Highly Modified, Low Air Void Asphalt Mixtures in Utah

Abstract: In the state of Utah, the Utah Department of Transportation (UDOT) has embraced a combination of innovative technologies, mix design parameters, and construction techniques to produce asphalt pavements that are demonstrating far superior performance compared to traditional paving options. The innovative technology is a more highly modified asphalt binder than had previously been used in Utah. The mix design parameters with this binder saw the target volumetrics adjusted into ranges that were once thought impossible. And the construction technique eliminated multiple lifts in favor of a single, thick lift, with increased density requirement to match the changes in the volumetric requirements from the mix design.
This combination of innovative features was installed at a very challenging location for a pavement in June of 2021. Namely, near Wendover Utah, at UDOT’s very busy port-of-entry, UDOT placed a six-inch asphalt pavement in a single lift, with higher field density requirements. The 50-gyration, 12.5 mm Superpave mixture had an allowable design air void range of 1.0-1.5% (3.5% at 75 gyrations UDOT standard) while targeting a voids in mineral aggregate (VMA) within a 15.0 – 17.0% range (14.0 to 15.0 UDOT standard). Thus, the allowable range for the voids filled with asphalt (VFA) was unusually high at 90 – 95% (70 to 80 UDOT standard). Up to 15% reclaimed asphalt pavement (RAP) was allowed. Field densities were above 97% of theoretical maximum density.
Extensive laboratory testing was also conducted on the mixture prior to the letting of a contract with it, as part of the mix design approval process, and during the construction. The most notable test on the mixture was the Hamburg wheel tracking test. The mixture was subjected to 40,000 passes on the Hamburg. 20,000 of these were at UDOT’s normal test temperature of 50°C, and the final 20,000 saw an increase in temperature to 54°C. Rutting values were 3.9 and 6.1 mm, respectively after 20,000 and 40,000 passes, respectively.
Field performance has exceeded the wildest expectations for the material. As a result of this exceptional performance, UDOT continues to expand its usage. From 2021-2023, four overlay projects were constructed including a three-inch single lift on a failed concrete pavement which received no pre-overly preparations, and five bridge decks overlays. Three contractors have been awarded these projects with consistently high construction quality as had been seen in Wendover. Moreover, several additional projects are in the works including the replacement of concrete ramps on Interstate interchanges in the Salt Lake City area, thick lifts, mill and overlays of various thicknesses, and more bridge decks.
UDOT continues to evaluate all the current installations. Moreover, UDOT has such high regard for the performance of these installations that over contracts totaling over 520,000 tons were contracted in 2024.
This paper will offer details on the explosion of UDOT's usage of this innovative asphalt mixture and the expansion that is now happening in other western states.