| Summary: | Since polymer modified asphalt cement (PMAC) has been employed for a decade, the lifetime and wear on some of these pavements is reaching a stage where resurfacing is necessary. This research focuses on the characterization of aged polymer modified asphalt cements (PMAC) to evaluate their potential for recycling. A styrene-butadiene-styrene tri-block (SBS) polymer modified asphalt cement was selected and characterized using standard asphalt binder qualification techniques, i.e., the Superpave PG protocol.
We developed a procedure to characterize the relative concentration of polymer in asphalt cements by gel permeation chromatography (GPC). Infrared spectrographic, thermogravimetric and rheological techniques were used to identify changes in the binder 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. Two field aged polymer modified asphalt cements were extracted from field-aged asphalt cores. An eight year old field aged polymer modified asphalt binder was recovered from a wearing course mixture located on US61 Hwy in Livingston Parish, Louisiana. Samples of three, five and seven year old field aged PMAC binders was recovered from a wearing course mixture located on Interstate I55 near Granada, Mississippi. A correlation between field aging time and simulated aging by PAV was developed; PAV with humidity proved to be the best prediction. A comparison was established between the field aged materials and a series of lab aged binders. All binders were characterized with respect to their composition and rheological properties. In general, residual polymer was detected using gel permeation chromatography analysis except when extensive oxidative age hardening of the binder had occurred. Samples from the surface of US61 were quite brittle at low temperature, as demonstrated by forced ductility tests. Core samples of the same asphalt binder were more tractable, thus less aged, but recycling of this material will require additives to restore the desired rheological properties to the binder blend.
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