Refinement of the bitumen fatigue failure definition in the current specification of the Linear Amplitude Sweep test

The asphalt binder plays a crucial role in the durability of asphalt mixtures, making the study of its fatigue resistance increasingly important. The Linear Amplitude Sweep (LAS) test effectively predicts fatigue life based on the Viscoelastic Continuum Damage (VECD) theory, where the failure criteria and failure definition significantly impact the results. However, the analysis of the current LAS test standard (AASHTO T 391–20), based on the Dissipated Strain Energy (DSE) approach, has shown a mathematical error in the failure definition. This paper aims to revise this mathematical error and propose a new failure point based on peak shear stress. LAS tests were conducted on RTFOT and PAV-aged bitumen at 15, 20, and 25°C. Both the current and revised failure definitions were used to predict the fatigue life of asphalt binders. The damage characteristic curves effectively illustrate the mathematical error in the current normalized damage at failure (D f ) formula. Based on the shear stress-strain curves, results indicate that the current failure point overestimates the fatigue life of asphalt binders, while the revised failure point underestimates it. A new failure point definition for the DSE approach, based on peak shear stress, is proposed. The results based on the new proposed criterion produce fatigue curves that closely align with those derived from the Pseudo-Strain Energy (PSE) approach. despite the differences in material integrity and damage formulas between the two approaches. Despite differences in material integrity and damage formulas between the two approaches, this strong correlation highlights the effectiveness of the new failure definition. • The D f of the current LAS test specification contains a mathematical error. • Current LAS failure definition overestimates binder fatigue life. • The D f of the current LAS test specification is based on an arbitrary definition. • DSE and PSE approaches present the same fatigue results for PSS failure definition. • The D f of the current LAS test specification should be reviewed.