An Overview of Black Space Evaluation of Performance and Distress Mechanisms in Asphalt Materials

Black space diagrams (BSD) representing rheological data of bituminous materials in the form of dynamic modulus (|G*| or |E*|) versus phase angle (δ) have been successfully used for interpretation of material behavior. Previous studies have used BSD for identification of testing geometry compliance errors when testing over multiple temperatures and loading times (frequencies); the screening of the “thermo-rheological simplicity” of various binders and mixtures, particularly with regards to the effect of polymer modification, wax content and oxidative ageing; and the detailed evaluation of the performance balance in term of “stiffness” versus “relaxation” needs. This overview paper details how these concepts and the Black space characterization of bituminous materials now include concepts of damage and healing (along with the effects of non-linearity, thixotropy and localized heating); the influence of the increased use of recycled asphalt pavement (RAP) proportions (along with effects of ageing and rejuvenation); and finally the fracture behavior and susceptibility limits for thermal, fatigue and durability cracking. New concepts such as the Glover-Rowe parameter that are based around BSD and linked to other forms of rheological indices such as the low temperature stiffness and relaxation rate parameters are introduced. Black space now provides a critical means of rheological characterization to investigate and evaluate the properties and performance of both binders and mixtures, particularly at a time when alternative binders (bio-binders, plastic modified binders, etc.) and increased pressures on re-use and recycling of materials in asphalt mixtures are becoming more prevalent.