UC Davis Institute of Transportation Studies

A comprehensive study on full-depth reclamation (FDR) of pavements with foamed asphalt has been completed for the California Department of Transportation by the University of California Pavement Research Center. A literature review revealed that very little research had been carried out on the reclamation of thick asphalt pavements (multiple overlays over a relatively weak base or subgrade). A mechanistic sensitivity analysis was carried out to identify key variables in the design of recycled pavements consisting primarily of recycled asphalt pavement. The findings of this analysis and the literature review were used to formulate a work plan for laboratory and field studies to address issues specific to recycling these thick asphalt pavements. A number of FDR projects were observed during the course of the study. Material was collected for a comprehensive laboratory investigation, which identified a number of key issues pertaining to mix design, including appropriate test methods for California, preparation of specimens (mixing moisture content and aggregate temperature), asphalt binder selection, target asphalt and active filler contents, aggregate gradations (fines content), specimen curing, and the interpretation of results. Visual assessments and Falling Weight Deflectometer testing were also carried out on selected projects at regular intervals. The study concluded that FDR with foamed asphalt combined with a cementitious filler is an appropriate pavement rehabilitation option for California. Projects should be carefully selected with special care given to roadside drainage. Appropriate mix and structural design procedures should be followed, and construction should be strictly controlled to ensure that optimal performance and life are obtained from the pavement. The following recommendations are made: 1) FDR with foamed asphalt combined with a cementitious filler should be considered as a rehabilitation option on thick, cracked asphalt pavements on highways with an annual average daily traffic volume not exceeding 20,000 vehicles. The technology is particularly suited to pavements where multiple overlays have been placed over relatively weak supporting layers, and where cracks reflect through the overlay in a relatively short time. Higher traffic volumes can be considered provided that adequate strength and durability can be achieved with the in-place materials. Alternatively, the recycled layer can be used as a subbase under a new base layer. 2) Project selection, mix design, and construction should be strictly controlled to ensure that optimal performance is obtained from the rehabilitated roadway. 3) Full-depth reclamation with asphalt emulsions and partial-depth reclamation with asphalt emulsions and foamed asphalt should also be evaluated, and guidelines prepared for choosing the most appropriate technology for a given set of circumstances.