An investigation of the mechanical properties of rubber modified asphalt mixtures using a modified dry process

Incorporating recycling tyres into asphalt mixtures contributes to solving a serious environmental problem as well as the potential of improving the mechanical performance of asphalt mixtures. The recycled tyre rubber is added by two technologies known as the dry process (when rubber particles are treated as an aggregate modifier) and the wet process (when rubber particles are treated as a binder modifier). Although, the dry process is easier and requires minimal or no modification in the asphalt plant, the inconsistency in field performance makes the dry process not widely used. The main reason for this is believed to be the lack of interaction between the rubber particles and binder. In order to overcome this issue fine rubber particles were used to enhance the interaction with the binder and reduce the springy nature of rubber particles that poses difficulties during the compaction process of mixtures. The mechanical performance-based properties for the control mixture (without adding rubber) and other different rubber asphalt mixtures were evaluated and characterised in terms of their fatigue resistance using the Indirect Tensile Fatigue Test (ITFT), rutting resistance using the Repeated Load Axial Test (RLAT). The stiffness modulus for the different mixtures was also measured by the means of Indirect Tensile Stiffness Test (ITSM). The results have shown that asphalt mixtures produced with the addition of crumb rubber using fine crumb rubber are able to reduce the permanent deformation rate as well as produce improvements in the fatigue cracking at lower strains levels.