Low-temperature rheological and fracture properties of polymer-modified bitumens

The low-temperature properties of several polymer-modified bitumens (PmB's) were studied. The rheological behaviour was analysed using a bending beam rheometer (BBR) and a dynamic shear rheometer (DSR). The fracture properties were measured using a three point bending test considering the linear elastic mechanics principles. The rupture facies of the fractured samples were observed by environmental scanning electron microscopy (ESEM) and cryo scanning electron microscopy (CSEM) in order to understand the rupture mechanisms and to explain the differences in terms of rupture properties between the samples. The study shows that the rheological behaviour under dynamic shear of the polymer-modified bitumen and the base bitumen are similar at low temperature. It seems that the rheological properties of the PmB's at low temperature are controlled by the properties of the higher modulus phase that means the bitumen matrix. In the opposite, the polymer addition improves the fracture properties of the binder because the polymer-rich phase is an obstacle for the crack propagation. In some cases, the crack bypasses the polymer-rich domains (crackdeflection) and the rupture occurs at the interface between the polymer-rich phase and the matrix. A high value of the fracture toughness (KIC ) is also attributed to the good interfacial adhesion between the two phases of the blend. In some other cases, the crack propagates through the polymer-rich domains which seem to be stretched. This mechanism (crack-bridging) requires a very good interfacial adhesion and can explain the high value of KIC measured for some samples.