Effects of Surface Roughness on Contact Angle Measurements on a Limestone Aggregate

Recent studies have shown that the sessile drop approach is a reliable method to measure contact angles on asphalt pavement materials. The measured contact angles, in turn, are utilized for computing the surface energy properties of asphalt binders and aggregates. Based on the surface energy and bonding strength characteristics of the materials, appropriate aggregates can be selected to construct pavements that are resistant to moisture damage. In this approach, surface roughness could be an important factor that could affect the contact angle measurements on aggregates. The main objective of the present study is to determine the differences in contact angle measurements on a limestone aggregate at different levels of surface roughness. Initially, contact angle measurements were conducted on selected points on the unpolished surface of the limestone specimen. Later, the same specimen was subjected to different stages of polishing using silicon carbide grits. At each stage, the contact angle measurements were repeated, as well as surface roughness was measured using a 2D profilometer. It was observed that there was a change in the contact angle measurements as the roughness of the surface decreased with polishing.