Rheological and fatigue characterisation of bitumen modified by anti-ageing compounds

When exposed to the ambient environment for an extended period, bitumen ages and causes the failure of asphalt pavement, the addition of anti-ageing compounds (AACs) to bitumen binders can prolong the service life of the pavement. This study investigates the effects of anti-ageing compounds on the fatigue performance of bitumen when subjected to different ageing conditions. The AAC-modified bitumen binders were tested by dynamic shear rheometer (DSR) and Fourier transform infrared spectroscopy test (FTIR) at different ageing conditions including unaged, short-term ageing by thin film oven test (TFOT) and long-term ageing by pressure ageing vessel (PAV). The fatigue performance of the AAC-modified bitumen was characterised by the dissipated energy ratio (DER), SHRP fatigue parameter and the DSR-cracking (DSR-C) approach developed by the authors. Linear amplitude sweep (LAS) tests were firstly run at 20 °C, 10 Hz and 0.1–15% controlled shear strain conditions, to obtain the phase angles and shear moduli at the undamaged conditions. Time sweep (TS) tests were then conducted at 5% shear strain, also at 20 °C and 10 Hz, and up to 24,000 loading cycles to obtain phase angles, shear moduli and DER at damaged conditions. The crack lengths in the TS tests were calculated by DSR-C model and then validated by the image analysis method. The results suggest that, compared to the DER or SHRP fatigue parameter, DSR-C predicted crack lengths show a more consistent and reliable agreement with laboratory measurements. DSR-C test can differentiate fatigue cracking performance among binders modified with AACs, and the normalised carbonyl index may be a reliable parameter to reflect the impact of ageing products on the fatigue resistance of AAC-modified binders. Bitumen samples modified with 12% (1 furfural: 5 Irganox 1076), 15% Irganox 1076 and 3.5% (3 DLTDP: 4 furfural) demonstrated the best anti-ageing behaviour by retarding carbonyl content growth and decreasing the fatigue damage among selected AACs without sacrificing the stiffness of binder. However, rutting susceptibility at earlier stages of service life needs further investigations.