Determining Asphalt Content for Recycled Asphalt Pavement (RAP) Materials

摘要

The State of Oregon uses significant amounts of Recycled Asphalt Pavement (RAP) in dense-graded mixes on State highways. The design process for these mixes relies on accurately knowing the amount of asphalt cement in the RAP materials being used. Beginning in 1997 ODOT began using ignition furnaces to determine RAP asphalt contents and gradations. Asphalt contents are determined by measuring the change in mass between the original dry RAP sample and the mass of the final residue aggregate sample after the asphalt is burned off in the ignition furnace. One shortcoming of the process is that a small portion of the aggregate is usually lost in the burning process. The amount of aggregate lost is on the order of 0.5% which may be considered significant for most RAP mixtures. This research attempted to use volumetric equations to solve for the RAP asphalt content by exploiting the constant nature of the Effective Specific Gravity of Aggregates, Gse. A solution is presented using a simplified equation which ignores the difference in Specific Gravity of Asphalt, Gb, between the RAP asphalt and the new added asphalt. This solution proved to be unstable and diverged significantly with only small changes in assumed Gb. A second more exact equation was derived to better account for the difference in Gb between the RAP asphalt and the new added asphalt. However, it's analytic solution collapsed to zero due to the dependent nature of the volumetric equation being used. Attempts to derive a second linearly independent equation failed; however, future research may lead to a complete solution to this equation.