Control of Full Depth Pulverized Aggregate Production using Ground Penetrating Radar

Many rural highways in Atlantic Canada are in poor condition due to limited maintenance funding available. The typical maintenance strategy has been to place an overlay on the damaged asphalt concrete layer to provide a new wearing surface, but this approach does not repair the damage embedded within the pavement structure. After a certain period of time, the original cracks reflect through the overlay, leading to its premature failure. A newer approach has been to repair these heavily damaged roads using a full depth pulverization technique which grinds and stabilizes the upper portion of the existing road to provide a new base layer that is free of defects. While this technique provides a more sustainable repair approach in re-using in-situ materials, the resulting base typically exhibits a high degree of variability. It is hypothesized that pulverizing the pavement to a constant depth, or using a retroactive control method to achieve a specific blend of asphalt concrete to granular base for the pulverized materials, may contribute to the observed variability in the recycled base layer. The objective of this research is to determine if ground penetrating radar thickness estimates can be used to improve variability in full depth pulverized aggregates by maintaining a constant blend ratio during pulverization. It is expected that improvements in the consistency of the full depth pulverized materials will lead to improvements in the compaction and consistency of the stabilized materials. Pulverized aggregate samples were obtained from two full depth recycled pavement rehabilitation projects utilizing retroactive depth control and GPR depth control, respectively. A wide degree of asphalt concrete/base blend ratio was observed for the retroactive control section, while greater consistency in the blend ratio was maintained in the GPR control section by subdividing the project according to various pulverization depths. The GPR control section exhibited lower variability in the gradation, optimum moisture content, optimum density, and California Bearing Ratio than the retroactively controlled section. It is expected that improvements in the consistency of the full depth pulverized materials will lead to improvements in the compaction and quality of the stabilized materials.