Crumb Rubber Modified Asphalt Research Articles

Microstructure and performance of crumb rubber modified asphalt

Crumb rubber modified asphalt (CRMA) was prepared by matrix asphalt preblending process (MAPP) which uses matrix asphalt as swelling agent in this study. Effects of the proportion of preblending matrix asphalt and properties of crumb rubber on performance of CRMA have been investigated. Scanning electronic microscope (SEM) and fluorescence microscope were adopted to characterize the microstructures of crumb rubber powder and CRMA, respectively. The experimental results indicated that the CRMA have better performance compared with matrix asphalt; the properties of crumb rubber display significant effects on the performance of CRMA, performance of CRMA are improved with the decrease of ash content and the increase of acetone extract. SEM graphs of crumb rubber pre and post preblending demonstrated that the morphological characteristic of preblended crumb rubber powder is obviously different from rubber powder without preblending, and the properties of rubber elastomeric are recovered and improved significantly. Micrographs of CRMB prepared under different conditions showed that compared with CRMB prepared by the traditional preparation process, the scattering state of rubber powder and matrix asphalt in CRMB prepared by MAPP is excellent, even and perfect polymer reticular structure is formed in the sample system.

Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt

In order to sort some important factors affecting the performances of CRM asphalt and evaluate the performances of different CRM asphalt, this study encompassed one kind of base asphalt binder, four kinds of crumb rubber, tread rubber (TR), heavy truck (HT), small truck (ST) and agriculture tire (AT) crumb rubber, two kinds of particle size, 60 mesh and 80 mesh, and three contents. Softening point, low temperature ductility, and penetration index are selected as basic evaluation indicators in analysis. Variance analysis shows that the crumb rubber content is the primary affecting factor in general, followed by the crumb rubber type, and particle size comes last. The greater the crumb rubber content is, the higher the softening point and the penetration index are, and the smaller the low temperature ductility is. Modified effects between 60 mesh and 80 mesh don’t manifest significant difference. The modified effects of TR-crumb rubber and HT-crumb rubber are better while the low temperature ductility of AT-CRM asphalt is the worst. Also according to the results of DSR and BBR test, TR-CRM asphalt has a better and comprehensive performance at the crumb rubber content of 20% by weight of base asphalt binder, and, if the price is also considered, selecting HT-CRM asphalt with the crumb rubber content of 15% is ideal. The study also finds an interesting phenomenon that the rutting factors of CRM asphalt may be remarkably different, although the softening points of them are the same.

Laboratory Study of the Effects of Compaction on the Volumetric and Rutting Properties of CRM Asphalt Mixtures

The compaction conditions (e.g., compaction temperature and compaction level) of crumb rubber modified (CRM) asphalt mixtures should be determined carefully because the viscosity and amount of the CRM binder affects the compactability of the mixtures. Furthermore, the properties of CRM mixtures relating to the compaction conditions have not been studied in great detail. In this study, a laboratory investigation was conducted on the volumetric and rutting properties of CRM mixtures as a function of compaction conditions. For this research work, four Superpave mix designs for four different asphalt binders (control, SBS modified, 10% rubber modified, and 15% rubber modified) were carried out to determine the optimum asphalt contents. A total of 260 specimens were fabricated using the Superpave gyratory compactor at four compaction temperatures (116, 135, 154, and 173°C) and five compaction levels (20, 40, 60, 80, and 100 gyrations). The volumetric properties were obtained and analyzed, and the rutting resistance of the mixtures was measured using the asphalt pavement analyzer. The results from this study indicated that: (1) the compaction temperatures used in this study significantly affected the volumetric properties of the CRM mixtures, unlike the control and SBS-modified mixtures; (2) in general, the air void contents of the mixtures were significantly influenced by the compaction levels; and (3) as expected, the higher air void contents of the CRM mixtures seemed to have a detrimental effect on the rutting resistance.

