THICKNESS VARIABILITY EFFECTS ON THE PROPERTIES OF UNSTABILIZED FULL DEPTH RECLAIMED AGGREGATES

Abstract

Inadequate financial allocation for road maintenance is a threat to the impaired rural highways in Atlantic Canada. The conventional means of pavement rehabilitation has been to place a hot mix asphalt concrete overlay on the existing worn out pavement which is only a short term adjustment. The purpose is to provide a smooth wearing surface at a low cost. This traditional way of pavement repair does not fix the damage embedded within the pavement structure. After a certain extent of time the cracks in the original pavement start to reflect to the smooth new wearing surface, causing deterioration on the overlay. The advanced approach which is becoming more popular is the application of Full Depth Reclamation (FDR). This technique helps to repair the extensively defective roads by pulverizing the flexible pavement along with a fraction of the underlying damaged base layer. Thus a damage free base layer can be obtained by stabilizing and recompacting the pulverized materials. FDR is a sustainable and an environmentally beneficial repair method as it re-uses the in-situ materials. FDR process has been used around the world for over 25 years yet confronts some difficulties regarding the fluctuation in the strength of materials in various projects. It is inferred that some of these difficulties are due to the variability and poor quality in the restored materials. The variability in the recycled base layer is a result of currently utilizing a retroactive depth control method to attain a specific blend of asphalt concrete to granular base for the pulverized materials. Two FDR projects applying two different pulverization control methods (conventional retroactive and GPR depth control methods) were analyzed to investigate the improvements in consistency of the restored materials by using Ground Penetrating Radar (GPR). A wide range of asphalt concrete/base layer blend ratio was detected in retroactive control section, while consistent blend ratio was maintained in GPR survey by mapping the variability in the depth of pavement and sub-dividing the test sections accordingly. A GPR controlled constant blend ratio during pulverization displayed improvements in consistency of materials, physical and mechanical properties and performance as anticipated. The materials obtained by using the conventional retroactive depth control method exhibited higher variability in grain size distribution, optimum moisture content, optimum density, California Bearing Ratio, resilient modulus and shear strength. All materials from both projects exhibited excessive air voids and inadequate fines content as the as-obtained particles acted as conglomerated particles and enough fines were not generated after the pulverization. It is recommended that efficient quality control, precise specifications and appropriate pulverization methods will provide more reliable and impressive FDR pavements.