Mechanical properties of crumb rubber modified asphalt using the dry process

The paper discusses the results of a laboratory study, conducted at the Experimental Road Laboratory of the University of Padova, which analysed the potentials of crumb rubber from road tyres as a component of bituminous mixtures, using the dry process. Three types of asphalt mixtures (Porous Asphalt, traditional Wearing Course and High Modulus asphalt concrete) were tested, containing two different gradings of rubber, and compared with non-added asphalts. The traditional Marshall methodology was used to identify the optimum bitumen content; the mixtures were also mechanically checked by means of the indirect tensile strength test, dynamic modulus test and creep test. The results have been encouraging: the crumb rubber asphalts show lower permanent deformations compared to mixtures without rubber at high temperatures; they also improve the mechanical behaviour in stiffness terms at the lowest temperatures, according to the most common Italian Specifications and Standards, so confirming the feasibility of successfully recycling crumb rubber from used tyres in road pavements.