Revealing the Thermodynamic Characteristics, Bonding Behavior, and Failure Patterns of the Asphalt-Aggregate Interface Containing SBS/CNT Micronanoparticles at the Molecular Scale

Abstract

This study sheds light on the analysis of the thermodynamic properties of the asphalt-aggregate interface under the modification of low-dimensional carbon nanotubes (CNTs) with styrene-butadiene-styrene (SBS) copolymers through molecular modeling techniques, and mainly addresses the following queries: How do asphalt, modifiers, moisture, and mineral molecules interact with each other? What are the regulations of the thermodynamic properties and energy conversions in asphalt-aggregate systems, especially in the presence of oxidation and moisture? How does the failure pattern and bond strength of the asphalt-aggregate system modified by CNTs develop under tensile forces? Supported by molecular dynamics (MD) simulation approaches, molecular models such as 12-component asphalt, three mineral components (CaO, SiO2, and Al2O3), long-chain SBS copolymer, and CNT tubular were developed for subsequent calculations. The surface energy of each component of the asphalt-aggregate model was determined at the molecular scale to quantify the intermolecular forces between the components and the integral tensile strength of the molecular structure. The effectiveness of aging behavior and moisture on thermodynamic properties and failure patterns of asphalt-aggregate systems containing polymer/CNT composites was evaluated. The results suggested that CNT molecules can promote the intermolecular interaction forces and interfacial energies at the asphalt-aggregate interfaces. The oxidative aging caused a degradation of the surface energy, cohesion energy of the asphalt modified by SBS/CNT additives, and leaded to complicated response on adhesive energies at asphalt-aggregate interface. The combination of alkaline mineral (CaO) and CNT was beneficial in decreasing the moisture susceptibility of the asphalt mix. The failure pattern was in cohesive cracking form within the asphalt and the bond strength was enhanced by CNTs. The increase in temperature weakens the intermolecular energies of the asphalt-aggregate system and its bond strength. This paper provided an explanation for the molecular energy conversion and the mechanical enhancement mechanism of low-dimensional CNTs in petroleum asphalt-based composites.