Field Trials of High-Modulus High-Binder-Content Base Layer Hot-Mix Asphalt Mixtures

About the report:

The purpose of this study was to document the field experience of the Virginia Department of Transportation (VDOT) in the use of high-modulus high-binder-content (HMHB) base layer hot-mix asphalt (HMA) mixtures.  Information was gathered with regard to the construction of HMHB base mixtures at three field trial sites in Virginia, and laboratory tests were conducted on samples that were gathered before and during construction.  The three locations were the sites of deep rehabilitation or new construction, and HMA base mixtures were used at designed asphalt content, designed asphalt content plus 0.4% additional asphalt, and/or designed asphalt content plus 0.8% additional asphalt. 

Two of the field trial locations had no construction-related issues; difficulties during compaction occurred at the third.  Laboratory testing of materials collected from this location showed the mixture to have a low air void content, a high percentage of voids filled with asphalt, and a binder performance grade that was lower than expected.  This was also the only location from which materials were collected for fatigue testing, the results of which did not show a clear relationship between binder content and fatigue life.  It is thought that the mixture production and construction issues at this location were site specific and not generally indicative of a larger trend when HMHB mixtures are used.

The research showed that HMHB mixtures incorporating 0.4% additional asphalt binder could be successfully constructed but was unable to determine if the same was true of HMHB mixtures incorporating 0.8% additional asphalt binder.  Further study may be needed to determine the maximum additional asphalt binder that can be successfully incorporated.  Additional studies using repeated-load permanent deformation should be conducted to determine if a cutoff value (or a range) of the flow number can be established to determine optimum performance.

This study documented the field and laboratory knowledge gained by VDOT when producing and placing HMHB mixture test sections in an effort to achieve a long-lasting perpetual-type flexible pavement.  These designs offer the potential to reduce fatigue cracking by incorporating additional asphalt binder and reducing the void content of the mixture.  The use of an adjusted binder grade or RAP to maintain the necessary stiffness for high binder contents should provide the necessary stiffness to minimize the susceptibility for rutting during service.  Quantification of the economic benefits of using HMHB mixtures is a future goal that can be realized after longer term study of field performance.

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