Quantitative Evaluation of the Blending Between Virgin and Aged Aggregates in Hot-Mix Recycled Asphalt Mixtures

Severe asphalt ageing and the difficulty in dispersing agglomerated particles within reclaimed asphalt pavement (RAP) hinder the uniform blending of virgin and aged mineral aggregates during plant-mixed hot recycling, compromising the durability of the recycled asphalt mixture. To accurately quantify the degree of blending between virgin and aged aggregate during thermal recycling and to optimise the mix design and mixing process for thermally recycled asphalt mixtures, a test method has been proposed. This method comprises key steps, including the preparation of asphalt mixtures, separation of virgin and aged materials, separation of the binder from aggregate, and calculation of the blending degree. It analyses the impact of varying mixing conditions on the blending degree of virgin and aged aggregate during the thermal recycling process. The results indicate that complete homogenization of virgin and aged aggregates during mixing is unattainable, with blending efficiency ranging from 40% to 60%. Increasing the amount of RAP has a negligible effect on blending efficiency. Appropriate increases in the amount of rejuvenating agent, mixing temperature, mixing time, and asphalt content enhance blending efficiency by 10% to 30%. The mixing sequence where RAP is first blended with virgin aggregate before incorporating virgin asphalt further enhances the blending efficiency of virgin and aged aggregates by approximately 20%. However, mixing temperatures exceeding 160 °C and mixing times exceeding 270 s caused secondary ageing of the asphalt, adversely affecting the blending degree of virgin and aged aggregates.