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This paper investigates the performance of crumb-rubber-modified (CRM) asphalt mixture. Two different asphalt mixtures containing two types of asphalt binder (#90 original asphalt and CRM asphalt) were used to prepare Marshall specimens and determine optimum asphalt content. Mechanical performances of asphalt mixes were evaluated by the wheel rutting test (WRT) (dynamic stability (DS)), midpoint beam bend test (MBBT), at low temperature, and indirect tensile test (IDT), at the freezing and thawing cycle. Superpave gyratory compactor (SGC) specimens were also prepared for the modulus test. Using the simple performance test (SPT) and universal testing system (UTS), viscoelastic mechanical characteristics were evaluated by static and dynamic modulus tests. Static modulus (E) data were measured by the un-confinement uniaxial compression test according to the specification of China. Moreover, dynamic modulus (E0) data were obtained by SPT. The crumb-rubber content varies from 0, 10 %, 20 %, to 30 % at the static modulus test. Two test temperatures were selected for the dynamic modulus test. The results indicated that the CRM asphalt mixture performs better than the standard asphalt mixture on dynamic behavior, rutting resistance, cracking resistance, and moisture stability.
The mixture design and performance characteristics of crumb rubber modified asphalt concretes were investigated in this research project to meet the requirements of the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, which has required each State to incorporate scrap tire rubber into its asphalt paving materials. Specifically, the objectives of this research encompass the following: (i) investigation of the rheological properties of asphalt-rubber binder to determine optimum content of crumb rubber; (ii) development of optimum mix design for various applications, including both wet and dry mix processes; (iii) characterization of mechanical properties of recommended paving mixtures, including resilient modulus, fatigue cracking behavior, low-temperature thermal cracking resistance, water sensitivity test, incremental creep test and loaded wheel track test; and (iv) comparison of performance of selected paving mixes.
The modification of asphalt mixtures with rubber in the conventional process includes specialized equipment for mixing and storage and concurrently necessitates reheating prior to use. Reacted and Activated Rubber (RAR) is a novel rubber-based asphalt mixture modifier that can be added into the mixture matrix without the complexities associated with wet mixing. The objective of this study was to design and assess the performance of RAR-modified dense-graded asphalt mixtures against key pavement distresses. Furthermore, the performance of RAR-modified mixtures was compared to the unmodified and commercially available rubber-modified asphalt-based mixtures. Two levels of RAR dosage at 2 and 4 % by total weight of mix were included with two different base binders. Four performance characteristics were analyzed: resistance to rutting at high temperatures, failure by fatigue, fracture energy, and susceptibility to moisture damage. Increased rut resistance and higher fatigue lives were observed for higher RAR contents. Statistical analyses revealed insignificant changes in fracture energy among the different mixtures, and all the mixtures were found to be resistant to moisture damage. RAR was concluded as a compatible promising rubber modifier with a significant potential to improve resistance of asphalt pavements against distresses and capable of providing extended life cycles. Because RAR showed significant improvement in the performance of the dense-graded asphalt mixtures, this study recommended expanding the scope of utilizing the RAR materials with other aggregate gradations both at the laboratory and field levels in future.
Focusing on asphalt paving technology, this work emphasizes quality control and quality assurance programmes in producing high-quality pavements. It combines theory and practice of asphalt paving including developments and information from the recently completed Strategic Highway Research Program which was designed to improve asphalt specifications, mix design and analysis systems.
The effect of 11 asphalt binders on the moisture sensitivity of a mixture were measured using the Hamburg Wheel- Tracking Device (Hamburg WTD). The Hamburg WTD tests a slab of hot- mix asphalt submerged in hot water by rolling a steel wheel across its surface. The binders consisted of two unmodified asphalt binders, an air- blown asphalt binder, and eight polymer- modified asphalt binders. The continuous high- temperature performance grades (PG's) ranged from 67 to 77. Two aggregates were used: diabase and limestone. The mixture results using the limestone aggegate could not be used to evaluate the asphalt binders because the Hamburg WTD crushed the limestone aggregate. A test temperature of 58 degrees Celcius was chosen for the diabase mixtures based on trial tests using the air- blown and unmodified PG 70- 22 asphalt binders. It was expected that most of the mixtures with polymer- modified asphalt binders would have greater resistance to moisture damage than the mixture with the unmodified PG 70- 22 asphalt binder because they would provide increased adhesion to the aggregate or create a network within the asphalt that was more resistant to water penetration. However, only one polymer- modified asphalt binder provided a greater resistance at a 5- percent level of significance. Some of the asphalt binders provided significantly different resistances to moisture damage that were not related to differences in cohesive strength as measured by the asphalt binder parameter G*/sin(delta) at 58 degrees Celcius. It was concluded that polymer- modified asphalt binders having the same G*/sin(delta) can provide different adhesive strengths and/or different resistances to water penetration. Reasons for these differences need to be determined.
Utilisation of scrap tire has been achieved through the production of crumb rubber modified binders and rubberised asphalt concrete. Terminal and field blended asphalt rubbers have been developed through the wet process to incorporate crumb rubber into the asphalt binder. Warm mix asphalt technologies have been developed to curb the problem associated with the processing and production of such crumb rubber modified binders. Also the lowered production and compaction temperatures associated with warm mix additives suggests the possibility of moisture retention in the mix, which can lead to moisture damage. Conventional moisture sensitivity tests have not effectively discriminated good and poor mixes, due to the difficulty of simulating field moisture damage mechanisms. This study was carried out to investigate performance properties of crumb rubber modified asphalt concrete, using commercial warm mix asphalt technology. Commonly utilised asphalt mixtures in North America such as dense graded and stone mastic asphalt were used in this study. Uniaxial Cyclic Compression Testing (UCCT) was used to measure permanent deformation at high temperatures. Indirect Tensile Testing (IDT) was used to investigate low temperature performance. Moisture Induced Sensitivity Testing (MiST) was proposed to be an effective method for detecting the susceptibility of asphalt mixtures to moisture damage, as it incorporates major field stripping mechanisms. Sonnewarm(TM), Sasobit(TM) and Evotherm(TM) additives improved the resistance to permanent deformation of dense graded mixes at a loading rate of 0.5 percent by weight of the binder. Polymer modified mixtures showed superior resistance to permanent deformation compared to asphalt rubber in all mix types. Rediset(TM) WMX improves low temperature properties of dense graded mixes at 0.5 percent loading on the asphalt cement. Rediset LQ and Rediset WMX showed good anti stripping properties at 0.5 percent loading on the asphalt cement. The American Association of State Highway and Transportation Official's Mechanistic-Empirical Pavement Design Guide (AASHTO MEPDG) software was used to predict long term low temperature performance of the mixtures in various areas of Ontario. Sasobit, Rediset LQ and Rediset WMX gave good 15 years prediction with stone mastic asphalt mixtures but the performance of dense graded mixtures was less satisfactory.