Characterization and molecular mechanism of the thermal-oxidative gradient aging behavior in asphalt films

To investigate the aging differences of asphalt films in the vertical aggregate direction, a three-layers model of oxygen-asphalt-aggregate was generated to explore the molecular mechanism of gradient aging. Moreover, the asphalt-aggregate specimens aged for 10, 20, and 40 h were layered for three parts. Fourier transforms infrared spectroscopy and thin layer chromatography-flame ionization detector tests verified the simulative findings. Eventually, the moduli of the asphalt pellicles were tested using nanoindentation test. Results denote that the oxygen's diffusion and distribution of four components are more sensitive to pressure. The aging grade and component content of the asphalt membranes at miscellaneous thicknesses have significant differences. The combined effects of component volatilization, oxidation reactions and component migration lead to mutates in the modulus gradient of the asphalt films. The carbonyl content difference between the top and bottom of the three binders are approximately 0.22,-0.13, and -0.27, respectively. Meanwhile, the maximum difference in modulus of binders and mastics are about 2.7 and 320.2 MPa.