Investigation of the effect of re-refined engine oil bottom on asphalt mixture performance and ecological implications

This study explores the use of re-refined engine oil bottom (REOB) as an alternative to bitumen in asphalt mixtures for flexible pavement structures. REOB is considered due to its low cost, availability, large production volume, and eco-friendliness. This paper investigates the effects of adding 5, 9, and 14 wt% of REOB to neat bitumen on the asphalt mixture's characteristics, mechanical behaviour, and ecological implications. The findings reveal significant reductions in indirect tensile strength by up to 51%, moisture resistance by up to 17%, rutting resistance by up to 79%, and cracking resistance at intermediate and low temperatures, especially when 14 wt% of REOB is added. While the heavy metal concentrations in both bitumen and REOB exceed permissible limits, the leached metal concentrations from the asphalt mixture remain within the safe range. Despite the potential environmental benefits of using REOB, the economic evaluations suggest that incorporating REOB into asphalt mixtures slightly increases the construction cost. Therefore, careful economic consideration should be performed for each project.