Three trial sections using two warm-mix asphalt (WMA) technologies were constructed in various locations in Virginia in 2006, and experiences with these trial sections were used in the development of the Virginia Department of Transportation’s special provision to allow the use of WMA.
WMA for two of the sections was produced using Sasobit, an organic additive (developed by Sasol Wax), and WMA for the third section was produced using Evotherm ET (developed by MeadWestvaco Asphalt Innovations) as the modification method. The sections were evaluated over a 2-year period to assess the initial performance of the WMA and compare it with that of hot-mix asphalt (HMA) control sections constructed at the same time. Coring and visual inspections were performed during the initial construction and at intervals of 3 months, 6 months, 1 year, and 2 years. The cores were tested to determine air-void contents and permeability prior to undergoing extraction and recovery of the asphalt binder for performance grading. In addition, for the two Sasobit trial sites, historic data, core data, and ground-penetrating radar scans were collected and compared to provide documentation of the pavement structure for future analysis.
Visual surveys indicated no significant distresses in either the WMA or HMA sections during the first 2 years in service. Evaluations of the core air-void contents indicated that generally the contents for the WMA and HMA were not significantly different in each trial. The air-void contents at different ages were significantly different in a few instances; however, no trends concerning air voids were observed. Permeability measurements did not indicate any trends concerning permeability over time. Performance grading of the recovered binder suggested that the WMA produced using Sasobit aged at a slightly reduced rate than the HMA, as indicated by decreased stiffening. No difference in performance grade was measured between the HMA and WMA produced using the Evotherm emulsion. Comparisons of historical data, core data, and ground-penetrating radar scans illustrated that each may indicate a slightly different pavement structure.
From the results of this 2-year investigation, in general, WMA and HMA should be expected to perform equally. Any instances of improved performance of WMA (as compared to HMA) will depend on the WMA technology employed. Some WMA technologies may contribute to reduced in-service binder aging, depending on production temperatures and the nature of the technology. Further evaluation of WMA technologies developed since the inception of this work is recommended to determine their potential for leading to improved performance.
During the period from February through October 2009, VDOT let maintenance contracts using HMA surface mixtures valued at approximately $101 million. If, conservatively, one-tenth of these mixtures were replaced with WMA produced using technologies having beneficial aging characteristics and the apparent trend of a 1-year reduction in the rate of aging continued, resulting in a 1-year deferment of repaving, VDOT could realize a one-time cost savings of approximately $1.15 million.