According to WPB, a new study has demonstrated that selected rejuvenating agents can substantially improve the laboratory fatigue performance of asphalt mixtures containing up to 60% reclaimed asphalt pavement (RAP). The findings highlight the potential of lubricant oil and vacuum bottom, a petroleum refining-derived material, to restore key properties of aged bitumen while enabling greater use of recycled materials in road construction.
The research, conducted by scientists in Iran, evaluated three rejuvenators: Waste Engine Oil (WEO), Lubricant Oil (LU), and Vacuum Bottom (VB). Asphalt mixtures incorporating 30%, 45%, and 60% RAP were examined to determine how different rejuvenating agents influence binder chemistry, fatigue resistance, and moisture susceptibility. The researchers optimized rejuvenator dosages using a viscosity-matching approach designed to approximate the rheological properties of virgin PG64-22 bitumen.
One of the most significant findings emerged from four-point bending fatigue tests on mixtures containing 60% RAP. At a strain level of 500 microstrain (µε), mixtures treated with lubricant oil and vacuum bottom achieved reported improvements of 76–85% in fatigue resistance. Under the more demanding strain level of 700 µε, the improvement remained positive but declined to 34–40%. These results demonstrate that rejuvenator effectiveness depends partly on loading conditions and that improvements measured at one strain level should not be generalized to all operating conditions.
Chemical analysis provided further insight into these differences. SARA testing showed that lubricant oil and vacuum bottom helped restore the colloidal balance of aged bitumen, reducing the measured asphaltene fraction from 27.0% to 17.5–18.1% and restoring aromatic content to 44.3–45.2%. Waste engine oil, by comparison, achieved only partial chemical recovery. Separate Linear Amplitude Sweep (LAS) testing also indicated improvements in binder fatigue life, with reported increases of 21% and 29% under the evaluated shear strain conditions.
The research identified improvements in moisture resistance as well. The mixture containing 60% RAP and lubricant oil, designated R60LU, achieved a Tensile Strength Ratio (TSR) of 90.7%, compared with 80.7% for the control mixture. This represents a 10-percentage-point improvement in a laboratory indicator used to assess susceptibility to moisture-related damage.
For the petroleum and bitumen industries, the findings are particularly relevant because they demonstrate how the chemical composition of rejuvenating agents can influence the performance of high-RAP asphalt. The results involving vacuum bottom also reinforce interest in the potential use of selected petroleum-derived heavy fractions as rejuvenating materials. However, the suitability of such products depends on their composition, compatibility with aged bitumen, and optimized dosage rather than their origin alone.
The study also highlights an important distinction between softening aged bitumen and restoring its overall performance. Reducing binder stiffness does not necessarily guarantee adequate resistance to fatigue cracking, moisture damage, or permanent deformation. The combined evaluation of chemical properties and mechanical performance offers a more comprehensive approach to selecting rejuvenators for high-recycled-content asphalt mixtures.
Although the laboratory results indicate that properly formulated mixtures containing 60% RAP can achieve fatigue and moisture resistance comparable to or better than the virgin mixture evaluated in the study, they do not establish equivalent improvements in actual pavement service life. Further validation under field conditions, traffic loading, environmental exposure, and long-term aging would be necessary before applying the findings broadly to commercial road construction.
For asphalt producers, bitumen suppliers, and refinery-linked material developers, the research suggests that higher RAP utilization could become more technically feasible through carefully selected rejuvenators. The commercial opportunity lies not simply in increasing recycled content, but in maintaining the performance characteristics required for durable pavement infrastructure.
By WPB
Reclaimed Asphalt Pavement, RAP 60%, Asphalt Rejuvenators, Vacuum Bottom, Lubricant Oil, Waste Engine Oil, Asphalt Fatigue Resistance, Bitumen Recycling, SARA Analysis, Moisture Resistance, Sustainable Pavement Technology
