Crumb Rubber Modified Asphalt Mixtures Research Articles

Experimental Study on the Phase Transition Characteristics of Asphalt Mixture for Stress Absorbing Membrane Interlayer

Asphalt mixtures used in stress absorbing membrane interlayers (SAMIs) play a significant role in improving the performance of asphalt pavement. To investigate the rheological properties and phase transition characteristics of asphalt mixtures used in SAMI with temperature changes, twenty-seven candidate mixtures with different binders, gradation types and binder contents were selected in this research. During the study, dynamic mechanical analysis method was employed to evaluate their temperature-dependent properties and a series of wide-range temperature sweep tests were conducted under a sinusoidal loading. Some critical points and key indexes from the testing curves such as glass transition temperature (Tg) can be obtained. Test results show that phase transition characteristics can better reflect the rheological properties of asphalt mixtures at different temperatures. Crumb rubber modified asphalt mixtures (AR) provide a better performance at both high and low temperatures. Additionally, the range of AR asphalt mixtures’ effective functioning temperature ΔT is wider, and the slope K value is greater than the others, which indicates that AR asphalt mixtures are less sensitive to temperature changes. Additionally, gradation type and asphalt content also influence the properties: finer gradation and more asphalt content have a good effect on the low-temperature performance of the asphalt mixtures; while mixtures with a coarser gradation and less asphalt content perform better at high temperature and they are less sensitive to temperature changes. Finally, AR asphalt mixture is more suitable to be applied in the SAMI due to its phase transition characteristics from this method.

Rheological and environmental characteristics of crumb rubber asphalt binders containing non-foaming warm mix asphalt additives

Introducing crumb rubber (CR) into asphalt binder can both provide environmental benefits such as conservation of natural resources and conservation of landfill space and significantly improve rheological and mechanical performance characteristics of asphalt binders. Incorporation of CR into asphalt binder demands some amount of kinematic energy to make modified asphalt binder sufficiently fluid for mixing and compaction purposes that liberates some greenhouse and fume emissions. By taking advantage of warm mix additives (WMA), it is possible to effectively reduce the production temperature of hot-mix asphalt mixtures to mitigate such environmental concerns. This study, Firstly, aims to investigate the CR dosage effect on the properties of asphalt binder containing different non-foaming warm mix additives: Sasobit and Evotherm M1. Secondly, the environmental concerns regarding CR inclusion into asphalt binder are evaluated by implementing gas chromatography-mass spectrometry (GC–MS) test. Rheological and mechanical tests have provided deep insight into the effects of such combinations of WMA and CR in asphalt binders and results indicated that a crumb rubber modified (CRM) asphalt binder with 15–20% CR yielded optimum performance concerning rutting, fatigue, and cracking performance. Furthermore, while both WMA additives can significantly improve the workability and enhance the rutting performance of CRM asphalt binders, they have a slightly negative effect concerning fatigue and cracking performance of CRM asphalt binders. From the environmental aspect, application of WMA additives also could potentially result in a 63–75% reduction in total emission of CRM asphalt mixtures containing 10–25% CR. Relationship between temperature and the total emission of CRM binders is not linear and it is more than likely a second-order polynomial relationship. Moreover, the results of emission analysis showed that CRM binders deliberate some hazardous fumes due to high temperature, which can be alleviated by incorporating WMA additives into the modified blend.

Effect of mixing sequence on asphalt mixtures containing waste tire rubber and warm mix surfactants

Abstract Crumb rubber modified asphalt mixture (CRMA) has gained rapid-growing interest as a sustainable paving material, because it allows value-added recycling of waste tire into durable and low-noise asphalt pavements. However, the poor workability of CRMA leads to higher construction temperature, which results in more energy consumption and hazardous emission. Surfactant, a typical warm mix asphalt additive, has been proven to be effective in alleviating the workability concern of CRMA without obviously deteriorating its mechanical properties. Nevertheless, performance of CRMA with surfactant may be influenced by the mixing sequence of different components (raw asphalt, crumb rubber, surfactant and aggregates), which unfortunately has not been well investigated yet. This study aims to address this issue by characterizing the engineering performance of warm CRMA prepared by six different mixing sequences. Properties including Marshall stability and flow value, workability, rheological property, rutting resistance, moisture sensitivity and fatigue resistance of prepared mixtures were measured and compared. Analytic hierarchy process (AHP) was employed to determine the optimal mixing sequence of warm CRMA considering the overall engineering performance. Test results showed that the effect of warm CRMA’s mixing procedure on its engineering performance is noticeable. Earlier incorporation of surfactant additive had limited negative influence on mechanical properties of warm CRMA but allows for more energy saving during the production of rubberized asphalt binder. The AHP analysis results indicated that among the six mixing sequences, the optimal option is to make rubber absorb surfactant first, then incorporating the rubber-surfactant compound to raw asphalt and finally blending the modified binder to aggregates.

