Volume 38, Issue 1 (January 2010)
Energy-Based Approach for Determining Flow Number
The Asphalt Mixture Performance Test (AMPT) is being used in research and is nearing completion to be adopted by highway agencies for evaluating the performance of asphalt concrete mixtures. The implementation of Superpave volumetric mixture design has occurred in nearly all state agencies in the United States. This implementation has been done mostly without an accompanying performance test. Researchers have been examining a number of candidate performance tests, and more recently a growing consensus is that a repeated, unconfined, and uniaxial loading test will become a part of the Superpave AMPT. This test will allow mixture designers to optimize binder content and aggregate structure by evaluating a mixture’s resistance to permanent deformation. The AMPT will allow contractors or state highway agencies to evaluate the performance of their mixtures in this test methodology. This paper examines an energy-based approach to determine flow number. The current method examines strain rate versus cycles, and the minimum point is the onset of tertiary flow and thus is defined as the flow number value. However, one low data point could result in a misleading flow number. Mathematically, it would be correct, but in practice it could be misleading in assessing the ability of a mixture to resist permanent deformation. The energy-based approach plots creep stiffness times cycles versus cycles and is able to identify a well-defined failure point. This well-defined point is defined as an energy-based flow number. It was found that this energy-based flow number can be 65–75 % greater than the current method for determining flow number.