Effect of modification processes on bond energy of asphalt binders

Performance of asphalt pavements depends on the properties of its constituent materials, mixture volumetrics, and external factors such as load and environment. An important material property that influences the performance of an asphalt mixture is the surface free energy of the asphalt binder and the aggregate. Surface free energy governs the adhesive bond strength between the asphalt binder and the aggregate as well as the cohesive bond strength of the asphalt binder. These bond energies in turn influence the resistance of the asphalt mixture to distresses such as fatigue cracking and moisture induced damage. Asphalt binders undergo several types of engineering and natural modifications that influence their chemical and mechanical properties. Three common examples of modifications are the addition of polymers, addition of additives (e.g., antistrip agents), and oxidative aging of the asphalt binder. This paper is part of a study conducted to examine the effect of different types of modifications on the surface free energy components of the asphalt binder. The change in surface free energy was used to calculate parameters that are related to the performance of the asphalt mixtures. Results from this study demonstrate that the magnitude and nature of change to the surface free energy and concomitant performance-related parameters varied significantly among different asphalt binders. For example, certain modifications improved the performance of some binders while adversely affecting the performance of others. The experiment and analysis methods presented in this study can be used to examine the influence of modifications on performance and optimize the engineering properties of binders and asphalt mixtures.