Effect of Reclaimed Asphalt Pavement Heating Temperature on the Compactability of Recycled Hot Mix Asphalt

The compactability of an asphalt mixture is related to the heating temperature of the materials, but the heating temperature of reclaimed asphalt pavement (RAP) is limited by the production process of hot-in-plant recycled mixtures. To choose a reasonable heating temperature for RAP according to the compactability, the compaction energy ratio (CER) obtained from the Superpave gyratory compactor compaction curve was developed. The CERs of fourteen kinds of asphalt mixtures made with different RAPs were compared, all of which were different in type, content, and heating temperature. The results indicated that CER is an effective energy index to evaluate the workability of a bituminous mixture, and it considers both the accumulated energy after each gyration and the number of gyrations. It was also found that increasing the heating temperature of the RAP cannot always improve the workability of the recycled mixture, because the higher heating temperature caused more hard-aged bitumen to be blended with soft virgin bitumen during the mixing process. At the same RAP heating temperature, increasing the RAP content made it more difficult to compact the mixture, especially for RAPs with styrene–butadiene–styrene (SBS) modified bitumen, and the recycled mixtures with SBS-modified bitumen were more difficult to compact than those with nonmodified bitumen.