Balanced Mix Design Benchmarking of Asphalt Mixtures Produced in Vermont

Performance testing is an important tool to complement volumetric properties for improving asphalt pavement performance. Vermont Agency of Transportation (VTrans) began evaluating the Hamburg wheel-tracking test (HWTT) in 2015, the Illinois flexibility index test (I-FIT) in 2018, and the indirect tensile cracking test (IDEAL-CT) as another index-based test to investigate along with the I-FIT, as a step toward balanced mix design (BMD) implementation. An increase in the use of recycled materials in asphalt mixtures produced in Vermont was anticipated in their Standard Specifications for Construction. This study is an attempt in this direction. The tests were conducted on reheated plant mixtures sampled from paving projects in Vermont and the results were analyzed to (1) develop baseline rutting and cracking performance; (2) evaluate the effects of mixture properties on performance test results; (3) compare IDEAL-CT results and I-FIT results; and (4) compare performance test results with specification criteria proposed by VTrans for evaluating the rutting and cracking resistance of asphalt mixtures. Several mixture properties, viz., nominal maximum aggregate size (NMAS), binder grade, binder content, and recycled content, were found to have significant effects on mixture rutting and cracking resistance. The test results showed a direct correlation between FI and CTindex for the dataset of VTrans mixtures. The information from this research will help VTrans to achieve its goal to move beyond the use of volumetric properties for asphalt mixture design and acceptance and serve as an example for other agencies in exploring the implementation of BMD for improving asphalt pavement performance.