United States Department of Transportation
i
Enhanced Characterization of RAP for Cracking Performance
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2020-02-01
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[PDF-14.73 MB]
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Edition:Final, 03/14/17-02/29/20
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Abstract:Even though reclaimed asphalt pavement (RAP) has economic and environmental benefits, the average percent usage of RAP in asphalt mixture in the United States is only 20.4%. Current Florida Department of Transportation (FDOT) specifications limit RAP usage to 20% in polymer-modified asphalt (PMA) mixtures and do not allow RAP in high-polymer (HP) mixtures. Literature indicated RAP binder stiffness and RAP gradation were important characteristics related to RAP mixture cracking performance. This study focused on evaluating the effect of these RAP characteristics on cracking resistance and on determining whether the current maximum RAP usage in PMA and HP mixtures may be increased with or without the need for RAP characterization. Twelve RAP sources were characterized using recovered RAP binder and aggregate to identify the range of RAP binder stiffness and RAP gradation for Florida RAP material. Eight out of 12 RAP sources, covering the range of these RAP characteristics encountered in Florida, were selected for further evaluation. The interstitial component fracture energy (FEIC) obtained from IC direct tension tests was used as a surrogate for a mixture fracture energy (FEmix) to assess all RAP mixture combinations. FEmix obtained from Superpave indirect tensile (IDT) tests was used to evaluate findings from FEIC results. Finer and stiffer RAP was more detrimental to cracking resistance than coarser and less stiff RAP. This indicated characterizing that RAP binder stiffness and RAP gradation was necessary to increase the current maximum RAP content in PMA mixture. A guideline to determine maximum RAP usage in PMA mixtures based on these two key RAP characteristics was developed to allow more than 20% RAP in PMA mixtures. Proposed guidelines which allow up to 40% RAP were validated by way of full mixture testing. Furthermore, it was concluded that incorporation of 20% RAP would sacrifice premium cracking performance expected of HP mixtures.
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