Implementation of nondestructive testing and mechanical performance approaches to assess low temperature fracture properties of asphalt binders

AbstractThis paper discusses some important issues related to the use of recycled thermoplastics and rubber tire waste in asphalt binders for hot-mix pavements. Both high temperature rheological and low temperature fracture studies are presented on recycled polyethylene, devulcanized and crumb rubber-modified asphalt binders. The results are compared to unmodified and commercially available modified binders. This research is especially timely in light of the U.S. Intermodal Surface Transportation Efficiency Act of 1991, Section 1038 which, starting in 1995, will force state and local governments to use significant amounts of recycled rubber tire or plastic waste in federally funded highway projects.High temperature rheological measurements of the loss modulus, loss tangent and complex modulus show a significant improvement when only small quantities of crumb rubber, devulcanized crumb rubber or waste polyethylene are added to the asphalt binders.The low temperature fracture performance of the modified asphalts is greatly influenced by the interfacial strength between the dispersed and continuous phase. The fracture toughness increases dramatically, only when low molecular weight polymers are grafted in-situ onto the rubber and polymer dispersed phases in order to strengthen the interface. This points to a crack-pinning mechanism as being responsible for the dramatic increase in fracture toughness that is observed in this work. Single phase, devulcanized crumb rubber-asphalt systems perform quite poorly at low temperatures.

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

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/1728-06 ◽

2000 ◽

Vol 1728 (1) ◽

pp. 36-42 ◽

Cited By ~ 58

Author(s):

Todd R. Hoare ◽

Simon A. M. Hesp

Keyword(s):

Low Temperature ◽

Performance Indicator ◽

Tension Test ◽

Asphalt Binders ◽

Direct Tension ◽

Direct Tension Test ◽

Fracture Testing ◽

Reliable Performance ◽

Temperature Fracture ◽

Notched Strength

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.

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