United States Department of Transportation
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Investigation of the use of recycled polymer-modified asphalt in asphaltic concrete pavements.
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2004-06-30
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[PDF-1.77 MB]
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Abstract:This report presents issues associated with recycling polymer modified asphalt cements (PMACs), particularly blending aged PMAC with new PMAC. A styrene-butadiene-styrene (SBS) PMAC was selected and graded using the Superpave Performance Grading (PG) protocol. Procedures were developed to separate the PMAC into its asphalt resin and polymer additive components and to characterize the relative concentrations of each component. Infrared spectrographic, thermogravimetric and rheological techniques were used to identify changes in the components as a result of aging. The impact of the extraction and recovery process on binder properties was found to be minimal. In this study, an SBS type elastomer PMAC meeting LADOTD specification for PAC-40HG and PG 70-22M was selected. A 19 mm nominal maximum aggregate size (NMAS) Superpave mixture was designed using virgin PAC- 40HG blended with four different percentages (0, 20, 40 and 60 percent) of Reclaimed PMAC (RPMAC), and virgin aggregates. The RPMAC was extracted from lab-aged and field-aged asphalt mixtures. An eight-year-old field-aged PMAC binder was recovered from a wearing course mixture located on Route US61, Livingston Parish, Louisiana. All binders were characterized with respect to their composition and rheological properties. Binders extracted from field cores revealed that the US61 binder was quite brittle at a low temperature as measured by both force ductility and bending beam tests. In addition, blends of the US61 extracted binder with virgin PMAC were prepared and analyzed. The resultant blends exhibited much stiffer properties than those produced from the corresponding concentrations of lab-aged PMAC, indicating that the Pressure Aging Vessel (PAV) procedure did not predict the field aging of PMAC binders. A 19 mm Superpave mixture containing blends of virgin PMAC with various percentages of lab-aged and field-aged PMAC binders and original aggregates was evaluated by a suite of fundamental engineering tests including beam fatigue, indirect tensile strength and strain (ITS), indirect tensile creep, Asphalt Pavement Analyzer rut (APA), and repeated shear at constant height (RSCH). Test results indicated that as the percentage of RPMAC binder in mixtures increased, the rutting resistance increased, but the fatigue resistance decreased. Both the rutting factor of G*/sin (delta) at a high temperature and the fatigue parameter of G* sin (delta) at an intermediate temperature of the Superpave binder correlated fairly well with the results of mixture performance tests.
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