the original asphalt are added. To capture rubber particles distribution within the bituminous matrix, a random generation method by using the MOA software (French acronym for random object modeller) was implemented based on rubber’s minimum and maximum particle sizes. In order to determine the viscoelastic properties of the original asphalt binder as well as the crumb rubber-modified ones, the dynamic shear rheometer (DSR) was used. The excellent agreement between the numerical FE modelling and experimental results witnessed the capability of biphasic finite element models to predict the visco-hyperelastic behaviour of crumb rubber-modified asphalt binders having an error lower than 9%.

Effect of used motor oil as a rejuvenator on crumb rubber modifier’s released components to asphalt binder

Asphalt binder modification by crumb rubber modifier (CRM) could enhance its rheological properties at high and intermediate temperatures by increasing its stiffness and elasticity. To obtain a modified binder blend with more enhanced intermediate- and low-temperature rheological properties, used motor oil (UMO) was introduced to the crumb rubber-modified asphalt (CRMA) binder. The enhanced high- and intermediate-temperature rheological properties of the modified binders were investigated using a temperature sweep test. UMO, used as a rejuvenator, can regulate the CRM role in the modified binder blend by creating a balance between the binder’s enhanced stiffness and fluidity. This was achieved by increasing |G*|/sin δ at high temperatures and decreasing |G*|.sin δ at intermediate temperatures. The mutual components between the CRM and the asphalt binder were explored by thermogravimetric analysis and Fourier transform infrared (FTIR) spectroscopy. UMO was found to have similar FTIR bands of the asphalt binder that helped the CRM particles to absorb more low-molecular-weight fractions at the beginning of the interaction time, which caused them to swell more and then dissolve, releasing their polymeric components in the asphalt binder’s liquid phase. Adding UMO with two and half percentage by the weight of the neat asphalt binder to the CRMA binder, interacted at 190°C–50 Hz–60 min, could increase the CRM dissolution and cause a greater release of CRM polymeric components into the asphalt binder matrix. This was assured by the presence of FTIR peaks at 911 and 966 cm−1 that are related to the polybutadiene, synthetic rubber in CRM.

Rheological properties and chemical characterisation of reacted and activated rubber modified asphalt binder

The objective of this study was to investigate the rheological and chemical properties of crumb rubber modified asphalt binder. Reacted and activated rubber (RAR) with different rubber contents were used to modify the asphalt binder, including 15%, 25%, 30%, 35% and 40% by mass of RAR modified asphalt binder. In general, the test results were favourable in rutting resistance performance, fatigue cracking resistance and low-temperature cracking resistance. The addition of RAR led to an improvement of elastic properties and a decrease in viscous features of the binders. The RAR behaved as an anti-cracking additive to increase the service life of asphalt pavements. At a strain level of 5.0%, the binder fatigue life of 15% RAR, 25% RAR, 30% RAR, 35% RAR, 40% RAR and 12% Terminal Blend were 13, 24, 30, 43, 45 and 18 times higher than that of the control binder, respectively. The absorbance growth height increased with increasing amounts of RAR additives in the Fourier Transform Infrared Spectroscopy spectra. A linear correlation was found between the RAR content of the binder and the area under the band at 3642 cm−1 and the ratio of the bands at 3642 and 1376 cm−1.

Chemical, thermophysical, rheological, and microscopic characterisation of rubber modified asphalt binder exposed to UV radiation

In this work, the effect of ultraviolet (UV) radiation on samples of asphalt binder mixed with crumb rubber is studied. Two sets of samples are characterised using a PG 64-22 neat binder with different percentages of rubber particles being 0, 16.6, and 20.0 wt.%. One set of the samples was stored at ambient temperature (called the unaged set) and the other was inserted inside an accelerated weathering tester for 100 h (called the UV-aged set). Thermal conductivity, chemical indices, rheology, and morphology of both sets of samples are tested using the flash method, differential scanning calorimeter (DSC), Fourier-Transform Infrared Spectroscopy (FTIR), dynamic shear rheometer (DSR), and Scanning Electron Microscope (SEM), respectively. Results show that the addition of rubber leads to a reduction of specific heat for the rubber-modified binders. Specific heat capacities of the three UV aged samples are larger than those of their unaged counterparts, and the 16.6%-aged has the highest value. FTIR spectra of the three unaged samples are very similar, whereas distinct changes occur after UV exposure. The normalised absorbance of the peak associated with S = O group increases and the peak for the aliphatic group decreases after UV aging, showing some evidence of oxidation due to UV aging. Use of crumb rubber in the binder decreases the thermal conductivity and 20.0 wt.% sample is even less conductive compared to the 16.6 wt.%. At all temperatures above 25°C, aged samples have lower thermal conductivity than the unaged ones, except neat binder which is opposite. Rheological measurements show that the complex modulus of the samples increases with the addition of rubber particles and also after aging. However, 16.6% rubber-modified sample shows the least increase in modulus after aging. Microscopic morphology shows that UV radiation causes cracks in both neat and rubber modified binder. Smaller cracks are seen to form, and the cracked pieces are stuck together in the rubber modified binders, whereas less cohesion between the cracks is observed in the neat binder.

