Investigation of the use of recycled polymer modified asphalt binder in asphalt concrete pavements

Since polymer modified asphalt cement (PMAC) has been employed for a decade, the lifetime and wear on of some of these pavements is reaching a stage where resurfacing will be necessary. This paper considers the potential problems associated with recycling PMAC's; in particular blending of virgin and aged PMAC. A styrene-butadiene-styrene PMAC was selected and characterized using typical asphalt binder qualification techniques, i.e., the Superpave PG protocol. Procedures were developed to separate the PMAC into its asphalt resin and polymer additive components as well as to characterize the relative concentrations of each component. Infrared and thermogravimetric spectrographic 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 has been ascertained and found to be minimal. An eight year old polymer modified asphalt binder was recovered from a wearing course mixture located on route US61 in Livingston Parish, Louisiana. The field aged binder was characterized with respect to its composition and rheological properties. No residual polymer was detected and extensive oxidative age hardening of the binder had occurred. The binder was quite brittle at low temperature as demonstrated by both force ductility and bending beam rheometer tests. Extensive age hardening both chemically and rheologically and all changes in its properties due to aging were noted. In addition, blends of virgin PMAC and US61 recovered binder were prepared and analyzed. The resultant blends showed much stiffer than anticipated under both low and high temperatures. A 19-mm Superpave mixture containing blends of virgin PMAC with various percentages of US61 binder 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 demonstrate that as the increase of the percentage of US61 binder in mixtures, the rutting resistance increased, whereas the fatigue resistance decreased. Both the rutting factor of G*/sin(delta) at high temperature and the fatigue parameter of G* sin(delta) at intermediate temperature of Superpave binder were found to correlate fairly well with the results of mixture performance tests.