United States Department of Transportation
i
Impact of Recycled Asphalt Shingles (RAS) on Asphalt Binder Performance
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2018-01-01
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[PDF-3.59 MB]
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Abstract:This study evaluated the effect of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) on virgin binder true grade and fracture energy density (FED). A mortar approach, which avoids the need for binder extraction, was adopted to quantify the RAP/RAS effect on virgin binder true grades by using the grade change rate (GCR) parameter. The existing data analysis method was found to yield unreliable RAP/RAS GCR results, and an alternative method was developed to predict the properties of RAP/RAS blended binders for GCR determination. The enhanced mortar approach successfully captured the stiffening effect of RAP/RAS: (1) RAS had greater GCR at high and low temperatures than the RAP; (2) the stiffest RAP had greater GCR than the other two RAPs; and (3) tear-off (TO) shingles exhibited greater high temperature GCR and slightly lower temperature GCR than the manufacture waste shingles. Results also revealed that RAP GCR is independent of RAP binder replacement rate, but RAS GCR increases exponentially with increased RAS binder replacement rate. Use of soft virgin binders appeared to effectively compensate for the stiffening effect of RAP/RAS, in terms of Superpave binder true grades. The limit of RAS content was found to be approximately half of the allowable RAP content for a given virgin binder. However, whereas RAP binder increased the FED of virgin unmodified binders, the opposite trend was observed for RAS binder, especially for the TO shingles which caused significant reductions in virgin binder FED. This is an important finding because decreased binder FED indicates deteriorated binder fracture tolerance. In addition, great caution should be exercised when polymer-modified asphalt (PMA) binders are used in RAP/RAS mixtures because both RAP and RAS decreased the PMA binder FED, with the RAS effect being much more pronounced. A follow-up study is recommended to extend the research efforts to mixture evaluation since mixture performance is governed by factors other than binder performance, such as RAP/RAS gradation and mixture gradation.
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