Laboratory evaluation of crumb rubber modified asphalt mixes

The paper presents the details of various investigations conducted for the laboratory evaluation of the performance of crumb-rubber modified asphalt mixes. Crumb rubber (CR) obtained from discarded truck and bus tires was used to modify 80/100 penetration grade asphalt cement. Fatigue and permanent deformation characteristics, temperature and moisture susceptibility, and oxidative aging are some of the performance indicators of mixes evaluated. A static indentation test was adopted for assessing the relative permanent deformation characteristics of different mixes. Three aggregate gradations: (1) superpave; (2) gradation specified by the Ministry of Surface Transport, India for asphalt concrete; and (3) one gap gradation, were considered in the investigation. Compared to normal mixes, CR modified mixes were found to have improved fatigue and permanent deformation characteristics. They also showed lower temperature susceptibility and greater resistance to moisture damage compared to normal mixes. Superpave mixes gave better overall performance compared to the mixes having other aggregate gradations.