Impact of Various Crumb Rubber Modifications on Asphalt Binder and Mixture Properties

As the price of asphalt binder continues to rise, state agencies are looking for sustainable ways to reduce the cost of asphalt pavements without compromising performance. One such alternative is the use of crumb rubber, derived from waste tires, in binders of asphalt mixtures. Blending virgin asphalt binder with ambient or cryogenic ground crumb rubbers along with additional modifiers to produce sustainable asphalt mixtures was studied. The modifiers evaluated include E-rubber (free flowing rubber pellets), SBS, sulfur, and Rpolymer (reactive polymer polyolefin blend coated micronized rubber particles). Thermogravimetric analysis was used to determine the natural rubber to synthetic rubber ratio in the ground tire rubbers. Gel permeation chromatography was used to investigate the molecular structure and changes occurring in the asphalt binder on blending with rubber/modifier. Scanning electron microscopy was used to examine the physical nature of the binder blends. All of the binder blends were evaluated using the multiple stress creep recovery test. Mixtures prepared from modified binders were characterized using semicircular bend (SCB) test at intermediate temperature and Hamburg wheel-tracking (LWT) test. Correlation of physical properties of crumb rubber modified asphalt binder with apparent molecular weight of binder components was examined. Asphalt mixtures containing ambient or cryogenic ground crumb rubber additives did not exhibit improved mixture intermediate temperature cracking performance as compared to conventional mixture as measured by SCB test Jc value. Addition of elastomeric high molecular weight polymer additives improved MSCR test results of binder blends when compared to rubber blends with no additional polymer additives. Addition of E-rubber or R-polymer to the asphalt binder improved SCB intermediate temperature test results of the corresponding mixtures. It was noted that the presence of high molecular weight elastomeric species in asphalt binder blends is necessary to obtain acceptable intermediate temperature cracking performance. Presence of crumb rubber in asphalt binder contributed to the increase in percent high molecular weight species that provided an enhanced mixture rut resistance.

Impacts of recycled crumb rubber powder and natural rubber latex on the modified asphalt rheological behaviour, bonding, and resistance to shear

The objective of this study is to investigate the rheological properties, bonding and resistancetoshear of the rubberized modified binders under different conditions. A base asphalt binder with penetration grade 60/70 was utilised in this study. The crumb rubber and natural rubber latex were added at different percentages for the modified bitumen production, and computed based on the mass of bitumen. Silane additives at the rate of 0.1% by mass of asphalt binder were used as a surfactant. A series of rheological properties and recovery test were conducted on all binders. While bond test and Layer-Parallel Direct Shear (LPDS) test were carried out in order to simulate the crack movement of pavement. The results show that the addition of crumb rubber and latex positively impacts the performance of the asphalt binder. The crumb rubber and natural rubber latex modified asphalt binder has comparatively identical elastic recovery outcomes, while it also helps in enhancing the stiffness in terms of softening and penetration value. However, natural rubber latex modified asphalt binder performed much better than crumb rubber modified asphalt binder in terms of torsional recovery. Whereas, rotational viscosity test has been useful in adopting the suitable temperature which is 160 °C in order to satisfy the needs of better workability and to ensure it is pumpable. Storage stability test proved that the modified asphalt binders are homogenous since the temperature differences are less than 5 °C. The dynamic shear rheometer (DSR) test proved that the modified asphalt binder has better resistance to rutting. Through DSR findings and activation energy, the modified asphalt binder were catogorize as less susceptible to temperature changes. Finally, the crumb rubber modified asphalt binder did well in terms of bonding strength, while the natural rubber latex modified asphalt binder performed well in terms of resistance to shear. Overall, both rubberized modified binders performed better than the control sample.

