Document Type

Article

Publication Date

5-4-2026

Department

Department of Civil, Environmental, and Geospatial Engineering

Abstract

This study evaluates the performance of recycled, long-term-aged rubber-modified asphalt (RMA) mixtures rejuvenated with soybean oil. Crumb rubber is widely used in asphalt mixtures for its ability to enhance elasticity, crack resistance, and durability. However, long-term aging leads to oxidative hardening, increased stiffness, and reduced cracking resistance, creating a need for effective rejuvenation strategies. To simulate extended field aging, plant-produced RMA mixtures were conditioned at 85 °C for five and ten days and subsequently treated with 10% soybean oil by binder weight. Mechanical performance was assessed using the Disc-Shaped Compact Tension test, Indirect Tensile Asphalt Cracking Test, Hamburg Wheel Tracking Test, and Rapid Shear Rutting Test. Rejuvenation effectively reversed aging-related deterioration, increasing fracture energy by 137–211% and improving cracking tolerance indices by 22–104%, thereby restoring or surpassing the cracking performance of unaged RMA mixtures. This improvement in flexibility was accompanied by reduced rutting resistance, with rutting tolerance indices decreasing by 52–70%, consistent with the softening effect of bio-based oils. Performance space diagrams further illustrated the trade-off between enhanced cracking resistance and increased rut susceptibility. Overall, the results demonstrate that soybean oil provides strong restorative capabilities for aged RMA mixtures, but achieving balanced field performance requires optimization of rejuvenator dosage.

Publisher's Statement

Copyright: © 2026 by the authors. Licensee MDPI, Basel, Switzerland. Publisher’s version of record: https://doi.org/10.3390/ma19091893

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Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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