High RAP Mixes Design Methodology with Balanced Performance

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) can significantly reduce the increasing cost of hot-mix asphalt paving, conserve energy, and protect the environment. This report presents a comprehensive study focusing on methodologies to improve the performance of high RAP content mixes. Firstly this report addresses one major concern—RAP variability. It was found that in Texas the RAP materials are consistent and have low variability in terms of aggregate gradation and asphalt content, within individual stockpiles. The authors evaluated the impact of RAP on optimum asphalt content (OAC), rutting/moisture resistance, and cracking resistance. OAC generally increases with more RAP (and RAS) usage, but the increase in OAC is small when the RAP content is below 20 percent; increasing RAP content always improves rutting/moisture resistance as measured in the Hamburg wheel tracking test (HWTT). However, in the laboratory cracking resistance always reduces with increasing RAP content, especially when RAP content is 30 percent and above and also when RAP/RAS combinations are used. Additionally, the use of 10–15 percent RAP, without lowering virgin binder PG grade has a small impact on rutting/moisture and cracking resistance, but the influence, especially on cracking resistance, is much more significant when higher levels area used. A balanced RAP mix design approach is proposed in this study. In the proposed balanced mix design approach the final asphalt content is selected after optimizing the mix density, HWTT, and Overlay Test (OT) requirements. RAP handling in the process of mix design is critical, especially the mixing and compaction temperatures for high RAP mixes. It was recommended that the mixing and compaction temperatures used for the virgin binder be used for the RAP mix as well. Finally, the balanced RAP mix design procedure is demonstrated and validated through the construction of field test sections containing different levels of RAP. One of the interesting findings is that cracking requirement in terms of OT cycles should vary, depending at least on climate (cold vs. hot), traffic (heavy vs. light), and existing pavement condition (overlay over cracked pavements vs. new construction). For asphalt overlays over severely cracked pavements, a minimum OT requirement of 300 cycles previously proposed was further validated with performance data from the RAP sections on IH40 near Amarillo, Texas. More work is needed to develop criteria for different climatic zone and different pavement conditions.

• Record URL:
  http://tti.tamu.edu/documents/0-6092-2.pdf
• 
• Corporate Authors:

  Texas Transportation Institute

  Texas A&M University System, 3135 TAMU
  College Station, TX  United States  77843-3135

  Texas Department of Transportation

  Research and Technology Implementation Office, P.O. Box 5080
  Austin, TX  United States  78763-5080

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Zhou, Fujie
  • Hu, Sheng
  • Das, Gautam
  • Scullion, Tom
• Publication Date: 2011-11

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Technical Report
• Features: Figures; Photos; References; Tables;
• Pagination: 46p

Subject/Index Terms

• TRT Terms: Asphalt pavements; Mix design; Overlays (Pavements); Pavement performance; Reclaimed asphalt pavements; Recycled materials; Rutting; Shingles; Waste products (Materials)
• Uncontrolled Terms: Asphalt shingles
• Geographic Terms: Texas
• Subject Areas: Highways; Materials; Pavements; I33: Other Materials used in Pavement Layers;

Filing Info

• Accession Number: 01362849
• Record Type: Publication
• Report/Paper Numbers: FHWA/TX-11/0-6092-2
• Files: TRIS, USDOT, STATEDOT
• Created Date: Feb 16 2012 10:14AM