Surface free energy components of aggregates from contact angle measurements using Sessile Drop method

Contact angle measurements are increasingly becoming important in analyzing the interaction energy between different geological materials both in dry and as well as wet conditions. One field where this new approach has been applied is the moisture damage in asphalt pavement mixtures. The moisture damage is simply known as the loss of bonding strength between asphalt binder and aggregate, and as well as within the binder itself in the presence of moisture. Therefore, it is important to know the surface energy parameters of these materials for realistic characterization of the moisture damage process in asphalt mixtures. Two laboratory testing devices and methods are currently used in determining the surface free energy components of aggregates and binders. The Wilhelmy Plate (WP) is usually employed for inferring the surface free energy parameters of asphalt binders and the Universal Sorption Device (USD) is usually used for inferring the surface free energy values of aggregates. This paper presents a new Sessile Drop (SD) testing device that can be used to measure contact angles directly on asphalt binder and aggregate specimens. The new device has been used for measuring contact angles and calculating surface energy parameters on an Oklahoma limestone aggregate. The laboratory tests indicate that there are significant differences between similar aggregates using the USD and SD methods.