Evaluation of Mixing and Compaction Temperatures (MCT) for modified asphalt binders using zero shear viscosity and Cross-Williamson model

The current study was conducted to examine the rheological properties and the performance characteristics of polymer-modified asphalt binders at various temperatures. Different types and concentrations of polymers were used; including Styrene Butadiene Styrene (SBS) with or without a cross linker, Honeywell (HW) and polyphosphoric acid (PPA) which were added based on the total weight of different Performance Grade bitumen contents. Two methodologies (traditional Superpave and zero shear rate viscosity (ZSV)) were used for comparing binder viscosity and mixing and compaction temperatures. Theory of ZSV measurement was used to assess the rheological characteristics of the asphalt binder while a rotational viscometer device was used to measure the relation of viscosity changes with shear rate for neat and modified Iraqi asphalt binders. The Cross Williamson model was used for the simulation of the viscosity–shear rate dependency for each of the studied temperatures. From the results, there were changes in the rheological properties of the bituminous binders after the modification process. The neat bitumen showed improved rheological properties after mixing with the modifiers. It was noticed that increases in the percentage of polymer had no effect on the calculated mixing and compaction temperatures by ZSV; however, an increase of about 8% was observed with the traditional system. Furthermore, the two methods were observed to provide slightly different values for the viscosity when applied over a considerable range of test temperature. For the modified binders, they showed different mixing and compaction temperatures when ranked according to their Superpave grading protocol or their ZSV. The ZSV for mixing temperature was lower by about 42–54 °C compared to the Superpave method. Keywords: Zero Shear Viscosity, Polymers, Rheology, Modified Asphalt, Superpave Grading, Shear Rate