Performance-based optimization of tire rubber modified asphalt mixtures

Tire rubber modification

Resumo

A quantity of approximately 45.000 tons of waste tires is burnt in incineration plants in Austria per year. New recycling technologies enable the production of high quality rubber and fiber products from recycled car tires. One field of application may be the use of recovered fibers and rubber products for the modification of asphalt mixtures for road pavements. Successful use of rubber modifications of asphalt mixtures is reported in literature, but no sufficient information is provided on a systematic approach for mix design of rubber modified asphalts based on performance oriented test methods. This paper deals with this question, and reports of an on-going research project, where a new type of fiber and/or rubber modified stone mastic asphalt (SMA) is developed on the basis of a systematic performance-based test procedure. Both, bitumen and asphalt performance are considered. At first, rheological binder tests, i.e. Bending Beam (BBT), Dynamic Shear Rheometer (DSR) and Rotational Viscosimeter (RV), are used to optimize the performance properties of the rubber modified binder. The rubber modification of the binder was done in the laboratory as wet process. Consequently, laboratory specimens of rubber modified asphalt mixture are exposed to performance-based tests, i.e. the Tensile-Stress-Restrained-Specimen-Test, the Uniaxial-Stress-Test, the Triaxial-Stress-Test, and the Nottingham-Asphalt-Test. Here also the dry process was investigated, where specially granulated rubber is mixed with the hot minerals before the bitumen is added. By means of these test methods, a prediction of the inservice performance of the asphalt mixture is possible, in regard to the low-temperature behavior, the stiffness properties, and the resistance to rutting. In a further step it will be analyzed, if the new asphalt mixture is a technically equivalent alternative, but economically favorable to conventional techniques.