Jones, David, Rongzong Wu, Bor-Wen Tsai, John T. Harvey (2011) Warm-Mix Asphalt Study: Test Track Construction and First-Level Analysis of Phase 3a HVS and Laboratory Testing (Rubberized Asphalt, Mix Design #1). Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-11-43
This is one of two first-level reports describing the third phase of a warm-mix asphalt study that compares the performance of two rubberized asphalt control mixes with that of seven mixes produced with warm-mix technologies. The control mixes were produced and compacted at conventional hot-mix asphalt temperatures (>300 F [150°C]), while the warm-mixes were produced and compacted at temperatures between 36°F (20°C) and 60°F (35°C) lower than the controls. This report discusses the mixes produced at the Granite Bradshaw Plant and covers the Cecabase®, Evotherm DATTM and Gencor Ultrafoam GX® warm-mix technologies. The test track layout and design, mix design and production, and test track construction are discussed, as well as the results of Heavy Vehicle Simulator (HVS) and laboratory testing. Key findings from the study include:
• Adequate compaction can be achieved on rubberized warm-mixes at lower temperatures. Roller operators should, however, be aware of differences in roller response between warm-mix and conventional hot mixes, and that rolling operations and patterns may need to be adjusted to ensure that optimal compaction is achieved.
• Optimal compaction temperatures will differ among the different warm-mix technologies. However, a temperature reduction of at least 60°F (35°C) is possible for some technologies.
• Equal and potentially better rutting performance compared to hot mix can be achieved from warm-mix asphalt provided that standard specified construction and performance limits for hot-mix asphalt are met.
• Laboratory test results indicate that use of the warm-mix technologies assessed in this study did not significantly influence performance when compared to control specimens. However, the mixes produced with chemical surfactant technologies did appear to be influenced in part by the lower mix production and construction temperatures, which would have resulted in less oxidation of the binder and consequent lower stiffness of the mix. Rutting performance under accelerated load testing did not appear to be affected, however, nor did fatigue performance or moisture sensitivity. The warm mix produced using water injection technology appeared to have lower moisture resistance compared to the other three mixes in all the laboratory moisture sensitivity tests, but still met Caltrans-specified performance requirements in most instances. This mix was produced at a higher temperature than the other two warm mixes and contained no moisture.
• Smoke and odors are significantly reduced on warm mixes compared to hot mixes, while workability is considerably better on warm mixes compared to hot mixes. The HVS and laboratory testing completed in this phase have provided no results to suggest that warm-mix technologies should not be used in rubberized asphalt in California.