VDOT’s initial warm mix asphalt (WMA) trials were constructed in 2006 and assessed the Sasobit additive and Evotherm DAT technology as compared to a control hot mix asphalt (HMA). The overlays on the sites have been assessed at regular intervals over the course of their lifespan, offering an opportunity to evaluate the long-term performance of these mixtures. This study evaluated the performance of these trial sections over 10 years.
During the testing performed as part of this study, cores were taken after 3 months, 6 months, 1 year, 2 years, 5 years, and 10 years of service to determine the rate of densification under traffic and to evaluate changes in the performance of the mixtures over time; in addition, binder was recovered from the cores and graded to evaluate the progression of aging. Pavement management data were also collected annually and evaluated for two of the three sites to determine the relative performance of the HMA and WMA sections.
HMA and WMA core air voids were generally similar. Permeability was related to air-void content and appeared to decrease over time. Dynamic modulus results were shown to be mixture dependent, with each mixture showing the effects of aging in a unique manner. Overlay test results indicated no significant differences between the HMA and WMA pairs; however,for two of the three site pairs, this was affected by the test variability. The flexibility index (FI) indicated no significant differences between the HMA and WMA pairs from two sites. The HMA cores from one site showed a significantly higher FI than the WMA cores; however, the WMA core results were similar to the results from the other two sites. Binder testing showed a clear stiffening effect with age for all binders. Evaluation of the DTc cracking parameter indicated that all binders except one HMA binder had exceeded the cracking limit of -5.0ºC by 10 years of service, indicating a potential need for remediation to prevent cracking.
Data extracted from VDOT’s Pavement Management System for two of the sections generally indicated that the HMA and WMA mixtures performed similarly. Although individual distress quantities varied over time, the critical condition index, load-related distress index,and non-load related distress index values for each HMA-WMA pair were similar after 10 years of service. Comparison of FI values and overlay test cycles to failure for the 10-year-old cores with deterioration values from the Pavement Management System indicated high correlations in many instances; however, the direction of the correlation was counterintuitive in many cases. These results are limited by the very small dataset evaluated.
Results of the investigation verified that the HMA and WMA mixtures performed similarly over 10 years of service. It was found that binder aging is causing a significant change in binder properties in service for both HMA and WMA that may affect mixture performance. In addition, relationships between performance-based properties of mixtures and in-service pavement performance were found to be promising, but they need further evaluation.