Multiscale Investigation of Moisture-Induced Structural Evolution in Asphalt–Aggregate Interfaces and Analysis of the Relevant Chemical Relationship Using Atomic Force Microscopy and Molecular Dynamics

Abstract

Chemical changes and intermolecular interactions in asphalt dominate the molecular reorganization and cause the evolution of micro- and mesostructures. Given the lack of knowledge regarding the molecular chemistry–microstructure relationship of the asphalt–aggregate interface, the moisture-induced adhesive failure occurring at this interface has not been fully understood. This study investigates the multiscale structures of the asphalt–aggregate interfaces exposed to water and establishes the relationship between the structures and molecular interactions. The meso- and micromorphologies of two types of treated interfacial asphalts were observed via optical microscopy and atomic force microscopy. The results show an undulated surface and boundary retreat in asphalts because of the overall interfacial tension. Dispersed microbumps measuring tens of nanometers in height progressively grow until they merge into large bumps with increasing water exposure depending on the types of asphalt and aggregates. Fourier transform infrared (FTIR) spectrometry results show enriched polar components at the surface of the treated interfacial asphalt and water diffusion driven by complex intermolecular forces. The molecular behavior simulated by molecular dynamics calculations reveals that aliphatic molecules amalgamate into nonpolar clusters, while polar molecules migrate out and act as a surfactant to stabilize the asphalt–water system driven by the interfacial tension gradient. Internal coalescence of nonpolar components results in protrusion of the asphalt’s surface, and the migration of polar components to the surface accounts for the increased absorption peaks of the polar groups. This phenomenon could explain the FTIR spectra and formation of microbumps. The state of absorbed water and nanostructures of the interfacial asphalt are dominated by intermolecular interactions among asphalt, water, and aggregates. This study provides deep insights into the structural evolution of asphalt from the chemical and molecular perspectives.

Micromorphology and Micromechanical Properties Evolution of Bitumen and Bitumen Fractions Using Atomic Force Microscopy Considering Temperature Effect

“…Other special structures were found in SK-70 and SK-SBS, namely, valleys (dark areas) and peaks (bright areas); the valleys are mainly distributed in SK-70 while the peaks are mainly distributed in SK-SBS. These special structures were believed to be formed by polar asphaltenes and resins covering the nonpolar clusters . It is also noted that temperature had an obvious effect on the surface micromorphology of bitumen; this effect also varied with the bitumen types.…”

“…These special structures were believed to be formed by polar asphaltenes and resins covering the nonpolar clusters. 38 It is also noted that temperature had an obvious effect on the surface micromorphology of bitumen; this effect also varied with the bitumen types. The special surface structures of bees and peaks located in ANDA-50 and SK-SBS faded away with the temperature rising from 25 to 65 °C, and the bitumen's surface became smoother.…”

A Review on Multiscale Modeling of Asphalt: Development and Applications

“…The interfacial adhesion plays a vital role in maintaining the integrity and the overall performance of asphalt materials. The intermolecular interactions at the wet asphalt/aggregate interface are more complicated than those of the bulk asphalt, because of the asphalt/mineral and water/mineral interactions, as well as the fact that the interface between asphalt and aggregate in asphalt mixture is mainly focused on the adhesion and cohesion performance of asphalt and aggregate [151,152]. In comparison with bulk asphalt, the adhesive properties of the asphalt/aggregate interfacial transition zone are more susceptible to moisture, and the interfacial debonding proceeds to strip.…”

Influence of Water on Gas Transport in Shale Nanopores: Pore-Scale Simulation Study

“…(2) The wall condition plays an important role in nanoscale fluid transport. 50 We use wettability to simplify the impact of wall condition. The organic pores are gas-wet.…”

“…Convection is simplified as viscous flow, which obeys Darcy’s law. (2) The wall condition plays an important role in nanoscale fluid transport . We use wettability to simplify the impact of wall condition.…”