Performance Comparison of Two Types of Asphalt Mixture with Two Approaches to Their Modification with Crumb Rubber

Polymer-modified bitumen (PMB) is widely used in motorway pavements due to its proven mechanical performance; however, economic and sustainability considerations have stimulated interest in alternative modification strategies. This study evaluates the mechanical performance of asphalt mixtures incorporating wet-process crumb-rubber-modified bitumen (CRMB) and a dry-process crumb rubber–bitumen concentrate (CRBC) system in comparison with conventional PMB mixtures in a motorway trial section. Particular emphasis was placed on comparing wet- and dry-process rubber modification approaches under the same production and service conditions. Surface and binder-course mixtures were assessed through volumetric characterization, indirect tensile strength ratio (ITSR), indirect tensile stiffness modulus (IT-CY) at 0 °C, 15 °C, and 27 °C, wheel tracking at 50 °C and 60 °C, and semicircular bending (SCB) fracture testing, including laboratory ageing. All mixtures met the relevant specification limits for volumetric properties, water sensitivity (ITSR ≥ 80%), and resistance to permanent deformation. Rubber-modified mixtures exhibited improved resistance to permanent deformation and reduced temperature susceptibility compared with PMB references. Stiffness results indicated improved high-temperature stability for CRBC mixtures, while fracture resistance showed temperature-dependent trends influenced by mixture type and binder modification. Overall, the findings demonstrate that both CRMB and CRBC mixtures achieved mechanical performance comparable to PMB under the evaluated conditions, supporting their use as technically viable alternatives for high-performance motorway pavements while promoting the beneficial reuse of end-of-life tyre rubber.