Full-Depth Recycling Study: Test Track Construction and First-Level Analysis of Phase 1 and Phase 2 HVS Testing, Forensic Investigation, and Phase 1 Laboratory Testing

This first-level report describes the first two phases of a study comparing the performance of four different full-depth pavement reclamation strategies, namely pulverization with no stabilization (FDR-NS), stabilization with foamed asphalt and portland cement (FDR-FA), stabilization with portland cement only (FDR-PC), and stabilization with engineered asphalt emulsion (FDR-EE). A literature review, the test track layout and design, stabilization and asphalt concrete mix designs, and test track construction are discussed, as well as the results of Heavy Vehicle Simulator (HVS) and preliminary laboratory testing, and a forensic investigation of the HVS test sections. A number of problems were experienced during construction of the FDR-PC and FDR-EE lanes on the test track and consequently only the FDR-NS and FDR-FA lanes and one section of the FDR-PC lane (5 percent measured cement content) were considered satisfactorily uniform for the purposes of HVS testing. The FDR-FA and FDR-PC sections performed very well under both dry and wet conditions, with testing under dry conditions terminated long before the terminal rut of 0.5 in. (12.5 mm) or average crack density of 0.75 ft/ft2 (2.5 m/m2 ) were reached (cracks were observed on the wet tests only). The two FDR-NS sections tested performed acceptably, with a section with thicker asphalt surfacing (0.4 ft [120 mm]) outperforming a section with thinner asphalt surfacing (0.2 ft [60 mm]) under both dry and wet conditions, as expected. Terminal rut was reached on both sections. No cracks were observed during dry tests, but cracking was severe after completion of the wet tests. Observations during a forensic investigation confirmed the measurements taken during HVS testing. The performance advantages of full-depth reclamation strategies that either use foamed asphalt with cement or cement only over those with no stabilization are clearly evident from the results. Additional laboratory and field testing is in progress to collect sufficient data for the development of mechanisticempirical design criteria (and revised gravel factors) for full-depth reclaimed pavements. However, there is sufficient evidence to show that pavements that are rehabilitated using full-depth reclamation strategies will satisfactorily withstand design traffic levels common in California. Rehabilitation using this approach offers additional advantages of speed of construction, minimal disruption to traffic, reuse of all materials, and does not require removal of material from the site. FDR with these stabilization approaches also effectively replaces extensively cracked existing asphalt layers, providing a new base and thus preventing the reflective cracking that is common in more traditional overlay projects. Future research should include life cycle cost analysis (LCCA) and environmental life cycle assessment (LCA) to compare FDR with overlay strategies for the range of pavement, climate and traffic conditions where the two strategies might be used. Future research on partial- and full-depth reclamation should be coordinated to facilitate consistent design and specification documentation, and to facilitate the preparation of a comprehensive guide covering all forms of pavement recycling.