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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

Successful High RAP Mixes Designed with Balanced Rutting and Cracking Requirements

A comprehensive study focusing on methodologies to improve the performance of high reclaimed asphalt pavement (RAP) content mixes is presented in this paper. One major concern that many agencies have is addressed, firstly, in this paper - that of RAP variability. In Texas, it was found that, within individual stockpiles, the RAP materials are consistent and have low variability in terms of aggregate gradation and asphalt content. In addition, when the authors evaluated the impact of RAP on optimum asphalt context (OAC), cracking resistance, and rutting/moisture resistance, they found that OAC generally increases with more RAP (and reclaimed asphalt shingles (RAS)) usage, but when the RAP content is below 20% the increase in OAC is small; and as measured in the Hamburg wheel tracking test (HWTT), increasing RAP content always improves rutting/moisture resistance. Yet, particularly when RAP content is 30% and above, and also when RAP/RAS combinations are used, it was found in the laboratory that cracking resistance always reduces with increasing RAP content. This study proposes a balanced RAP mix design approach. The authors recommend the use of the Overlay Tester (OT) to directly measure cracking resistance of RAP mixes and the HWTT for evaluating rutting/moisture resistance, recognizing the challenge of accurately estimating voids in mineral aggregates of the RAP mix. Furthermore, a maximum density of 98% is recommended to avoid over densification and potential bleeding for Texas dense-graded hot mix asphalt (HMA) mixes designed using the Texas gyratory compactor. The final asphalt content is selected after optimizing the mix density, HWTT, and OT requirements in the proposed balanced mix design approach. The mixing and compaction temperatures used for the virgin binder should be used for the RAP mix as well, as was recommended. Finally, through the construction of field test sections containing different levels of RAP, the balanced RAP mix design procedure is demonstrated and validated. The fact that cracking requirement in terms of OT cycles should vary, depending on the climate (cold vs. hot), traffic (heavy vs. light), and existing pavement condition (overlay over cracked pavements vs. new construction), is one of the interesting findings. A minimum OT requirement for overlays over severely cracked pavements of 300 cycles previously proposed was further validated with performance data from the RAP sections on Interstate Highway (IH) 40 near Amarillo, Texas. In order to develop criteria for different climatic zone and different pavement conditions, more work is needed.

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  • English

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  • Accession Number: 01523080
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Apr 24 2014 11:58AM