## 1 Introduction  
In the road construction in our country, asphalt pavement is becoming more and more dominant, with the advantages of safety, comfort and being easy to repair [1; 2]. Most of the new and improved roads are built with asphalt mixtures. However, under the action of long-term wheel rolling and sun exposure, asphalt will gradually age, and its performance will no longer meet the requirements of relevant specifications, increasing the driving risk [3; 4]. For these aged asphalt roads, in addition to the repaired part, a large amount of recycled asphalt pavement (RAP) will be generated in the subsequent pavement maintenance work. In order to reduce environmental pollution, it is very necessary to reuse the amount of RAP [5; 6; 7]. In recent years, many researchers have demonstrated that the thermal regeneration of RAP is feasible, and they used waste engine oil, waste cooking oil and other regenerators to regenerate old asphalt, trying to restore its performance to the level of new asphalt [8; 9; 10; 11; 12]. [PERSON] et al. [13] evaluated the performance of asphalt pavement with RAP. The results showed that the test indexes of recycled asphalt mixture with 30% RAP meet the requirements of the specifications, except moisture content and low-temperature crack resistance. [PERSON] et al. [14] extracted and studied old asphalt on RAP milled from pavement that was used for 6 years. By using a high-speed mixer at 150 \({}^{\circ}\)C and at 1300 r/min, 1-3% waste vegetable oil and waste engine oil were fully mixed with the aged asphalt. The results showed that waste oil can make the physical properties of old asphalt close to the level of new asphalt. [PERSON] et al. [15] found that the use of waste engine oil can effectively improve the three physical properties of old asphalt. [PERSON] et al. [16] studied the regeneration effect of waste vegetable oil on aging asphalt, and the results showed that waste vegetable oil can not only improve the road performance of aging asphalt, but also ensure its safety performance and anti-aging performance. However, there is still a gap between the performance of a waste engine oil, recycled asphalt binder and new asphalt binder [17; 18; 19; 20]. Therefore, some scholars began to modify the waste engine oil, recycled asphalt binder to improve its performance. One of the methods to modify recycled asphalt binder is to mix some micro and nano materials. Among many micro and nano materials, carbon nanotubes are an ideal filler material for modification. Carbon nanotubes have a unique porous structure, which can adsorb oil in a regenerant and can improve the compatibility of light components of regenerant and asphalt [21; 22]. At present, the effect of carbon nanotubes on asphalt modification has been widely studied [23; 24; 25; 26; 27]. [PERSON] et al. [28] studied the viscoelastic behavior of multi-walled carbon nanotubes (MWNTs) and crumb-rubber-modified asphalt. The results showed that the addition of MWNTs and crumb rubber increased the high-temperature viscosity of the substrate and reduced the temperature sensitivity of the substrate. In addition, the permanent deformation resistance, creep recovery and stress relaxation properties of asphalt significantly improved after the addition of these two modifiers. [PERSON] et al. [29] studied the effect of carbon nanotubes on asphalt binders. The results showed that carbon nanotubes improved the high-temperature properties and permanent deformation resistance of binders and mixtures. [PERSON] et al. [30] discussed the effects of carbon-nanofiber-modified asphalt binder and carbon-nanotube-modified aggregate on the moisture sensitivity of an asphalt mixture. The indirect tensile strength test results showed that asphalt binders and aggregates modified by carbon nanofibers and carbon nanotubes could, respectively, improve the indirect tensile strength and tensile strength ratio of the mixture.