## 1 Introduction  
Recycling reclaimed asphalt pavement (RAP) has good economic and environmental benefits. In the case of a RAP dosage between 20-50%, it can save the cost of construction by 14-34% [1], which can reduce the exploitation of non-renewable resources (e.g., stone and asphalt), and thus reduce energy consumption and pollution emission in mining and transportation [2]. However, when RAP dosage goes beyond 20%, there is a gradual increase in the deterioration of pavement's fatigue cracking and low-temperature cracking [3], and the compact of asphalt mixture will also be damaged [4]. To solve the shortcomings of rejuvenated asphalt mixture with a high dosage of RAP, it often requires the addition of a rejuvenator [5]. Rejuvenators mainly include vegetable oil and petroleum-based extracted oil [6], among which vegetable oil has attracted much attention in recent years because of its renewable advantage.  
In 2012, [PERSON] et al. [7], on the basis of the indicators (e.g., penetration, soften point, and viscosity), pointed out that there was no clear difference in the performance between rejuvenatedasphalt with fring vegetable oil and virgin asphalt. In 2014, [PERSON] et al. [8; 9] utilized frying vegetable oil to rejuvenate aged asphalt, and the study showed that frying soybean oil significantly improved the fatigue property and low temperature anti-cracking property of aged asphalt, but the ductility was not effectively improved, and high temperature performance became poorer with the increase of frying soybean oil. In 2016, [PERSON] et al. [10] added methyl alcohol into frying vegetable oil and made a chemical modification under alkalis catalysis, and it was found that the asphalt that was rejuvenated by the modified frying vegetable oil could achieve a better rutting resistance. In 2017, [PERSON] et al. [11] appraised the effects of vegetable oil with different deep-frying times on the rheological performance of aged asphalt, and the study exhibited that vegetable oil of a higher aging degree could result in a higher viscosity and a better rutting resistance. In summary, frying vegetable oil can restore the penetration of aged asphalt, as well as improve the fatigue property and low-temperature anti-cracking property of aged asphalt; however, high-temperature rutting resistance will become poorer. Vegetable oil, after modification or further aging, can reduce the damage of vegetable oil on rutting resistance. Herein, in this study, it was considered to apply highly aged waste vegetable oil of high viscosity to rejuvenate aged asphalt. The waste vegetable oil is sourced from the byproduct after the extraction of fatty acid from vegetable oil, and this byproduct is named as W-oil in this paper. W-oil is the byproduct obtained by eight-hour distillation at 300-400 \({}^{\circ}\)C after the acidification of vegetable oil. W-oil has a higher viscosity and deeper aging degree than that of frying vegetable oil. The output of W-oil is large in China, and the main treatment measure taken at present is combustion, which has not been effectively utilized. Therefore, it is necessary to explore the application of W-oil in rejuvenating asphalt.