The Effect of Reacted and Activated Rubber on the Performance of Gap and Dense Graded Asphalt Mixtures

Production and implementation of wet-process rubber modified asphalt is associated with several difficulties all around the world. In recent years, Reacted and Activated Rubber, RAR, has been designed and introduced to the asphalt industry to alleviate the problems involved with the production and implementation of rubber modified bitumen. It is composed of soft bitumen, fine Crumb Rubber and different fillers including hydrated lime and AMBS and is produced by hot blending and activation of rubber particles with an asphalt binder. RAR is added directly to the pug-mill in asphalt plant via a dry mixing process. Although the effect of RAR on asphalt performance has been evaluated with desirable results in different parts of the world, further investigation is required to show its performance for asphalt mixtures with different gradation types. It is attempted in this research to design the dry-method RAR and the wet-process crumb rubber modified asphalts of dense and gap gradations based on the volumetric properties of Superpave gyratory compactor specimens and to evaluate them by performance testing compared to unmodified asphalts. Permanent deformation, fatigue as well as fracture properties of RAR modified asphalts were evaluated and compared to those of unmodified and crumb rubber modified asphalts. The results revealed that rubber modification of asphalt mixtures increases stiffness, decreases permanent deformation and the RAR is as effective in rutting as the rubber modified bitumen. The fatigue life of CR modified asphalts is more than unmodified ones and the fatigue performance of RAR modified asphalts is sensitive to mix gradation. Furthermore, rubber modification reduces flexibility index, increasing asphalt fracture cracking potential. Changing aggregate gradation and mix design characteristics is essential for rubber modified asphalts with an enhanced performance against all pavement distresses.