16 SPRING/SUMMER 2022 FAILURE? What if BMD is a Trenton M. Clark, PE, President, Virginia Asphalt Association There Are Many Different Measures of Success For the better part of two decades, researchers and departments of transportation have invested millions of dollars into laboratory asphalt mixture testing in order to improve design and performance. Much effort has been spent on directly measuring the physical engineering properties of asphalt mixtures through devices such as the AMPT (Asphalt Mixture Performance Tester) in an effort to improve the predictive modeling for flexible pavement design. While this approach has benefits, it also has several shortcomings, such as the time required during mix design and usefulness during actual asphalt production. Therefore, researchers and agencies have turned their attention to less complicated testing procedures that can be used during mix design and production. While these procedures do not produce fundamental engineering properties such as modulus and flow number, they do provide a method to assess material performance against a set of minimum or maximum thresholds. Essentially, agencies are hoping to improve cracking resistance while not resulting in rutting/deformation. In other words, balance distress modes to maximize performance. In the end, agencies such as VDOT have stated that to be successful, a Balanced Mix Design (BMD) process must result in new asphalt mixes that perform better than the “recipe” mixes resulting from conventional Superpave design. But if BMDmixes are no better, will BMD be a failure?
RkJQdWJsaXNoZXIy Nzc3ODM=