Crumb Rubber Modified Binders

RILEM Technical Committee 279 WMR is dedicated to the Valorization of Waste and Secondary Materials for Roads. Its Task Group 2 investigated Crumb Rubber (CR) as an additive to enhance the performance of bitumen. CR recycled from end-of-life tires (ELTs) was chosen for this investigation because crumb rubber modified bitumen (CRMB) has been used to improve bituminous mixtures performance for fatigue and reflective cracking. The success of these mixtures is due to the CRMB viscosity that allows the use of an increased amount of bitumen compared to conventional mixtures. Because the viscosity of the CRMB is a function of the CR surface, and presently various types of CRs are produced, it is crucial to verify how these materials perform as a bitumen modifier. Interlaboratory experiments were performed on four types of CR, obtained from mechanical grinding, cryogenic process, waterjet pulverization and reacted and activated rubber. Three base, 35/50, 50/70 and 70/100, bitumen were used for the modification. Mechanical and chemical properties of CRMB were investigated. Despite some differences in the non-mechanical tests, i.e., penetration, softening point and viscosity, the results of the mechanical tests (complex shear modulus) suggest that the bitumen penetration grade ultimately dictates CRMB response.