Effect of the Original Clustering Degree of Reclaimed Asphalt Pavement and Design Parameters on Properties of Recycled Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) has brought enormous potential economic and environmental benefits to society. However, the cluster phenomenon of RAP particles in recycled hot-mix asphalt (HMA) has limited the extensive usage of RAP to a certain extent. Therefore, this research evaluated the effect of the original clustering degree of RAP and design parameters on the properties of recycled HMAs and the qualitative status of RAP cluster in recycled mixes. Six groups of mixes were designed, including one control group in which the RAP particles were designed as completely no cluster status, three experimental groups in which the RAP particles were designed at different original clustering degrees, and another two groups designed under different preheating temperatures and blending time. Then, the volumetric indicators, water stability, rutting, thermal cracking, and abrasion performance of each group were evaluated. It can be found that the RAP cluster was partially dispersed during the mixing and varied with different design parameters. The incomplete dispersion of fine RAP cluster acted as a “fake coarse aggregate” and affected the volumetric results and performance of final mixtures. Therefore, it may be inaccurate to design the aggregate gradation of recycled HMAs solely based on the extracted curve or the black curve of original RAP particles. The dispersion process of the RAP cluster during the mixing should not be ignored. In addition, the results also indicated that the original clustering degree of RAP particles may need to be carefully controlled during the construction.