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Full-Depth Recycling with Foamed Asphalt in California: Guidelines for Project Selection, Design, and Construction


Research Report

UC Pavement Research Center, Sustainable Transportation Center

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Suggested Citation:
Jones, David, Pengcheng Fu, John T. Harvey (2009) Full-Depth Recycling with Foamed Asphalt in California: Guidelines for Project Selection, Design, and Construction. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-09-50

Full-depth reclamation/recycling/ (FDR), or deep in-situ recycling (DISR), of damaged hot-mix asphalt pavement with foamed asphalt and an active filler (e.g., portland cement or lime) to provide a stabilized base for a new hot-mix asphalt (HMA) wearing course, is a pavement rehabilitation strategy of increasing interest worldwide. The process, hereafter referred to by the acronym FDR-FA, provides a rapid on-grade method of rehabilitation that entails pulverizing the existing asphalt concrete pavement and a portion of the underlying granular base to a maximum depth of 12 in. (300 mm), whilst at the same time mixing-in the foamed asphalt, active filler and water, grading and compacting the recycled mixture, and overlaying the prepared surface with a new layer of hot mix asphalt (HMA). The procedure results in minimal traffic disruption and, most importantly, it reuses all the aggregates in the pavement, thereby minimizing the environmental impacts associated with extraction and transport of new aggregates. 

The technology was introduced to the California Department of Transportation (Caltrans) in March 2000 and the Department’s first 10 centerline mile (16 km) pilot study was completed in 2001 on State Route 20 in Colusa County. Since then, a number of roads have been rehabilitated in the state (Caltrans, county, and city) using this process. Most Caltrans FDR-FA projects are on pavements with thick, cracked HMA layers over a relatively thin, weak natural aggregate base. Recycling of this type of pavement structure distinguishes California practice from that of other states and countries investigating and using this technology. Pavement technology in South Africa and Australia, where considerable research on the topic has been undertaken, typically relies on good quality granular material or cement-treated base and subbase layers for the primary load-carrying capacity of the pavement, with the thin hotmix asphalt (<2 in. [50 mm]) or aggregate surface treatment layers (chip seals) providing little or no structural integrity. Consequently, in those countries the recycled material consists mostly of recycled natural aggregate and cracked cement-stabilized layers, which is reflected in their research, experience, and guideline documentation. Practice in Europe has been intermediate between that of California and South Africa, with the recycled material generally consisting of a mix of asphalt-bound and natural aggregate materials. 

The differences between practices in California and elsewhere in the world generated sufficient interest for the initiation of a research project at the University of California Pavement Research Center (UCPRC) to monitor the performance of projects, and to carry out laboratory testing to identify any issues related to recycling thicker asphalt pavements. A report documenting this research study has been prepared (1). The 2 UCPRC-GL-2008-01 study found that FDR-FA is theoretically suited to the rehabilitation of any HMA pavement, the main limitation being whether the recycled layer is structurally adequate for the design traffic. This will be governed by the quality of the materials being recycled, the support provided by the underlying layers, variability in materials and subgrade conditions along the project, drainage, and the ability to construct the layer to the specified requirements. This guideline incorporates key findings from the research study that are applicable to project selection, mix design, structural design, and construction of FDR-FA projects in California.