Experimental teaching design for the preparation of warm-mix asphalt mixtures rejuvenated with waste oil and the evaluation of their pavement performance

To enrich the experimental teaching and practical components of the Road Engineering Materials course and to address the industry’s green development needs for the resource utilization of reclaimed asphalt pavement (RAP) and the coordinated disposal of waste cooking oil and waste engine oil in asphalt pavement maintenance, this study developed a comprehensive experimental teaching case on the preparation and pavement performance analysis of warm-mix waste-oil-rejuvenated asphalt mixtures (WMAs).

A base oil was prepared by blending waste engine oil and waste cooking oil at a ratio of 5:6, together with dioctyl adipate as a plasticizer, C9 petroleum resin as a tackifying resin, and a DWMA-1 warm-mix additive to produce a warm-mix waste-oil rejuvenator. Test results showed that all performance indicators met the technical requirements for rejuvenators. Aged asphalt was prepared through laboratory accelerated aging, and the optimum rejuvenator dosage was determined to be 12% based on penetration, ductility, softening point, and other indices, thereby producing warm-mix waste-oil-rejuvenated asphalt. With AC-16C used as the target gradation, old aggregates were extracted from RAP by the ignition method, and new aggregates were added to compensate for the finer characteristics of RAP aggregates. WMA with RAP contents of 30%, 50%, and 70% were designed, and hot-mix recycled asphalt mixtures (HMA) with the same RAP contents were used as control groups. The Marshall mix design method was applied to determine the optimum asphalt content under different RAP dosages. Next, high-temperature stability (Marshall stability test and rutting test), low-temperature cracking resistance (low-temperature bending test), water stability (freeze–thaw splitting test and immersion Marshall test), and fatigue performance (four-point bending fatigue test) were systematically evaluated.

The results showed that the dynamic stability of the WMA increased by up to 6.2% compared with HMA at the same RAP content; the maximum flexural tensile strain increased by up to 57.3%; the freeze–thaw splitting strength ratio and residual stability were considerably improved; and the fatigue life increased by up to 106.5%. Overall, the WMA had better pavement performance than the HMA. As RAP content increased, high-temperature performance improved gradually, whereas low-temperature performance, water stability, and fatigue performance declined. Considering all performance indicators comprehensively, the optimum RAP content was determined to be 30%. Simultaneously, course practice was conducted based on a reconstruction project of old branch roads in Xiqing District, Tianjin, establishing an integrated teaching model combining theoretical instruction, laboratory operation, and field construction. After construction, pavement smoothness, compaction, and other indicators met specification requirements. Practical results showed that more than 95% of students significantly improved their practical and collaborative abilities, and more than 88% independently completed experimental testing related to WMA.

This study achieved the coordinated resource utilization of waste oil and RAP, consistent with the green development concept under the “dual-carbon” goals. Meanwhile, it transformed scientific research outcomes into experimental teaching resources, providing theoretical support, technical reference, and an innovative teaching model for the reform of the Road Engineering Materials course and the promotion of green recycling technology for asphalt pavements.