Modeling percentages of cohesive and adhesive debonding in bitumen-aggregate interfaces using molecular dynamics approaches

Abstract

When an asphalt mixture cracks, adhesive debonding occurs along bitumen-mineral interfaces and cohesive debonding occurs within bitumen films. At microscale, the two debonding processes can happen simultaneously but it is unknown for their percentages. This study aims to determine the percentages for cohesive and adhesive debonding and investigate how the material and external factors can affect these percentages using molecular dynamics (MD) modeling. The pull-off simulations of bitumen-calcite interfaces were performed at different bitumen film thicknesses, pull-off velocities and temperatures. The percentages of cohesive debonding were calculated as the area ratio of the remained bitumen molecules over the total interface. Results show that the percentage of cohesive debonding increases from 29% to 65% with thicker bitumen films, and decreases from 86% to 59% with higher loading velocities. When temperature rises, the percentage of cohesive debonding increases from 61.3% to 88.2%. Quartz presents a weak adhesion to bitumen, and thus a complete (100%) adhesive debonding occurs regardless of bitumen thickness. Microcline shows a very strong adhesion to bitumen due to its high polarity. The modeled cohesive debonding percentage with different variables were verified and found consistent with the laboratory pull-off testing results available from the existing studies.