The influence of thermal history on binder rutting indicators

Binder properties, believed to relate to asphalt rutting, were investigated and compared with each other. Included are: parameters derived from oscillatory tests (e.g. the "zero" shear viscosity and the SHRP rutting parameter), parameters derived from static and repeated creep tests and the traditional R&B softening point. Various binders were tested, including low and high polymer modified bitumen, and bitumen modified with commercial waxes. This study shows that for unmodified bitumen all the investigated binder parameters correlate well with each other and would give similar classifications regarding the rutting susceptibility. For modified binders, the parameters related to low frequency or long loading times, give a different ranking than those related to higher frequencies, as for example the SHRP parameter. The storing and preparation conditions prior to the rheological measurement can have a large influence, especially in the range of long loading times or low frequencies. For elastomer modified binders, the homogenization temperature and the corresponding change in micro-structure can have a large impact. For binders with semicrystalline modifiers, the storage time and storage temperature before testing can introduce large changes in the polymer network building up. The thermal history effects in rheological tests can be related to variations in crystallinity, as shown by calorimetry, or to variations in morphology, as revealed by fluorescence microscopy. Some of the binders were also investigated in the presence of filler, to see if the thermal effects play a similar role in mastic (binder(+)filler) as in the neat binder