Correcting the Volumetric Properties of Plant-Produced Hot-Recycled Asphalt Mixtures Based on Blending Efficiency

In the design of optimum asphalt content (OAC) for the production of hot central plant recycling asphalt mixture (RHMA), traditional methods assume full blending between aged binder in reclaimed asphalt pavement (RAP) and virgin binder. However, only partial blending occurs in practice, with the unblended aged binder acting as inert black aggregate , leading to reduced effective asphalt content and compromised performance at high RAP contents. This study introduces the degree of blending (DOB) to evaluate blending efficiency and investigates the effects of material composition and mixing processes on DOB. Based on measured DOB values, key volumetric characteristics in the Marshall mix design [voids in mineral aggregate (VMA) and voids filled with asphalt (VFA)] were corrected, and the OAC was redetermined. Pavement performance was assessed through rutting, semicircular bending, and freeze-thaw splitting tests. Results show that DOB-corrected RHMA exhibits reduced VMA and VFA values (e.g., VMA and VFA decreased by 2.76%–6.55% and 0.72%–5.09%, respectively, at 50% RAP). The revised OACs (4.40%, 4.64%, 4.81%) were higher than original values. DOB-based design improved low-temperature cracking resistance and moisture stability, with increases in fracture energy, fracture toughness, and tensile strength ratio (TSR) by 6.24%–13.67%, 5.69%–8.26%, and 2.5%–3.6%, respectively. Although high-temperature stability decreased by 23.9%, it remained above that of virgin mixtures and met specification requirements.