*2.1. BRA*

The BRA was produced from the waste residues during the production of cooking oil, and is a sustainable regenerative agent for aged bitumen; it was supplied by the Wuhan Daosheng Transportation Technology Co., LTD, Wuhan, China. The technical parameters of the BRA are shown in Table 1.


**Table 1.** Technical parameters of BRA.

#### *2.2. Mix Design of BRA-Rejuvenated RAP*

The RAP was crushed and divided into four grades of 10–15 mm, 5–10 mm, 3–5 mm, and 0–3 mm; the size distribution of each grade of RAP is shown in Table 2. The bitumen contents of different sizes of RAP aggregates are shown in Table 3. The actual bitumen content of the RAP mix was 4.5%.



**Table 3.** Bitumen contents of different sizes of RAP aggregates.


The low dosages of new bitumen and epoxy resin were applied as the enhancement additives, in an effort to improve the mechanical properties and road performance of the BRA-rejuvenated RAP. The dosages of new bitumen and epoxy resin are shown in Table 4. The ratio of additives was measured by the weight of the RAP.

**Table 4.** The dosages of new bitumen and epoxy resin.


#### *2.3. Chemical Structure Analysis Tests*

The Fourier-transform infrared spectrometer (*FTIR,* NICOLET 6700 FLEX, Thermo Fisher, Waltham, MA, USA) was used to determine the chemical structure of unaged bitumen, aged asphalt, BRA, and BRA-rejuvenated RAP. The testing specimens were prepared at a ratio of 1:20 with carbon disulphide (CS2) solution according to the film method in GB/T 6040-2019, pressed into shape, and then subjected to FTIR spectroscopy. The scanning spectral wavenumber range of the test instrument was from 4000 cm−<sup>1</sup> to 400 cm<sup>−</sup>1.

#### *2.4. Molecular Weight Distribution Tests*

Gel permeation chromatography (GPC, Agilent PL-GPC50, Varian, PaloAlto, Santa Clara, CA, USA) was used to measure the molecular weight distribution of the BRA. Firstly, 0.4 mg of BRA and 2 mL of tetrahydrofuran solution were placed in the bottle; then, the sample solution was filtered into the test glass container using a filter with a 0.45 μm pore size microporous filter membrane, and then 50 μL of the sample was injected into the injector. The flow rate of the solution through the gel column was 1 mL/min.

#### *2.5. Mixing and Indoor Regeneration of BRA-Rejuvenated RAP*

The different grades of RAP were mixed according to the mix design of the BRArejuvenated RAP, and then the BRA was added to the mixing machine and mixed for 120 s. The mixing temperature was atmospheric temperature. Then, the mixture was stored at atmospheric temperature for 24 h to allow the aged bitumen to be fully activated by the BRA. After 24 h, the epoxy resin was added to the BRA-rejuvenated RAP for a second mixing, with a mixing time of 90 s. The mixture was then used to manufacture the test specimens. The Marshall specimens of BRA-rejuvenated RAP were mixed in the same way as commonly used dense-grade HMA, and the specimens were compacted 75 times for each side. The specimens were cured at 40 ◦C for 2 days. For the BRA-rejuvenated RAP with enhancement additives (new bitumen or epoxy resin), firstly, the new bitumen was heated to 130 ◦C, and then the BRA was added to the melted bitumen; we then used a high-speed shearing machine to stir the mixture for 15 min. The BRA-modified bitumen was manufactured to regenerate the RAP. The low viscosity of the BRA-modified bitumen ensured that it could mix freely with the RAP at room temperature.
