Investigating the Field Performance of High- Recycled Asphalt Pavement Mixtures with Bio-oil Recycling Agent

The use of recycling agents (RAs), along with recycled asphalt pavement (RAP) modifiers, has been increasing over recent years. However, the field performance of asphalt mixtures containing high-RAP materials modified with RAs has raised some concerns with the long-term performance of RAs. This study evaluated the laboratory and field performance of high-RAP mixtures with and without bio-oil RA. Five sets of plant-produced specimens were collected: 1) plant-produced laboratory-compacted; 2) field-compacted, cored after paving; 3) field-compacted, cored after one year; 4) field-compacted, cored after two years; and 5) field-compacted, cored after three years. The Hamburg wheel tracking test was used to evaluate the specimens' resistance to rutting and moisture damage, while the semi-circular bending test was performed to examine the cracking resistance of specimens. The laboratory test results showed that using the bio-oil RA increased cracking resistance and decreased rutting and moisture damage resistance of the RAP-blended mixtures. However, after one and two years of exposure to environmental conditions and traffic loads, the specimens modified by RA showed better moisture damage and rutting resistance. The cracking resistance of laboratory and field-aged specimens, estimated by flexibility index, implied that the bio-oil RA used in this study could not provide long-term improvement for the RAP-blended mixtures. Field observations suggest that using bio-oil RA may have resulted in inferior pavement performance compared with the control section. However, drawing conclusions based on just two years of data might yield inconclusive results. Longer field performance monitoring is, therefore, warranted for a more comprehensive analysis.