Moisture Sensitivity of Modified Asphalt Binders: Factors Influencing Bond Strength

Bond strength is a critical parameter in evaluating a binder's ability to resist moisture-induced damage. The influence of polymer modification, moisture conditioning, and long-term aging on the bond strength of asphalt binders was measured by means of the modified pull-off test method previously developed to evaluate moisture sensitivity of asphalt binders using the pneumatic adhesion tensile testing instrument (PATTI). The pull-off test is able to distinguish between binders with the same performance grade but different chemical properties due to modification. However, the exact effect of modification on bond strength cannot be determined without consideration of the binder's physical properties. Moisture conditioning was the most influential factor on bond strength. Long-term laboratory aging increased cohesive strength of asphalt binders. However, aging combined with moisture conditioning decreased adhesive strength of binders. Comparisons of binder resistance to permanent deformation with pull-off tensile strength highlight the need for a test method that measures adhesive properties, namely, bond strength, of asphalt binder and mastics. Finally, recommendations are provided to improve the ability of the pull-off test method to determine bond strength.