Evaluation of reclaimed asphalt pavement for surface mixtures.

SPR-3018The Indiana Department of Transportation has successfully used Reclaimed Asphalt Pavement (RAP) for decades because of its economicand environmental benefits. Because of uncertainties regarding the types of aggregates contained in RAP and their resulting frictionalproperties, however, INDOT has until recently disallowed the use of RAP in asphalt surface mixtures. In addition, the hardened asphaltbinder in the RAP could potentially increase the occurrence of thermal cracking. This research was conducted to explore the effects onRAP with poor or unknown aggregate qualities to establish maximum allowable RAP contents to provide adequate friction. The effectsof RAP on thermal cracking were then investigated at the potential allowable RAP contents.Laboratory testing showed that the addition of poor quality RAP materials did impact the frictional properties and cracking resistance ofthe mixtures, but that lower amounts of RAP had little effect. The frictional performance of the laboratory fabricated and field sampledRAP materials was acceptable at contents of 25% but may be questionable at 40%.Field friction testing was also conducted on existing roadways with RAP to explore their field frictional performance. Several low volumeroadways and one experimental interstate project were tested. The field results showed acceptable performance after 3 to 5 years oflow volume traffic at RAP contents of 15\u201025% and after more than 10 years of interstate traffic with 15% RAP.The low temperature testing showed an increased susceptibility to thermal cracking as the RAP content increased but the change incritical cracking temperature was relatively small at the 25% RAP level. At 40% RAP without a change in the virgin binder grade, thecritical cracking temperature was about 6\ub0C warmer than the control mixture. This finding supports the need for a binder grade changefor RAP contents greater than 25%, as indicated in other research and as required by the current INDOT specifications