Adhesion mechanisms of SBS modified asphalt mixtures: Molecular dynamics and density functional theory analysis under aging and chloride erosion

The study aims to understand the adhesion damage mechanism of SBSMA (Styrene-Butadiene-Styrene Modified Asphalt) at the interface with aggregates in complex service environments. Molecular models of SBS at various aging stages were created and assessed for their physicochemical properties, such as infrared spectra and chemical reactivity, using quantum chemical simulation methods. The accuracy of the SBSMA models was verified through parameters like density and cohesive energy density. Interface models with different mineral aggregates in pure water and salt solutions were constructed to study the adhesion characteristics under varying thermo-oxidative aging intensities, mineral types, and chloride salt concentrations. The study found that as aging intensity increases, SBS molecules experience agglomeration, chain breaking, and polarity enhancement. This leads to intensified migration and diffusion, causing competitive adsorption at the interface and a tendency for SBS molecules to be adsorbed more on the side of the aggregates. Water molecules can permeate the aggregate surface, forming a strong hydrogen bonding network and occupying numerous adsorption sites, which weakens the adhesion properties between asphalt and aggregate. However, the presence of ions disrupts this network, and ionic bridges can indirectly increase the adhesive strength between asphalt and aggregate, particularly with age. Using a calcium carbonate substrate results in ion pairs being adsorbed close to the aggregate, forming a solvated shell layer with upper water molecules, which delays the increase in adhesion energy. This study provides significant insights into composite modification and reclaimed pavements of SBSMA, highlighting the impact of aging intensity, mineral type, and chloride concentration on the adhesion properties of asphalt-aggregate interfaces.