Waste engine oil and polyphosphoric acid enhanced the sustainable self-healing of asphalt binder and its fatigue behavior

Asphalt self-healing capability is critical to the asphalt industry's sustainable development. The paper attempts to explore the feasibility of waste engine oil (WEO) and polyphosphoric acid (PPA) to enhance self-healing of asphalt binder and its fatigue behavior. The different proportion of WEO and PPA were mixed with asphalt to modify asphalt initially. Dynamic shear rheometer (DSR) test and linear amplitude sweep (LAS) test were adopted to establish the modulus master curve and evaluate fatigue behavior. With the aim of estimating the healing degree of asphalt binders, evaluating indicators consist of fatigue life recovery, modulus recovery and dissipated energy recovery were adopted based on fatigue-healing test. The phase state transition of asphalt binders related to temperature was determined by differential scanning calorimetry (DSC) test. Ultimately, to evaluate modification effect of different additives on asphalt binder comprehensively, radar chart method is employed. It can be concluded that the addition of PPA and WEO improves fatigue performance and self-healing of asphalt binder. As for additives with 2% PPA and 2% WEO, 1% PPA and 4% WEO, fatigue life in LAS predicted model presents extreme value, increasing by 1000% and 1150% than original asphalt respectively. The raise of anti-permanent deformation for asphalt modified by WEO/PPA can be attributed to the presence of PPA. Compared with original asphalt, a significant increase of fatigue life recovery, modulus recovery and dissipated energy recovery is observed at asphalt modified with 6% WEO regardless of PPA content. Additionally, the healing indicators increment of the original asphalt is larger than modified asphalt with the extension of the healing time. This is because most of damage of modified asphalt could recover at a relatively short time. Analysis of the DSC indicates that the two peak temperatures of original asphalt are lower than that of modified asphalt. It helps to improve self-healing and fatigue behavior of asphalt binder. Overall, a promising way to promote the sustainable development of asphalt industry is put forward.