Simplified protocol for fatigue cracking characterization of asphalt mixtures using the direct tension cyclic fatigue test

Abstract

Several test methods exist to characterize asphalt mixtures with respect to their fatigue cracking resistance, but only a few can be used in mechanistic models for pavement performance predictions. The direct tension cyclic fatigue test is one such test method because it measures fundamental properties of asphalt mixtures. However, the amount of material and time required for specimen fabrication and preparation are substantial, which impairs the implementation of this test method. Thus, this paper proposes a simplified protocol to characterize asphalt mixtures with respect to fatigue cracking using the direct tension cyclic fatigue test. First, the method to estimate the appropriate Superpave gyratory compacted samples’ mass was evaluated and recalibrated, reducing the amount of material needed to obtain test specimens with acceptable air void content. Second, a statistical analysis showed that reusing specimens tested via AASHTO TP 132 for the direct tension cyclic fatigue test does not yield significant differences at either material or pavement levels. Finally, a practical example indicated that the recalibrated mass estimate equation and the reuse of specimens for the direct tension cyclic fatigue test result in substantial savings of material and time. The simplified protocol proposed in this paper has several advantages when either partially or fully implemented including testing mixtures with limited amount of material (e.g., field cores), replacing problematic specimen data, and expediting performance testing.