Quantification of Viscous and Fatigue Dissipation of Asphalt Concrete in Four-Point Bending Tests

Different methods are available to quantify the fatigue damage of the asphalt mixtures. Among these, methods based on the concept of dissipated energy are used predominantly. Characterizing fatigue damage using the concept of dissipated energy is complicated due to the presence of other modes of dissipation, for instance, viscous dissipation. Hence, most of the investigations attempt to separate the dissipation due to damage from the viscous dissipation. One of the widely used approaches to separate fatigue dissipation involves the use of a parameter called pseudostrain. The area under the stress-pseudostrain curve, called the dissipated pseudostrain energy, is used to characterize fatigue. In this study, the usefulness or otherwise of this approach to separate fatigue and viscous dissipation is explored. Toward this, experimental investigations were conducted using four-point bending for four types of asphalt mixtures at two different temperatures and four strain levels. It was observed that although the concept of pseudostrain to characterize the fatigue damage holds good in some specific cases, it cannot be adopted for all experimental data collected in this study. In view of this, a new strategy to separate the total dissipation into viscous and fatigue dissipation is proposed based on a constitutive assumption for the viscous dissipation of damaged asphalt concrete. This new method is then used to quantify fatigue damage in this study.