Investigating the effect of a bio-oil additive on high RAP bituminous mixtures at the mastic scale

This study explores the impact of a bio-oil additive on mixtures containing high percentages of RAP at the mastic level. Mastics containing 40%, 50% and 70% RAP were evaluated through rheological and mechanical tests. Rheological properties were assessed using a Dynamic Shear Rheometer (DSR), while the Mastic Direct Tension Test and Mastic Creep Test analysed mechanical performance. A Digital Image Correlation (DIC) system was employed to examine strain distribution at the fracture point. The key innovation lies in evaluating the rejuvenation capacity of the additive at the mastic level using combined DSR and DIC techniques. The results show that the bio-oil improves elastic recovery and reduces viscosity, confirming its rejuvenating effect on aged bitumen through creep compliance and strain localisation analysis. However, the study also emphasises the need for precise dosage calibration. Accurate additive dosing is critical to balance reduced stiffness with the risk of increased rutting in high RAP mixtures.