Bailey method design for a dense asphalt concrete and its influence on permanent plastic deformations resistance

Historically, asphalt mixes have been designed considering the professional experience and proper values of volumetric parameters, such as continuously graded aggregate (gradation curve does not have any abrupt slope change), and respecting the technical specifications limits that are related. Taking that into account the asphalt binder rheological behavior is analyzed as well as the designed mix mechanical response to modeled static and/or dynamic loads that try to simulate the field conditions. However, it has been proved that not always these initial design criteria consider all the variables that condition the granular stability of the system. The present work develops the method proposed by Robert Bailey, from the Illinois Department of Transportation, applied to a dense asphalt mix NMPS 20 mm (HMA - D20). The method proposes to optimize the aggregate skeleton to achieve a lower rate of permanent deformations of the mixtures in service. This optimization is done considering the relation between gradation and voids changes in the mix properties. To that end Control sieves are defined, these allow a more accurate aggregate blend evaluation. In order to show how these considerations modify the dense asphalt mix properties a comparison was done between one conventionally designed mix and one designed with the Bailey method (in both cases the optimum binder content was determined by the Marshall method). These mixes were submitted to dynamic loads at 60 °C with the Wheel Tracking Test, evaluating rut resistance in each case.