Impact of Lower Asphalt Binder for Coarse HMA Mixes

Project Details







Minnesota Department of Transportation

Principal Investigator
Dave Eshan
Co-Principal Investigator
Chris Williams

Director, AMPP

About the research

Historically, asphalt mixes in Minnesota have been produced to be fine-graded. In recent years, however, a large number of relatively coarse-graded mixes have been produced and used in highway construction. These coarse-graded mixes typically have a low total asphalt-binder content compared to the fine-graded ones.

The performance of the coarser low asphalt content mixes is unknown, but some preliminary testing has shown that these mixes may be prone to premature cracking. Furthermore, the use of coarser mixes with lower asphalt content increases permeability, making these coarser mixes more prone to moisture-induced damage. The increased permeability of mix is counter to pavement design assumptions of a dense-graded surface layer that drains water over the surface and away from underlying granular layers. Thus, pavements with a permeable asphalt mix will be more susceptible to moisture damage as well as other distresses because of the reduction of unbound layer modulus values.

A study is needed to quantify the performance effects and pavement service life of these lower-asphalt-binder coarse mixes. It is important to evaluate the asphalt mixes that are produced locally according to Minnesota Department of Transportation (MnDOT) 2360 specifications and placed in Minnesota. The primary goals of this research is to quantitatively and qualitatively determine if the low-asphalt-binder coarse mixes are prone to performance issues and to make recommendations regarding potential solutions to alleviate any identified problems.

This project will evaluate 10 to 12 low-asphalt-binder content mixes from actual field projects. The field samples will be subjected to a battery of tests to determine the pavement performance using fracture energy, dynamic modulus, and permeability measurements. The lab results will be analyzed to predict the severity of distress and life expectancies of the pavements. An in-depth statistical analysis will also be conducted to identify and quantify the effects of total asphalt-binder content on pavement performance. Final outcomes will include quantitative measures of how asphalt-binder content in coarse-graded mixes affects pavement performance and recommendations on whether changes are necessary to the MnDOT asphalt mix specifications.