Real-time microscopic and rheometric observations of strain-driven cavitation instability underlying micro-crack formation in asphalt binders

ABSTRACT

We observed and analysed the early stages of formation and growth of instabilities in binders that lead to crack formation. A monotonic mechanical strain was applied to a thin, confined film of binder between two transparent plates; meanwhile, the bulk of the binder was observed using dark field microscopy to capture its behaviour as the strain increased. During the application, the formation of small cavities that rapidly grew was observed, which corresponded with notable points on a similar test that measured the load in the specimen. A three-stage model is used to describe the nucleation of the first cavity, of subsequent cavities and the growth of existing cavities that closely track the engineering stress–strain behaviour. In addition, it was observed that a cavity forms from a single microstructural feature, but not every feature forms a cavity. A theoretical model for this formation is presented. The growth of these cavities and their choice of nucleation sites suggests that although the density and distribution of the microstructure may not be critical to the formation of cavities that lead to failure, the presence and material properties of these microstructural entities compared to the matrix may be the factor that dictates damage nucleation.

KEYWORDS:

• Asphalt binder
• cavitation
• poker chip test
• fracture
• damage

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge the support of the Texas Department of Transportation, Robert Welch Foundation Grant F-1038, and National Science Foundation Grant CMMI-1053925. Division of Civil, Mechanical and Manufacturing Innovation.