Characterisation of polymer-modified asphalt binders using the dynamic shear rheometer

Bitumen is a viscoelastic substance, and it is widely acknowledged that its mechanical behaviour is influenced by both loading time and temperature. The performance of asphalt mixtures is significantly affected by the behaviour of bitumen, which in turn impacts the service life of flexible pavements. The dynamic shear rheometer is a commonly used tool for assessing the physical and rheological properties of both unmodified and modified asphalt binder (PMB). In this investigation, three binders were chosen: 40/60 penetration unmodified bitumen, a hard styrene butadiene styrene (SBS) polymer-modified binder, and a softer SBS polymer-modified binder. These binders were analysed using penetration, softening point, and dynamic shear rheometer frequency sweep tests. The dynamic shear rheometer data revealed that the complex modulus master curves highlighted the stiffening effect of SBS polymer modifiers, which became more evident at low frequencies and high temperatures. Regarding the phase angle master curves, the results indicated that both PMBs experienced a notable reduction in phase angle at low frequencies and high temperatures, resulting in a significant improvement in the elasticity of the bitumen. Finally, the black diagram results suggested that both PMBs, which contained SBS modifiers, displayed a plateau region where the phase angle remained constant and shifted towards lower values.