United States Department of Transportation
i
Determination of the Binder Grade and Performance of High Percentage RAP-HMA Mixes
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2016-05-01
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[PDF-2.14 MB]
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Abstract:This study’s purpose was to better understand the effects of incorporating more RAP on the performance of a 9.5 mm Superpave surface course mixture. The performance and workability characteristics of the mixtures were evaluated using two different Warm Mix Asphalt (WMA) technologies and a softer virgin binder grade. The WMA technologies were organic and chemical based. Mixtures incorporating up to 50% RAP were designed with the same binder content and gradation as the control mixture. At RAP contents beyond 50%, the gradation and binder content of the mixture could not be maintained. Confirmation of the AASHTO blending charts recommended the use of asphalt binder grades not typically specified in Massachusetts. Binder data indicated that mixtures edged closer to the cracking failure zone as the amount of RAP increased. The use of softer binder and WMA technologies helped to reverse the trends, but the mixtures remained within the onset of cracking zone. Mixture performance data indicated reduced rutting performance, increased fatigue cracking resistance, and improved mixture workability when the softer binder was utilized. The use of either WMA technology did not significantly impact the rutting or fatigue cracking resistance, but did improve mixture workability. Using a softer binder or a WMA technology alone did not yield a mixture with the same performance as an all-virgin material mixture. Thus, using higher percentages of RAP in HMA must be carefully developed to reflect variations in individual mixtures based on the properties of RAP, total amount of RAP, available virgin binders, and WMA technologies available. The use of asphalt rejuvenators should be investigated for these types of mixtures to help reuse more of the binder in the RAP.
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