Using Black Space Diagrams to Predict Age-Induced Cracking

Abstract

Asphalt aging is typically monitored through rheological changes at high pavement temperatures. Asphalt quality in laboratory aging experiments is then ranked using classic measures such as absolute viscosity ratios or changes in ring and ball softening point. However, this study [1,2] suggests that location on Black Space Diagrams at lower pavement temparatures is a better predictor for block cracking and related failure mechanisms associated with highly oxidized asphalt.

Three unmodified asphalts were PAV aged for 20, 40, and 80 hours. Modulus and phase angle were determined using DSR for intermediate temperatures, while stiffness and m-values using BBR were measured at low temperatures. Proposed aging functions such as Glover-Rowe’s Damage Parameter and Anderson’s R-value were compared to lab results on Black Space Diagrams. The key finding from the binder phase of this study is that location in Black Space is an important performance measure for cracking. However, the initial quality of the asphalt as determined in Black Space is just as important to performance as rheological changes in modulus and phase angle occurring during aging.

Aged mixtures were then tested in the BBR to determine whether binder aging trends would translate to mixture properties. One surprising finding was that microdamage forms in unconfined, highly aged mixture specimens as they cool. Findings from this study suggest that environmental effects models and timing strategies for pavement preservation should be revised to consider binder properties in Black Space, where both the initial asphalt quality and the effects of oxidation on key physical properties can be monitored. A new approach links initial binder quality with oxidative aging to propose a non-load induced cracking parameter for performance-related specifications.