Effective Design and Control of Full Depth Reclaimed Pavements

Abstract

The traditional method of repairing damaged roads in Atlantic Canada has been to place a hot mix asphalt overlay over the existing road. Though this method provides a new, smooth wearing surface to drive on, it is merely a short term fix. With time, the cracks in the original pavement will reflect to the surface of the new pavement, resulting in failure of the overlay. An alternative option gaining more prominence is the use of a Full Depth Reclamation (FDR) technique, which involves pulverizing the flexible pavement, along with a portion of the underlying layer. This material is then stabilized and recompacted to produce a new base layer that is free of damage.

Though FDR has been used for a number of years, there are still problems with variability in the strength of the materials in some projects. It is hypothesized that some of these problems are due to variability and poor quality in the reclaimed materials. It is believed that current pulverization methods contribute to the variability being observed in these materials. Two FDR projects employing different pulverization control methods were studied to examine how the consistency of the reclaimed materials can be improved through the use of a Ground Penetrating Radar (GPR) survey to map the variability in the depth of the pavement. Controlling the thickness ratio of asphalt concrete to granular base materials being pulverized was shown to improve the consistency of materials, properties, and performance.

The second phase of this research project studied how improving the gradation of the reclaimed materials with the addition of a crusher dust might result in improved performance of stabilized base materials, in this case stabilized with expanded asphalt. The effect of construction variability on the improved materials was also studied by varying both the moisture content, and asphalt content from optimum conditions, as might be expected during construction. Results indicated that the quality of the stabilized FDR materials can be significantly improved by bringing the material gradation closer to the theoretical maximum density gradation. The performance of the stabilized materials can be affected by both the mixing moisture content, and the asphalt content used during stabilization. This suggests that effective quality control, and stricter specifications on the constructed product would result in more reliable, effective FDR pavements.