The effects of compaction temperature on CRM mixtures made with the SGC and the Marshall compactor

The compaction temperature of crumb rubber modifier (CRM) asphalt mixes needs to be determined cautiously because the viscosity and the amount of the CRM binder affects the compactability of the mixtures. In this study, a laboratory investigation was carried out on the volumetric properties of CRM mixtures fabricated using the Superpave gyratory compactor (SGC) and the Marshall compactor as a function of compaction temperature. Two CRM binders were incorporated into HMA mixtures. Two other mixtures were produced with the control binder (PG 64-22) and SBS-modified binder (PG 76-22) and used for comparison purposes. The CRM binders were produced using one base binder (PG 64-22) with 10% or 15% ambient CRM (−40 mesh) by weight of the binder. For this research, the Superpave and the Marshall mix designs for four different asphalt binders were conducted to determine the optimum asphalt contents (OAC). A total of 128 specimens were manufactured using the SGC and the Marshall compactor at various compaction temperatures (116, 135, 154, and 173°C). The volumetric properties were obtained and analyzed using the statistical methods. The results from this study indicated that (1) the compaction temperatures used in this study significantly affected the volumetric properties of the CRM mixtures, regardless of the compaction methods (the SGC and the Marshall compactor); (2) the CRM mixtures in both the SGC and the Marshall compactor showed the higher VMA values than the control and SBS-modified mixtures; (3) a general trend of the volumetric properties as a function of compaction temperature and compaction method was found for the CRM mixtures used in this study.

Rheological characteristics of crumb rubber-modified asphalts with long-term aging

ABSTRACT SHRP asphalts AAD-1 (less-compatible) and ABD (more compatible) were mixed with crumb rubber and their rheological properties were studied as a function of long-term oxidative aging. Master curves were constructed by shifting the aging time-frequency data to assist in the interpretation. The results show that the stiffness effect of crumb rubber to asphalt AAD-1 is higher than to asphalt ABD. Addition of crumb rubber to both asphalts AAD-1 and ABD reduced viscosity build-up with aging. In addition, rubber modification dramatically increased the elasticity of both asphalts. It is possible that rubber modification will improve rutting resistance because of the increased viscosity and elasticity at high temperatures and improve thermal cracking and fatigue resistance by either decreasing viscosity or lowering viscosity build-up with aging at low temperatures.

Centrifugal simulation of vibration reduction generated by high-speed trains using rubber-modified asphalt foundation and EPS barrier

When constructing a high-speed railway route in urban areas, the reduction of ground vibration and noise generated by the passage of a high-speed train is of vital importance for environmental considerations. This paper describes the results of a laboratory study on ground vibration caused by high-speed trains, using a series of centrifuge model tests to investigate the effect of a vibration reduction method which uses a crumb rubber-modified asphalt (CRMA) layer at the vibration source and an EPS barrier at the transmission path. It was found through centrifuge tests that CRMA, which is a material with high shear stiffness and damping ratio, can reduce the vibration away from the source especially when working together with EPS barrier. Therefore, CRMA has great potential as a foundation material for high-speed railway trackbed.

Shear Modulus and Damping Ratio of Rubber-modified Asphalt Mixes and Unsaturated Subgrade Soils

This paper presents the results of an investigation into the potential application of rubber-modified asphalt in railroad trackbeds by measuring its shear modulus and damping ratio. The measurements of the shear modulus and damping ratio were also conducted on typical subgrade soils. A number of resonant column tests were conducted on subgrade soil samples and the crumb rubber-modified asphalt (CRMA) mix samples with different rubber contents and rubber types. The fine crumb rubber is dissolved in the hot asphalt binder (for a period of time) as an additive to modify the properties of the binder. The measurements were conducted under a wide range of confining pressures and strain levels to simulate stress and strain conditions expected in the typical railway foundation. Cyclic triaxial tests were conducted on subgrade soil samples to study soil characteristics under dynamic loads. It was found that CRMA is a material with high shear stiffness and damping ratio, making it a very attractive material for vibration attenuation of railroad trackbeds.

