20 SPRING/SUMMER 2022 those terms, when compared to the impetus behind BMD implementation, an asphalt mix of equal performance will be deemed a failure. However, is that really the case? BMD can be a success even if the overall performance of asphalt mixes is not improved. There are three main successes agencies can achieve as well as the contracting industry. The first success comes in the area of knowledge. For too long asphalt mixes have been designed to meet a set of metrics—asphalt content, aggregate gradation bands and volumetric properties. In general, this approach has worked. Like any normal distribution of performance, some mixes have performed better than expected, many have performed as expected and Recently, the National Center for Asphalt Technology (NCAT) completed a report for NCHRP (NCHRP Project 20-07 Task 406) outlining a model for BMD implementation. A few important points were made in that report. First, an agency needs to evaluate the numerous lab performance tests available that fit the state. For example, the predominant cracking experienced in Montana will be different than the cracking in Florida. While fatigue cracking may occur in Montana, temperature-induced thermal cracking may be more relevant to the Montana Department of Transportation (MDT) in selecting a cracking test protocol. Florida DOT may be more concerned with fatigue cracking and rutting due to high pavement temperatures. Once a test or set of tests are selected, a second important step is to baseline the current or standard mixes used in the state. As the old adage goes, if you do not know where you are, how can you know where you are going? Through extensive lab testing, contractors and the agency can determine a benchmark or baseline for existing materials by nominal maximum aggregate size and binder type. By cross-referencing the standard mixes with performance data from a pavement management system, an agency can begin to determine what “better” means by using BMD. But What if Better Isn’t Achieved? While so much time, effort and funding has been invested in BMD, what if BMD does not produce better mixes? What if the only outcome is a different mix design process? Would that make BMD is a failure? According to Merriam-Webster’s Dictionary, failure is defined as “omission of occurrence or performance, state of inability to perform a normal function…a lack of success.” In △ continued from page 18 Agencies should not miss the forest for the trees. Proper implementation of a performance-based BMD approach will have long term benefits through knowledge gained, reduced costs, and improved sustainability. " " WHAT IF BMD IS A FAILURE? BMD experimental mix being laid at VTTI.
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