Warm-Mix Asphalt Study: First-Level Analysis of Phase 2 HVS and Laboratory Testing, and Phase 1 and Phase 2 Forensic Assessments

This first-level report describes the second 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®, EvothermTM, and Sasobit®. The results of the second phase of Heavy Vehicle Simulator (HVS) and laboratory testing are discussed. The study includes these key findings: • Based on the results of HVS testing and a forensic investigation of the test track, it is concluded that the use of any of the three warm-mix asphalt technologies included in this experiment will not significantly influence the rutting performance or moisture sensitivity of the mix. • The duration and rut depths of the embedment phase of the warm-mix sections were approximately half that of the control, an opposite trend to that observed in Phase 1, indicating that the effects of oxidation of the binder at lower temperatures may only influence rutting performance in the first few months after construction. • No difficulty was experienced in the preparation of field-mixed, laboratory-compacted specimens at actual construction temperatures. Lower air-void contents were achieved in the laboratory-prepared specimens compared to specimens sampled from the HVS test track. • Limited laboratory moisture sensitivity testing confirmed 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. The HVS and laboratory testing completed in this phase of the study support the findings of the first phase of testing in that no results were obtained to suggest that the warm-mix technologies assessed in this study should not be used in new construction, rehabilitation, or pavement preservation applications in California. Final recommendations on the use of warm-mix asphalt will only be made after further research and monitoring of full-scale pilot studies on inservice pavements is completed. It is recommended that use of warm-mix technologies continue in full-scale pilot studies on in-service pavements until a decision is made on statewide use.