Louisiana Experience with Crumb Rubber-Modified Hot-Mix Asphalt Pavement

A comparative study of laboratory and field performance of several applications of crumb rubber-modified (CRM) hot-mix asphalt in Louisiana is presented. Eight CRM asphalt pavement sections were constructed by eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare with the performance of pavement sections built with CRM asphalt mixtures. To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength and strain, and indirect tensile resilient modulus were conducted on field compacted Marshall specimens. Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index, pavement structure numbers measured through the Dynaflect (dynamic deflection determination) system, and visual inspections of cracks. The results indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better performance indices (rut depth, fatigue cracks, and international roughness index numbers) than the corresponding control sections after 5 to 7 years of traffic.

A Model for Oxidative Aging of Rubber-Modified Asphalts and Implications to Performance Analysis

Oxidative aging of asphalt binders is a primary cause of binder-related long-term road failures. Viscosity hardening is primarily due to the oxidative conversion of polar aromatics to asphaltenes; oxidation is indicated by carbonyl formation. The aging of unmodified asphalts yields a constant, aging-temperature independent “hardening susceptibility” (HS) relation between viscosity change and the growth of the infrared carbonyl peak. Crumb-rubber-modified asphalts (CRMA) exhibit superior aging characteristics, lower hardening rates, and, often, lower oxidation rates, throughout the aging simulation range. However, CRMA materials may exhibit a hardening susceptibility that varies with aging temperature, suggesting either enhanced diffusion resistance or a kinetic competition between the oxidation sites of the rubber polymer and the asphalt's polar aromatics. This evidence suggests that the commonly accepted high-temperature, high-pressure, long-term aging technique is of questionable value when applied to C...

Accelerated Loading Performance and Laboratory Characterization of Crumb Rubber Asphalt Pavements

ABSTRACTThis paper presents the findings of laboratory characterization and field performance evaluation of crumb rubber modified (CRM) asphalt pavements. In this study, a wet process (Wet Rouse) asphalt rubber was used as CRM. Laboratory mixture characterization included the indirect tensile strength (ITS), indirect tensile resilient modulus (MR), indirect tensile creep test, axial creep test, Superpave frequency sweep at constant height (FSCH), simple shear at constant height (SSCH), and repetitive shear at constant height (RSCH) tests. Field accelerated loading (ALF) evaluation included the performance comparison of three different pavement designs that included: 1: conventional structure (no CRM), 2: CRM in the wearing course mix, and 3: CRM in the base course mix. Based on the results of this study, the authors concluded that CRM asphalt mixtures and conventional mixes behaved very similarly in their laboratory characterization. ALF test lane contained CRM asphalt mixtures at base course exhibited significantly smaller rut depth than the test lane containing conventional mixtures, whereas, test lane with CRM mix at surface wearing course had similar rut depth as the lane with conventional mixes.

Structural Layer Coefficients of Crumb Rubber–Modified Asphalt Concrete Mixtures

Structural layer coefficients for crumb rubber–modified (CRM) asphalt concrete mixtures were developed from the backcalculated moduli values using the falling weight deflectometer (FWD) test results on in situ pavements. Several test sections of recently built crumb rubber–modified pavements on three routes in Kansas (I-135, K-32 and US-56) were selected for this study. I-135 is a newly built asphalt pavement and the other two are gap-graded CRM overlays. Deflection data were collected with a Dynatest 8000 FWD at 21 locations at 7.5-m intervals on each test section on I-135, 22 locations on K-32, and 11 locations on US-56. For CRM asphalt mix overlays, the average surface layer coefficients from the equal mechanistic approach of analysis were found to vary between 0.11 and 0.46 with most values falling around 0.30. This indicates a lower structural layer coefficient value for the asphalt-rubber mix compared with the conventional asphalt concrete. For newly constructed CRM asphalt pavements, the structural layer coefficients varied from 0.25 to 0.48, with the average value around 0.35. These values are close to the design layer coefficient values used for conventional asphalt concrete layers. Large variabilities in computed structural layer coefficients for the rubblized jointed reinforced concrete pavement were observed. The structural layer coefficients computed for this layer varied from 0.10 to 0.35.

