Estimation of re-refined engine oil bottom content in bitumen and its chemo-rheological effects as an additive and rejuvenator

This study investigates the performance of three types of re-refined engine oil bottom (REOB) in bitumen modification, focusing on their roles as additives, anti-aging agents, and rejuvenators. Neat and aged 60/70 penetration-grade bitumen samples were modified with 5–11 wt% REOB and evaluated using penetration, softening point, ductility, viscosity, FTIR, and inductively coupled plasma mass spectrometry (ICP-MS). The results indicate that adding 9 wt% REOB increased penetration by up to 45% and reduced the aging index by 14%, demonstrating its effectiveness as a softening and anti-aging additive. However, ductility and FTIR analyses revealed that REOB lacks functional rejuvenating capabilities, acting primarily as a physical softener rather than chemically restoring aged binders. A multiple linear regression model was developed using ICP-MS results to estimate REOB content in bitumen with high accuracy (R² = 0.98), providing a reliable quality control tool. Additionally, a human health risk assessment showed that REOB-modified bitumen does not increase carcinogenic or non-carcinogenic risks compared to neat bitumen. These findings contribute to a deeper understanding of REOB's limitations and potential in sustainable bitumen applications.