Abstract
Different microstructures of the same polymer-modified bitumen (PMB) were obtained by subjecting the bitumen modified with styrene-butadiene-styrene (SBS) copolymer to isothermal annealing at various temperatures. The effects of the morphology on the rheological properties of SBS-modified bitumen were investigated within the high-temperature range. The PMB microstructures were quantitatively evaluated using image analysis. A dynamic shear rheometer was used to measure the rheological parameters of the PMB samples and perform the multiple stress creep and recovery (MSCR) test. A quantitative basis could be established on which to discuss the relationship between the PMB morphology and rheology. The image analysis indicated that conditioning by isothermal annealing evidently led to a difference in the microstructure of the samples. Variation of the thermal history is demonstrated to be a practical way to vary the morphology of the PMB with the same raw materials and formulation. Compared with the two-phase morphology, the single-phase microstructure tended to have a narrower linear viscoelastic (LVE) region of the PMB. Within the LVE region, especially at low frequencies, the homogenous PMB can store more energy when experiencing loadings and is more elastic. Outside the LVE region, based on the MSCR test results, the homogenous morphology could assist in reaching a higher percentage of strain recovery after the creep period.
Highlights
The modification of bitumen with synthetic polymers for paving applications is a globally popular practice
The images of the microstructures captured by fluorescence microscopy are shown in Fig. 3 on the left
Lu et al [32] reported additional details on the morphological analysis. This result implies that variation of the annealing temperature changed the thermodynamic stability of the polymer-modified bitumen (PMB) from the stable ITA160 to the unstable ITA120, probably because of the existence of an upper critical solution temperature (UCST) for the system [21,33]
Summary
The modification of bitumen with synthetic polymers for paving applications is a globally popular practice. This modification helps to improve certain engineering properties of bituminous binders, for example, the rheological properties [1,2]. An important and critical research topic regarding polymer-modified bitumen (PMB), to ensure its high performance, is the relationship between the PMB microstructure and its rheological properties. This is further related to another fundamental research question, that is, the way in which the morphology of PMB originates under various conditions.
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