Field Performance of 9.5-mm Nominal Maximum Aggregate Size Asphalt Pavement in Washington State

This paper compares Washington State Department of Transportation (WSDOT) 9.5- and 12.5-mm nominal maximum aggregate size (NMAS) mixtures using cost, mix design, field quality assurance, and field pavement management system data for contracts completed between 2007 and 2017. During this time, WSDOT's use of 9.5-mm NMAS mixtures increased to about 21% of contracts and 26% of tonnage to address asphalt pavement durability concerns. The construction bid price and average weighted asphalt content of 9.5-mm NMAS mixtures exceed 12.5-mm NMAS mixtures by about $9 per metric ton and 0.7%, respectively. The overall average weighted field density for both 9.5- and 12.5-mm NMAS mixtures is about 93%. Although there is not sufficient statistical evidence to conclude that 9.5-mm NMAS mixtures produce a different overall average weighted structural and rutting condition over time than 12.5-mm NMAS mixtures, 9.5-mm NMAS mixtures produce slightly higher condition averages at ages 9 and 10.