Additional Asphalt to Increase the Durability of Virginia's Superpave Surface Mixes

About the report:

Although Superpave has been successful in preventing rutting, many believe that the design asphalt content needs fine-tuning to produce durable mixes. This investigation used various laboratory tests to test samples of field surface mixes (12.5 mm and 9.5 mm) to predict changes in mix properties as extra asphalt was added. Permeability, 50-blow Marshall volumetrics, rutting, and fatigue tests were used. An analysis tool using gyratory compaction was also used to predict what the level of pavement voids would have been had higher asphalt contents been used. For most of the mixes, properties improved as the asphalt content was increased. The asphalt content could have been increased as much as 0.5 percent in most of the mixes with no harmful effects. It is reasonable to expect that the beneficial effects would increase the life of a surface mix by approximately 5 percent. The Virginia Department of Transportation (VDOT) uses approximately 2 million tons of asphalt in surface overlays per year at a cost of approximately $35 per ton. The cost of adding 0.5 percent more asphalt would be approximately $1 per ton. With an estimated increased service life of 5 percent, VDOT would save approximately $1 .5 million per year. The researcher recommended that the effects of increasing the design asphalt content of Superpave mixes be explored and tested in the field.

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