Virginia’s Experience with 9.5-mm Nominal-Maximum-Aggregate-Size Stone Matrix Asphalt

Abstract

Construction data from two Virginia stone matrix asphalt (SMA) field projects that used 9.5-mm nominal-maximum-aggregate-size (NMAS; Superpave® definition) gradations are presented. Analyses were conducted to evaluate breakpoint sieve size, rut resistance, design compaction effort, and permeability. Rut resistance and permeability results for 9.5-mm NMAS mixes were compared with those for more conventional Virginia 19.0- and 25.0-mm NMAS SMA mixes produced by the same contractor and with the same aggregate source. A sieve size of 2.36 mm was confirmed as being the appropriate breakpoint for 9.5-mm NMAS SMA. For this gradation, 9.5-mm NMAS SMA with both performance-graded binder (PG) 70-22 and PG 76-22 was as rut resistant as previous Virginia SMA mixtures, as tested with the Asphalt Pavement Analyzer. The data for these sections indicate that 9.5-mm NMAS SMA should be designed with 75 gyrations instead of the currently recommended 100 gyrations. SMA with a 9.5-mm NMAS was also shown to be less permeable at the same air void level as the more commonly used 19.0- and 25.0-mm NMAS SMA.