Evaluation of Using Higher Percentages of Recycled Asphalt Pavement in Asphalt Mixes in Virginia

In 2007, the Virginia Department of Transportation (VDOT) decided to allow higher percentages of recycled asphalt pavement (RAP), i.e., more than 20 percent, in hot-mix asphalt with no change in binder grade. Because of this increase, one section of the contract provisions in certain plant-mix overlay schedules around the state had to be rewritten to raise the limit on the proportion of recycled material to 30 percent from the customary 20 percent. The allowance of higher RAP percentages should result in a lower cost of asphalt mix per ton, especially given the recent rising cost of asphalt cement and virgin aggregates. The purpose of this study was to estimate the effect of increased RAP percentages on performance and relative mixture cost on specific VDOT paving projects in 2007. Projects using more than 20 percent RAP were conducted in three VDOT districts. In addition, several value engineering proposals for using increased percentages of RAP submitted by contractors were accepted and carried out in another district. Six contractors produced a total of 129,277 tons of mix containing 21 to 30 percent RAP from seven asphalt plants in four VDOT districts. Mix containing less than 20 percent RAP was also sampled and tested for comparison purposes. Laboratory tests performed on samples collected during production revealed no significant difference between the higher RAP mixes and the control mixes for fatigue, rutting, and susceptibility to moisture. Binder was recovered from asphalt mix sampled during construction and graded to determine the effect of adding higher percentages of RAP. There were no construction problems attributed to the use of the mix with the higher RAP percentage. Only slight price adjustments were applied to 2 of the 10 high-RAP projects, and these adjustments were not due to the higher RAP percentage. Analysis of bid data found that the inclusion of a contract specification that allowed the higher RAP percentages had a small, statistically insignificant impact on the bid prices for surface mix items. However, value engineering proposals received for jobs that were not advertised with the high-RAP specification showed that the use of over 20 percent RAP could reduce costs in at least some cases.