Development of a Tribological Test for Measuring Asphalt Lubrication Characterization

Abstract

Asphalt lubrication is of great importance for determining asphalt mixture workability and the resulting mixture density after paving and compaction. In this study, a tribological testing protocol for asphalt binders based on the standard ball-on-plate apparatus was developed to measure the asphalt lubricating property in the form of a Stribeck curve. The impacts of various additives, including polymers, warm mix additives, recycling agents, and recycled asphalt binder, on asphalt lubricity were evaluated. The asphalt blends with distinct lubricity behavior were selected and the corresponding mixtures were prepared using the same mix design to evaluate the effect of asphalt lubrication on mixture workability measured using the gyratory compactor N₉₂ index. The results demonstrate that asphalt Stribeck curve is a material-dependent master curve regardless of the testing temperature. The developed tribological test protocol can be used to differentiate the effects of common asphalt additives on asphalt lubrication. The results indicate that the types of polymer used have a very important role in defining lubrication properties. One elastomeric polymer used in the study is found to negatively affect lubrication of the base binder, while another functionalized polyethylene improves the properties. The trends are validated through the mixture workability evaluation using the N₉₂ index. The consistency in results from the lubrication measure and workability evaluation highlights the significant role of asphalt lubricating properties in determining the mixture workability mechanism.