Study on the Performances of Waste Crumb Rubber Modified Asphalt Mixture with Eco-Friendly Diatomite and Basalt Fiber

A sustainable and environmentally friendly society is developing rapidly, in which pavement engineering is an essential part. Therefore, more attention has been paid toward waste utilization and urban noise pollution in road construction. The object of this study was not only to investigate the mix proportion of waste crumb modified asphalt mixtures with diatomite and basalt fiber but also to evaluate the comprehensive performances including sound and vibration absorption of modified asphalt mixtures. Firstly, the mix proportion scheme was designed based on Marshall indices and sound and vibration absorption properties according to the orthogonal experimental method. Considering the specification requirements, as well as better performances, the optimal mix proportion was determined as follows: diatomite content at 7.5%, basalt fiber content at 0.3%, and asphalt-aggregate ratio at 5.5%. The range and variance analysis results indicated that asphalt-aggregate ratio has the most significant influence on volumetric parameters, diatomite has the most significant influence on sound absorption, and basalt fiber has the most significant influence on vibration reduction. Furthermore, the conventional pavement performances and sustainable sound and vibration absorption performances of modified asphalt mixtures were also analyzed. The results showed that the performances of modified asphalt mixtures were improved to different extents compared to the base asphalt mixture. This may be attributed to the microporous structure property of diatomite and the spatial network structure formed by basalt fibers. The pavement as well as sound and vibration absorption performances of the waste crumb modified asphalt mixture with diatomite and basalt fiber would be a good guidance for asphalt pavement design.

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.

Influence of the Naphthenic-Aromatic Content of the Base Binder on the Characteristics of Crumb Rubber Modified Binders and Asphalt Mixtures

The extent of rubber-bitumen interaction in crumb rubber modified (CRM) binders depends on the contact time of rubber-bitumen as well as the temperature and mixing energy. However, this can vary depending on the composition of the base binders as well as the characteristics of the rubber particles (composition, method of grinding, and size). The present study aims to determine the influence of the composition of the base binders and the type of rubber on the properties of the crumb-rubber modified (CRM) binders and the performance of the asphalt mixtures produced with them. To carry out this project, two different base binders were chosen with the same penetration grade but different naphthenic-aromatic content (56.7 versus 46.0%). Additionally, different types of ambient ground rubber powder were evaluated: two different sources (70% of truck tyres +30% of passenger car tyres and 100% of truck tyres) and two different maximum particle sizes (0.8 and 1.25 mm). According to the main results of this study, higher naphthenic-aromatic content of the base binder results in greater modification of the CRM binders. Likewise, asphalt mixtures made with CRM binders from base binder with higher naphthenic-aromatic content appear to offer better performance in terms of water resistance and fatigue life.

Modification of the dry method for mixing crumb rubber modifier with aggregate and asphalt based on the binder mix design

Mechanical characteristics of the asphalt binders and mixtures were enhanced by utilising modifiers. The crumb rubber modifier has been introduced to the asphalt modification as an environmentally friendly procedure of scrap tires, to improve the mechanical characteristics of the asphalt. This study aims to modify the dry method for mixing crumb rubber modifier with asphalt and aggregate based on the binder mix design. To achieve this goal crumb rubber modified asphalt mixtures were prepared and tested by applying various tests such as Marshall Stability test, indirect tensile strength test, and wheel tracking test. Three mixing methods of CRM were studied regarding evaluating the stability, rutting, and moisture susceptibility. The crumb rubber modifier dry mixing method was modified and named the complex process. Better results were achieved for enhancing mechanical properties.

