Application of Microcalorimeter to Characterize Adhesion between Asphalt Binders and Aggregates

Adhesion between asphalt binder and aggregate in a dry state as well as in the presence of water is critical to the performance and durability of asphalt mixtures. According to the literature, distress mechanisms in asphalt mixtures such as rutting, fatigue cracking, and moisture-induced damage are correlated to the nature and quality of adhesion between asphalt binder and aggregate. Surface free energy components of aggregates and asphalt binders can be used to compute the work of adhesion between the two materials in a dry condition as well as the thermodynamic potential of water to displace the asphalt binder from the surface of the aggregate. This paper presents a methodology to estimate the surface free energy components of aggregates using the microcalorimeter. The microcalorimeter is a relatively fast and simple alternative tool to estimate surface free energy components of aggregates compared to other techniques such as the gas adsorption method. In addition to surface energy measurement, the application of the microcalorimeter to directly measure the total energy of adhesion between the asphalt binder and the aggregate at mixing temperatures and the hydrophilicity of different aggregates at ambient temperatures is also demonstrated. Both of these properties influence the performance of asphalt mixtures in dry conditions and in the presence of water.