Extending the Black diagram of bitumen to three dimensions

The ordinary Black diagram of bitumen has only two dimensions. Thus, it does not differentiate the complex shear modulus and phase angle measured under different temperature and frequency conditions. This study proposes to extend the Black diagram to three dimensions by adding a temperature axis. It leads to the combination of multiple necessary ordinary plots in the same three-dimensional (3D) space. In this 3D space, the location, shape, and eventually colour of the plot (either curve or surface) can together indicate the unique temperature-dependency and time-dependency of the bituminous binder's rheological properties, even the interplay between them. Hence, polymer-modified bitumen is distinguished from neat bitumen and harder bitumen is distinguished from softer bitumen. Furthermore, the additional temperature axis in the 3D Black diagram also enables direct visualisation and precise quantitative evaluations of bitumen properties by various current technical criteria in the same space, avoiding the inconvenient use of multiple ordinary plots. This may lead to the development of a practical tool towards more effective and efficient evaluation of rheological properties of bitumen.