Highway Asset Management Framework for Longevity of Infrastructure – A Case Study for China-Pakistan Economic Corridor

Pavement management system (PMS) affords objective information and useful data analysis to make consistent, cost-effective, and defensible decisions related to the pavement preservation at network and project level. Pavement functional and structural evaluations using performance indicators such as international roughness index (IRI), surface distress, rutting, deflection data etc. are the key element of PMS. A departure from exiting stand-alone evaluation practices, this research presents project-level functional and structural evaluation and its integration into a PMS framework for more accurate and realistic forecasting of the pavement needs over the analysis period. A case study of an in-service pavement is presented to demonstrate the applicability of proposed framework. Owing to the non-availability of time-series performance data at present, pavement serviceability and structural capacity data before and after of an in-service pavement rehabilitation was explored for overlay treatments (conventional and crumb rubber- modified (CRM) asphalt mixtures) effectiveness analyses. Results of functional evaluation quantified the extent to which CRM improves the functional performance of the pavement, in terms of the drop in IRI. CRM asphalt mixture exhibited relatively superior functional performance in contrast to conventional asphaltic wearing course by a margin of 8% higher drop in IRI, on average. Non-destructive testing technique for pavement structural evaluation using falling weight deflectometer (FWD) data was employed to assess structural capacity of pavements. A computer-aided program was developed for estimation of structure number effective (SNeff) to be used as an input for overlay design using AASHTO empirical method. Moreover, mechanistic-empirical (M-E) design method was employed using evaluation of layer moduli and overlay design (ELMOD) program for overlay thickness design and pavement remaining service life (RSL). Comparison of pre- and post-rehabilitation deflection data endorsed roadbed soil stiffness and structural adequacy. RSL estimated through traffic data (truck load repetitions) validated the results obtained using empirical and M-E methods. Application of KENPAVE program for evaluation of pavement overlay thickness design was also demonstrated by conducting damage analysis. Integrating structural evaluation with functional evaluation into an overall framework of PMS is envisaged to provide systematic and objective procedures for monitoring and evaluating pavement performance, selecting optimal type of treatment and its thickness design.

Engineering properties of crumb rubber modified dense-graded asphalt mixtures using dry process

The development and production of high quality asphalt are crucial in the effort to meet current demands for the construction of roads. Crumb rubber is an industrial waste and one of the best ways to reduce the amount of this waste is by recycling it in the asphalt industry. Crumb rubber obtained from scrap tyres has been proven to be an effective additive for the modification of the properties of asphalt mixtures. This study presents a laboratory evaluation of the properties of crumb rubber modified asphalt mixture using the dry process method by adding three different sizes of crumb rubber, namely fine (≤1.18mm), coarse (≥1.18 but ≤3.35 mm), and combination of both fine and coarse (50/50), at three different percentages of crumb rubber, 0, 1.5 and 2.5% of the total weight of the aggregate. Crumb rubber was used to modify the dense graded mixture of asphaltic concrete wearing course 14 (ACWC14). The effect of crumb rubber in the mixture was investigated in terms of the volumetric properties using the Marshall Mix Design and mixture performance testing was conducted by means of resilient modulus, dynamic creep, and abrasion loss. Results showed that fine crumb rubber improved most of the properties of asphalt mixtures compared to other types of mixtures; this could be due to the partial interaction between rubber particles and bitumen which simultaneously act as an elastic aggregate in the mixture.

Estimation and Analysis of Energy Conservation and Emissions Reduction Effects of Warm-Mix Crumb Rubber-Modified Asphalts during Construction Period

In order to solve the serious environmental problems caused by the rapid increase in the number of waste tires and unproper storage of waste tires, modifying the asphalt mix for roadway pavement by adding rubber crumb from recycled waste tires is one of the highly effective approach to solve the problem and can achieve the sustainable use of rubber resources. The application of warm-mix crumb rubber-modified asphalt (CRMA) overcomes some issues of the hot-mix CRMA, such as high temperature and high energy consumption. However, there is a lack of estimation methodology for the energy conservation and emission reduction during the production process of warm-mix CRMA. This study develops the estimation models for the evaluation of energy conservation and emissions reduction during different production stages of waste rubber powder, asphalt, CRMA, hot-mix CRMA, and warm-mix CRMA. A list for gas emissions during the mixing and paving process of CRMA mixtures was established through the simulated mixing measurement and paving site measurement. The results show that for each metric ton of CRMA mixture produced, warm mixing can reduce energy consumption by 18~36% and decrease gas emissions during different stages by 15~87% compared to hot mixing. The Evotherm warm-mix CRMA mixture with DAT as warm mix agent (Ev-DAT warm-mix CRMA mixture) is more energy-efficient by saving approximately 108.56 MJ of energy and reducing gas emissions during mixing and paving by at least 32% and 73%, respectively. This model can improves the technical standard of warm-mix CRMA and the energy conservation assessment.

