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• Asphalt mixture containing high-proportion RAP was prepared by SMC regenerant. • The failure strength master curve of high-content RAP asphalt mixture was obtained. • The fatigue performance of high-proportion RAP asphalt mixture was studied. Reclaimed Asphalt Pavement (RAP) is a cleaner production widely used in road engineering. In order to investigate the failure strength and long-term performance of high-proportion RAP asphalt mixture, this research prepared two high-content RAP recycled asphalt mixtures (50% and 60% RAP-RAM) with the gradation of AC-20 based on Styreneic Methyl Copolymer (SMC) regenerant. Firstly, indirect tensile (IDT) strength tests were implemented on 50% and 60% RAP-RAM at four temperatures and six loading rates. Secondly, IDT fatigue tests at six stress levels were carried out. The relationships of strength and temperature, strength and loading rate were obtained based on strength test results. The master curve model of indirect tensile strength and loading rate of high-proportion RAP recycled asphalt mixture was established by linear and Sigmoidal functions. On the basis of the Sigmoidal strength master curve equation, the fatigue stress ratio was calculated. Finally, this paper established the fatigue equation of the high-content RAP recycled asphalt mixture based on the fatigue stress ratio. The analysis results show that 50% and 60% RAP-RAM based on SMC regenerant show favorable strength and fatigue properties. In addition, increasing the proportion of RAP improves the strength of the mix while reducing the loading rate sensitivity of strength. However, the fatigue performance of the mix reduces by increasing RAP content. The fatigue equation based on the fatigue stress ratio takes the factors of temperature and loading rate into account, reflecting the mix's fatigue performance more realistically. The strength and fatigue performance results verify the reliability of the high-content RAP recycled asphalt mixture based on SMC regenerant and provide a reference for the effective utilization of RAP which can generate environmental benefits of saving aggregate and asphalt and reducing energy consumption and carbon emissions. [ABSTRACT FROM AUTHOR]

• Two kinds of bio-oils are used together in pavement materials to improve the utility. • The response surface method is used to determine the optimal dosage of modifiers. • The properties of bio-asphalt are evaluated from the macroscopic and microscopic perspectives. Bio-asphalt is a potential pave material in road engineering. In order to realize comprehensive utilization of a variety of bio-oils and improve the road performance of bio-asphalt, this study chose two different sources of bio-oil for effective utilization. First, vegetable oil was used to prepare mixed bio-asphalt through high-speed shearing. Polyurethane and castor oil were added to the bio-asphalt for modification to obtain castor oil-based polyurethane-modified bio-asphalt (CPBA). Based on the Box-Behnken Design, the penetration test and softening point test of the CPBA were carried out to evaluate its conventional performance. Temperature sweep, multiple stress creep recovery test, and bending beam rheometer test was conducted to evaluate its macroscopic rheological properties. Fourier transform infrared reflection (FTIR) was shown to reveal its modification mechanism. Scanning electron microscopy (SEM) was performed to observe its microscopic morphology and verify the effect of polyurethane modification. The results manifest that castor oil-based polyurethane can increase the high-temperature properties of bio-asphalt. However, when the amount of castor oil is too high, it will also weaken the high-temperature properties of CPBA. The high-temperature properties of CPBA depend on castor oil content, polyurethane content, and stress level. Vegetable oil and castor oil can improve the low-temperature properties of asphalt. Instead, the chemical reaction production of polyurethane or polyurethane and castor oil with asphalt negatively influences the low-temperature properties of asphalt. The optimal polyurethane content, castor oil content, and vegetable oil content determined using the response surface method were equal to 20.00%, 33.61%, 8.38%. FTIR results manifest that polyurethane can chemically react with castor oil but not with vegetable oil. Vegetable oil mainly plays a role in improving the compatibility of CPBA. SEM results also show that under the action of vegetable oil, the appearance and structure of the reaction products of polyurethane and castor oil have been greatly improved. The polyurethane application in bio-asphalt makes a variety of bio-oil used, improving bio-asphalt performance and availability. [ABSTRACT FROM AUTHOR]