Developing Recommendations for Allowable RAP Contents in Idaho Asphalt Mixes

This research study focused on evaluating the effects of high recycled Asphalt Pavement (RAP) contents on asphalt mix performance. Until recently, the Idaho Transportation Department (ITD) did not impose any restriction on the amount of RAP allowed in an asphalt mix. As a result, pavement sections were constructed in Idaho with up to 54 percent RAP (by binder replacement). Some industry and DOT staff raised concerns regarding this practice. Subsequently, ITD placed a temporary limit of 30 percent as the maximum allowable RAP content in a mix. However, to find a permanent answer to this question, the current research study was initiated in collaboration with Boise State University, and later with Oklahoma State University. Extensive review of published literature was carried out on the effects of high RAP contents on asphalt mixture performance. A survey of state DOTs was carried out to gather information regarding their current practices with respect to maximum allowable RAP contents. Extensive laboratory testing was performed to assess the cracking resistance of different asphalt mixtures collected from across Idaho with varying RAP contents. Recommendations have been provided to help ITD adopt a systematic approach to facilitate the design of and construction with asphalt mixtures with high RAP contents.


  • English


  • Status: Completed
  • Funding: $160000
  • Contract Numbers:

    RP 269

  • Sponsor Organizations:

    Idaho Transportation Department

    P.O. Box 7129, 3311 West State Street
    Boise, ID  United States  83707-1129
  • Project Managers:

    Santi, Mike

  • Performing Organizations:

    Boise State University, Boise

    Department of Civil Engineering
    ET 201B
    Boise, ID  United States  83725

    Oklahoma State University, Stillwater

    School of Civil & Environmental Engineering
    Stillwater, OK  United States  74078
  • Principal Investigators:

    Mishra, Debakanta

  • Start Date: 20170518
  • Expected Completion Date: 20191231
  • Actual Completion Date: 20210531

Subject/Index Terms

Filing Info

  • Accession Number: 01661926
  • Record Type: Research project
  • Source Agency: Idaho Transportation Department
  • Contract Numbers: RP 269
  • Files: RIP, STATEDOT
  • Created Date: Mar 6 2018 6:29PM