Fatigue properties of crumb rubber asphalt mixtures used in railways

The use of asphalt mixtures in railway tracks provides a positive contribution to the bearing capacity, stability, durability and more importantly damping properties of the railway structure particularly for the new generation of low-vibration-railway track systems. However, one of the main concerns in the use of asphalt mixtures in railways is their fatigue cracking caused by the repeated traffic loading. The present study focused on the fatigue damage behavior of asphalt mixtures in the railways through using the viscoelastic continuum damage theory. Three experiments of creep compliance, constant crosshead rate and cyclic fatigue tests were carried out on some asphalt mixtures with different air void contents and aging conditions. Based on the results obtained, the crumb rubber modification of railways asphalt mixtures at low stress levels increases the fatigue life of asphalt up to 7.2 times while this increase is at the most 3.6 for the highway asphalt mixture. Furthermore, reducing the air void content from 4% to 2% for the crumb rubber modified asphalt mixture increases the fatigue life by 9.4 times at high stress levels and 18.2 times at low stress levels, which is a great improvement. It was shown that the lowest fatigue life is obtained in the aged crumb rubber modified mixture (i.e., 20 percent of unmodified asphalt mixture).

Performance Evaluation of Crumb Rubber-Modified Asphalt Mixtures Based on Laboratory and Field Investigations

Research studies often propose additives to improve the mechanical properties that extend pavement service life by reducing the rate of permanent deformation of conventional asphalt mixtures. However, questions remain regarding the consistency and efficacy of additives compared to the conventional mixtures, particularly under different conditions of loading and climate inherent to various countries and locations. To shed further light, this paper presents a laboratory and field evaluation of Marshall and Superpave Gyratory-compacted crumb rubber-modified and traditional asphalt concrete mixtures. A laboratory-based study was conducted to ascertain the resilient modulus, indirect tensile strength, and permanent deformation of crumb rubber-modified asphalt mixtures. The Marshall stability and resilient modulus of mixtures prepared with crumb rubber-modified mixtures were increased on average by 30 and 43%, respectively, as compared to the control mixtures, whereas the permanent deformation of the crumb rubber-modified mixtures was improved on average by 12% in contrast to the control mixtures. Field investigations on short-term effectiveness revealed crumb rubber-modified asphalt mixture treatment exhibited on average 36.16% drop in International Roughness Index. In contrast, the control mixture pavement showed 24.20% drop in International Roughness Index. The results indicate and quantify the extent to which crumb rubber improves the performance of the conventional mixtures, in terms of the performance criteria specified.

Performance evaluation of dry process crumb rubber-modified asphalt mixtures with nanomaterial

Using crumb rubber (CR), especially at high percentages, in asphalt pavement using dry process has less popularity than wet process due to the adverse effect of this method on adhesion and/or cohesion, causing two principal problems: first, causing poor performance of the mixture (i.e. fatigue and rutting performance), second, causing the mixture more susceptible to moisture damage. This study aims to improve the usage of CR using dry process by modification of binder with nanomaterial namely Zycosoil. For this objective, asphalt mixtures modified with Zycosoil at three contents of 1%, 2.5% and 4% by weight of binder, and CR at three contents of 1%, 3% and 5% by weight of aggregate. The Zycosoil effects on binder properties were investigated by ductility, softening point, penetration, rotational viscosity and dynamic shear rheometer tests. Also, the mechanical properties of mixtures, including moisture susceptibility, indirect tensile strength, stiffness modulus, rutting resistance and fatigue behaviour were evaluated. The results indicate that Zycosoil modification improves the rheological characteristics of binder, causing an improvement in mixtures resistance against moisture, rutting and fatigue damages. Furthermore, the mixtures performance is negatively affected by using high content of CR that this impact is enhanced by Zycosoil modification.