Viscosity Characteristics of Rubber-Modified Asphalts

The authors of this investigation present a state-of-the-art review of crumb-rubber modified (CRM) asphalt concrete technology and explain the results of viscosity measurements of CRM asphalt cements using a Brookfield viscometer. Literature was reviewed for both the wet process and the dry process. The reaction in the wet process that occurs between rubber particles and asphalt binder is not chemical in nature, but a diffusion of the light aromatic components of the binder into the crumb rubber. The result is a reduction in the vicosity of the binder, which depends on the type of the binder, the type of the rubber, the mixing temperature, and the mixing energy. The crumb-rubber particles in the dry process replace aggregate particles in the asphalt concrete mix, while due to the limited mixing time permitted, no significant reaction occurs between the crumb rubber and the binder. Brookfield viscometer testing of the CRM binder was performed following a variation of the American Society for Testing and Materials (ASTM) standards D2196-86 and D4402-87. Three binders with CRM percentages of 0, 3, 5, 7, 12, and 18 were tested. The CRM particle size was finer than sieve size Number 80. The viscosity of the CRM asphalt cement initially decreased in time, until the temperature of the crumb-rubbber chips reached that of the binder. This occurred in about 30 to 40 minutes, when a minimum viscosity value was reached called the viscosity. The high-percentage CRM, however, experienced a linear increase in viscosity with time at a rate of approximately 180 cP/hr as mixing continued past the stabilized viscosity.

Recycling of Plastic and Rubber Tire Waste in Asphalt Pavements

AbstractThis paper discusses some important issues related to the use of recycled thermoplastics and rubber tire waste in asphalt binders for hot-mix pavements. Both high temperature rheological and low temperature fracture studies are presented on recycled polyethylene, devulcanized and crumb rubber-modified asphalt binders. The results are compared to unmodified and commercially available modified binders. This research is especially timely in light of the U.S. Intermodal Surface Transportation Efficiency Act of 1991, Section 1038 which, starting in 1995, will force state and local governments to use significant amounts of recycled rubber tire or plastic waste in federally funded highway projects.High temperature rheological measurements of the loss modulus, loss tangent and complex modulus show a significant improvement when only small quantities of crumb rubber, devulcanized crumb rubber or waste polyethylene are added to the asphalt binders.The low temperature fracture performance of the modified asphalts is greatly influenced by the interfacial strength between the dispersed and continuous phase. The fracture toughness increases dramatically, only when low molecular weight polymers are grafted in-situ onto the rubber and polymer dispersed phases in order to strengthen the interface. This points to a crack-pinning mechanism as being responsible for the dramatic increase in fracture toughness that is observed in this work. Single phase, devulcanized crumb rubber-asphalt systems perform quite poorly at low temperatures.

Portable conditioning units for airplanes

In the production of Terminal Blend (TB) rubberized asphalt, degradation of crumb rubber in asphalt matrix can help improve the storage stability and workability of crumb rubber modified asphalt. However, degradation process of crumb rubber modified (CRM) binders was not clear from molecular components to rheological properties. This study investigated chemical and rheological perspectives of the degradation process of CRM asphalt under high interaction temperature (220–280 °C) and extended curing time (2–8 h), namely high-cured CRM asphalt. Attenuated Total Reflection (ATR) Fourier Transform Infrared (FT-IR) Spectroscopy was used to characterize the degradation behaviors of CRM binders at varying curing temperatures and times. Active Polymer Index (API) was defined as the ratio between band areas at 978–918 cm−1 and 850–785 cm−1 of FTIR tests to characterize the released active polymer from vulcanized crumb rubber. Besides, dynamic shear rheometer (DSR) was used to perform elastic recovery (ER) test, dynamic oscillatory test and multiple stress creep recovery (MSCR) test. Test results indicated that the critical degradation temperature was 260 °C in this limited study. Interaction temperature contributed more to the degradation than interaction time. Pearson correlation analysis indicated that API derived from ATR-FTIR test was a good indicator of degradation of CRM binders.