Mechanical Analysis of Failure Processes at Bitumen/Aggregate Interface

The experience reported herein focuses on the advanced characterization of adhesive/cohesive failure at bitumen/aggregate interfaces. A modified Pneumatic Adhesion Tensile Testing Instrument (PATTI) was developed to integrate the conventional measure of pressure with the additional measure of vertical displacement. The measurement of vertical displacement was used to estimate the deformation within the bitumen film and therefore the final strain at failure. This provided specific functional characteristics, specifically linked to the possibility of estimating the total work done by the external forces to separate the bitumen/aggregate interfaces. Energy-based criteria for adhesive/cohesive tensile failure were consequently established accounting for the elongation of the bitumen film. The interface bond energy and its stability upon moisture conditioning were then measured for different bitumen-aggregate systems. The bond energy was found to be highly dependent on the specific characteristics of the asphaltic interfaces and primarily connected with bitumen grading and composition. The analysis of the detachment surfaces addressed further relations between the changes recorded in bond energy, the characteristics of the asphalt film and the progressive shift from cohesive to adhesive failure.