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The objective of this project was to evaluate the performance of Georgia's mixes designed by using the Superpave® gyratory compactor. Mixes designed with numbers of design gyrations that are too high would be rut resistant but may be difficult to compact adequately in the field and may lack sufficient durability because of reduced asphalt binder content. The following conclusions were made on the basis of an evaluation of field projects and from laboratory volumetric and performance testing with various aggregate sources and gyration levels: (a) It is unlikely that Superpave mixtures will reach the design air voids of 4.0% during the life of the pavement. After nearly 5 years, the average air voids measured in the wheelpaths were 5.7% for Superpave projects and 3.8% for Marshall projects. On the basis of volumetric comparisons, 66 gyrations with the laboratory-produced mix gave approximately the same density achieved on the Superpave projects in the field. (b) The difference between 4-in.-diameter Marshall samples and 6-in.-diameter gyratory samples for moisture susceptibility was not statistically significant enough to assign a relationship between the tensile strength ratio (TSR) for samples with a diameter of 4 in. and the TSR for samples with a diameter of 6 in. (c) Although the asphalt binder content was an important factor in extending fatigue life, aggregate source and strain level were the most significant variables affecting fatigue results.

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.

This research evaluated the effect of reclaimed asphalt pavement (RAP) on the combined overall performance of stone matrix asphalt mixtures in Georgia. Four types of RAP were combined at four levels (0%, 10%, 20%, and 30%) with four aggregate sources, with the use of a one-fourth fraction factorial design. Granite materials common to Georgia were used exclusively in this study for both RAP and virgin aggregate. Testing was performed to evaluate the binder effect on resistance to moisture susceptibility, rutting potential, thermal cracking potential, and fatigue life of the recycled mixtures. The following main findings are applicable only to the RAP and virgin aggregates used in this study. Virgin aggregate had a greater effect on Los Angeles abrasion loss and percent flat and elongated particles than did the addition of RAP. Increasing RAP content resulted in higher tensile strengths (conditioned and unconditioned) for moisture susceptibility testing. Up to 20% RAP can be used without significantly affecting performance. Only fatigue life (at high strain levels) decreased significantly with the addition of 30% RAP. Fine-graded RAP reduced virgin binder requirements, which translates into increased economic benefits. However, mixes are stiffer because they have higher aged-to-virgin binder ratios and may be more susceptible to fatigue cracking. Adding up to 30% RAP had little effect on low-temperature performance grade properties, which may indicate that the grade of virgin binder does not have to be adjusted to provide the desired low-temperature binder properties.