Low-Temperature Fracture Testing of Asphalt Binders: Regular and Modified Systems

The results of low-temperature fracture testing of a large number of both regular and modified asphalt binders are discussed. Two Strategic Highway Research Program (SHRP) binders (Materials Reference Library Codes AAG-2 and AAN) were evaluated with 5 percent by weight of a variety of commonly used polymer modifiers. Specimens of three different sizes were tested in a three-point bend configuration, both with and without a notch. The original SHRP effort was aware of the need for a rigorous fracture mechanics-type binder test, but because of a lack of time and resources, only the bending beam rheometer and the direct tension test were ultimately developed. Some of the differences between failure strain and fracture toughness measurements are discussed, as well as how these differences may relate to pavement performance. The results of this study demonstrate that there is a large range of notch sensitivities and fracture energies for different polymer-modified binders, suggesting that the ductile-to-brittle transition (as measured with the direct tension test) may not be a totally reliable performance indicator. Fracture energy may be a better choice, since it combines the notched strength with a stiffness to yield a true material property that is independent of sample size and configuration.