Use of Crumb Rubber as an Additive in Asphalt Concrete Mixture

As the rapidly growing number of vehicles in Indonesia, the waste of tire rubber becomes a major environmental concern. The use of crumb rubber, which is the recycled tire rubber, as an additive in hot mix asphalt mixture is considered as a sustainable construction method. The purpose of this study was to investigate the effect of adding crumb rubber to asphalt mixture using wet process. The laboratory hot mix asphalt design tests were done by Marshall Method procedure. In this study, two different crumb rubber contents (1% and 2% by weight of asphalt mixture) and two different crumb rubber sizes (#40 and #80) were investigated. A comparative study was done among the unmodified and modified asphalt concrete mixtures considering the Marshall Stability value and the volumetric properties. The results showed that crumb rubber is recommended as an additive in asphalt mixture, as all the test results are within the standard requirements. The addition of crumb rubber tended to increase the strength and quality of asphalt mixture. However, it should be more concern about durability of asphalt mixture because of the lower asphalt content in crumb rubber modified asphalt mixture.

Effects of Diatomite and SBS on Freeze-Thaw Resistance of Crumb Rubber Modified Asphalt Mixture

Asphalt mixture is susceptible to moisture damage under the effect of freeze-thaw (F-T) cycles. In this paper, crumb rubber (CR) was used to modify stone mastic asphalt (SMA) and the effects of diatomite and styrene butadiene styrene (SBS) on antifreezing performances of crumb rubber modified SMA (CRSMA) were investigated. Regression analysis and modified grey model (MGM) were used to construct the prediction models for properties of modified mixtures. CRSMA, CR and diatomite modified SMA (CRDSMA), and CR and SBS modified SMA (CRSSMA) were prepared in laboratory, respectively. Process of F-T cycles was designed. Air void, indirect tensile strength (ITS), and indirect tensile stiffness modulus (ITSM) were measured to evaluate the antifreezing performances of CRSMA, CRDSMA, and CRSSMA. Results indicate that air voids increase with the increasing of F-T cycles. ITS and ITSM all decrease with the increasing of F-T cycles. The addition of diatomite and SBS can reduce the air void and improve the ITS and ITSM of CRSMA. CRSSMA presents the lowest air void, highest tensile strength, and largest stiffness modulus, which reveals that CRSSMA has the best F-T resistance among three different kinds of mixtures. Moreover, MGM (1, 2) models present more favorable accuracy in prediction of air void and ITS compared with regression ones.

Effect of Addition of Dry Crumb Rubber on the Performance of Terminal Blend Crumb Rubber Modified Asphalt Mixtures

Three major methods are used to produce crumb rubber modified asphalt pavement: the dry process (CRDry), the terminal blend process (CRTB), and the wet process (CRWet). Although the CRDry process replaces the portion of fine aggregate in the asphalt mixture with crumb rubber (CR) particles, the CRWet process incorporates CR particles into hot liquid asphalt before it is mixed with aggregates. CRTB is known as a special type of CRWet process in which the CR is blended with asphalt binder at the asphalt terminal. In general, the CRWet process can integrate 15% to 22% CR by weight of the binder. This amount ranges from 10% to 12% in the CRTB process as a result of the limitations associated with transportation and pumping. This study investigated the feasibility of increasing the CR content of CRTB modified asphalt mixtures. The addition to the mixture of about 0.5% CR (by weight of the mix) through the CRDry process doubled the amount of rubber to be found in a conventional CRTB mix. The relative performances of the CRTB and the CRTB+CRDry processes [i.e., crumb rubber hybrid (CRHY)] were investigated with respect to their linear viscoelastic properties, rutting susceptibility, moisture damage, resistance to fatigue, and low temperature cracking. It was shown that it was possible to increase the amount of CR in the mixture through the use of the CRHY method proposed here, without adverse effect on the performance of the mixture.

