Molecular dynamics study on improvement effect of polyethylene terephthalate on adhesive properties of asphalt and cement-based composite interface

Revealing the bonding mechanism between asphalt and cement-based materials is crucial for understanding the strength formation of semi-flexible pavement (SFP) materials and improving the performance indicators of SFP roads. Based on molecular dynamics simulation, the interface models of calcium silicate hydrogel (C-S-H) with virgin asphalt, polyethylene terephthalate (PET)-modified, and PET additive (PETA)-modified asphalt were established. At the molecular scale, the adsorption energy was used to predict the bond strength of the three interfaces, the radial distribution function was used to explore the interaction mode and stability of the interface and the static structure characteristics of the interface were analyzed in combination with the relative concentration. Finally, the interface's dynamic behaviour was analyzed through mean square displacement and diffusion coefficient. The simulation results show that after adding PET and PETA, the adhesion energy between the asphalt and C-S-H gel increases by 0.72% and 17%, respectively. Modified asphalt has a smaller interfacial interaction zone and faster molecular diffusion than virgin asphalt. In addition, the interface system containing PETA exhibits stronger hydrogen bonding and significant homopolar aggregation behaviour. Overall, the adsorption effect of PETA-modified asphalt on cement-based materials was better than that of PET-modified asphalt and raw asphalt.