(Received 29 October 2001; accepted 12 March 2002)
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The dynamic shear rheometer (DSR) is being used currently by the asphalt pavement community for determination of the viscoelastic properties of asphalts following the recommendations of the Strategic Highway Research Program. The Superpave specification parameter |G*| sinδ was identified as the term to be used in rating the asphalt binders for their fatigue resistance. However, in subsequent research work, it was found that this parameter did not relate well with the accumulation of fatigue damage of mixtures measured through a beam fatigue test under strain-controlled conditions. This led researchers to seek other methods of characterizing fatigue resistance behavior of asphalt binders. The suggested new test was a binder fatigue test using the time sweep on the DSR. The number of cycles to fatigue failure Nf was chosen as the criterion for rating the fatigue resistance of the binder.
The present work reevaluates the binder fatigue test in order to establish the proper window for choosing the correct experimental conditions for getting meaningful results that would describe true fatigue behavior and not experimental artifacts. The fatigue tests are conducted at different temperatures of Te (°C) for various binders in order to ensure equistiffness conditions (identical initial complex modulus |G*i| values) at the start of the test. It is shown that the cycles to fatigue failure is directly a function of the initial loss modulus G″i, or in other words, the Superpave specification parameter |G*i| sinδi, and is also related to the loss modulus obtained through a strain sweep G″s or |G*s| sinδs at the temperature Te (°C). It is recommended that a specification temperature TIS = Te (G″s/|G*s|) = Te sinδs be used for ranking the binders in terms of their expected fatigue behavior.
Senior Research Fellow, FHWA-TFHRC-HRD-11, McLean, VA
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