Influence of Moisture on Bond Strength of Asphalt-Aggregate Systems
Copeland, Audrey R.
Moisture is a major source of degradation of hot mix asphalt (HMA) used in highway pavements. Moisture damage occurs when there is a loss of bond either at the asphalt-aggregate interface or within the asphalt mastic. The presence of moisture may strip asphalt binder from the aggregate (adhesive failure) and/or weaken the asphalt mastic (cohesive failure) resulting in pavement cracking and deformation. Bond strength is determined via a direct tensile test utilizing the Pneumatic Adhesion Tensile Testing Instrument (PATTI). The usefulness of the direct tensile test is determined for asphalt binders and mastics and the influence of moisture on tensile strength of asphalt binders and mastics and between asphalt and aggregate pairs is evaluated. The results of the experiments verify that moisture degrades the bond strength of asphalt binders, mastics, and between asphalt and aggregate. Results from the direct tensile test experiments are then linked to moisture diffusion simulations and bond strength degradation as a function of the amount of moisture at the asphalt-aggregate interface is established. Based on this relationship, the amount of damage that occurs over time in regards to the amount of moisture at the interface is quantified. Finally, limit-state based reliability analysis concepts are introduced to formulate a performance criterion for moisture-induced damage of asphalt-aggregate systems. The moisture-induced damage parameter is an integral part of a larger framework developed for predicting moisture-induced damage in asphalt mixtures.