Development of new performance indices to evaluate the fatigue properties of asphalt binders with ageing

Abstract

This work presents the development of new fatigue performance indices for asphalt binders based on viscoelastic continuum damage (VECD) theory and failure energy. Five plant-produced asphalt mixtures were subjected to three different conditioning levels (short-term ageing during production and loose mix ageing for 5 and 12 days at 95°C in the laboratory) and the corresponding binders were extracted and recovered. Direct Tension Cyclic Fatigue (DTCF) tests were performed on the mixtures to characterise the mixture fatigue properties using the simplified viscoelastic continuum damage (S-VECD) analysis approach. Frequency and temperature sweep tests and the Linear Amplitude Sweep (LAS) test using a Dynamic Shear Rheometer (DSR) were conducted on the recovered binders to evaluate the binder rheological and fatigue properties. Three new performance indices are explored from the LAS test: Strain Tolerance (ε_T), Strain Energy Tolerance (Ε_f), and Average Reduction in Integrity to Failure (I^R). These indices were used to track the evolution of binder fatigue properties with ageing. A unique aspect of these indices is that they capture the failure point of the binder during the LAS test and combine the stress and strain histories of the material. Compared with the traditional A and B parameters from the LAS test, the new indices show a consistent decrease in the fatigue properties of the binders with ageing. The newly proposed parameters show improved correlations with mixture fatigue performance index (D^R) from the DTCF test, indicating their potential for evaluation of asphalt mixture fatigue properties. In addition, the new indices developed from this study have been shown to effectively capture the ageing gradient within the pavement structure and can also be used together with the binder rheological indices (e.g. G-R parameter and ΔTc) to evaluate both environmental and fatigue cracking of asphalt pavements at the same time.

KEYWORDS:

• Viscoelastic continuum damage (VECD) theory
• Linear Amplitude sweep (LAS) test
• fatigue performance
• ageing gradient
• rheological indices