Field compaction of thick recycled material layers

Full-depth reclamation techniques present numerous advantages in pavement rehabilitation. Typically, a thick layer of stabilized or unstabilized reclaimed materials is left behind the recycling machine, which is used as the base layer consisting of these latter recycled asphalt pavement material (RAP). The compaction of the thick layer, especially when unstabilized, is particularly critical for adequate performance. In Quebec, the smooth drum compaction is often used to compact the reclaimed materials. Previous studies demonstrated the difficulties associated with the convenient compaction of the reclaimed materials through its entire thickness, especially the presence of a vertical compaction gradient. Sheep or pad foot compactors are two common compaction machines used to ensure good densification during primary compaction of recycled materials. A research project was initiated to document and quantify the effects of compaction conditions and equipment on the response and performance of the reclaimed materials. An experimental embankment of reclaimed materials was built and divided in three sections compacted using different compaction procedures. Sheepsfoot roller, with and without vibration, was used in the first two sections, while the third section was compacted using a vibrating smooth drum roller. The density, stiffness and vertical density gradient were monitored with a nuclear gage, dynamic cone penetrometer and light weight deflectometer tests. Grain-size analysis was also performed on all experimental sections. The use of vibration along with Sheepsfoot roller improved both density and mechanical response of the compacted layer significantly. The penetration and density tests also revealed a significant difference in compaction throughout the thick layer of reclaimed materials. Using the sheepsfoot provided a stiffer base layer, and the smooth drum resulted in a vertical density gradient. Finally, significant differences in the grain-size distribution were found following the compaction when the sheepsfoot compactor was used.