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Increasing Durability of Hot Mix Asphalt Pavements Designed with the Superpave System

Principal Investigator(s) 

State Highway Administration (SHA) concerns with the lower asphalt levels in HMA mixes have lead efforts to explore strategies to increase the asphalt content in Superpave mixes. National studies identified methods for adjusting binder content without compromising rutting performance of asphalt mixtures and remaining loyal to the Superpave philosophy. The applicability of these methods to Maryland SHA conditions were addressed based on the findings of recent National Cooperative Highway Research Program projects, ongoing discussions with SHA engineers, and experts’ feedback in this area. Furthermore, this study addressed the differences in HMA properties that have been observed over the years between samples taken at the plant versus behind the paver. A large set of SHA QA and QC data was analyzed statistically in the context of current specifications and pay factors to evaluate potential risks to both SHA and contractors. The research team developed the Operating Characteristic (OC) curves based on the QA data and for estimating the risks to SHA and contractors (Type I and II risks). With the aid of a new simulation tool the associated pay factors (PF) and expected pay (EP) were analyzed using the population characteristics and considering potential correlations between the HMA mix parameters. 

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