Rheological and aging behaviors of liquid rubber modified asphalt binders

To provide a quality option for road materials in cold regions and reduce the energy consumption of modified asphalt in road engineering, liquid styrene butadiene rubber (LSBR) was selected to modify asphalt. In this study, under the condition of 60 °C, base asphalt (SK-90#) was modified by LSBR and the rations of LSBR were 1 wt%, 3 wt%, 5 wt% and 7 wt% of base asphalt. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were used to investigate the rheological properties (fatigue performance and low temperature cracking resistance performance) and anti-aging performance of asphalt binders. The results showed that LSBR had a negative effect on the high temperature performance of asphalt binder, but it had the best improving effect on ductility in conventional properties. After aging procedure, the deformation resistance ability of the modified asphalt binder was greater than the recovery deformation ability. LSBR effectively improved the low temperature cracking resistance and obviously improved the fatigue performance of asphalt binders. The modified asphalt binders had good anti-aging ability when the test temperature was under 5 °C and the LSBR content was no more than 3 wt% of base asphalt. Considering the comprehensive properties of LSBR modified asphalt binders, the mixing content of LSBR should be no more than 3 wt%.

Performance Analysis of Compound Rubber and Steel Slag Filler Modified Asphalt Composite.

A new treatment method of combined crumb rubber and steel slag modifier for asphalt binders was proposed in this work. The viscosity, rheological properties, and thermogravimetric analysis of modified asphalt mortar were then investigated. The modified asphalt composite was prepared in laboratory by two steps. Rubber powder was firstly added into hot asphalt flux to make rubber modified asphalt (RA), and then RA binders were wrapped with steel slag powder by granulation machine to make compound rubber and steel slag filler modified asphalt composite (RSAC). Test results showed that the viscosity–temperature susceptibility of RSAC was superior to that of modified asphalt binder with only one additive. The softening point differences of RSAC was 2.1 °C. The complex modulus and phase angle were significantly influenced by the addition of steel slag fillers. Creep tests show that a better anti-permanent deformation performance of RSAC can be obtained, which means a better low temperature performance could be predictable. The CAM (Christensen-Anderson-Marasteanu) and Burgers models can be used to describe the change of complex modulus and viscous-elasticity performance of RSCA. The lower value of me (0.6344) and R (0.1862) from the CAM model indicated that RSAC was slightly related to the sensibility of frequency. The higher value of λ∞ and E0 of RSAC indicated a better ability of shear-creep resistance.

Evaluation of Rheological and Moisture Damage Properties of Crumb Rubber–Modified Asphalt Binder

Abstract This study investigates the influence of crumb rubber (CR) particles on the rheological and moisture damage properties of asphalt binder. A control neat asphalt binder (AC-10) and 30# CR are chosen for the preparation of CR-modified asphalt (CRMA) binder. A total of four different CR dosages (0, 5, 10, and 15 % by weight of binder) was selected for the preparation of four combinations of CRMA binder. The rheological performance of CRMA binders was investigated based on Superpave rutting parameter, multiple stress creep recovery, Superpave fatigue parameter, and linear amplitude sweep (LAS) test using dynamic shear rheometer. Moisture damage response of CRMA binder was evaluated using surface free energy and bitumen bond strength test. CR particles significantly enhanced rut resistance of neat asphalt binder at high temperatures with improved stiffness properties and elastic response. Superpave fatigue factor and LAS test results showed that CRMA binder containing a CR dosage up to 10 % has improved fatigue life and is less susceptible to strain amplitude at an intermediate temperature. CRMA binder with 5 % CR predominantly shows better resistance to moisture damage with good interfacial energy and compatibility ratio at the aggregate interface. However, BBS test results imply that the contribution of high dosages of CR (5 to 15 %) is significant in improving the bond strength and moisture damage resistance of CRMA binder.

Effect of liquid anti-stripping agents on moisture sensitivity of crumb rubber modified asphalt binders and mixtures

Influence of three liquid anti-stripping agents (ASAs) (named as M1, T9 and LOF-6500) with three dosages (0.25%, 0.50%, and 0.75%) on laboratory performance of crumb rubber modified asphalt (CRMA) mixture was investigated. The performance included aggregate–CRMA binder adhesion bond, water stability, high-temperature stability and low-temperature anti-cracking property, which were evaluated by surface free energy (SFE), freeze-thaw indirect tensile strength (ITS), Marshall stability and low-temperature ITS tests, respectively. The results manifest that the addition of ASAs can improve effectively the adhesion bond between aggregate and CRMA binder under dry or wet condition. Compared with three ASAs, the CRMA containing LOF-6500 has the highest wet adhesion energy. With regard to M1 and LOF-6500, the CRMA incorporating 0.75% dosage shows the highest dry and wet adhesion energy. Additionally, the water resistance and high-temperature stability of CRMA mixture are improved obviously by incorporating ASAs despite of the types and dosages. However, the ASAs can lower the low-temperature anti-cracking property of CRMA mixture in certain degree, and the influence of T9 is less than that of M1 or LOF-6500.