*2.3. Chemical Structure and Thermal Stability Characterizations of L-DMA*

FTIR spectra of MAA, L-DOPA, and L-DMA were recorded on a Thermo Nicolet 6700 Fourier-transform spectrophotometer (Waltham, MA, USA). In all cases, 16 scans were collected at a resolution of 2 cm−<sup>1</sup> for the spectrum in the range of 4000–400 cm−<sup>1</sup> .

TGA was used to determine the thermal stability of L-DMA, which was carried out using the synchronous thermal analyzer (TA TGA55, New Castle, DE, USA) The L-DMA was protected in an N<sup>2</sup> atmosphere at a flow rate of 20 mL/min, in the temperature range from room temperature to 800 ◦C at a heating rate of 10 ◦C/min.

#### *2.4. Preparation of L-DMA-Modified Asphalt*

We added a certain mass ratio of L-DMA into the heated 70# base asphalt and mixed manually for ten minutes. To guarantee a good dispersion of L-DMA, a shear apparatus was used to disperse L-DMA at a rate of 4000 r/min for 40 min at a temperature of 170 ◦C. The dosage of L-DMA was 1%, 2.5%, 5%, 7.5%, and 10% of asphalt, respectively.
