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.