Research has shown that the minimum thickness of a plant-mix asphalt paving lift should be three times the nominal maximum aggregate size (NMAS) of the aggregate blend for fine-graded mixtures and four times the NMAS for coarsegraded mixtures. Lift thicknesses thinner than this are difficult to compact due to aggregate packing. However, there is little guidance on a maximum lift thickness.
The topic of resilience has begun circulating in many different fields and forums. The transportation community is no different, with the Transportation Research Board (TRB) hosting their second transportation resilience conference in 2019, the 2nd International Conference on Transportation System Resilience to Natural Hazards and Extreme Weather, bringing together researchers and practitioners to discuss this important topic. The asphalt paving community needs to join this discussion and work specifically to understand the benefits and appropriate applications of asphalt pavement in preparation of, or in response to, natural disasters or changing climate conditions.
California’s long-life asphalt pavement design is a perpetual pavement design that aims to produce a pavement that lasts 40 years or longer with minimal maintenance. A recent project on I-5 near Sacramento put this concept to the test.
A critical step in achieving long-lasting asphalt pavement performance begins with mixture design. An asphalt mixture should possess adequate stability (i.e., resistance to permanent deformation/rutting) and durability (i.e., resistance to cracking) for the intended design application (pavement). Recently, State Departments of Transportation (DOTs) researched and implemented a variety of approaches, including Balanced Mixture Design (BMD), aimed at improving the long-term performance of asphalt mixtures. Defined as “using performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mixture aging, traffic, climate and location within the pavement structure” Balanced Mixture Design means designing the right mixture for the right job.
Many performance test options exist for rutting and cracking evaluation of asphalt mixtures. Some are fundamental, while others are more empirical. Likewise, there are significant differences between tests related to total test time (specimen preparation + testing), complexity, and overall cost. Selecting the ‘best’ test can be a complex and debatable process.