Dosage and Mixing-Time Optimization of Polymer Blending with Bitumen through Fluorescent Microscopy

Abstract

Polymer modified bitumen (PMB) is a widely popular flexible pavement binder with capabilities such as high rutting resistance and excellent extreme weather performance. One of the most common polymers for PMB is styrene-butadiene-styrene (SBS) which is mixed with bitumen in 3-8% w/w in presence of a cross-linker (generally sulfur based). SBS absorbs lighter part of bitumen (aromatics) and become fluorescent which can be seen under a fluorescent microscope and evaluated for PMB network quality. In this study, elastomeric polymer SBS “A” was mixed at different dosage (2%-6% w/w) and for different durations under high shear mixer (1 hour). After addition of cross-linker, low speed mixing was applied for different durations (0.5hr to 6 hours). In each case, sampling was done at 0.5-1hr interval. Softening point test and microscopy was done on each sample. Microscopy images were further processed using ImageJ for a better understanding of particle size, particle distribution, and interlinks. A general correlation between the fluorescent microscopy image parameters and softening point was observed. However, it was noted that correlation coefficients were different for different SBS. Despite lack of universal correlation, the study shows that the image processing can indicate optimized dosage and mixing time for a given set of bitumen and SBS. Using microscopy to identify optimized blending state will reduce time and resource requirement at PMB formulation process.