Extending bitumen with waste oils: a literature review on the use of REOB/VTAE

The asphalt industry continues to adapt to challenges arising from the limited availability of bituminous binders with consistent properties. One such challenge is the use of Re-refined Engine Oil Bottoms (REOB). Detectable only through advanced chemical analysis, REOB can modify bitumen properties in ways that are often overlooked and, in many cases, unexpected. This literature review examines the classification of REOB, the variability of its production, the regulatory challenges surrounding its use and the properties of REOB modified bitumen. Particular attention is given to technical concerns, including ageing susceptibility, phase behaviour changes, increased mixture stiffness, and interactions with other additives. The review also critically evaluates publications presenting favourable claims for REOB use, highlighting areas where conclusions may be premature. Recommendations are provided for researchers, regulatory bodies, and industry stakeholders to promote safe and informed implementation. Special focus is placed on regions outside the United States, where REOB use is poorly documented and recent cases of unexpected workability problems and premature pavement distress have drawn attention to its potential risks.