Evaluating Georgia's Compaction Requirements for Stone Matrix Asphalt Mixtures

This study determined a compaction level for stone matrix asphalt (SMA) mixes with the Superpave® gyratory compactor (SGC) that would match a 50-blow Marshall compaction using aggregates and mix designs common in Georgia. SMA mix designs were prepared with five aggregate sources using a 50-blow Marshall compaction and using 50, 75, and 100 gyrations with an SGC. Optimum asphalt contents from the mix designs were compared. Aggregate breakdown from each of the compactions was analyzed. Laboratory rutting tests were conducted on each mix design by using the asphalt pavement analyzer (APA). Results of the laboratory mix designs indicated that generally 35 gyrations in the SGC provided the same density as Marshall compaction. At 50 gyrations, the optimum asphalt contents for the SMA mixtures were 0.1% to 0.5% less than when the Marshall hammer was used; however, four of the five mix designs with 50 gyrations met Georgia Department of Transportation (DOT) specifications. Aggregate breakdown was slightly less with the SGC than with the Marshall hammer. APA tests showed that the mix designs were not sensitive to asphalt content, and all passed Georgia DOT requirements. Testing with plant-produced SMA mixtures confirmed that 34 gyrations in the SGC yielded specimen densities equivalent to the Marshall compaction. For the plant-produced mixtures, compaction in the SGC caused less aggregate breakdown than with the Marshall hammer. The field mixtures also performed well in APA testing. On the basis of results from the laboratory and field mixes, 50 gyrations are recommended with the SGC to replace 50-blow Marshall compaction for SMA mix design in Georgia.