Impact of high recycled mixed on HMA overlay crack development rate

Abstract

Illinois has many years of experience using various reclaimed materials in highway construction; and in recent years, recycled asphalt shingles (RAS) have been adopted for use in hot-mix asphalt (HMA), along with much higher amounts of reclaimed asphalt pavement (RAP). These reclaimed asphalt materials usually contain aged asphalt binders, which may increase the mix brittleness and hence, a challenge for maintaining a flexible pavement and ensuring good performance. To counter these hard asphalt binders, softer asphalts are incorporated into the HMA. The goal is for the final mix to provide acceptable mix properties for the life of the pavement. To determine the impact of recycled materials on pavement performance, this study monitored nine field projects in terms of the testing, construction, and performance of surface mixes that have a variety of asphalt binder replacement levels from RAP and RAS which used different virgin asphalt binder grades. Simple performance tests (Hamburg wheel tracking test and the Illinois flexibility index test [I-FIT]) were used to evaluate the mix designs. Flexibility index (FI) from the I-FIT showed good correlation with field crack development, especially after first year performance of the mix. Early-age field performance showed that placing the HMA overlay directly over existing bare concrete pavement or milling off all the HMA and placing new overlay on concrete pavement results in higher extents of cracking in early age than the sections that left an HMA layer in place. Regardless of which mix type is designed and what material sources are used, the performance of mix should be evaluated to ensure it has sufficient flexibility to resist cracking before the mix is used in road construction. This allows owners and contractors to use low-cost reclaimed and recycled materials to the extent possible without negatively impacting pavement performance.

Keywords:

• early performance
• hot-mix asphalt overlays
• recycled mixes
• Illinois flexibility index
• balanced mix design

Acknowledgements

The support for this study was provided by Illinois Department of Transportation (IDOT) as part of the ongoing ICT R 27-161 research project. The authors would like to express their sincere gratitude to IDOT for funding this research. The assistance from Jim Trepanier, Tom Zehr, Brian Pfeifer, Ryan Sheley, Joe Vespa, LaDonna Rowden, George Houston, and Tim Murphy is acknowledged. The field data collection by IDOT personnel and Engineering & Research International (ERI) Inc. is also greatly appreciated. Thanks go to Jim Meister, Greg Renshaw and students at Illinois Center for Transportation (ICT) for conducting laboratory testing. The contents of this paper reflect view of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of ICT or IDOT. This paper does not constitute a standard, specification, or regulation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Illinois Department of Transportation [ICT R27-161].