Warm-Mix Asphalt Study: Test Track Construction and First-Level Analysis of Phase 1 HVS and Laboratory Testing

This first-level report describes the first phase of a warm-mix asphalt study, which compares the performance of a control mix, produced and constructed at conventional hot-mix asphalt temperatures, with three mixes produced with warm-mix additives, produced and compacted at approximately 35°C (60°F) lower than the control. The additives tested included Advera WMA®, Evotherm DATTM, and Sasobit®. 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 warm-mixes at lower temperatures. • Optimal compaction temperatures are likely to differ between the different warm-mix technologies. However, a temperature reduction of at least 35°C (60°F) is possible. • Based on the results of HVS testing, it is concluded that the use of any of the three warm-mix asphalt technologies used in this experiment will not significantly influence the rutting performance of the mix. • Laboratory moisture sensitivity testing indicated that all the mixes tested were potentially susceptible to moisture damage. There was, however, no difference in the level of moisture sensitivity between the control mix and mixes with the additives assessed in this study. • Laboratory fatigue testing indicated that the warm-mix technologies used in this study will not influence the fatigue performance of a mix. • Quality control checks on the mix immediately after production revealed that lower specific gravities and higher air-void contents were recorded on the warm mixes. • The cost benefits of using the warm-mix technologies could not be assessed in this study due to the very small quantities produced. The HVS and laboratory testing completed in this phase have provided no results to suggest that warm-mix technologies should not be used in California. Final recommendations on the use of this technology will only be made after further research and monitoring of full-scale pilot studies on in-service pavements is completed. Interim recommendations include: • The use of warm-mix technologies should continue in full-scale pilot studies on in-service pavements. • HVS testing to assess moisture sensitivity should continue to confirm the laboratory findings. • Laboratory testing on laboratory-mixed, laboratory-compacted specimens should proceed to determine whether representative mixes can be produced in the laboratory and to determine how and whether test results differ from field-mixed, field-compacted specimens.