2 nd Workshop on Four Point Bending, Pais (ed.), © 2009. University of Minho. ISBN 978-972-8692-42-1 133 Comparison of Bitumen Fatigue Testing Procedures Measured in Shear and Correlations with Four-Point Bending Mixture Fatigue C.M. Johnson, H.U. Bahia, & A. Coenen University of Wisconsin, Madison, Wisconsin, USA ABSTRACT: Characterizing the contribution of bitumen fatigue resistance to asphalt pavement performance remains a hurdle to implementing a unified bitumen fatigue criterion in specifica- tions. This study is intended to explore preliminary validation of the most promising bitumen fa- tigue testing procedures using four-point flexural bending of asphalt mixtures. One mixture gra- dation and compaction level was used to isolate the relative fatigue performance of three polymer-modified bitumens. It is anticipated that testing of bitumen using the Dynamic Shear Rheometer (DSR) can be used as a fatigue performance indicator, thereby reducing the need for costly mixture fatigue testing. Three bitumen test procedures are highlighted in this study; one mimics the cyclic loading of conventional fatigue, the second is a monotonic test procedure that measures the ability of the material to withstand loading energy prior to damage, and the third is a sweep test in which the strain is increased continuously with number of cycles. The compari- son of the different bitumen testing procedures to flexural fatigue is presented herein. The re- sults show that there are no simple correlations, and depending on the loading conditions se- lected, the ranking of binders could vary by test method. 1 INTRODUCTION There is currently a significant amount of effort being focused on the development of bitumen test procedures that can more accurately determine the critical material failure properties asso- ciated with pavement distresses such as rutting, fatigue and thermal cracking. Fatigue damage in particular has proven quite troublesome to evaluate in the bitumen alone, as it typically requires multiple repeated load cycles over a testing period that can last for hours. However, there is lit- tle argument that the bitumen/mastic phase of asphalt concrete is most critical for resisting fati- gue damage, and thus must be evaluated for fatigue performance. This study hopes to evaluate new test methods for determining the damage resistance and fatigue performance of different bi- tumens by comparing their results with four-point bending fatigue test data on mixtures pre- pared using the same bitumens. Currently, the SuperPave performance grading specification relies on a parameter derived from the linear viscoelastic dissipated energy (W) under cyclic shear loading, defined by Equa- tion 1: (1) ) δ ( γ π sin | * | 2 0 ⋅ ⋅ ⋅ = G W where γ 0 is the applied strain, |G*| is the complex shear modulus, and δ is the phase angle. As the values of applied strain are within the linear visco-elastic limit for the test, the G* and δ are independent of the strain, thus the parameter |G*|sin δ. A maximum value was set as the specifi- cation limit in order to limit dissipated energy, as it was assumed that large values could indi- cate energy being dissipated into more damage accumulation. However, recent studies have
Comparison of Bitumen Fatigue Testing Procedures Measured in Shear and Correlations with Four-Point Bending Mixture Fatigue
May 20, 2023
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