Characterization of foaming attributes to binder tribology and rheology to better understand the mechanistic behavior of foamed asphalt

Abstract

In the asphalt foaming process, water is encapsulated inside asphalt binder in the form of numerous small to large size water bubbles. Though larger water bubbles dissipate shortly after foaming, smaller bubbles or micro-bubbles take a longer time to dissipate and hence, a fraction of added foaming water content (FWC) might remain undissipated in the form of micro-bubbles or diffused water. The study speculates that these water bubbles or undissipated water might be related to tribological and rheological characteristics, rather than binder viscosity only. As such the study characterizes FWC and associated foaming attributes to tribological, and rheological characteristics to better understand the foaming effects on mechanistic behavior of foamed asphalt. Tribological and rheological tests were conducted on foamed asphalts with varying FWCs and on a controlled un-foamed asphalt binder. A ball-on-three-plates apparatus assembled in a dynamic shear rheometer (DSR) was utilized for the tribological test. In addition, foaming characteristics were evaluated by various foaming parameters utilizing a laser-based non-contact method. The results yield a better understanding of foaming effects on mechanistic behavior of foamed asphalt in terms of foam expansion, stability, lubrication, frictional resistance, and viscoelastic responses.