Determining the %RAP or %RAS in Asphalt Mixtures

A vast majority of hot-mix asphalt (HMA) on Kansas Department of Transportation (KDOT) projects are produced by drum mix plants. In these plants virgin aggregates and RAP are fed into the drum using belts that are calibrated to control the quantity. Virgin binder is pumped from a storage tank based on the totalizer input. In current practice the totalizer is used to determine the percent RAP or RAS in HMA. However, measurement of binder content in a mix and recording virgin binder tank stabs has led to concerns that totalizers may not accurately measuring the RAP quantity in a mixture. Indeed, the totalizer measurement is not capable of differentiating the relative proportion of the input quantities and can only provide an integrated mass. KDOT has done detailed analysis of data from one project and found that the estimated amount of RAP back-calculated from the mix quantity and virgin asphalt content varied anywhere from 31% to as high as 70%. The design RAP content on this project was 40%. Aleatory variability of RAP input is expected and there is associated variability with the binder content of the HMA mixture. The skew of the back-calculated RAP content toward excess RAP is concerning and indicates a need for tighter controls on HMA mix proportions. KDOT has defined expected variabilities or testing variances/tolerances associated with the AC content of the HMA mixture and RAP as defined in the KDOT test method. There are also tolerances associated with the quantity of virgin AC and total HMA mix produced. However, these variabilities cannot explain the variation of the RAP quantities obtained. Thus, an in-depth investigation of data from multiple projects and an independent verification of the expected RAP quantity is needed.

• Supplemental Notes:
  • Final report is pending.

Language

• English

Project

• Status: Active
• Funding: $47240
• Contract Numbers:

  K-TRAN: KSU-22-2

  RE-0836-01

  C2185

• Sponsor Organizations:

  Kansas Department of Transportation

  Eisenhower State Office Building
  700 SW Harrison Street
  Topeka, KS  United States  66603-3754
• Performing Organizations:

  Kansas State University Transportation Center

  Kansas State University
  Department of Civil Engineering
  Manhattan, KS  United States  66506
• Principal Investigators:

  Jones, Christopher

  Hossain, Mustaque

• Start Date: 20210701
• Expected Completion Date: 20240731
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Hot mix asphalt; Mix design; Reclaimed asphalt pavements; Recycled materials; Shingles
• Subject Areas: Highways; Materials; Pavements;

Filing Info

• Accession Number: 01832305
• Record Type: Research project
• Source Agency: Kansas Department of Transportation
• Contract Numbers: K-TRAN: KSU-22-2, RE-0836-01, C2185
• Files: RIP, STATEDOT
• Created Date: Jan 7 2022 12:09PM