In the past years, the use of liquid additives as bitumen modifiers has increased to tailor the rheology of bitumen for a wide range of applications. Their chemical composition and mutual interaction result in specific phase morphologies in the binders. Hence, there is a need to evaluate the phase morphology of complex binders and the impact of additives on their physical properties. The RILEM Technical Committee 272-PIM ‘Phase and Interphase behaviour of innovative bituminous Materials’, Task Group TG1 assessed the phase and interphase properties of bituminous binders. Some preliminary results are presented on blends using three liquid additives and a neat 35/50 bitumen. The goal of formulating the blends was to achieve similar consistency of a pen grade 70/100 bitumen at the original state and to evaluate the binders at both original and after aging. Physical properties were evaluated through rheological characterisation using a dynamic shear rheometer (DSR) in a wide range of conditions. The phase morphology was assessed using atomic force microscopy (AFM). Differential scanning calorimetry (DSC) was also used for the characterisation of the thermal behaviour of the binders. While conventional properties, as obtained from the routine binder testing methods, hardly distinguish between blends, the cross-over temperature, derived from DSR measurements, enabled to dictate the impact of liquid additives on the physical properties of bituminous binders at intermediate temperature. AFM confirmed a difference in phase morphology between the blends, whereas some binders displayed new phases at original and aged conditions. Glass transition, as determined by DSC, also showed a difference in the low-temperature domain that may be explained with the difference in phase morphology. Overall, an in-depth understanding of microstructure morphology and glass transition behaviour of complex binders can assist in designing future specifications to distinguish durable bituminous materials better.