Discussion on the bitumen fatigue parameters interpretation for Linear Amplitude Sweep and time-sweep tests: Insights from ageing

The bitumen ageing phenomenon is a crucial factor determining the fatigue cracking resistance of asphalt mixtures. Therefore, a reliable representation of changes in the fatigue life of bitumen binders with ageing is fundamental for flexible pavement performance prediction. This study aims to investigate and select the Linear Amplitude Sweep (LAS) test conditions in terms of rational fatigue life predictions of bitumen binders based on the results of time-sweep (TS) fatigue tests performed in Dynamic Shear Rheometer (DSR). Testing was performed on two neat bitumen binders (35/50, 50/70) and one polymer-modified bitumen (PmB 25/55–60) in the unaged, short-term aged (RTFOT), and long-term aged (PAV) states. The Zero-Slope Strain (ZSS) and Limit Strain (LS) levels were introduced to the data analysis to determine a common strain amplitude to be applied in fatigue life calculations based on LAS testing. Correlations between the fatigue life values obtained in TS (Nf,TS) and LAS (Nf,LAS) tests were analysed considering the influence of strain amplitude, temperature, and the degree of ageing. The statistical analysis confirmed that given the specific LAS test conditions and calculation parameters, the relationship between the Nf,LAS and Nf,TS values can be reliably described, taking into account the impact of ageing processes.