Laboratory Investigation of Crumb Rubber Modified Asphalt Binder and Mixtures with Warm-Mix Additives

This study evaluated the effects of warm mix asphalt (WMA) additives on the compaction temperature and properties of crumb rubber modified (CRM) asphalt binder and mixture. Two different WMA additives (named as Sas and Evm) were used to prepare warm-mix CRM asphalt binder and mixture. The viscosity of different warm-mix CRM asphalt binders and mastics was measured at different temperatures. The rheological and mechanical properties of different warm-mix CRM asphalt binders were tested. At the mixture level, the volumetric properties of different warm-mix CRM asphalt mixtures were experimented by Gyratory compactor at different temperatures and the performance of different warm-mix CRM asphalt mixtures were evaluated. It was found that both of the two WMA additives could lower the compaction temperatures of CRM asphalt mixtures by 10–20 °C. However, they have different influences on rheological properties of CRM binder and performance of CRM mixture. The Sas warm-mix additive can improve the anti-rutting performance of CRM mixture but may degrade its low-temperature performance and moisture stability. The Evm warm-mix additive has no adverse effects on the high-temperature and low-temperature performance of CRM asphalt mixtures and can improve its moisture stability.

Characterization of Low Temperature Crack Resistance of Crumb Rubber Modified Asphalt Mixtures Using Semi-Circular Bending Tests

AbstractThe objective of this study was to assess the low temperature anti-cracking performance of crumb rubber modified asphalt mixtures by performing the semi-circular bending tests. The flexural tensile strength, fracture energy density, and fracture resistance were used to evaluate the rubber modified asphalt mixture's performance based on fracture mechanics J-integral concept. The semi-circular bending (SCB) tests were conducted to study the effect of crumb rubber dosage, crumb rubber size, and testing temperature on the low temperature anti-cracking performance of rubber modified asphalt mixtures. Two gradations (a dense gradation mixture and a gap-gradation mixture) were selected, and five rubber application dosages (15, 18, 20, 22, and 25 %, all by the weight of base binder) were studied in the paper. The tests were performed at temperatures of 0, −10, and −20°C. The testing results indicated that the flexural tensile strength and fracture energy density increased initially, reached to a peak point and then decreased with the increase of rubber dosage. Flexural tensile strength and fracture energy density reached its maximum value at the 20 % rubber dosage among the five rubber application dosages. The flexural tensile strength, fracture energy density, and the J-integral fracture toughness of the gap-graded rubber asphalt mixture specimens were higher than those of the dense gradation. The smaller sized particle rubber modified mixture provided a better low temperature anti-cracking performance as compared to those with bigger particle sizes. Through the comprehensive consideration of laboratory test results and field results, it was recommended that the J-integral fracture toughness should be no less than 2.8 KJ/m2 for new asphalt rubber pavement in Shannxi province.

A stochastic viscoelastic–viscoplastic constitutive model and its application to crumb rubber modified asphalt mixtures

An idealized asphalt mixture is modified with either fine or coarse rubber particles by a dry process. A large number of uniaxial compression tests are performed upon samples of the idealized asphalt mixture and the fine and coarse crumb rubber modified (CRM) asphalt mixtures. A stochastic viscoelastic–viscoplastic constitutive model with a lognormally distributed random parameter is proposed to describe their mechanical behaviors. It is shown that the model can approximately predict the probability distribution of the random material strain responses. The influences of the crumb rubber modifiers on the material mechanical properties are quantitatively evaluated. It is found that the fine CRM asphalt mixture exhibits the largest elasticity among the three asphalt mixtures considered.

Backcalculation of Swollen Crumb Rubber Modulus in Asphalt Rubber Binder and Its Relation to Performance

A method is presented to estimate the engineering properties of swollen rubber particles within crumb rubber–modified (CRM) asphalt binders. It was observed that the backcalculated modulus of swollen rubber within the CRM asphalt binder was related to performance. Thus improper mixing temperatures as well as interaction times could lead to the insufficient swelling of rubber and to a performance worse than anticipated in CRM asphalt mixtures. The backcalculated modulus of the rubber within the CRM asphalt could be used as a quality control tool, which could be measured during construction. An experimental approach was taken to investigate the mechanisms of interaction between the asphalt binders and crumb rubber and their effect on the modulus of the rubber within the CRM asphalt binder. The experimental program included dynamic shear modulus (| G*|) as well as linear amplitude sweep tests. These tests were performed on neat binder, CRM binders mixed at three temperatures, neat binder mixed at these three temperatures (without the rubber), and the residual binder obtained through the drainage of the CRM binders (i.e., by filtering out the rubber particles). In addition to the experimental approach, a three-dimensional finite element (FE) based micromechanical model of the | G*| test was developed with ABAQUS software. The FE model provided insight into the relationship between the microscale and macroscale material behavior (i.e., the stiffening and softening effects of rubber in CRM asphalt binders).