The morphology of SBS modified bitumen in binders and in asphalt mix

The morphologies of SBS modified binders and their asphalt mixes were studied using fluorescence microscopy. In a first part, the morphology of an SBS polymer in different bituminous binders was investigated as a function of the preparation method, in particular as a function of the cooling rate and isothermal annealing periods. Storage stable and unstable SBS-bitumens, as defined by the tube test after 3-day at 180 degrees C, were selected. The microscopic observations showed that the morphology strongly depends on the thermal history of the respective samples. These microscopic observations are supported by the differences seen in the rheological properties and in the force ductility curves of the respective binders. In a second step, the morphology of the SBS binders was investigated directly in the corresponding asphalt mix. The morphology was studied in compacted specimens as well as in the loose mix using several preparation procedures. Asphalt specimens were sliced in plane or alternatively in thin sections according to the methods developed by the Danish Road Institute. Also cold fractured asphalt surfaces were investigated. The analysis of the asphalt surfaces showed clearly that the morphology in the asphalt mix was very similar for all the binders tested, and was in most cases rather different from the morphology observed in the binder specimens. In the asphalt mix, the SBS phase is located in separate and distinct domains; this was observed for all the mixes tested. The observations suggest that the differences in PMB morphologies between compacted asphalt and binders is an important factor that should be considered when investigating the properties of polymer modified binders, and especially when searching for performance related binder tests.