Effect of alkyl chain length on the demulsification process of cationic emulsified asphalt on a CaCO3 surface

Emulsified asphalt cold recycled mixture (CRM) materials benefit from energy savings, environmental friendliness, and economic convenience. The in-service performance of CRM relies largely on the micro-interaction at the interface between the alkaline aggregate and cationic emulsified asphalt but lacks an in-depth interpretation at the molecular level. This study investigated the influence of the alkyl chain length of cationic emulsifiers (C12TAC, C14TAC, C16TAC, and C18TAC) on the demulsification process of cationic emulsified asphalt on a CaCO3 surface via a microscopic molecular dynamics (MD) simulation framework combined with macroscopic demulsification experiments. The emulsification asphalt/CaCO3 system was established by molecular-level MD simulations. The visualized statistical data were used to investigate the influence of alkyl chain length on the adsorption behavior, concentration distribution (CA), diffusion coefficient (DA), and adhesion work (W) of emulsified asphalt on the CaCO3 surface. The conductivity experiment tested the demulsification time of emulsified asphalt on the CaCO3 surface, which revealed the effect of alkyl chain length on the demulsification speed at the macro level and further verified the simulation results. Research results revealed the following conclusions: (1) The electrostatic force is the main factor driving asphalt molecules to the surface of alkaline aggregate (CaCO3), while the van der Waals force leads to the reversal of repulsive forces. Therefore, the electrostatic potential distribution dominates the adhesion strength between the emulsified asphalt and the alkaline aggregate. (2) The relative concentration peak and diffusion coefficient of cationic emulsified asphalt are positively related to the number of carbon atoms in the alkyl chain. (3) The electrostatic force and adhesion work increase by 6.8 % when two carbon atoms are added to the alkyl chain of the emulsifier. This proves that the carbon atom content of the alkyl chain determines the adhesion of cationic emulsified asphalt. (4) The demulsification time is proportional to the number of carbon atoms in the range of 12–18. This demonstrates that enhancing the adhesion strength of emulsified asphalt and controlling the demulsification time can be achieved by adjusting the alkyl chain carbon atom content. [Display omitted] •Strong electrostatic attraction between resin molecules and CaCO3 leads to a significant accumulation of resin molecules on the surf